In this study, laser oscillation welding was utilized to offer an effective solution for the joint welding of heat-treatment-free die-cast aluminum alloys, which expands the practical applications of automotive structural parts and heat sinks for electronic devices. The effects of oscillation amplitude on the macro-morphology, microstructure, and properties of the alloy weld were examined, and a molten pool flow model was developed to compare the behavior of the molten pool with and without oscillation. The results show that increasing the oscillation amplitude eliminates the coarse Al₁₅(Fe,Mn)₃Si₂ phase, resulting in a finer and more uniform distribution of the eutectic Si and Mg₂Si phases. At an oscillation amplitude of 7 mm, the maximum tensile shear load and displacement were 2761 N and 1.17 mm, respectively. Laser oscillation was found to enhance the fluidity of the molten pool, reduce porosity, improve weld quality, and effectively decrease cracks and inhomogeneous grain distribution. These findings provide a research basis for optimizing the laser oscillation welding process and for the practical welding of fabricated devices.