Low-alloy-correlated reversal of the precipitation sequence in Al-Mg-Si alloys

As commonly known, upon ageing at 180 degrees C or above, the precipitation sequence in Al-Mg-Si alloys shall be (roughly) as follows: supersaturated solid solution ->beta ''-> beta ' (/B'/U2), where the beta '-precipitates form after the beta ''-precipitates. Here we report that in a lean Al-Mg-Si alloy the beta ' (/B'/U2)-precipitates can form immediately upon 180 degrees C-ageing. Nevertheless, applying natural ageing can gradually recover the precipitation sequence and eventually the beta ''-precipitates become dominant over beta '-precipitates. This indicates that the precipitation sequence is strongly correlated with alloy-content and natural-ageing clusters. (C) 2017 Elsevier B.V. All rights reserved.