1. Chapter 11: Metal Alloys - Applications and Processing
ISSUES TO ADDRESS...
• How are metal alloys classified and how are they used?
• What are some of the common fabrication techniques?
• How do properties vary throughout a piece of material
that has been quenched, for example?
• How can properties be modified by post heat treatment?

2. Taxonomy of Metals Steels Cast Irons <1.4 wt% C 3-4.5 wt% C
Alloys
Steels
Ferrous
Nonferrous
Cast Irons Cu Al Mg Ti
<1.4wt%C
3-4.5
wt%C
Steels
<1.4 wt% C
Cast Irons
3-4.5 wt% C
microstructure:
ferrite, graphite
cementite Fe 3 C
cementite
1600
1400
1200
1000
800
600
400 1 2 4 5 6
6.7 L g
austenite +L
+Fe3C a
ferrite +
L+Fe3C d
(Fe)
Co , wt% C
Eutectic:
Eutectoid:
0.76
4.30
727°C
1148°C
T(°C)

3. Steels Low Alloy High Alloy low carbon <0.25 wt% C Med carbon
high carbon
wt% C
plain
HSLA
heat
treatable
tool
austenitic
stainless
Name
Additions
none
Cr,V
Ni, Mo
Cr, Ni Mo
Cr, V,
Mo, W
Cr, Ni, Mo
Example
1010
4310
1040 43 40
1095
4190
304
Hardenability + ++
+++ TS - + ++ EL + + - - -- ++
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
V. corros.
increasing strength, cost, decreasing ductility
resistant

4. Steels Nomenclature AISI & SAE 10xx Plain Carbon Steels
11xx Plain Carbon Steels (resulfurized for machinability)
15xx Mn (10 ~ 20%)
40xx Mo (0.20 ~ 0.30%)
43xx Ni ( %), Cr ( %), Mo ( %)
44xx Mo (0.5%)
where xx is wt% C x 100
example: steel – plain carbon steel with 0.60 wt% C
Stainless Steel -- >11% Cr

5. System and Composition of Plain Carbon Steel and Alloy Steel

6. Low carbon

7. Medium, High carbon

8. Plain Carbon Steel Low carbon Medium carbon High carbon
Good formability and weldability
Strengthening by coldwork
Structure usually pearlite and ferrite
Medium carbon
Can be quenched to form martensite or bainite
Compromising structure between ductility and strength
High carbon
Low toughness and formability
Good hardness and wear resistance
Can form martensite by quenching but risk of cracking
Compare to other engineering materials
High strength and stiffness, reasonable toughness, easy to recycle and low cost
Rust easily, require surface protection

9. Effect of alloy elements
Bi, Pb - improve machinability
B % - powerful hardenability agent
Cr 0.5-2% - increase hardenability, 4-18% - corr. resist.
Cu % corrosion resistance
Mn % - combine with S to prevent brittleness
Mo 0.2-5% - stable carbides
Ni 2-5% - toughener, 12-20% - corrosion resistance
Si % - strength, 2% - spring, higher% - magnetic p.
S % - free machining
Ti - fix C in inert particles, reduce mart. hardn. in Cr steels
W - hardness at high temperature
V - stable carbide, inc. str. with remain ductility, fine grain

10. Alloy Steels HSLA Large applications
High yield (nearly twice of plain C steel), good weldability and acceptable corrosion resistance
Limited ductility and hardenability
Resist to form martensite in weld zone
Dual-Phase Steel
Quench from temp. above A1 but below A3 to form structure of ferrite and martensite
Strength comparable to HSLA while improve formability with no loss of weldability
Automotive structure and body application

11. Alloy Steels Free-machining steels S, Pb, Bi, Se, Te or P
Making chip-breaking discontinuity in structure and a build-in lubrication
Higher cost may compensated with higher speed and lower wear of cutting tools
Additives may reduce concerned properties such as strength, ductility
cold working also improve machinability
Bake-Hardenable steel sheet
Significant in automotive steel sheet
Low carbon steel
Good formability and increase strength after forming with heat exposure in paint-baking process
Good spot weldability, crash energy, low cost easy recycle

12. Alloy Steels Maraging Steels Super high strength alloy
Typical composition is 0.03% C, 8.5% Ni, 7.5% Co, 0.1% Al, 0.003% B, 0.1% Si, 4.8% Mo, 0.4%Ti, 0.01% Zr, 0.1% Mn, 0.01%S and 0.01%P
Can be hot worked to get soft, tough, low martensite and easy to machine
Can be cold worked and aging with a yield of 1725 MPa and %EL 11%
Weldability
Steel for HighTemp.
Good strength, corrosion resistance, creep resistance
Plain C steel – 250 C
Conventional alloy – 350 C
High temp. ferrous alloy tend to has low carbon (less than 0.1%)
Can be used at higher than 550 C

