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Engineering Materials

2189101

Chedtha PuncreobutrDepartment of Metallurgical Engineering

Chulalongkorn University

Applications and processing

of metals and alloys

http://pioneer.netserv.chula.ac.th/~pchedtha/

Metals and their uses

22189101 – Engineering MaterialsChedtha Puncreobutr

Metals and Alloys


IronCopper

AluminiumZincTin

Gold

Brass ( Copper & Zinc)

Steel (Iron & Carbon)

Cast Iron (Iron & Carbon)

Duralumin (Aluminium & Copper)

Bronze (Copper, Tin, Phosphorus)

(a mixture of two or more materials)

Pure Metals Alloys

Carbon and alloy steels


Carbon steels

Classified as low, medium and high:

1. Low-carbon steel or mild steel, < 0.3%C, bolts, nuts and sheet plates.

2. Medium-carbon steel, 0.3% ~ 0.6%C, machinery, automotive and agricultural equipment.

3. High-carbon steel, > 0.60% C, springs, cutlery, cable.

Stainless steels

• Characterized by their corrosion resistance, high strength and ductility, and high chromium content.

• Stainless as a film of chromium oxide protects the metal from corrosion

Tool steels

• Designed for high strength, impact toughness, and wear resistance at a range of temperatures.

• Alloying with Mo, W, Cr

Fe-C True Equilibrium Diagram


Graphite formation

promoted by

• Si > 1 wt%

• slow cooling

1600

1400

1200

1000

800

600

4000 1 2 3 4 90

L

g +L

+ Graphite

Liquid +

Graphite

(Fe) C, wt% C

0.6

5740°C

T(°C)

g + Graphite

100

1153°Cg

Austenite 4.2 wt% C

+ g

Steel and its uses


Steel is the most commonly used metal and is used in everything from Sewing needles to Skyscrapers

HMS Ark Royal

The Golden Gate Bridge

Advantages:

Disadvantages:

Low Cost, High Strength & Easy to work with.

Rusts

Stainless Steel and its uses


Stainless Steel is a mixture of Steel and Chromium

Advantages:

Disadvantages:

Does not rust

More difficult to Join tan ordinary Mild Steel

Cutlery

Gateway Arch in St Louis – 304 series SS

Surgical Instruments

Cookware

Cast iron and its uses


Cast Iron is a mixture of Iron and 2% Carbon.

Advantages:

Disadvantages:

Low Cost, Casts well, High Strength (under compression)

Rusts, Brittle, Difficult to join, Low Strength (under tension)

Fence Engine Block Pan

Nonferrous Alloys


NonFerrous Alloys

• Al Alloys-low r: 2.7 g/cm3

-Cu, Mg, Si, Mn, Zn additions -solid sol. or precip.

strengthened (struct. aircraft parts & packaging)

• Mg Alloys-very low r: 1.7g/cm3

-ignites easily -aircraft, missiles

• Refractory metals-high melting T’s-Nb, Mo, W, Ta• Noble metals

-Ag, Au, Pt -oxid./corr. resistant

• Ti Alloys-relatively low r: 4.5 g/cm3

vs 7.9 for steel-reactive at high T’s

-space applic.

• Cu AlloysBrass: Zn is subst. impurity(costume jewelry, coins, corrosion resistant)Bronze : Sn, Al, Si, Ni are subst. impurities (bushings, landing gear)Cu-Be: precip. hardened for strength

Aluminium and its uses


Advantages:

Disadvantages:

Lightweight, Malleable, Ductile & Does not corrode, Low melting point (660 C)

Higher Cost than steel, Harder to Weld

• Aluminium is found primarily in bauxite ore and is

remarkable for its ability to resist corrosion (due to

the phenomenon of passivation) and its light weight.

• Structural components made from aluminium and

its alloys are vital to the aerospace industry and very

important in other areas of transportation and

building.

Copper and its uses


Advantages:

Disadvantages:

Malleable, Ductile, Good Conductor of heat & electricity, Does not corrode to any great extent

High Cost & Rather soft

• Copper is one of the oldest metals known to man.

