Mechanical Properties of the Mg-Gd-Y-Zn-Zr Alloys with Different Morphologies of Long-Period Stacking Ordered Phases

Long-period stacking ordered (LPSO) phases with different morphologies and distributions were obtained in the direct chill cast Mg-6.9Gd-3.2Y-1.5Zn-0.5Zr (wt.%) alloy by controlling the homogenization time or cooling rate. Microstructural evolution and the effect of various LPSO phases on the mechanical properties were investigated. There is no obvious α-Mg grain growth during homogenization at 510 °C. Intragranular thin-platelet and coagulated LPSO phases hardly improve the strength but help to develop the ductility. Numerous lamellar phases, which contain "ABCA"-type building blocks with RE and Zn segregation, form during the furnace-cooling process. Lamellar phases, which exhibit lower thermostability compared with the thin-platelet LPSO, slightly improve the tensile yield strength and induce numerous cracks which result in the premature fracture.