Enhancing mechanical properties of dissimilar pure Cu/Mg AZ31B friction stir welds via ultrasonic assistance

-Joining dissimilar pure copper (Cu) and magnesium (Mg) alloy AZ31B through friction stir welding (FSW) presents considerable metallurgical challenges due to contrasting thermo physical properties and brittle intermetallic compound formation at the weld interface. This study examines FSW of Cu/Mg AZ31B butt joints using a tool rotational speed of 1070 rpm, welding speed of 31.5 mm/min, tilt angle of 2°, and a 1.5 mm pin offset toward the Mg AZ31B side to optimize heat generation and material flow. Conventional FSW produced an ultimate tensile strength (UTS) of 110 Map, limited by inadequate inter-material mixing and interfacial defects. To overcome these constraints, ultrasonic-assisted friction stir welding (UAFSW) was implemented, superimposing high-frequency acoustic energy to enhance material plasticization, reduce flow stress, and promote dynamic recrystallization in the weld nugget. The UAFSW joints achieved UTS of 125 Map, representing a ~13.6% improvement over conventional FSW. This enhancement is attributed to acoustic softening and cavitations driven grain refinement, improved inters material mixing, and reduced interfacial defect density. These findings establish ultrasonic assistance as a viable strategy for welding dissimilar material systems, with significant implications for electrical, automotive, and lightweight structural applications requiring reliable Cu–Mg joints.