Plastic damage and deformation defect of friction stir welding for aluminum alloy

2219 aluminum alloy plates were welded by friction stir welding, which was a solid bonding technology to solve the traditional problems for aluminium alloy welding. The morphology, microstructure and mechanical properties of the joint were investigated. Through analyzing the flowing pattern of the plastically deformed metal in the nugget zone, the strength weakening of the joint were analyzed and summarized. The reason of weakening strength was due to the plastic deformation and damage of the metal, which resulted in the defect formation and the mutational interface. The results show that the well-formed weld beam is similar to the base metal, which has the plastic fracture morphology. However, if there are pores, holes and other welding defects in the weld beam, the fracture morphology is brittle fracture, then the tensile strength is about 70% of base metal and the elongation is about 7%, which means that the advantages of high strength aluminium alloy are not fully utilized.