Heat treatment of age hardenable aluminium alloys utilizing secondary precipitation

The process is for ageing heat treatment of an age-hardenable aluminium alloy which has alloying elements in solid solution. The process includes holding the alloy at an elevated ageing temperature which is appropriate for ageing the alloy to promote precipitation of at least one solute element, herein termed "primary precipitation" for a period of time which is short relative to a T6 temper. Resultant underaged alloy then is cooled from the ageing temperature to a lower temperature and at a sufficiently rapid rate to substantially arrest the primary precipitation. The cooled alloy then is exposed to an ageing temperature, lower than the elevated ageing temperature for primary precipitation, so as to develop adequate mechanical properties as a function of time, by further solute element precipitation, herein termed "secondary precipitation".