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Non-ferrous metals
From last lecture
Division of metals into ferrous and non-ferrous categories: Iron and steel = general purpose metals
over 90% byweight of alloys in general industrial use (1995)
Non-ferrous metals
used in niche applications where
properties of iron and steel are inadequate
Main drawbacks of iron and steel:
Low corrosion resistance
High density
High temperature strength could be better
(Poor electrical conductivity)
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high temperaturestrength
corrosionresistancelow density
Mg
Al
Ti
Ni
Co
Cu
noble metals
(Au, Pt, Ag)
Ta
Pb
ZnSn
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high temperaturestrength
corrosionresistancelow density
Mg
Al
Ti
Ni
Co
Cu
noble metals
(Au, Pt, Ag)
Ta
Pb
ZnSn
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Light alloys: Mg, Ti, Al
Problem:
Does lower density mean lower mass of component?
1.72.7
4.5
7.98.9 8.9
10.5
19.3
21.5
0
5
10
15
20
25
Mg Al Ti Fe Cu Ni Ag Au Pt
Density (g/cm3)
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Solution:
Ashby diagram
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density (log scale)
Youngs modulus(log scale)
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Designing for minimum weight
e.g. Beam (thickness variable, other dimensions constant)
Wish to achieve a given stiffness for minimum weight
For given stiffness and mass,
CE
=
3/1
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0
0.2
0.4
0.6
0.8
1
1.2
Mg Al Ti Fe
Mass
(nominal units)
Mass required to produce beam of given stiffness
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Aluminium
Properties:
Low density (2.7 g/cm3
) Very good corrosion resistance in common environments (due to
protective oxide layer, can be improved by anodising)
Ductile (fcc crystal structure)
High electrical and thermal conductivity
BUT, low melting point: 660C (e.g. mp of iron is 1535C)
restricts use at high temperatures
Also, Youngs modulus not particularly high (E = 70 GPa)
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Applications: Aerospace & air travel: structural components of planes, fuel
tanks in spacecraft
Building and construction: panels, roofs, window frames
Packaging: beverage cans, foil
Transport: bikes, car engine parts, bus bodies
Electrical: e.g. overhead cables
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International Alloy Designation System
(Classification of wrought alloys)
Designation Main alloying elements Applications (e.g.) 1xxx >99 wt% Al Foil, cables
2xxx Cu Aircraft
3xxx Mn Cooking pans
4xxx Si5xxx Mg Beverage cans
6xxx Mg & Si Window frames
7xxx Zn Aircraft
8xxx Others, including Li
(No universally accepted designation system for cast alloys)
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Strengthening mechanisms in wrought alloys
Distinguish between heat-treatable(precipitation hardeningpossible) and non-heat-treatable
Non-heat-treatable alloys strengthened through work-hardening(1xxx, 3xxx and 5xxx series) and solid solution
strengthening (5xxx series)
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Maximise strength by optimising precipitate distribution
age-hardening
Precipitation hardening
T(C)
t
550
150
1. Solution treat
uniformdistribution of Cu atoms
2. Quench
freezesolid solution inplace
3. Age
allow precipitation to occur
fine
distribution of second phase
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