Study on the surface fluctuation characteristics of liquid metal under gas jet excitation

To address the challenge of in-situ monitoring of melt pool dynamics in laser additive manufacturing (LAM), this work proposes a gas-jet excitation method to probe surface wave behavior in liquid metals. Using an In51Bi32.5Sn16.5 alloy (melting point ≈ 60 °C), controlled airflow was applied across temperatures from 90 °C to 60 °C, and surface ripple evolution was captured via high-speed imaging. Image analysis revealed that both wave velocity and wavelength decrease markedly with cooling: stable concentric ripples form at 70 °C, while coherent waves vanish at 60 °C due to incipient solidification. Numerical simulations qualitatively reproduced the ring-like waves and keyhole-like depressions, showing trend-level consistency with the experimental observations. The findings suggest that gas-jet-excited surface-wave characteristics may provide potential observable signals for characterizing the near-solidification state of liquid metal and may offer a conceptual basis for future melt-pool monitoring methods.