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AerospaceMetals > Aluminium > Flashcards

Aluminium Flashcards

1
Q

What is T3?

A

Solution treated, cold worked and naturally aged to a substantially
stable condition. Allows for cold working to increase strength and also for
cold work involved in flattening or straightening.

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2
Q

What is T4?

A

Solution treated and naturally aged to a substantially stable condition.

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3
Q

What is T6?

A

Solution treated and artificially aged.

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4
Q

What is T7?

A

Solution treated and overaged to lower than peak strength in order to
improve another property e.g. stress corrosion cracking resistance.

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5
Q

What is T73?

A

Solution treated and overaged by a two stage ageing treatment to lower than
peak strength in order to improve SCC resistance.

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6
Q

what is TXX6?

A

(e.g. T736) Indicates the 1st step in a two stage ageing process is the T6
treatment.

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7
Q

What is Tx51?

A

(e.g. T351 & T851) applies to products which receive no further straightening
after stretching, e.g. plate.

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8
Q

What is TX52?

A

(e.g. T7352 & T73652) applies to products that are stress relieved by
compressing after solution treatment (strain typically 1-5%).

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9
Q

What is T8?

A

Solution treated, cold worked and artificially aged beyond peak strength.

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10
Q

What are the properties of aluminium?

A

Low Density
Highly resistant to most forms of corrosion
superb conductor of electricity
Non-Magnetic and noncombustible
non toxic and impervious
strong
ductile

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11
Q

how abundant is aluminium?

A

3rd in the crust

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12
Q

Applications of aluminium?

A

construction
packaging
transport
electrical
other

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13
Q

how is aluminium extracted?

A

Aluminium is extracted from bauxite, a mixed oxide ore
containing about 50% hydrated alumina

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14
Q

What is Bayer Process?

A

It is separated from the other oxides by dissolution and reprecipitation by reaction with sodium hydroxide

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15
Q

What is Hall-Haroult process?

A

It is then dissolved in a molten salt mixture of cryolite (Na3AlF6
)
and electrolytically reduced to molten aluminium

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16
Q

how much power is consumed per tonne of aluminium
produced?

A

14,000 kWh/tonne

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17
Q

Describe the Hall-Heroult Process

A

Graphite anodes
molten Al2O3 and Na3AIF6
Graphite lines tank (cathode)
Al collects molten on the bottom

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18
Q

What kind of process is Hall- Heroult?

A

Continuous
Bath running all the time

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19
Q

What Direct Chill (DC) casting?

A

Semi continous
Liquid metal into water cooled metal mold
Hydraulic ram withdraws aluminium at a draw rate
produces billet

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20
Q

Why do we get eutectic forming in aluminium non-equilibrium?

A

Segregation of 2 different phase elements
Reduces melting temp

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21
Q

How is eutectic removed?

A

Homogenisation
After solidification the alloy is heated to a temp below eutectic temo and held for a long time ( up to 24hrs)

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22
Q

What are the main alloying elements of 1xxx

A

99% min Al

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23
Q

What are the main alloying elements of 2xxx

A

Copper

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24
Q

What are the main alloying elements of 3xxx

A

Manganese

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25
Q

What are the main alloying elements of 4xxx

A

Silicon

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26
Q

What are the main alloying elements of 5xxx

A

Magnesium

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27
Q

What are the main alloying elements of 6xxx

A

Magnesium and silicon

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28
Q

What are the main alloying elements of 7xxx

A

Zinc

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29
Q

What are the main alloying elements of 8xxx

A

other

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30
Q

What do F, O, H and T mean?

A

F - As fabricated
O - annealed wrought
H - Cold worked
T - Heat Treated

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31
Q

What alloys are work hardenable

A

1xxx
3xxx
5xxx

32
Q

what are some typical applications of 1xxx

A

foil
Architectural
Decorations
Power transmission

33
Q

What are typical applications of 3xxx

A

Drinks cans

34
Q

strength of 3xxx, annealed vs cold worked

A

Annealed - 40 MPa
Cold worked - 185MPA

35
Q

how is 3xxx hardened?

A

SS hardening from Mn
Dispersion strengthening via MnAl6 particles

36
Q

what are the advantages of 5xxx aluminium?

A

Much more recyclable than 3xxx
lower densitty
does not rust
high strength
formable
bright surface finish

37
Q

What is the strenght of 5xxx annealed vs cold worked?

A

Annealed - 40-160MPa
Cold worked - 300 MPa

38
Q

What are the disadvantages of 5xxx Aluminium

A

weldability
Repairability
yield point phenomena

39
Q

what is the main strengthening mechanism of 5xxx aluminium

A

solid solution strengthening by mg dissolved in Al matrix

40
Q

Why does the strength increase with with SS strengthening in 5xxx aluminium?

A

Mg has effect on lattice strain

41
Q

What is homogenisation?

A

After solidification the alloy is heated to a temp below the eutectic temp and held for a very long time ( can be 24 hours) to remove the eutectic and to homogenise the solute content.

42
Q

What does aging temperature determine?

A

Determines rate of nucleation and growth of precipitates

43
Q

What happens to 1xxx when RX

A

drop in strength but increase in ductility

44
Q

What effect does ageing time have?

