Metallographic Characterization on Microstructure and Defects of Aluminum Alloy Friction Stir Welding Joints

The metallographic characterization of aluminum alloy friction stir welding joints was introduced and summarized from three aspects:joint low magnification morphology, microstructure characteristics of various regions, and defect characteristics. The results show that there were three kinds of macro morphology, including riverbed style, drum style and kettle mouth style. The microscopic characteristics of the joints could be analyzed from two aspects of recrystallization and second phase distribution. The essence of onion-ring defect was the alternate distribution of unequal size recrystallized grains or different number of disperse phase particles. The Z-shaped line defect was formed by the diffuse distribution of the oxide film on the original interface. The kissing-bond defect and the hook-shaped defect were pseudo connection defects. The hole defect and tunnel-shaped defect were mainly caused by the insufficient heat input during the welding process.