Mechanical testing and evaluation of high-speed and low-speed

MECHANICAL TESTING AND EVALUATION OF HIGH-SPEED AND LOW-

SPEED FRICTION STIR WELDS

A Thesis by

Nitin Banwasi

Bachelor of Engineering, Bangalore University, Bangalore, India 2000

Submitted to the College of Engineering and the faculty of the Graduate School of

Wichita State University in partial fulfillment of the requirements for the degree of

Master of Science

Fall 2005

EXPERIMENTAL TESTING AND EVALUATION OF HIGH-SPEED AND LOW-

SPEED FRICTION STIR WELDS

I have examined the final copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Mechanical Engineering.

George E. Talia, Committee Chair

We have read this thesis and recommended its acceptance:

Dr. Hamid M. Lankarani, Department Chair, Committee Member

Dr. Krishna K. Krishnan, Committee Member

ii

DEDICATION

To My Parents

iii

ACKNOWLEDGEMENTS

I am grateful to all that are part of my efforts during my work both academically and

personally. I am thankful to my committee chair, Dr.George E.Talia, for being not only

supportive in my endeavors but also patient and informative. I appreciate the involvement

of both Dr. Hamid M. Lankarani and Dr. Krishna K. Krishnan for their involvement in its

fulfillment. I also want to remember fellow student’s help and suggestions in making it

possible with gratitude.

iv

ABSTRACT

The potential of the Friction Stir Welding (FSW) process is easily observed in the

creation of defect free welds in almost all of the Aluminum alloys. The success and

applicability of the process, however, will depend on the performance of the welds

compared to other joining processes. Experimental testing and evaluation are necessary

for the determination of the mechanical response of Friction Stir Welds and vital to the

development and optimization of the FSW process. The goal of this experimental testing

of Friction Stir Welds is to obtain the data necessary to begin understanding the effects of

the FSW process. An attempt has been made to systematically examine the effects of

FSW process parameters and alloy on the weld properties. An attempt has been made to

evaluate and compare High Speed and Low Speed Friction Stir Welds.

v

TABLE OF CONTENTS

1. INTRODUCTION 1

1.1. Welding 3

1.2. The physical nature of joining 4

1.3. Welding, from a metallurgical point of view 4

1.4. A metallurgical classification of the welding processes 5

1.5. Types of welding 5

1.6. Solid state welding 7

1.7. Friction welding 7

1.8. Rotary friction welding 8

2. ALUMINUM WELDING

2.1. Introduction 9

2.2. Characteristics of Aluminum 10

2.3. Aluminum alloy designation – wrought alloys 11

2.4. Nonheat treatable Aluminum alloys 12

2.5. Heat treatable Aluminum alloys 12

2.6. Wrought Aluminum alloys 12

2.7. Welding Aluminum 14

3. FRICTION STIR WELDING

3.1. Introduction 17

3.2. Different parameters in FSW 18

3.3. Process advantages 20

3.4. Microstructure classification 22

vi

3.5. Joint geometries 24

3.6. Applications 25

4. MECHANICAL TESTING AND METALLOGRAPHY

4.1. Testing 28

4.2. Tensile Test 28

4.3. Tensile Specimens 29

4.4. Hardness Test 30

4.5. Types of hardness tests 31

4.6. Factors for selection of hardness testing methods 32

4.7. Rockwell hardness test 32

4.8. Metallographic specimen preparation basics 34

5. EXPERIMENTAL PROCEDURE

5.1. Tensile test 37

5.2. Hardness test 37

5.3. Metallographic analysis 38

6. RESULTS AND DISCUSSIONS

6.1. Effect of changing welding speed at constant weld pitch 40

6.2. Temper effects on required loads and weld energy 41

6.3. Alloy effects on specific weld energy 42

6.4. Low-speed friction stir weld 1 43




vii







6.14. Tool geometry effects 97

6.15. High-speed friction stir weld 11 100







7. CONCLUSIONS AND FUTURE SCOPE 121

8. REFERENCES 125

viii

LIST OF FIGURES

1.1. Friction stir welding process 2

1.2. Master chart of welding and allied processes 6

1.3. Friction stir welding and processing technologies 8

3.1. Friction stir welding 18

3.2. Microstructure of a friction stir weld 20

4.1. Tensile test specimen 29

4.2. Rockwell principle 33

6.1. Required energy and specific weld energy at constant weld pitch 40

6.2. X-axis force for welds made at constant weld pitch 41

6.3. Specific weld energy as a function of welding speed 42

6.4(a). Hardness graph – across the weld 46

6.4(b). Microstructure of the weld 47

6.5(a). Hardness graph – across the weld @ 10”/min 52

6.5(b). Hardness graph – across the weld @ 15”/min 52

6.6(a). Hardness graph – across the weld @ 10”/min 58

6.6(b). Hardness graph – across the weld @ 15”/min 58

6.6(c). Peak/Yield stress of the weld – 10”/min @ 750, 760 & 600 rpm 59

6.6(d). Break stress of the weld – 10”/min @ 750, 760 & 600 rpm 60

6.6(e). Weld 2 – change in stress due to change in welding pitch 61

6.6(f). Weld 3 – change in stress due to change in welding pitch 62

6.6(g). Weld 2 & weld 3 – change in hardness due to change in welding pitch 63


ix

6.7(b). Microstructure of the weld nugget 68






6.11(b). Peak/yield stress variation 85

6.11(c). Break stress variation 85

6.11(d). Variation in hardness 86


6.12(b). Microstructure of the weld nugget 92


6.13(b). Microstructures of the weld 96

6.14(a). Specific weld energy as a function of welding speed and tool geometry 97

6.14(b). Required weld power as a function of tool geometry and welding speed 98

6.14(c). Transverse tensile strength of the welds as a function of tool geometry

and welding speed 99

6.14(d). X axis force as a function of tool geometry and welding pitch 99



6.16(a). Microstructure of the weld nugget 106

6.17(a). Microstructure of the weld nugget 109

6.18(a). Hardness graph - across the weld 113

x


6.18(c). Variation in peak and yield stress 114

6.18(d). Variation in break stress 114

6.18(e). Variation in hardness 115

xi

LIST OF TABLES

6.4(a). Tensile test data of parent 1 – Alclad 2024-T3 43 6.4(b). Tensile test data of parent 2 - Al 7075-T6 44 6.4(c). Tensile test data of the weld 44 6.4(d). Hardness test data – along the weld 45 6.4(e). Hardness test data – across the weld 46 6.5(a). Tensile test data of parent 1 – Alclad 2024-T3 48 6.5(b). Tensile test data of parent 2 – Al 7075-T6 48 6.5(c). Tensile test data of weld @ 10”/min 49 6.5(d). Tensile test data of the weld @ 15”/min 49 6.5(e). Hardness test data – along the weld 51 6.5(f). Hardness test data – across the weld 51 6.6(a). Tensile test data of parent1 – Alclad 2024-T3 54 6.6(b). Tensile test data of parent 2 - Al 7075-T6 54 6.6(c). Tensile test data of the weld @10"/min 55 6.6(d). Tensile test data of the weld @ 15"/min 55 6.6(e). Hardness test data - along the weld 57 6.6(f). Hardness test data - across the weld 57 6.7(a). Tensile test data of parent1 - Alclad 2024-T3 64 6.7(b). Tensile test data of parent 2 - Al 7075-T6 65 6.7(c). Tensile test data of the weld 65 6.7(d). Hardness test data- along the weld 66 6.7(e). Hardness test data - across the weld 67

xii

6.8(a). Tensile test data of parent1 – Alclad 2024-T3 69 6.8(b). Tensile test data of parent2 - Al 7075-T6 69 6.8(c). Tensile test data of the weld 70 6.8(d). Hardness test data – along the weld 71 6.8(e). Hardness test data – across the weld 71 6.9(b). Tensile test data of the parent – Al 6061-T6 74 6.9(b). Tensile test data of the weld 74 6.9(c). Hardness test data – along the weld 75 6.9(d). Hardness test data – across the weld 75 6.10(a). Tensile test data of the parent – Al 6061-T6 77 6.10(b). Tensile test data of the weld 78 6.10(c). Hardness test data – along the weld 79 6.10(d). Hardness test data – across the weld 79 6.11(a). Tensile test data of the parent – Al 6061-T6 81 6.11(b). Tensile test data of the weld 82 6.11(c). Hardness test data - along the weld 83 6.11(d). Hardness test data – across the weld 83 6.12(a). Tensile test data of the parent – Al 2024-T3 88 6.12(b). Tensile test data of the weld 89 6.12(c). Hardness test data – along the weld 90 6.12(d). Hardness data – across the weld 90 6.13(a). Tensile test data of the parent – Alclad 2024-T3 93 6.13(b). Tensile test data of the weld 93

xiii

6.13(c). Hardness test data – along the weld 94 6.13(d). Hardness test data – across the weld 95 6.14. Tool geometry 97 6.15(a). Tensile test data of the parent - Al 7075-T6 100 6.15(b). Tensile test data of the weld 101 6.15(c). Hardness test data – along the weld 102 6.15(d). Hardness test data – across the weld 102 6.16(a). Tensile test data of the parent Al 7075-T6 104 6.16(b). Tensile test data of the weld 105 6.16(c). Hardness test data – along the weld 106 6.17(a). Tensile test data of the parent Al 7075-T6 107 6.17(b). Tensile test data of the weld 108 6.17(c). Hardness test data – along the weld 109 6.18(a). Tensile test data of the parent Al 7075-T6 110 6.18(b). Tensile test data of the weld 111 6.18(c). Hardness test data – across the weld 112 6.18(d). Hardness test data – across the weld 112 6.19(a). Tensile test data of the parent Al 7075-T6 116 6.19(b). Tensile test data of the weld (tilted). 117 6.19(c). Tensile test data of the weld (untilted). 117 6.20(a). Hardness test data of the weld 119 6.21(a). Hardness test data of the weld 120

xiv

CHAPTER 1

INTRODUCTION

Friction Stir Welding (FSW) was developed at and patented by The Welding Institute

(Cambridge, UK) in 1991. Since the time of its invention, the process has been

continually improved and its scope of application expanded. Friction Stir Welding is a

solid state joining process combining deformation heating and mechanical work to obtain

high quality, defect free joints. Friction stir welding is especially well suited to joining

Aluminum alloys in a large range of plate thickness and has particular advantages over

fusion welding when joining of highly alloyed Aluminum is considered [1].

Because of many demonstrated advantages of FSW over fusion welding techniques, the

commercialization of FSW is proceeding at a rapid pace. Much of the work done to bring

FSW to production applications has been of a very practical nature, driven primarily by

the pressing industrial need. Industry, federal laboratories and universities have been

investigating this technique for joining Aluminum, Steel, Titanium, Metal matrix

composites and even hard metals. Research and engineering is rapidly progressing across

many fronts. Fundamental research is investigating critical phenomenon through process

modeling, microstructure studies, properties and tool wear. FSW has matured to a point

where laboratory research is beginning to transition to Aluminum alloy structural

applications [1].

1

In principle, Friction Stir Welding is a very simple process. The two plates to be welded

are butted together (lap and other configurations are also possible) and clamped to a rigid

backing plate. The rotating FSW tool is plunged into the plates at the joint line and

traversed along the line, forming the joint.

Fig 1.1: Friction stir welding process [34].

Because the FSW process has only recently become a subject of wide study, there are

currently no large databases of weld properties and, in fact, no specifications on how to

make or test friction stir welds currently exist. In general, the process is robust and a wide

nge of processing parameters and tool designs can be used to make metallurgically

fects may be made

ra

sound welds in a given alloy and plate thickness. While weld free of de

using a wide range of processing parameters, the chosen process parameters may

significantly affect the mechanical properties of the weld either through direct

modification of the weld microstructure or by indirect influence (e.g. by modification of

residual stress state) [1].

2

1.1. Welding

Welding can be defined as the joining of two components by a coalescence of the

surfaces in contact with each other. This coalescence can be achieved by melting the two

parts together – fusion welding – or by bringing the two parts together under pressure,

perhaps with the application of heat, to form a metallic bond across the interface. This is

known as solid phase joining [2].

th

Welding is by no means a new science. According to some researchers, its origin dates

back to the very beginning of the technology of metals. For instance, some welded copper

utensils have been traced to the days of the Sumerian civilization (14 century B.C).

Also, welding is mentioned by the prophet Isaiah in the Old Testament, by the Greek

historian Herodotus in his “Clio”, by the Latin writer Pliny the Elder in his “Naturalis

Historia”, and by many other prominent contributors to ancient history. Coming down

Welding is the most economical and efficient way to join metals permanently. Welding

ranks high among industrial processes and involves more sciences and variables than

those involved in any other industrial process. In many cases welding is the most cost

effective and structurally sound joining technique. Welding can be performed almost any

through the ages, welding and its application progressed rather slowly, principally

because of the limitations of the primitive methods used and of the empirical technical

knowledge available. However, toward the end of the 19th century and the beginning of

the 20th century, the art and science of welding began to advance at a very rapid pace.

Today it constitutes, by far, one of the most important and widely used tools for the

joining of metals [9].

3

where out doors, indoors, under sea or in space. Some of the processes cause sparks

where as others do not even require extra heat. Most of the things we use in our daily life

are welded.

1.2. The Physical Nature of Joining [5]

atoms on the opposing metallic

tly

pla s

distanc g. At this

poi p

single s

1.3. W etallurgical Point of View [5]

he forces inherent in the metallic objects can bring about perfect coalescence only if:

• The oxides and other non-metallic films present on real metallic surfaces can

either be removed or completely dispersed from the areas being joined.

of the proposed joint

to a

Theoretically, to produce a weld, one need only bring the

surfaces close enough to establish the spontaneous attractive forces. Ideally, two perfec

ne urfaces, if treated in this fashion, would be drawn together spontaneously until the

e separating them corresponds to the equilibrium interatomic spacin

nt, erfect “coalescence” would result and the two objects would merge to comprise a

olid body.

elding, From a M

T

• The distance separating the metallic atoms on one surface

from those on the opposing surface of the joint can be reduced consistently

value approximately the equilibrium atomic spacing for the metal, thus producing

a metallic bond.

4

1.4 M

Basical

• s, in which externally applied forces play an

important role in the bonding operation, whether consummated at room or

elevated temperature.

elding Processes, in which the joining operation involves melting

and solidification, and any external forces applied to the system play no active

role in producing coalescence.

1.5. Types W

1. Arc welding

• Submerged Arc Welding

• Gas Metal Arc and Flux Cored Arc Welding

• Gas Tungsten Arc Welding

• Plasma Arc Welding

• Electroslag and Electrogas Welding

2. Resistance Welding

3. Flash Welding

4. Oxyfuel Gas Welding

• Friction Welding

. A etallurgical Classification of the Welding Processes [5]

ly, it is convenient to divide the welding processes into two major categories:

The Pressure Welding Processe

• The Fusion W

of elding

• Shielded Metal Arc Welding

5. Solid State Welding

5

• Friction stir welding

fusion Welding

6. Electron Beam Welding

7. Laser Beam Welding

8. Brazing

9. Soldering

10. Induction welding

• Dif

Fig 1.2: Master chart of welding and allied processes [30].

6

1.6. Solid State Welding (SSW)

Solid state welding is "a group of welding processes which produces coalescence at

temperatures essentially below the melting point of the base materials being joined

without the addition of a brazing filler metal. Pressure may or may not be used".

