Abstract: The friction stir welding technique for magnesium-aluminum dissimilar alloys used in new energy vehicle battery trays was explored, aiming to optimize the welding process and enhance the quality and performance of the weld joints. Utilizing AZ91D alloy as the welding material, the effects of welding speed and rotational speed on the welded joints were investigated, the joints both macroscopically and microscopically were analyzed. The results indicate that the optimal joint quality is achieved when the traverse speed is controlled between 100 mm/min and 150 mm/min, and the rotational speed is between 300 and 400 r/min. Under these parameters, the welded joints exhibit high compactness and uniform element distribution. The joints demonstrate excellent mechanical properties, including high tensile strength and good hardness characteristics. Additionally, the optimization of welding speed and rotational speed significantly affects the grain refinement in the weld zone, further enhancing the overall performance of the joints. This research provides vital technical references and practical application prospects for the welding of magnesium-aluminum dissimilar alloys in new energy vehicle battery trays.