Abstract:The microstructure evolution of Mg-5.9Zn-1.6Zr-1.6Nd-0.9Y alloy during homogenization was investigated by differential thermal analysis, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-Ray diffraction. Also, the Vikers hardness was measured. It was found that the microstructure of as-cast Mg-5.9Zn-1.6Zr-1.6Nd-0.9Y alloy consists of α-Mg, and Mg3(Y,Nd)2Zn3 phases．The alloy has an endothermic peak at 510 ℃ before homogenization. The endothermic peak disappears in the alloy homogenized at 500 °C for 16 h. A small quantity of Mg3(Y,Nd)2Zn3 phases dissolve at 470 ℃ and 490 ℃．However, after homogenization at 500 ℃ for 16 h, there are only a small number of rich-Y and rich-Nd fine particles (Mg3(Y,Nd)2Zn3) dispersing at grain boundary, and dendritic segregation is almost eliminated. Therefore, the optimum homogenization parameter is 500 ℃ for 16 h. Homogenization can effectively decrease the hardness of the as-cast Mg-5.9Zn-1.6Zr-1.6Nd-0.9Y alloy from 185.2 HV to 144.2 HV.