The oldest of all welding processes forge welding belongs to this group. Others include

1.7. Friction Welding

aterials by the heat obtained from mechanically induced

sliding motion between rubbing surfaces. The work parts are held together under

pressure. This process usually involves the rotating of one part against another to

generate frictional heat at the junction. When a suitable high temperature has been

reached, rotational motion ceases and additional pressure is applied and coalescence

occurs [33].

cold welding, diffusion welding, explosion welding, friction welding, hot pressure

welding, and ultrasonic welding. These processes are all different and utilize different

forms of energy for making welds [30].

Friction, which requires relative motion, pressure and time, is an efficient thermal energy

source for the welding of materials. Friction welding is a solid state welding process

which produces coalescence of m

7

Fig 1.3: Friction welding and processing technologies [32].

1.8. Rotary Friction Welding

Two variants of the rotary friction welding process have been developed. These are

known as conventional ‘continuous drive friction welding’ and stored energy friction

welding where the most widely adopted is inertia friction welding. In both these methods,

friction welds are made by holding a rotating component in contact with a non-rotating

component while under a constant or increasing axial load. The interface reaches the

appropriate welding temperature, at which point rotation is stopped and the weld

completed [31].

8

CHAPTER 2

2.1. Introduction

ALUMINUM WELDING

Aluminum is the most abundant metal in nature. Some 8% by weight of the Earth’s crust

ce of Aluminum was postulated by Sir Humphrey Davy in the first decade of

the nineteenth century and the metal was isolated in 1825 by Hans Christian Oersted. It

remained as somewhat of a laboratory curiosity for the next 30 years when some limited

rocess [2].

Pu A

nontox

easily f oys

wit m

very us

Aluminum is the most difficult metal to weld. Aluminum oxide should be cleaned from

the surface prior to welding. Aluminum comes in heat treatable and non heat treatable

alloys.

is Aluminum. Many rocks and minerals contain a significant amount of Aluminum.

Unfortunately, Aluminum does not occur in nature in the metallic form. In rocks,

Aluminum is present in the form of silicates and other complex compounds. The ore from

which most Aluminum is presently extracted, Bauxite, is a hydrated Aluminum oxide [1].

The existen

commercial production began, but it was not until 1886 that the extraction of Aluminum

from Bauxite became a truly viable industrial p

re luminum is a silvery-white metal with many desirable characteristics. It is light,

ic (as the metal), nonmagnetic and nonsparking. It is somewhat decorative. It is

ormed, machined and cast. Pure Aluminum is soft and lacks strength, but all

h s all amounts of Copper, Magnesium, Silicon, Manganese and other elements have

eful properties [4].

Heat treatable aluminum alloys get their strength from a process called ageing.

9

Sig ic

aging [

2.2. Characteristics of Aluminum [2]

Lis f Aluminum, contrasted

wit

• The difference in the melting points of the two metals and their oxides. The

• The oxide film on Aluminum is durable, highly tenacious and self-healing. This

ance.

• The coefficient of thermal expansion of Aluminum is approximately twice that of

Steel.

• The coefficient of thermal conductivity of Aluminum is six times that of Steel.

• The specific heat of Aluminum – the amount of heat required to raise the

temperature of a substance – is twice that of Steel.

nly three-quarters that of Copper but

ises.

• Alu n

• Alu n elasticity three times that of Steel.

nif ant decrease in tensile strength can occurs when welding aluminum due to over

3].

ted below are the main physical and chemical Characteristics o

h those of Steel:

oxides of Iron all melt close or below the melting point of the metal; Aluminum

oxide melts at 20600 C, some 14000 C above the melting point of Aluminum.

gives the Aluminum alloys excellent corrosion resist

• Aluminum has high electrical conductivity, o

six times that of Steel.

• Aluminum does not change color as its temperature r

mi um is non-magnetic.

mi um has a modulus of

10

• Alu n its crystal structure on heating and cooling, unlike

Ste w mations or phase changes at specific

tem

2.3. Aluminum Alloy Designation – Wrought Alloys [6]

Pure Aluminum is readily alloyed with many other metals to produce a wide range of

echanical properties. This means by which the alloying elements

to classify Aluminum alloys into two

categories: nonheat treatable and heat treatable.

• 2xxx – Al-Cu alloys

• 3xxx – Al-Mn alloys

8xxx – Al + other elements

mi um does not change

el hich undergoes crystal transfor

peratures.

physical and m

strengthen Aluminum are used as the basis

1. First digit – Principal alloying constituent(s)

2. Second digit – Variations of initial alloy

3. Third and fourth digits – Individual alloy variations

• 1xxx – Pure Al (99.00% or greater)

• 4xxx – Al-Si alloys

• 5xxx – Al-Mg alloys

• 6xxx – Al-Mg-Si alloys

• 7xxx – Al-Zn alloys

•

• 9xxx – Unused series

11

2.4. Nonheat Treatable Aluminum Alloys [6]

The initial strength of the nonheat treatable Aluminum alloys depends primarily upon the

hardening effect of alloying elements such as Silicon, Iron, Manganese and Magnesium.

These elements affect increase in strength either as dispersed phases or by solid solution

strengthening. The nonheat treatable alloys are mainly found in the 1xxx, 3xxx, 4xxx,

and 5xxx alloy series depending upon their major alloying elements.

2.5. Heat Treatable Aluminum Alloys [6]

p

their properties by solution heat treating and quenching, followed by either natural or

artificial aging. The heat treatable alloys are found primarily in the 2xxx, 6xxx and 7xxx

alloy series.

2.6. Wrought Aluminum Alloys [6, 2]

rties, and excellent

workability. Moderate increases in strength may be obtained by strain hardening. Iron

and silicon are the major impurities.

The initial strength of Aluminum alloys in this group depends upon the alloy

composition, just as the nonheat treatable alloys. Heat treatable Aluminum alloys develo

1xxx: This series represent the commercially pure Aluminum, ranging from the baseline

1100 (99% min Al) to relatively purer 1050/1350 (99.5% min Al) and 1175 (99.75% min

Al).These grades of Aluminum are characterized by excellent corrosion resistance, high

thermal and electrical conductivities, low mechanical prope

12

2xxx: The major alloying element in 2xxx series alloys is Copper. The alloys in this

series are heat treatable and possess good combinations of high strength (especially at

elevated temperatures), toughness and in specific cases, weldability. They are not

resistant to atmospheric corrosion and so are usually painted or clad in such exposures.

the melting range. For

this reason, Aluminum-Silicon alloys are used in welding wire and as brazing alloys for

joining Aluminum, where a lower melting range than that of the base metal is required.

w characteristics and medium strength.

lloying element is Magnesium and when it is used as a major alloying

element or with Manganese, the result is a moderate-to-high-strength work-hardenable

alloy. Magnesium is considerably more effective than Manganese as a hardener, about

0.8% Mg being equal to 1.25% Mn, and it can be added in considerably higher

quantities. Alloys in this series possess excellent corrosion resistance even in salt water

6xxx: Alloys in the 6xxx series contain Silicon and Magnesium. Although not as strong

as most 2xxx and 7xxx alloys, 6xxx series alloys have relatively good formability,

3xxx: The major alloying element in 3xxx series alloys is Manganese. These alloys are

strain hardenable, have excellent corrosion resistance and are readily welded, brazed and

soldered.

4xxx: The major alloying element in 4xxx series alloys is Silicon, which can be added in

sufficient quantities (up to 12%) to cause substantial lowering of

These alloys have good flo

5xxx: The major a

and very high toughness even at cryogenic temperature to near absolute zero.

13

weldability, machinability, and relatively good corrosion resistance, with medium

strength.

7xxx: Zinc, in amounts of 1 to 8% is the major alloying element in 7xxx series alloys.

These alloys are heat treatable and possess very high strength.

8xxx: The alloys in this series have high conductivity, strength and hardness.

2.7. Welding Aluminum

GTAW Welding

es when high quality, precision welding is required.

MIG Welding

Gas Metal Arc Welding (GMAW) is frequently referred to as MIG welding. MIG

ing

process.

Gas Tungsten Arc Welding (GTAW) is frequently referred to as TIG welding. TIG

welding is a commonly used high quality welding process. TIG welding has become a

popular choice of welding process

In TIG welding an arc is formed between a non consumable tungsten electrode and the

metal being welded. Gas is fed through the torch to shield the electrode and molten weld

pool. If filler wire is used, it is added to the weld pool separately.

welding is a commonly used high deposition rate welding process. Wire is continuously

fed from a spool. MIG welding is therefore referred to as a semiautomatic weld

14

Flux Cored Welding

Flux Cored Arc Welding (FCAW) is frequently referred to as flux cored welding. Flux

mmonly used high deposition rate welding process that adds the

benefits of flux to the welding simplicity of MIG welding. As in MIG welding wire is

continuously fed from a spool. Flux cored welding is therefore referred to as a

semiautomatic welding process.

is generally more forgiving than MIG welding. Less

precleaning may be necessary than MIG welding. However, the condition of the base

metal can affect weld quality. Excessive contamination must be eliminated.

Shielded Metal Arc Welding (SMAW) is frequently referred to as stick or covered

elding is among the most widely used welding processes.

Resistance Welding

Resistance Spot Welding (RSW), Resistance Seam Welding (RSEW), and Projection

Welding (PW) are commonly used resistance welding processes. Resistance welding

cored welding is a co

Self shielding flux cored arc welding wires are available or gas shielded welding wires

may be used. Flux cored welding

Stick Welding

electrode welding. Stick w

The flux covering the electrode melts during welding. This forms the gas and slag to

shield the arc and molten weld pool. The slag must be chipped off the weld bead after

welding. The flux also provides a method of adding scavengers, deoxidizers, and alloying

elements to the weld metal.

15

uses the application of electric current and mechanical pressure to create a weld between

two pieces of metal. Weld electrodes conduct the electric current to the two pieces of

metal as they are forged together.

The welding cycle must first develop sufficient heat to raise a small volume of metal to

the molten state. This metal then cools while under pressure until it has adequate strength

to hold the parts together. The current density and pressure must be sufficient to produce

a weld nugget, but not so high as to expel molten metal from the weld zone.

Electron Beam Welding

Electron Beam Welding (EBW) is a fusion joining process that produces a weld by

impinging a beam of high energy electrons to heat the weld joint. Electrons are

The electron beam is always generated in a high vacuum. The use of specially designed

orifices separating a series of chambers at various levels of vacuum permits welding in

medium and no vacuum conditions. Although, high vacuum welding will provide

maximum purity and high depth to width ratio welds.

elementary atomic particles characterized by a negative charge and an extremely small

mass. Raising electrons to a high energy state by accelerating them to roughly 30 to 70

percent of the speed of light provides the energy to heat the weld.

16

CHAPTER 3

FRICTION STIR WELDING

3.1. Introduction [11]

Conventional friction welding has been around for many years, but relies on relative

motion between the parts to be joined while pressure is applied. The need to move one or

oth parts restricts the conventional friction process between relatively simple shapes –

thus joining plate or sheet is almost impossible. In Friction Stir Welding (FSW), a

cylindrical, shouldered tool with a profiled probe is rotated and slowly plunged into the

int line between two pieces of sheet or plate material, which are butted together. The

parts have to be clamped onto a backing bar in a manner that prevents the abutting joint

faces from being forced apart. Frictional heat is generated between the wear resistant

welding tool and the mat uses the latter to soften

without reaching the melting point and allows traversing of the tool along the weld line.

The plasticized material is transferred from the leading edge of the tool to the trailing

b

jo

erial of the work pieces. This heat ca

edge of the tool probe and is forged by the intimate contact of the tool shoulder and the

pin profile. It leaves a solid phase bond between the two pieces. The process can be

regarded as a solid phase keyhole welding technique since a hole to accommodate the

probe is generated, then filled during the welding sequence.

17

Figure 3.1: Friction stir welding [11].

The whole of rotating device between the machine spindle and the work piece is referred

In a non-cylindrical tool the terms ‘leading edge’ (front face of shoulder during welding)

and ‘trailing edge’ (rear face of shoulder during welding) are used, whereas in cylindrical

tools there is clearly no edge, and so the terms ‘leading face’ and ‘trailing face’ may be

preferred. ‘Probe leading face’ is the front face of the probe during welding. Similarly

As the tool may in some circumstances be tilted through a small angle, part of the

shoulder may be embedded deeper into the work piece. That part of the shoulder which

experiences the greatest penetration is referred to as the ‘heel’ and the maximum depth of

the shoulder penetration below the work piece surface is defined as the ‘heel plunge

3.2. Different parameters in FSW [11]

to as the ‘tool’. The part of the tool, which is embedded in work piece during welding, is

referred to as the ‘probe’. The part of the tool, which is pressed onto the surface of the

work piece during welding, is referred to as the ‘shoulder’.

‘probe trailing face’ is the rear face of the probe during welding.

18

depth’. The angle of tilt is referred to as the ‘tilt angle’, or ‘travel angle’. In some

instances the tool is tilted sideways, and in this case the angle is described as the

‘sideways tilt angle’ or ‘work angle’.

The side of the weld where the local direction of the tool is the same as the traversing

direction or the side of the weld where direction is the same as the direction of rotation of

e shoulder is called the ‘advancing side’. Similarly, the side where the directions are

opposite and the local movement of the shoulder is against the traversing direction or side

of the weld where direction of travel is opposed to direction of rotation of shoulder is

he total area of the tool on the work piece surface is

described as the ‘tool shoulder footprint’.

Forces are an important part of friction stir welding technology. The force applied

parallel to the axis of rotation of the tool (Z-direction) is the ‘down force’, and the force

applied parallel to the welding direction (X-direction) is the ‘traversing force’. The force

developed in a direction perpendicular to both X and Z forces is ‘Side force’ (Y-

direction).

th

called the ‘retreating side’. T

The term ‘Welding speed’ is preferred to traversing speed or traversing rate, which is the

rate of travel of tool along joint line. ‘Tool Rotation speed’ is the rotation speed of the

friction stir welding tool. ‘Clockwise Rotation’ is when viewed from above the tool,

looking down onto the work piece.

19

3.3 r

The key benefits of this newly developed welding process include an increase in joint

efficiency and process robustness, as well as a greater range of applicable alloys that can

be welded. Friction Stir Welding will permit production-welding opportunities relative to

dissimilar alloys and m ht to be "unweldable" such as Aluminum

alloy. Com materials for this welding process. Friction

tise and training. The process advantages result from the fact that the FSW process

(as all Friction Welding of metals) takes place in the solid phase below the melting point

of t m erefore include the ability to join materials

that e

are as f

s

• No spatter

. P ocess Advantages [11]

aterials previously thoug

posite materials are also candidate

Stir Welding's solid-phase, low distortion welds are achieved with relatively low costs,

use simple energy efficient mechanical equipment, and require minimal operator

exper

he aterials to be joined. The benefits th

ar difficult to fusion weld, for example 2000 and 7000 Aluminum. Other advantages

ollows:

• Low distortion, even in long weld

• Excellent mechanical properties as proven by fatigue, tensile and bend tests

• No fume, No porosity

• Low shrinkage

• Can operate in all positions

• Energy efficient

20

Fric n ily available machine tool technology. The

pro s tomation and adaptable for robot use. Its main advantages

are:

erfect weld preparations - thin oxide layers can be accepted

• No grinding, brushing or pickling required in mass production

The limitations of the FSW process are being reduced by intensive research and

development. However, the main limitations of the FSW process are at present:

The repeatable quality of the solid-phase welds can improve existing products and lead to

a number of new product designs previously not possible. Welds with the highest quality

can be achieved by Friction Stir Welding. The crushing, stirring and forging action of the

tio Stir Welding can use existing and read

ces is also suitable for au

• Non-consumable tool, No filler wire

• One tool can typically be used for up to 1000m of weld length in 6000 series

aluminum alloys

• No gas shielding for welding aluminum

• No welder certification required

• Some tolerance to imp

• Welding speeds are moderately slower than those of some fusion welding

processes (up to 750mm/min for welding 5mm thick 6000 series aluminum alloy

on commercially available machines)

• Work pieces must be rigidly clamped

• Backing bar required

• Keyhole at the end of each weld

21

FSW tool produces a weld with a finer microstructure than the parent material. The weld

metal strength can be, in the as welded condition, in excess of that in the thermo-

mechanically affected zone.

