The effect of heat treatment on microstructure of the melt-spun Mg–7Y–4Gd–5Zn–0.4Zr alloy

The microstructure evolution of the melt-spun Mg–7Y–4Gd–5Zn–0.4Zr alloy during annealing treatment has been investigated by using X-ray diffraction (XRD), optical microscope (OM), differential scanning calorimetry (DSC) and transmission electron microscope (TEM). The results indicated that two kinds of primary grains were contained in the melt-spun alloy. One was the supersaturated magnesium matrix, and the other was the 18R-LPSO phase. The 18R-LPSO phase transformed into the 14H-LPSO phase during annealing treatment at 300 °C for 0.5 h. The new precipitate of the 14H-LPSO phase was found at 300 °C for 5 h. Lots of linear precipitates formed as well as some precipitate with quadrangular morphology in matrix at 500 °C for 0.5 h. The melt-spun alloy displayed the highest hardness of 103 NHV after annealing treatment at 300 °C for 5 h.