Ordliste
Heat treatment — definition
Controlled heating and cooling that raises the strength of a heat-treatable aluminium alloy through the full section.
The mechanism is called precipitation hardening. The strengthening elements are dissolved into the matrix at high temperature, the part is quenched so they stay in solution, and it is then aged under control. During ageing, fine particles precipitate that obstruct dislocation movement — and that is what raises yield and tensile strength.
Note: this is not surface hardness. It is strength through the full section.
The key limitation: high pressure die castings normally cannot be heat treated. Trapped gas expands during solution treatment and raises blisters under the surface. A part that needs heat treatment therefore usually has to be gravity cast — and that choice has to be made before the tool is designed.