Microstructure and mechanical properties of a peak-aged Mg-5Y-2.5Nd-1.5Gd-0.5Zr casting alloy

Microstructures and mechanical properties of a Mg-5Y-2.5Nd-1.5Gd-0.5Zr casting alloy under various peak-aging conditions were thoroughly investigated. The results indicate that there are a certain amount of stable cuboid, lamellae and irregular-shaped intermetallic phases, which were identified as RE7Zr phase (face-centered cubic structure, a = 0.7406 nm), Y-enriched and Nd-enriched Mg45.9RE9.08 phases (face-centered cubic structure, a = 2.2344 and 2.28 nm, respectively), respectively, using transmission electron microscopy (TEM). In addition, the samples with peak-aging treatment especially at relatively lower temperatures exhibit outstanding aging hardening response and good tensile properties. Based on TEM observations, the high strength and the good ductility of the studied alloy are mainly attributed to precipitation strengthening from the dense fine precipitates in the α-Mg grains and the coordination on inhomogeneous deformation of the denuded zones around the relatively large β precipitates, respectively.