The most common gas used for TIG welding, or Tungsten Inert Gas welding, is Argon (Ar). Helium (He) can be added to increase the penetration and fluidity of the weld pool. Argon or argon/helium mixtures can be used for welding all grades.
Argon is an inert, colorless, and odorless gas that is ideal for TIG welding because it provides effective shielding around the tungsten electrode and weld pool, preventing oxidation and contamination.
In some cases, a mixture of Argon and Helium or Argon and Hydrogen may be used to increase the heat input and penetration of the weld. The choice of gas depends on the type of metal being welded and the desired welding characteristics.