MIG welding uses a hand-held gun that contains a spool-fed wire electrode, along with a gas nozzle that delivers a stream of gas to the weld site.
This gas prevents the contact of oxygen, nitrogen, and other environmental gases with the weld bead – which helps ensure consistent, strong results.
Contamination can lead to a low-quality weld on your workpiece, so choosing the right gas is absolutely essential for the best results. But what’s the best gas for MIG welding? Unfortunately, the answer is not that simple.
Different metals require different types of gases for the best results, although in most cases, a 75/25 argon and CO2 mix will let you get good results on most metals.
But let’s take a look at some of your options now, and discuss how you can choose the right MIG welding gas for your job.
MIG Gases
If you’re going to be MIG welding, there are two main gases that are used: pure argon and an argon/carbon dioxide mix. The most common (and recommended) Ar/CO2 mix is a 75/25 ratio, with 75% of it being argon and 25% of it being CO2.
Which one is used for what?
When you’re working with mild steel or stainless steel, you’ll want to use an Ar/CO2 mix.
If you’re working with aluminum, then you’ll want to use pure argon.
Pure argon (an inert gas) gives shallow penetration but a wider bead profile in a weld. It also results in less spatter.
CO2 (a semi-inert gas) can be used on its own, as it gives deeper penetration than argon (plus it’s cheaper). However, it produces a harsher, less stable arc, which results in a lot of spatter.
Combining the two gives you a fully penetrative weld and good arc characteristics without a crazy amount of spatter. That’s why a 75/25 Ar/CO2 gas mix is the best for mild and stainless steel. These days it is often advertised as ‘MIG gas’ as well.
What is the purpose of shielding gas for MIG welding?
Welding produces a molten puddle made up of the base metal and filler metal being fused together. Shielding gas protects that puddle from atmospheric contaminants like nitrogen and hydrogen.
Without shielding gas, the finished weld would be very weak and peppered with pinpoint holes once it solidifies — a defect known as porosity. Shielding gas acts as a blanket over the molten weld puddle, keeping atmospheric contaminants out.
The type of gas used also has an effect on the characteristics of the weld. Your gas choice can impact spatter levels, arc stability and arc performance along with many other factors.
In addition, the desired welding transfer you want to achieve is dependent on the type of shielding gas you’re using. So if you want to do a spray transfer, globular transfer or short-circuit transfer, you need to select a certain type of shielding gas for each transfer mode in MIG welding.
For example, a shielding gas that is high in argon makes it difficult to achieve short-circuit transfer mode but easier to achieve spray transfer.
MIG Welding Gas – Choosing The Right Gas
Many MIG welding applications lend themselves to a variety of shielding gas choices. You need to evaluate your welding goals and your welding applications in order to choose the correct one for your specific application. Consider the following as you make your selection:
- The cost of the gas
- The finished weld properties
- Preparation and post-weld clean up
- The base material
- The weld transfer process
- Your productivity goals.
The four most common shielding gases used in MIG welding are Argon, Helium, Carbon Dioxide, and Oxygen. Each provides unique benefits and drawbacks in any given application.
Carbon Dioxide (CO2)
Carbon dioxide is a “semi-inert” gas that is relatively resistant to chemical change, but to a lower extent than inert gasses like argon and helium.
It’s used frequently in MIG welding, often on its own (100% CO2), or as a small percentage of a helium or argon gas mix. A 75/25 MIG Argon and CO2 mix is the most popular gas for MIG welding sales, making up more than 90% of the gas we sell at Vern Lewis Welding Supply.
CO2 is much cheaper than inert gas, and it allows the bond to penetrate very deeply into the metal when welding.
However, it has a much harsher arc that can be more difficult to control, and its semi-inert nature leads to more weld spattering, so the weld requires more cleanup compared to a noble gas.
Carbon dioxide is particularly useful when working with ferrous metals like mild steel. 100% CO2 is sometimes used for this purpose, but this is a more “old school” approach used for specialty wires – for general MIG welding purposes, 72/25 Argon/CO2 or a tri-mix of CO2, argon, and helium is much more common.
Argon
For companies that place an emphasis on weld quality, appearance, and reducing post-weld cleanup, a mixture of between 75 – 95 percent Argon and 5 – 25 percent CO2 may be the best option.
It will provide a more desirable combination of arc stability, puddle control, and reduced spatter than pure CO2.
This mixture also allows the use of a spray transfer process, which can produce higher productivity rates and more visually appealing welds. Argon also produces a narrower penetration profile, which is useful for fillet and butt welds.
If you’re welding a non-ferrous metal, aluminum, magnesium, or titanium you’ll need to use 100 percent Argon.
Oxygen
Oxygen, also a reactive gas, is typically used in ratios of nine percent or less to improve weld pool fluidity, penetration, and arc stability in mild carbon, low alloy, and stainless steel.
