Effects of laser beam oscillation modes on the spatiotemporal dynamics of metal-vapor plasma plume during pulsed TIG–laser hybrid welding

Laser beam oscillation provides an effective approach for regulating the spatial distribution of heat input during pulsed tungsten inert gas–laser hybrid welding. However, the effects of laser beam oscillation modes on the spatiotemporal dynamics of the metal-vapor plasma plume have not been clarified. In this study, the dynamic responses of the metal-vapor plasma plume under four laser beam oscillation modes were analyzed: no oscillation, figure-eight, infinity-shaped, and circular modes. By synchronously acquiring electrical signals, optical emission spectra, and high-speed images, the spectral redistribution and kinematic features of the hybrid plume were quantitatively characterized. The results show that the pulsed current dominates the expansion and contraction rhythm of the plume, whereas high-frequency laser beam oscillation modifies the emission intensity and the relative contributions of Ar-related plasma emission and Fe-related metal-vapor emission. Boltzmann analysis indicates distinct apparent excitation responses and multiline fitting characteristics under different oscillation modes. High-speed imaging reveals distinct trajectory-dependent spatial organization of the main high-luminance region: Under the no-oscillation condition, the high-luminance region remains concentrated near the fixed coupling region; the figure-eight mode exhibits obliquely oriented reciprocating centroid migration; the infinity-shaped mode promotes longitudinal extension of the main high-luminance region along the welding direction; and the circular mode forms a broad near-center statistical activity envelope. These results demonstrate distinct beam-oscillation-mode-dependent spatiotemporal responses of the metal-vapor plasma plume, providing a diagnostic basis for welding process monitoring and subsequent beam-path and process optimization.