目的 解决薄板在激光熔覆过程中产生复杂残余应力、变形及晶粒粗大等问题，提高熔覆层的质量和零件装配可靠性。方法 提出一种液氮冷却氮气的激光熔覆同步气体冷却方法。采用双椭球热源，综合考虑随温度变化的热物性参数、热传导、热辐射、光粉相互影响、凝固过程中相变潜热的作用，建立同步气体冷却的激光熔覆三维数值模型，对不同冷却距离(d)下的瞬态温度场、熔池流场及应力演变过程进行数值计算。同时，利用热电偶对温度场分布进行验证，并采用扫描电子显微镜(SEM)和显微硬度仪分析其显微组织及涂层的硬度。结果 引入冷却氮气增强了熔池表面与外界环境之间的热交换，从而改善了熔池的温度分布，加快了熔池的冷却速度。常规激光熔覆和同步气体冷却激光熔覆的熔池流场变化趋势基本相同，呈现中心向四周流动，中心流速小，边缘流速大，熔池前方的流速大于熔池后方。当冷却距离为5 mm时，基体横向最大残余应力由204 MPa降至181 MPa，熔覆层顶部残余应力从190 MPa降至172 MPa，界面结合区残余应力从234 MPa降至211 MPa，基板两侧翘曲变形量减少了50%。当冷却距离为10 mm时，涂层的晶粒组织明显细化，中部柱状晶的无序排列程度明显增大，涂层的显微硬度从348.2HV0.2提高到375HV0.2。结论 该方法可以有效减小基体的残余应力和变形，为更好控制激光熔覆涂层的晶粒和微观组织提供了一种新方法。

Laser cladding technology is an advanced surface modification technology for metal materials, which has been widely used in various industrial fields such as automotive industry, aerospace, petrochemical industry, etc. However, in the actual forming process, due to the differences in thermophysical properties between the fusion cladding material and the base material as well as the existence of a high temperature gradient in the heated zone, which leads to plastic deformation due to high local thermal stress, the subsequent cooling contraction phase generates high residual stress, easily leading to deformation of the part. The work aims to reduce the complex residual stress, deformation and coarse grain size generated during laser cladding of thin plates and improve the quality of the cladding layer and the reliability of part assembly.