Study of plastic deformation and interface friction process for ultrasonic welding

Ultrasonic spot welding (USW) is attracting increasing attentions in joining of dissimilar metals. Previous experimental results show that material plastic deformation and interface friction plays key role for joint formation process. In the present study, experimental and theoretical analysis was carried out to study USW of copper and aluminium. Evolution of interface friction and surface deformation was obtained quantitatively. Meanwhile, theoretical analysis was proposed to research material flow and contact behaviour between faying interfaces of specimens. Conclusions can be made that interface friction resulted in tremendous plastic deformation, which was beneficial for joint formation. Growth rate of plastic deformation decreased as welding proceeds. Compression stress and cyclical shear stress induced by ultrasonic vibration determined direction and degree of material flow.