Tensile behaviour of AA 5052-AA

6063 lap joints through friction

stir spot welding process

Dr.J.Srinivas

Associate Professor, Mechanical Engg.,

NIT Rourkela

Presentation outline

• Introduction

• Methodology

• Results and Discussion

• Conclusions

• References

Introduction • Currently, for assembling aluminum alloy parts, resistance

spot welding, riveting and laser spot welding are employed

intensively.

• All these conventional processes have disadvantages such

as poor weld strength, large heat residual stress and

distortion, tool consumption during joining and formation of

different defects.

• In the recent years, the new spot welding process was

developed called friction stir spot welding (FSSW).

• Friction stir spot welding (FSSW) is a modification of the

friction stir welding (FSW) process that can effectively

replace the resistance spot welding technique used in the

automotive industry. FSSW exhibits several advantages in

welding dissimilar materials.

FSSW background

• In 2000, FSSW has been proposed to create a spot weld

using frictional heat.

• The bonding between the two thin sheets was mainly

achieved by the frictional heat and high applied pressure.

• In FSSW, under the tool, there are

(a) stir zone (SZ),

(b) heat-affected zone (HAZ)

(c) thermomechanically affected zone (TMAZ)

• SZ has finer equaixed grains than the TMAZ.

Principle of FSSW• A non-consumable rotating tool is plunged into the workpieces.

• The maximum penetration of the tool into the workpiece, from the

point that the pin is tangent to the workpiece surface is called plunge

depth.

• Upon reaching to the specified plunge depth, the rotating tool is held

in that position for a predetermined time.

• Subsequently, the rotating tool is retracted from the welded joint

leaving behind a friction stir spot weld.

Factors affecting the mechanical properties

• The mechanical properties of FSSW joints depend

on the amount of generated heat, material

plasticization around the pin and weld geometry.

• All of these factors can be controlled by the main

process parameters such as plunge depth, dwelling

time and rotating velocity.

Recent works on FSSWS.No Authors Year Work carried-out

1 Kai Chen; Xun Liu; Jun NiJ. Manuf. Sci. Eng 139(8), 081016 (May 25, 2017

2017 FSSW of Aluminum and steel wasillustrated and investigated failureusing a lap shear tests whichrevealed that cross nugget failure isthe only failure mode

2 Yufeng Sun, Hidetoshi Fujii, Shijie Zhu, Shaokang GuanJournal of Materials Processing Technology, 264, 2019, 414-421

2019 Illustrated 3 sheet friction stir spotwelding of Aluminum alloy

3 Q. Chu, W. Y. Li, X. W. Yang, J. J. Shen, W. B. WangJournal of Materials Science & Technology, 34, 2018, 1739-1746

2018 Proposed FSSW of Al-Li alloys with probeless tool

4 Isam Jabbar Ibrahim, GuneyGuven YapiciJournal of Manufacturing Processes, 35, 2018, 282-288

2018 Joint of 6061-T6 and 2024-T3 aluminum alloys was prepared with intermediate layer t avoid the key hole defect.

Objectives of present work• Preparation of the lap joints of two dissimilar aluminum

alloys AA5052 and AA6063 with specially prepared tool.• Samples with varying depth of cut, tool rotation and plunge

time.• Lap shear strength is measured for all the specimen using a

computerized universal testing machine.• The transient temperature distribution on either side of

weld nugget is also measured using dual Laser Infraredthermometer.

• The results of welded lap joints at different parameters arecompared for two cases where AA5052 samples are kept atthe top and bottom faces of AA6063 samples separately.

• A generalized regression model is developed to find lapshear and temperaturesat the weld nugget as a function ofinput variables.

Experimental approach• AA5052 and AA 6063 aluminum alloy in the form of a

sheet with 2mm thickness was used.

• Lap-shear configuration has been utilized, which was

made by two 30mmx100mm sheets.

• Also, a 15mmx30mm area has been used for the

overlap.

• The welding overlap samples are prepared as per AWS

standards by using a square headed pin profiled

shoulder tool on vertical milling machine with variation of

plunge time and rotational speed of the tool.

Chemical compositions

S.no. Element Percentage

1 Si 0.2-0.6

2 Fe 0.0-0.35

3 Cu 0.0-0.1

4 Mn 0.0-0.1

5 Mg 0.45-0.9

6 Zn 0.0-0.1

7 Ti 0.0-0.1

8 Cr 0.1 max

9 Al balance

AA6063S.no. Element Percentage

1 Cu 0.1

2 Mg 2.2-2.8

3 Si 0.25

4 Fe 0.4

5 Mn 0.1

6 Zn 0.1

7 Ti -

8 Cr 0.15-0.35

9 Al Balance

AA5052

Tool geometry

S.No. Specifications Dimensions (in mm)

1 Length of the tool 100

2 Width of the square pin 3

3 Height of square pin 2.2, 2.8, 3.2 and 3.5

4 Diameter of the shoulder 9

5 Diameter of the head 12

6 Length of the shank portion 55

7 Height of the shoulder 2

8 Length of the head portion 40

The welding tool was made from hot-work tool steel of H13,

which was tempered and hardened to 45–48 HV

Temperature Measurements• There are 2 sets of dissimilar samples considered: (1) AA5052

on top and AA6063 on bottom (2) AA6063 on top and AA5052on bottom. Total there are 18 samples prepared.

