Numerical investigation of the effect of laser beam oscillation mode on the grain growth process during laser welding of aluminum alloy

The weld microstructure greatly affects the welding quality during laser welding (LW). A multi-scale numerical model consisting of a macro-scale heat transfer model, a novel transient solidification conditions (SCs) model and a micro-scale phase field model is developed in this paper. The validity of the model is verified by the experimental results. The transient SCs and grain growth (GG) processes under different laser beam oscillation modes during LW of aluminum alloy are calculated. It is found that with the increase in solidification time under the circular and sinusoidal oscillation modes, the temperature gradient (TG) decreases overall, the pulling velocity (PV) increases overall, and the SCs exhibit the characteristics of periodic fluctuation. Compared with the GG process under the non-oscillation mode, the fluctuant transient SCs lead to the grain remelting during the GG processes under the circular and sinusoidal oscillation modes. Additionally, the grain remelting degree under the sinusoidal oscillation mode is smaller than that under the circular oscillation mode. The results show that the developed model is helpful for understanding the GG process during oscillating LW and hence improving the weld microstructure and welded joint performance.