Which shielding gas is typically used for GMAW of mild steel with ER70S-6 wire?

• A. 100% Argon
• B. 50% Argon, 50% CO2
• C. 75% Argon and 25% CO2
• D. CO2 only

Answer: (C)

Shielding gas choice in GMAW directly shapes arc stability, heat input, and the bead's appearance. For mild steel welded with ER70S-6 solid wire, a blend of mostly Argon with a touch of CO2—about 75% Argon and 25% CO2—provides a stable arc and good wetting, producing a smooth, well-formed bead with solid penetration. Argon helps stabilize the arc and improve bead quality, while the CO2 adds heat to promote proper penetration and keeps the arc transfer stable at typical welding currents. Pure Argon is more expensive and often yields less penetration on carbon steel, while pure CO2 can cause more spatter and a rougher bead. A 50/50 blend can work but typically doesn’t offer the same bead quality and arc stability as the 75/25 mix, making the 75/25 blend the standard choice.