Why You Can’t Use the Same Gas for MIG and TIG Welding?

Last Updated on June 10, 2020 by Gary Hargrave

When it comes to shielding gases for MIG and TIG welding, we’re actually talking about active and inert gases, the former for MIG welding, and the latter for TIG welding. Over the years, I’ve learnt a few things about them. I tell you what, for some reasons, you cannot use them interchangeably.

So why we can’t use the same gas for MIG and TIG welding? The use of an inert gas for MIG welding often results in a narrow and tall weld bead with an undercut that weakens the weld. An active gas for TIG welding may cause oxidation and bad weld, and quick burnout of the non-consumable tungsten electrode.

As you know welding processes require gases which affect the arc stability, welding speed, heat transfer characteristics, penetration, and hence the weld quality, we cannot use them randomly. For example, carbon dioxide (CO2) comes on top of other reactive gases for MIG welding, whereas argon is an undisputed choice for TIG welders.

You shouldn’t just switch them because the output won’t probably be what you would desire. Let me give you a simple explanation.

Reasons Why Argon Is Good for TIG Welding

TIG welding requires a shielding gas to protect the tungsten electrode from hydrogen, nitrogen, and oxygen which may cause contamination to it. Also, a controlled distance between the electrode and the metal being welded is to be maintained.

These particular settings demand a controllable, stable arc which is something argon helps you with, keeping your weld environment sufficiently inert. Thus, argon comes on top of other gases for the process.


Reasons Why Pure Argon Is NOT Good for MIG Welding

I’ve seen people using argon for many of their MIG welding projects without mixing any constituent. It is okay but only when you can accept an imperfect weld bead. Would you like a tall, narrow weld bead that has an undercut only to reduce its ductility and solidity? I guess brittle welds aren’t good either.

I can’t help passing a warning. By using an inert gas like argon, you’ll put your welding machine to rigorous uses because proper penetration requires much higher power output.

Now, I’m bringing carbon dioxide into the discussion to help you understand why this particular gas is effective for MIG welding, and not as much for TIG welding.

Carbon Dioxide is a big NO for TIG welders.

Metals that are used in the TIG process are vulnerable to oxidation in the presence of certain chemicals or substances, such as air, hydrogen, oxygen, and water.

If any of these exists in the atmosphere where you’re working, they may interact with your weld puddle and result in welding defects like brittleness, carbide precipitation, cracks, and loss of corrosion resistance.

Being an active gas, CO2 raises the arc voltage and increases blowhole porosity. It can also cause the non-consumable tungsten electrode to burn too much.

CO2 is an attractive choice for MIG welders.

Carbon Dioxide is the only reactive gas that you can use without mixing with an inert gas. In its vapor form, CO2 provides pretty deep penetration, one of the desirable benefits you want to have while welding some thick materials. However, the usability of this gas takes a rather reverse turn when you use it on thin materials.

I think you already have a good idea about the topic being discussed. Well, whatever I’ve told so far is all about 100% argon or carbon dioxide. Apart from these gases, only helium is usable without mixing anything, but that’s restricted to seam works. Also, you shouldn’t do this on steel because you’ll have to deal with a lot of spatters.

But I can tell you that the world of welding wouldn’t be able to come this far if not for the mixtures of different shielding gases. At this point, I would like to talk about some of the most useful combinations which produce far better outputs than either of the above gases alone can do.

Some mixtures work wonder on steels while others are simply great for aluminum and alloys. So, I’ll help you figure out –

which combination  of gases to choose for which material

1. Stainless Steel

If your project involves stainless steel and a lot of welding work, you are likely to see that the weld is really good and so is the surface finish. Like most welding experts, I always choose argon when I want to TIG weld stainless steel. The grade is not very relevant because all you need is a stable arc, which argon takes care of.

Some gas mixtures can be used too. Argon with hydrogen makes a good choice for austenitic steel while argon with nitrogen works well for duplex types. Being present in a mixture, hydrogen scavenges oxygen around the weld pool and helps you get a clean surface which saves you the hassles of cleaning the weld.