3.3. Microstructure Classification [11]

The first attempt at classifying microstructures was made by P L Threadgill (Bulletin,

March 1997). This work was based solely on information available from Aluminum

e evident from work on other materials that the behavior of

Aluminum alloys is not typical of most metallic materials, and therefore the scheme

als. It is therefore proposed that the

scheme is used. This has been developed at TWI, but has been

discussed with a number of appropriate people in industry and academia, and has also

system divides the weld zone into distinct regions as follows:

alloys. However, it has becom

cannot be broadened to encompass all materi

following revised

been provisionally accepted by the Friction Stir Welding Licensees Association. The

A. Unaffected material or parent metal

Figure 3.2: Microstructure of a friction stir weld [11].

B. Heat affected zone (HAZ)

22

C. Thermo-mechanically affected zone (TMAZ)

Unaffected material or parent metal: This is material remote from the weld, which has

not been deformed, and which although it may have experienced a thermal cycle from the

weld is not affected by the heat in terms of microstructure or mechanical properties.

Thermo-mechanically affected zone (TMAZ): In this region, the Friction Stir Welding

tool has plastically deformed the material, and the h

D. Weld Nugget

Heat affected zone (HAZ): In this region, which clearly will lie closer to the weld

centre, the material has experienced a thermal cycle, which has modified the

microstructure and/or the mechanical properties. However, there is no plastic deformation

occurring in this area. In the previous system, this was referred to as the "thermally

affected zone". The term heat affected zone is now preferred, as this is a direct parallel

with the heat affected zone in other thermal processes, and there is little justification for a

separate name.

eat from the process will also have

exerted some influence on the material. In the case of aluminum, it is possible to get

significant plastic strain without recrystallisation in this region, and there is generally a

distinct boundary between the recrystallised zone and the deformed zones of the TMAZ.

In the earlier classification, these two sub-zones were treated as distinct micro structural

regions. However, subsequent work on other materials has shown that aluminum behaves

in a different manner to most other materials, in that it can be extensively deformed at

high temperature without recrystallisation. In other materials, the distinct recrystallised

23

region (the nugget) is absent, and the whole of the TMAZ appears to be recrystallised.

This is certainly true of materials, which have no thermally induced phase transformation,

which will in itself induce recrystallisation without strain, for example pure Titanium, b

Titanium alloys, Austenitic Stainless Steels and Copper. In materials such as Ferritic

Weld Nugget: The recrystallised area in the TMAZ in Aluminum alloys has traditionally

been called the nugget. Although this term is descriptive, it is not very scientific.

the tool shoulder (which is clearly part of the TMAZ)

should be given a separate category, as the grain structure is often different here. The

microstructure here is determined by rubbing by the rear face of the shoulder, and the

material may have cooled below its maximum. It is suggested that this area is treated as a

separate sub-zone of the TMAZ.

3.4. Joint Geometries

The process has been used for the manufacture of butt welds; overlap welds, T-sections,

fillet, and corner welds. For each of these joint geometries specific tool designs are

ccessfully tested.

Steels and a-b Titanium alloys (e.g.Ti-6Al-4V), understanding the microstructure is made

more difficult by the thermally induced phase transformation, and this can also make the

HAZ/TMAZ boundary difficult to identify precisely.

However, its use has become widespread, and as there is no word, which is equally

simple with greater scientific merit, this term has been adopted. It has been suggested

that the area immediately below

required which are being further developed and optimized. Longitudinal butt welds and

circumferential lap welds of Al alloy fuel tanks for space flights have been Friction Stir

Welded and su

24

The S ial, annular, non-linear, and three-

dim s ity has no influence on the solid-phase welding process, it

can

1.

2.

3.5. Applications

Shipbuilding and marine industries

Helicopter landing platforms

. for sailing boats

F W process can also cope with circumferent

en ional welds. Since grav

be used in all positions, viz:

Horizontal

Vertical

3. Overhead

4. Orbital

The shipbuilding and marine industries are two of the first industry sectors, which have

adopted the process for commercial applications. The process is suitable for the following

applications:

• Panels for decks, sides, bulkheads and floors

• Aluminum extrusions

• Hulls and superstructures

•

• Offshore accommodation

• Marine and transport structures

• Masts and booms, e.g

• Refrigeration plant

25

Aer p

space industry is welding prototype parts by Friction Stir Welding.

Opportunities exist to weld skins to spars, ribs, and stringers for use in military and

civilian aircraft. This offers significant advantages compared to riveting and machining

from solid, such as reduced manufacturing costs and weight savings. Longitudinal butt

wel a lap welds of Al alloy fuel tanks for space vehicles have been

friction o be used to increase the

size f forming. The Friction Stir

Welding process can therefore be considered for:

• Wings, fuselages, empennages

• Cryogenic fuel tanks for space vehicles

• Aviation fuel tanks

• External throw away tanks for military aircraft

• Military and scientific rockets

Railway industry

The minum extrusions which

ma e Applications include:

• High speed trains

• Rolling stock of railways, underground carriages, trams

• Railway tankers, goods wagons and Container bodies

os ace industry

At present the aero

ds nd circumferential

stir welded and successfully tested. The process could als

o commercially available sheets by welding them before

• Repair of faulty MIG welds

commercial production of high-speed trains made from Alu

y b joined by friction stir welding has been published.

26

Lan t

The friction stir welding process is currently being experimentally assessed by several

and suppliers to this industrial sector for its commercial

application. A joint EWI/TWI Group Sponsored Project is investigating representative

joint designs for automotive lightweight structures. Potential applications are:

• Engine, chassis cradles and wheel rims

• Attachments to hydro formed tubes

• Tailored blanks, e.g. welding of different sheet thicknesses

• Space frames, e.g. welding extruded tubes to cast nodes

• Truck bodies, Tail lifts for lorries, Mobile cranes

• Armor plate vehicles and Fuel tankers

ses and airfield transportation vehicles

• Motorcycle, bicycle frames and Repair of aluminum cars

• Articulated lifts and personnel bridges

Construction industry

ent is possible for:

d ransportation

automotive companies

• Ships, bu

• Magnesium and magnesium/aluminum joints

The use of portable FSW equipm

• Aluminum bridges

• Facade panels made from aluminum, copper or titanium

• Window frames and Aluminum pipeline.

27

CHAPTER 4

MECHANICAL TESTING AND METALLOGRAPHY

4.1. Testing [7]

1. Test development: to create or refine the test method itself.

2. Design: to create or select materials for specific applications.

3. Quality control: to verify that incoming material is acceptable.

4.2. Tensile Test [7]

ermine several characteristics about the mechanical behavior of the

material.

There are several reasons for performing tensile tests. The results of tensile tests are used

in selecting materials for engineering applications. Tensile properties frequently are

included in material specifications to ensure quality. Tensile properties often are

measured during development of new materials and processes, so that different materials

and processes can be compared. Finally, tensile properties often are used to predict the

behavior of a material under forms of loading other than uniaxial tension.

Mechanical testing of materials is generally performed for one of the following reasons:

Uniaxial tensile test is one of the most frequently performed mechanical tests. This type

of test generally involves gripping a specimen at both ends and subjecting it to increasing

axial load until it breaks. Recording of load and elongation data during the test allows the

investigator to det

28

The strength of a material often is the primary concern. The strength of interest may be

measured in terms of either the stress necessary to cause appreciable plastic deformation

or the maximum stress that the material can withstand. Also of interest is the material’s

ductility, which is a measure of how much it can be deformed before it fractures. Low

ductility in a tensile test to fracture under other

forms of loading.

The figure below shows a typical tensile test specimen. It has enlarged ends or shoulders

for gripping. The important part of the specimen is the gage section. The cross-sectional

area of the gage section is reduced relative to that of the remainder of the specimen so

that deformation and failure will be localized in this region. The gage length is the region

nts are made and is centered within the reduced section. The

distances between the ends of the gage section and the shoulders should be great enough

so that the larger ends do not constrain deformation within the gage section.

often is accompanied by low resistance

4.3. Tensile Specimens [7]

over which measureme

Figure 4.1: Tensile test specimen [11].

29

A tensile test involves mounting the specimen in a machine and subjecting it to tension.

The tensile force is recorded as a function of the increase in gage length. When force-

elongation data are converted to engineering stress and strain, a stress-strain curve that is

identical in shape to the force-elongation curve can be plotted. The advantage of dealing

with stress versus strain rather than load versus elongation is that the stress-strain curve is

virtually independent of specimen dimensions.

4.4. Hardness Test [8]

Hardness has a variety of meanings. To the metal industry, it may be thought of as

resistance to permanent deformation. To the metallurgist, it means resistance to

penetration. To the lubrication engineer, it means resistance to wear. To the design

engineer, it is a measure of flow stress. To the mineralogist, it means resistance to

scratching. To the machinist, it means resistance to machining. Hardness may also be

e plastic

flow stress of materials.

or a definite time

interval and a measurement is made of the size or depth of the indentation. Hardness is

not a fundamental property of a material. Hardness values are arbitrary and there are no

absolute standards of hardness. Hardness has no quantitative value, except in terms of a

referred to as mean contact pressure. All of these characteristics are related to th

Hardness test is one of the most valuable and widely used mechanical tests for evaluating

the properties of metals as well as certain other materials. The hardness of a material

usually is considered resistance to permanent indentation. In general, an indenter is

pressed into the surface of the metal to be tested under a specific load f

30

given load applied in a specific manner for a specified duration and a specified penetrator

shape.

The principal purpose of the hardness test is to determine the suitability of a material for

a given application or the particular treatment to which the material has been subjected.

The importance of hardness testing has to do with the relationship between hardness and

other properties of material. The hardness test is simple, easy and relatively

nondestructive.

Hardness test is divided into two categories: Macrohardness and Microhardness.

Macrohardness refers to testing with applied loads on the indenter of more than 1 Kg and

covers, for example, the testing of tools, dies and sheet material in the heavier gages. In

microhardness testing, applied loads are 1 Kg and below and material being tested is very

thin (down to 0.0125 mm). Applications include extremely small parts, thin superficially

hardened parts, plated surfaces and individual constituents of materials.

4.5

1. Indentation tests

2. Microhardness testing

4. Special indentation tests

5. Rebound principle

6. Abrasion and erosion testing

7. Laboratory wear tests

. Types of Hardness Tests [8]

3. Scratch hardness test

31

8. Service tests

9. Electromagnetic testing

1. Hardness range of the test material

2. Size of the workpiece

3. Shape of the workpiece

4. Degree of flatness of the workpiece

4.6. Factors for Selection of Hardness Testing Methods [8]

5. Surface condition of the workpiece

6. Nature of the test material: homogeneous or nonhomogeneous

7. Effect of indentation marks

8. Number of identical pieces to be tested

9. Equipment availability

The Rockwell hardness test method consists of indenting the test material with a diamond

cone or hardened steel ball indenter. The indenter is forced into the test material under a

preliminary minor load F0 usually 10 kgf. When equilibrium has been reached, an

indicating device, which follows the movements of the indenter and so responds to

changes in depth of penetration of the indenter, is set to a datum position. While the

preliminary minor load is still applied an additional major load is applied with resulting

increase in penetration. When equilibrium has again been reach, the additional major load

is removed but the preliminary minor load is still maintained. Removal of the additional

4.7. Rockwell Hardness Test [15]

32

major load allows a partial recovery, so reducing the depth of penetration. The permanent

increase in depth of penetration, resulting from the application and removal of the

additional major load is used to calculate the Rockwell hardness number.

HR = E - e

F0 = preliminary minor load in kgf

F1 = additional major load

F = total load in kgf

e = permanent increase in depth of penetration due to major load F1 measured in units of

0.002 mm

E = a constant depending on form of indenter: 100 units for diamond indenter, 130 units

HR = Rockwell hardness number

D = diameter of steel ball

in kgf

for steel ball indenter

Figure 4.2: Rockwell Principle [15]

33

Advantages of the Rockwell hardness method include the direct Rockwell hardness

number readout and rapid testing time. Disadvantages include many arbitrary non-related

scales and possible effects from the specimen support anvil.

Metallography is the study of a materials microstructure. Analysis of a materials

microstructure aids in determining if the material has been processed correctly and is

Documentation - Metallographic analysis is a valuable tool. By properly documenting

the initial specimen condition and the proceeding microstructural analysis, metallography

provides a powerful quality control as well as an invaluable investigative tool.

rest and for easier handling. Depending upon the

material, the sectioning operation can be obtained by abrasive cutting (metals and metal

matrix composites), diamond wafer cutting (ceramics, electronics, biomaterials,

minerals), or thin sectioning with a microtome (plastics).

proper cutting speed, load and

coolant.

4.8. Metallographic Specimen Preparation Basics [14]

therefore a critical step for determining product reliability and for determining why a

material failed. The basic steps for proper metallographic specimen preparation include:

Sectioning and Cutting - Following proper documentation, most metallographic samples

need to be sectioned to the area of inte

Proper sectioning is required to minimize damage, which may alter the microstructure

and produce false metallographic characterization. Proper cutting requires the correct

selection of abrasive type, bonding, and size; as well as

34

Mounting - The mounting operation accomplishes three important functions (1) it

protects the specimen edge and maintains the integrity of a materials surface feature (2)

fills voids in porous materials and (3) improves handling of irregular shaped samples,

especially for automated specimen preparation. The majority of metallographic specimen

mounting is done by encapsulating the specimen into a compression mounting compound

(thermosets - phenolics, epoxies, diallyl phthalates or thermoplastics - acrylics), casting

into ambient cast able mounting resins (acrylic resins, epoxy resins, and polyester resins),

and gluing with a thermoplastic glues.

r course grinding is required to planarize the specimen and to reduce

the damage created by sectioning. The planar grinding step is accomplished by

decreasing the abrasive grit/ particle size sequentially to obtain surface finishes that are

ready for polishing. Care must be taken to avoid being too abrasive in this step, and

actually creating greater specimen damage than produced during cutting (this is

especially true for very brittle materials such as silicon).

The machine parameters which effect the preparation of metallographic specimens

includes: grinding/polishing pressure, relative velocity distribution, and the direction of

grinding/polishing.

ing - The purpose of the rough polishing step is to remove the damage

produced during cutting and planar grinding. Proper rough polishing will maintain

specimen flatness and retain all inclusions or secondary phases. By eliminating the

previous damage and maintaining the microstructural integrity of the specimen at this

Planar Grinding - o

Rough Polish

35

step, a minimal amount of time should be required to remove the cosmetic damage at the

final polishing step.

