Friction stir diffusion welding realized by a novel tool with turbo-like pin

Abstract The hook structure in friction stir lap welding (FSLW) joint is an undesirable structure due to its detrimental effect on tensile lap-shear strength (TLSS). For this reason, a friction stir diffusion welding (FSDW) technique realized by a series of specially designed tools with a turbo-like pin was put forward. 2024-T4 Al alloy with an alclad layer on the surface was chosen as the researched material. Different from the conventional FSLW joint, a basin-like stir zone and a flat bonding interface without hook structure are formed in the FSDW joint. A“turbocharging effect”is formed in the center region of the turbo-like pin, which promotes the material to flow downward and enhances the diffusion bonding at the lap interface. Two diffusion bonding mechanisms, including the heat affected zone bonding and the thermo-mechanically affected zone bonding, are formed at the lap interface. Adjusting the blade number and the plunge depth enables the transformation of these two bonding mechanisms. The joint fabricated by the turbo-like pin with four blades at the plunge depth of 1.3 mm has the maximum TLSS of 12.21 kN and fractures at the SZ edge of top sheet. The FSDW realized by the novel tool provides a new approach to acquiring a high-quality lap welding joint.