Effect of copper on precipitation and baking hardening behavior of Al-Mg-Si alloys

The effects of copper on the ageing precipitation behavior of as-quenched and pre-aged AA6016 aluminum alloy were studied by differential scanning calorimetry (DSC), Vickers hardness measurement and transmission electronic microscopy (TEM). The results indicate that the addition of copper facilitates the growth of clusters (GP I) to the critical size during pre-ageing. Therefore, the addition of copper accelerates the transition from GP I (pre-β″) to GP II (β″) during final artificial ageing, and finally results in the favorable paint-bake response. However, the one with the copper level of 0.3% does not show significant baking hardening response as expected. Pre-aging can also reduce the detrimental effect due to natural aging of copper-containing alloys.