Investigation on competitive growth of the grains from multidimensions in oscillating laser welding of aluminum alloy

The competitive growth of the grains has significant influence on the grain morphology and solute concentration (SC) distribution in oscillating laser welding (OLW). Understanding the microstructure evolution process is beneficial for controlling the weld microstructure effectively. In this paper, the competitive growth of the grains in OLW is explored by analyzing multidimensional evolution processes of grain morphology and SC distribution based on the macro and micro coupled numerical model including the macroscale heat transfer model, transient solidification conditions model, and microscale phase field model. The simulation results are found in good agreement with the experiment results by comparing weld cross section and primary dendrite arm spacing. Some columnar grains exhibit coarse primary dendrites and developed secondary dendrites. The secondary dendrites grow towards multiple directions and may further suppress the growth of some grains. The variation in SC distribution is caused by the diffusion and redistribution of solute which are promoted by the secondary dendrites. The findings can provide guidance for improving the microstructure in OLW.