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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 sealed-barrier 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.

Ultrasound assistance was applied to friction stir transient liquid phase spot welding (FSTLPSW) to attain a high-quality dissimilar copper-aluminum joint in this study. Different ultrasound-assisted times were selected for comparing with the conventional condition without ultrasound. The interfacial microstructure evolution of conventional joint was analyzed combined with the measured temperature cycle. The ultrasound assistance improved the joint quality by regulating the interfacial microstructure. Cavitation erosion, broken IMC particles and thicker eutectic layer appeared in ultrasound-assisted joint. The highest tensile shear strength of 7.38 kN was obtained under the ultrasound-assisted time of 60 s which was 43.1 % higher than that of the conventional joint. The fracture location transferred from IMC layers to eutectic layer under the ultrasound assistance.