Study on the evolution of the microstructure, phase composition, three‐dimensional morphology, and hardness in the solution treatment of Mg−7.80Gd−2.43Y−0.38Zr alloy

Abstract

AbstractThe evolution of the microstructure, phase composition, three‐dimensional morphology, and hardness of Mg−7.80Gd−2.43Y−0.38Zr (wt.%) alloys during solution treatment at 480 °C is investigated using scanning electron microscopy (SEM), electron probe micro‐analyzer, nanoindentation, and x‐ray tomography. The as‐cast alloy consists of an α‐Mg matrix phase and divorced eutectics, including the secondary and the supersaturated magnesium phases. The chemical composition of the secondary phase is similar to that of Mg7.22(Gd, Y), and the nanoindentation hardness of the secondary phase is significantly higher than that of the α‐Mg matrix phase, according to the energy‐dispersive spectroscopic and nanoindentation analyses. The three‐dimensional morphology and quantitative information, such as the number and volume fraction of the secondary phases during the solution treatment, are discussed in detail. A large number of small acicular secondary phases are found near the large secondary phase after solution treatment at 480 °C for 1 h, while the acicular phase disappears completely after 2 h. The secondary phase dissolves into the α‐Mg matrix after solution treatment for 8 h, and the solution‐treated alloy primarily consists of an α‐Mg matrix phase and a cuboid‐shaped phase, which was identified as (Gd,Y)H2.