The effects of the use of different shielding gas mixtures in laser welding of metals

The paper makes use of the solution of the system of Saha equations derived for any mixture of ionized monatomic gases. This solution is specifically applied to the case of two-component mixtures of the gases used as shields in the process of laser welding, namely Ar plus He, Ar plus O₂, Ar plus N₂ and Ar plus H₂. The number densities of electrons and ions, the degrees of ionization of the plasma as well as the refractive indices and the inverse Bremsstrahlung absorption coefficients are presented as functions of temperature for a variety of volume ratios of the gases in the mixtures. The properties of the mixture of helium and argon change dramatically as the volume ratio of the two gases is altered. This mixture is also most interesting insofar as laser welding is concerned because it causes only very slight defocusing of the laser light above the keyhole.