Learn how to select the right shielding gas for different materials and processes. Discover gas mixtures, flow rates, and their effects on weld quality.
Introduction
Shielding gas protects the weld pool from atmospheric contamination and affects weld quality, penetration, and appearance. At Fulei Metal, we select appropriate gases for each material and process.
Functions of Shielding Gas
Protects molten weld pool from oxygen and nitrogen. Prevents porosity and oxidation. Stabilizes the arc. Affects weld penetration and bead shape. Influences weld appearance and cleaning.
Gas Types
Argon
Inert gas. Suitable for all materials. Standard for TIG welding. Good arc stability. Good cleaning action in AC TIG (aluminum). Limited penetration for MIG on steel.
Helium
Inert gas. Hotter arc than argon. Deeper penetration. Faster travel speed. More expensive. Used in mixtures for thick materials.
CO2
Active gas. Used for MIG on carbon steel. Deep penetration. Low cost. Produces more spatter. Not suitable for stainless or aluminum.
Oxygen
Active gas. Small amounts (2-5%) added to argon. Improves arc stability. Better wetting. Used for MIG on stainless and some steel.
Hydrogen
Reactive gas. Small amounts (1-5%) added to argon. Reduces oxide. Increases heat. Used for TIG on stainless. Never use on carbon steel (cracking risk).
Gas Mixtures by Material
Carbon Steel MIG
100% CO2: deep penetration, more spatter, lowest cost. 75% Ar / 25% CO2 (C25): best all-around, smooth arc, less spatter. 85% Ar / 15% CO2: good for spray transfer. 90% Ar / 10% CO2: for pulsed spray.
Carbon Steel TIG
100% Argon: standard for all TIG on steel.
Stainless Steel MIG
98% Ar / 2% O2: good wetting, stable arc. Tri-mix (90% He / 7.5% Ar / 2.5% CO2): excellent for short-circuit. Never use standard CO2 mixtures.
Stainless Steel TIG
100% Argon: standard. Argon + 2-5% H2: for faster travel and better oxide reduction. Never use hydrogen on carbon steel.
Aluminum MIG
100% Argon: standard for thin materials. 75% Ar / 25% He: for thicker sections, hotter arc. 50% Ar / 50% He: for very thick aluminum.
Aluminum TIG
100% Argon: standard AC TIG. 50% Ar / 50% He: for thick aluminum, more heat.
Flow Rates
TIG
8-15 liters per minute. Too low: porosity, contamination. Too high: turbulence, waste. Larger cups need more flow.
MIG
10-15 liters per minute for indoor work. 15-20 for outdoor or drafty areas. Too low: porosity. Too high: turbulence draws in air.
Gas Quality
Use welding-grade gas (99.996% purity minimum for argon). Moisture causes porosity. Impurities affect weld quality. Verify gas certificates. Use proper regulators.
Back Purging
For full-penetration stainless welds: purge the back side with argon. Prevents oxidation (sugar). Flow rate: 5-10 lpm. Use soluble purge plugs or dams. Critical for food, medical, and corrosive applications.
Conclusion
Selecting the right shielding gas is essential for weld quality. At Fulei Metal, we use appropriate gases and mixtures for each material and process, ensuring optimal weld quality.
Shielding Gas: What Each Mixture Changes, and Where It Backfires
Gas choice is usually inherited rather than chosen. It affects arc stability, penetration profile, spatter and, on stainless and aluminium, the surface condition of the finished weld.
| Gas or mixture | What it does | Where it suits | Where it backfires |
|---|---|---|---|
| Pure argon | Stable arc, narrow penetration finger | TIG on all materials; MIG on aluminium | On steel MIG it gives poor wetting and an unstable arc; it needs a small oxidising addition |
| Argon plus 2-5% oxygen | Low spatter, good wetting, stable spray | Spray and pulsed MIG on carbon steel | Not for aluminium; oxygen is harmful there |
| Argon plus 8-12% CO2 | Good penetration with moderate spatter | Short-circuit and pulsed MIG on steel, general fabrication | Slightly more spatter than low-CO2 mixes |
| Argon plus 18-25% CO2 | Deeper penetration, lower gas cost | Short-circuit MIG on thicker steel | More spatter and higher heat input; a poor choice for thin cosmetic sheet |
| Pure CO2 | Deepest penetration, lowest gas cost | Heavily scaled or thicker steel where appearance does not matter | High spatter, no spray transfer, and poor results on thin sheet |
| Argon plus 25-50% helium | Hotter, faster, wider penetration profile | Aluminium and copper sections where heat is lost quickly | Cost, and helium raises the voltage for a given arc length |
| Argon plus 1-2% oxygen for stainless | Stable spray arc on stainless | Spray and pulsed MIG on austenitic stainless | Hydrogen additions are restricted to fully austenitic welds; they crack ferritic and martensitic grades |
Flow rate matters as much as composition, and it fails in both directions. Too little flow lets air into the shield; too much creates turbulence that draws air in anyway. For sheet metal work, roughly 6-12 L/min for TIG and 12-18 L/min for MIG covers most cases, with the correct value depending on cup size, stick-out and whether there is any draught. The verification is simple: a weld bead that is bright and evenly rippled indicates the shield held, while a dull, speckled or blackened surface means it did not.
Frequently Asked Questions
Can I use the same gas for steel and aluminium?
No. Aluminium needs pure argon, or argon-helium for thicker sections. A CO2-bearing steel mix oxidises aluminium and produces a black, sooty weld.
Why does the weld look fine for the first few centimetres and then turn porous?
Usually the shield is being disturbed after the start, by a draught, by too high a flow rate causing turbulence, or by spatter building up in the nozzle. Check the nozzle and the gas hose before changing anything else.
Is more gas flow always safer?
No. Above the correct range the flow becomes turbulent and aspirates air into the shield, producing exactly the porosity it was meant to prevent. Increasing flow should always be tested rather than assumed.
Questions about a specific part are usually faster to answer against the drawing — send it through the route below.
About these figures. The reference values above come from our own production range; send the drawing for review lists the machines and materials behind them, and common welding defects and prevention explains the adjacent steps that change the result. For your own part, sheet metal welding service is the fastest route to a quote — the earlier we see the drawing, the more of it can still be adjusted without cost. The tolerance context is set out in welding parameter optimisation.