lecture 2(metal) [read-only] [compatibility mode].pdf

8/10/2019 Lecture 2(metal) [Read-Only] [Compatibility Mode].pdf

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Lecture 2

Fabrication &Fabrication &

Thermal ProcessThermal Process

of Metalsof Metals


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....

You should be able to state the purpose andYou should be able to state the purpose anddescribe heat treatment rocess in metaldescribe heat treatment rocess in metal

You should be able to name and describeYou should be able to name and describe

You should be able to provide a suitableYou should be able to provide a suitable


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Fabrication of MetalsFabrication of Metals --MethodsMethods

Metal Fabrication MethodsMetal Fabrication Methods

. . .

Sha e of metal Molten metal is Two or more parts

piece changed by

plastic deformation.

poured into a mouldcavity having

desired sha e.

are joined to for asingle piece

certain ductility canbe formed.

Suitable for

hard/brittle metal. Miscellaneous


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. orm pera o s. orm pera o s

Deformation is achieved at Deformation is achieved

o or ng

temperature at which

recrystalisation can occursbelow the recrystalisation

temperatures

Large deformation is possible.

Deformation can be repeated (soft and ductile)

Metals strain hardened

Higher quality surface finish

Oxidation might occurs bad surface finish

Better mec an ca propert es

Variety of mechanical properties can be formedCloser dimension control of the final piece


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FORMING

Forging Rolling Extrusion Drawing

Stamping

force

die tensileA Addie

Ao Adblankorce

die

Aroll ram billet

container

forcedie holder

Ao

Aextrusion

roll

Ao container die


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Direct

Forging

Mechanically working or deforming a singleMechanically working or deforming a single

piece of a hot metalpiece of a hot metal

Hammered or pressed into a desired shapeHammered or pressed into a desired shape

Mould used to place hot metal in beforeMould used to place hot metal in before

being shaped into desired shapebeing shaped into desired shape

Use for producing large parts; steel shaftsUse for producing large parts; steel shaftsIndirect

Forging

,,connecting rods, or tools like wrenchconnecting rods, or tools like wrench


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ampamp

Mechanically working or deforming a sheet of metalMechanically working or deforming a sheet of metal

sizesize

,,

doors, metal plates etcdoors, metal plates etc


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Rollers

Passing a piece of metalPassing a piece of metalbetween two rollsbetween two rollsMetal

Thickness reduced withThickness reduced with

rolling passrolling pass Cold or hot rolling.Cold or hot rolling.

Cold rolling produces sheet,Cold rolling produces sheet,

strips, foils which can bestrips, foils which can berecrystallised after rollingrecrystallised after rolling


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Mould

A bar of metal is forcedA bar of metal is forcedthrough a die orifice bythrough a die orifice by

Metal Ram

a compressive force thata compressive force that

is applied to a ramis applied to a ram

Rods, tubing, wires,Rods, tubing, wires,

i esi es Mould

Anything withAnything withMetal

Ram


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A bar of metal is drawnA bar of metal is drawnthrou h a die orifice b athrou h a die orifice b a

mould

compressive force that iscompressive force that is

a lied to a rama lied to a rammetal

Start with rods to form wiresStart with rods to form wiresorce


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Cite the best method for the production of:Cite the best method for the production of: Copper wire for electrical cableCopper wire for electrical cable

Aluminium serving platesAluminium serving plates

Automotive bodyAutomotive body Nickel sheet for battery electrodesNickel sheet for battery electrodes

Aluminium foilsAluminium foils

Steel wrenchSteel wrench

II--beam for structural buildingbeam for structural building


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Cite the best method for the production of:Cite the best method for the production of: Copper wire for electrical cableCopper wire for electrical cable --drawingdrawing

Aluminium serving platesAluminium serving plates forging/sheet metal (stamping)forging/sheet metal (stamping)

Automotive bodyAutomotive body -- stampingstamping Nickel sheet for battery electrodesNickel sheet for battery electrodes -- rollingrolling

Aluminium foilsAluminium foils -- rollingrolling

Steel wrenchSteel wrench -- forgingforging

II--beam for structural buildingbeam for structural building extrusionextrusion


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..

Molten metal is poured into a mould cavityhaving the desired shape. Upon

so ca on, e me a assumes e s ape

of the mould but experiences some

shrinkage.

Casting is best used:

To produce metal product of complex shape and

size. Other method is not a licable.

