Patent ID: 7037391

Claim:
A process for the ageing heat treatment of an age-hardenable aluminium alloy, wherein the process includes the preliminary step of selecting an age hardenable aluminum alloy which has been solution heat treated and quenched to retain alloying elements in solid solution, and wherein the process further includes the stages of: (a) artificially ageing the alloy by holding the alloy at an elevated ageing temperature which is appropriate for a T6 temper for the alloy, for a period of time which is shorter than the time for a full T6 temper at said temperature for thereby ageing the alloy to promote precipitation of at least one solute element, wherein said period of time produces underaged alloy having not less then 40% and not more than 85% of the maximum hardness and strength obtainable from said full T6 temper; (b) quenching the underaged alloy, in a suitable fluid medium, from the ageing temperature for stage (a) to cool the underaged alloy at a sufficiently rapid rate and to a sufficiently low temperature of from −10° C. to 65° C. thereby to substantially arrest the precipitation; and (c) exposing the quenched alloy produced by stage (b) to an ageing temperature, lower than the ageing temperature of stage (a) and not exceeding 90° C. so as to develop adequate mechanical properties as a function of time, by a secondary precipitation comprising further solute element precipitation.