Hardening of an Al–Cu–Mg alloy containing Types I and II S phase precipitates

The effect of different thermo-mechanical treatments, including up to 10% cold work, on the hardness of the 2024 (Al–Cu–Mg) alloy was studied. Artificial ageing was conducted through heating at a constant rate to specific temperatures followed by rapid cooling. It was found that quenched only alloy 2024, which is found to form Type II S precipitates, possesses lower hardness compared to cold worked alloy 2024, on ageing to temperatures below 300 °C. Cold working lowers the temperature required for S phase precipitation to start while decreasing the quenching rate is seen to give higher hardness on ageing to temperatures below 200 °C. Type II S precipitate is found to result in lower hardening as compared to that due to Type I S precipitate. The reason for this is suggested to be due to the larger size of Type II S precipitate. The hardness of solution treated and subsequently cold worked and artificially aged 2024 is increased if the quenching is conducted in water at 80 °C. This effect is notable if the ageing temperature is below about 200 °C.