Formation and characterization of microstructure of as-cast Mg–6Gd–4Y–xZn–0.5Zr (x = 0.3, 0.5 and 0.7 wt.%) alloys

Mg–6Gd–4Y–xZn–0.5Zr (x = 0.3, 0.5 and 0.7 wt.%) alloys were prepared via conventional ingot metallurgy (I/M) in this study. The as-cast microstructures of these alloys were established by X-ray diffraction (XRD) analyses, optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM) observations. Lamellar stacking order (SF) and 14H-type long period stacking order (LPSO) structure within α-Mg matrix are formed in the three as-cast alloys. The eutectic secondary phase is (Mg,Zn)24(Gd,Y)5 for the alloy containing 0.3 wt.% Zn, while, it is (Mg,Zn)3(Gd,Y) for the alloys containing 0.5 wt.% Zn and 0.7 wt.% Zn. Moreover, X phase-(Mg,Zn)12(Gd,Y) is formed in the latter two as-cast alloys. - Highlights: • LPSO structure has first been found in as-cast Mg–6Gd–4Y–xZn–0.5Zr. • X-phase exists in as-cast Mg–6Gd–4Y–0.3(0.5)Zn–0.5Zr. • Zn content results in different β-phase in the studied alloys