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