Rough polishing is accomplished primarily with diamond abrasives ranging from 9

micron down to 1 micron diamond. Polycrystalline diamond because of its multiple and

small cutting edges, produces high cut rates with minimal surface damage, therefore it is

the recommended diamond abrasive for metallographic rough polishing on low napped

polishing cloths.

Final Polishing - The purpose of fi to remove only surface damage. It

should not be used to remove any damage remaining from cutting and planar grinding. If

the damage from these steps is not complete, the rough polishing step should be repeated

nal polishing is

or continued.

Etching - The purpose of etching is to optically enhance microstructural features such as

grain size and phase features. Etching selectively alters these microstructural features

based on composition, stress, or crystal structure. The most common technique for

etching is selective chemical etching and numerous formulations have been used over the

years. Other techniques such as molten salt, electrolytic, thermal and plasma etching have

also found specialized applications.

36

CHAPTER 5

EXPERIMENTAL PROCEDURE

5.1. Tensile test

The most common measure of FSW quality after visual inspection for surface breaking

defects may be the transverse tensile test (loading direction perpendicular to the welding

irection.

These straps were then cut or machined into a ‘dog-bone’ shape, according to the ASTM

standards. The tensile tests were carried out at room temperature at a crosshead speed of

1 mm/min using a computer controlled testing machine. Load and strain ranges were

selected so that the test will fit the range. The tensile properties of each weld were

ress, Yield stress

and the elongation were recorded. These properties of the weld were then compared with

that of its parent metal to obtain the weld or joint efficiency.

5.2. Hardness Test

direction) [1]. The objective of transverse tensile test is to determine whether or not the

weld is suitable for its intended use. The Low-Speed Friction Stir welds and the High-

Speed Friction Stir welds were cut into straps perpendicular to the welding d

evaluated by a number of samples or tensile specimens cut from the same weld. The data

obtained from the tensile test such as Peak load, Break stress, Peak st

Rockwell hardness tester was employed to measure the hardness of the welds. The

hardness was measured in two ways:

37

Along the weld or longitudinal hardness of the weld: The hardness values of the weld

were recorded on the weld, from the starting point of the weld to the end point. This

shows the variation of the weld hardness from beginning to the end of the weld.

Across the weld or transverse hardness of the weld: Hardness measurements were made

across a weld, in a line, perpendicular to the welding direction. Made on the top surface

of the weld, a hardness traverse is a useful tool to help identify the weak zones of a weld.

The hardness values of the weld were then compared with that of its parent metal to

obtain the relative hardness of the weld or the hardness joint efficiency.

5.3. Metallographic Analysis

Metallographic analyses of the welds were carried out to detect weld defects present and

the microstructure of the weld zone. The welds were cross-sectioned perpendicularly to

the welding direction for metallographic analyses. These samples were then mounted in a

transparent epoxy. These mounted samples were then grinded and polished on abrasive

silicon carbide sheets. The samples were then fine polished, etched with Keller’s reagent

and observed by optical microscopy.

38

CHAPTER 6

In the early days of Friction Stir Welding, most welding was performed on modified

machine tools. The level of instrumentation available for process monitoring was often

minimal leading to a great deal of speculation on the quantitative effects of process

variable and tool geometry

RESULTS AND DISCUSSIONS

changes. Generally, these changes were correlated either with

improved joint strength or the ability to make a weld with greater speed: these are at best

indirect correlations with the true, physical, process changes. As the sophistication of

effects and high fidelity models of the process developed using

this understanding, we may in time be able to predict many of the effects which must

now be determined via trial and error [21].

Because the FSW process has only recently become a subject of wide study, there are

urrently no large databases of weld properties and, in fact, no specifications on how to

make or test friction stir welds currently exist. In general, the process is robust and a wide

range of processing parameters and tool designs can be used to make metallurgically

und welds in a given alloy and plate thickness. While weld free of defects may be made

using a wide range of processing parameters, the chosen process parameters may

significantly affect the mechanical properties of the weld either through direct

FSW equipment has increased, so has our ability to quantify the effects of process

variables. Correlation between the indirect effects of process changes and the direct

effects will greatly enhance our understanding of the process. With sufficient

understanding of these

c

so

39

modification of the weld microstructure or by indirect influence (e.g. by modification of

residual stress state) [1].

A series of welds was made in 6.4 mm thick plate at a weld pitch of 0.43 mm/rev. In

order to m

6.1. Effect of Changing Welding Speed at Constant Weld Pitch [21]

aintain constant weld pitch, the welding speed and the rpm were increased by

Fig 6.1: Required power and specific weld energy at constant weld pitch.

is indicates that weld

pitch is not, as sometimes suggested, a very good indicator of weld energy. Neither does

an advance per revolution that produces good welds at one speed guarantee good welds at

another.

the same factors for the various welds. Z axis load was varied to accommodate the

varying weld speeds.

0

500

1000

1500

2000

2500

3000

welding speed, mm/s

Pow

er (w

atts

) or E

nerg

y (J

/mm

)

0 2 4 6

Specific weld energypower

In the Fig 6.1, the relationship of weld power and the specific weld energy to welding

speed at constant weld pitch is illustrated. Weld energy decreases and the required power

increases with increasing welding speed at constant weld pitch. Th

40

Fig 6.2: X-axis force for welds made at constant weld pitch.

In the Fig 6.2, the relationship of X axis force to welding speed at constant weld pitch is

illustrated. The increase in X axis force with increasing welding speed at constant weld

pitch may indicate that the material being involved in the process is in different stages of

evolution when welded using different speeds. It is also interesting to note the lack of

rofo

.2. Temper Effects on Required Loads and Weld Energy [21]

Alloys 7075 and 7050 were each welded in three different tempers (0, T6 and T7). The

plate thickness was 9.5 mm and the same tool was used for all welds. All six welds were

made using 240 rpm tool rotation rate and 2.4 mm/s welding speed. For all six welds, the

x axis forces did not vary by more than 12%. The weld energies for both 7050 and 7075

varied by less than 3%. These results indicate that the composition is critical and the

welding forces and torques may be independent of starting microstructure.

0

2

8

10

12

X-xi

s f

ce, k

4

6

0 1 2 3 4 5 6

Welding speed, mm/s

aor

N

p und effect of the Z axis force on the weld energy and power.

6

41

6.3. Alloy Effects on Specific Weld Energy [21]

Al 6061-T6, Al 7075-T6 and Al 2024-T3 were welded at three different welding speeds

of 1.3 mm/s, 2.4 mm/s and 3.3 mm/s. For each weld, the specific weld energy decreases

with increase in welding speed. This effect may be observed in Fig 6.3.

Fig 6.3: Specific weld energy as a function of welding speed.

he highest energy per unit weld length is observed when welding alloy 6061. This is

probably because of the relatively high thermal conductivity of the alloy and hence,

thermal energy would diffuse away from the weld zone at the greatest rate in 6061. The

ecreasing welding speed are essentially

the same for all the alloys tested.

0

500

ecifi

c

1000

1500

2000

2500

0 1 2 3 4

Welding Speed, mm/s

Sp

wel

d en

ergy

, J/m

m

7075-T66061-T62024-T3

T

relative changes in weld energy associated with d

42

6 LO D O EL

6.4.1. Tensile Test – Parent 1 (Al

SI

.4. W-SPEE FRICTI N STIR W D 1

Peak

Load

Peak

(lb) Stress (psi)

BS(

1121.63 37387.70 3541

1121.63

56081.60 5362

1121.63

56081.60 5363

Avg

1121.63

49850.30 47

Table 6.4(a): Tensi

Mate ad

Type of Joint: Lap

Rotational Speed: 7

Tool Shoulder Diam

rials: Alcl 2

Welding Speed: 10”

Weld Spe ioncificat s

(0.0 Al (0.04

50 rpm

eter: 0.375 in

024-T3 80”) & 7075-T6 0”)

/min

clad 2024-T3)

reak tress psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

Tangent

(%)

Modulus

(psi)

41.30 16.20 37387.70 15.2 735124

48.60 16.00

56081.60

13.8

1084599

48.60

15.00

56081.60 13.7

998141

579.5

15.70

49850.30

14.2

939288

le test data of parent 1 – Alclad 2024-T3.

43

6.4 . Ten st – 2 ( -T

S

.2 sile Te Parent Al 7075 6)

I

Peak Peak Break Stress (psi)

Break Elongation

(%)

Yield Tangent Yield Stress (psi)

Stress (psi)

Elongation (%)

Load (lb)

Modulus (psi)

1

722.61

72261.30 70314.90 11.10

72261.30 8.8 2324608

2

712.88

71288.10 68368.50 10.30 71288.10 8.8

2035341

3

693.42

69341.70 67395.30 10.20 69341.70 8.6 2086943

Avg 709.64

70963.70 68692.90 10.50 70963.70 8.6

2148964

6.4.3. Tensile Test - Weld

SI

Table 6.4(b): Tensile test data of parent 2 - Al 7075-T6.

Peak Load

Peak Stress

Break Stress

Break Yield Stress

Yield Elongation

Tangent Elongation Modulus

(lb) (psi) (psi) (psi) (%) (psi) (%) 1

1637.44 54581.20 54256.80 7.30 54581.20 7.30 911848

2 1715.29 57176.50 56852.10 8.10 57176.50 8.10 924842 3

688.40 6.20 980258 1520.65 50688.40 50364.00 6.20 50

4 1549.85 51661.60 51661.60 7.00 51661.60 7.10 843674

Avg

1566.53 52217.73 51986.01 7.10 52217.73 7.1 941437

Table 6.4(c): Tensile test data of the weld.

44

• The joint efficiencies (weld / parent ratio) of the weld with respect to parent 1

(Alclad 2024-T3) are 1.09 and 1.05 for Break stress and Peak / Yield stress

respec plies that the tensile strength of the weld is more than parent

1.

• The joint efficiencies of the weld with respect to parent 2 (Al 7075-T6) are 0.76

and 0.74 r Break s nd Peak / Y ess respec This implies that

the tensile strength of the weld is less than parent 2.

• The average break and yield elongation of the weld is much lower than the

average break and yield elongation of its parents.

fractured in the TMAZ on the retreating side.

• Parent 2, even though has a better tensile properties than parent 1, was the first to

fracture. This might be due to the constant contact of parent 2 with tool shoulder.

6 rdn t – A he W

Parent

tively. This im

fo tress a ield str tively.

• All the weld tensile test specimens

.4.4. Ha ess Tes long t eld

SI No

Al 7075-T6

Alclad 2024-T3

dWel

1 84.30 70.00 77.00 2 84.00 69.40 74.60 3 84.70 68.90 74.60 4 84.00 70.20 76.50

Avg 84.25 69.63 75.68

Table 6.4(d): Hardness test data – along the weld.

45

6.4 H

SI No

.5. ardness Test – Across the Weld

Parent HAZ TMAZ Nugget TMAZ HAZ Parent

Weld

76.20

73.80

75.70

84.80

83.80

84.30

81.10

77.80

73.40

68.90

73.80 72.50 76.80 83.70

84.10 81.90 73.40 77.00 74.70 69.50 84.30

Avg 84.07 80.27 71.90 75.67 73.67 74.00 84.27

Table 6.4(e): Hardness test data – across the weld.

1. HARDNESS TEST ( HRB )

70.00

72.00

74.00

76.00

78.00

80.00

82.00

84.00

86.00

0 1 2 3 4 5 6 7 8

HR

B

Figure 6.4(a): Hardness graph – across the weld.

• As seen in the ss value compared to

parent 1 and is softer than parent 2. The hardness joint efficiencies are 1.10 and

0.90 for parent 1 and parent 2 respectively.

region (i.e. softened

region) has occurred in each joint [10].

Table 6.4(d), the weld has a better hardne

• It can be seen from Figure 6.4(a) that a hardness degradation

46

• There are two low hardness zones on the two sides of the weld center, but the

minimum hardness value exists in the low hardness zone on the retreating side,

accordingly the joint is fractured on the retreating side [10]. This implies that the

tensile properties and fracture locations are related to the hardness profile of the

weld.

6.4.6. Microstructure

Figure cros e of

.5. LOW-SPEED FRICTION STIR WELD 2

6.4(b): Mi tructur the weld.

6

ateri clad 2

Type of Joint: Lap

el :

Rotational Speed: 7

Tool Shoulder Diam

M als: Al

W ding Speed 10”

Weld Specifications

024-T3 (0. Al 7 (0.0

15

60 rpm

eter: 0.375 in

080”) & 075-T6 40”)

/min & ”/min

47

6.5.1. Tensile Test – Parent 1 (Alclad 2024-T3)

SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

1121.63

735124 37387.70 35441.30 16.20 37387.70 15.2

2

1121.63

56081.60

53648.60

16.00

56081.60

13.8

1084599

3

1121.63

56081.60

53648.60

15.00

56081.60

13.7

998141

Avg 1121.63 49850.30 47579.5 49850.30

15.70

14.2

939288

bl e ata o nt 1 2024

6.5.2. Tensile Test – Parent 2 (Al 7075-T6)

Ta e 6.5(a): T nsile test d f pare – Alclad -T3.

SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

722.61

8.8

2324608 72261.30 70314.90 11.10 72261.30

0

10.30

71288.10

8.8

2035341 2 712.88 71288.10 68368.5

3

693.42

69341.70

67395.30

69341.70

8.6

2086943

10.20

Avg 709.64 70963.70 68692.90 10.50 70963.70 2148964

8.6

Table 6.5(b): Tensile test data of parent 2 – Al 7075-T6.

48

6.5.3. Tensile Test – Weld (10”/min)

S

I Peak

Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

1559.58

0

969705 51986.00 51986.00 6.70 51986.00 6.7

2

1452.53 48417.50 48093.10 6.50 48417.50 6.50 836114

3

1559.58 51986.00 51337.20 6.90 51986.00 6.80 895946

Avg

50796.50

50472.10

6.70

50796.50

6.70

900588 1523.90

ensile Test – Weld (15”/min)

Table 6.5(c): Tensile test data of weld @ 10”/min.

6.5.4. T

SI

Peak Break Break

Peak Load (lb)

Stress (psi)

Stress (psi)

Elongation(%)

Yield Stress

Yield Elongation

Tangent Modulus

(psi) (%) (psi) 1

1374.67 45822.30 32521.70 5.60 45822.30 4.80 1013254

2

1384.40 46146.70 45822.30 5.90 46146.70 5.80

844730

3

1403.87 46795.50 46795.50 6.50 46795.50 6.50 773184

Avg 1387.65 46254.83 41713.17 6.00 46254.83 5.70

877056

Table 6.5(d): Tensile test data of the weld @ 15”/min.

49

• The joint efficiencies (weld / parent ratio) of the weld @ 10”/min with respect to

is more than

The joint efficiencies of the weld @ 10”/min with respect to parent 2 (Al 7075-

tress and Peak / Yield stress respectively. This

implies that the tensile strength of the weld is less than parent 2.

• The verage break and longation of the weld @ 10 is much lower

than he ave d f

• Th int effici (weld / pa io) of the weld @ 15”/min with respect to

parent 1 (Alclad 2024-T3) are 0.88 and 0.93 for Break stress and Peak / Yield

stre spectiv his implie e tensile s of the weld is less than

parent 1.

