Non-Ferrous Flashcards
What is the difference between Ferrous and non-Ferrous alloys?
Ferrous alloys mostly contain iron (e.g. mild steel, carbon steel, etc) that are primarily used for their tensile strength and durability. Non-ferrous alloys don’t contain mostly iron and typically have properties like resistance to corrosion, thermal conductivity and lightweight.
Why do we need to use a Bayer process to extract aluminium?
Because AL is most abundant in bauxite form we need a way to convert the bauxite into alumina economically, We do this through the Bayer process.
What are the steps to the Bayer process?
1) Dissolve crush bauxite in sodium hydroxide
2) The alumina reacts to this to produce a solution of sodium aluminate.
3) insoluble impurities are removed
4) Alumina Trihydrate precipitate from the solution
5) Heated to gamma alumina the more to alpha-alumina
What is the Hall-Heroult process?
This is a process to extract alumina into aluminium using a Cathode Anode and an Electrolyte. this typically needs 2 tonnes of alumina to produce 1 tonne of aluminium.
How does work hardening occur?
Plastic deformation causes dislocation generation and multiplication. Some dislocation pairs annihilate during deformation while the remaining dislocations act as a barrier for the movement of other dislocations making it harder to deform metals and alloys with a large number of dislocations in them.
What are the types of work hardening?
Strain hardening, hardening as a result of increasing dislocation density
Substructure hardening, hardening as a result of the formation of substructures.
What is Substructure?
The substructure is the structure formed within a grain when dislocation tangles, which are formed from an increased amount of plastic deformation, rearrange themselves into small-angle grain boundaries.
What are the stages of work hardening?
1) Easy glide region, work hardening is not significant
2) Linear hardening region, high work hardening rate, and strain hardening dominates.
3) Parabolic hardening region, work hardening rate reduced, and substructure hardening dominates
What is the effect of temperature on work hardening?
The magnitude of work hardening decreases with increasing temperature at which plastic deformation occurs. Once this temperature is high enough work hardening disappears.
What does Heat treatment of Al alloy do?
Heat treatment increases the strength of AL alloys by generating a large number of very fine precipitates (precipitation hardening).
How does precipitation hardening increase strength?
If a grain contains a large number of precipitates the dislocations will have to interact with the precipitates which makes it harder for dislocations to move through the grains which increases the strength of the alloys.
How are effective precipitates created?
1) Solution treatment and homogenisation to dissolve coarse particles
2) Quenching to retain the solutes in the supersaturated solution at room temperature
3) Ageing to force a large number of very fine precipitates
What are the benefits of Mg alloys?
Low density and high melting points
