Fundamentals of MIG: What Gas is Used For MIG Welding

Welding Gas tank, what gas is used for mig welding

When creating the perfect MIG gun there is a lot for you to consider. From what torch to select to what gas to use, you need to determine which is best for your application.

So in this article, we are going to discuss:

  • What is shielding gas?
  • Types of gas
  • What gas is used for MIG Welding?
  • Consumables to select

Let’s dive in!

What Is Shielding Gas?

MIG welding with shielding gases produces cleaner and faster welds and removes the need to frequently stop to replace electrodes like you would in stick welding. Reduced clean-up and increased efficiency also come with using shielding gases, but it helps to understand the role these gases play in the welding process, as well as what gas is used for MIG welding and their specific properties.

The main intent of using a shielding gas is to avoid exposing the molten weld pool to the oxygen, hydrogen, and nitrogen in the air around you. Various problems can arise from the reaction of these elements in the weld pool, including excessive spatter, and holes in the weld bead, known as porosity, that results in weaker welds.

Technically, when carbon dioxide or oxygen is used, it is no longer MIG, or Metal Inert Gas, welding. It is then MAG, or Metal Active Gas, welding. This is because neither carbon dioxide nor oxygen is an inert gas. MIG welding utilizes inert shielding gases, such as helium or argon, whereas MAG uses active gases instead.

Types of Gas

The choice of gas depends on several factors, including the type of metal being welded, the desired welding characteristics, and cost considerations. Welding procedures and industry standards provide guidelines for selecting the appropriate gas or gas mixture for a specific welding application.

Inert Gases

Inert gases, such as argon and helium, do not readily react with external elements like oxygen and nitrogen. They are chemically stable and provide excellent shielding properties in welding. Argon is the most commonly used inert gas in welding applications due to its affordability and effectiveness.

Helium, although more expensive, is sometimes used for specific applications that require higher heat input. Inert gases create a stable arc, minimize spatter, and protect the weld pool from atmospheric contamination, resulting in high-quality welds.

Active Gases

Active gases, also known as reactive gases, have the ability to react with external elements during the welding process. These gases can affect various aspects of welding, including arc stability, weld penetration, and spatter generation. Active gases are typically used with ferrous metals like steel.

Carbon dioxide (CO2) is a common example of an active gas used in welding. When used in small quantities, it can enhance weld penetration and increase the welding speed. However, excessive use of active gases can lead to issues such as increased spatter and decreased weld quality.

Semi-Inert Gases

Semi-inert gases, like carbon dioxide, exhibit properties of both inert and active gases. They partially react with the weld pool and external elements, making them classified as active gases. Carbon dioxide is commonly used as a shielding gas in welding, often in combination with argon. Keep reading to learn more about how it is used in MIG welding.

Choosing the Right Gas: What Gas is Used for MIG Welding?

Different gases play different roles in the welding process, from weld penetration to arc stability to the finished weld itself. Choosing the consumables that provide continuous and even gas delivery is also a very important aspect to consider in your MIG welds.

Be sure to evaluate your project goals in order to select the right gas for the weld at hand. Things to keep in mind when selecting include:

  • Cost
  • What preparation entails
  • The base material you’ll be welding
  • The finished weld properties
  • What needs to be done for post-weld clean-up

The four most common shielding gases used in MIG welding are carbon dioxide, argon, oxygen, and helium. Each has its unique benefits, and drawbacks, in any given implementation.

Of course, it is always a good idea to consult with your supplier for recommendations on gases that match the welding wire you’ll be using. You can even consult with the wire’s manufacturer for suggestions too. They will most likely provide several options, ranging from the best gas option to gas that will provide the minimum acceptable welds, as well as their prices. However, your MIG welder may have an electrode and gas recommendation guide on the inside panel which will provide you with a list of several options.

Carbon Dioxide (CO2)

CO2 is, by far, the most common and is one of the only gases that can be used in its pure form without needing the addition of inert gas, such as argon or helium. Because of this, CO2 is the most cost-effective option and a good choice if project costs are a priority.

Pure CO2, also known as 100% CO2, provides a deep weld penetration, making it handy when needing to weld thick materials. That being said, pure CO2 is limited to only the short circuit welding process and produces a less than stable arc as well as more spatter than when it is combined with other gases (also known as ‘mixed gases’).

Pure CO2 is good for projects where the aesthetics of the weld are either not important, or the weld cannot be seen, such as on the underside of a car. Post weld clean-up is also a little more involved.


Argon allows for narrower penetration, which is handy for butt and fillet welds. It also boasts a smooth and relatively fluid arc. If you are going to be welding non-ferrous metals, like titanium, aluminum, or magnesium, you’ll need to use pure argon. Mix argon with hydrogen, helium, or oxygen. This helps intensify arc characteristics and aid in metal transfer.

what gas is used for mig welding

Mixed Argon Gases

If weld quality and aesthetics are important, mixed gases are good to use. You have several options that vary from between 75-95% argon to 5-25% CO2. Argon is an inert gas, meaning it does not readily react with other substances, while carbon dioxide is a semi-inert gas. The combination of these gases creates an effective shielding gas that protects the weld zone from atmospheric contamination.

