Radial Additive Friction Stir Repairing of Mechanical Hole Out of Dimension Tolerance of AZ31 Magnesium Alloy Assisted by Stationary Shoulder:Process and Mechanical Properties

Radial additive friction stir repairing(R-AFSR)assisted by stationary shoulder was put forward in the present study,which can be employed to repair the mechanical hole out of dimension tolerance of AZ31 magnesium alloy sheet.The results show that the stationary shoulder has sealed-barrier,heat-sink and extra-forging effects.The heat-sink effect improves the microstructure uniformity along the stir zone(SZ)thickness and the surface appearance of repaired hole,and the sealedbarrier and extra-forging effects eliminate the super-fine grain band in the SZ.Therefore,these three effects improve the formation quality of repaired region,thereby enhancing the mechanical properties of repaired mechanical hole compared with conventional R-AFSR.The tensile and compressive shear strengths of the repaired hole by stationary shoulder R-AFSR both increase first and then decrease when the rotating speed changes from 1200 to 1800 rpm,and these maximum values,respectively,reach 190±3 MPa and 64.5±2 MPa at 1400 rpm.The addition of stationary shoulder during R-AFSR can obtain a higher-quality repaired hole and broaden the repairing process window.