激光熔覆时熔池对流运动对熔覆层成分和气孔缺陷分布具有较大影响。通过在灰铸铁和45钢两种基体上进行激光熔覆NiCuFeBSi系合金的工艺试验,对熔池的对流运动形式进行了机理分析与试验验证。结果表明,受熔池强对流运动影响,熔覆层气孔呈均匀弥散化分布趋势;且自熔覆层底部向顶部方向合金元素分布均匀,无缓慢过渡特征。根据YAG激光光斑能量的高斯分布特征,获得了熔池对流运动的驱动力是熔池温度分布不均形成的熔池表面张力梯度。而且熔池表面张力梯度与激光能量密度,熔池温度,熔体对流运动速度是彼此密切相关的。熔池对流运动机理分析表明,热流密度越高,温度越高,表面张力梯度越大,熔体对流运动速度越大。 The convection motion of the molten pool has a great influence on the composition of cladding layer and the distribution of stomatal defects during laser cladding. Through the experiment of laser cladding NiCuFeBSi alloy on both gray cast iron and 45 steel, the mechanism of convection movement in the molten pool was analyzed and verified by experiments. The results show that, due to the strong convection movement in the weld pool, the stomatal distribution of the cladding layer presents a uniform dispersion trend, and the alloying elements distribute uniformly from the bottom to the top of the cladding layer without any slow transition. According to the Gaussian distribution of YAG laser spot energy, the driving force of convection motion of molten pool is obtained, which is the surface tension gradient of molten pool caused by the uneven distribution of temperature in molten pool. And the melt pool surface tension gradient and laser energy density, bath temperature, melt convection speed are closely related to each other. The analysis of mechanism of convection motion in the pool shows that the higher the heat flux density is, the higher the temperature is, the larger the surface tension gradient is and the greater the convection velocity is.