They produce better arc stability and reduce spatter compared to 100% CO2. Mixed gases can also be used in the spray transfer process that, in turn, provide more visually appealing welds as well as increased productivity.

Argon/CO2 mixtures are good for welding low-alloy, some stainless steel, and carbon metals. Be aware, however, that higher CO2 levels may cause increased spatter. The specific composition of the shielding gas can vary depending on the metal being welded and the desired characteristics of the weld.

For example, when welding stainless steel, a mixture of argon and helium may be used to improve heat transfer and penetration. Aluminum welding often requires a pure argon gas or a mixture of argon and helium.

C25 Gas

A commonly used gas referred to as “C25” or “75/25” gas indicates that it contains 75% argon and 25% carbon dioxide. If you’re wondering what gas is used for MIG welding, this mixture would be your best bet. It is often considered the best choice for a number of reasons, including its versatility, arc stability, and weld penetration.

The argon component of the C25 mixture helps maintain a stable welding arc, resulting in smooth and consistent welds. It allows for better control over the weld puddle, especially in manual welding applications.

Also, the argon component of the C25 mixture helps maintain a stable welding arc, resulting in smooth and consistent welds. It allows for better control over the weld puddle, especially in manual welding applications. With its improved weld penetration, it is especially beneficial for welding thicker materials.


A reactive gas, oxygen is typically only used in small amounts when added to shielding gases, usually between 1-9%. This improves weld pool fluidity, as well as arc stability and penetration in stainless steel, mild carbon, and low alloy metals. Oxygen with aluminum, copper, magnesium or other exotic metals can cause oxidation.

Oxygen/argon blends are typically used on stainless steel and plain carbon metals. It produces a stable arc with limited spatter. Higher levels of oxygen, however, may make out-of-position welding hard due to the fact that it will increase puddle fluidity.

Oxygen-Enhanced Shielding Gas

In some cases, a small amount of oxygen may be intentionally introduced into the shielding gas mixture, particularly when welding certain metals like stainless steel or aluminum. This controlled addition of oxygen is known as oxygen-enhanced shielding gas. The oxygen content is carefully regulated to promote desirable oxide formation on the surface of these metals, which can improve the appearance and corrosion resistance of the weld.

Oxygen can cause the formation of oxides, which can reduce the mechanical properties and overall strength of the weld. Therefore, maintaining a controlled environment with minimal oxygen content is essential for producing high-quality welds.


Generally used on non-ferrous metals, helium can also be used on stainless steel. It works well with thick metals due to its wide and deep penetration abilities.

what gas is used for mig welding

It is usually used in ratios of 25-75% helium to 75-25% argon. By adjusting these ratios, you can alter the penetration and bead profile. When used on stainless steels, helium is usually used in a tri-mix gas combination with CO2 and argon. Helium is also used to prevent oxidation during the welding of metals like stainless steel, aluminum, magnesium, and copper alloys.

Helium does create a hotter arc, which provides faster travel speeds and, thus, increased productivity. That being said, helium is more expensive and does require a higher flow rate than argon does. Weighing out the value of the cost of the gas against productivity rates is important to keep in mind when considering using helium.

Other Gases

Hydrogen serves as a shielding gas in high-temperature applications, such as stainless steel. It is often mixed with argon for use on austenitic stainless steel.

Nitrogen is used as a purging gas for welding stainless steel tubes. Added to argon in small amounts, it can also be used as a shielding gas for stainless steel.

Propane is typically used in scrap yards for cutting carbon steel where cut quality is not important. If your application does not require high-cut quality, propane is a rather cost-effective option.

Choosing Consumables

What consumables you attach to your MIG gun are just as important as selecting the correct gas to use. The diffuser, contact tip, and nozzle all play an important role in making sure the weld pool is adequately protected from the air around you.

If your diffuser is clogged with any spatter or if your nozzle is too narrow, you run the risk of too little shielding gas getting out to protect the weld pool. This allows pockets of air into the gas, which can lead to spatter, porosity, and even contaminated welds.

Ensure you are selecting MIG gun consumables that can resist the build-up of spatter. You also have a wide enough nozzle bore to be confident in your shielding gas protection.

Some manufacturers make nozzles with a built-in spatter guard. This can double your gas diffusion, which will give you a much more consistent gas flow. The selection of your consumables does demand careful evaluation of the pieces. As well as the project at hand, and your operational priorities.

Get High-Quality Consumables with American Torch Tip

Now that you know what gas is used for MIG welding, it’s time to select the perfect gas diffuser. If you need a gas diffuser or nozzle for your MIG gun you have come to the right place. We have a wide selection of quality consumables and parts to help you achieve clean cuts.

Contact us or call 800-342-8477 to learn more about our most durable MIG welding parts, torches & guns.

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