Welding Shielding Gas (What Gases Do MIG Welders Use?)

welding shielding gas

Shielding gases are an essential aspect of MIG welding, also known as metal inert gas welding. Without a gas shield, the innate contaminants found in the atmosphere would cause various quality problems in the resulting weld, including porosity, splatter, and tarnishing.

What gases do MIG welders use? While most MIG welders use a combination of argon, helium, carbon dioxide, and oxygen, other shielding gases are also used, such as hydrogen, nitric oxide, sulfur hexafluoride, and dichlorodifluoromethane. These gases are used as additives to stabilize the welding arc or enhance the quality of the weld.

Learning how to use shielding gases correctly is a crucial part of learning how to MIG weld. Keep reading to find out more about the gases MIG welders use and how they affect welding.

MIG Welding Shielding Gas

MIG welding requires the use of shielding gas to protect the molten weld pool from atmospheric contaminants like oxygen, nitrogen, and hydrogen, which can lead to weaker welds and excessive spatter. Shielding gas also helps to produce cleaner and faster welds, and eliminates the need for frequent electrode replacement.

There are different types of shielding gases available such as Argon, Helium, Carbon Dioxide, and Oxygen, and the choice of gas depends on the type of metal being welded, desired welding characteristics, and cost considerations.

Carbon dioxide is the most commonly used gas and provides deep weld penetration and cost-effectiveness. Welding wire manufacturers or suppliers can provide recommendations on the best shielding gas to use with the welding wire being used for the project.

It’s important to select the right shielding gas for the weld at hand to achieve a clean, slag-free weld and boost productivity while reducing clean-up.

Which Gas Is The Most Commonly Used Shielding Gas for Welding?

The most commonly used shielding gas for welding depends on the type of metal being welded and the desired welding characteristics.

For example, argon is the preferred gas for welding non-ferrous metals like aluminum, and it is usually blended with CO2 or O2 to weld steel. CO2 is commonly used for welding steel, but it delivers a less stable arc and more spatter.

Oxygen dramatically affects the weld and can be blended with CO2 or Ar to improve arc stability, penetration, and weld pool fluidity. Helium is an expensive gas, but it produces a hotter arc, improving weld penetration and making it beneficial for welding thick aluminum.

What Is 75% Argon 25% CO2 Used For?

75% Argon and 25% CO2 mixture, also known as 75-25 welding gas, is mainly used for welding mild steel, carbon steel, and low alloy steel. This binary gas mixture is preferred in MIG welding to ensure arc stability, maintain puddle control, and reduce spatter while delivering consistent results.

However, it cannot be used for welding stainless steel or aluminum. The mode of metal transfer when using 75/25 welding gas is a short circuit or globular transfer, depending on the welding current and voltage range.

This gas mixture is classified as SG-AC-25 according to AWS A5.32 specification.

Why Is CO2 Used In Welding?

CO2 is frequently used as a shielding gas in gas metal arc welding of carbon steels. This is because it is a reactive gas that produces oxygen and carbon monoxide during the welding process, which oxidizes the weld metal. However, CO2 has a deep-penetrating capability, and its use is therefore advantageous in welding thicker materials.

Despite its benefits, CO2 produces a lot of spatter and fumes during welding. Argon and CO2 mixtures are used to complement each other’s strengths and weaknesses.

Why Is CO2 Not Used In TIG?

CO2 is not used as a shielding gas for TIG welding because it contains oxygen, which can cause oxidation and result in a bad weld. CO2 is an active gas that conducts electricity, breaks surface tension on the molten metal, and quickly burns the tungsten electrode.

On the other hand, TIG welding requires pure Argon as a shielding gas to protect the tungsten electrode and maintain a stable arc. Argon settles over the weld pool and protects the metal from air contaminants, resulting in a bright appearance with little to no porosity.

Helium can also be used for TIG welding, but it is expensive and hard to find, making it more feasible for large industrial applications.

