Formation of a lamellar 14H-type long period stacking ordered structure in an as-cast Mg–Gd–Zn–Zr alloy

A novel as-cast Mg96.82Gd2Zn1Zr0.18 alloy was produced by conventional ingot metallurgy. By scanning electron microscope and transmission electron microscope observations, its as-cast microstructure is mainly composed of the α′-Mg solid solution, the coherent fine-lamellae and the eutectic. The β-phase ((Mg,Zn)3Gd) as the second phase in eutectic has a face-center cubic structure. While, the coherent lamellae consist of the 2H–Mg and the 14H-type long period stacking ordered (LPSO) structure. At present, the lamellar 14H-type LPSO structure has first been observed within α′-Mg matrix in the as-cast Mg–Gd–Zn–Zr alloys. It can be concluded that the lamellar 14H-type LPSO structure within α′-Mg matrix is a special structure obviously different from α-Mg matrix (2H-type structure) in structure, composition, and formation condition.