Answer: Acts as a shielding gas
Shielding gases are inert or semi-inert gases that are commonly used in several welding processes. Their purpose is to protect the weld area from oxygen, and water vapor . Improper choice of a welding gas can lead to a porous and weak weld, or to excessive spatter.
Argon being an inert gas is a cost-effective shielding gas because of its low relativity with metal to provide an inert atmosphere.