The change of structure

hardness and wear resistant of remelted hypereutectic Al-Si alloy has been observed by remelting surface of the alloy piston with CO

2

continuous transverse-flow laser. The results show that the microstructure of remelted alloy consists of remelting zone

transition zone and matrix zone. Compared with that in matrix zone

the grain size in transition zone is obviously refined

where primary Si is converted from bulky polygonal or square into cell

and eutectic Si is transformed from needle-like strip into fine particle. The hardness of surface remelting zone is increased by 40 Hv

superior to matrix in wear resistant. The refinement mechanism of the remelting zone is analyzed.