Welding Reference Library · Gases & Cylinder Safety

Argon and Argon Mixes

Argon is the base shielding gas for TIG welding and for most MIG welding. Adding CO2, oxygen or helium changes the arc, penetration and bead shape, and each common mix has a typical job.

Ref WG-0404AWS A5.32

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

What it is

Shielding gas keeps air away from the molten weld pool. Argon is inert, easy to ionize and gives a stable arc. On its own it is used for all TIG welding and for MIG welding aluminum and other non-ferrous metals.

For MIG welding steel, pure argon gives a narrow, unstable transfer. Small additions of an active gas fix this:

CO2 adds heat and broader penetration and stabilizes short-circuit transfer.
Oxygen in small amounts stabilizes the arc and improves wetting in spray transfer.
Helium adds heat and wider penetration. See the Helium and Helium Mixes sheet.

Mixes are named by their percentages, argon first unless noted. "75/25" means 75% argon and 25% CO2.

Common mixes

Mix	Common name	Typical use
100% argon	Pure argon	All TIG welding; MIG on aluminum and non-ferrous
75% Ar / 25% CO2	C25, 75/25	Short-circuit MIG on carbon steel; good for thin and general work
90% Ar / 10% CO2	90/10	Spray and pulsed MIG on carbon steel
98% Ar / 2% O2	98/2 oxygen	Spray MIG on stainless and carbon steel
98% Ar / 2% CO2	98/2 CO2	Spray and pulsed MIG on stainless
95% Ar / 5% O2	95/5	Spray MIG on carbon steel
90% He / 7.5% Ar / 2.5% CO2	Tri-mix	Short-circuit MIG on stainless

Blends vary by supplier. Check the cylinder label and the wire maker's recommended gases.

How to use it

Match the gas to the base metal, process and transfer mode. See the Shielding Gas Selection Chart.
Check the wire classification. Some flux-cored wires are classified with a specific gas.
Set the flow rate per the welding procedure or wire maker, and check it with a flowmeter.
Use a regulator and hoses rated for the gas.

Key points

Higher CO2 content gives more spatter and deeper penetration; higher argon gives smoother beads and less spatter.
Oxygen-bearing mixes are not used on aluminum.
Stainless steel is sensitive to CO2 content. Too much carbon pickup affects corrosion resistance. Follow the filler maker's gas list.
Gas changes can affect weld properties. Coded work must use the gas named on the WPS.
Argon is heavier than air and can displace oxygen in tanks, pits and small rooms. Ventilate.

Common mistakes

Using 75/25 to TIG weld. TIG needs inert gas.
Using 100% CO2 settings with a mixed gas, or the reverse.
Changing gas on coded work without requalifying.
Leaving cylinder valves open in a closed space.

Governing standards: AWS A5.32 (welding shielding gases); ISO 14175 (shielding gas classification); the WPS and the filler metal maker's data.

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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