Ultrasonic welding of Cu to Al cables bonding: Evolution of microstructure and mechanical properties

Ultrasonic welding (USW) was conducted on BVR2.5 Cu and BLV6 Al cables in this study, aiming to identify the microstructure evolution and the mechanical properties of the joint. The effect of different welding energies (200–500 J) for the performance of the joint was investigated. With increasing in welding energy, the tensile strength first increases up to the peak load (409.85 ± 8.95 N) at the welding energy of 300 J, and then decreases. Further, the mechanism of microstructure evolution under 300 J welding energy was analyzed. Plastic deformation and discontinuous dynamic recrystallization (DDRX) were found in the Cu grains during the welding, while dynamic recovery (DRV), dynamic recrystallization (DRX) and grain growth were found in the Al grains. During ultrasonic vibration, the texture unit {001}〈110〉 restarted to form by the Cu grains rotation along the crystal direction 〈110〉, and the Al grains were broken up forming the ultrafine equiaxed grains (about 1.9 μm). The recrystallized Cu grains have no strong oriented textures, and the Al grains grow up with the strong texture of Brass{110} 〈112〉. Fracture analysis suggests that the good interface bonding between Cu and Al cables can be achieved due to the influence of plastic deformation and recrystallization during ultrasonic welding.