Characteristics of interface reaction layer and joining strength of AA6061/Ti6Al4V dissimilar joints in ultrasonic-assisted resistance spot welding

Ultrasonic-assisted resistance spot welding (UaRSW) was employed to join AA6061 and Ti6Al4V. The intermetallic compound (IMC) formation and joining strength of Al/Ti joints were compared with those from conventional resistance spot welding (RSW). The thickness of the IMC layer was reduced from 200 nm to 120 nm with ultrasonic assistance, which effectively prevented excessively thick IMC formation at the nugget centre region. The length of the joining interface increased by 20% in UaRSW joints, resulting in a serration-shaped interface that provided a larger and more robust bearing area. The fracture crack propagation in UaRSW underwent directional changes due to the improved joining strength, ultimately leading to button pullout failure instead of interfacial failure.