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How does argon shielding gas protect a weld from oxidation?

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Welder in a blue uniform and protective helmet using shielded metal arc welding to join metal pieces, with bright sparks and smoke visible at the welding point. — welding Shielded metal arc welding.

In gas-shielded arc welding, argon acts as a protective barrier to prevent oxidation of the molten metal.1

When metals are heated to their melting point, they react readily with atmospheric oxygen, which can create oxide layers that prevent proper bonding and lead to brittle, compromised joints. To prevent this, argon is released in a continuous stream from an annulus surrounding the welding torch. Because argon is an inert gas, it does not chemically react with the metal. Instead, it physically displaces the surrounding air, creating an inert atmosphere that shields the molten pool from contact with atmospheric oxygen. This process ensures the integrity of the weld deposit by maintaining the desired chemical composition of the metal.123