The bonding layer evolution and mechanical properties of 6061Al/DP590 ultrasonic-assisted friction stir diffusion welding joints

Welding of DP590 steel and 6061 aluminum alloy presents considerable challenges, due to their significant differences in physical properties. This study successfully achieved joining using friction stir diffusion welding (FSDW) with low heat input and adding a Zn interlayer, achieving a maximum strength of 153.5 N/mm. By ultrasonic-assisted friction stir diffusion welding (Ua-FSDW), joints could be welded at lower rotational speeds. Under low heat input conditions, a continuous, uniform, and thin intermetallic compound (IMC) layer formed at the interface, increasing the tensile shear strength to 345.6 N/mm, an improvement of approximately 125.14% compared to FSDW. The fracture mode transitioned from interfacial peeling to steel substrate tearing. The strengthening mechanisms induced by ultrasonic assistance were revealed by establishing physical models for interface layer formation and transformation in FSDW and Ua-FSDW.