Influence of Ca and Al on LPSO Phase in Mg-Gd-Zn Alloys and Their Mechanical Properties

Three alloys of Mg96.5Gd2.5Zn1, Mg96Gd2.5Zn1Ca0.5 and Mg95Gd2.5Zn1Ca0.5Al1 were prepared by a conventional gravity casting method. The influence of Ca and Al alloying elements on long-period stacking ordered structure (LPSO) phase formation in as-cast Mg-Gd-Zn alloy and their microstructural evolution and mechanical properties after solution solution treatment and hot extrusion were investigated. The results show that a small amount of Ca added to the as-cast Mg96.5Gd2.5Zn1 alloy promotes W phase to segregate, grow and connect to networks, which further develops into coarse 14H-LPSO cell structure and block 18R phase dispersed in the cell after solid solution treatment, and into long fibers after extrusion that significantly improves the strength and ductility of the alloy. The as-cast Mg95Gd2.5Zn1Ca0.5Al1 alloy consists of equiaxed α-Mg grains, a large number of network18R LPSO phases distributed in the grain boundary, and a small amount of network eutectic Al2Gd phase. After solution treatment, part of the network 18R is decomposed into 14H to form a randomly oriented, discretely distributed 18R strips, which promote considerable dynamic recrystallization of 14H and α-Mg grains during extrusion deformation and result in the slightly lower strength and higher ductility of Mg95Gd2.5Zn1Ca0.5Al1 alloy compared to those of Mg95Gd2.5Zn1Ca0.5 alloy. © 2019, Science Press. All right reserved.