Hypereutectic ZL117 alloy piston was prepared by semi-solid squeeze casting,and variation tendency of primary Si in different position of the piston was investigated through analysis of microstructure evolution.The results show that the diameter of primary Si particle and solid phase rate are increased from up to down.The diameters of middle and under parts are 16.6% and 24.7%larger than that of the up one,respectively.Meanwhile,the solid phase rate at the under part is 345% higher than that of the bottom part.It can be concluded that the Si content is the smaller than that of the middle and under parts,and in contrast with the middle and under parts,the Si refinement in the upper part is desirable.