Abstract:A semi-solid metal ingot of ZK60-2Ca alloy was prepared by near-liquidus casting, and its microstructure evolution was studied. It is found that due to the special refining effect of Zr, ZK60-2Ca alloy directly achieves a spherical or nearly spherical structure, without the process of dendrite spheroidization. The effect of cooling rates on the casting microstructure was also investigated through adopting different moulds with various cooling rates. The effects of holding time on the microstructure of the alloy were also studied. The results indicate that with the casting temperature decreasing and holding time extending to 60 min, the grains are refined and homogenized gradually, the grain size is 21 mm as well as the roundness is 1.29. With a bigger cooling rate, the grains become smaller and spherical. In addition, the evolution mechanism of casting microstructure for near-liquidus casting was discussed