Argon vs Argon/CO2 Mix: Which Welding Gas for Which Job

Every MIG and TIG welder in Australia faces this decision, and the wrong choice means porous welds, wasted gas money, or both. This guide settles it with the actual science, the Australian prices, and the practical answer for your workshop.

The Short Answer

Use pure argon for:

Use argon/CO2 mix for:

The percentages matter. The most common Australian mix is 93% argon / 7% CO2 (often sold as "Argoshield Light" or equivalent), which works for most steel MIG welding. Heavier fabrication may use 82% argon / 18% CO2 for deeper penetration on thicker material.

• TIG welding (any material)
• MIG welding aluminium
• MIG welding stainless steel (with specialist blends)
• MIG welding mild steel
• MIG welding carbon steel
• Flux-cored wire that specifies gas-shielded operation

Why the Difference Matters

argon is a noble gas — it doesn't react with anything. That makes it perfect for:

The trade-off: pure argon produces a narrower, more focused arc on steel. For MIG on mild steel, this means less penetration and a narrower weld bead — not ideal for structural work.

Adding CO2 to argon changes the arc characteristics:

The Australian standard mixes:

• TIG welding: The tungsten electrode needs a completely inert atmosphere. Any CO2 would contaminate it and destroy the electrode.
• Aluminium MIG: Aluminium forms an oxide layer instantly when exposed to air. Pure argon's cleaning action breaks through this layer. CO2 makes aluminium welding impossible.
• Stainless TIG: The chromium in stainless steel reacts with CO2, degrading corrosion resistance.
• Wider, hotter arc: CO2 is reactive — it breaks down in the arc, adding thermal energy. The result is deeper penetration and a wider bead profile.
• Better wetting: The molten pool flows more smoothly, reducing undercut on edges.
• More spatter: The downside. Higher CO2 percentages mean more cleanup.
• Cheaper: CO2 is significantly less expensive than argon, so mixes cost less per refill.

Australian Gas Prices (Observed August 2026)

Based on our live gas price tracker — the first structured pricing data available for Australian welding gas:

*Traditional rental pricing uniform across BOC, Supagas, Air Liquide, and Coregas per government panel contract (WA CUA GAS2023, verified September 2025).

Important: Coregas is owned by Nippon Sanso Holdings (Supagas' parent), not BOC as commonly assumed. BOC acquired the Coregas *industrial* business only in some markets — the Australian consumer gas business (Trade N Go at Bunnings) operates under Nippon Sanso.

All prices from our live gas price tracker — the only structured pricing data available for Australian welding gas. Confidence ratings per data point.

For the full rent-vs-buy-vs-swap analysis, see our complete gas buying guide.

Bottle Sizes: How Long They Last

At 10L/min flow rate (standard for MIG), a D bottle lasts roughly 4 hours of trigger time. If you're welding 2 hours per weekend, a D bottle is about 2 months of welding.

The Decision Tree

1. Welding aluminium? → Pure argon. No exceptions.

2. TIG welding anything? → Pure argon. CO2 destroys tungsten electrodes.

3. MIG on mild steel under 6mm? → argon/CO2 mix (5-12% CO2).

4. MIG on structural steel over 6mm? → argon/CO2 mix (12-18% CO2).

5. MIG on stainless steel? → Specialist mix (usually argon + helium + CO2). Check the wire manufacturer's spec.

6. Only welding occasionally? → Consider gasless flux-cored wire instead. See our gasless MIG guide.

Common Mistakes

Using pure argon for MIG on steel. It works, but you get a narrow, tall bead with poor wetting. It's like using a scalpel where you need a paintbrush. The weld will be mechanically sound but cosmetically rough and slower to lay down.

Using too much CO2 for thin material. High CO2 percentages burn through thin sheet. If you're welding car panels, stay at 5-8% CO2 or lower.

Not checking your regulator. argon and argon/CO2 mixes use different regulator fittings in some cases. Using the wrong regulator can be dangerous and wastes gas.

Buying a G-size bottle for home use. If you're welding 2 hours a month, a G bottle's rental will cost you more per welding hour than paying a fabricator to do the job. Our bottle size and price guide has the full math.

What the Machine Manufacturers Say

Most MIG welder manuals specify a gas type and flow rate. UNIMIG, Cigweld, and Kemppi all publish gas requirements per model. Check your machine's spec before buying gas — some synergic machines have gas-specific programs that won't run correctly with the wrong mix.

Our machine database includes gas requirements for every tracked model.

Frequently Asked Questions

Can I use pure CO2 for MIG welding?

Yes, but expect significantly more spatter and a rougher bead. CO2-only is the cheapest option but requires more cleanup. Most welders find the extra cost of an argon-mix/">argon mix is worth the reduced finishing time.

Can I mix my own argon and CO2?

Technically possible with the right equipment, but dangerous and unnecessary. Pre-mixed bottles are available from all major suppliers and the mixing ratio is precise.

How do I know when to switch from mix to pure argon?

The moment you weld aluminium or use TIG. If you're only doing steel MIG, you never need pure argon.

Is BOC the only option?

No. Supagas, Air Liquide, and Coregas all supply welding gas in Australia. We're building a price comparison across all suppliers. BOC is the largest but often not the cheapest.

What flow rate should I use?

10-15 L/min for MIG, 8-12 L/min for TIG. Higher flow rates waste gas without improving weld quality. If you're getting porosity with adequate flow, check for draughts in your workspace before turning up the gas.