Shielding Gas For MIG welding

MIG (Metal Inert Gas) welding is a popular welding process that uses a shielding gas to protect the weld from contaminants. But with various shielding gases to choose from, it can be challenging to know which one is the best for your project.

This article will provide a comprehensive overview of the various shielding gases used in MIG welding, their properties, benefits, and drawbacks, and when to use each one for optimal results.

Importance Of Shielding Gas In MIG welding

Shielding gas plays an integral role in MIG welding by protecting the molten weld pool and the surrounding base material from atmospheric contamination. Without the use of shielding gas, the weld pool and base material are exposed to oxygen, nitrogen, and other gases in the atmosphere. Once atmospheric gases reach the weld pool, they interact with molten weld puddles, causing oxidation, porosity, and eventually cracking. The welded joint loses its corrosion resistance, becomes brittle, and is highly prone to failure.

The most commonly used shielding gases for MIG welding are argon,helium, carbon dioxide, and various mixtures of different shielding gases. Mixtures provide excellent arc stability and weld characteristics. However, each shielding gas provides different results, so let's talk more about their properties.

Photo by @hungary_welder

Inert Gases In MIG Welding

Inert gases are non-reactive, meaning they don't interact with the atmosphere, electrode (MIG wire), or base metal. They provide a protective layer that shields the weld from outside contaminants and prevents oxidation which can weaken the overall strength of the weld.

Argon and helium are the most common shielding gases used in MIG and TIG welding. They can reduce the risk of weld porosity, which is a common defect caused by the presence of air or other contaminants. They can also reduce the risk of weld cracking and help to improve the strength, arc stability, and overall quality of the weld.

Source: https://makemoneywelding.com/8-ways-to-avoid-weld-porosity/

If we look at the acronym for MIG welding - Metal Inert Gas welding, we can realize they are the most critical welding gas in the GMAW welding method. Let's see how each performs in different situations.

1. Argon Gas in MIG Welding

Argon is a noble gas and one of the most widely used shielding gases due to its ability to provide a stable arc and excellent shielding of the weld with high-quality and clean welds. In addition, argon is denser than air, so it helps to displace the air around the weld area and create a protective atmosphere. This helps to prevent oxygen and other contaminants from reacting with the weld pool and causing defects such as porosity or cracking.

Pure argon creates a steady arc, allows good arc starts at low amp applications when welding thin materials, and produces more visually appealing welds. It is also a versatile choice that can be used for welding a wide range of materials, including mild steel, stainless steel, aluminum, and copper.

However, 100% argon shielding gas has its drawbacks. Argon produces a wine glass, shallow penetration, and bead profile, which can cause fusion issues when welding thick materials. In addition, pure argon has somewhat worse arc characteristics when MIG welding mild steel since iron oxide attracts the arc, causing instability and wondering. That's why many welders turn to mixtures. By mixing two or even three gases, you get the best out of each, but we will talk more about them later in the article.

Source: https://weldguru.com/mig-welding-with-100-argon/

 

2. Helium In MIG Welding

Like argon, helium is another inert gas that does not react chemically with other elements, including MIG wire, weld metals, or the atmosphere. Helium also provides good arc characteristics, but welders usually choose it due to its high heat due to greater ionization potential. The high heat of Helium produces deep weld penetration and creates a broader bead profile, which works excellent with thicker pieces, which is where pure argon comes short.

Source: https://www.nagwa.com/en/explainers/840185315807/

However, pure helium is rarely used in MIG welding simply because it is not cost-efficient. helium is significantly more expensive than CO2 and lighter than argon, so it requires a higher flow rate to achieve good gas coverage. Even though small doses of helium can be used when welding thick non-ferrous metals, many welders found carbon dioxide a suitable replacement.

Semi-reactive and Reactive Shielding Gases in MIG Welding

Reactive and semi-reactive gases, as their name states, can react chemically with other elements. However, unlike tungsten electrodes in TIG welding, MIG wire is not suspectable to contamination from semi-reactive gas such as CO2, so it can be used as pure. MIG welding utilizes carbon dioxide and oxygen reactive gases, of which CO2 plays a significantly more crucial role in MIG welding, and here is why.

