Repairing Volume Defects of Al-Cu Alloy Joints by Active-Passive Filling Friction Stir Repairing

In this study, active-passive filling friction stir repairing (A-PFFSR) process was employed to repair the volume defects in friction stir welding (FSW) joints of Al-Cu alloy. The volume defects with varied geometries were first machined into taper holes, which are similar to keyhole defect by a rotational tool with a threaded pin. Then, the keyhole defect was effectively filled with the materials around the keyhole and an additional filler using a number of nonconsumable pinless tools with the shoulders having six spiral flutes. The macro/microstructures, microhardness, and tensile properties of the repaired joints were investigated. The influences of plunge speed on macro/microstructures and mechanical properties of the repaired joints have been analyzed too. It was noticed that decreasing plunge speed was effective to improve the frictional heat and material flow, which increased joint surface integrity avoiding interfacial drawbacks. No cavity and kissing bond defects were found during the plunge speed of 2 mm/min and rotational speed of 1800 rpm. Across the thickness direction, the microhardness in the filling zone (FZ) presented bigger value in the bottom and smaller value in the middle. With the increase of plunge speed, tensile strength and elongation of the repaired joints gradually decreased at the constant rotational speed. When the plunge speed is 2 mm/min, the tensile strength and elongation of the repaired joint reached 348.69 MPa and 9.1%, which were equivalent to 88.32% and 89.92% of the base Al-Cu alloy, respectively.