Types of MIG Welding Gas

Two main kinds of inert gas are used in MIG welding—argon and helium. Carbon dioxide and oxygen are also used in welding, but these are not entirely inert gases. As a result, they are only added into welding gas mixtures in small amounts to increase weld penetration or add other welding effects. In small amounts, these semi-inert and reactive gases don’t negatively impact weld quality.

Before You Continue Reading Learn More About Gas welding flames – Here, you can find an article from our website about Different types of gas welding flames and their applications | Ultimate Guide

There are also small amounts of special gases that are added to MIG welding mixtures to enhance specific types of MIG welding. These gases are usually added to counteract the specific metallurgical properties of the metals being welded, such as using hydrogen in the welding of nickel for a cleaner welding surface or the use of sulfur hexafluoride in aluminum welding to avoid ozone contamination.

Here is a breakdown of the various gases used in MIG welding:

Nr.Type of MIG welding gases
4Carbon dioxide
5Nitric oxide
6Sulfur hexafluoride
types of mig welding gases
  • Argon: Argon is a welding gas that is typically used with non-ferrous metals. This includes metals such as magnesium, titanium, or aluminum. Because it allows for narrow penetration, argon is an appropriate shielding gas for tight welds such as butt and fillet welds. Shielding gas mixtures with mostly argon are popular for maintaining a clean-looking weld.
  • Helium: Helium is used in MIG welding to increase the fluidity of a weld pool as well as increase the travel speed, or the speed at which the welder can move the welding gun along the seam. While helium is one of the more expensive welding gases used and requires a higher flow rate than other types of mixtures, it is nevertheless a popular choice for the welding of aluminum, copper, and magnesium.
  • Oxygen: Since oxygen is a reactive gas, it is only used in minimal amounts as part of a shielding gas mixture in MIG welding in addition to argon. Oxygen is only used in specialized applications for MIG welding, such as spray transfer welding. Because it can increase the amount of slag and oxidation, it is not a suitable mixture for use with exotic metals or metals prone to oxidation such as aluminum.
  • Carbon dioxide: Carbon dioxide is the only reactive gas used in welding that doesn’t require the addition of inert gas, but it is often mixed with inert gases to stretch them since it is the most economical of the welding gases. Carbon dioxide is rarely used in welding alone since it can cause spattering of the weld pool and creates instability in the welding arc.
  • Nitric oxide: Nitric oxide is used as a small-percentage additive in shielding gas mixes to reduce ozone that is produced by the weld, decreasing the chance of contamination of the weld. It is also a fantastic choice for increasing welding arc stability while welding high-alloyed stainless steel or aluminum.
  • Sulfur hexafluoride: As an additive, sulfur hexafluoride is most popular in the MIG welding of aluminum. This tricky metal is prone to both oxidation and porosity while being heated in a weld. Sulfur hexafluoride serves as a force to bind hydrogen to the weld site and decrease the resulting brittleness of the joint.
  • Hydrogen: Hydrogen is a small-percentage additive that is typically used in a mixture with argon to increase weld pool fluidity and prevent contamination of the welding surface. As an additive to argon and carbon dioxide, hydrogen can help to mitigate some of the oxidizing effects that carbon dioxide can have as a replacement for oxygen. Hydrogen shielding mixes are usually used in the welding of stainless steel or nickel.
  • Dichlorodifluoromethane: Dichlorodifluoromethane is a specialty shielding additive that is used specifically for aluminum-lithium alloys. Outside of specialized aluminum welds, dichlorodifluoromethane mixtures are not commonly used in MIG welding.

While inert gases can be used in a pure mixture as a shielding gas, mixtures of multiple shielding gases in different proportions are more commonly used. These mixtures impart different shielding qualities depending on the ratios of the elements present in the resulting mix.

MIG shielding gas mixes are usually given a designator based on which shielding gas is being mixed with argon (the base shielding gas for most MIG shielding gas mixtures) and in what proportions.

For example, an argon-carbon dioxide mixture that is 50% argon and 50% carbon dioxide is designated as a C-50 mix, while a mixture that is 98% argon and 2% oxygen is an O-2 mix.

Why Is Shielding Gas Used in MIG Welding?

