Natural-aging-induced reversal of the precipitation pathways in an Al–Mg–Si alloy

Abstract For Mg-excess Al–Mg–Si alloys, when aged at 180 °C, the alloys are hardened mostly by the monoclinic β ″-phase precipitates, whereas when aged at 250 °C, the alloys are hardened mainly by the hexagonal β′ -phase precipitates. Here we show that applying natural aging prior to artificial aging can gradually modify and eventually reverse the precipitation pathways, such that the β ′-precipitates become dominating in the alloy upon 180 °C-aging, whereas the β ″-precipitates are prevailing upon 250 °C-aging. This precipitation scenario leads to a decreased age-hardening potential in the naturally aged alloy upon 180 °C-aging, while an increased age-hardening potential upon 250 °C-aging.