Which shielding gas combinations are commonly used for GMAW on carbon steel, stainless steel, and aluminum?

• A. Carbon steel: 75% Argon/25% CO2 (or 100% CO2); Stainless: 98% Argon with 2% O2 (or 2% CO2); Aluminum: 100% Argon
• B. Carbon steel: 100% Argon; Stainless: 100% Argon; Aluminum: 100% Argon
• C. Carbon steel: 50% Argon/50% CO2; Stainless: 50% Argon/50% CO2; Aluminum: 50% Argon/50% CO2
• D. Carbon steel: 25% Argon/75% CO2; Stainless: 10% Argon/90% CO2; Aluminum: 0% Argon

Answer: (A)

Shielding gas choice in GMAW is about shaping the arc, bead quality, and oxide control for each metal. For carbon steel, a mix that includes argon with a bit of CO2 provides arc stability and good spray transfer without excessive spatter; 75% Argon/25% CO2 (or sometimes 100% CO2) is a common practical option. Stainless steel benefits from a mostly inert shield with a small additive (argon with a little oxygen or CO2) to stabilize the arc and help clean the weld bead; 98% Argon with 2% O2 (or a small amount of CO2) is a typical choice. Aluminum welds require a very pure, inert shield to prevent oxide formation, so 100% Argon is the standard shielding gas.

That’s why the described combinations align with common practice across the three materials: carbon steel with Argon/CO2 or CO2, stainless with a high-Argon shield plus a tiny additive, and aluminum with 100% Argon. Other options would either overreact with the aluminum, fail to stabilize the stainless arc, or introduce too much spatter or oxidation on carbon steel.