CHAPTER
11
Applications and
Processing of Metal Alloys
Introduction
Ferrous alloys
Nonferrous alloys
Forming operations
Casting
Miscellaneous techniques
Annealing processes
Heat treatment of steels
Precipitation hardening
2
Chapter 11: Applications and
Processing of Metal Alloys
ISSUES TO ADDRESS...
• How are metal alloys classified and what are their
common applications?
• What are some of the common fabrication techniques
for metals?
• What heat treatment procedures are used to improve the
mechanical properties of both ferrous and nonferrous alloys?
3
Applications and Processing of Metal Alloys
The aluminum beverage can in
various stages of production.
The can is formed from a single
sheet of an aluminum alloy.
Production operations include
drawing (抽製), dome forming
(圓頂成型), trimming (修邊),
cleaning, decorating (裝飾), and
neck and flange forming
(修頸與凸緣成型).
4
Ferrous Alloys
金屬合金
Figure 11.1 Classification scheme
for the various ferrous alloys.
鐵合金 非鐵合金
鋼 鑄鐵
低合金鋼
灰鑄鐵 延性鑄鐵 白鑄鐵 展性鑄鐵 變緊密
的石墨鐵
高合金鋼
低碳鋼 中碳鋼 高碳鋼
5
工具鋼 不銹鋼
Classification of Metal Alloys
Metal Alloys
Ferrous Nonferrous
Steels
Steels Cast Irons
Cast Irons
<1.4 wt% C
<1.4wt%C 3-4.5 wt%C
3-4.5 wt% C
T(ºC) microstructure: ferrite,
1600 graphite/cementite
d
1400 L
g+L
1200 g 1148ºC L+Fe3C
austenite Eutectic:
1000 4.30
g+Fe3C
a800 727ºC Fe3C
ferrite Eutectoid: cementite
600 0.76 a+Fe3C
400
0 1 2 3 4 5 6 6.7
(Fe)
Co , wt% C 6
Steels
Low Alloy High Alloy
low carbon Med carbon high carbon
<0.25 wt% C 0.25-0.6 wt% C 0.6-1.4 wt% C
heat
Name plain HSLA plain plain tool stainless
treatable
Cr,V Cr, Ni Cr, V,
Additions none none none Cr, Ni, Mo
Ni, Mo Mo Mo, W
Example 1010 4310 1040 43 40 1095 4190 304, 409
Hardenability 0 + + ++ ++ +++ varies
TS - 0 + ++ + ++ varies
EL + + 0 - - -- ++
Uses auto bridges crank pistons wear drills high T
struc. towers shafts gears applic. saws applic.
sheet press. bolts wear dies turbines
vessels hammers applic. furnaces
blades Very corros.
resistant
increasing strength, cost, decreasing ductility
7
Refinement of Steel from Ore
Coke
Iron Ore Limestone
BLAST FURNACE
heat generation
gas C + O2 CO2
refractory
vessel reduction of iron ore to metal
layers of coke CO2 + C 2CO
and iron ore 3CO + Fe2O3 2Fe +3CO2
air purification
slag
Molten iron CaCO3 CaO+CO2
CaO + SiO2 + Al2O3 slag
8
Ferrous Alloys
Iron-based alloys
• Steels
• Cast Irons
Nomenclature for steels (AISI/SAE)
10xx Plain Carbon Steels
11xx Plain Carbon Steels (resulfurized for machinability)
15xx Mn (1.00 - 1.65%)
40xx Mo (0.20 ~ 0.30%)
43xx Ni (1.65 - 2.00%), Cr (0.40 - 0.90%), Mo (0.20 - 0.30%)
44xx Mo (0.5%)
where xx is wt% C x 100
example: 1060 steel – plain carbon steel with 0.60 wt% C
Stainless Steel >11% Cr
9
Cast Irons
• Ferrous alloys with > 2.1 wt% C
– more commonly 3 - 4.5 wt% C
• Low melting – relatively easy to cast
• Generally brittle
• Cementite decomposes to ferrite + graphite
Fe3C 3 Fe (a) + C (graphite)
– generally a slow process
10
Fe-C True Equilibrium Diagram
Cementite decomposes to
T(ºC)
ferrite + graphite 1600
Fe3C 3 Fe (a) + C (graphite)
1400 L Liquid +
g +L Graphite
Graphite formation 1200 g 1153ºC
promoted by Austenite 4.2 wt% C
1000
• Si > 1 wt% g + Graphite
a+g
• slow cooling 800
740ºC
600 0.65
a + Graphite
400
0 1 2 3 4 90 100
(Fe) C, wt% C
11
Types of Cast Iron
Gray iron
• graphite flakes
• weak & brittle in tension
• stronger in compression
• excellent vibrational dampening
• wear resistant
Ductile iron
• add Mg and/or Ce
• graphite as nodules not flakes
• matrix often pearlite – stronger
but less ductile
12
Types of Cast Iron (cont.)
