Aluminium Flashcards
What is T3?
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.
What is T4?
Solution treated and naturally aged to a substantially stable condition.
What is T6?
Solution treated and artificially aged.
What is T7?
Solution treated and overaged to lower than peak strength in order to
improve another property e.g. stress corrosion cracking resistance.
What is T73?
Solution treated and overaged by a two stage ageing treatment to lower than
peak strength in order to improve SCC resistance.
what is TXX6?
(e.g. T736) Indicates the 1st step in a two stage ageing process is the T6
treatment.
What is Tx51?
(e.g. T351 & T851) applies to products which receive no further straightening
after stretching, e.g. plate.
What is TX52?
(e.g. T7352 & T73652) applies to products that are stress relieved by
compressing after solution treatment (strain typically 1-5%).
What is T8?
Solution treated, cold worked and artificially aged beyond peak strength.
What are the properties of aluminium?
Low Density
Highly resistant to most forms of corrosion
superb conductor of electricity
Non-Magnetic and noncombustible
non toxic and impervious
strong
ductile
how abundant is aluminium?
3rd in the crust
Applications of aluminium?
construction
packaging
transport
electrical
other
how is aluminium extracted?
Aluminium is extracted from bauxite, a mixed oxide ore
containing about 50% hydrated alumina
What is Bayer Process?
It is separated from the other oxides by dissolution and reprecipitation by reaction with sodium hydroxide
What is Hall-Haroult process?
It is then dissolved in a molten salt mixture of cryolite (Na3AlF6
)
and electrolytically reduced to molten aluminium
how much power is consumed per tonne of aluminium
produced?
14,000 kWh/tonne
Describe the Hall-Heroult Process
Graphite anodes
molten Al2O3 and Na3AIF6
Graphite lines tank (cathode)
Al collects molten on the bottom
What kind of process is Hall- Heroult?
Continuous
Bath running all the time
What Direct Chill (DC) casting?
Semi continous
Liquid metal into water cooled metal mold
Hydraulic ram withdraws aluminium at a draw rate
produces billet
Why do we get eutectic forming in aluminium non-equilibrium?
Segregation of 2 different phase elements
Reduces melting temp
How is eutectic removed?
Homogenisation
After solidification the alloy is heated to a temp below eutectic temo and held for a long time ( up to 24hrs)
What are the main alloying elements of 1xxx
99% min Al
What are the main alloying elements of 2xxx
Copper
What are the main alloying elements of 3xxx
Manganese
What are the main alloying elements of 4xxx
Silicon
What are the main alloying elements of 5xxx
Magnesium
What are the main alloying elements of 6xxx
Magnesium and silicon
What are the main alloying elements of 7xxx
Zinc
What are the main alloying elements of 8xxx
other
What do F, O, H and T mean?
F - As fabricated
O - annealed wrought
H - Cold worked
T - Heat Treated
What alloys are work hardenable
1xxx
3xxx
5xxx
what are some typical applications of 1xxx
foil
Architectural
Decorations
Power transmission
What are typical applications of 3xxx
Drinks cans
strength of 3xxx, annealed vs cold worked
Annealed - 40 MPa
Cold worked - 185MPA
how is 3xxx hardened?
SS hardening from Mn
Dispersion strengthening via MnAl6 particles
what are the advantages of 5xxx aluminium?
Much more recyclable than 3xxx
lower densitty
does not rust
high strength
formable
bright surface finish
What is the strenght of 5xxx annealed vs cold worked?
Annealed - 40-160MPa
Cold worked - 300 MPa
What are the disadvantages of 5xxx Aluminium
weldability
Repairability
yield point phenomena
what is the main strengthening mechanism of 5xxx aluminium
solid solution strengthening by mg dissolved in Al matrix
Why does the strength increase with with SS strengthening in 5xxx aluminium?
Mg has effect on lattice strain
What is homogenisation?
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.
What does aging temperature determine?
Determines rate of nucleation and growth of precipitates
What happens to 1xxx when RX
drop in strength but increase in ductility
What effect does ageing time have?
Determines the size of precipitates
what are the effects of increases aging temperature?
Decreases undercooling - less driving force for nucleation get fewer nuclei
Increases diffusion of solute - precipitates grow faster
What are the 3 stages of ageing?
Nucleation
Growth
Coarsening
What does a under aged distribution of precipitates look like?
Large number of very small underdeveloped precipitates
What does a peak aged distributions of precipitates look like?
Optimum size and distribution of precipitates
What does overaged look like?
A few large precipitates spaced far apart
Which alloys are Heat treatable?
2xxx
6xxx
7xxx
8xxx
what are the applications of 2xxx aluminium?
Airframe and skin structure
T4 (damage tolerant) condition for lower wing
Heavy engineering
What is the order of strength of 2xxx, 6xxx, 7xxx? lowest to highest
6xxx -> 2xxx -> 7xxx
What are some disadvantages of 2xxx
SCC and corrosion resistance are poor
How are the highest strengths of 2xxx achieved?
Cold working between quenching and artificial ageing
what is the θ Phase for 2xxx?
High Cu:Mg ratio.
Excess Cu
Al2Cu
What is S phase for 2xxx?
Low Cu:Mg Ratio
Al2CuMg
What are the applications of 6xxx
Structural and architectural applications
Door frames
75% of industrial extrusions
What are some advantages of 6xxx
Easily extruded at high speeds
good anodisable surface finish
Good corrosion resistance and weldability
6xxx disadvantages
Not as strong as 7xxx
Not as thermally stable as 2xxx
What can you add to 6xxx to increase strength
Cu
What can you add to 6xxx to restore corrosion resistance?
Cr
What is the precipitation sequence of 6xxx
SSSS → rod GP zones → β’ needles →
equilibrium Mg2Si plates
What is the precipitation sequence of 2xxx
SSSS → lath GP zones → S’ laths → S
laths.
What are the dilute and concentrate makeups of 6xxx additions?
- Mg + Si < 1 wt. % (Dilute)
- Mg + Si > 1 wt. % ( concentrate)
What are properties of dilute 6xxx?
Age well at RT (natural ageing) -> metastable GP zone
GP zones act as nucleation sites during artificial ageing (T6)
Homogeneous distribution of Mg2Si precipitates
What are the properties of Concentrate 6xxx
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
What is the effect of adding silicon to 6xxx ?
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
what is the effect of adding magnesium to 6xxx
negligable effect on SolidSolutionHardening
in excess it casues dramatic decrease in extrudibility
changes tear initiation mechanism
decreases ductility and toughness
Better corrosion resistance
what is the effect of Mg2Si on 6xxx
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
What is the effect of adding iron to 6xxx
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
What are the effects of adding copper to 6xxx
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
What is the effect of adding manganese and chromium to 6xxx
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
What is the effect of adding V to 6xxx?
Increase strength
Increase toughness
refining grain size during casting
What is the effect of adding Pb and B to 6xxx?
Improve machinability
What is the effec of adding Zn to 6xxx
Provide solid solution strengthening
What is the effect of adding Ti and B to 6xxx
Increase solidifcation rate
Influence final grain size
What are the applications of 7xxx?
Upper wing structures (compressive stresses)
Bridges
Tanks
Rockets
