Al-20Si alloy was modified treatment by P and RE compound addition

and the copper mold was used to cool castings with different thickness.The effects of composite modification on Si phase morphology and the wear behavior of the alloy parts were analyzed by OM and SEM.The results reveal that the recalescence temperature of the alloy is reduced due to the high heat storage coefficient of the copper mold and the decrease of the wall thickness of the casting

which is together with the composite modification to refine Si significantly.The average grain size of primary Si in the castings with 5 mm thickness is only 7.1μm.As the grain size decrease

its hardness is increased gradually and wear rate is decreased.With the decrease of castings thickness gradually

the wear mechanism of alloy is characterized by from stripping-wear to a mixed mechanism of abrasive wear and adhesive wear.