High-power fiber laser incident beam absorptivity variation of molten pool surfaces during their solid-liquid-gas state evolution

The thermal and ablation effects of lasers are widely used in laser additive manufacturing, laser welding, laser cleaning, and laser cladding technologies. Absorptivity is the core index of laser beam-thermal energy conversion efficiency. This paper analyzed the irradiated material's absorption behavior during the solid-liquid-gas evolution of laser-ablated metal surfaces by comparing the temperature fields and the corresponding weld cross- sections for different laser action periods, considering the fusion and vaporization latent heats. The solid- liquid-gas state evolution of high-power fiber laser-irradiated metal surfaces occurs during several milliseconds, with a short solid-phase existence period, since fusion or melting time is much shorter than the vaporization time. As the solid-liquid-gas state evolves, the average absorptivity and the share of thermal conduction energy loss decrease with the laser action time, while the fusion energy loss gradually increases. The solid-phase surface of the metal in laser processing absorbs significantly more incident laser energy than the liquid-phase one. The longer the solid-phase occurrence period of the metal surface during the laser action, the greater its average absorptivity of the incident laser. By increasing the laser spot area and scanning rate, the solid-phase period of the laser-irradiated metal surface can be increased, improving its incident laser absorptivity.