Abstract: In situ gradient composites of Al-16wt%Si alloy, which possess the microstructures of accumulated primary silicon in the inner layer and eutectic in the rest layers or accumulated primary silicon from the outer layer to the inner layer,have been achieved by changing the rotation rate of centrifugal casting. The formation process of the composites has been analyzed, and the microstructure, hardness, wear ability and the phase structure of the composites have been also investigated.