Effect of molten pool convection on pores and elements distribution in the process of laser cladding

The molten pool convection has a great impact on elements and pores distribution during the laser cladding process. In this paper, the form of molten pool convection was investigate in terms of laser cladding NiCuFeBSi alloys on the substrate of gray cast iron and 45 steel. Results indicated that the distribution forms of pores and elements in the clad layer are uniform and dispersive due to the molten pool convection. Moreover, element distribution is also uniform without any slow transition from the bottom of clad layers to the top by means of electron probe microanalysis (EPMA). And according to the Gaussian distribution of energy in the YAG laser beams, it can be concluded that the driving force of convection is the surface tension gradient due to the non-uniform distribution of molten pool temperatures. Those of the laser thermal density, the molten pool temperature, the convective speed and the surface tension gradient are closely related with each other. It indicates that the temperature increases as the laser thermal density rising. The higher temperature is, the larger surface tension gradient will be as well as the convective speeds.