Microstructures and mechanical properties of 7N01-T4 aluminum alloy joints by active-passive filling friction stir repairing

The volume defects such as keyhole, tunnel and cavity in friction stir welding (FSW) joint are detrimental to mechanical properties. In this study, a new method called active-passive filling friction stir repairing (A-PFFSR) was put forward to eliminate the disadvantages induced by these defects, while 7N01-T4 aluminum alloy was chosen as research object. The results show that keyhole with the depth of 4 mm can be successfully repaired and better metallurgical bond is attained under rational parameters using A-PFFSR process. Cavity or kissing bond defect may easily appear at the interface between filling zone and thermo-mechanically affected zone, which can be effectively eliminated by increasing rotational velocity. Mechanical properties of A-PFFSR joint increase with the increase of rotational velocity. When the rotational velocity of 1600 rpm and constant plunge speed of 2 mm/min are used, the tensile strength and elongation of repaired joint reach the maximum values of 311.1 MPa and 7.6%, equivalent to 82.1% and 95.8% of the defect-free FSW joint, respectively. Moreover, the defect-free repaired joint fractures at the HAZ and the fracture surface morphology is characterized by various dimples, indicating typical ductile fracture.