Multi-physics multi-scale simulation of the solidification process in the molten pool during laser welding of aluminum alloys

摘要

The solidification microstructures directly determine the performance of laser welds. However, the present understanding of the dynamic solidification behavior within the melt pool during laser welding is still limited. This paper developed a multi-physics multi-scale model to investigate the complex solidification process during laser welding of 5083 aluminum alloy. The model combines the macroscale model for heat and mass transfer, the microscale model for polycrystalline alloy solidification, and the continuous Gaussian nucleation distribution model for heterogeneous nucleation. The model is validated by comparing with experimental results from three aspects, namely, the fusion profile, the grain structure and the dendritic structure, and good agreements are achieved. The whole solidification process, from the planar growth to cellular growth, columnar dendritic growth and equiaxed dendritic growth, in the laser weld pool is studied through analyzing the evolution of the temperature, solute concentration and constitutional undercooling fields. In particular, the distribution of constitutional undercooling in the liquid ahead of the solidification front is predicted quantitatively. The relationship between the constitutional undercooling distribution and the nucleation/growth of equiaxed grains is demonstrated, which reveals the selective growth behavior of the columnar grains and equiaxed grains at different locations in the laser weld.