Influence of loading time on the microstructures and performance of Cu/Al joints by bonding at a low temperature of 160°C

Purpose This study aims to investigate the effect of ultrasonic loading time on the interfacial microstructure evolution and mechanical properties of Cu/Al joints bonded at 160 °C using a composite solder composed of Sn–Ag–Cu (SAC)0307 and Zn mixed powder. Design/methodology/approach Cu/Al joints were fabricated using SAC0307-Zn composite solder under different ultrasonic loading durations. The interfacial microstructure, fracture morphology and shear strength of the joints were systematically analyzed to clarify the relationship between ultrasonic-assisted bonding, atomic diffusion behavior and joint performance. Findings Prolonged ultrasonic loading accelerated Zn–Cu atomic diffusion and promoted the formation and growth of Cu5Zn8 and CuZn4 intermetallic compounds. The shear strength first increased and then decreased, reaching a maximum of 33.93 MPa at 7 s, 89.13% higher than that without ultrasound. Increased ultrasonic duration enhanced Al–Zn solid solution formation and metallurgical bonding, while excessive loading at 9 s produced a Sn-rich layer that hindered Zn diffusion and reduced joint strength. Originality/value This work reveals the mechanism by which ultrasonic loading time regulates interfacial reactions, atomic diffusion and mechanical performance in low-temperature Cu/Al bonding using SAC0307-Zn composite solder. The findings provide useful guidance for optimizing ultrasonic-assisted solid-state bonding processes for reliable Cu/Al dissimilar-metal joints.