New technique of radial-additive friction stir repairing for exceeded tolerance holes

Radial-additive friction stir repairing (R-AFSR) was proposed to repair exceeded tolerance holes. Here, AZ31 Mg alloys were selected as the primary research object. Good metallurgical bonding appeared in the repaired zones due to atom diffusion induced by thermo-mechanical behaviors. The diameter of the exceeded tolerance hole was reduced from 10 to 8 mm. The stir zone and partial thermo-mechanically affected zone were characterized by fine and equiaxed grains. The average grain size in the stir zone was less than 10 μm, attributing to high microhardness values. A high-quality repaired joint with the maximum tensile strength of 183 MPa was achieved, equivalent to 93.8% of the joint with the standard hole for AZ31 Mg alloys. Compressive shear strength and compression rate of the repaired joint reached 58.4 MPa and 26.1%, up to 75% and 74.6% of the joint with the standard hole. The fracture surface morphologies exhibited the typical ductile fracture. Therefore, R-AFSR has great prospects to repair the exceeded tolerance holes.