用２ｋＷ连续ＣＯ２激光对过共晶Ａｌ－１８Ｓｉ合金以不同能量密度和扫描速度进行快速熔凝处理。用扫描电镜、电子微区分析仪分析了微观结构。从计算机对Ａｌ－Ｓｉ合金ｆ－ｎｆ系统的非平衡理论计算所得的共生区及实验结果的分析可见，当能量密度和扫描速度决定的凝固条件处于共生区中部时，过共晶Ａｌ－Ｓｉ合金激光表面处理可以得到共晶间距低于２００ｎｍ的完全共晶结构。 The hypereutectic Al-18Si alloy was rapidly fused at different energy densities and scanning velocities with 2kW continuous CO2 laser. The microstructure was analyzed by scanning electron microscopy and electron microanalyzer. From the computer analysis of the non-equilibrium theoretical calculations of the f-nf system of Al-Si alloy and the experimental results, it can be seen that when the solidification conditions determined by the energy density and the scanning speed are in the middle of the symbiotic zone, the hypereutectic Al-Si alloy Laser surface treatment can result in a complete eutectic structure with eutectic spacing below 200 nm.