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 degrees 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 degrees 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 degrees C. This effect is notable if the ageing temperature is below about 200 degrees C. (C) 2010 Elsevier Ltd. All rights reserved.