It causes oxidation of the weld metal, however, so it is not recommended for use with aluminum, magnesium, copper, or other exotic metals.
Helium
Helium, like pure Argon, is generally used with non-ferrous metals, but also with stainless steel. Because it produces a wide, deep penetration profile, Helium works well with thick materials and is usually used in ratios between 25-75 percent Helium to 75-25 percent Argon.
Adjusting these ratios will change the penetration, bead profile, and travel speed. Helium creates a ‘hotter’ arc, which allows for faster travel speeds and higher productivity rates. However, it is more expensive and requires a higher flow rate than Argon.
You’ll need to calculate the value of the productivity increase against the increased cost of the gas. With stainless steel, Helium is typically used in a tri-mix formula of Argon and CO2.
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.
Common shielding gases for MIG welding
Hobbyist welders most commonly use three types of filler metals to match the base material they are welding: solid steel wire to weld mild steel, aluminum wire to weld aluminum and stainless steel wire for stainless. The shielding gas options vary based on the material being welded.
Welding gas for mild steel
A 75% argon/25% carbon dioxide mix (sometimes referred to as “C25 gas”) is very common for welding mild steel. It produces minimal spatter and provides good arc characteristics.
It also has a good bead profile, allowing it to wash out well at the toes of the weld. One drawback: this mix is more expensive than other options.
Another gas used for mild steel is 100% carbon dioxide, sometimes called C100. It’s a good alternative that is less expensive than a 75%/25% shielding gas mixture, but it can produce a bit more spatter and result in a slightly erratic arc.
However, as technology in welding power sources designed for DIY users improves, the machines provide better performance with a 100% CO2 gas than the machines of 10 or 15 years ago.
While it’s less common for the DIY user, if you’re going to get into a spray transfer mode with MIG welding (such as when you’re welding a thicker plate), a 90% argon/10% CO2 gas, or C10 gas, is a good option for that.
Welding gas for aluminum
The most common gas used for MIG welding aluminum is 100% argon. This gas allows you to get into a spray transfer or pulsed spray transfer mode easily for aluminum due to its low ionization value.
Another benefit of 100% argon gas is that it can also be used for TIG welding aluminum. So if you MIG weld aluminum and also TIG weld in your shop, this is a handy gas to have on hand because it covers both processes.
While there are many helium/argon gas blends that work for aluminum, these gases aren’t a good option for most DIY welders because of the very high cost of helium. Also, aluminum is highly sensitive to contamination, so avoid using a gas with CO2, which can introduce carbon into the weld.
Welding gas for stainless steel
There are many gas combinations available for MIG welding stainless steel. Many MIG welding power sources have traditionally been designed for short-circuit transfer mode to be used with a helium trimix shielding gas for stainless.
Helium helps the puddle wash out without adding too much inductance, providing a good bead profile and good bead characteristics. But as mentioned above, the cost of helium today can be prohibitive for DIY welders.
In recent years there has been a shift as manufacturers design MIG welding power sources to be used with different gas combinations for welding stainless steel.
A 98% argon/2% CO2 blend is a good option for stainless. Just as with aluminum, it’s important to avoid introducing too much CO2 into the mix with stainless as it can cause porosity or other weld defects.
An argon/CO2 gas mixture is a versatile option. It can be used for short-circuit transfer, spray transfer and pulsed spray transfer modes. It still provides a good bead profile with decent wetting characteristics and is much more affordable than a helium gas mix.
Welding gas for silicon bronze
Using a silicon bronze filler metal to join dissimilar metals or a variety of coated materials is becoming increasingly common with DIY welders for applications such as automotive repair and for art and sculptural welding.
Using an ERCuSI-A silicon bronze filler metal results in what is essentially a MIG brazing process.
Typically, you want to use a 100% argon shielding gas. This allows for a nice short-circuit transfer that helps the puddle wash out when using silicon bronze filler metal.
Conclusion: How to Choose the Best Gas for MIG Welding
If you’re searching for the best gas to use for MIG welding that has broad application, the 25% carbon dioxide and 75% argon or anything similar to that such as an 80/20 mix, is possibly your best choice.
If you’re on a budget and won’t mind cleaning up a little additional spatter, carbon dioxide is inexpensive at excellent when it comes to experimentation and hobby welding. 100% argon is the way to go for MIG welding aluminum, or generally TIG welding.
With stainless steel, things get more costly when more helium is mixed with argon and carbon dioxide or Oxygen. There, you also have the option of selecting a cheaper C2 with a 98/20 mix.
Always take into account the metals you want to weld and ensure that you’re getting the most out of your gas flow. Don’t forget that the key to a dependable bead pattern and avoiding overheating the metal is your preferred gas and your gas flow rate.