Active-passive filling friction stir repairing of casting defects in ZL210 aluminum alloys

Active-passive filling friction stir repairing (A-PFFSR) was employed to eliminate the casting defects in the ZL210 aluminum alloys. Based on a six-spiral-grooves pinless tool, effects of rotating velocity on microstructures and mechanical properties of the repaired joints were investigated. The casting defects were firstly drilled into taper holes by a tool with a threaded pin, and then the keyhole defect was successfully filled with the materials surrounding the keyhole and an extra filler via the A-PFFSR. Increasing rotating velocity was propitious to improving frictional heat and material flow, which enhanced joint surface integrity and eliminated interfacial defects. However, the extremely high heat input induced by the rotating velocity of 1800 rpm easily led to the severe joint softening. When the rotating velocity was 1600 rpm, the maximum tensile strength of sound repaired joints was approximately equivalent to that of base ZL210 alloys, realizing the quasi repairing of the ZL210 aluminum alloys.