A

Determines the size of precipitates

45
Q

what are the effects of increases aging temperature?

A

Decreases undercooling - less driving force for nucleation get fewer nuclei
Increases diffusion of solute - precipitates grow faster

46
Q

What are the 3 stages of ageing?

A

Nucleation
Growth
Coarsening

47
Q

What does a under aged distribution of precipitates look like?

A

Large number of very small underdeveloped precipitates

48
Q

What does a peak aged distributions of precipitates look like?

A

Optimum size and distribution of precipitates

49
Q

What does overaged look like?

A

A few large precipitates spaced far apart

50
Q

Which alloys are Heat treatable?

A

2xxx
6xxx
7xxx
8xxx

51
Q

what are the applications of 2xxx aluminium?

A

Airframe and skin structure
T4 (damage tolerant) condition for lower wing
Heavy engineering

52
Q

What is the order of strength of 2xxx, 6xxx, 7xxx?

A

6xxx -> 2xxx -> 7xxx

53
Q

What are some disadvantages of 2xxx

A

SCC and corrosion resistance are poor

54
Q

How are the highest strengths of 2xxx achieved?

A

Cold working between quenching and artificial ageing

55
Q

what is the θ Phase for 2xxx?

A

High Cu:Mg ratio.
Excess Cu
Al2Cu

56
Q

What is S phase for 2xxx?

A

Low Cu:Mg Ratio
Al2CuMg

57
Q

What are the applications of 6xxx

A

Structural and architectural applications
Door frames
75% of industrial extrusions

58
Q

What are some advantages of 6xxx

A

Easily extruded at high speeds
good anodisable surface finish
Good corrosion resistance and weldability

59
Q

6xxx disadvantages

A

Not as strong as 7xxx
Not as thermally stable as 2xxx

60
Q

What can you add to 6xxx to increase strength

A

Cu

61
Q

What can you add to 6xxx to restore corrosion resistance?

A

Cr

62
Q

What is the precipitation sequence of 6xxx

A

SSSS → rod GP zones → β’ needles →
equilibrium Mg2Si plates

63
Q

What is the precipitation sequence of 2xxx

A

SSSS → lath GP zones → S’ laths → S
laths.

64
Q

What are the dilute and concentrate makeups of 6xxx additions?

A
  1. Mg + Si < 1 wt. % (Dilute)
  2. Mg + Si > 1 wt. % ( concentrate)
65
Q

What are properties of dilute 6xxx?

A

Age well at RT (natural ageing) -> metastable GP zone
GP zones act as nucleation sites during artificial ageing (T6)
Homogeneous distribution of Mg2Si precipitates

66
Q

What are the properties of Concentrate 6xxx

A

Higher strenghs
Age well at RT (Natural ageing) -> metastable GP zone
T6 reduces strength
GP zones redissolve on heating- decrease in nucleation sites for Mg2Si precipitates
Need to age immediately after Quench

67
Q

What is the effect of adding silicon to 6xxx ?

A

AlFeSi phase is detrimentral to billet properties in unspheroidised form β
Homogenisation must change this phase to alpha phase
extrudability is linked to Si makeup

68
Q

what is the effect of adding magnesium to 6xxx

A

negligable effect on SSH
in excess it casues dramatic decrease in extrudibility
changes tear initiation mechanism
decreases ductility and toughness
Better corrosion resistance

69
Q

what is the effect of Mg2Si on 6xxx

A

The principle strengthening phase
Equilibrium ratio of Mg:Si is 1.73:1
Improves tensile properties
Decrease in extrudability because of cracking
Reduces required storage time between storing and artificial ageing due to growth of fine precipitates after ageing
Precipitates must be fine and uniformely dispersed

70
Q

What is the effect of adding iron to 6xxx

A

Can reduce strength
can refine Mg2Si precipitates
reduction in corrosion resistance
increase in toughness
grain boundary pinning effect
small amounts of Fe means normal grain growth and recrystalisation

71
Q

What are the effects of adding copper to 6xxx

A

unclear
either no effect or reduction in the corrosion resistance
increases strength by refining Mg2Si precipitates a small amount of SSH
No effect on toughness
Improves alloy brightness after bright dripping and anodising

72
Q

What is the effect of adding manganese and chromium to 6xxx

A

present as impurities or deliberate
Increase toughness by fomring incoherent stable dispersoids during homogenisation
increase quench sensitivity by providing sites for Mg2Si nucleation
Mn preferred as less harmful to finish and extrusion speed

73
Q

What is the effect of adding V to 6xxx?

A

Increase strength
Increase toughness
refining grain size during casting

74
Q

What is the effect of adding Pb and B to 6xxx?

A

Improve machinability

75
Q

What is the effec of adding Zn to 6xxx

A

Provide solid solution strengthening

76
Q

What is the effect of adding Ti and B to 6xxx

A

Increase solidifcation rate
Influence final grain size

77
Q

What are the applications of 7xxx?

A

Upper wing structures (compressive stresses)
Bridges
Tanks
Rockets

AerospaceMetals (3 decks)

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