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Gas Basics for MIG Welding

Date: 16-03-2023

Gas Basics for MIG Welding - Alphaweld Insights

The shielding gas selection for MIG welding has a strong effect on the produced weld. Choosing an inadequate welding gas for your application can produce undercut, burn-through, and spatter and negatively impact your welding efficiency

Ferrous and non-ferrous metals have different shielding gas needs when MIG welding. Not only does the welding gas protect the weld from the atmosphere, but it impacts the metal transfer rate, weld contour, welding speed, and molten pool fluidity. In this article we’ll cover the most commonly used MIG shielding gasses and help you make the right choice.

The Two Welding Gas Types

Two shielding gas types are employed for arc welding: inert and reactive. Some metals must be welded with inert gasses, while others benefit from adding reactive gasses to the gas mixture.

Inert Shielding Gasses - The two inert gases used for welding are argon (Ar) and helium (He). These gasses do not react with the welded metal. You must weld non-ferrous metals with pure inert gasses or their mixtures, but they also play a key role in welding ferrous metals.

Reactive Shielding Gasses - Oxygen (O2) and carbon dioxide (CO2) are the most commonly used reactive shielding gasses. They amplify arc stability and penetration when added to inert gasses like argon. Reactive gasses can only be used for welding carbon steel, stainless steel, and low-alloy steel.

MIG Welding Shielding Gas Selection

The exact proportions of shielding gas mixtures depend on the welded metal and the desired finish quality. While inert and reactive gasses can be principally separated as shielding gasses for non-ferrous and ferrous materials, the nuances of their use make all the difference.

MIG Shielding Gas Selection Based On Welded Material
Metals Shielding Gas Choices
Carbon Steel

100% CO2
(Deep penetration)

75% Ar + 25% He
Stainless Steel 75% Ar + 25% He
(May lose corrosion resistance)
10% Ar + 85-90% He + 2-5% CO2
(Optimal results)
Aluminium 100% Ar

Ar + 25, 50, or 75% He
(Deep penetration)

Magnesium 100% Ar

Ar + 25, 50, or 75% He
(Deep penetration)

Nickel Alloys 100% Ar

Ar + 25, 50, or 75% He
(Deep penetration)


Mild Steel

The mixture of 75% argon and 25% CO2 is the most popular shielding gas type on the market, often referred to as the ‘MIG gas’ because it’s used to weld mild steel.

You shouldn’t use 100% argon to weld carbon steel because this material has uneven iron oxides on its surface. These oxides attract the arc in the pure argon gas environment, resulting in irregular arc movement. However, adding either CO2 (10-25%) or oxygen (1-3%) produces an even iron oxide film on the surface for the arc to follow, which improves arc stability.

Using 100% carbon dioxide to MIG weld carbon steel is also possible. But, the arc may get too erratic without the argon’s ionisation potential. However, pure CO2 provides very deep penetration and costs less than argon blends.

Stainless Steel

Stainless steel alloys can be very challenging to work with. While you can use the same 75% argon and 25% CO2 welding gas mixture to weld stainless steel, the CO2 may diminish its corrosion resistance. So, consider the required finish quality before employing the same 75/25 gas you would use for MIG welding mild steel.

The best shielding gas for MIG welding stainless steel is the popular ‘tri-mix’ gas. It’s a helium-based mixture with argon and CO2. Industry-standard mixtures are 85-90% helium, 5-10% argon, and 2-5% CO2.


To MIG weld aluminium, you must use either pure argon gas or a mixture with helium. Don’t attempt to weld aluminium with reactive shielding gasses. Even a small addition of oxygen or carbon dioxide will ruin the weld. 

Helium creates a similar effect for aluminium as CO2 for steel. It amplifies penetration and welding speed, but it slightly reduces arc stability. Consider adding up to 50% helium to argon when welding thick aluminium parts or if your MIG welder doesn’t have enough amperage to weld thick aluminium.

Selecting Your Shielding Gas Regulator

There are two types of gas regulators: CO2 and argon regulators. CO2 regulators are designed specifically for 100% CO2 gas tanks, while argon regulators are intended for use with argon/CO2/helium mixtures. Therefore, you cannot use an argon-type regulator with a 100% CO2 gas bottle. They work only with pure argon gas and argon blends.

The Harris 801 Argon Flowgauge Regulator is a high-quality regulator sufficient for most workshops. But, the Harris 825 Argon Regulator offers more precise gas readings on its large gauges.

If you wish to use pure CO2, the Harris 801 CO2 Flow Regulator is a great choice for most jobs. But, since CO2 is a very cold gas, we recommend the Tesuco Heat Sink CO2 Regulator for maximum freezing resistance at high flow rates.

Need Help Choosing Your Gas Equipment?

Shielding gas selection is a crucial step before MIG welding. If you have more questions about shielding gasses or how to choose a gas regulator, Alphaweld is here for you. 

To speak with our team, give us a call on (08) 9456 8000 or get in touch and our experts will gladly assist you.