As you develop interests in MIG welding stainless steel, you need to remember that the metal comes with a sluggish weld bead. Having some experience in this particular matter, I count on a helium-based gas mixture that contains 90%, 7.5%, and 2.5% (Helium, Argon, and CO2). What’s the benefit?

Helium features high thermal conductivity that allows you to achieve good fusion into your base plate and a flatter weld bead. Thus, it helps counteract that sluggish bead properties. But the cost of this mixture is considerably high.

For a more affordable option, you can try another mix that contains argon and oxygen or carbon dioxide (98%/2%). This will result in a weld colder than the one produced by the helium-based mixture. This coldness doesn’t allow the molten weld pool to wet out, but you can still go ahead with the weld profile.

2. Steel (Carbon and Low Alloy)

You may have discovered that MIG welding works best on some steels like low alloy and carbon. You want to use mixtures of argon and one of the active gases, such as carbon dioxide or oxygen. I can’t point out the exact amount of those active gases in the mixture because it depends on your preferred application. But 75%Ar/25%CO2 makes an ideal combination where weld penetration has to be really good and you need effective wetting characteristics of the weld bead.

You can find some uses for your TIG welding skills too. Sometimes, you may want to make joints maintaining high precision, or an almost flawless surface finish is what you need. Using argon as the only gas, you can initiate the arc easily but chances are that you may not like the welding speed. Well, here’s a piece of advice.

Mix helium with argon to achieve a greater speed with improved penetration and fusion as the bonus. Helium might be required in a higher volume in the mixture if you’re about to weld materials with thick sections.

3. Non-Ferrous Alloys (Aluminum, Titanium, and Copper)

While some might prefer TIG to MIG welding on these alloys, many would say otherwise because both processes are okay depending on what you’re doing and which gas or mixtures you’re using.

I guess it is the only area where you can use the same gases for both welding tasks. There are three choices, such as pure helium, pure argon, and mixtures of these gases in varying proportions.

For aluminum, or copper, or other alloys, only argon can be good, but if it is thicker than 0.5 inch, you’ll need greater heat penetration, and here comes the mixture of helium. This time, I’ll tell you about some useful gas mixtures, all containing argon, and helium.

  • 75% Argon and 25% Helium: It is a common mixture that provides the best results when used on copper alloys.
  • 70% Argon and 30% Helium: Check the thickness of the section of the metal being welded. If it is thin or moderately thick (1/2 inch), this mix will provide you an improved fusion profile with increased heat penetration. The job of helium here is to minimize the defect rates and thus lower porosity levels.
  • 60% Argon and 40% Helium: It results in good penetration with a fluid weld pool, but you should do it on nickel alloys only.
  • 50% Argon and 50% Helium: For metals with even thicker sections, I prefer a mix of these gases in an equal amount to an argon-based mixture. Besides a fluid weld pool, you’ll achieve better penetration and fusion, needless to say lower defect rates. I like this gas mixture for one more reason that it requires no preheating efforts.
  • 30% Argon and 70% Helium: Fluid weld pool, excellent penetration, and fusion are some of the benefits of this mixture. But I wouldn’t use it unless the metal has a lot of sections that are very thick.

Final Words

Maybe, you’ve figured out the fact that there are many choices for MIG projects. For example, argon mixed with carbon dioxide (proportion may range from 5% to 25%) provides wonderful results and makes for considerable welding efficiency.

Also, argon with oxygen (1% to 5%) or tri-mixes containing argon, carbon dioxide, and helium are ideal for projects that involve different types of spray arc welding tasks.

However, you’ve only a few gases and blends for TIG welding. So, be thoughtful about the gas you’re going to use for a TIG project.

I hope you’ve got the answers you wanted. Got more questions or anything to share with me? I would appreciate your messages. Safe welding!

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