Abstract: The effect of halide surfactant (such as NaCl, ZnCl2, LiCl, KF and so on) on the weld penetration of laser welding aluminum alloy is studied, and it is found that the halide surfactant can significantly increase the weld penetration. To study the mechanism that the halide surfactant is beneficial to fiercely increasing the welding penetration, the high-speed camera and technique of spectroscopic analysis is used to explore the influence of halide surfactant on physical parameter of plasma, such as temperature, volume and so on. And the experiment of two-sheet tungsten is conducted to explorer the influence of halide surfactant on flowage of welding pool. It is found that the halide surfactant can reduce the temperature of plasma, which leads to decrease the refection, scattering and inverse bremsstrahlung absorption of laser in the plasma, and increase the input of laser to workpiece. And the halide surfactant can change the state of circulation in the weld pool and make the penetration deepen.

Key words: Active laser welding, Halide surfactant, Inverse bremsstrahlung absorption, Plasma