Welding Reference Library · Gases & Cylinder Safety

Shielding Gas Selection by Process

Common shielding gases and mixes for MIG, flux-cored and TIG welding by base metal and transfer mode, and how gas choice affects penetration, spatter and appearance.

Ref WG-0403AWS A5.32AWS A5.18AWS A5.20AWS A5.36AWS D1.1

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Shielding gas protects the molten weld pool from the atmosphere and shapes the arc. Inert gases (argon, helium) do not react with the weld; active gases (carbon dioxide, oxygen) take part in arc behavior and change penetration, bead shape and spatter. AWS A5.32 classifies welding shielding gases. The filler metal classification and the welding procedure (WPS) usually specify the gas or gas family; on code work the gas is an essential or supplementary variable and must match the WPS.

How to identify

  • Cylinder label shows the gas or mix percentages (e.g. "Argon 75% / Carbon Dioxide 25%").
  • Flux-cored wire classifications carry a gas designator: C = 100% CO2, M = argon-CO2 mix (typically 75–80% argon) as tested by the manufacturer.
  • Self-shielded flux-cored wires (e.g. E71T-11) need no external gas.

Common selections

Process / metalCommon gasesNotes
GMAW short-circuit, carbon steel75% Ar / 25% CO2; 100% CO275/25 gives less spatter and better appearance; CO2 gives deeper penetration and lower cost
GMAW spray / pulse, carbon steelArgon with about 5–10% CO2, or argon with 1–5% O2Higher argon content is needed for spray transfer
GMAW, stainless steelTri-mix (helium-argon-CO2) for short-circuit; 98% Ar / 2% O2 or 98% Ar / 2% CO2 for sprayLow active-gas content limits oxidation and carbon pickup
GMAW, aluminum100% argon; argon-helium for thicker sectionsNever use CO2 or O2 mixes on aluminum
GTAW (TIG), most metals100% argonArgon-helium for thick aluminum or copper; some hydrogen mixes for austenitic stainless only
FCAW gas-shielded, carbon steel100% CO2 or 75–80% Ar / balance CO2, per the wire's C or M designatorUsing the wrong gas changes weld-metal chemistry and properties

Key points

  • Gas choice must match the WPS on code work; changing gas may require requalification.
  • Flow rate is set in cubic feet per hour (CFH) or L/min at the gun; drafts and nozzle size change the need. Excess flow wastes gas and can cause turbulence and porosity.
  • Leaks in hoses and fittings are a major hidden cost and can pull air into the gas stream.
  • CO2 regulators can freeze at high flow; heaters or manifolds may be needed.
  • Inert gases displace oxygen; ventilate enclosed work areas.

Common mistakes

  • Running "M" flux-cored wire on 100% CO2.
  • Using a 75/25 cylinder for TIG.
  • Turning up flow to fix porosity caused by a leak or draft.

Governing standards: AWS A5.32; AWS A5.18; AWS A5.20; AWS A5.36; AWS D1.1.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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