How To Choose the Right Gas For Welding Different Metals

The first research about welding in the protective atmosphere was carried out in the 1920s, and the results were outstanding. The welders dealt with brittle and porous welds that occurred once the molten weld puddle reacted with atmospheric gases.

The research results highlighted the importance of shielding gases in welding, so even today, no one recommends MIG or TIG welding without one. Although everyone understands the significance, many beginners wonder how to choose the right gas for welding different metals.

In this comprehensive article, we'll help you choose the suitable shielding gas for mild steel, stainless steel, and aluminum, as well as some exotic metals you could encounter in your welding journey.

Why is Shielding Gas Important?

The shielding gas is crucial to MIG and TIG welding because it creates a protective atmosphere around the weld. Why these two methods you may ask? Because both use bare filler metal (solid MIG wire or TIG rod) that is not self-shielded.

Once the filler metal and base metal melt, they become prone to contamination. The molten metal reacts with atmospheric gases such as oxygen or nitrogen, causing brittleness, porosity, oxidation, and other defects that affect the appearance and structural integrity of the weld.

The solution for this is the introduction of shielding gas. Inert and semi-inert gases such as Argon, Helium, or CO2 create a protective atmosphere. Inert, or non-reactive gases control contamination and prevent molten metal from reacting with the atmosphere, eliminating most welding defects we mentioned.

So, whenever you are MIG welding or TIG welding, you must use a shielding gas or a mixture of gases to get the best and cleanest results. Things are somewhat different regarding Flux-cored arc welding and Stick or MMA welding. These welding methods use a self-shielded electrode, which contains flux that creates a protective layer of slag. So when you Stick weld or use FCAW, there is no need for a shielding gas.

Types of Shielding Gases

Before we discuss the gases for the specific metal type, you should first understand the three primary types. Based on their reactivity and composition, all shielding gases can be divided into three groups:

• Inert gases: Gases such as Argon and Helium are inert, or nonreactive, producing the cleanest protective atmosphere. These are used in critical applications and when welding exotic or non-ferrous metals.
• Semi-reactive gases: CO2 or carbon dioxide is known as semi-reactive gas, as it only partially reacts with the atmosphere. This gas has various advantages, such as low price and good penetration, leading to a variant of MIG welding referred to as Metal Active Gas welding (MAG). However, it can yield messy welds with excessive spatter in large percentages. Additionally, you cannot use CO2 with TIG welding.
• Reactive gases: Gases such as oxygen or nitrogen are something you are trying to force away from your welds. However, in small doses, up to 5% of the mixture, they can improve the weld pool fluidity, penetration, welding speed, and other welding performances. These are typically used when welding stainless steel or different variations of carbon steel.

You should know one more thing when choosing the right shielding gas. Pure shielding gases such as 100% Argon, Helium, or CO2 often show weaknesses such as lack of stability or penetration, or excessive penetration. That's why, whenever possible, welders use mixtures of two or three shielding gases, to get the best out of it.

Learn more about welding shielding gases in our comprehensive article .

Shielding Gases for Different Metal Types

Now that you understand the foundation of shielding gases and options, it is time for specific recommendations. All metals can be classified based on the iron content and atomic structure.

Based on iron iron content, we are seeing three primary types:

• Ferrous metals contain iron: Typical examples are steel, cast iron, and iron alloys such as stainless steel, etc.
• Non-ferrous metals are non-magnetic as they do not contain iron or only the smallest additives. Typical examples are aluminum, copper, lead, nickel, tin, titanium, and zinc.
• Metal alloys are a combination of more than one element including another metal. Some examples include brass (copper and zinc), steel (iron and carbon), etc.

The iron content can greatly affect the weldability of the metal. That's why most welders use this classification when considering the preparation, including the shielding gas choice.

In addition, metals can be classified based on atomic structure. The structure is based on the periodic table, so we are seeing alkaline, transition, or alkaline earth metal. However, you are less likely to use this classification as a welder.

Quick Shielding Gas Selection Sheet

Choosing a suitable gas for the given material type is surely important. But, further in the text, we will help you understand why each mix or gas is the best choice for the given applications.

Choosing a Shielding Gas For Steel

Steel is a ferrous metal, a mixture of iron and alloying elements such as carbon and more. Based on carbon content, there are several types of steel, known as low-carbon steel or mild steel, medium-carbon or high-carbon steel.

As the carbon content increases, the metal becomes more durable and resistant, but also harder to weld. Carbon creates a brittle structure prone to cracking once it heats up or starts to cool down.

You will likely weld mild steel as a beginner or a hobby welder. Mild steel is the most forgiving welding metal, but it requires good preparation and proper shielding gas choice. You can use any method to weld mild steel, but we'll discuss the ones that include shielding gas: MIG and TIG welding.

MIG Welding Gas For Mild Steel

MIG welding is a beginner-friendly, fast, and efficient method often used to weld mild steel. Beginners, hobbyists, and DIY users love MIG because of its low-skill requirements. But as part of the preparation, you will need a correct shielding gas.

You can use several gases to MIG weld mild steel, but the most common ones are argon and CO2.

