Microstructure and mechanical properties of friction plug repair welding joint by shoulder auxiliary heating for 6082 aluminum alloy

Friction plug repair welding by shoulder auxiliary heating based on filling friction stir welding(FSW) for 6082 aluminum alloy was used to repair keyhole volume defects by(FSW). Well-formed plug repair welding joints were obtained at different rotation speeds of plug. The results shown that microstructure in different areas of the joint changed obviously due to heat input and material deformation. The microstructure and distribution of the joint were similar under different rotation speed of plug rod. The welding joint can be divided into 6 parts: nugget zone, filling zone, bonding surface zone, shoulder affected zone, thermos-mechanically affected zone and heat affected zone. Nugget zone and shoulder affected zone have fine equiaxed grains, filling zone retained the original plug rod structure. The bonding surface zone is the transition zone between the base metal and the plug rod. The grain deformed obviously in thermos-mechanically affected zone, and the grain grown up in heat affected zone. The microhardness of the joint was higher than that of the base metal, the tensile strength was up to 260 MPa, which is 83.9% of the base metal, the elongation after fracture is 6.5%, and the fracture toughness is obvious.