Formation of 14H long period stacking ordered structure and profuse stacking faults in Mg–Zn–Gd alloys during isothermal aging at high temperature

This paper proposes a time–temperature-transformation diagram of an Mg–Zn–Gd alloy. An Mg97Zn1Gd2 (at.%) alloy shows different precipitation sequences at low, medium and high temperatures. Low-temperature aging at <523 K brings about coherent β′-phase precipitation to a α-Mg solid solution, resulting in increase in strength of the alloys. However, aging at medium and high temperatures >623 K led to strengthening of the Mg–Zn–Gd alloy, owing to the formation of profuse stacking faults and 14H long period stacking ordered structure from the supersaturated α-Mg matrix, respectively.