• During the spot welding, with the help of Dual Laser InfraredThermometer, the temperatures on the areas that are along withthe spot are observed on each specimen.

• Along with the temperatures, the plunge time and speed arerecorded.

45

50

55

60

65

1 2 3 4 5 6

Tem

per

atu

re in

deg

C

position

Lap shear test• For the evaluation of the joint strength, mechanical test samples

are prepared and tested under a tensile load at a displacement

rate of 0.025 mm/s utilizing an Instron mechanical test frame (100

t) where force and displacement values were captured.

• Standard metallographic sample preparation techniques including

grinding, polishing and etching were utilized. Samples were etched

with Keller’s reagent (190 ml H2O, 5 ml HNO3, 3 ml HCl and 2 ml

HF).

• Scanning electron microscopy (SEM) were used for characterizing

the weld zones.

Results and Discussion• Input process parameters:

1.Speed : 760 rpm, 1130 rpm, 1340 rpm, 2000 rpm

2. Plunge time: randomly measured

LAP JOINT

SPECIFICATIONS

SPEED(rpm) PLUNGE

TIME(sec)

ULTIMATE

TENSILE

STRENGTH(MPa)

MAXIMUM

LOAD (kN)

TENSILE STRESS AT

YIELD (OFFSET

O.2%) (MPa)

AA5052-AA6063 2000 13.92 26.76 1.12 14.3475

AA5052-AA6063 1340 14.36 22.93 1.30 16.54647

AA5052-AA6063 760 15.92 21.54 1.26 16.32897

AA5052-AA6063 1130 15.21 19.84 1.16 13.45675

AA5052-AA6063 760 16.29 13.39 1.05 17.13521

AA5052-AA6063 2000 16.37 18.54 1.65 14.56456

AA5052-AA6063 1340 15.15 19.32 1.83 16.59823

AA5052-AA6063 1130 14.17 12.54 1.45 14.52897

AA5052-AA6063 760 15.19 13.32 1.52 14.62197

Stress-strain diagram

760 rpm with two different plunge times: 16.29 seconds and 15.19 seconds

Test results with AA6063 sample above AA5052 sample

LAP JOINT

SPECIFICATIONS

SPEED(rpm) PLUNGE

TIME(sec)

ULTIMATE

TENSILE

STRENGTH(MPa)

MAXIMUM

LOAD (kN)

TENSILE STRESS

AT YIELD (OFFSET

O.2%) (MPa)

AA6063-AA5052 2000 14.28 13.20 1.34 12.30765

AA6063-AA5052 1340 15.23 13.42 1.72 11.19623

AA6063-AA5052 760 16.52 11.33 1.42 17.98543

AA6063-AA5052 1130 16.41 13.63 1.36 18.35867

AA6063-AA5052 760 14.48 12.25 1.22 16.65208

AA6063-AA5052 2000 16.29 16.28 1.76 14.93165

AA6063-AA5052 1340 15.28 14.42 1.23 13.98213

AA6063-AA5052 1130 14.51 18.32 1.36 17.59238

AA6063-AA5052 760 15.59 19.80 1.24 12.36891

Plunge time vs Maximum load

• Two cases at 760 rpm are considered; one withAA5052 plates on top and other with AA6063plates on top

1

1.1

1.2

1.3

1.4

1.5

1.6

15 15.2 15.4 15.6 15.8 16 16.2 16.4

Max

imu

m lo

ad (

kN)

stirring time

AA5052 plates on top surface

1.2

1.25

1.3

1.35

1.4

1.45

14 14.5 15 15.5 16 16.5 17

max

imu

m lo

ad (

kN)

plunge time in sec

AA 6063 plates on top of AA5052

Microstructure around the joint• According to the microscopic investigations, at shorter times of stirring it was

found that the joint had been produced uniformly. However, the longer times

caused more material flow and stirring, which led to more partially bonded

regions.

Conclusions

• Temperature distribution on both the sides of spot

welded region was measured using infrared

thermometer during welding. It was observed that

temperatures on 6063 side are higher.

• Static strength of friction stir spot welds of AA6063

and AA5052 alloys in the various conditions of stirring

time of welding have been investigated.

• The mechanical behavior of different welding

conditions proved great improvement between certain

plunge times and decreases there after.

• Nugget pull-out was the failure mode observed in

tensile tests.

References1. Rosendo T, Parra B, Tier M, et al. Mechanical and microstructural

investigation of friction spot welded AA6181-T4 aluminium alloy.

Mater Design 2011; 32:1094–1100.

2. Zhang Z, Yang X, Zhang J, et al. Effect of welding parameters on

microstructure and mechanical properties of friction stir spot welded

5052 aluminum alloy. Mater Design 2011; 32: 4461–4470.

3. Tozaki Y, Uematsu Y and Tokaji K. Effect of processing parameters

on static strength of dissimilar friction stir spot welds between

different aluminium alloys. Fatigue Fract Eng Mater Struct 2007; 30:

143–148.

4. Rosendo T, Tier M, Mazzaferro J, et al. Mechanical performance of

AA6181 refill friction spot welds under Lap shear tensile loading.

Fatigue Fract Eng Mater Struct 2015; 38: 1443–1455.

5. Lin Y-C and Chen J-N. Influence of process parameters on friction

stir spot welded aluminum joints by various threaded tools. J Mater

Process Technol 2015; 225: 347–356.