• The joint efficiencies of the weld @ 5”/min with respect to parent 2 (Al 7075-

ress and Peak / Yield stress respectively. This

implies that the tensile strength of the weld is less than parent 2.



l th tens spec ract the T on t ating

ren n th as a ensil rtie aren s the

ctu s mi nstan ct w sho

• The weld @ 10”/min has better tensile properties than the weld @ 15”/min.


stress respectively. This implies that the tensile strength of the weld

parent 1.

•

T6) are 0.73 and 0.72 for Break s

a yield e ”/min

t rage break an yield elongation o its parents.

e jo encies rent rat

ss re ely. T s that th trength

1

T6) are 0.61 and 0.65 for Break st

• Al e weld ile test imens f ured in MAZ he retre side.

• Pa t 2, eve ough h better t e prope s than p t 1, wa first to

fra re. Thi ght be due to its co t conta ith tool ulder.

50

6.5.5. Hardness Test

Parent

– Along the Weld

Weld

SI No

Al 7075-T6 Alclad 2024-T3 Weld -10”/min Weld – 15”/min

1 83.70 69.60 78.70 77.70 2 6.70 84.00 69.00 80.50 73 83.40 68.80 79.50 78.80 4 84.10 68.80 79.10 76.30 5 83.70 69.50 81.20 77.70

Avg 83.78 69.14 79.80 77.44

Table 6.5(e): Hardness test data – along the weld.

6.5.6. Hardness Test – Across the Weld

SI No


15”/min

Interface

10”/min

83.70

83.60

83.90

77.70

79.00

77.40

78.60

78.40

80.60

76.80

77.00

77.20

77.30

83.20

83.80

83.50

74.90

74.60

77.70

71.20

74.20

Avg

83.73

77.20 76.87 78.90 75.00 76.23 83.50

Table 6.5(f): Hardness test data – across the weld.

51

Weld2 Hardness Test (HRB) 10"/min

82.00

83.00

84.00

HR

B76.00

78.00

80.00

81.00

85.00

0 1 2 3 4 5 6 7 8

77.00

79.00

Figure 6.5(a): Hardness graph – across the weld @ 10”/min.

Weld2 Hardness Test (HRB) 15"/min

76.00

77.00

78.00

79.00

80.00

81.00

82.00

83.00

84.00

85.00

0 1 2 3 4 5 6 7 8

HR

B

Figure 6.5(b): Hardness graph – cross the weld @ 15”/min.

• As seen in the Table 6.5(e), the weld @ 10”/min has a better hardness value

compared to parent 1 and is softer than parent 2. The hardness joint efficiencies

are 1.15 and 0.95 for parent 1 and parent 2 respectively.

52

• As seen in the Table 6.5(e), the wel 15”/m a bet rdnes e

to a er th nt dne t eff


• The hardness profiles of both the welds are almost the same, as seen in Figures

6 um s v ng in MAZ on the

retre ting side. Accordingly ens fractured in the TMAZ on

the retreating side.

• The int rdness values

lower than the two welds.

6.6. LOW SPEED FRI TION STIR WELD 3

d @ in has ter ha s valu

compared parent 1 nd is soft an pare 2. The har ss join iciencies

6.5(a) and .5(b), with the minim hardnes alue existi the T

a all the tensile specim

erface between weld @ 10”/min and weld @ 15”/min has ha

C

Materials: Alclad 2

Type of Joint: Lap

W e

Rotational S

Tool Shoulder Diam

elding Spe d: 10”

peed: 6

Weld S tiopecifica ns

024-T3 (0.080”) & Al 7075-T6 (0.040”)

& 1

eter: 0.375 in

/min 5”/min

00 rpm

53

6 . Te est – t 1 (A 024

.6.1 nsile T Paren lclad 2 -T3)

SI Peak Break Break Yield Yield Tangent

Peak Stress (psi)

Stress (psi)

Elongation(%)

Stress (psi)

Elongation (%)

Load (lb)

Modulus (psi)

1

1121.63 37387.70 35441.30 16.20 37387.70 15.2 735124

2

1121.63 56081.60 53648.60 16.00 56081.60 13.8 1084599

3

1121.63

56081.60 53648.60 15.00 56081.60 13.7 998141

Avg

1121.63

49850.30

47579.5

15.70

49850.30

14.2

939288

Table 6.6(a): Tensile test data of parent1 – Alclad 2024-T3. 6.6.2. Tensile Test – Parent 2 (Al 7075-T6)

S Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield I Stress

(psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

722.61

72261.30

70314.90

11.10

72261.30

8.8

2324608

2

712.88

71288.10

68368.50

10.30

71288.10

8.8

2035341

3

693.42

6

2086943 69341.70 67395.30 10.20 69341.70 8.

Avg

709.64

70963.70

68692.90

70963.70

8.6

2148964

10.50

Table 6.6(b): Tensile test data of parent 2 - Al 7075-T6.

54

6.6.3. T

.6(c): Tensile test data of the weld @10"/min.

6.6.4. Tensile Test - Weld (15"/min) SI

ensile Test - Weld (10"/min)

Table 6

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

116.90

3.60

994281 1111.90 37063.30 30575.20 6.70 35

2

1296.81 43227.00 39658.60 9.50 43227.00 4.30

1042696

3

1209.22 40307.40 31548.40 7.60 40307.40 4.60 879070

Avg 1206.79 40226.28 35035.80 7.90 39739.68 4.40

937781

st data of the weld @ 15"/min.

SI

Table 6.6(d): Tensile te

Peak

Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

0

889318 1364.94 45497.90 39334.20 10.00 45497.90 5.3

2

1413.60 47119.90 44952.70 5.70 47119.90 5.50

907242

3

1306.54 43551.40 39009.80 9.90 43551.40 5.00 891491

Avg 1369.80 45660.08 40657.73 8.90 45660.08 5.30 908639

55



stre spectiv his implie e tensile s of the weld is less than

parent 1.

• T nt effic of the we 0”/min with t to parent 075-

T6) are 0.44 and 0.64 for Break stress and Peak / Yield stress respectively. This

implies that

• The average break and yield elongation of the weld @ 10”/min is much lower


3) are 0.74, 0.81 and 0.80 for Break stress, Peak stress

d Y ess ively imp t the stre the weld is

s th ent 1

e j icien the 15 with t to 2 (A

T6) are 0.51, 0.57 and 0.56 for Break stress, Peak stress and Yield stress

respec This im sile s


average break and yield el

• All the weld tensile test specimens fractured in the TMAZ on the retreating side.

The parent 2 of two of the tensile specimen fractured in HAZ.


fracture. This might be due to its constant contact with tool shoulder.

• The weld @ 10”/min has better tensile properties than the weld @ 15”/min.

ss re ely. T s that th trength

he joi iencies ld @ 1 respec 2 (Al 7


than the average break and yield elongation of its parents.

parent 1 (Alclad 2024-T

an ield str respect . This lies tha tensile ngth of

les an par .

• Th oint eff cies of weld @ ”/min respec parent l 7075-

tively. plies that the ten trength of the weld is less than parent 2.

ongation of its parents.

56

6.6.5. Hardness Test - Along the Weld

Parent Weld

SI No

Al 7075-T6 Alclad 2024-T3 Weld -10”/min Weld – 15”/min

1 82.80 69.30 77.00 75.10 2 83.50 68.30 77.80 74.20 3 82.40 68.80 76.70 74.80 4 82.90 69.80 77.70 75.00 5 82.90 69.60

Avg 82.78 69.16 77.30 74.78

Table 6.6(e): Hardness test data - along the weld.

6.6.6. H

SI No

ardness Test - Across the Weld

Parent

HAZ TMAZ Nugget TMAZ HAZ Parent

15"/min

Interface

10"/min

82.90

83.20

83.30

78.90

78.20

79.80

75.40

73.60

76.80

75.00

74.80

77.70

74.20

73.00

76.40

77.50

75.00

78.80

82.50

82.90

82.90

Avg

83.13 78.97 75.27 75.83 74.53 77.10 82.77

Table 6.6(f): Hardness test data - across the weld.

57

Hardness - across the Weld 3 @ 10"/min

76.00

77.00

78.00

79.00

80.00

81.00

82.00

83.00

84.00

0 1 2 3 4 5 6 7 8

HR

B

Figure 6.6(a): Hardness graph - across the weld @ 10"/min.

Hardness - across the Weld 3 @ 15"/min

73.00

74.00

75.00

76.00

77.00

78.00

79.00

80.00

81.00

82.00

83.00

84.00

0 1 2 3 4 5 6 7 8

HR

B

Figure 6.6(b): Hardness graph in.







- across the weld @ 15"/m

58

• Th Figures

6.6(a) and 6.6(b), with the minimum dness value existing in the TMAZ on the

• and weld @ 15”/min has hardness values

6.6. C

e hardness profiles of both the welds are almost the same, as seen in

har

retreating side. Accordingly all the tensile specimens fractured in the TMAZ on

the retreating side.

The interface between weld @ 10”/min

lower than the two welds.

7. omparison - Weld 1, Weld 2 and Weld 3

48000

50000

52000

54000

Stress

42000

44000

46000

Peak / Yield

(psi)

10"/min @ 600 rpm

10"/min @ 750 rpm

10"/min @ 760 rpm

Figure 6.6(c): Peak/yield stress of weld - 10"/min @ 750,760 & 600rpm.

59

Figure 6.6(d): Break stress of weld - 10"/min @ 750, 760 & 600 rpm.

• It can be seen from Figures 6.6(c) and 6.6(d) that the tensile properties of each

joints change considerably with the change in the welding pitch (the ratio of the

rotational speed to the welding speed

• When the welding pitch is smaller than 75 r/in, the tensile properties of the joints

increases with the increase in the welding pitch.

• When the welding pitch is greater than 75 r/in, all tensile properties tend to

decrease with the increase in the welding pitch.

• These results indicate that a softening effect has taken place in the joint. The

softened levels or the tensile propert s of the joints are significantly affected by

the welding parameters. For example, the welding pitch of 75 r/in, corresponding

to the rotational speed of 750 rpm and the welding speed of 10"/min, is optimum

for the tensile properties of the joints in case of welds 1, 2 & 3.

0

10000

20000

30000

40000

50000

60000

Bre

ak S

tres

s (p

si)

10"/min @ 600 rpm

10"/min @ 0 rpm

10"/min @ 760 rpm75

).

ie

60

• None of the tensile test specimens fai on the advancing side of the joint, which

implies that the tensile properties of the welds are not the same on either sides of

the weld center. This also implies that the retreating side of the joint is weaker

th



accordingly the joint is fractured on the retreating side. This implies that the

tensile properties and fracture locations are related to the hardness profile of the

weld.

Figure 6.6(e): Weld 2 - change in stress due to change in welding pitch.

led

an the advancing side.

0

10000

20000

30000

40000

50000

60000

10"/min 15"/min

Welding Speed (in/min)

Stre

ss (p

si)

Peak / Yield Stress (psi)Break Stress (psi)

61

It can be seen from Figure 6.6(e) that the ten weld 2 change considerably

with change in its welding pitch. Break, Peak and Yield stress of weld 2 decrease with the

decrease in the welding pitch from 76 r/in to 50.67 r/in (i.e. increase in welding speed

from 10"/min to 15"/min).

Figure 6.6(f): Weld 3 - change in stress due to change in welding pitch.

It can be seen from Figure 6.6(f) that the tensile properties of weld 3 too changes

considerably with change in its welding pitch. Peak and Yield stress of the weld decrease

the welding pitch from 60 r/in to 40

r/in (i.e. increase in welding speed from 10"/min to 15"/min).

sile properties of

and its Break stress increases with the decrease in

0

10000


5000

1500020000

3000035000400004500050000

10"/min 15"/min

Str

psi)

Peak Stress (psi)25000

ess

(

Break Stress (psi)Yield Stress (psi)

62

Figure 6.6(g): Weld 2 & weld 3 - change in hardness due to change in welding pitch

Figure 6.6(g) shows the change in the hardness of weld 2 and weld 3, along the weld,

pitch. In weld 2, as the welding pitch decreases from 76 r/in

50.67 r/in, there is a decrease in the hardness of the weld. In weld 3, the hardness along

th eld wit decre the w pitch 60 r/ r/i

76

77.5

78

79

79.5

80

10"/min 15"/min

pee in)

Har

dnes

sB

)

76.5

77

78.5 (H

R

Welding S d ( min/

Weld 2

73.574

74.5

7676.5

7777.5

78

10" 15"

W lding Spee (in/min)

Har

(HRB

)

7575.5

dnes

s

73

/min /min

e d

Weld 3

with change in the welding

to

e w reduces h the ase in elding from in to 40 n. These

63

results indicate that softening ak th w a

welding speed.

6.7. LOW-SPEED FRICTION STIR WELD 4

6.7.1. T

SI

effect t es place in e weld ith an incre se in its

Materials: Alclad 2

Type of Joint: Lap -

W e

Rotational Speed: 7

Tool

elding Sp ed: 10”

Shoulder Diam

ensile Test – Parent 1 (Alclad

Peak

Load (lb)

Peak Stress (psi)

BreakStres(psi)

1

2217.39

55434.80

53260

Table 6.7(a): Tensile te

Weld icatSpecif ions

024-T3 (0.080”) & Al 7075-T6 (0.063”)

Double pass

in

60 rpm

/m

eter: 0.375 in

2024-T3)

s

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi)

4.80 27.2 1880680.9

29.30

5543

Alclad 2024-T3.

st data of parent1 -

64

6.7.2. Tensile Test – Parent 2 (Al 7075-T6)

SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

2156.52

1.00

.00

1088848.006846 65976.50 20.10

68461 18.6

ble 6.7(b ile test data ent 2 - Al 7 .


SI

Ta ): Tens of par 075-T6

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

reak BElongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi)

3.90 13621.20 3.90 381015 1 973.91 13621.20 13621.20

2

947.83 13256.30 13256.30 5.80 13256.30 5.80 396472

3

965.22 13499.50 13377.90 4.10 13499.50 4.10 363561

4 947.83 13256.30 13256.30 4.00 13256.30 4.00 358545 5 973 362 349 4 136 364711

.91 1

1.20 1

9.50

.10

21.20

4.00

A

961 345 340 4 134 372861 vg .72 1 0.90 1 2.24 .38 50.90 4.36


65



respectively. This implies that the tensile strength of the weld is less than parent1.


and 0.19 for Break stress and Peak / Yield stress respectively. This implies that




• All the weld


6.7.4. Hardness Test – Along the weld

Parent

tensile test specimens fractured in the TMAZ.

fracture.

SI No Al 7075-T6

Alclad 2024-T3

Weld

1 88.50 70.20 77.60 2 88.60 69.30 77.80 3 88.60 70.00 78.30 4 89.10 70.00 78.30 5 89.10 70.40 78.60

Avg 88.78 69.98 78.12

Table 6.7(d): Hardness test data- along the weld.

66

67

6.7.5. Hardness Test - Across the Weld

SI No


Weld

86.30

85.20

87.20

83.50

80.50

76.10

75.80

79.20

78.70

77.00

78.00

84.50

79.40

82.00

88.50

89.00

86.00

83.30

76.30

78.20

77.60

Avg

86.23

82.43 76.07 78.70 77.53 81.97 87.83

Table 6.7(e): Hardness test data - across the weld.

