Gas MIG Welding: A Complete Guide (2023)

I usually weld with stick welding but have recently switched to MIG welding which gives me more control over my work. I can vary the gas mix to find the combination that works best for different projects and materials. When I saw my results, I wanted to learn more about MIG welding gases.

MIG welding gas is an essential part of the welding process. Various gases can be used for MIG welding, each with its own advantages and disadvantages. the purpose of this The gases are intended to protect the electrode and base material from atmospheric oxygen and moisture.

This guide provides an overview of common welding gases: argon, helium, carbon dioxide and oxygen. Understanding the pros and cons of each gas will help you choose the right one for your project.

Gas MIG Welding: A Complete Guide (1)


Why is a gas used in MIG welding?

Before we continue, let's be clear that there is no such thing as "gasless" MIG welding (MIG stands for Metal InertGas). Below, we compare MIG with Flux Cored Wire Arc Welding (FCAW), which is technically not gasless but does not have an external source of gas.

The main purpose of using gas in MIG welding is to protect the weld pool from oxidation, water vapor and contamination. Gases such as hydrogen and nitrogen can affect the quality and texture of the work. They are absorbed by the molten metal, and when the metal freezes, they are trapped as voids.

Gas welding uses a solid wire and a "shielding gas" (usually Argon-CO2mixture, although other gases are also used). A gas tank supplies the shielding gas and releases it through a nozzle.

Without an external shielding gas, you will have to replace your solid wire coil with a tubular wire coil. These wires generate their own shielding gases when they melt, which is why they are also known as self-shielding (this process is known as flux-core arc wielding, or FCAW).

MIG welding has less smoke.

When using a MIG welder, the welder emits shielding gases such as argon and CO2(Note that the CO2is a semi-inert gas) to prevent the hot wire and base metal from coming into contact with atmospheric oxygen to prevent combustion and oxidation.

In contrast, gasless welding uses flux-cored wire. This is a yarn with a cleaning agent called "Flux" in the middle. The flux is melted during the soldering process, releasing gases and liquid slag that prevent the base metal from oxidizing.

These gases, along with vapors from consumables and base metals, consist of metal particles and small amounts of carbon monoxide. They can cause short-term effects such as nausea and drowsiness andserious long-term effectssuch as lung damage and cancer when inhaled regularly.

Therefore, it is highly recommended to use a respirator when welding without gas and ensure good ventilation or a fan. These gases also interfere with the visibility of the weld pool.

Fumes can also contaminate the metal you are working with. However, you can easily clean the bumps with a spray or a cloth.

Although MIG welding produces less smoke, it still produces certain harmful gases such as nitrogen dioxide and ozone. Ozone is colorless and odorless and is not filtered by a respirator. Therefore, a ventilation system is still necessary in MIG welding.

MIG does not produce dross (typical) and produces less spatter.

Slag is a coating that forms on your weld. It mainly consists of chemical compounds and other materials such as oxides, but it may also contain quartz sand. The presence of slag in your weld can be identified as an elongated crust that is either continuous or discontinuous along the length of the weld.

Generally protected against gassun day MEdoes not include filler wire. With FCAW, this slag splatters onto the base metal with each weld, solidifies, and must be cleaned with a wire brush, chipping hammer, or emery.

Spatter refers to droplets of molten metal that splatter in all directions and solidify during welding. While it is difficult to completely eliminate spatter, shielded gas arc welding generally produces less spatter. In comparison, using a tubular wire generates more spatter due to flow. Spills can be removed with hand tools or anti-spill spray.

In this regard, the use of gas in welding makes the work less dirty, less time-consuming and does not require additional cleaning work.

Exotic metals cannot be welded without gas.

Every now and then, if you've been soldering long enough, you'll come across someone selling flux-cored wire that claims to weld aluminum or other exotic metals. Although some laboratory fluxes can weld aluminum, they require extreme care in handling and storage and are basically impractical for general use.

Aluminum is soft and highly sensitive, so when molten it is very reactive to atmospheric gases and contaminants. It also doesn't visibly glow when it heats up, making it difficult to determine the condition of your solder.

ComArc welding with cored wire(FCAW), the gases released from the flux are less reactive than aluminum and do not provide effective protection for your solder. In addition, cast aluminum absorbs hydrogen and moisture very quickly. You'll likely end up with an overly porous solder that doesn't hold very tight.

Soldering aluminum with FCAW can result in scorching, porosity, or pooling of solder falling onto the workpiece unless you are extremely careful with voltage, wire speed, travel speed, and the type of flux used.

Therefore, to melt aluminum safely, MIG orTIG weldingit's the way to go. However, you cannot use CO2as a shielding gas, as molten aluminum is more reactive than CO2. You would need to use 100% argon or, for aluminum larger than 0.5 inch, an argon-helium mixture.

Gas MIG Welding: A Complete Guide (2)

What gas do you use for MIG welding?

There are several gases that you can use with yourMIG welder. Carbon Dioxide (CO2) and argon are the most popular gases. Small percentages of oxygen and helium are also used for certain solders.

For most commercial solders, you would use a mixture called C25, which contains 25% carbon and 75% argon. Welding gases are stored in high pressure cylinders. You can buyC25 bottlesfrom your local welding shop and evenorder them online from Amazon.

Gas MIG Welding: A Complete Guide (3)

80 cu/ft 75% Argon 25% CO2 Weld Tank Cylinder CGA 580 - COMPLETE

  • All HP cylinders come with a 10 year hydrostatic test date.

