Welding Shielding Gas Overview

The first steps in welding included joining two pieces using a bare electrode, but the issues soon emerged. The welds were highly porous and brittle due to the interaction between weld area and gases in the atmosphere, leading to cracking and eventually failure of entire weldments.

Noticeable research in overcoming these issues was done during the 1920s when the first scientists used external gas supplied around the arc. The discovery of welding shielding gas laid a foundation for modern welding we know today and two of the most popular welding processes - TIG and MIG welding.

Shielding gases play a crucial role in welding to this day, so we will discuss their properties and good and bad sides.

Tig welding Aluminum.

Source: https://www.youtube.com/watch?v=9S2OdtwHWoE

What is The Welding Shielding Gas?

The shielding gas in welding protects the molten weld pool as it solidifies from interacting with atmospheric gases such as hydrogen and nitrogen. If there is no shielding, the gases enter the weld pool and stay trapped or evaporate in the form of tiny bubbles from the weld, leading to the welding defect commonly known as porosity. The porosity can also happen inside the weld, affecting its integrity, causing cracking and, eventually, failure.

In Stick and Flux core welding, a protective layer of flux contained in the core of the wire or the electrode protects the weld puddle. However, Gas Tungsten Arc Welding and Gas Metal Arc Welding processes (TIG and MIG) rely on external shielding gases.

Source: https://weldguru.com/what-is-flux-in-welding/

Besides the shielding, welding gases can also impact arc stability, penetration, heat transfer, and pre and post-weld preparation and cleaning. Therefore, welding gases are more than just a shield of your weld.

Shielding gas choice can make or break your welding project, so it is crucial to know the difference and properties of each. Since choosing the right shielding gas is often overlooked, we made this comprehensive guide on the most common shielding gases and their mixtures.

Types Of Shielding Gases

Shielding gases are categorized by their reactivity with other elements and gases into three groups: inert gases, semi-reactive and reactive gases.

• Inert gases, or non-reactive gases, as their name states, are capable of resisting any chemical reactions or any interaction with electrode, weld metal, or the atmosphere. As a result, they are often used in critical applications that require cleanliness with low amounts of spatter. Argon and helium are commonly used inert gases in welding, and they can be used with both TIG and MIG welding.
• Semi-reactive gases, as you can deduce, only partially react with their environment. Therefore, they provide decent weld pool protection but with a certain amount of spatter and post-weld cleaning. Carbon dioxide is a typical and maybe the most widely used shielding gas in the MIG welding process.
• Reactive gases aggressively react with compounds and other elements, so they create changes in the state of the weld or the welding conditions, leading to porosity, brittleness, or cracking. However, a reactive gas such as oxygen, nitrogen, or hydrogen increases the heat or pool fluidity when added in 1-3% to a two or tri-gas mixture. Nevertheless, increasing the value of reactive gas can cause the sole issues we are trying to avoid by introducing shielding. In addition, reactive gases contaminate tungsten electrodes, making the welding arc highly erratic. As a result, these are not commonly used in TIG welding.

Understanding the major groups of shielding gasses is a good foundation, but to know which one is the best for your welding project, you will have to dig deeper. The following section will explain how common welding gases perform in specific applications.

Argon Inert Gas In Welding

Argon is an inert gas that stays perfectly stable at high temperatures of welding arc that can even reach 5.000 F. As an inert gas, argon resists interaction with weld metal and electrode, creates a unique welding atmosphere, and pushes away all other gases from the weld puddle. Therefore, the structural integrity of the material remains unaffected.

Argon also provides reliable and easy welding arc starts in alternating current (AC) applications and performs well at lower voltages. These positive characteristics make argon one of the most widely used shielding gases in welding, but it is not without its drawbacks.

Even though pure argon provides a stable arc and unmatched cleanliness, which is crucial when welding aluminum, titanium, and magnesium, the weld shows a broader finish and somewhat poor weld penetration profile, also known as wine glass or finger. While these results can pass for butt and fillet welds, pure argon is not widely used in welding steel or overhead and out-of-position welding due to its density.

Tig welding Aluminum.

Source: https://www.youtube.com/watch?v=9S2OdtwHWoE

Another con of argon, or any noble gas, is the price. It is pricier than CO2 or reactive gases, which you find in the atmosphere, so welders usually use it in shielding gas mixture for improved economics, welding results, and properties of the finished weld. Nonetheless, critically clean applications will often require 100% argon shielding.

Helium Inert Gas in Welding

Helium is another inert gas that found its way into welding due to its good shielding characteristics and welding performance, but also broader penetration compared to argon. The helium produces a wide, deep penetration profile, which makes it excellent when welding thick material.

Like argon, pure helium shows excellent results when welding magnesium, copper, and aluminum. However, the arc stability is significantly lower when welding steel and shows weak arc characteristics in low-amp applications. In addition, helium requires higher gas flow, which, combined with high cost, doesn't make 100% helium shielding the most economical and best shielding gas choice.