Figure 6.7(a): Hardness graph - across the weld.

HARDNESS TEST ( HRB )

74.00

76.00

78.00

80.00

82.00

84.00

88.00

90.00

0 1 2 3 4 5 6 7 8

HR

B

86.00

68

A in th e 6.7 e we a bet ness com


ar a ect

• The hardness of the weld does not vary much on both sides of the weld center,

with th ingly all the

tensile specimens fractured in the TM Z.

ss values, it displays very poor tensile

properties.

6.7.6. Metallography

Fig 6.7(b): Microstructure of the weld nugget.

• s seen e Tabl (d), th ld has ter hard value pared to

0.88 for p ent 1 and p rent 2 resp ively.

e minimum hardness value existing in the TMAZ. Accord

A

• Though the weld has good hardne

68


6.8.1. Tensile Test – Parent 1 (Al

SI

Peak Load (lb)

Peak Stress (psi)

BS(

1

2191.30

54782.60 523

Ta le 6.8(a): Tensi

6.8.2. Tensile Test – Parent 2 (A

SI

b

Peak Load (lb)

Peak Stress (psi)

BS(

1

2173.91 69013.10

670

Table 6.8(b): Ten

Materials: Alclad 202

Type of Joint: Lap – D

Welding Speed: 15”/m

Rotational Speed: 760

Tool Shoulder Diame

Weld Specifications

4-T3 (0.080”) & Al 7075-T6 (0.063”)

ouble pass

in

rpm

ter: 0.375 in

clad 2024-T3)

reak tress psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi)

91.30

31.10

54782.60

28.30

780511

le te f parent1 – Alclad 20 -T3.

l 7075-T6)

st data o 24

ak retress psi)

Break Elongation

(%)

Yield Stress (psi)

eld YiElongation

(%)

Tangent Modulus

(psi)

1277115

80.70

19.70

69013.10 17.70

sile test data of parent2 - Al 7075-T6.

69


SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

730.43 10215.90 10215.90 3.60 10215.90 3.60 306131

2 756.52 10580.70 10459.10 3.80 10580.70 3.70 319643 3

713.04 9972.60 9729.40 3.50 9972.60 3.40 345836

Avg

733.33 10256.40 10134.80 3.63 10256.40 3.57 323870




respectively. This implies that the tensile strength of the weld is less than parent1.


and 0.15 for Break stress and Peak / Yield stress respectively. This implies that

the tensile str



• All the weld tensile test specimens fractured in the TMAZ.

ength of the weld is less than parent 2.

70

6.8 H

Parent

.4. ardness Test – Along the weld

SI No Al 7075-T6

Alclad 2024-T3

Weld

1 88.70 68.60 79.60 2 89.30 69.00 80.20 3 87.70 68.10 83.90 4 87.90 70.40 83.40

Avg 88.40 69.03 81.78

Table 6.8(d): Hardness test data – along the weld.


SI No


Weld

87.90

87.00

83.80

81.50

83.60

75.10

76.40

72.00

77.00

78.50

77.00

75.90

77.10

73.60

78.20

82.20

80.40

87.40

87.70

88.50

86.70

Avg

87.20

82.97 74.50 77.50 75.53 80.27 87.87

Table 6.8(e): Hardness test data – across the weld.

71

HARDNESS TEST ( HRB )

72.00

74.00

76.00

78.00

80.00

82.00

84.00

86.00

88.00

90.00

0 1 2 3 4 5 6 7 8

HR

B

Figure 6.8(a): Hardness graph - across the Weld.

• As seen in the Table 6.8(d), the weld has a better hardness value compared to


0.93 for parent 1 and parent 2 respectively.

• The hardness of the weld does not vary much on both sides of the weld center,

with the minimum hardness value existing in the TMAZ. Accordingly all the

tensile specim ctur e TM

• Though the weld has good hardness values, it displays very poor tensile

.

ens fra ed in th AZ.

properties

72


Fig 6 rostr of t

6.9. HIGH-SPEED FR

.8(b): Mic ucture he weld.

ICTION STIR WELD 6

Materials: Al 6061-T

Type of Joint: Butt

Welding Speed: 15”


Tool Shoulder Diam

Weld Specifications

6 (0.125”)

/min

00 rpm

eter: 0.375 in

73

6.9.1. Tensile Test

– Parent (Al 6061-T6)

SI Peak

Peak Break Stress (psi)

Load (lb)

Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

4037.50

64600.00 59502.80 20.80 64600.00 17.70 1367795

2

4019.80 64316.90 59361.20 20.80 64316.90 18.00 1320557

Avg

4028

445

943

20

644 1344176.65 6 8.45 5 2.00 .80 58.45

17.85

able 6.9(b): Tensile test data of the parent – Al 6061-T6. 6.9.2. Tensile Test

SI

T

- Weld

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

3232.21 51715.40 49520.80 8.20 51715.40 7.30 1283741

2

3218.94 51503.00 49308.40 8.80 51503.00 7.80 1324307

3

3223.36 51573.80 49166.80 8.20 51573.80 7.10 1294124

4

3218.94 51503.00 49096.00 8.40 51503.00 7.40 1295279

Avg 3226.52 51624.37 49450.00 8.50 51624.37 7.59 1283318

le 6.9(b): Tensile test data of the weld. Tab

74

• The joint efficiencies (weld / parent ratio) of the weld with respect to parent (Al

6061-T6) are 0.83 and 0.80 for Break stress and Peak / Yield stress respectively.

The average break and yield elonga• tion of the weld is much lower than the

•

6.9.3. Hardness test – along the Weld


All the weld tensile test specimens fractured in the HAZ.

SI NO PARENT WELD

1 51.50 21.80

2 49.90 21.00

3 46.90 20.00

Avg 49.43 20.93

Table 6.9(c): Hardness test data – along the weld.

eld

SI No

6.9.4. Hardness Test – across the w


Weld

49.80

48.40

50.50

16.40

14.80

13.80

27.70

27.70

26.80

21.80

21.00

20.00

29.80

27.70

26.70

20.20

18.20

18.80

51.50

49.90

49.00

Avg

49.60 15.00 27.40 20.93 28.10 19.10 50.13

Table 6.9(d): Hardness test data – across the weld.

75

Hardness (HRB) acr

0.00

20.00

40.00

0 1 2 3 4 5 6 7 8

oss the Weld, Al6061-T6 @ 15"/min

10.00

30.00

HR

B

50.00

60.00

Figure: 6.9(a): Hardness graph - across the weld.

• As seen in the Table 6.9(c), the weld is softer than the parent. The hardness joint

efficiency is 0.42.

gure 6.9(a) that a hardness degradation region (i.e. softened

region) has occurred in each joint, with the weld nugget having a hardness value

less than the TMAZ hardness values.

• There are two low hardness zones on the two si the w enter, e

m l n th hard on trea

accordingly the joint is fractured on the retreating side. From Figure6.6(c) it can

be found that the minimum hardness occurs in the HAZ adjacent to the TMAZ on

the retreatin e join actu HAZ on the r

side and the fracture surface is parallel to the TMAZ / HAZ interface on the

retreating side [10].

• It can be seen from Fi

des of eld c but th

inimum hardness va ue exists i e low ness zone the re ting side,

g side. Th refore, the t is fr red in the etreating

76

6.1

6.10.1. Tensile Test – Parent (Al6

SI

0. LOW-SPEED FRICTION STIR WELD 7

Materials: Al 6061-T6 (0

Type of Joint: Butt

Welding Speed: 20”/min


Tool Shoulder Diameter

Peak Load

Peak Stress

BrSt

(lb) (psi) (p 1

3921.30

67242.20 6097

2

3830.93 65692.60 5934

Avg

3876.12

66467.40 6015

Table 6. Tens

10(a):

Weld Specifications

.125”)

rpm

: 0.375 in

061-T6)

eak ress

Break

si) Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 0.00

23.10

67242.20

19.60

1563554

6.60 21.50 65692.60

18.30

1566628

8.30

.30

66

18.95

156509122 467.4

ile te

st data of the parent – Al 6061-T6.

77


SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

3262.91 55952.20 53369.50 9.00 55952.20 8.10 1366549

2 3262.91 55952.20 54402.50 8.40 55952.20 7.60 1425574

Avg

3262.91 55952.20 53886.00 8.70 55952.20 7.85 1396062

Table 6.10(b): Tensile test data of the weld.



This implies that the tensile strength of the weld is less than parent.



• All the weld tensile test specimens fractured in the HAZ.

78

6.1 .

0.3 Hardness Test – Along the weld

SI NO PARENT WELD

1 50.90 28.50

2 49.80 28.50

3 48.90 27.00

Avg 49.87 28.00


.10.4. Hardness Test – Across the Weld

SI No

6


Weld

49.80

51.70

50.00

26.70

25.80

27.00

29.78

30.40

29.60

28.50

28.50

27.00

34.30

32.40

34.40

29.80

31.40

30.60

49.60

50.40

48.70

Avg

50.50

26.50 29.93 28.00 33.70 30.60 49.60


79

Hardness (HRB) across the Weld A -T6, 20'/min

0

20

30

50

0 1 2 3 4 5 6 7 8

l6061

10

40

60

HR

B


• As seen i rdness joint

efficiency is 0.56.

Figure 6.10(a) that a hardness degradation region (i.e.

softened region) has occurred in each joint, with the weld nugget having a

ha alu han t Z h value

• There are two low hardness zones on the two si the w enter, e

m l n th hard on trea

accordingly the joint is fractured on the retreating side. From Figure 6.7(c) it can


the retreatin e join actu HAZ on the r

side and the fracture surfa is paralle

retreating side.

n the Table 6.10(c), the weld is softer than the parent. The ha

• It can be seen from

rdness v e less t he TMA ardness s.

des of eld c but th

inimum hardness va ue exists i e low ness zone the re ting side,

g side. Th refore, the t is fr red in the etreating

ce l to the TMAZ / HAZ interface on the

80


.11.1. Tensile Test – Parent (Al6061-T6)

Weld Specifications

Materials: Al 6061-T6 (0.125”)

Type of Joint: Butt


Rotational Speed: 1500 rpm

Tool Shoulder Diameter: 0.375 in

6

Peak Break SI Peak

Stress (psi)

Load (lb)

Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

4042.37

646

58303.

0

64

19.60

149483077.90 90 23.0 677.90

2

4051.22

64819.50

58445.60

23.40 64819.50

20.10

1373849

3

4006.96

64111.30

57737.30

.30

64

19.90

129250523 111.30

4

4042.37 64677.90

57879.00

23.20 64677.90

20.00

1395983

Avg

4035.73

9.90

138929264571.65 58091.45 23.23 64571.65 1

data of the parent – Al 6061-T6.

Table 6.11(a): Tensile test

81


SI Peak

Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

3378.41 54054.60 52921.50 9.30 54054.60 8.40 1295614

2

3382.84 54125.40 52496.50 9.90 54125.40 9.00 1317391

3

3378.41

.40

131381954054.60 52638.20 9.20 54054.60 8

4

3391.96

54267.10

53133.90

9.40

54267.10

8.60

1293661

Avg

3382.84

54125.43

52797.53

9.45

54125.43

8.60

1305121



6061-T6) are 0.91and 0.84 for Break stress and Peak / Yield stress respectively.

This implies



• The weld tensile test specimens fractured in the HAZ, with one of the specimen

fracturing in the weld nugget due to crack like defect in the joint.

that the tensile strength of the weld is less than parent.

82

6.11.3.

Hardness Test – Along the Weld

SI NO PARENT WELD

1 50.00 27.60

2 50.40 28.80

3 52.40 23.20

Avg 50.93 26.53

a - along the weld.


SI No

Table 6.11(c): Hardness test dat


Weld

50.40

51.50

51.20

24.80

24.80

25.20

28.60

29.00

28.30

26.60

27.60

27.00

28.80

29.70

28.60

27.80

28.20

28.60

50.00

52.40

50.80

Avg

51.03

24.93 28.63 27.10 29.03 28.20 51.10


83

Hardness (HRB) across the Weld, Al 6061-T6 @ 25"/min

0

10

20

30

40

50

60

0 1 2 3 4 5 6 7 8

HR

B


• It can be seen from Figure 6.11(a) that a hardness degradation region (i.e.

softened region) has occurred in each joint, with the weld nugget having a

hardness value less than the TMAZ hardness values.





the retreating side. Therefore, the joint is fractured in the HAZ on the retreating

side and the fracture surface is parallel to the TMAZ / HAZ interface on the

retreating side.


efficiency is 0.52.

84

6.11 .

Figure 6.11(c): Break stress variation.

.5 Comparison - Weld 6, Weld 7 & Weld 8

Figure 6.11(b): Peak/yield stress variation.

49000

50000

52000

53000

54000

55000P

k/Y

ld S

tss

(p

51000


eaie

res

56000

57000

i)

15"/min 20"/min 25"/min

47000

48000

49000

50000

51000


Bre

ak S

trp

52000

53000

54000

55000

ess

(si

)

15"/min 20"/min 25"/min

85

• It can be seen from Figures 6.11(b) and 6.11(c) that the tensile properties of each

joints change considerably with the change in the welding pitch.

Figure 6.11(d): Variation in hardness.

• It can be seen from Figures 6.11(d) that the hardness values of each joints change

considerably with the change in the welding pitch.

• When the welding pitch is smaller than 75 r/in, the tensile properties and the

hardness of the joints decreases with the decrease in the welding pitch.

• When the welding pitch is greater than 75 r/in, all tensile properties and the

hardness of the joints tend to increase with the decrease in the welding pitch.

• These results indicate that a softening effect has taken place in the joint. The

the joints are significantly affected by

the welding parameters. For example, the welding pitch of 75 r/in, corresponding

to the rotational speed of m ldin d o s

fo ile properties o

0

Welding Sp

5

10

15

20

25

30

eed (in/min)

Har

dnes

s (H

RB)

15"/min 20"/min 25"/min

softened levels or the tensile properties of

1500 rp and the we g spee f 20"/min, i optimum

r the tens f the joints in case of welds 6, 7 & 8.

86

• e t s fai the sid joi


the weld center. This also implies that the retreating side of the joint is weaker

dv e

• The hardness of the weld center is lower than TMAZ, but the m imum hardness

value exists in the HAZ on the retreating side, accordingly the joint is fractured in

HAZ o s and fracture

locations are related to the hardness profile of the weld.

None of th tensile tes specimen led on advancing e of the nt, which

than the a ancing sid .

in

n the retreating side. This implies that the tensile propertie

87

6.1

6.12.1. Tensile Test – Parent (Al 2024-T3)

SI

2. LOW-SPEED FRICTION STIR WELD 9

Weld Specification


Type of Joint: Butt




Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

3917.32

87051.60

84100.70

28.40 86658.10

22.90

1826437

2

3873.06

86068.00

83707.20

.60

85

22.30

183893827 674.50

3

3917.32 87051.60

84297.40

27.20 87051.60

22.30

1805899

Avg

3904.04

3.55

183059286756.53 83658.05 28.05 86559.78 2

Table 6.12(a): Tensile test data of the parent – Al 2024-T3.