1. Carbon Dioxide Shielding Gas For MIG Welding

Carbon dioxide is one of the commonly used shielding gas in MIG welding steel applications, including mild steel or low alloy steel, due to its decent arc performance and low cost. CO2 in MIG welding provides excellent penetration and increases arc fluidity, allowing a spray transfer process, which is known as the fastest. As a result, it is a common choice when you need to get the job done quickly and cheaply.

Source: https://weldguru.com/welding-transfer-modes/

Carbon dioxide is the only semi-reactive gas that can be used pure. By acknowledging the advantages, many welders started using 100% CO2, which led to a form of MIG welding - known as MAG (Metal Active Gas) welding. However, like any other gasses, CO2 is not without its drawbacks.

Pure CO2 tends to create less likely aesthetic weld beads with lots of weld spatter. Therefore, it is suitable only when weld appearance is not crucial. Additionally, CO2 reacts when MIG welding non-ferrous metals or stainless steel, causing oxidation and defects in the finished weld, so you should use it only when MIG welding steel.

Due to unfavorable weld appearance and high penetration properties, CO2 is often mixed with argon gas. By mixing these two, you get the best out of each, and maybe the most popular shielding gas mixture, C25.

75% Argon and 25% Carbon Dioxide Mixture Shielding Gas

Photo by @stevensullivan47

 

2. Oxygen In MIG Welding

Oxygen is a reactive gas that you are actually trying to keep out of your weld pool to avoid weld defects and contamination. However, in small doses, usually 5% or less, it can increase the weld pool fluidity, which increases the overall welding speed and improves penetration and arc stability when welding stainless steel, low alloy, and mild steel.

However, even the smallest doses can react and cause oxidation if you try to MIG weld aluminum, copper, or magnesium. That's why this shielding gas selection should be used only when necessary and with care.

	Argon	Helium	CO2
Weld penetration	Moderate	High	High
Arc Stability	Good at low amps, Medium to low on steel	Good	Good
Weld Spatter	Low to none	Medium or low	High
Reactivity	Non-reactive	Non-reactive	Can react with base metal
Welding Speed	Medium	Medium	High
Welding Costs	Moderate	High	Low
Metal Thickness	Medium	Thick	Medium and Thick
Metal Types	Works best with aluminum, magnesium, nickel, copper	Works best with thicker ferrous and, non-ferrous metals	Limited to Steel

Shielding Gas Mixtures In MIG Welding

As you can understand from the previous section of the article, shielding gases rarely perform well when used pure. Therefore, welders usually turn mixtures of two or three gases. A mixture of gases can provide a more consistent, stable arc when welding. By varying the ratio of the gases, welders can fine-tune the weld quality for different applications. Mixtures of gases can also help to reduce the cost of welding. For example, if possible, you can replace Helium which is expensive and requires a higher flow rate, with CO2, which is cheaper and shows somewhat similar arc characteristics.

The most commonly used shielding gas mixtures for MIG welding include Argon/Helium, Argon/CO2, Argon/O2, or a tri-mix of Argon/Helium/O2.

1. Argon/CO2 Shielding Mixture

By mixing the 75% or argon with 25% carbon dioxide, you get one of the best and most cost-efficient shielding gas mixtures for mild steel. Many welders swear by this mixture, which is often referred to as the C25 mix. The high content of argon in this mixture produces clean welds with great arc stability and minimal spatter, while 25% of CO2 improves the penetration and bead profile that argon lacks.

FCAW with C25 mix

Source: https://www.reddit.com/r/Welding/comments/8owctl/home_depot_flux_core_with_my_c25_gas_mix_on_was_a/ 

Since you are not using too much CO2, your MIG gun produces less spatter, and you avoid issues with weld appearance that occur with CO2-rich mix or pure carbon dioxide gas. Additionally, the CO2 gives you the ability to turn on spray transfer on your MIG welder, which will allow you to get the job done quickly, and you avoid issues with arc stability when MIG welding steel with pure argon.

