Patent ID: 7025839

Claim:
A process for the heat treatment of an age-hardenable aluminium alloy which has alloying elements in solid solution, wherein the process includes the stages of: (a) artificially ageing the alloy at an elevated temperature T A , wherein the artificial ageing is conducted for a period sufficient to achieve strengthening of the alloy which corresponds to from 50% to 95% of the maximum strengthening obtainable by a full T6 temper for the alloy at the temperature T A ; (b) quenching the alloy from the temperature T A at the end of the period for stage (a) to arrest primary precipitation of solute elements and to provide the alloy in an underaged condition; (c) holding the quenched alloy at a temperature T B which is below the temperature T A and is in the range of from −10° C. to 120° C. to achieve secondary nucleation or continuing precipitation of solute elements; and (d) holding the alloy at a temperature T C in the range of(T A −50° C.) to (T A +50° C.) for further artificial ageing of the alloy; wherein the alloy is further strengthened by the combination of steps (c) and (d) to a level of substantially maximum strength which is in excess of the maximum strength obtainable for the alloy by the full T6 temper at temperature T A .