Effects of electromagnetic compound field on the dendrite growth of laser cladding

A single steady magnetic field (SMF) and an electromagnetic compound field with downward Lorentz force (EDLF) were applied to laser cladding process. The influence of the electromagnetic compound field on the dendritic growth was investigated. The microstructure of the dendrites was characterized using optical micro-scopy (OM) and electron backscatter diffraction (EBSD). It is shown that both SMF and EDLF can result in the grains coarsening, and the effect of EDLF is greater than that of SMF. With 1.2 T EDLF, large angle grain boundary (>10 degrees) frequency is depressed. The velocity distribution, heat flux distribution and solidification interface cooling rate were also studied with a 2D multi-physics model. The results show that the velocity of molten pool is suppressed by the magnetic field and the solidification interface becomes flat when EDLF is applied. The suppression flow of the molten pool decreases the dendrite nucleation rate and improves the heat flux stability of the solidification front, which results in the enlarged gain size and improved grain texture. Small-curvature solidification interface occurs with the application of the EDLF, which can reduce the competition for the growth dendrite, and the grains of the cladding layer become coarser than the case of the application of the SMF.