For metal alloys having low ductility that

forging is impossible


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Mould made out of sand using a shape

made by a prototype

Mould made out of

metalmolten

mac ne o es reshape)

Mould made out of plaster/sandusing a final desired shapepattern made using waxMolten metal

wax


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Exam le of roductExam le of roductproduced by castingproduced by casting


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a asa as

The mould is

made out sandusing a shape

Molten metal

.

Economical!

Sand cast

2-piece mould

Molten metal is placed at one opening

and once the metal is solidified, mouldLarge parts; Automotive

the moulds.cy n er oc s, re

hydrants, large pipe fittings


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To produce high volume products, low melting pointalloys (e.g. Zn, Al and Mg) and small products

Clamped& cooled

Mould ismade out ofmetal (die).

Molten metal is placesin a two-part mouldunder ressure.

The mould canbe opened toeject the

piece (cast piece)


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xamp es o e casxamp es o e cas


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Investment CastinInvestment CastinThis process is capable of producing precise detail and dimensional accuracy inparts weighing many pounds to just a few ounces. Precision investment castingsare able to reduce costs in many cases due to reduced machining and less

material waste.Molten metalplaster of

furnace

wax

poure n emould

par s san

Pattern ismade out of

Mould is madeusing thepattern by

Once cooled,metal part isremoved from

When mould isheated, thewax/plastic burns off

pouring plasterof paris

the mouldleaving a cavity


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ves me asves me as

nves men as ng s su a e or ow vo ume, comp ex s apes

like jewelry, dental crown, turbine blades, weaponry,


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xerc sexerc se

Cite the best method for the production of:Cite the best method for the production of: Gold earGold ear--rin srin s

Pipe connectionPipe connection

Large engine block for a truckLarge engine block for a truck


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..

Miscellaneous

Powder Processing Welding

Materials with low To oint two arts

ductilityOther working

procedures are difficult

together


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ow er e a ur yow er e a ur y

ressure

Micron sized or nanosized metal powders areplaced in a die

Powders

heat

diePressure applied to compact

the powders

areacontact

densify

Uniaxial press

Heat sometimes applied during

point contactat low T

densificationby diffusion at

During heating, particles started to bedensified assist by high temperature

g erand solidify

Finish product will be removed fromthe die


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What would be the advantageWhat would be the advantage

an sa van a es o pow eran sa van a es o pow ermetallurgy?metallurgy?

AdvantagesAdvantages DisadvantagesDisadvantages


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ee

Similar or dissimilar metals can be joined.Similar or dissimilar metals can be joined.Joinin bond is metallur ical not mechanicalJoinin bond is metallur ical not mechanical

Arch, gas welding, soldering and brazingArch, gas welding, soldering and brazing

Done by melting work pieces and adding a filler material to form a

pool of molten material (the weld puddle) that cools to become a

Arc welding refers to a group of welding processes that use a

.

and the base material tomelt themetals at thewelding point.


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ea ec e o eea ec e o e

Workpieces arejoinedbya filler material which isheated toahigh temperature.

This resulted in fusion joint betweenthe2parts

The region adjacent to the weld will experience microstructure and property

alterations.

Heat-affected-zone (HAZ). Knowledge of HAZ is required to make sure the

joiningstays intact andnot failed

fused base metal

filler metal (melted)base metal (melted)

unaffectedunaffectedheat affected zone

p ece p ece


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ee


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ThermalThermal

Processing ofProcessing ofMetalsMetals


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Thermal Processing of MetalsThermal Processing of Metals

Annealing: Heat to high temperature, Tanneal, then cool slowly.

tress e e : e ucestress caused by:

-plastic deformation-nonuniform cooling

p ero ze stee s :Make very soft steels forgood machining. Heat just

below TE

& hold for

Types of

-p ase rans orm.

Full Anneal (steels):Make soft steels for

15-25 h.

Annealing

Process Anneal:

good forming by heatingto get , then cool in

furnace to get coarse P.

ega e e ec ocold working by(recovery/

recrystallization)

Normalize (steels):Deform steel with largegrains, then normalize

.