That's why you usually see helium in two or tri-gas mixtures. For example, helium is generally combined with argon in TIG welding, where argon helium mixture takes the best out of both gases - good arc start characteristics, arc stability, good shielding, low spatter, proper penetration, and all that at a more reasonable price compared to using pure helium shielding.

Source: https://www.youtube.com/watch?v=9S2OdtwHWoE

Carbon Dioxide (CO2) In Welding

Carbon dioxide is a semi-reactive gas that can react in specific situations, but it shows promising results when MIG welding steel. Its price is one of the main reasons that makes CO2 one of the most commonly used gases in MIG welding. Unlike helium, carbon dioxide is easy to extract, and you can even refill your bottle at paintball, home aquarium, or brewery shops.

Due to its high popularity among welders, you may come upon MAG term, which refers to Metal Active Gas welding, which includes MIG welding with reactive gases such as CO2 or oxygen. Metal inert gas (MIG) and MAG today are often used to describe the same process since many MIG welders started introducing CO2 or reactive gases into their mixture.

Is the affordable price the only reason welders use carbon dioxide as shielding gas? The answer is no. Carbon dioxide as a shielding gas provides excellent penetration, improves welding speed, and grants good mechanical properties to the welded steel. That's why welders often use 100% CO2 to economically MIG weld thicker steel, but only when the cleanliness weld aesthetics are not crucial.

MIG Welding with 100% CO2.

Source: https://www.youtube.com/watch?v=pTsithkxj8U&t=190s

However, high content of CO2 produces lots of spatter, fumes, and shaky arc, and due to higher penetration, it is not the most suitable shielding when welding sheet metal. In addition, carbon dioxide can react with tungsten electrodes, so you shouldn’t use it with the TIG welding process. The oxygen content in CO2 also limits the use in welding corrosion-resistant materials, but small amounts in tri-gas mixtures can improve arc when welding stainless steel.

Keep in mind that welding with pure CO2 will require a dedicated gas flow regulator. This regulator has a specific connector that fits CO2 tanks, but the biggest issue is the temperature resistance. Typical argon/CO2 regulators can freeze at higher 100% CO2 flow, so make sure your regulator is rated to deal with pure CO2 gas.

Source: https://weldingpros.net/mig-welding-with-100-co2/

Reactive Shielding Gases In Welding

As a hobbyist, you rarely get a chance to use reactive gases for your shielding operation, but they are partially helpful. For example, even though oxygen, nitrogen, or hydrogen cause corrosion and porosity, they can improve weld fluidity, penetration, or other properties of the weld when welding mild carbon, low alloy steels, and stainless steel. On the other hand, due to reactivity, these cannot be used to weld aluminum, magnesium, copper, or other exotic metals.

Common reactive gases used in welding are:

• Oxygen is a highly reactive gas that causes oxidation once it reaches the weld pool. However, when added in small amounts of 1-9% in the shielding gas mix, the oxygen improves weld pool fluidity, penetration, and arc performances. As a result, welders commonly use it when they want to achieve spray transfer and get the job done more quickly. However, oxygen shielding is not recommended when welding titanium, magnesium, copper, or other non-ferrous metals.
• Hydrogen is one of the gases you are actually trying to get out of your weld pool. Still, you can use it as a shielding gas in high-temperature applications to increase arc stability and weld bead performance. There is even a specific welding process that utilizes pure hydrogen shielding called Atomic Hydrogen Welding. Nevertheless, as an occasional welder, you are more likely to use it in mixtures that include 1-2% hydrogen when welding austenitic stainless steels.

Source: https://theweldings.com/atomic-hydrogen-welding/

• Nitrogen is the most abundant natural gas and makes up the majority of our atmosphere. It is typically used as a purging gas, but it can serve as a shielding gas in specific applications. Typically, 1-2% of nitrogen is used in a tri-gas mixture to weld stainless steels, nickel-copper, and nickel-based alloys.

Shielding Gas	Penetration	Arc Stability	Spatter	Price	Cleanliness/ reactivity	Welding Speed
Argon	Poor profile	Good even at low amp AC	Low to none	Medium to High	Exceptionally Clean	Medium to low
Helium	Broader Profile	Good stability overall	Low to none	High	Exceptionally clean	Medium
CO2	Deep	Medium	High	Low	Will react with non-ferrous metals	Medium to high
Reactive Gases	Medium to deep	Medium	Medium	Low	Extremely reactive	High fluidity

Commonly Used Shielding Gas Mixtures

As you might have deduced, each welding gas doesn't perform exceptionally well on its own, or it is expensive to use as pure, so the welders typically use blends. Two or tri-gas combinations are used to get the best out of each welding gas to provide good shielding gas coverage and match the weld metal properties but also improve weld properties, reduce costs, and post-cleaning time.

This section of our article will address the commonly used shielding gas mixtures, explaining how and when they are used.