88


SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi)

345 672 662 13 767 16616151 2.55 7 3.40 7 5.10 .30 23.40 13.30

2

3518.95 78198.90 78002.20 14.80 78198.90 14.70 1661268

3

3496.82 77707.10 77707.10 14.70 77707.10 14.70 1656029

Avg

3494.61 77657.90 77559.55 14.45 77657.90 14.40 1642937






• The weld tensile test specimens fractured in the TMAZ.

89

6.12.3.

SI NO


PARENT WELD

1 73.80 72.80

2 72.00 71.60

3 74.10 65.50

4 74.40 67.50

Avg 73.70 68.70



SI No


Weld

73.80

73.70

72.90

70.80

68.00

66.60

64.30

68.70

69.60

65.90

64.40

71.90

68.30

70.00

74.10

73.80

73.70 73.50 64.00 71.00 68.30

Avg

73.46

70.76 64.96 69.76 66.20 70.06 73.86

Table 6.12(d): Hardness data – across the weld.

90

Hardness (HRB) - Across the Weld.

64.00

65.00

66.00

67.00

68.00

69.00

70.00

71.00

72.00

73.00

74.00

75.00

0 1 2 3 4 5 6 7 8

HR

B



efficiency is 0.93.

It can be seen from F .12(a a ha degr reg

so regio occu each j

t a es o

minimum hardness value exists in the l w hardness zone on the retreating side,


th im ess in on trea

Therefore, the joints fractured in the TMAZ on the retreating side

• igure 6 ) that rdness adation ion (i.e.

ftened n) has rred in oint.

• There are wo low h rdness zon n the two sides of the weld center, but the

o

be found at the min um hardn occurs the TMAZ the re ting side.

.

91

6. . M aph12.5 etallogr y

Fig 6.12(b): Microstructure of the weld nugget.


Weld Specifications

Materials: Alclad 2024-T3 (0.080”)

Type of Joint: Butt



n Tool Shoulder Diameter: 0.375 i

92

6.13.1. Tensile Test – Parent (Alclad 2024-T3)

SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

3788.96

94723.90

91846.80

28.80

94723.90

26.90

1549111

2

3749.12

93728.00

91182.90

93728.00

25.00

162482327.30

3

3762.40

94060.00

91293.50

29.10

94060.00

26.90

1658996

4

3802.24

95055.90

92178.80

95055.90

27.30

154755928.80

Avg 3775.68

94391.95 91625.50

28.50

94391.95

26.53

1595122

Table 6.13(a): Tensile test data of the parent – Alclad 2024-T3.


SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Yield Stress (psi)

Elongation (%)

Tangent Modulus

(psi) 1

2642.53 66063.30 3.50 66063.30 66063.30 3.50 1988631

2

2629.25 65731.30 3.50 65731.30 65731.30 3.50 1977220

3

2646.96 66174.00 3.60 66174.00 66174.00 3.60 1937763

Avg

2635.89 65897.33 3.55 65897.33 65897.33 3.55 1952399


93


clad 2024-T3) are 0.72 and 0.70 for Break stress and Peak / Yield stress

respectively. This implies that the tensile strength of the weld is less than parent.



• All the weld tensile specimens failed in the weld nugget due to crack like defects

in the joint.

6.13.3. Hardness Test – Along the Weld

OSI N Parent Weld

1 70.20 57.00

2 69.94 58.80

3 70.00 57.40

Avg 70.09 57.85


94


SI No


Weld

70.40

70.00

70.40

66.90

68.80

68.20

62.70

61.80

62.30

57.40

58.70

57.80

62.40

65.70

64.40

69.20

70.90

68.30

70.00

70.20

69.98

Avg

70.26

69.46 70.06 67.96 62.26 58.00 64.16


Hardness (HRB) - across the Weld

0.00

40.00

50.00

60.00

70.00

80.00

5 6 7 8

HR

B

20.00

30.00

10.00

0 1 2 3 4

Figure 6.13(


efficiency is 0.83

• It can be seen from Figure 6.13(a) that a hardness degradation region (i.e.

softened region) has occurred in each joint.

a): Hardness graph - across the weld.

.

95

• The hardness values decrease gradually across the weld, with the minimum

hardness value in the weld center or weld nugget. Hence all the tensile specimens

failed at the weld nugget.


Fig 6.13(b): Microstructures of the weld.

96

6.14. Tool Geometry Effects [21]

or a given alloy and plate thickness, the required z-axis load for production of a sound

eld is primarily a function of shoulder diameter.

Tool Number Pin Dia (mm) Shoulder Dia (mm)

F

w

1 10 25

2 8 25

3 12 25

4 10 20

5 10 30

6 10 28

7 7.2 20

Table 6.14: Tool geometry.

Table 6.14, tools 1, 2 and 3 all required approximately the same loads. Tool number 5,

ith the large ber 4,

ith the smallest shoulder, needs loads as much as 40% lower than the other tools.

Fig 6.14(a): Specific weld energy as a function of welding speed and tool geometry.

In

w st shoulder, required z-axis loads from 5-10% greater while tool num

w

04 6

l number

Spec

i 500

1000

1500

2000

2500

0 2

Too

fic w

eld

ener

gy, J

/mm

3.3 mm/s weldingspeed2.4 mm/s weldingspeed1.3 mm/s weldingspeed

97

In Fig 6.14(a), the specific weld energy as a function of welding speed and tool geometry

is shown. For each tool, increased welding speed (for the rpm’s chosen in this study)

results in reduced weld energy. In addition, for each welding speed, tool number 4

mallest shoulder) results in the lowest weld energy and tool number 5 (largest shoulder)

sults in the ool 3) also increases

e weld energy and the required power, but this effect is less than that associated with

e shoulder diameter changes.

wer as a function of tool geometry and welding speed.

In Fig 6.14(b), the required power for the three welding speeds is plotted against the tool

umber. In this case, it is shown that the highest welding speed requires the greatest

ower delivery from the machine and again, the shoulder size appears to be the primary

eterminant of the power requirement for a given set of welding parameters (rpm and

elding speed).

(s

re highest weld energy. The use of a large diameter pin (t

th

th

Fig 6.14(b): Required weld po

0

500

1000

1500

0 2 4 6

Tool number

Rere

d po

2000

2500

er, w

a

3000

3500

qui

wtts


n

p

d

w

98

6 si of t s a of to me

welding speed.

Fig 6.14(c) shows the transverse tensile strength of the welds as a function of tool

geome . tool how easin wel

results in a small but consistent increase in the tensile strength of the weld.

Fi .14(d s X rce nc ge an p

force on the elding too in the X direction is a ritical vari le in that, if it become too

large the too s

wi incr e d gh t rmediate welding speed weld has the

highest advance per revolution.

Fig .14(c): Transverse ten le strength he weld s a function ol geo try and

try and welding speed For each , it is s n that incr g the d speed

Fig 6.14(d): X axis force as a function of tool geometry and welding speed.

g 6 ) show axis fo as a fu tion of tool ometry d welding s eed. The

w l c ab s

l will break due to bending stres es. For each tool, the X axis force increases

th easing w lding spee even thou he inte

375380

0

385390395400

415420425430

6

umb

Tran

sver

se te

nsng

th, M

Pa

405410

ile s

tre2

n

4

erTool


0

2

4

6

12

4 6

number

X-ax

is fo

rce,

8

10

kN 1.3 mm/s welding

speed

0 2

Tool

2.4 mm/s weldingspeed3.3 mm/s weldingspeed

99

6.15. HIGH-SPEED FRICTION STIR WELD 11

6.15.1. Tensile Test – Parent Al 7075-T6

SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

3279.93

104957.70

99008.70

10.40

104957.70

8.70

2425350

2

3293.21

105382.60

100141.80

10.30

105382.60

8.80

2340873

3

3293.21

10538

99433.60

.50

105382.60

9.20

23313912.60 10

Avg

3288.78

105240.97

99528.03

10.40 105240.97

8.90

2365871

Table 6.15(a): Tensile test data of the parent - Al 7075-T6.

Weld specification


Type of Joint: Butt




Shoulder angle: 3.773

Pin length: 0.053 in

0

100

6.15.2. Tensile Test of the Weld

SI

Peak Load

Peak Stress

Break Stress

reak B

(lb) (psi) (psi) Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

426.19

27496.20

27496.20

4.80

27496.20

4.80

1207796

2

416.67

26881.70

26881.70

4.00

26881.70

4.00

1305856

311

012

012

1

201 21307913 .90 2 2.90 2 2.90 .90 22.90

1.90

Avg

384.92 24833.60 24833.60 3.60 24833.60 3.60 1548148


• The joint ef ect to parent (Al





• The weld tensile test specimens fractured in the weld nugget.

ficiencies (weld / parent ratio) of the weld with resp

101

6.1 .5.3 Hardness Test – Along the Weld

SI NO Parent Weld

1 88.80 55.20

2 88.90 51.50

3 88.80 51.90

4 88.80

Avg 88.83 52.90



SI No


Weld

90

90.00

60.80

66.70

73.50

72.80

55.40

51.50

72.30

74.10

58.50

0

63.80

90.00

90.00

90.00

89.90

.00

62.90

70.80

50.90

77.80

61.6

Avg 90.00

63.50 72.40 52.60 74.73 61.30 90.00


102

Hardness across the weld

0

10

20

30

40

50

60

ness

(HRB

)

70

80

90

100

0 3 6 8

Hard

1 2 4 5 7

1 ess – ac ld.

i 6 weld ter t t. The hardn

efficiency is 0.60. It can be seen from Figure 6.15(a) that a hardness degradation

region (i.e. softened region) has occurred in each joint.

d d ros ld, nimu rdne

in the weld center or weld nugget. Hence all the tensile specimens failed at the

weld nug


6 cros e of nugg

Figure 6. 5(a): Hardn graph ross the we

• As seen n the Table .15(c), the is sof han the paren ess joint

• The har ness values ecreases ac s the we with the mi m ha ss value

get.

Figure .15(b): Mi tructur the Weld et.

103


6.16.1. Tensile Test – Parent Al 7

SI

Peak Load (lb)

Peak Stress (psi)

BrStr(p

1

3279.93

104957.70 9900

2

3293.21 10538 0012.60 1

3

3293.21

105382.60 9943

Avg

3288.78

105240.97 9952

Table 6.16(a): Ten

al -

Type of Joint: Butt

Welding Sp

Materi s: Al 7075 T6 (

eed: 1”/min



Pin length: 0.053 in


Weld specification

) 0.062”

rpm

: 0.375 in

075-T6

eak ess si)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 8.70

10.40

104957.70

8.70

2425350

41.8

.30

105382.60

8.80

23408730 10

3.60

105382.60

9.20

233139110.50

8.03

.40 105240.97

8.90

2365871 10

sile test data of the parent Al 7075-T6.

104

6.16.2. Tensile Tes

SI

t of the Weld

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi)

.90

35483.90

4.00

35483.90

4.00

16486181 550.00 35483

2

207.14

13364.10

12749.60

1.90

13364.10

1.80

3225932

3

292.86

18894.00

18279.60

2.50

18894.00

2.50

1366332

4

473.81

30568.40

30568.40

3.80

30568.40

3.80

1345966

Avg

381.00

24577.60

24270.38

3.05

24577.60

3.03

1896712





average break and yield elongation of its parent.



105

6.16.3. Hardness Test – Along the Weld.

SI NO Parent Weld

1 88.80 56.8

2 88.90 62.7

3 88.80 62.6

4 88.80

Avg 88.83 60.70



y


efficienc is 0.68.

Fig 6.1 ostru of th gget.

6(a): Micr cture e weld nu

106


6.1 .

SI

Weld specification

al - )

Type of Joint: Butt



Tool Shoulder Diameter: 0.375 in Pin length: 0.053 in


Materi s: Al 7075 T6 (0.062”

0

7.1 Tensile Test – Parent Al 7075-T6

Peak Load

Peak Yield Stress

Yield

(lb) Stress

Break Stress

Break Elongation

(%) (psi) (psi) (psi) Elongation

(%)

Tangent Modulus

(psi) 1

3279.93 104957.70 99008.70 0.40 104957.70

8.70

2425350

1

2

3293.21

105382.60

100141.80

10.30

105382.60

8.80

2340873

3

3293.21

10538

99433.60

.50

105382.60

9.20

23313912.60 10

Avg

3288.78

105240.97

99528.03

105240.97

8.90

236587110.40

Table 6.17(a): Tensile test data of the parent Al 7075-T6.

107


SI Peak

Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

445.24 28725.00

28725.00

3.40

28725.00

3.40

1949039

2

350.00 22580.60

22580.60

2.90

22580.60

2.90

1439180

3

216.67

13978.50

13978.50

1.50

13978.50

1.50

1526225

4

435.71

28110.60

28110.60

3.40

28110.60

3.40

1418963

5

369.05

23809.50

23809.50

3.30

23809.50

3.30

1268191

Avg

363.34

0

152032023440.84 23440.84 2.90 23440.84 2.9



nd Peak / Yield stress respectively.





7075-T6) are 0.24 and 0.22 for Break stress a

108

6.17.3. Hardness Test – Along the Weld

SI NO Parent Weld

1 88.80 70.10

2 88.90 66.70

3 88.80 66.50

4 88.80 72.50

Avg 88.83 68.95



y


efficienc is 0.78.

Fig 6.17(a): Microstructure of th nu

e weld gget.

109


6.18.1. Tensile Test – Parent Al 7075-T6

SI

Peak Load

Peak

(lb) Stress

Break

(psi) Stress

Break

(psi) Elongation

(%)

Yield Stress

Yield

(psi) Elongation

Tangent

(%) Modulus

(psi) 1

3279.93 104957.70 99008.70 10.40 104957.70 8.70

2425350

2

3 5382.60 8.80 2340873

293.21

105382.60

100141.80

10.30

10

3 3293.21

9.20

2331391

105382.60

99433.60

10.50

105382.60

Avg

3288.78

10524

99528.03

.40

105240.97

8.90

23658710.97 10

Table 6.18(a): Tensile test data of the parent Al 7075-T6.

Weld speci ationfic


f Joint: Butt

W lding Speed: 1”/min


ho m 5 in Pin length: 0.053 in Shoulder an

Type o

e

Tool S ulder Dia eter: 0.37

gle: 21.3540

110


SI

Peak Break Break Yield Stress (psi)

ield Y

Peak Load (lb)

Stress (psi)

Stress (psi)

Elongation(%)

Elongation (%)

Tangent Modulus

(psi)

3.80

33640.60

3.80

14718621 521.43 33640.60 33640.60

2

671.43

43318.00

43318.00

6.00

43318.00

6.00

1134024

3

376.19

24270.40 24270.40 3.00 24270.40 3.00 1449471

4 652.38 42089.10 42089.10 3.40 42089.10 3.40 1302887

5

595

840

840

3

384 1125304.24 3 2.50 3 2.50 .40 02.50

3.40

471

041

041

3

304

14184586 .43 3 4.70 3 4.70 .30 14.70 3.30

Avg

548.02

35355.88

35355.88

3.82

35355.88

3.82

1317001








111

6.1 .8.3 Hardness Test – Along the Weld

SI NO Parent Weld

1 88.80 64.70

2 88.90 39.10

3 88.80 72.5

4 88.80 26.2

Avg 88.83 50.62

Table 6.18(c): Hardness test data – across the weld.