14. Bake hardenable steel
Dual Phase Steel

15. Tool Steels High carbon, high strength ferrous alloy
Water hardening (W)
Cold Work
O – Oil hardening
A – Air hardening
D – High C high Cr
Shock resistance (S)
High speed
T – W base, M – Mo base
Hot work
H1-H19 – Cr base
H20-H39 – W base
H40-H59 – Mo base
Plastic mold (P)
Special purpose
L – Low alloy
F – carbon-tungsten
High carbon, high strength ferrous alloy
Balance of toughness, strength and wear resistance

16. Tool Steels

17. Stainless Steels Series Alloys Structure 200 300 400 500
Cr, Ni, Mn or Ni
Cr and Ni
Cr, (C)
Low Cr (<12%) and (C)
Austenitic
Ferritic or martensitic
Martensitic
Oxide of additive elements is tough, adherent, corrosion resistance and heals itself
Ferritic stainless steel
Normally contain >12% Cr (Cr is ferrite stabilizer)
Corrosion resistance
Limited ductility or formability but weldable (no martensite can form in weld zone)
The cheapest stainless steel

18. Stainless Steels Martensitic Stainless
The lower content of Cr lead to more stable of austenite at high temp.
Slow cool may allow carbide of Cr (loss of chromium oxide film)
Higher cost than ferritic stainless steel due to the heat treatment (austenitization, quench, stress relief and temper
Austenitic Stainless
Ni is austenite stabilizer
The most expensive stainless due to Ni cost
Mn and N are used as stabilizer instead of Ni to reduce cost but lower quality
Non-magnetic, highly corrosion resistance except HCl and other helide acid/salt
Outstanding formability(FCC)
304 alloy (18-8) is popular one, high response to CW

19. Popular stainless steels

20. Stainless Steel (1)

21. Stainless Steel (2)
Precipitation hardenable stainless steel is the special class
Martensitic or austenitic type, modified by addition of alloying elements like Al to form hard intermetallic compound during temper

22. Cast Iron Ferrous alloys with > 2.1 wt% C
more commonly wt%C
low melting (also brittle) so easiest to cast
Cementite decomposes to ferrite + graphite
Fe3C  3 Fe () + C (graphite)
generally a slow process
So phase diagram for this system is different (Fig 12.4)

23. Fe-C True Equilibrium Diagram
Graphite formation promoted by
Si > 1 wt%
slow cooling
Gray cast iron
Ductile or Nodular iron
White iron
Malleable iron
Compacted graphite iron
1600
1400
1200
1000
800
600
400 1 2 3 4 90 L g +L
 + Graphite
Liquid +
Graphite
(Fe)
Co , wt% C
0.65
740°C
T(°C)
 + Graphite
100
1153°C
Austenite
4.2 wt% C
a + g
Cast irons have graphite

24. Production of Cast Iron

25. Types of Cast Iron Gray iron graphite flakes
weak & brittle under tension
stronger under compression
excellent vibrational dampening
wear resistant
Ductile iron
add Mg or Ce
graphite in nodules not flakes
matrix often pearlite - better ductility

26. Types of Cast Iron White iron <1wt% Si so harder but brittle
more cementite
Malleable iron
heat treat at ºC
graphite in rosettes
more ductile

27. Types of Cast Iron Compacted Graphite Iron Mg/Ce and others are added
Worm-like shape graphite
Microstructure is between gray cast iron and ductile iron
Sharp edge of graphite should be avoided
High thermal conductivity
Better resistance to thermal shock, fracture and fatigue
Lower oxidation at elevated Temp.

29. Limitations of Ferrous Alloys
Relatively high density
Relatively low conductivity
Poor corrosion resistance
Nonferrous Alloy

30. Nonferrous Alloys NonFerrous Alloys • Cu Alloys • Al Alloys
Brass: Zn is subst. impurity
(costume jewelry, coins,
corrosion resistant)
Bronze
: Sn, Al, Si, Ni are
subst. impurity
(bushings, landing
gear)
Cu-Be :
precip. hardened
for strength
• Al Alloys
-lower r
: 2.7g/cm3
-Cu, Mg, Si, Mn, Zn additions
-solid sol. or precip.
strengthened (struct.
aircraft parts
& packaging)
NonFerrous
Alloys
• Mg Alloys
-very low r
: 1.7g/cm3
-ignites easily -
aircraft, missiles
• Ti Alloys
-lower r
: 4.5g/cm3
vs 7.9 for steel
-reactive at high T -
space applic.
• Refractory metals
-high melting T
-Nb, Mo, W, Ta
• Noble metals
-Ag, Au, Pt -
oxid./corr. resistant

