What is the role of shielding gas during laser welding?

Right into the protective gas blowing can effectively protect the weld molten pool reduce or even avoid oxidation, reduce splash in the welding process and reduce weld porosity, stimulates the weld molten pool solidification evenly spread out, make weld forming uniform appearance, for some special metal can reduce steam plume or shielding effect of the laser plasma cloud, increase the effective utilization of laser.
If the protective gas is not blown correctly, it may lead to poor welding seam and reduced mechanical properties of welding seam, which may lead to serious interference of metal in weld pool by external forces, resulting in weld collapse, crack or uneven molding. The larger the shielding gas flow rate is, the more the laser energy will affect the weld depth.
Argon Ar
Ar of ionization energy relative to the minimum, under the effect of laser ionization degree is higher, is not conducive to control the formation of plasma cloud, can effective utilization of laser produce certain effect, but the Ar activity is very low, it is difficult to react with common metals, and Ar cost is not high, in addition, the density of Ar is bigger, is conducive to sink to the weld molten pool above, can better protect the weld molten pool, thus can be used as a conventional protective gas.
Nitrogen N2
The ionization energy of N2 is moderate, higher than that of Ar and lower than that of He. Under the action of laser, the ionization degree is general, which can better reduce the formation of plasma cloud and increase the effective utilization rate of laser. Nitrogen can react with aluminum alloy and carbon steel at a certain temperature to produce nitride, which will improve the brittleness of the welding seam, reduce the toughness, and have a great negative impact on the mechanical properties of the welding seam joint. Therefore, nitrogen is not recommended to protect the welding seam of aluminum alloy and carbon steel. Nitrogen and stainless steel chemical reactions produced nitride can improve the strength of weld joints, will be conducive to the improvement of the mechanical properties of the weld, so when welding stainless steel can use nitrogen as a protective gas.
Helium He
He has the highest ionization energy, under the effect of laser ionization degree is low, can very good control the formation of plasma cloud, laser can be work well in the metal, and He is very low, active basic does not react with metals, is a good welding protective gas, but He is too costly, general mass production products will not use the gas, He is generally used in scientific research or very high value-added products.