No matter which shielding gas is used in a MIG welding application, shielding gas is a crucial aspect of the welding operation.

Without a proper gas shield, oxygen levels in the surrounding atmosphere during a weld will cause unsightly slag and spatter in the resulting weld. Other contaminants in the atmosphere will also decrease the quality of the weld’s appearance. These contaminants also introduce quality issues and porosity that can significantly decrease the safety and integrity of the weld over time.

There are a few atmospheric elements that are the primary factors behind corrosion of the weld site without a shielding gas:

  • Hydrogen
  • Nitrogen
  • Oxygen

These common atmospheric gases that form a majority of the gases found in our atmosphere are what is known as reactive gases. This means that when they come into contact with the welding arc, they are subject to chemical reactions that can negatively affect the resulting weld. Only a few of the gases in the Earth’s atmosphere are inert, which means they will not react with a welding arc. Most of the gases in the atmosphere are semi-reactive or reactive. 

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Certain metals, such as aluminum or copper, are particularly vulnerable to atmospheric contamination during a weld without proper gas shielding. Without shielding, the gases found in the atmosphere react with the welding arc and increase the incidence of welding defects such as:

  • Porosity: Porosity is a welding flaw in which gas bubbles become trapped in a cooled weld. This, in turn, leads to significant weakness in the integrity of the resulting joint. Porosity occurs when gas is absorbed into metal when it is in a molten form mid-weld, then is released as the weld cools down.
  • Brittleness: Brittleness is a property in welding where the resulting metal does not show evidence of deformation but has lost structural integrity at the molecular level. This makes the metal subject to shatter and fracture without warning. Brittle welds are identified by a granular appearance on the weld’s surface area.
  • Spatter: Spatter is the name in welding for the small blobs of molten metal that are cast off from the welding arc during a weld. Not only does spatter detract from the appearance of the weld, but it also increases the chance of injury to the welder from flying molten metal that can burn through cloth and skin. Spatter is usually caused by contaminated or poor-quality welding filler but can also be caused by certain shielding gases such as carbon dioxide.
  • Oxidation: Since oxygen comprises over 20% of the Earth’s atmosphere, oxidation is one of the most significant threats to the integrity of a weld without shielding gas. Oxidation is corrosion that causes the surface of the weld to appear tarnished or blackened. Oxidation is both an aesthetic defect and a chemical state that can introduce weakness to the welding joint.
welding spatter

Not only do these quality issues negatively affect the resulting appearance of the weld, but in industrial-grade welding, they can also degrade the integrity of the weld to the point that it will not pass a safety engineering inspection. For home projects, a few imperfections can be forgiven, but at the industrial level, these kinds of welding imperfections will not suffice.

This means that proper gas shielding in MIG welding is essential not just to make sure that a weld looks good, but also that it remains strong and stable at the molecular level. Learning how to use a shielding gas properly is one of the most important aspects of becoming a welder.  

Related Article: What’s the Difference Between TIG and MIG Welding? Which one is better?

The Difference Between Inert and Reactive Gases in MIG Welding

A significant difference when determining which shielding gas to use is to determine whether it is an inert or reactive gas. Argon forms the basis for most welding mixes because it is a stable, inert gas that does not react with either the welding arc or the surrounding atmosphere.

It is a shielding gas that produces the narrowest penetration field of any other shielding gas, but argon is commonly mixed with carbon dioxide to decrease the cost of the overall shielding gas mixture. In either case, the resulting inert mixture serves as a shield around the weld pool to keep it from coming into contact with reactive gases such as oxygen and hydrogen.

Oxygen is present in the atmosphere in a relatively large percentage (20.95%). At the same time, hydrogen is present at a much smaller percentage, but both reactive gases will cause quality issues in a weld if shielding gas is not used to guard the weld pool and arc against them.