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Definition:Definition:

material will be heated at high

tem erature leave at thattemperature for a period of time

follow by cooling


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e o s o nnea ne o s o nnea n

1.1. You need an oven (furnace)You need an oven (furnace)2.2. Place the metal samples which you wish to anneal in the ovenPlace the metal samples which you wish to anneal in the oven

3.3. Heat the furnace to desired temperatureHeat the furnace to desired temperature

4.4. Make sure ou use the ri ht heatin rate to aid thermal shockMake sure ou use the ri ht heatin rate to aid thermal shock

5.5. Set the annealing time (i.e. how long you would want to annealSet the annealing time (i.e. how long you would want to anneal

your samples)your samples) -- soakingsoaking

6.6. Once the annealing is done, cool down the furnaceOnce the annealing is done, cool down the furnace

7.7. Make sure the coolin rate is ri htMake sure the coolin rate is ri ht


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easo s o eaeaso s o ea

1. Process annealing heat treatment to negate (counteract)effects of cold work. During cold work, metal suffers severe

deformation (hence it strain-hardens) and with process

annealing, recovery and recrystalisation occurs

2. Internal residual stress formed in metal because of plastic

deformation (machining, grinding) and non-uniform cooling.

.


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orma zorma z

Heat treatment to refine the grains (decrease grain size)

Produces more uniform grains (size and distribution)

trengt o stee a so increases

Heating to temperature > upper critical temperature (see phase diagram)


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Heat treatment of Carbon SteelHeat treatment of Carbon Steel

(Formation of Martensitic Steel)(Formation of Martensitic Steel)

Quench austenite >726

o

C (in water, air or oil) Upon quenching, martensite formed

Cooling is not uniform.

The outer part of the metal will cooled quicker compared

to the inner art

Hardenability property which determines the depth

and distribution of hardness induced by quenching from

It is a parameter which measure the rate at which

hardness drops off the distance into the interior of a

Quenching

spec men as a resu o m n s e mar ens e con en .


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orma o o ar e s eorma o o ar e s e

Austenite

Quenching

of austenite Martensite

ar ens e orme

on the surface

High

hardness

Low

hardness

Hardenability


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Test used to measure

Hardemability Test

ardness,

HRC

20

40

60

specimenflat ground

1

H 0 1 2 3

600A

P

T(C) 0%100%

24C water

phase field)

400

200A M

M(start)

s,HRC

Martensite

Martensite

FinePearlit

earlite0 M(finish)

Hardne

s

Pearlit

e

0.1 1 10 100 1000

Time (s)Distance from quenched end

Heat TreatmentsHeat Treatments


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Heat TreatmentsHeat Treatments

a)a) AnnealingAnnealingT(C)Austenite (stable)

TE

A

c) Tempered 600

P

ar ens e

400

B

AAdapted from Fig. 10.22, Callister 7e.

200M + A

M + A50%

90%

a)

c)

time (s)

10 103

105

10-1


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rec p a o ar erec p a o ar e

Introducing small uniformly dispersed particlesIntroducing small uniformly dispersed particles(second phase) within original phase matrix.(second phase) within original phase matrix.

The small particles are called precipitates andThe small particles are called precipitates and

can be formed by appropriate heat treatmentcan be formed by appropriate heat treatmentThe strengthening processThe strengthening process increased inincreased in

resistance to dislocation motion by latticeresistance to dislocation motion by lattice

strains which are established in the vicinity ofstrains which are established in the vicinity ofsmall precipitated particlessmall precipitated particles


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Preci itation Hardenin ;Preci itation Hardenin ;

example (READ)example (READ)

DuraluminDuralumin isis anan aluminiumaluminium alloyalloy containingcontaining 44wtwt%% copper,copper, asas wellwellasas smallersmaller amountsamounts ofof otherother elementselements.. TheThe impuritiesimpurities inin thethe

andand sincesince thethe distributiondistributionofof thethecoppercopper atomsatoms cancan bebe variedvaried usingusingheatheat treatments,treatments, aavarietyvariety ofof microstructures,microstructures, andand hencehencepropertiesproperties

TheThecoppercopper formsforms precipitatesprecipitates ofof CuAlCuAl22 withinwithin ananaluminiumaluminiummatrixmatrix..eseese precp aesprecp aes n ern er ee movemenmovemen oo soca onssoca ons anan

substantiallysubstantially strengthensstrengthens thethe alloyalloy.. ThisThis processprocess isis widelywidely usedused totomakemake strongstrong aluminiumaluminium alloysalloys forfor structuralstructural purposes,purposes, andand isisnownnown asas precp a onprecp a on ar enngar enng ..


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o ura umo ura um

Discuss how these

precipitates hindersdislocation movement.


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rec p a o ar erec p a o ar e

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