采用额定功率为3 kW的Nd∶YAG固体激光器对镁合金进行激光熔凝实验,通过金相显微镜、扫描电镜、能谱仪、维氏显微硬度计、电化学工作站等仪器表征试样的显微组织、物相、硬度和耐腐蚀性能。结果表明:在激光功率为2 kW、激光扫描速度为40 mm/s时,试样表面无裂纹和严重凹陷,熔凝区表层组织为等轴晶,内部组织为放射性枝晶;随着激光扫描速度的提高,表层等轴晶尺寸减小,熔凝区内部放射性枝晶逐渐变为非放射性枝晶;激光熔凝后热影响区组织深入基体晶界中,热影响区与基体交界处呈不规则形貌。能谱仪和线扫描结果显示,熔凝区表层元素出现烧损,导致熔凝区硬度峰值出现在靠近表层位置,且随扫描速度的提高,硬度峰值呈下降趋势,激光熔凝后,熔凝区耐腐蚀性能增强。

We carry out a laser melting experiment of magnesium alloy by using a Nd∶YAG solid-state laser with rated power of 3 kW. The microstructure, phase, hardness and corrosion resistance of the sample are characterized by metallographic microscope, scanning electron microscopy, energy spectrometer, Vickers microhardness tester, and electrochemical workstation. The results show that when the laser power is 2 kW and the laser scanning speed of 40 mm/s, the surface of the sample has no cracks and severe depression. The surface structure is the melted zone is equiaxed crystals, and the internal structure is radioactive dendrites. With the increase of the laser scanning speed, the equiaxed crystal size of the surface layer decreases, and the radioactive dendrites in the melted zone gradually become non-radioactive dendrites. After laser melting, the heat-affected zone is organized into the grain boundary of the matrix, and the boundary between the heat-affected zone and the substrate is irregular. The energy spectrometer and line scanning results show that the surface elements in the melted zone are burnt, resulting in the peak hardness of the melted zone appearing in the near-surface. With the increase of the scanning speed, the peak hardness shows a downward trend, after laser melting, the corrosion resistance of the melting zone increases.