White iron
• < 1 wt% Si
• pearlite + cementite
• very hard and brittle
Malleable iron
• heat treat white iron at 800-900ºC
• graphite in rosettes
• reasonably strong and ductile
13
Types of Cast Iron (cont.)
Compacted graphite iron
• relatively high thermal conductivity
• good resistance to thermal shock
• lower oxidation at elevated
temperatures
14
Production of Cast Irons
15
Limitations of Ferrous Alloys
1) Relatively high densities
2) Relatively low electrical conductivities
3) Generally poor corrosion resistance
16
Nonferrous Alloys
• Cu Alloys • Al Alloys
Brass: Zn is subst. impurity -low r: 2.7 g/cm3
(costume jewelry, coins, -Cu, Mg, Si, Mn, Zn additions
corrosion resistant) -solid sol. or precip.
Bronze : Sn, Al, Si, Ni are strengthened (struct.
subst. impurities aircraft parts
(bushings, landing & packaging)
gear) NonFerrous • Mg Alloys
Cu-Be : -very low r: 1.7g/cm3
precip. hardened Alloys -ignites easily
for strength -aircraft, missiles
• Ti Alloys
-relatively low r: 4.5 g/cm3 • Refractory metals
-high melting T’s
vs 7.9 for steel • Noble metals -Nb, Mo, W, Ta
-reactive at high T’s -Ag, Au, Pt
-space applic. -oxid./corr. resistant
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Introduction
Ferrous alloys
Nonferrous alloys
Forming operations
Casting
Miscellaneous techniques
Annealing processes
Heat treatment of steels
Precipitation hardening
18
Metal Fabrication
• How do we fabricate metals?
– Blacksmith - hammer (forged)
– Cast molten metal into mold
• Forming Operations
– Rough stock formed to final shape
Hot working vs. Cold working
• Deformation temperature • Deformation below
high enough for recrystallization
recrystallization temperature
• Large deformations • Strain hardening occurs
• Small deformations
19
Fabrication of Metals
鍛造 輥軋 擠製 抽製 砂模 鑄模 包覆模 消失模 連續模 焊接
粉末
冶金
Figure 11.7 Classification scheme of metal fabrication techniques
discussed in this chapter.
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Metal Fabrication Methods (i)
FORMING CASTING MISCELLANEOUS
• Forging (Hammering; Stamping) • Rolling (Hot or Cold Rolling)
(wrenches, crankshafts) (I-beams, rails, sheet & plate)
force
die roll
Ad
A o blank A d often at Ao
elev. T
roll
force
• Drawing • Extrusion
(rods, wire, tubing) (rods, tubing)
Ao
die Ad container
tensile die holder
Ao force
force ram billet extrusion Ad
die
container die
die must be well lubricated & clean ductile metals, e.g. Cu, Al (hot)
21
Metal Fabrication Methods (ii)
FORMING CASTING MISCELLANEOUS
• Casting- mold is filled with molten metal
– metal melted in furnace, perhaps alloying
elements added, then cast in a mold
– common and inexpensive
– gives good production of shapes
– weaker products, internal defects
– good option for brittle materials
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Metal Fabrication Methods (iii)
FORMING CASTING MISCELLANEOUS
• Sand Casting
(large parts, e.g.,
• What material will withstand T >1600ºC
auto engine blocks)
and is inexpensive and easy to mold?
• Answer: sand!!!
Sand Sand
• To create mold, pack sand around form
molten metal (pattern) of desired shape
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Metal Fabrication Methods (iv)
FORMING CASTING MISCELLANEOUS
• Investment Casting
(low volume, complex shapes
e.g., jewelry, turbine blades)
• Stage I — Mold formed by pouring wax I
plaster of paris around wax pattern.
Plaster allowed to harden.
• Stage II — Wax is melted and then
poured from mold—hollow mold
II
cavity remains.
• Stage III — Molten metal is poured
into mold and allowed to solidify. III
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Metal Fabrication Methods (v)
FORMING CASTING MISCELLANEOUS
• Die Casting • Continuous Casting
-- high volume -- simple shapes
-- for alloys having low melting (e.g., rectangular slabs,
temperatures cylinders)
molten
solidified
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Metal Fabrication Methods (vi)
FORMING CASTING MISCELLANEOUS
• Powder Metallurgy • Welding
(metals w/low ductilities) (when fabrication of one large
part is impractical)
pressure
filler metal (melted)
base metal (melted)
fused base metal
heat
heat-affected zone
area unaffected unaffected
contact piece 1 piece 2
densify
• Heat-affected zone:
point contact densification
by diffusion at
(region in which the
at low T
higher T microstructure has been
changed).
