Arc welding and multipass friction stir welding ( Multi-FSW) were applied as the repair welding
technique for tunnel defects of FSW joints. Microstructures and mechanical properties of repaired joints were analyzed
and the influences of the repair welding process on joint properties were evaluated. The experimental results indicate
that mechanical properties of Multi-FSW joints will not decrease obviously. Compared with FSW joints, repaired
joints made using TIG + FSW have similar microstructures and show no microstructural deterioration. The repair weld鄄
ing method is proved to be effective and feasible for the repair of the longitude welding tunnel defect of a rocket fuel
tank.