Argon/CO2 Mixture

If you ask any MIG welder out there for a shielding gas recommendation for common steel, he will tell you it is argon/carbon dioxide. The typical choice is a C25 mixture that includes 75% argon and 25% carbon dioxide, but the content of gases can vary from 95% – 75% argon and 5% – 25% CO2.

As a rule of thumb, the thicker the metal gets, the more CO2 you add, but the content should be at most 25%. This combination is, for a reason, the most popular among MIG welders. It combines the cleanliness, good shielding, and excellent arc start and stability of argon with penetration, fluidity, and low price of CO2.

Source: https://www.youtube.com/watch?v=C09LC-lltWo&t=38s

By mixing these two, you limit the cons of individual gases - low penetration and high prices from pure argon and spatter and somewhat worse weld appearance from pure CO2. So, this is a win-win gas shielding choice. In addition, you can use MIG spray transfer with it, which is known as highly productive, so you can get the job done quicker. 

Overall, an argon/CO2 mixture is one size fits all choice for MIG welding mild steel. However, it is unsuitable for TIG welding or any welding that includes joining aluminum, stainless steel, or other non-ferrous metals due to possible oxygen contamination. Unlike pure CO2, you can use your typical argon/CO2 regulator, and our recommendation for smooth and reliable gas feed is certainly a YesWelder flow meter regulator.

 

 

YesWelder® Flow Meter Gas Regulator for Argon/CO2 Welding

Argon/Helium Mixture

Mixing argon and helium is your go-to choice when TIG welding aluminum or other non-ferrous metals. Due to their price, mixtures typically take 75% Argon and 25% helium. While you can deal with thin metals with pure argon, adding helium provides a deeper level of penetration, delivers a wide finish on the weld, and increases weld fluidity.

Generally, you can tweak the levels of both argon and helium to include 25-75% of each shielding gas according to your application. Adding more helium results in a hotter arc, allowing faster travel speeds and higher productivity rates. However, you want to add it sparingly when welding thinner materials, and beware of the high prices of both noble gases, especially helium. This shielding gas blend works well in both MIG and TIG welding.

210 AMPS, Helium / Argon Mixtures | Aluminum TIG Welding 

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

Argon/Oxygen or CO2

You already know that adding oxygen increases the risk of oxidation of the weld pool, but in extremely small doses, it can have positive effects. For example, mixing 98-99% argon with 1-2% O2 will stabilize the arc and improve the fluidity that allows spray transfer while reducing levels of spatter and fume. So surprisingly, this mixture is used when MIG welding austenitic, duplex, ferritic, or high alloy austenitic stainless steel.

Adding 1-5% CO2 will ensure better short-arc welding and positional welding properties, but it is not so commonly used. Adding both CO2 or O2 to the mixture means you shouldn't use it with TIG welding due to electrode contamination, but in exceptional cases, 0.5% of reactive gases can be added.

Argon/Hydrogen

Even though Hydrogen is a reactive gas, it prevents any oxygen in the air from getting into the weld. Therefore, by adding up to 5% hydrogen additive to 95% argon, you achieve high welding speed and deep penetration in TIG welding. But remember that this mixture is only used to weld austenitic stainless steel and nickel alloys.

When dealing with mild steel, aluminum, martensitic, ferritic or duplex stainless, or alloy steels, hydrogen content causes porosity and cracking, the very two issues you are trying to avoid by using an appropriate shielding gas.

Hydrogen Induced Cracks

Source: https://www.pipingengineer.org/weld-imperfections-hydrogen-induced-cracks/

Tri-Gas Mixtures

As a beginner, you are most likely to use manual welding of common steel or specific stainless steel, which two gas mixtures can successfully perform. However, advanced applications call for tri-gas combinations. These are usually used in MIG welding, where you have a lot more room to experiment by adding reactive gases and utilizing their positive arc characteristics. These are some of the common shielding gases mixtures:

Argon/CO2/Oxygen – you can't go wrong with the C25 mixture, but adding small amounts of oxygen additionally increases weld fluidity and possibilities for metal transfer mode. As a result, you can use it with spray arc weld transfer when you need to get the job done more quickly. Still, you retain the good arc stability, penetration, and weld appearance of C25 mixture.

Argon/Helium/CO2  mixture is widely used to achieve a pulsed-spray transfer in MIG welding stainless steel. Small amounts of CO2 (1-2%) increase the travel speed, and you get proper penetration, bead shape, arc stability, and control over the thin metal distortion.

Helium/Argon/CO2  is an industry-standard mixture when MIG welding stainless steel using a short-circuit transfer method. This mixture produces a good bead shape and color match, but it's not as versatile as other blends.

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

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

Final Thoughts

Shielding the weld pool in MIG and TIG welding is crucial for achieving the best results and solid welds. But different shielding gases serve more than just a shield. They can impact the stability, penetration, and overall properties of the weld, so choosing the right one for your operation is crucial.

Understanding how each shielding gas performs will help you a lot in your next welding project, and we hope our article was helpful in that.