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Introduction
Ferrous alloys
Nonferrous alloys
Forming operations
Casting
Miscellaneous techniques
Annealing processes
Heat treatment of steels
Precipitation hardening
27
Thermal Processing of Metals
Annealing: Heat to Tanneal, for an extended time, then cool slowly.
• Stress Relief: Reduce • Spheroidize (steels):
stresses resulting from: Make very soft steels for
- plastic deformation good machining. Heat just
- nonuniform cooling below Teutectoid & hold for
- phase transform. 15-25 h.
• Full Anneal (steels):
Types of Make soft steels for
good forming. Heat
Annealing to get g, then furnace-cool
to obtain coarse pearlite.
• Process Anneal:
Negate effects of
• Normalize (steels): Deform
cold working by
steel with large grains. Then heat
(recovery/
treat to allow recrystallization
recrystallization)
and formation of smaller grains.
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Fe – Fe3C
29
Heat Treatment Temperature-Time Paths
a) Full Annealing A
b) Quenching P
c) Tempering
(Tempered
Martensite) A
B
b) a)
c)
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Hardenability -- Steels
• Hardenability – measure of the ability to form martensite
• Jominy end quench test used to measure hardenability.
flat ground
specimen
(heated to g
phase field) Rockwell C
24ºC water hardness tests
• Plot hardness versus distance from the quenched end.
Hardness, HRC
Distance from quenched end
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Reason Why Hardness Changes with
Distance
• The cooling rate decreases with distance from quenched end.
Hardness, HRC
60
40
20 distance from quenched end (in)
0 1 2 3
T(ºC) 0%
600 100%
400
M(start)
200
AM
0 M(finish)
0.1 1 10 100 1000
Time (s)
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Hardenability vs Alloy Composition
100 10 3 2 Cooling rate (ºC/s)
• Hardenability curves for
60
Hardness, HRC
five alloys each with, 100
80 %M
C = 0.4 wt% C 4340
50
40 4140
8640
5140
20
0 10 20 30 40 50
Distance from quenched end (mm)
• "Alloy Steels" 800
(4140, 4340, 5140, 8640) T(ºC) TE
600
-- contain Ni, Cr, Mo A B
(0.2 to 2 wt%) 400
-- these elements shift
the "nose" to longer times M(start)
200
(from A to B) M(90%)
-- martensite is easier 0 -1
10 10 103 105 Time (s)
to form 33
Influences of Quenching Medium &
Specimen Geometry
• Effect of quenching medium:
Medium Severity of Quench Hardness
air low low
oil moderate moderate
water high high
• Effect of specimen geometry:
When surface area-to-volume ratio increases:
-- cooling rate throughout interior increases
-- hardness throughout interior increases
Position Cooling rate Hardness
center low low
surface high high
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Introduction
Ferrous alloys
Nonferrous alloys
Forming operations
Casting
Miscellaneous techniques
Annealing processes
Heat treatment of steels
Precipitation hardening
35
Precipitation Hardening
• Particles impede dislocation motion.
700
• Ex: Al-Cu system
T(ºC) L CuAl2
• Procedure:
-- Pt A: solution heat treat
600 a+L a q+L
A
(get a solid solution) 500 q
-- Pt B: quench to room temp. C a+q
400
(retain a solid solution)
-- Pt C: reheat to nucleate 300
small q particles within 0 B 10 20 30 40 50
(Al) wt% Cu
a phase. composition range
available for precipitation hardening
• Other alloys that precipitation
harden: Temp.
• Cu-Be Pt A (sol’n heat treat)
• Cu-Sn
• Mg-Al Pt C (precipitate q)
Time
Pt B
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Precipitation Hardening
-Al-Cu alloy:
With time and the subsequent diffusion
of copper atoms, zones become particles
as they increase in size. These
precipitate particles then pass through
two transition phases (q” and q’), before
the formation of the equilibrium q phase
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Influence of Precipitation Heat
Treatment on TS, %EL
• 2014 Al Alloy:
• Maxima on TS curves. • Minima on %EL curves.
• Increasing T accelerates
process.
tensile strength (MPa)
30
%EL (2 in sample)
400
20
300
149ºC 10
200 204ºC 149ºC
204ºC
100 0
1min 1h 1day 1mo 1yr 1min 1h 1day 1mo 1yr
precipitation heat treat time precipitation heat treat time
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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.
-- increases with alloy content.
• Precipitation hardening
--hardening, strengthening due to formation of
precipitate particles.
--Al, Mg alloys precipitation hardenable.
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