Improving weld strength of magnesium to aluminium dissimilar joints via tin interlayer during ultrasonic spot welding

Welding of magnesium to aluminium alloys is enormously challenging due to the formation of brittle Al₁₂Mg₁₇ intermetallic compounds (IMCs). This study was aimed at improving the strength of dissimilar joints of AZ31B-H24 magnesium alloy to 5754-O aluminium alloy by using a tin interlayer inserted in between the faying surfaces during ultrasonic spot welding. The addition of tin interlayer was observed to successfully eliminate the brittle Al₁₂Mg₁₇ IMCs, which were replaced by a layer of composite-like tin and Mg₂Sn structure. Failure during the tensile lap shear tests occurred through the interior of the blended interlayer as revealed by X-ray diffraction and SEM observations. As a result, the addition of a tin interlayer resulted in a significant improvement in both joint strength and failure energy of magnesium to aluminium dissimilar joints and also led to an energy saving because the optimal welding energy required to achieve the highest strength decreased from ∼1250 to ∼1000 J.