Effect of multimodal microstructure evolution on mechanical properties of Mg–Zn–Y extruded alloy

Abstract

A high strength Mg–Zn–Y alloy featuring increased ductility and a multimodal microstructure is developed. The microstructure of the extruded Mg–Zn–Y alloy consists of three regions: a dynamically recrystallized α-Mg fine-grain region with random orientation; a hot-worked α-Mg coarse-grain region with strong basal texture; and a long-period stacking ordered (LPSO) phase grain region. Having found that bimodal microstructure evolution in the α-Mg matrix is influenced by the morphology of the LPSO phase in the as-cast state, the authors investigate the effect of secondary dendrite arm spacing (SDAS) in the cast state on the microstructure evolution and mechanical properties of the extruded Mg–Zn–Y alloy. Mg–Zn–Y alloy ingots with various SDAS are obtained by temperature-controlled solidification techniques at various cooling rates. Mg–Zn–Y ingots are extruded at 623 K and an extrusion ratio of 10. A decrease in SDAS is associated with dynamic recrystallization of the α-Mg phase region and a high dispersion of fiber-shaped LPSO phase during extrusion. An increase in dynamically recrystallized α-Mg grains with very weak texture improves ductility; the effective dispersion of the hot-worked α-Mg grains with a strong basal texture and the fiber-shaped LPSO phase grains conspire to strengthen the alloy.