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Argon is usually mixed with CO2or other gases, but is often used independently. It is one of the chemically "noble" or inert gases. This means that it has very little tendency to react with the atmosphere or the base metal.

The use of argon provides a narrower penetration profile and helps maintain a stable arc angle. Pure argon gas is used to weld non-ferrous metals such as aluminum, titanium or copper.

carbon dioxide

Reines CO2as a shielding gas it is a popular choice for many MIG welders. It is the only gas that works without the addition of inert gas and is relatively inexpensive.

CO2MIG welding offers a deep penetration profile, a hot arc and is suitable for thick materials. However, this generates more spatter and the arc is not as stable as with an argon-carbon mixture. 100% CO2only allows short-circuit transmission.


Oxygen is often used in less than 1/10ºto improve penetration, maintain good wetting (i.e. increase weld pool fluidity) and harden the arc. It is used in spray overlay welding of alloys and stainless steels.

However, it can form dross and should not be used with reactive alloys such as copper and aluminum. Excessive oxygen consumption can cause oxidation of the MIG electrode, resulting in more holes in the weld pool.

Even though we all look at oxygen the same way, that's not necessarily true. Ooxygen cylindersYou see the purest form of oxygen in hospitals, which is not of the same quality as what is used for soldering.


Helium is another inert gas commonly mixed with 25-75% argon. It is used for wider and deeper penetration and for welding stainless steel or non-ferrous metals such as aluminum. It has a high flow rate, which means the cylinder will empty faster.

Helium requires a higher voltage and creates a high-energy hot arc. It is often used in small amounts in a "Tri-Mix" mixture to adjust arc characteristics, penetration profile and prevent oxidation. Helium is added to pure argon when welding exotic metals greater than 0.5 inch thick.

What is the best mixture of argon and carbon for MIG welding? (What gas mixture is used to weld sheet metal?)

The exact argon-carbon mixture depends on the metal you are working with and the type of solder joint you prefer. I usually work with C25, but I can do most of my work with pure CO2when I run out of C25.

The most common mix for MIG welding is C25 (75% Argon and 25% Argon). C25 only allows short circuiting and spherical metal transfer. For the average amateur, this method offers the best value for money.

  • More argon generally means tighter and reduced penetration. May be preferred for fillet and butt welding. However, if you are welding stainless steel, for example, you want a lower argon to CO2 ratio.

The use of argon helps to stabilize the arc and produce less spatter. Argon's inertness makes it desirable for reactive metals such as aluminum and magnesium. When working with soft metals, you generally want an argon mix. Pure argon is not commonly used for welding.

  • The CO2 contributes to deeper penetration and increases the heat and energy of the arc. Since CO2 is not inert, it does not prevent oxidation as effectively as argon or helium. It also generates a noticeable amount of splash.

You can also go with 100% CO2 seThey won't work on thin or exotic metals like aluminum. The arc is less stable than if you mixed an inert gas and there is more cleaning to do after each weld.

Gas MIG Welding: A Complete Guide (4)

The C50 mixture (50% Argon and 50% CO2)it's not as wet as the C25 and the solder tends to stick where you applied it. C50 is widely used for short arc welding of pipes, especially when the surface contains contamination.

By increasing the proportion of argon in an argon-carbon mixture to 80% or more, you improve weld penetration and reduce spatter (thus increasing deposition rate). You can use all four transmission modes even with such a high argon ratio.

If you intend to weld sheet metal, it is best to use an argon-based mixture (ie at least 75% argon) - the higher the argon content, the less heat and spatter.

C15 (85% Argon and 15% CO2)is popular with many companies working with structural and carbon steel. If you are working with thick metals (approx. 0.5 cm) or prefer to weld mill scale, the C15 is suitable.

The C15 also supports all four metal transmission modes. By switching between transfer modes, you can weld both thin and thick metal parts. However, due to 85% argon, wetting can be stronger, although with practice you can get better control of the weld pool.

C15 short circuit transfer works well when welding sheet metal and there is less chance of burning than CO2misturas made from

If you want to go for aesthetics, you can use aC10 mixture (90% Argon and 10% CO2).The resulting weld is smoother and flatter with less spatter to clean up.

The penetrating power of C10 is good, but less than that of C15 or C25. C10 is good for spray transfer and generally not good for short circuit transfer with many welders.

The bow becomes less energetic as you move downC5 (95% Argon and 5% CO2). One of the main benefits of the C5 is that it allows for good impulse spray transfer. It is suitable for welding through lamination flakes. However, if you've never used it before, you'll need to get used to the puddle control.

Compound C5 can also be used for short circuit transfer, although you must carefully adjust the welding parameters so that the heat released is not too low.

MIG welding gas prices

Gas prices depend on bottle size, type of gas and where you live. A 40, 80, or 125 cubic foot (CF) cylinder is sufficient for most home welders.

Noble gases like argon and helium are more expensive than CO2or oxygen. You can expect to pay between $150 and $350 the first time you buy a full bottle. Top-up packs are usually much cheaper. Refilling a 125 CF cylinder can cost as much as $40 for pure argon, $30 for C25, and $20 for oxygen.

Volume (CF)average Cost of an empty bottle
20$ 110
40$ 140
80$ 200
125$ 235


There are several welding gas mixtures available on the market. Each combination results in a unique penetration profile and transmission mode. In general, carbon dioxide and argon are used independently or mixed together, sometimes with helium or additional oxygen. MIG welding gases produce less smoke and spatter than traditional welding.

Below is a helpful YouTube video on gas welding for beginners.

More reviews about welding machines

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