SI No


Weld

90.00

65.90

73.60

64.70

74.30

89.90

88.90

63.50

63.90

49.50

40.30

64.40

65.90

70.20

90.00

90.00

90.00

61.30

71.30

55.40

71.80

Avg

89.60

63.60 69.60 56.53 62.13 66.83 90.00


112

Hardness across the weld

0

10

20

30

40

50

60

70

80

100

0 1 2 3 4 5 6 7 8

Hard

ness

(HRB

)

90



efficiency is 0.57. It can be seen from Figure 6.18(a) that a hardness degradation

region (i.e. softened region) has occurred in each joint.

• The hardness values decreases across the weld, with the minimum hardness value

.18.5. Microstructure

Figure 6.18(b): Microstructure of the weld.

in the weld center or weld nugget. Hence all the tensile specimens failed at the

weld nugget.

6

113

6.18.5. Comparison – Weld 11, Weld 12, Weld 13 and Weld 14

): Variation in break stress.

• It can be seen from Figures 6.18(b) and 6.18(c) that the tensile properties of each

joints change considerably with the change in the shoulder angles.

`

Figure 6.18(c): Variation in peak & yield stress.

Figure 6.18(d

0

5000

Pe

10000

25000

40000

Shoulder Angles (deg)

akld

si)

35000

15000

20000

30000/Y

ie S

tre

s (p

s

3.773 deg 9.886 deg 15.786 deg

21.354 deg

0

5000

10000

20000

30000

lder Angle (deg)

Br

tres

s)

40000

15000

eak

S

25000

35000

(psi

Shou

3.773 deg 9.886 deg 15.786 deg

21.354 deg

114

Figure 6.18(e): Variation in hardness.

• It can be seen from Figures 6.18(d) that the hardness values of each joints change

considerably with the change in the shoulder angles.

• When the shoulder angle is smaller than 15.7860, the tensile properties decreases

with increase in the shoulder angle and the hardness of the joints increases with

le.

• When the shoulder angle is greater than 15.7860, all tensile properties increase

wi incr the er the ss t

decrease with the increase in the shoulder angle.

The joints have the best tensile properties and lowest hardness value, of the four

w en ld s 21. nd dne e an

tensile properties, of the four welds, when the shoulder angle is 15.7860.

The minimum hardness value exists in the weld nugget, accordingly the joints

fr n u

0

20

40

0

70

houl e (

H

80

10

30ar

dne

50RB

6)

the increase in the shoulder ang

th the ease in should angle and hardne of the join s tend to

•

elds, wh the shou er angle i 3540 a highest har ss valu d lowest

•

actured i the weld n gget.

S de nglr A deg)

ss (H

3.773

9.886 deg

15.786 deg

54 deg 21.3 deg

115

6.19. HIGH-SPEE

6.19.1. Tensile Test – Parent (Al 70

SI

D FRICTION STIR WELD 15

Peak Load (lb)

Peak Stress (psi)

BreaStres(psi

1

3

279.93 104957.70 99008

2

3293.21 105382.60 100141

3

3

105382.60

99433293.21

Avg

3288.78 105240.97 99528

Table 6.19(a): Tensi

rial 075-

e of utt –

in 2

otational peed: 12000

Mate s: Al 7 T6 (

Typ Joint: B Ti

Weld g Speed: ”/min

R S


Weld specification

25”)

an

rpm

0.1

lted d U d ntilte

: 0.375 in

75-T6)

k s )

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi)

.70 10.40 104957.70 8.70 2425350

.80 10.30 105382.60 8.80 2340873

.60

10.50

105382.60

9.20

2331391

.03 10.40 105240.97 8.90 2365871

le test data of the parent Al 7075-T6.

116

6.19.2. Tensile Test – Weld (Tilted)

SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

637.39

20396.60

20396.60

3.10

20396.60

3.10

976818

2

699.36

22379.60

22379.60

3.10

22379.60

3.10

1119785

3

885.00

28328.70

28328.70

2.60

28328.70

2.60

2331391

Avg

740.58

23701.63

23701.63

2.93

23701.63

2.93

1059765

Table 6.19(b): Tensile test data of the weld (tilted).

6.19.3. Tensile Test – Weld (Untilted)

SI

Peak Load (lb)

Peak Stress (psi)

Break Stress (psi)

Break Elongation

(%)

Yield Stress (psi)

Yield Elongation

(%)

Tangent Modulus

(psi) 1

402.80

12889.50

12889.50

1.70

12889.50

1.70

793020

2

358.53

11473.10

11473.10

1.50

11473.10

1.50

808284

3

309.84

9915.00

9915.00

0.80

9915.00

0.80

1262390

Avg

357.06

11425.87

11425.87

1.33

11425.87

1.33

954565

Table 6.19(c): Tensile test data of the weld (untilted).

117

• The jo ien eld / parent ratio weld (tilted) with respect to

parent (Al 7075-T6) are 0.24 and 0.23 for ak stress d Peak / Yield stress

respectiv . This s tha nsile th of the weld is more than the

parent.

• The joint efficiencies of the weld (untilte respe arent (Al 7075-T6)

are 0.12 d 0.11 reak str ss and Peak / Yield stress respectively. This

implies that the ten ength weld than p

• The average break and yield elongation of the weld (tilted) and weld (untilted) are

much lower than the average break and yield elongation of its parent.

• sile properties than the weld (untilted).

int effic cies (w ) of the

Bre an

ely implie t the te streng

d) with ct to p

an for B e

sile str of the is less arent.

• All the weld tensile test specimens fractured in the weld nugget.

The weld (tilted) has better ten

118

6.20. HIGH-S FR STIR WELD 1

6.2 .

Welds

PEED ICTION 6

0.1 Hardness Test – Along the Weld

SI NO Parent

1 2 3

1 88.80 65.00 69.90 60.10

2 88.90 71.70 68.40 48.10

3 88.80 62.50 63.80 43.80

4 88.80

Avg 88.83 66.40 67.37 50.67

Table 6.20(a): Hardness test data of the weld.

• The hardness weld efficiency (weld/parent) obtained are 0.75, 0.76 and 0.57 for

welds 1, 2 and 3 respectively.

We ificatld spec ion

Materials: Al 707 0.125

Type of Joint: Butt – Cerami

Welding peed:



5-T6 ( ”)

c tool

S 1”/min

119

6.21

6.21.1.

Welds

. HIGH-SPEED FRICTION STIR WELD 17


SI NO Parent

1 2 3

1 88.80 46.10 66.20 56.30

2 88.90 44.30 42.00 60.00

3 88.80 53.50 57.80 32.40

4 88.80

Avg 88.83 47.97 55.33 49.57

Table 6.21(a): Hardness test data of the weld.

• The hardness weld efficiency (weld/parent) obtained are 0.54, 0.62 and 0.56 for

welds 1, 2 and 3 respectively.

Weld specification


Type of Joint: Butt – Ceramic tool




120

CHAPTER 7

CONCLUSIONS AND FUTURE SCOPE

1.

f the joint is weaker

3.

tial amount of material is moved from the retreating side of the weld to the

4.

et and TMAZ. The retreating side of the joint has a more

The average break and yield elongation of the weld is much lower than the


2. None of the tensile test specimens failed on the advancing side of the joint, which


the weld center. This also implies that the retreating side o

than the advancing side.

The flow patterns on the advancing side and retreating sides of the weld are

different. The FSW can be roughly described as an in-situ extrusion process

where the tool shoulder, the pin, the backing plate and the cold base material form

an extrusion die. Near the top of the weld, because of the shape of the tool, a

substan

advancing side. This movement of material causes vertical mixing in the weld and

a complex circulation of material around the longitudinal axis of the weld. This

may be one of the reasons for the failure of the weld in the retreating side [1].

The microstructure of the advancing side is characterized by a sharp boundary

between the nugg

complex microstructure, with no clear boundary between the nugget and TMAZ.

Also the texture is the strongest on the advancing side and weak on the retreating

side. This may be another reason for the failure of the weld in the retreating side

[35].

121

5.

ts fractured on the retreating side. This implies that the tensile

6. eld tensile test specimens fractured in

7.

pitch is

rties tend to decrease with the increase in the welding pitch.

8. The hardness values of Al 7075-T6 and Alclad 2024-T3 Lap joints reduce with a

decrease in the welding pitch. This indicates that softening effect takes place in

the weld with an increase in its welding speed (i.e., decrease in the welding pitch).

9. The Al 6061-T6 Butt joints fractured in the Heat Affected Zone (HAZ). In this

case the minimum hardness zone occurs in HAZ and the fracture surface is

parallel to the TMAZ / HAZ interface on the retreating side.

10. The properties of Al 6061-T6 Butt joints change considerably with the change in

the welding pitch. When the welding pitch is smaller than 75 r/in, the tensile

properties and the hardness of the joints decreases with the decrease in the

welding pitch. When the welding pitch is greater than 75 r/in, all tensile properties

and the hardness of the joints tend to increase with the decrease in the welding

pitch.

There are two low hardness zones on the two sides of the weld center, but the


accordingly the join

properties and fracture locations are related to the hardness profile of the weld.

The Al 7075-T6 and Alclad 2024-T3 Lap w

the TMAZ on the retreating side.

The tensile properties of Al 7075-T6 and Alclad 2024-T3 Lap joints change

considerably with the change in the welding pitch. When the welding

smaller than 75 r/in, the tensile properties of the joints increases with the increase

in the welding pitch. When the welding pitch is greater than 75 r/in, all tensile

prope

122

11. In Al 2024-T3 Butt joints the minimum hardness occurs in the TMAZ on the

retreating side. Therefore, the joints fractured in the TMAZ on the retreating side.

12. All the Alclad 2024-T3 Butt weld tensile specimens failed in the weld nugget due

to crack like defects in the joint and the weld nugget is the minimum hardness

zone in this case.

13. The properties of the welds change considerably with the change in the shoulder

angles. When the shoulder angle is smaller than 15.7860, the tensile properties

decreases with increase in the shoulder angle and the hardness of the joints

increases with the increase in the shoulder angle. When the shoulder angle is

greater than 15.7860, all tensile properties increase with the increase in the

shoulder angle and the hardness of the joints tend to decrease with the increase in

the shoulder angle.

14. Weld energy decreases and the required power increases with the increase in

welding speed at constant weld pitch [21].

15. X axis force increases with the increase in the welding speed at constant welding

pitch. This may indicate that the m terial being involved in the process is in

different stages of evolution when welded using different speeds [21].

16. The highest energy per unit weld length is required when welding Al 6061-T6.

This is probably because of the relatively high thermal conductivity of the alloy

[21].

a

123

Because the Friction Stir Welding process has only recently become a subject of wide

study, there are currently no large databases of weld properties and, in fact, no

specifications on how to make or test friction stir welds exist. In general, the process is

robust and a wide range of processing parameters and tool designs can be used to make

metallurgically sound welds in a given alloy and plate thickness. In this thesis, only a few

friction stir welds, welded in a limited range of welding speed, rotational speed, were

tested for their mechanical properties and fra e locations. Tool parameters of the welds

considered were not extensive. Further studies have to be done, considering most of the

welding parameters, on a wider range of values. Different types of tools, tool parameters

have to be considered to determine the effect they have on the resultant welds. Fatigue

analysis, shear tests have to be conducted. Some of the tables in this thesis report may not

contain all the experimentally obtained values. But the average value in the tables was

calculated considering all the values obtained experimentally.

ctur

124

REFERENCES

125

1. Anthony P. Reynolds, ‘Friction stir welding of Aluminum alloys’, Handbook of

Aluminum, 2004.

2. Gene Mathers, ‘The welding of Aluminum and its alloys’, 2002.

3. www.weldingengineer.com

4. www.world-aluminum.org

5. Allan R. Pfluger, Richard E. Lewis, ‘Weld imperfections’, Proceedings of a

symposium at Lockheed Palo Alto Research Laboratory, Palo Alto, California,

1996.

6. Mandal, N.R., ‘Aluminum welding’, 2002.

7. Patricia Han, ‘Tensile testing’, 1992.

8. Harry Chandler, ‘Hardness testing’, 1999.

9. Boniface E. Rossi, ‘Welding Engineering’, 1954.

10. Huijie Liu, Fujii, H., Maeda, M., Nogi, K., ‘Tensile properties and fracture

locations of friction-stir welded joints of 6061-T6 Aluminum alloy’, Journal of

materials science letters, 22, 2003.

11. www.twi.co.uk

12. Harry Udin, Edward R. Funk, John wulff, ‘ Welding for engineers’, 1954.

13. Tylecote, R. F., ‘The solid phase welding of metals’, 1968.

14. www.metallographic.com

15. www.gordonengland.co.uk

16. Kenneth Budinski, ‘Engineering materials: properties and selection’, 1983.

17. Carl E. Cross, David L. Olson, Stephen Liu, ‘Aluminum welding’, handbook of

Aluminum, 2004.

126

18. Fletcher, M. J., ‘Friction welding’, 1972.

19. Reynolds, A. P., Lockwood, W. D., Seidel, T.U., ‘Processing property correlation

in friction stir welds’, Materials science forum, Vol 331-337, 2000.

20. Cederqvist, L., Reynolds, A. P., ‘Factors affecting the properties of friction stir

welded Aluminum lap joints’, Welding research supplement.

21. Reynolds, A. P., Wei Tang, ‘Alloy, tool geometry, and process parameter effects

on friction stir weld energies and resultant FSW joint properties’, Friction stir

welding and processing, TMS, 2001.

22. Ulysse, P., ‘Three dimensional modeling of friction stir welded process’,

International journal of machine tools & manufacture, 42, 2002.

23. Lippold, J. C., Ditzel, P. J., ‘Microstructure and properties of Aluminum friction

stir welds’, Materials science forum, vol 426-432, 2003.

24. Fonda, R. W., Bingert, J. F., ‘Texture and microstructure development in the heat

affected zone of friction stir welds’, Friction stir welding and processing II, TMS,

2003.

25. Beate Heinz, Birgit Skrotzki, Gunther Eggeler, ‘Microstructural and mechanical

characterization of a friction stir welded Al alloy’, Materials science forum, vol

331-337, 2000.

26. Rhodes, C. G., Mahoney, M. W., Bingel, W. H., Spurling, R. A., Bampton, C. C.,

‘Effects of friction stir welding on microstructure of 7075 Aluminum’, Scripta

materialia, vol 36, 1997.

127

128

27. Liu, G., Murr, L. E., Niou, C. S., Mclure, J. C., Vega, F. R., ‘Microstructural

aspects of the friction stir welding of 6061-T6 Aluminum’, Scripta materialia, vol

37, 1997.

28. Benavides, S., Li, Y., Murr, L. E., Brown, D., Mclure, J. C., ‘Low temperature

friction stir welding of 2024 Aluminum’, Scripta materialia, vol 41, 1999.

29. Thomas, W. M., Nicholas, E. D., Kallee, S. W., ‘ Friction based technologies for

joining and processing’, Friction stir welding and processing, TMS, 2001.

30. www.arconweld.com

31. Thomas, W. M., Nicholas, E. D., Kallee, S. W., ‘ Friction based technologies for

joining and processing’, Friction stir welding and processing, TMS, 2001.

32. Thomas, W. M., Dolby, R. E., ‘ Friction stir welding developments’, TWI,

Cambridge, UK.

33. www.key-to-metals.com

34. www.msm.cam.ac.uk

35. www.hkltechnology .com

Documents

Mechanical testing and evaluation of high-speed and low-speed