Effect of shielding gas on the plasma plume in pulsed laser welding

According to the theory of plasma sheath layer, the charge-voltage of plasma was measured by the principle of plasma probe to investingage the effect of shielding gas on the plasma plume in bead-on-plate welding by pulsed laser. The electron temperature, electron density, IB linear absorption coefficient of plasma and transmittance rate are interrelated and important parameters to estimate the energy absorption mechanism in laser welding. The results showed that Helium atmosphere suppresses the plasma eruption in laser welding more effectively than the Argon atmosphere, which is shown to reduce the electron temperature of plasma and shorten the duration of plasma eruption. Compared with the suppressing effect of Argon atmosphere, Helium atmosphere can more effectively suppress the inverse bremsstrahlung absorption effect of plasma induced in laser welding, improve the transmittance rate of laser energy, so as to improve the absorption efficiency of materials to laser energy, which is conducive to higher welding efficiency. In addition, a larger shielding gas flow can also suppress the increase of electron density and the inverse bremsstrahlung absorption effect of plasma, and increase the transmittance rate of laser energy. So, a larger shielding gas flow in laser welding is beneficial to suppress the plasma eruption either in Helium atmosphere or in Argon atmosphere. (C) 2018 Published by Elsevier Ltd.