Radial-additive Friction Stir Repairing For Exceeded Tolerance Hole

Radial-additive friction stir repairing(R-AFSR)was proposed to repair the exceeded tolerance hole.In this paper,AZ31 magnesium alloy was taken as the research object.The exceeded tolerance hole was repaired by R-AFSR.The surface forming,material flow,cross section morphology,microstructure and mechanical properties of the exceeded tolerance hole were studied under conventional and stationary shoulder auxiliary processes.The results displayed that the exceeded tolerance hole was successfully repaired under conventional and stationary shoulder auxiliary processes.As for the filling material(FM)and base material(BM),the interface clearance on the upper surface disappeared.No defects occur and the surface of the repair area was smooth.The repaired region was divided into four typical zones,namely BM,heat affected zone(HAZ),thermo-mechanically affected zone(TMAZ)and stir zone(SZ).In the conventional R-AFSR,the maximum tensile strength of the repaired hole reached 183 MPa,equivalent to 93.8% of the standard hole under the parameter of 1400 rpm.The compressive shear strength and compressive rate of the standard hole were 78 MPa and 35% respectively.The compressive shear strength and compressive rate of repaired region reached the maximum values of 58.4 MPa and 26.1% when the rotating velocity was 1400 rpm,equivalent to 75% and 74.6% of those of the standard hole.The microhardness was the largest near the edge of the repaired hole,and the value was 85.4HV.The fracture morphology was a typical ductile fracture mode.In the stationary shoulder R-AFSR,the tensile strength obtained at 1400 rpm was 190 MPa,which was equivalent to 97.4% of the standard hole.The tensile properties of the exceeded tolerance hole repaired by the stationary shoulder were more than 90% of the standard hole.The compressive shear strength and compressive rate of repaired region reached the maximum values of 64.5 MPa and 28.9% when the rotating velocity was 1400 rpm,equivalent to 82.7% and 82.6% of those of the standard hole.At four different parameters,the fracture morphology was a typical ductile fracture mode.