Microstructure and mechanical properties of Mg/Al dissimilar metals joint by Sn foil-assisted oscillation laser welding

Stannum (Sn) foil-assisted oscillation laser welding of AZ31 magnesium (Mg) and 6061 aluminum (Al) alloys in butt joint were performed. Influence of linear oscillation laser-Sn foil coupling on microstructure and mechanical properties of Mg/Al dissimilar metals joints was studied. The temperature field and flow field distribution including chemical potential of each element were also calculated. The results demonstrate that increasing Mg content induces a significant reduction in Sn's chemical potential to 227 kJ/mol, driving preferential Sn diffusion toward the Mg-rich region and thereby promoting Mg-Sn compound formation. Conversely, the driving force for Al atom diffusion decreases with the increase of Sn content, which suppresses the formation of Mg-Al compounds. Under linear oscillation conditions, whether or not Sn foil is added, the maximum tensile load of Mg/Al joint first increases and then decreases with the increase of oscillation frequency, and it reaches a maximum value of 997.68 N at 50 Hz with the addition of Sn foil, which is 18% higher than that without foil. The improved joint properties are dominated by metallurgical regulation of Sn foil, which benefits from the enhanced fluidity of molten pool and heat transfer in the width direction of molten pool leading to the reduced difference in dissolution amounts of Mg and Al sides and the phase composition transformation from Mg ₂ Al ₃  + Mg ₁₇ Al ₁₂ +ɑ-Mg to Mg ₁₇ Al ₁₂  + Mg ₂ Sn compounds.