The discovery of alloying copper and tin to make

bronze (the first ever alloy) was a major step

forward because bronze is harder, tougher and

stronger than copper

Tin and its uses


Advantages:

Disadvantages:

Does not corrode

Heavy & Rather soft, Expensive

• Tin is seldom used in its pure form but

is often added to other metals to form

Alloys such as bronze, bell metal,

Babbitt metal, die casting alloy, pewter,

phosphor bronze, soft solder,

Solder (Lead Tin alloy)

Zinc and its uses


• The most common use for Zinc is galvanising,

This is the process of dipping mild steel in a

tank of molten Zinc, this provides a corrosion

resistant coating

Galvanized Steel Bucket

Zinc is also used for sacrificial anodes on the hull of steel boats

Materials Processing

14

Materials processing:

a set of transformations of input elements into products

Methods chosen depend on:

(1) Properties of materials

(2) Size and shape of finished product

(3) Cost


Metal processing overview


Steel Making


Forming operation

17

• Forming operations (forging, rolling, drawing, extrusion) are

where the shape of metal is changed by plastic deformation

• Forming processes are commonly classified into

cold-working and hot-working operations

• Deformation must be induced by an external force or stress.

The magnitude of which must exceed the yield strength of the

material


Cold-working

18

• Temperature at which the deformation take place is “cold”

relative to the absolute meting temperature

• Cold-working (plastic deformation) of metal results in an

increase in strength or hardness and a decrease in ductility

• Close dimensional control of the finished piece

• Good quality surface finish

• When cold-working is excessive, the metal will fracture

before reaching the final shape


Hot-working

19

• Material remains relatively soft and ductile during deformation

because it does not strain harden, hence large deformations are

possible

• Hot-working processes (rolling, extrusion or forging) is typically

used in the first step of converting cast ingot into wrought product


• Deformation energy requirements are less than that for cold-

working

• However, most metals experience some surface oxidation,

which results in material loss and a poor final surface finish

Forming operation


Rolling


Rolling


Rolling

23

Plastic deformation

Rollers in compression

thick slab

thin sheet


Hot rolling and Cold rolling


Hot rolling and Cold rolling

25

slab

bloom

billet

sheetcoil

bar rod

structural

ingot


Forging

26

• Forging is the process where metal

(Fe, Ti, Al) is heated and shaped by

plastic deformation (compressive

forces)

• The compressive force typically

comes from successive blow or

continuous pressing)

• Forged articles have outstanding

grain structures and best

combination of mechanical

properties.

• Wrenches, automotive crankshafts

and piston connecting rods

generally formed by forging


Forging


Die Forging

28

Closed-Die Forging

Open-Die Forging


Extrusion

29

Suitable for ductile metals such as Cu and Al


Extrusion of Tubing


Drawing


Casting

32

• Casting is pouring liquid metal into

carefully designed mould cavity

and solidifies into a desired shape

under controlled conditions

• The first step in all manufacturing

processes involving metal


Casting


Sand Casting


Investment Casting

35

Investment casting - A casting process that is used for making complex

shapes or casting of precious metals, also known as the lost wax process.

• The pattern is made of low melting materials (such as plastic or wax)

which is then coated with ceramic to form a mould.

• After the wax is melted and drained, metal is poured into the mould


Investment Casting

36

Applications:

• The process is more expensive than sand casting but provide superior

surface finish and better controlled solidification conditions

• Very thin sections can be produced and the process allows for high

dimensional accuracy

complex shapes (e.g. superalloys turbine

blade and turbocharger)

Costly materials

(gold and silver

jewellery, bronze

sculpture and

titanium medical

parts)


Die Casting

37

Die casting - A casting process in which molten metal/alloys is forced

into a die (permanent mould) under pressure and is held under pressure

during solidification

Advantages:

• High production rate

• Very low unit cost

• Good smooth surface finish

• Excellent dimensional accuracy

• Limit only to relative small pieces

and to alloys of low melting

points such as Zn, Al and Mg


Continuous Casting


Welding


Welding


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Applications and processing of metals and alloyspioneer.netserv.chula.ac.th/~pchedtha/Lecture6_Engineering... · Applications and processing of metals and alloys ... • Alloying