Microstructure and failure behavior of ultrasonic-assisted resistance spot welded AA6061/Ti6Al4V joints

Abstract

The ultrasonic-assisted resistance spot welding (UaRSW) technique was applied to join AA6061 aluminum alloy to Ti6Al4V titanium alloy, the microstructure and mechanical performance of the joints with and without ultrasonic were investigated. Ultrasonic increased the maximum load by 43%, doubled the displacement at fracture and significantly enhanced energy absorption capacity. The solid phase transformation zone formed in Ti6Al4V, and its microstructure was lath martensite. Due to the welding defects and coarse columnar dendrite, conventional spot welded joints fractured by interfacial failure mode with poor performance. Ultrasonic promoted the diffusion of AA6061, removed the welding defects, generated consistent equiaxed grains in weld zone, and the joints fractured in AA6061 base metal by button pull-out mode result from the higher bonding strength.