Chapter 11: Applications & Process. Of Metal Alloys

Chapter 11: Applications andProcessing of Metal AlloysISSUES TO ADDRESS. What are some of the common fabrication techniquesfor metals? What heat treatment procedures are used to improve themechanical properties of both ferrous and nonferrous alloys?Chapter 11 - 1

Metal FabricationHow do we fabricate metals?1. Refining (Extraction)2. FormingRefiningForming–Rough stock formed to final shapeHot workingvs.Cold workingChapter 11 - 2

Production of Iron from OreIron OreCoke (carbon)Limestone (CaCO3 to remove slag)(Fe2O3 and impurities)BLAST FURNACEgasrefractoryvessellayers of cokeand iron oreairslagMolten ironheat generationC O2 CO2reduction of iron ore to metalCO2 C 2CO3CO Fe2O3 2Fe 3CO2purificationCaCO3 CaO CO2CaO SiO2 Al2O3 slagWorld annual production: 109 tonChapter 11 - 3

Production of Copper1. Mining copper sulfides (CuFeS2, Cu2S)2. Remove Fe (through oxides)3. Oxidize copper sulfides into copper oxides anddecompose Cu2O to obtain copper2Cu2S 3O2 2Cu2O 2SO22Cu2O 4Cu O24. Further refining with help of (sulfuric) acid digestionand electro-deposition or further meltingCu2 2e- CuAnnual world production: 20x106 ton 80% of all copper recycledChapter 11 - 4

Production of AluminumAl bonds to oxygen strongly, difficult to reduce bycarbon (as compared with Fe or Cu) or by thermaldecomposition (as for Cu)Electrolytic production in molten salt of Na3AlF6-CaF2:2Al2O3 4Al 3O2World annual production: 40x106 tonChapter 11 - 5

Metal Fabrication Methods (i)FORMINGCASTINGMISCELLANEOUS Forging (Hammering; Stamping) Rolling (Hot or Cold Rolling)(wrenches, crankshafts)force(I-beams, rails, sheet & plate)rolldieA o blankA d often atelev. T DrawingforceAoAdroll Extrusion(rods, wire, tubing)dieAo(rods, tubing)Aotensileforcediedie must be well lubricated & cleanAdforcecontainerrambilletAdapted fromFig. 11.8,Callister &Rethwisch 8e.die holderAdextrusiondieductile metals, e.g. Cu,Al (hot)Chapter 11 container6

Metal Fabrication Methods (ii)FORMINGCASTINGMISCELLANEOUS Casting- mold is filled with molten metal– metal melted in furnace, perhaps alloyingelements added, then cast in a mold– common and inexpensive– gives good production of shapes– weaker products, internal defects– good option for brittle materials and/or complexshapeChapter 11 - 7

Metal Fabrication Methods (iii)FORMINGCASTINGMISCELLANEOUS Sand Casting(large parts, e.g.,auto engine blocks)SandSandmolten metal Model material need to withstand T 1500ºC and is inexpensive and easyto mold, e.g., sand To create mold, pack sand around form(pattern) of desired shapeChapter 11 - 8

Metal Fabrication Methods (iv)FORMINGCASTINGMISCELLANEOUS Investment Casting(low volume, complex shapese.g., jewelry, turbine blades) Stage I — Mold formed by pouring plasterof paris (CaSO4.2H2O) around wax pattern.Plaster allowed to harden.waxI Stage II — Wax is melted and thenpoured from mold—hollow moldcavity remainsII Stage III — Molten metal is pouredinto mold and allowed to solidify.IIIChapter 11 - 9

Metal Fabrication Methods (v)FORMINGCASTING Die Casting-- high volume-- for alloys having low meltingtemperaturesMISCELLANEOUS Continuous Casting-- simple shapes(e.g., rectangular slabs,cylinders)moltensolidifiedChapter 11 - 10

Metal Fabrication Methods (vi)FORMINGCASTING Powder Metallurgy(metals w/low ductilityor very high melting points)MISCELLANEOUS Welding(when fabrication of one largepart is impractical)pressurefiller metal (melted)base metal (melted)fused base metalheatareacontactdensifypoint contactat low Tdensificationby diffusion athigher Tunaffectedpiece 1heat-affected zoneunaffectedAdapted from Fig.piece 211.9, Callister & (Electro) plating orother electrodepositionRethwisch 8e.(Fig. 11.9 from IronCastingsHandbook, C.F.Walton and T.J.Opar (Ed.), 1981.)Chapter 11 - 11

