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MIG Welding With 100% Argon Shielding Gas

Running out of MIG gas in the middle of a project is a problem most welders will eventually face.

Since many of us also have a tank of pure Argon on hand for other types of welding, would MIG welding with 100% Argon on mild steel allow you to finish your project without a trip to the gas supplier?

Or, is it possible to MIG weld with Argon alone, and get by with using 100% Argon welding gas for all your MIG and TIG work?

In this article:

MIG Welding with 100% Argon Shielding Gas

Can I MIG Weld Steel Using 100% Argon Gas?

As a hobby welder, I keep one bottle of C25 gas and another of 100% Argon for aluminum MIG work. Once a MIG bottle gets low, it’s impossible to know how long the gas will last.

When starting a new project with a low cylinder, my options are: risk running out mid-project, choose to invest in another bottle of C25, or trade-in the not-completely empty cylinder for a full one.

Not liking those choices, I looked into MIG welding with 100% Argon as an option.

I found that, yes, 100% Argon can be used to MIG weld steel, but expect a weak, brittle, and unattractive weld bead.

Diagram showing weld bead when MIG welding with 100% Argon compared to a blended MIG shielding gas.
MIG weld bead profile of 100% Argon (top left) compared to MIG mix (bottom right).

Using 100% Argon gas for MIG welding doesn’t provide enough thermal conductivity for a fluid weld pool on ferrous metals. The outer edges of the arc remain cool, resulting in a tall and narrow penetration profile with minimal fusion, along with an undercut that further weakens the weld.

MIG welds using 100% Argon shielding gas on mild steel are known for losing ductility, which causes brittleness.

MIG Welding with Argon

I will use 100% Argon to MIG weld steel as long as:

  • Weld appearance is not important
  • No one will get hurt if the weld fails
  • A failed weld won’t otherwise cause a world of trouble for me

Also consider that with more spatter and an erratic arc, on top of a stiff weld puddle, welding with pure Argon is not enjoyable. For regular use, MIG welding with Argon alone is not a suitable replacement for MIG-mix shielding gas.

There’s plenty of talk on the forums from others who have had success MIG welding with pure Argon shielding gas, and I found these tips:

  • It’s natural to want to turn up the heat when you see the high, narrow, cold-looking welds. But with the narrow penetration profile of pure Argon, you’re likely to burn through thin materials before the bead flattens out.
  • Bevel your joints to achieve better fusion for stronger welds.

More about pure Argon shielding gas:

  • Atomic symbol: Ar
  • They harvest pure Argon from the atmosphere in air separation plants.
  • Easily displaces air from above because it’s denser and heavier than air.
  • Because it’s chemically inert, 100% Argon does not react with other materials.
  • Argon is insoluble in molten metal.
  • Promotes the spray transfer process.
  • It’s easy to ionize, so Argon enables longer arcs at lower voltages and is not sensitive to changes in arc length.
  • Used alone mostly on non-ferrous materials such as aluminum, copper, magnesium, nickel and their alloys.
  • Performance on steel improves when Argon is blended with active gases such as carbon dioxide, helium, or oxygen.

Here’s a welding instructor MIG welding with straight Argon shielding gas (13 min.):

Is there really any doubt about how Bob feels about pure Argon MIG welds?

Of course, he’s a professional responsible for teaching and maintaining the highest of welding standards. But he also has the experience and resources to make that happen.

Me? Sure, sometimes I want pretty welds (I’d settle for more of my welds to look like the ones Bob described as “Blah!”). But more often, I need to finish the job using what I have on hand.

What Else Can You MIG Weld with 100% Argon Gas?

Straight Argon is an excellent shielding gas for MIG welding aluminum.

And because of its purity and low moisture content, 100% Argon is also a suitable shielding gas for MIG welding other non-ferrous metals:

  • Copper under ⅛” (including alloys)
  • Nickel under ⅛” (including alloys)
  • Magnesium
  • Titanium

Helium, with its higher thermal conductivity (and cost), is often blended with pure Argon for use on thick non-ferrous materials.

Ductility is the capability of a metal to be permanently bent, twisted, or otherwise manipulated without breaking or cracking.”

Tusla Welding School

How About MIG Welding Stainless Steel With 100% Argon?

Stainless steel gets its corrosion-resistant properties through the addition of chromium and nickel alloys. These alloys reduce the weldability when using MIG with 100% inert shielding gases.

MIG welding stainless steel with 100% Argon shielding gas produces poor welds and is not recommended.

Adding even a small amount of active gas to pure Argon, as in a 98%Ar/2%O2 or 98%Ar/2%CO2 blend, will improve the arc and bead characteristics.

For best results, use a tri-mix blend of 90%He/7.5%Ar/2.5%CO2 when MIG welding stainless steel.

MIG welder and cylinder of Argon sheliding gas

CO2 Blends Perform Better Than Pure Argon to MIG Weld Steel

At low temperatures, CO2 is an inert gas. But at welding temperatures, CO2 becomes reactive and its cleaning action improves.

When added to pure Argon welding gas in small amounts, usually 5 to 25%, CO2 helps to stabilize the welding arc. With an Argon/CO2 MIG mix, you’ll get a more fluid weld pool with improved penetration on steel, along with reduced weld spatter.

With too much CO2, the arc becomes rough, and the amount of spatter increases. When MIG welding with 100% CO2, the strong penetration characteristic becomes harder to control on thin metals.

You’ll find Argon/CO2 blends labeled according to the percentage of CO2 gas in the mix. C25 is a mixture of 25% CO2 with 75% Argon and is the most widely used MIG mix.

TIG Welding with 100% Argon is More Effective on Steel

Shielding gases have different jobs in different processes.

In MIG welding, where the consumable filler material forms the electrode, the metal transfers across the arc to the weld. While with TIG welding, we feed the filler metal into an arc established between the material and the tungsten electrode.

TIG welding benefits from a shielding gas that remains 100% inert at welding temperatures, and pure Argon fits the bill. When used in TIG welding, Argon promotes easy starting, stable arcs, and keeps the non-consumable tungsten electrode clean.

Related: What Size Welding Gas Cylinder for MIG or TIG?

The bottom line

In a pinch, you can use straight Argon gas for MIG welding steel, but an Argon/CO2 blend is a better choice.

As with all project materials, it’s our responsibility to choose a fastening method suitable for the intended use of the finished project. This is true whether using screws, staples, adhesives, or welding.

The next time you’re caught short on MIG shielding gas, go ahead, try MIG welding with 100% Argon. Just know that your welds may be weak and brittle. Use sound judgment and test your work so that no one gets hurt.

Photo of author
Dave Jones
Dave began welding to repair equipment used in his small business. Now as a hobby, he enjoys researching, testing and writing on welding topics. Other interests include photography, RVing and just about anything to do with dogs—especially retrievers. Reach him at [email protected].