How to choose a welding shielding gas
The shielding gas protects the molten pool from oxygen and nitrogen, but it also shapes the arc. Argon gives a smooth, stable arc and low spatter. CO₂ gives deeper penetration at a lower price but a harsher arc. Helium raises arc voltage and heat input, which helps on thick or highly conductive metals such as aluminum.
Gas blends by material
Carbon steel
C25 (75/25 Ar/CO₂) is the standard for MIG. Straight CO₂ is the cheapest and penetrates deepest. Argon-rich blends with 2-10% CO₂ or O₂ enable spray transfer for faster welding on thicker plate.
Stainless steel
Use argon with 2% CO₂ or O₂ for MIG to limit carbon pickup. Tri-mix with helium gives hotter, better wetting short-circuit welds. TIG uses pure argon, and austenitic grades can use argon with a small hydrogen addition.
Aluminum
Pure argon for MIG and TIG; add helium for thick sections.
Short-circuit, globular and spray transfer
The gas decides which metal transfer modes are available. Above roughly 80% argon, the arc can reach spray transfer at high current, with almost no spatter. With high CO₂ content you are limited to short-circuit and globular transfer.
Frequently asked questions
What is the best shielding gas for MIG welding mild steel?
75% argon / 25% CO₂ (C25) is the best all-round choice: stable arc, low spatter and good appearance. Use 100% CO₂ when cost and penetration matter more than bead appearance, and 90/10 Ar/CO₂ for spray transfer on thicker plate.
What gas do you use for MIG welding aluminum?
100% argon. For thick aluminum, a 75% argon / 25% helium blend gives a hotter arc and deeper penetration.
Can I TIG weld with CO₂?
No. TIG welding needs an inert gas, normally 100% argon, because CO₂ would destroy the tungsten electrode. Argon-helium blends are used for more heat.
What shielding gas flow rate should I use?
For MIG welding indoors, 12-18 L/min (25-35 CFH) is typical, TIG uses 7-12 L/min (15-25 CFH). Increase flow slightly for drafts, but excessive flow causes turbulence that pulls air into the weld pool.
Do flux-cored wires need shielding gas?
Gas-shielded flux-cored wires need 100% CO₂ or an Ar/CO₂ blend. Self-shielded wires carry their own shielding flux and need no gas, which suits outdoor work.
More welding tools
- Welding Calculator - Settings, heat input, filler weight, cost, carbon equivalent, duty cycle and unit converter.
- Fillet Weld Strength Calculator - Throat, allowable load, safety factor and required leg size per AWS D1.1.
- Welding Electrode Selector - Compare stick electrodes by position, power source and application, with amp ranges.
- Welding Amperage Chart - Settings tables by material thickness for every process, in mm and inches.