Eliminating hole defects and improving microstructure and mechanical properties of friction stir welded joint of 2519 aluminum alloy via TIG arc

Two different joints of 2.5 mm thick 2519-T87 aluminum alloy sheets were obtained by conventional friction stir welding (FSW) and tungsten inert gas (TIG) arc assisted FSW. The mechanical properties of the joints were evaluated by hardness and tensile tests at room temperature. The results show that the introduction of TIG arc results in apparently higher tensile strength and elongation of the joint with the increment rates of 16.9% and 209.1%, respectively. The mechanism has been discussed based on microstructural examination by using optical microscope, scanning electron microscope, electron backscatter diffraction analyses, electron probe microanalyzer and scanning transmission electron microscope. The TIG arc assisted FSW eliminated the hole defects, reduced onion rings area and helped to form a higher density of finer θ′ hardening precipitates, which contributed to the higher mechanical properties.