31. Non-Ferrous Alloys
Cast Alloy – Forming or shaping by appreciable deformation is not possible, ordinarily by casting. So, brittle.
Wrought Alloy – amenable to mechanical deformation
Sometimes the heat treatability of an alloy is frequently mentioned as “heat treatable”

32. Cu and its alloys
3 important properties are high electrical and thermal conductivity, useful strength with high ductility and corrosion resistance
Heavily than iron
Pure Cu – wire, cable
Cu-Zn – brass – popular
alpha brass - ductile, form.
beta brass – Zn rich, brittle
Cu-Ni – high thermal conductivity, high strength at high temperature
Cu-Sn - bronze
Al and its alloys
The most important of non-ferrous metal
Light weight, corrosion resist., good elec./thermal cond., workability, recycle
Serious weakness is low modulus of elesticity
Pure Al – soft, ductile
Alloy for mechanical appl.
strength as HSLA level
Alloy for corrosion resist.
difficult to weld
Al-Li – high strength, great stiffness, lighter weight

33. Mg and its alloys
Lightest of commerc. Metal
Pure Mg – weak
Alloy – poor ductility, wear, creep and fatigue
Modulus less than Al
In positive side, high strength/weight ratio, high energy absorption, good damping of noise/vibration
Higher purity alloy – good corrosion resistance
Formability – at high temp.
Good machinability/weldab.
Fire hazards
Ti and its alloys
Strong, light weight, corrosion resistance
Good mechanical properties up to 535 C
High cost, fabrication difficulty, high energy content and high reactivity at elevated temperature
Fabrication can be by casting, forging, rolling, extrusion or welding

34. Refractory metal
Extremely high melting T
Nb (2468 C), Mo, W (3410 C), Ta
Ta-Mo to improve corrosion resistance
Super alloys
Use in aircraft turbine component
Difficult to form and machine
Special methods are used, EDM, electrochemical, ultrasonic m/c
Noble metals
Au, Ag, Pt, Pd, Rh, Ru, Ir and Os
Expensive
Miscellaneous nonferrous
Ni (coating) Pb Sn
Alkaline

35. Metal Fabrication How do we fabricate metals?
Blacksmith - hammer (forged)
Molding - cast
Forming Operations
Rough stock formed to final shape
Hot working vs Cold working
• T high enough for • well below Tm recrystallization • work hardening
• Larger deformations • smaller deformations

36. Metal Fabrication Methods - I
FORMING
CASTING
JOINING A o d
force
die
blank
• Forging (Hammering; Stamping)
(wrenches, crankshafts)
often at
elev. T
roll A o d
• Rolling (Hot or Cold Rolling)
(I-beams, rails, sheet & plate)
tensile
force A o d
die
• Drawing
(rods, wire, tubing)
die must be well lubricated & clean
ram
billet
container
force
die holder
die A o d
extrusion
• Extrusion
(rods, tubing)
ductile metals, e.g. Cu, Al (hot)

37. Metal Fabrication Methods - II
FORMING
CASTING
JOINING
Casting- mold is filled with metal
metal melted in furnace, perhaps alloying elements added. Then cast in a mold
most common, cheapest method
gives good production of shapes
weaker products, internal defects
good option for brittle materials

38. Metal Fabrication Methods - II
FORMING
CASTING
JOINING
• Sand Casting
(large parts, e.g.,
auto engine blocks)
trying to hold something that is hot
what will withstand >1600ºC?
cheap - easy to mold => sand!!!
pack sand around form (pattern) of desired shape
Sand
molten metal

39. Metal Fabrication Methods - II
FORMING
CASTING
JOINING
• Sand Casting
(large parts, e.g.,
auto engine blocks)
Investment Casting
pattern is made from paraffin.
mold made by encasing in plaster of paris
melt the wax & the hollow mold is left
pour in metal
Sand
molten metal
• Investment Casting
(low volume, complex shapes
e.g., jewelry, turbine blades)
plaster
die formed
around wax
prototype
wax

40. Metal Fabrication Methods - II
FORMING
CASTING
JOINING
• Sand Casting
(large parts, e.g.,
auto engine blocks)
• Die Casting
(high volume, low T alloys)
Sand
molten metal
• Continuous Casting
(simple slab shapes)
molten
solidified
• Investment Casting
(low volume, complex shapes
e.g., jewelry, turbine blades)
plaster
die formed
around wax
prototype
wax

41. Continuous casting

43. Metal Fabrication Methods - III
FORMING
CASTING
JOINING
• Powder Metallurgy
(materials w/low ductility)
• Welding
(when one large part is
impractical)
• Heat affected zone:
(region in which the
microstructure has been
changed).
piece 1
piece 2
fused base metal
filler metal (melted)
base
metal (melted)
unaffected
heat affected zone
pressure
heat
point contact
at low T
densification
by diffusion at
higher T
area
contact
densify

