MIG welding with shielding gas helps produce high quality welds because you prevent the weld pool from being exposed to elements in the atmosphere which will contaminate the weld and produce defects.
There are different types of MIG welding gas to choose from, all suitable to different requirements. Here’s how to find the right shielding gas mix.
What gas is used for MIG welding?
Most commonly used gases when MIG welding are Carbon Dioxide (CO2), Argon (Ar), Oxygen (O2) and Helium (He). These are often mixed together in one gas cylinder.
The two most commonly used shielding gases in welding mild steel are a 75% argon 25% CO2 mixture and pure CO2. Pure CO2 is a cheaper option, but produces lower quality welds.
Gas MIG welding is a great way to repair or build things, because it uses electricity to create a weld. Different gases suit different needs, so you need to evaluate which gas mixture is best for your needs. The cost of gas and the quality of the weld are two of the main factors to consider when choosing a shielding gas for MIG welding. We have explained the different types of gases and MIG applications below.
Argon and Carbon Dioxide (CO2) Mix
Argon and CO2 are popular shielding gases in welding. The presence of argon helps to narrow the penetration, provides much greater arc stability and reduces spatter, producing a smooth spray arc transfer.
When you use Argon and CO2 together, the mixture will usually contain between 75% and 95% Argon and between 5% and 25% CO2. Mixtures with higher CO2 will produce more spatter, but mixtures with Argon over 80% can have an arc that becomes too fluid and hard to control, which is particularly problematic if you’re performing out-of-position welding.
Argon and CO2 mix is more expensive than pure CO2. If you want to reduce post weld cleanup time and are willing to pay a little extra, then look at pure CO2. Argon CO2 mix is good choice if you want to reduce material costs.
Argon/CO2 mix facts:
- Less spatter
- Reduced clean up time
- Expensive
- High weld quality
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Pure Carbon Dioxide (CO2)
CO2 is the least expensive shielding gas which makes it a popular choice of MIG welding gas where low material costs is an essential consideration.
The major problem with CO2 is that it makes the arc less stable than other gas mixes, which results in spatter. If you need to spend time cleaning the welds, this could result in increased costs, but if aesthetics aren’t important then it’s a good choice.
CO2 is a good choice for thicker metals or if you want to get the most penetration out of a 110V MIG welder. It also provides deep penetration, which makes it a good choice for autobody sheet metal. If you want to get better quality welds with CO2, buy an Argon/CO2 mix and then use it with your MIG welder.
Pure CO2 facts:
- Cheap
- Deep penetration
- Lots of spatter
- Not suitable for thin metal
Pure Argon
Pure Argon gas can be used to MIG weld, but only if you’re welding a non-ferrous metal such as aluminum, magnesium or titanium. MIG welding aluminum and other non-ferrous metals should use 100 percent Argon shielding gas for the best quality welds. If you’re welding with helium, mixing it with Argon works best.
As a general rule, 100% argon gas is not recommended for welding steel. It won’t provide enough thermal conductivity to MIG weld ferrous metals, and the weld will be weak.
Pure Argon facts:
- Best for non-ferrous metals
- Not suitable for steel
Argon and Helium mix
When MIG welding non-ferrous metals, helium is used to increase heat. This helium provides a very wide penetration and has a higher flow rate than argon so it’s possible to have a greater welding speed than pure argon.
Helium costs more than air, but the increased travel speed and penetration make it worth it. The percentage of helium used can range from 25% to 75%, with more helium providing wider penetration and travel speed.
Generally, a higher percentage of helium is required for thicker base metal. 75% helium would only really be used to weld aluminum of thickness 1 inch and above in the flat position.
Argon and Helium mix facts:
- Best for non-ferrous metals
- Wide penetration
- Fast welding speed
Pure Helium
Helium can be used on its own for MIG welding non-ferrous metals, but it’s better to use with electrode negative in TIG welding. High helium content is best used for MIG welding on thicker materials. Welding speed can be increased high to increase productivity, but it’s expensive and rarely used compared to argon and helium argon mixes.
Pure Helium facts:
- Best for non-ferrous metals
- Suitable for thick base metal
- Rarely used
Argon and Oxygen mix
Oxygen isn’t a base gas, but can be mixed with argon and carbon dioxide in amounts of 1% to 5%. It helps stabilize the arc, improves the weld pool fluidity, and improves the quality of the weld and penetration. The downside of oxygen is that it causes oxidation of the metal, so shouldn’t be used when welding aluminum, magnesium or copper. Oxygen and argon are typically used for spray transfer on stainless steel to help produce a stable arc—which makes welding out of position less problematic.
Argon and Oxygen mix facts:
- Can cause oxidation in aluminum, magnesium and copper
- Helps stabilize the arc
Amelia Darwine
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