Ultrasonic spot welding of dissimilar Al/SS sheets with various surface conditions: an experimental investigation

In this experimental study, ultrasonic metal welding (USMW) is introduced to join Al and SS thin sheets by varying surface conditions and weld energies. This research aims to enhance joint performance by properly controlling process parameters. Al/SS joints made at weld energy of 2550 J have the highest tensile shear and T-peel loads for the lubricated surface condition. The peak failure energy and critical stress intensity of the joints are also achieved under the aforementioned welding condition. With rising weld energy, the bond density increases and effective thickness decreases, revealing the increment in plastic deformation under the sonotrode knurls at the Al side. The upsurge in the microhardness values at the welding interface demonstrates the influence of natural aging and softening at the weld zone. Distinct mutual diffusion, wavy-like interface, dimple islands and swirl pattern flow appear at the Al/SS weld cross-section and fracture surfaces.