Friction-stir welded defects and repairing weld process of thick aluminum plates with telescopic stir-pin

By using the telescopic stir-pin,25 mm-thickness 2219-T6 aluminum alloy couple plates were successfully friction-stir welded,and no plunge-through defect induced by the press amount of tool-shoulder was observed in the multi-pass repairing welding process.The microstructures in sound friction-stir welds,material-loss typed and weak-link typed weld defects were observed.The results show that the weld along the weld-thickness direction can be divided into shoulder-affected and pin-affected zones.The formation of defects is associated with the change of the welding parameters,and the inner material-loss typed defects follow volume conservation relationship.For the welds with different-size root flaws prepared by telescopic stir-pin,a non-linear relationship exists between the root-flaw depth and the weld tensile strength.In addition,under the unified welding parameters,by adjusting the telescopic pin length,the effects of multi-pass welding on the microstructure and properties of the resultant welds were investigated.