Annealing of MetalsAnnealing: Heat to certain temperature Tanneal, then cool slowly. Stress Relief: Reduce Spheroidize (steels):stresses resulting from:- plastic deformation- nonuniform cooling- phase transform.Make very soft steels forgood machining. Heat justbelow Teutectoid & hold for15-25 h.Types ofAnnealing Process Anneal:Negate effects ofcold working by(recovery/recrystallization)Based on discussion in Section 11.7, Callister & Rethwisch 8e. Full Anneal (steels):Make soft steels forgood forming. Heatto get g, then furnace-coolto obtain coarse pearlite. Normalize (steels): Deformsteel with large grains. Then heattreat to allow recrystallizationand formation of smaller grains.Chapter 11 - 12

Quenching & Hardenability -- Steels Hardenability – measure of the ability for steel to formmartensite – a meta-stable phase with very high hardnessspecimenheated to gphase T(e.g., 727C)24ºC waterflat groundRockwell Chardness testsAdapted from Fig. 11.11,Callister & Rethwisch 8e.(Fig. 11.11 adapted fromA.G. Guy, Essentials ofMaterials Science,McGraw-Hill BookCompany, New York,1978.)Hardness, HRC Plot hardness versus distance from the quenched end.Adapted from Fig. 11.12,Callister & Rethwisch 8e.Distance from quenched endChapter 11 - 13

Reason Why Hardness Changes withDistance/Cooling RateHardness, HRCFor steel, faster cooling – harder (certain hard (meta-stable) phaseformation); slower cooling – softer (less or no hard phaseformation)6040200123distance from quenched end tart)Adapted from Fig. 11.13, Callister &Rethwisch 8e. (Fig. 11.13 adapted from H.Boyer (Ed.) Atlas of IsothermalTransformation and CoolingTransformation Diagrams, AmericanSociety for Metals, 1977, p. 376.)A M0 M(finish)0.11101001000Time (s)Chapter 11 - 14

Influences of Quenching Medium &Specimen Geometry Effect of quenching medium:MediumairoilwaterRate of coolinglowmoderatehighHardnesslowmoderatehigh Effect of specimen geometry:When surface area-to-volume ratio increases:-- cooling rate throughout interior increases-- hardness throughout interior increasesPositioncentersurfaceCooling ratelowhighHardnesslowhighChapter 11 - 15

Precipitation Hardening Particles impede dislocation motion and make alloys harder & stronger Ex: Al-Cu system700 Procedure:T(ºC)LCuAl600-- A: solution heat treatment Lq L(get uniform solid solution)A500q-- B: quench to room temp. qC(uniform solid solution)400-- C: reheat/aging to nucleate small300precipitates (q within phase)0 B 10 20 30 40 50(Al)wt% Cu Other alloys that displayprecipitation hardening: Cu-Be Cu-Sn Mg-Alcomposition rangeavailable for precipitation hardeningTemp.A (sol’n heat treat)Adapted from Fig. 11.24, Callister & Rethwisch 8e.(Fig. 11.24 adapted from J.L. Murray, InternationalMetals Review 30, p.5, 1985.)Adapted from Fig. 11.26, Callister & Rethwisch 8e. (Fig. 11.26 is courtesy ofG.H. Narayanan and A.G. Miller, Boeing Commercial Airplane Company.)C (precipitate q)Adapted from Fig.11.22, Callister &Rethwisch 8e.2BTimeMicrostructure of Alwith fine precipitatesChapter 11 16

Influence of Precipitation HeatTreatment on TS & %EL400300200100149ºC204ºC1min1h 1day 1mo 1yrprecipitation heat treat time%EL (2 in sample)tensile strength (MPa)Example of Al Alloys: Maxima on TS curves w/ aging time yet min on EL% curve Increasing T accelerates precipitation hardening process Too long aging decreases strength again due to “overageing” or growth of precipitates302010204ºC0149ºC1min1h 1day 1mo 1yrprecipitation heat treat timeAdapted from Fig. 11.27, Callister & Rethwisch 8e. (Fig. 11.27 adapted from Metals Handbook:Properties and Selection: Nonferrous Alloys and Pure Metals, Vol. 2, 9th ed., H. Baker (ManagingEd.), American Society for Metals, 1979. p. 41.)Chapter 11 - 17

Summary Ferrous alloys: steels and cast irons Non-ferrous alloys:-- Cu, Al, Ti, and Mg alloys; refractory alloys; and noble metals. Metal fabrication techniques:-- forming, casting, miscellaneous. Hardenability of metals-- measure of ability of a steel to be heat treated. Precipitation hardening--hardening & strengthening due to formation ofprecipitate particles.--Al, Mg alloys precipitation hardenable.Chapter 11 - 18

Chapter 11 - 18 Ferrous alloys: steels and cast irons Non-ferrous alloys: -- Cu, Al, Ti, and Mg alloys; refractory alloys; and noble metals. Metal fabrication techniques: -- forming, casting, miscellaneous. Hardenability of metals -- measure of ability of a steel to be heat treated. Precipitation hardening