为了研究激光处理后镁合金表面组织的变化，采用CO₂激光对AZ91镁合金表面以氦气作为保护气体的条件下进行处理，对处理过的试样用光学显微镜进行观察，并用显微硬度计测量其截面的显微硬度值，取得了试样表面和截面的组织照片和沿截面的硬度分布曲线。结果表明，激光处理过的镁合金表面与未经处理的镁合金表面相比晶粒得到了明显的细化，且随着激光扫描速度的降低，晶粒更细，而熔凝层的深度随着速度的增加而减小，同时在细化后的晶粒的晶界上的β相基本上消失，对其截面进行的显微硬度的测量结果显示其硬度相对未处理的试样有明显的提高，且晶粒越小显微硬度值越高，符合Hall－Petch公式。

In order to study the surface tissue variation of the magnesium alloy treated by laser,the surface of AZ91 magnesium alloy was treated by CO₂ laser under the protection of helium gas. The treated workpiece was observed through optical microscope,and the microhardness value of the cross section was tested by microhardness tester. The result of the experiment showed that the grain size of the treated magnesium alloy was refined to the primitive magnesium alloy,the grain size of the magnesium alloy becoming smaller with the decrease of the scanning speed,and that the β phase along the grain boundary decreased distinctly. The microhardness test of the cross section showed that the microhardness value of the treated section enhanced distinctly,and the smaller of the grain size,the harder of the cross section,according to the Hall-Petch formula.