Gas MIG Welding: A Complete Guide (2023)

I normally glue, but I've recently switched to MIG welding and it has given me more control over my work. I can vary the mix of gases 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.

Gas MIG welding is an integral part of the welding process. Various gases can be used for MIG welding, each with their own advantages and disadvantages. The purpose of this Gases are intended to protect the electrode and the 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). Next we compare MIG to cored wire welding (FCAW), which is not technically gasless but does not have an external gas source.

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 alter the quality and texture of the work. They are absorbed by the molten metal and get stuck as voids as the metal freezes.

In gas welding, a solid wire and a "shielding gas" (usually argon-CO) are used2Mixing, 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 cored 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-cored arc-grip, or FCAW).

MIG welding has less smoke.

During MIG welding, the welding machine releases shielding gases such as argon and CO2(Note that CO2is a semi-inert gas) to prevent the hot wire and base metal from contacting atmospheric oxygen to prevent combustion and oxidation.

In gasless welding, on the other hand, a flux-cored wire is used. This is a wire with a cleaning agent called "Flux" in the middle. The flux melts during the welding process, releasing gases and liquid slag that prevent oxidation of the base metal.

These gases, along with fumes 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 dizziness andsevere long-term effectssuch as lung damage and cancer when inhaled regularly.

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

The fumes can also contaminate the metal you are working with. However, you can easily clean stains with a spray or cloth.

Although MIG welding produces less fume, it still produces certain harmful gases such as nitrogen dioxide and ozone. Ozone is colorless and odorless and cannot be filtered through a respirator. Therefore, a ventilation system is still required in MIG welding.

MIG produces no dross (typical) and generates less spatter.

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

Usually gas protectedMIG weldingit implies no filler wire. With FCAW, this slag is flung onto the base metal with each weld, solidifies, and must be removed with a wire brush, chipping hammer, or grinder.

Spatter refers to droplets of molten metal that shoot out in all directions and solidify during welding. Although it is difficult to completely eliminate spatter, arc welding generally produces less. In comparison, using a cored wire generates more spatter due to the flux. Spatter can be removed with hand tools or anti-spatter spray.

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

Exotic metals cannot be welded without gas.

If you weld long enough, you'll occasionally come across someone selling a flux cored wire that claims to weld aluminum or other exotic metals. While 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 very delicate, making it highly reactive to atmospheric gases and contaminants when molten. It also doesn't noticeably glow when heated, making it difficult to tell the condition of your soldering.

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

Welding aluminum with FCAW can result in burns, porosity, or the weld pool falling through the workpiece unless you are incredibly careful with voltage, wire speed, travel speed, and type of flux used.

To safely melt aluminum, MIG orTIG weldingis the way to go. However, you cannot use CO2as a protective gas, as molten aluminum is more reactive than CO2. You would need to use 100% argon or, for aluminum thicker than 0.5 inch, a mixture of argon and helium.

Gas MIG Welding: A Complete Guide (2)

What gas do you use for MIG welding?

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

For most commercial solders I would use a blend called C25 which is 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 at amazon.

Gas MIG Welding: A Complete Guide (3)

80 Cubic Feet 75% Argon 25% CO2 CGA 580 Weld Gas Cylindrical Tank - FULL

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

Prices from the Amazon Product Advertising API at:

Product prices and availability are as of the date/time shown and are subject to change. All pricing and availability information displayed on [relevant Amazon sites, as applicable] at the time of purchase applies to the purchase of this product.


Argon is usually mixed with CO2or other gases, but is often used independently. It is one of the chemically "noble" or inert gases. That means 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 aluminium, titanium or copper.

carbon dioxide

reines CO2as a shielding gas 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, hot arc and is suitable for thick materials. However, this creates more spatter and the arc is not as stable as with a mixture of argon and carbon. 100% CO2it only allows short-circuit transmission.


Oxygen is often used at less than 1/10Isto improve penetration, to obtain good wetting (ie to increase the flowability of the molten weld pool) and to harden the arc. It is used in spray overlay welding of alloys and stainless steel.

However, it can generate dross and should not be used with reactive alloys such as copper and aluminum. Excessive use of oxygen can cause the MIG electrode to oxidize, creating more pores in the weld pool.

Although we can all consider oxygen to be the same, this is not necessarily true. Heoxygen cylindersthe ones you see in hospitals contain the purest form of oxygen, which is not of the same quality as that used for welding.


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

Helium requires a higher voltage and creates a hot, high-energy arc. It is often used in small amounts in a "tri-mix" to adjust arc properties, penetration profile and prevent rusting. Helium is added to pure argon when welding exotic metals thicker than 0.5 inch.

What is the Best Argon Carbon Mixture for MIG Welding? (What gas mixture is used to weld sheet metal?)

The exact mixture of argon and carbon depends on the metal you are working with and the type of weld transfer 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 mixture for MIG welding is C25 (75% argon and 25% argon). C25 allows only short circuit and spherical transfer of the metal. For the average hobbyist, this method is the best value for money.

  • More argon generally means tighter and less penetration. May be preferable for fillet and butt welds. However, if you are welding stainless steel, for example, you will need a lower argon to CO2 ratio.

The use of argon helps stabilize the arc and produces less spatter. Argon's inertness makes it desirable for reactive metals such as aluminum and magnesium. You typically need an argon mix when working with soft metals. Pure argon is not commonly used in welding.

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

You can also go with 100% CO2 andThey don't work on thin or exotic metals like aluminum. The arc is less stable than if you mix an inert gas and you have to clean more after each weld.

Gas MIG Welding: A Complete Guide (4)

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

By increasing the proportion of argon to 80% or more in a mixture of argon and carbon, you would improve weld penetration and reduce spatter (and therefore increase deposition rate). Even with such high argon proportions, you can use all four types of transmission.

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)It is popular with many companies working with mild steel and carbon steel. If you are working with thick metals (approx. 0.5 cm) or prefer to weld through mill scale, C15 is sufficient.

C15 also supports all four metal transfer 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.

The short circuit transfer of C15 works well when welding sheet metal and there is less risk of burns than CO2Mixtures based on

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 lower than that of C15 or C25. C10 works well for spray transfer and is generally not good for short circuit transfer with many welders.

The arc becomes less energetic as it moves downC5 (95% Argon and 5% CO2). A key benefit of C5 is that it allows good pulsed spray transfer. It is suitable for welding through mill scale. However, if you've never used it before, you'll need to get used to the puddle control.

The C5 compound can also be used for short-circuit transfer, but you must carefully adjust the welding parameters so that the heat output does not become 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 anywhere from $150 to $350 when buying a complete cylinder for the first time. Refill packs are usually much cheaper. Refilling a 125 CF cylinder can cost up to $40 for pure argon, $30 for C25, and $20 for oxygen.

Volume (FC)Average cost of an empty bottle


Various welding gas mixtures are available on the market. Each combination offers a unique penetration profile and delivery mode. Generally, carbon dioxide and argon are used independently or mixed together, sometimes with helium or oxygen added. MIG welding fumes produce less smoke and spatter than traditional stick welding.

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

More reviews of welding machines

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