Enhanced creep performance in an Al–Cu–Mg–Ag alloy through underageing Original Research Article

Tests at 130 °C and 150 °C have shown that the creep resistance of an Al–Cu–Mg–Ag alloy is significantly increased if it is heat-treated at an elevated temperature to an underaged condition rather than the fully hardened, T6 temper. This beneficial effect of underageing is manifest in reduced rates of secondary creep. Similar results have been obtained for the commercial alloy 2024. Delays at ambient temperature after underageing and before testing lead to secondary precipitation and a progressive decrease in creep performance that eventually reverts to close to that for the T6 condition. This detrimental effect may be overcome by slow cooling from the underageing temperature, which arrests or impedes subsequent secondary precipitation. Microstructural observations suggest that the enhanced creep resistance in the underaged condition is a consequence of the presence of “free” solute in solid solution that is not yet involved in precipitation.