However, since CO2 is semi-reactive gas, C25, or 75/25% Ar/CO2 mixture can cause oxidation and contamination when MIG welding aluminum, stainless steels, or non-ferrous metals. Therefore its applications are limited to mild steel, but as a hobbyist, occasional or DIY welder, most of your projects will include welding this metal.

2. Argon/Helium Mixtures

Mixing argon and helium is more common in TIG welding, where tungsten electrode is prone to contamination by a high content of reactive gases, such as CO2. Mixing 25-75% of argon with 25-75% of helium increases the arc performance and penetration while retaining the excellent cleanliness of the weld. So basically, this mixture shows a similar result to the C25 mix. However, since helium is more expensive than carbon dioxide, this mixture is not so cost-efficient when looking to GMAW weld mild steel.

Nonetheless, if you are looking to MIG weld thick pieces of non-ferrous weld metal such as aluminum, magnesium, copper, or nickel alloys, the argon/helium mixture is your choice. This mixture won't contaminate the base metal or specialized aluminum wire.

Mig welding with 75% helium and 25% argon

Photo by @madebyauger from TikTok

Keep in mind that there are no specific rules like with the C25 mixture, so you can tweak the content of argon and helium in the range of 25-75%. Increasing helium content will provide deep penetration, but as the content rises, the arc becomes less stable.

3. Argon/Oxygen Mixture

Gas Metal Arc Welding with argon/oxygen mixture is used in specialized applications when you need to weld carbon steel, low alloy steel, or stainless steel. In these applications, 1-3% of O2 stabilizes the arc and improves weld fluidity. When welding stainless steels, 0.5-1% oxygen prevents the refractory scale of chromium oxide.

However, keep in mind that this is a specialized mixture that you are less likely to use in your everyday applications. Since the sole purpose is to avoid oxygen contamination in the weld, you should avoid using more than 3% of it on steel and 1% on stainless steel.

4. Argon/Helium/CO2 Mixture

Like with argon/oxygen, specific applications may even call for a tri-gas mixture. Commonly, that's the case when GMAW welding stainless steel, where mixing 10% argon, 85-88% helium, and 2-5% CO2 will yield the best results. This mixture provides enough heat to battle the thermal properties of the stainless steel, resulting in good penetration, stable arc, increased weld fluidity, and the ability to battle the formation of chromium oxide, which can interfere with the properties of the weld.

Chromium(III) oxide. Source: https://en.wikipedia.org/wiki/Chromium%28III%29_oxide

 

How To Choose The Best Shielding gas for MIG welding?

Many seasoned welders will, without a doubt, tell you that C25, or a mixture of 75% argon and 25% CO2 is the best shielding gas for MIG welding. This is true in a way, but choosing the best shielding gas mixture or single gas for GMAW isn't a simple process. To choose the best gas for your MIG applications, you should consider the following:

• Type of metal
• Metal thickness
• Weld transfer process
• Overall costs
• Desired mechanical properties and weld appearance of the finished weld
• Productivity goals

However, now that you understand the properties of most common shielding gases and their mixtures, you can easily choose the correct gas. In addition, we dedicated the final section of our article to summarize everything we learned today.

	100% Argon	100% CO2	75% Argon/ 25% CO2	Argon/Helium	Argon/ 1-3% O2	Argon/ Helium/ CO2
Mild Steel	Poor arc stability	Cheap and fast for thick pieces	The best choice	Not commonly used	More stable and faster than pure Argon	Not used
Stainless Steel	Not used	Not suitable	Can be used with risk of corrosion	Not commonly used	Stable arc	Best choice
Aluminum	Best choice	Not suitable	Not suitable	Good for thicker pieces	Not suitable	Not suitable
Other Non-ferrouus metals	Best choice	Not suitable	Not suitable	Good for thicker pieces	Not suitable	Not suitable

1. What Is The Best Shielding Gas For MIG Welding Mild (Carbon) Steel?

The best shielding gas for mild steel welding with GMAW is, without a doubt, a mixture of 75% argon and 25% CO2 - a C25 mixture. As we said, this mixture brings out the advantages of both gases - good penetration and shielding gas coverage, reliable arc starts and stability, weld fluidity, and low amounts of spatter. In addition, the mixture overcomes the drawbacks of pure gases that result in a lack of penetration in thick pieces, unstable arc on steel, lots of hard spatters, and poor-looking weld beads. You can use it to successfully weld steel with hobbyist MIG welders such as YesWelder MIG 205DS-B.

