Effect of Al-Sr master alloy on the formation of long period stacking ordered phase and mechanical properties of Mg-Gd-Zn alloy

The rapid formation of profuse fine Long Period Stacking Ordered Structure (LPSO) lamellae is especially desired for Mg-Gd-Zn alloys as type II wherein LPSO phases are difficult to form in as-cast state and prolonged heat treatments are necessary. The aim of this work is to investigate the effect of various Al-10 Sr master alloy additions (0, 0.6, 1.8, in wt. %) on LPSO formation in as-cast Mg-14.02Gd-2.33Zn alloy and the microstructural evolution during subsequent heat treatment and ECAP processing as well as their mechanical behavior variations. Minor addition of 0.6 wt. % Al-Sr master alloy introduces abundant 18R and 14H-LPSO phases in as-cast Mg-Gd-Zn alloy, and accelerates the microstructural evolution into high density of well-aligned long fiber-like 14H nanolamellae only through short-time solid solution and 1-pass ECAP processing as well as low-temperature aging. While a higher level of 1.8 wt. % (Al-Sr) addition produces short rod-like 14H particulates and considerable hard Al2Gd, network (Mg, Al)3Gd intermetallic compounds deteriorating the mechanical property. Consequently, processed Mg-Gd-Zn-0.6(Al-Sr) alloy exhibits a superior mechanical property due to synergistic effects of long fiber-like LPSO phase strengthening and grain refinement strengthening and so on. This paper provides an effective and economical method to fabricate high-performance Mg-Gd-Zn alloys reinforced with LPSO phases.