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Why are helium and argon used as protective gases during welding?

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Neon — noble gas A road in Tokyo lined with neon signs.

Helium and argon are used as protective gases during welding because they are noble gases, which are characterized by their reluctance to react chemically with other substances.1

When metals are heated to their melting point during welding, they become highly reactive and can easily oxidize upon contact with atmospheric oxygen. This oxidation can create brittle joints and prevent proper bonding. By using an inert gas like helium or argon, welders can create a continuous, chemically unreactive environment that displaces the air around the arc. This protective shield prevents the molten metal from contacting oxygen, nitrogen, or other atmospheric gases that would otherwise compromise the integrity of the weld.21