Aluminium Alloys are supplied in a very wide range of tempers with two principal groups:
Non-heat treatable alloys - Alloys whose strength/mechanical properties are achieved by cold working (rolling, extruding, etc.). Sometimes called work hardening alloys, Temper is denoted by letter H.
Heat treatable alloys - Alloys whose strength/ mechanical properties are achieved by heat treatment followed by cooling and natural or artificial ageing. Temper denoted by letter T.
Solution heat treating - The process of heating aluminium at prescribed temperature for a prescribed time and then cooling rapidly usually by quenching in water.
Natural ageing (T1, T2, T3, T4) - The process which occurs spontaneously at ordinary temperature until the metal reaches a stable condition. This hardens the metal after solution heat treatment.
Artificial ageing (T5, T6, T9) - The process of heating for a prescribed period (2-30 hours) at a prescribed low temperature (100-200ºC) until the metal reaches a stable condition. This hardens/increases strength after solution heat treating quicker than natural ageing and to a greater level.
Non Heat-Treatable Alloys
Work hardening (H14) - General term for processes which increase strength of aluminium and reduce the ductility, (e.g. rolling, drawing, pressing, stamping). Sometimes called strain-hardening.
Partial annealing (H24) - A heating process which reduces strength and increases ductility of aluminium after work hardening. Sometimes called temper let-down.
Stabilising (H34) - A low temperature thermal treatment or heat introduced during manufacture which stabilises the mechanical properties. This process usually improves ductility and is only applied to those alloys which, unless stabilised, gradually age-soften at room temperature, (i.e. non-heat treatable range.) The purpose of stabilising is to relieve the residual internal stress in the metal. Mainly used for 5000 series alloys.