Abstract: Al-based sudden change composites reinforced with mixture of primary Si and Mg2Si particles were prepared by centrifugal casting.Microstructure and properties of the composites were investigated by using optical microscopy,XRD and hardness tester.The results show that there were two layers including enforcement layer(inner layer) and un-reinforced layer(outer layer).Microscopic boundary between the two layers was obvious.Plenty of primary Si and Mg2Si segregated in the inner layer,and only a few of particles in the outer layer.The hardness showed increasing trendency from inner layer to outer layer.The wear resistance difference between inner layer and outer layer was big under small load ,but small under large load.The effect of the reinforcement primary Si particles on wear resistance improvement was more remarkable than that of Mg2Si particles.