In this paper, the laser beam oscillation welding (LBOW) was utilized to weld a 2 mm thick AA2060 aluminum-lithium (Al-Li) alloy plate. The weld pool behaviors under three scanning paths (pure laser, O-shaped, and ∞-shaped) were investigated. It was observed that the O-shaped scanning path resulted in the most stable welding process. In addition, the weld macroscopic formation, microstructure, and mechanical property between different paths were studied. The results showed that pure laser and ∞-shaped patterns produced welding defects such as spatters and collapse during the welding process, while the O-shaped pattern exhibited good macroscopic formation at varying laser powers. The O-shaped pattern promoted the finest grain in the weld center and reduced the heat input during the welding process. The equiaxed grain zone (EQZ) width of the O-shaped pattern is the smallest compared to the other two patterns at high laser power. In addition to this, the O-shaped pattern could effectively reduce the porosity in the weld. When an O-shaped scanning pattern was adopted at the ideal laser power parameter of 3000 W, the microhardness of the weld center increased by approximately 5.6% compared to pure laser mode.

In this study, a new deep-penetration variable-polarity tungsten inert gas (DP-VPTIG) welding process, which is performed by a triple-frequency-modulated pulse, was employed in the welding fabrication of 8 mm AA7075 aluminum plates. The electric signal, arc shape, and weld pool morphology of the welding process were obtained by means of high-speed photography and an electric signal acquisition system under varying parameters of the intermediate frequency (IF) pulse current. The principle of the arc characteristics and the dynamic mechanism of the weld melting during the process are explained. In addition, the macroforming, microstructure, and microhardness of the welded joints were investigated. The results indicate that, with an intermediate frequency pulse of 750 Hz, the arc displayed a higher energy density and a more effective arc contraction, which improved weld appearance and penetration. Moreover, the impact and stirring action of the arc refined the microstructure grains of the weld center. Therefore, this new welding method is feasible for welding medium-thickness aluminum alloy plates without a groove.