Enhance mechanical properties of refill friction stir spot welding joint of alclad 7050/2524 aluminum via suspension rotating process

Alclad layer is a challenge to ensure the mechanical properties of refill friction stir spot welding (RFSSW) alclad 7050/2524 joint. In this study, RFSSW with suspension rotating process (SRP) was designed to improve the mechanical properties by strengthening the alclad layer. The thermal cycles, microstructures and mechanical properties of the joints welded without and with SRP were compared. The results indicated that SRP increased the high temperature dwell time of the stir zone bottom, which promoted more alloy being stirred into and mixing with the alclad, beneficial for strengthening the alclad. When with SRP, the tensile shear strength of joint reached 11 kN, improved by about 30% compared with joint without SRP.