YesWelder MIG-205DS-B Multi-Process MIG Aluminum Welder

If we look at the list of requirements above, the argon/CO2 mixture has it all. It can be used on various metal thicknesses, allows spray transfer. Its overall costs are lower compared to argon/helium mixture, and you get the desired mechanical properties, with high production and good-looking weld bead. The only disadvantage of the C25 mixture is the inability to work as efficiently with metals other than mild steel.

2. What Is The Best Shielding gas For MIG Welding Aluminum?

Welding aluminum with a MIG welder like YesWelder YWM-211P will require a 100% Argon shielding gas. Compared to carbon steel, aluminum aggressively reacts with CO2 or oxygen, which results in poor welds, so there is no room for experiments with reactive gases. Since aluminum usually comes in thinner pieces, you can expect reliable, clean, and stable low amp welds with 100% argon.

YesWelder YWM-211P Double Pulse Aluminum MIG Welder

However, if you are dealing with thicker pieces of aluminum, you can add Helium to the gas blend to increase penetration. The ideal range is 75% argon and 25% helium because you get desirable penetration and arc performance without increasing the operational costs. You can increase the content of Helium if you feel like you are still running cold, but more than 50% helium will result in a globular transfer which isn't the fastest.

Source: https://weldguru.com/welding-transfer-modes/

Besides aluminum, you should consider the approach of shielding the weld with 100% argon on thin and medium-thickness pieces and an argon/helium mixture of thick pieces of most non-ferrous metals, such as magnesium, copper, or nickel alloys.

3. What Is The Best Shielding Gas For MIG Welding Stainless steel?

GMAW welding stainless steels will require two-gas mixtures of argon and CO2 or argon and O2, or a tri-gas mixture of argon, Helium, and CO2. As a hobby welder, you can use the 75% argon, 25% CO2 mix for stainless steel and a machine such as YesWelder YWM-200, but be careful. A high content of CO2 can introduce carbon in the weld joint, which affects the corrosion resistance capabilities of stainless steel. Ideally, the CO2 content shouldn't be higher than 5%, but DIY welders can get away with C25.

YesWelder YWM-200 4-in-1 Multi-Process Aluminum MIG Welder

An alternative two-gas mixture for stainless steel includes 98-99% argon and no more than 2% oxygen. The addition of oxygen prevents the refractory scale of chromium oxide, increases welding speed, and stabilizes the arc. However, be cautious when introducing reactive elements to your shielding gas when welding stainless steel.

Finally, most seasoned welders will tell you that a mixture of argon, helium, and CO2 is the best shielding gas choice for GMAW welding on stainless steel. This is a specialized mixture that includes 10% argon, 85-88% helium, and 2-5% CO2, and provides optimal results on stainless steels, including good arc performance, enough heat, and desirable properties of the weld, but with higher costs and higher operational requirements.

MIG Welding Stainless Steel with Tri Mix Gas (90% Helium, 7.5% Argon, 2.5% CO2)

Source: https://www.youtube.com/watch?v=Z75xvCrVwpc

Conclusion

Shielding gases play a crucial role in MIG welding, and selecting the right one is essential to ensuring the quality and safety of the weld. It's important to consider the type of metal, the welding position, and the desired outcome when choosing a shielding gas.

Argon, carbon dioxide, helium, and blends of these gases are the most common options for MIG welding. Each has its own unique properties and benefits, and choosing the right one will ultimately depend on the specific requirements of your project.

 

👏 You may be interested in the following:

• Welding Shielding Gas Overview
• How To MIG Weld Stainless Steel Like a Pro
• MIG vs. MAG Welding -  Is There a Difference?