Temper designations for heat-treatable aluminum alloys

Precipitation hardening or age hardening can be applied only to those groups of alloys which are heat treatable (i.e. 2XXX, 6XXX and 7XXX wrought series). Firstly, a supersaturated solid solution (SSSS) is made by solution heat treatment. Secondly the ageing process that occurs after quenching may be accelerated by heating the alloy until second and coherent phase is precipitated. This coherent phase strengthens the alloys by obstructing the movements of dislocations. In heat treatable aluminum alloys, temper designations are shown as follows:

• T1 Cooled from an elevated process temperature and aged (natural aging) at ambient temperature to a substantially stable condition.
• T2 Cooled from an elevated-temperature forming process, cold worked and naturally aged to a substantially stable condition.
• T3 Solution heat treated, cold worked, and naturally aged to a substantially stable condition. Solution heat treatment involves heating the product to an elevated temperature, usually in the 932–1022F (500–5508C) range. At this temperature, the alloy becomes a single-phase solid solution that is cooled rapidly (quenched) so that a second phase does not form. This is designated as the W condition, which is an unstable condition.
• T4 Solution heat treated and naturally aged to a substantially stable condition.
• T5 Cooled from an elevated-temperature forming process and artificially aged (holding for a specific time a temperature above the ambient temperature).
• T6 Solution heat treated and artificially aged. The aging process is usually maintained until maximum or near-maximum strength is achieved.
• T7 Solution heat treated and overaged. Products that have been aged beyond the point of maximum strength to provide some special characteristics, such as improved corrosion resistance or ease of forming, are included in this designation.
• T8 Solution heat-treated, artificially aged, and cold worked.
• T9 Cooled from an elevated-temperature forming process, cold worked, and artificially aged.

This should not be confusing to hardening and tempering as in steels.