Welcome to histalu.orgThe site for the history of aluminium
In its main applications, aluminium is used in the formation of alloys, which increases its mechanical resistance, but often to the detriment of other properties. To find the best compromise between the properties for a given use, metallurgists act on the composition of the alloy, but also on the thermal or thermo-mechanical treatments to which it is subjected.
magnesium, silicon, copper, manganese and zinc, alone or in combination.
These alloying elements generally represent only a couple of percentage in the compound metals. There are several hundred commercial alloys.
Wrought Alloys (wrought = hot deformation), cast in plates or billets then hot transformed by rolling, spinning, forging, forging, etc.
The main properties required of these alloys are, depending on the application:
Casting alloys, cast in moulds from which (almost) finished products emerge. They therefore do not undergo significant deformation but must have, depending on the application, some of the other properties above, and also other attributes: a good quality of flow, little shrinkage on solidification, no formation of cracks... a large proportion of casting alloys come from remelted recycled metal.
Heat treatments act on the properties of alloys by modifying their microstructure. Work hardening (cold deformation) hardens metals. However, brought to high temperature, a work-hardened metal recrystallizes, then regains its initial properties when cold. Also, at high temperature, the alloying elements tend to disperse into the matrix lattice, forming what is called a solid solution. Rapidly cooled (quenching), the solution will keep the high temperature structure cold. Then the atoms of the alloying elements tend to come together, giving fine precipitates of intermetallic compounds which harden the metal. This happens either at or slightly above room temperature (ageing) or more rapidly at higher temperature (tempering).
“Heat treated” alloys are subjected to high temperature solution treatment, followed by quenching and tempering, which gives them high mechanical strength. This is the case for the alloys used by the aeronautical, space and armament industries.