Tips for Improved MIG Gas Shielding

There are many steps you can take to make your MIG gas shielding more effective. Here are some of the things you can do to create a better gas shield while MIG welding:

Tip – Nr:Improvement MIG Gas Shielding
1Research your specific equipment and materials
2Make sure that all your equipment is sound
3Make sure that your shielding gas matches your filler wire
4Keep your filler at the leading edge of the weld pool
5Make sure that all welding workspaces are adequately ventilated
Improve MIG Gas Shielding
  • Research your specific equipment and materials. Every piece of welding equipment from consumables to MIG welding guns has slightly different operating standards and parameters to follow. It’s necessary to go over the instruction manual for your equipment carefully and know which kind of project your materials are designated for. Using the wrong materials or using materials in the wrong way can result in a failed weld.
  • Make sure that all your equipment is sound. This means checking all hookups and connections as well as making sure there is no debris in the welding area that could potentially contaminate the weld. Having an atmospheric guard against contamination is useless if the weld becomes contaminated by environmental debris.

Learn More About: Personal Protective Equipment for Welders – PPE | List, and Requirements

  • Make sure that your shielding gas matches your filler wire. Each different type of filler wire or metal surface type will require a different type of shielding gas or mixture for optimal weld results, so research this information and make sure you’re welding with the correct shielding gas for your project before welding.
  • Keep your filler at the leading edge of the weld pool. This will ensure that your filler remains squarely within the confines of the gas shield and will also ensure that your weld remains even and steady. Moving the filler wire outside of the gas shield may lead to oxidation or spatter.
  • Make sure that all welding workspaces are adequately ventilated. Not only should certain metals containing chromium or beryllium not be welded without respirators and exhaust ventilation, but ventilation should also be used to control general welding fumes.

It may take some practice over several projects to learn how to move a filler wire smoothly while maintaining a stable gas shield around the weld pool. However, learning how to perform these two tasks simultaneously is vital to becoming a skilled welder.

How to Choose a MIG Shielding Gas

Deciding which MIG shielding gas to use can depend on a variety of different factors. Here are some of the things you should look into when deciding what shielding gas to invest in for your welding shop:

  • Price: The higher a gas mixture is in argon or helium, the more expensive it is likely to be. These more expensive shielding mixtures are necessary for some exotic metals or alloys to prevent oxidation. In less finicky welding projects, argon mixtures with a carbon dioxide ratio are more commonly used. For industrial or bulk welding projects, the overall expense is usually a factor in shielding gas proportions.
  • Filler metal type: Different shielding gases and mixtures are best used with different kinds of metals—research the filler wire used in your specific project, and you can usually find a recommended shielding gas mixture. It’s always best to verify that you have the correct shielding gas for your filler wire before starting your welding operation.
  • The desired welding result: Some welds don’t require a smooth or clean aesthetic look, some can be easily cleaned up afterward if any oxidation occurs, and other welding projects (such as those on exotic materials) must be done with specialized shielding mixtures to produce the cleanest results.
  • Joining material: Like the filler wire, the type of metal used in the joining surfaces will affect the best shielding gas used with that welding project. Knowing what types of metal you intend to weld together is crucial to knowing what shielding gas you need to use.
aluminum table welding
image credit: lincolnelectric.com

All welding projects are slightly different in their scope and practical applications, so knowing ahead of time what is required of the resulting weld is a good first step to figuring out which shielding gas you should use.

If you’re new to MIG welding, it can also be helpful to consult with a more experienced welder or a clerk in a welding supply shop for further recommendations.

Can Shielding Gas Be Skipped During MIG Welding?

There are certain types of MIG and TIG welding where shielding gas isn’t used, but these welds require filler that is either flux-coated or flux-cored. These welds are still shielded against atmospheric contaminants but use flux shielding rather than gas shielding.

MIG welding with flux rather than gas shielding is often recommended to beginner MIG welders who are unfamiliar with the operation of gas cylinders while welding. A gasless MIG welder is also a good choice for working in outdoor operations since the gas shield cannot be affected by environmental winds.

Knowing What Shielding Gas to Use Is Vital for MIG Welding

Not only is welding a technical skill that involves having steady hands, but it also requires the foresight to research a project ahead of time to know which supplies will be necessary to pull the weld off with the best possible result.

