A numerical study of dynamic behavior of the molten pool in laser welding of aluminum alloy

During the laser welding process of aluminum alloy, the high reflectivity of aluminum alloy to laser and the severe fluctuation of the keyhole lead to highly unstable energy absorption, which readily induces defects such as spatter and porosity. Furthermore, the multi-physical field coupled dynamic behaviors within the molten pool, involving heat transfer, fluid flow, phase transformation, and element evaporation, are difficult to capture and quantify, resulting in a lack of precise theoretical guidance for this process. To address these issues, a multiple-reflection laser absorption model for the keyhole in the aluminum alloy laser welding molten pool was established. Basic assumptions were applied to the laser welding process to simplify the calculation of the molten pool mathematical model. The governing equations for the laser welding molten pool were established. Finally, the laser welding molten pool process was simulated. Experimental results demonstrate that employing a laser incident angle of 30° reduces the molten pool flow velocity by approximately 40%, effectively suppressing the spatter phenomenon. When the welding speed is increased to 8.0 m/min, the escape efficiency of molten pool bubbles is enhanced by 50%, and the uniformity of element diffusion is significantly improved. The comprehensive optimization of parameters can improve weld formation quality by more than 35%. The study provides an effective numerical analysis tool for understanding keyhole dynamics and molten pool behavior in aluminum alloy laser welding, significantly enhancing the comprehension of defect formation mechanisms. The established models and optimization results can offer a theoretical basis and parameter design guidance for the development of high-quality and high-efficiency aluminum alloy laser welding processes.