44. Thermal Processing of Metals
Annealing: Heat to Tanneal, Soaking, then cool slowly. •
Stress Relief: Reduce •
Spheroidize
(steels):
stress caused by:
Make very soft steels for
-plastic deformation
good machining. Heat just
-nonuniform cooling
below TE & hold for
-phase transform.
15-25 h. •
Full Anneal
(steels):
Types of
Make soft steels for
Annealing
good forming by heating
to get g
, then cool in
furnace to get coarse P. •
Process Anneal:
Negate effect of •
Normalize
(steels):
cold working by
Deform steel with large
(recovery/
grains, then normalize
recrystallization)
to make grains small. (air cool)

45. Fe-Fe3C diagram

46. Heat Treatments Annealing Quenching Tempered Martensite a) b) c) TE
800
Austenite (stable) a) b)
Annealing TE
T(°C) A
Quenching P
600
Tempered Martensite B
400 A
100%
50% 0% c) 0%
200
M + A
50%
M + A
90% -1 3 5 10 10 10 10
time (s)

47. Hardenability--Steels
• Ability to form martensite
• Jominy end quench test to measure hardenability.
24°C water
specimen
(heated to g
phase field)
flat ground
Rockwell C hardness tests
• Hardness versus distance from the quenched end.
Hardness, HRC
Distance from quenched end

48. Why Hardness Changes with Position
• The cooling rate varies with position. 60
Martensite
Martensite + Pearlite
Fine Pearlite
Pearlite
Hardness, HRC 40 20
distance from quenched end (in) 1 2 3
600
400
200 A M P
0.1 1 10
100
1000
T(°C)
M(start)
Time (s) 0%
100%
M(finish)

49. Hardenability vs Alloy Composition
Cooling rate (°C/s)
Hardness, HRC 20 40 60 10 30 50
Distance from quenched end (mm) 2
100 3
4140
8640
5140
1040 80 %M
4340
• Jominy end quench results, C = 0.4 wt% C
• "Alloy Steels"
(4140, 4340, 5140, 8640)
--contain Ni, Cr, Mo
(0.2 to 2wt%)
--these elements shift the "nose".
--martensite is easier to form.
T(°C) 10 -1 3 5
200
400
600
800
Time (s)
M(start)
M(90%)
shift from
A to B due
to alloying B A TE

50. Equivalent distance and Bar diameter
(Quenched in water)
(Quenched in oil)

51. Radial hardness profile
(Quenched in water)
(Quenched in oil)

52. Quenching Medium & Geometry
• Effect of quenching medium:
Medium
air
oil
water
Severity of Quench
low
moderate
high
Hardness
low
moderate
high
• Effect of geometry:
When surface-to-volume ratio increases:
--cooling rate increases
--hardness increases
Position
center
surface
Cooling rate
low
high
Hardness

53. Precipitation Hardening
• Particles impede dislocations.
• Ex: Al-Cu system
• Procedure: 10 20 30 40 50
wt% Cu L
+L a
a+q q
+L
300
400
500
600
700
(Al)
T(°C)
composition range
needed for precipitation hardening
CuAl2 A
--Pt A: solution heat treat (get a solid solution) B
Pt B
--Pt B: quench to room temp. C
--Pt C: reheat to nucleate small q crystals within a crystals.
Other precipitation systems: • Cu-Be • Cu-Sn • Mg-Al
Temp.
Time
Pt A (sol’n heat treat)
Pt C (precipitate )

54. Precipitate Effect on TS, %EL
• 2014 Al Alloy:
• TS peaks with
precipitation time.
• Increasing T accelerates
process.
• %EL reaches minimum
with precipitation time.
%EL (2 in sample) 10 20 30
1min 1h
1day
1mo
1yr
204°C
149 °C
precipitation heat treat time
precipitation heat treat time
tensile strength (MPa)
200
300
400
100
1min 1h
1day
1mo
1yr
204°C
non-equil.
solid solution
many small
precipitates
“aged”
fewer large
“overaged”
149°C

55. Metal Alloy Crystal Structure
Alloys
substitutional alloys
can be ordered or disordered
disordered solid solution
ordered - periodic substitution
example: CuAu FCC Cu Au

56. Metal Alloy Crystal Structure
Interstitial alloys (compounds)
one metal much larger than the other
smaller metal goes in ordered way into interstitial “holes” in the structure of larger metal
Ex: Cementite – Fe3C

57. Summary • Steels: increase TS, Hardness (and cost) by adding
--C (low alloy steels)
--Cr, V, Ni, Mo, W (high alloy steels)
--ductility usually decreases w/additions.
• Non-ferrous:
--Cu, Al, Ti, Mg, Refractory, and noble metals.
• Fabrication techniques:
--forming, casting, joining.
• Hardenability
--increases with alloy content.
• Precipitation hardening
--effective means to increase strength in
Al, Cu, and Mg alloys.