From do-it-yourself weekend warriors to industry professionals, there is a wide variety of welding projects that people undertake. No shielding gas can be recommended across the board for all MIG welding projects. But knowing which one is right for your project can be the difference between a welding success and a welding failure.

MAG Welding

If you are thinking of branching out into the world of professional welding, MIG welding with gas might not solve all of your welding needs. Eventually, you may need a MAG welder, which stands for Metal Active Gas. As the name suggests, MAG uses combinations of active gases more frequently with argon or helium.

Similarities and Differences to MIG

While you may sometimes need some carbon dioxide in MIG, you primarily would not be mixing chemicals in a home welding environment. But when you need “more power,” as Tim from Home Improvement might say, you need to go MAG. This is primarily used in the following industries:

  • Auto manufacturers
  • Commercial construction
  • Aviation
  • Electronics

And other industries when welding needs to be done very strongly and rapidly. Often times, like with the 2020 Weldpro above, you can use the same machines. It depends on the manufacturer though.

Which Gases to Use

Similarly to MIG, MAG welding uses argon or helium (although less often). We recommend learning how to mix these from a qualified welding instructor first. However just to give you an idea, mixtures are typically these percentages of active gases (with argon filling out the remainder):

  • Oxygen 2% to 5%
  • Carbon Dioxide 5% to 25%
  • 10% Carbon dioxide and 5% oxygen

Advice on Getting the Best Weld

Welding is much more of an art form than other construction projects. You are not just hammering in a nail or gluing something down. Welding requires patients and a little TLC. Here are some additional tips to help you get the best possible weld:

  • Slow down: if you just are not getting your weld to stay put longer than a couple weeks, it is probably because you rushed through the project. Try to take it slow and make sure you really cover all the gaps the first time. It is always better to do it correctly once than have to set up again in the future.
  • Make sure you have the right angle: With no gas MIG welding, you want to hold the gun at 10 to 15 degrees off the metal so you reduce space for exposure as much as you can. If you are using gas, 20 to 30 degrees is fine since exposure is not as much of an issue. This is closer to straight on, making aiming a bit easier.
  • Get hydrogen out of the picture: Chemically speaking, hydrogen is the biggest foe of welding. To that end, never clean the metal with water first; always use either the brush or grinder. In addition, avoid things like:
    • Rust
    • Paint
    • Grass
    • Dirt
  • Sound is important: Have ear protection on, but make sure you are hearing a consistent buzzing sound while welding in order to get the best weld. If it is sporadic, you are falling off target.
  • Keep welder grounded: This is not plugging your cell phone in to charge. This is a complex machine. The last thing you want is an electrical surge while you are welding.
  • Keep the nozzle on the gun clean: Good welders always make sure the metal they are working on is cleaning, but the gun nozzle often goes overlooked. Make sure you clean it ever so often to avoid a bad arc. In addition, this can prevent your gas shield from working properly.
  • MIG Dip– Rather than cleaning the nozzle ever so often, another option is to keep MIG dip nearby. Simply dip the nozzle in the container while it is still hot to keep the nozzle consistently clean. Give this MIG dip a try.
  • Keep the setting side of your machine close to you. Often times this is located on the same side as the power button, so this should not be that much of an issue. Not all brands are designed this way though. Try to keep these buttons close to you too, so you can easily adjust without having to leave your work too long.
  • Going along with that, do not take unnecessary breaks mid-weld. Your work surface looks a bit different through your mask vs with the naked eye. If you break for too long, you might get confused where you were, or which pass you were making when you get back.

Recommended Reading

Can MIG Welders Weld Aluminum? | How to successfully weld Aluminum?

How to Weld Aluminum at Home >> A Beginner’s Guide

Can Steel and Aluminum Be Welded Together?| All You Need To Know

What Welding Rod to use for Cast Iron? | Guidelines for Welding Cast Iron

MIG Welding Gases >> Tutorial video

David Harper

David is the Co-Founder and Senior Editor at weldingtroop.com. David's an experienced fitter and tuner/welder who's passionate about helping others develop in life through new skills and opportunities.

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