Precipitation reactions and the differential scanning calorimetry responseof AA6111 alloy

The Al-Mg-Si-Cu alloy AA6111 is extensively used for automotive skins in No rth America and it may be subjected to a range of thermal histories dependi ng on the properties required. Unfortunately, the majority of the heat trea tments involve very low temperatures which result in extremely fine scale c lusters and precipitates that cannot be resolved in conventional transmissi on microscopy. This makes it difficult to interpret what transformations ar e involved and following the precipitation reactions by mechanical property measurements gives only global information. Differential Scanning Calorime try (DSC) provides an alternative means of monitoring precipitation. It is shown that DSC can be used very effectively to "fingerprint" the stage of p recipitation in the alloy and indicate its subsequent age hardening respons e to further heat treatment, such as the paint bake response of a formed pa rt.