Heat resistant Mg-Gd-Y-Zn-Zr magnesium alloy engine piston was produced by metal gravity casting.Various defects encountered in the filling and solidification process were analyzed and eliminated by modifying the processing technology.The results show that the misrun defects in the piston skirt

piston top and feeding riser can be eliminated by increasing the cross-sectional area of runner.The coldshut defects in the piston pin-hole and skirt can be prevented by increasing the wall thickness of piston pin-hole and improving the preheating temperature to 250 ℃.The slag and cold-shut defects in the filling process can be inhibited by deleting the feeding riser near the runner.Amounts of secondary phases are distributed along grain boundary in the as-cast microstructure of Mg-Gd-Y-Zn-Zr alloy piston.Some secondary phases are dissolved into theα-Mg matrix after T6 treatment

so the Vichers-hardness of piston skirt reaches 158.