Shielding Gas in Welding: What Argon and CO2 Do

In MIG and TIG, the molten metal needs a protective atmosphere while it cools. Without it, oxygen and nitrogen from the air contaminate the weld and leave it porous and weak. The gas provides that protection. Here's what each one does.

What shielding gas is for

Gas flows out of the torch nozzle and forms an invisible cloud over the weld puddle, pushing the air away. Good gas flow means clean beads; poor flow or wind means porosity. It's not an accessory — it's part of the weld.

75% Argon / 25% CO2 mix: the MIG standard

The most-used mix for welding carbon steel with solid ER70S-6 wire. Argon stabilizes the arc and CO2 adds penetration. It gives a smooth arc, little spatter, and a good finish. If you're only keeping one MIG cylinder, make it this one.

Straight CO2: cheaper, deeper penetration

100% CO2 costs less and penetrates deeper, but the arc is harsher and spatters more. It's common in heavy and production work where finish is secondary. For a beginner in a shop, the 75/25 mix is friendlier.

Straight Argon: for TIG and aluminum

In TIG, straight Argon (or Argon/Helium mixes) is required: the tungsten and the puddle need very clean shielding. It's also the gas for welding aluminum in MIG, where straight Argon runs with special wire.

Practical tips

• Check for leaks at fittings and hoses: lost gas is lost money
• Set flow between 15 and 20 CFH for indoor MIG (more if there's a breeze)
• Secure the cylinder upright, always with its cap on when not in use
• A small cylinder runs out faster than you think — estimate your usage before a big project

The right gas is the difference between a clean bead and one full of pores.

Need a cylinder, regulator, or refill? At RGV Welding Supply we handle gases and regulators — visit us in Pharr or Weslaco.