Argon is an inert gas that provides a very clean welding atmosphere, but it has its drawbacks. 100% argon in MIG welding steel lacks penetration and doesn't produce the most stable arc. In addition, it can be expensive to use with mild steel, which is why many welders add CO2.

Adding 25% of carbon dioxide to 75% produces a C25 mixture, which shows the best results when MIG welding mild steel. The argon in the mixture provides a highly clean atmosphere, while the CO2 supplies enough penetration and arc stability. That's why many seasoned welders recommend 75/25 Argon/CO2 when MIG welding mild steel.

Another alternative includes using 100% CO2 on MIG welding mild steel. Pure carbon dioxide is a very cheap solution when you need to finish the job quickly and cheaply, and you don't care about weld aesthetics. With its high penetration and heat CO2 can cause a lot of spatter and create messy welds. Nonetheless, due to its popularity, there is a variant of MIG called Metal Active Gas welding, that includes using pure CO2 as shielding.

TIG Welding Gas For Mild Steel

TIG welding is a complex welding technique with the highest skill requirements, but it yields the highest quality results. Many welders use it to weld thin and delicate, non-ferrous metals, but you can also use it for mild steel.

Unlike MIG welding, TIG welding requires the highest quality, pure inert gas shielding. The reason is the tungsten electrode that carries the arc and gets heated as you weld. The tungsten also requires the shielding, but it must be inert.

So, to TIG weld mild steel, you will need either Argon or Helium. 100% Argon is the best choice for most TIG welding applications, including welding thin mild steel. This shielding gas produces a more stable arc with TIG welding, but it also lacks some penetration. While the penetration drawbacks are not so notable on thin pieces, welding thick stock can present issues.

That's why welders add 25% of helium, or even up to 50% when TIG welding mild steel thicker than 1/4". The helium in the mixture provides similar benefits to CO2. It produces higher penetration and stabilizes the arc, which is great when welding thicker steel. However, TIG is not known for its performance on thick stock. Therefore, many turn to Stick or Flux-cored arc welding in those applications.

Choosing The Gas For Stainless Steel

Stainless steel is a corrosion-resistant type of steel thanks to its added chromium content. Chromium gives steel a silver-shiny look and makes it resistant to rust when welded properly.

However, stainless steel can be somewhat tricky to weld, and it requires precise heat control. Prolonged exposure to higher heat can cause carbide precipitation or oxidation. Both conditions affect the primary advantage of stainless steel - its corrosion resistance.

Besides the heat control, you will need the correct shielding gas for stainless steel, so let's see what your options are.

MIG Welding Gas For Stainless Steel

To successfully weld stainless steel you can use MIG welding. But to get satisfying results, you will need a proper shielding gas. When MIG welding stainless steel , welders recommend Argon-rich mixtures with 97-98% Argon and 2-3% CO2.

The primary concern of this mixture is the semi-reactivity of CO2, which can cause oxidation. That's why welders recommend only up to 5% of CO2, but ideally, 2-3% will do fine. These small amounts of CO2 will stabilize the arc and provide enough penetration, without the risk of oxidation or overheating. Instead of CO2, you can add up to 3% oxygen (O2) to achieve a spray transfer on stainless steel.

A more complex alternative for MIG welding on stainless steel is a tri-gas mixture of argon, helium, and CO2. The mixture of 90% Helium, 7.5% argon, and 2.5% CO2 produces a short-circuit metal transfer MIG. This transfer is sometimes desired in MIG welding stainless steel. The con of this mixture is the high price of helium and complexity for beginners.

Another alternative for high welding speed on MIG welding stainless steel is a tri-gas mixture of oxygen, argon, and helium. In this mixture, oxygen takes no more than 1%, helium is 35% while argon balances the mixture. This is another complex mixture, but it produces good results on all stainless steel types in all welding positions.

TIG Welding Gas For Stainless Steel

TIG welding stainless steel is not as complex as MIG, at least regarding the shielding gas selection. Since TIG does not work with reactive or semi-reactive gasses, you can't do too much wrong if you use 100% Argon on stainless steel.

As noted, argon shows somewhat better stability with TIG welding, and since it is often used on thin metals, penetration is not the biggest concern. Pure argon will help you finish the job, but you can add some helium if you notice any issues.

Helium added to argon improves weld pool fluidity and can encourage deeper penetrating welds. However, keep in mind that helium also raises the heat, so unless you know what you are doing, adding more helium can cause oxidation.

Choosing The Shielding Gas For Aluminum

Many welders consider aluminum one of the hardest metals to weld. This non-ferrous metal has a surface aluminum-oxide layer that provides corrosion resistance. But, this layer can create various issues during the welding, since it has a different melting point than base metal.

In addition, the thermal properties of aluminum make it heat-sensitive. Improper heat control can create cold welds or a burn-through. Thus, it's not a surprise many consider aluminum the most challenging metal to weld.

Luckily, choosing the right shielding gas for aluminum is not so demanding. Due to its ability to form an aluminum oxide surface layer, molten aluminum can severely react with the atmosphere. Unshielded or poor protection creates brittle and porous welds with lots of spatter.

That's why welding aluminum requires inert gases such as Argon or Helium. Pure (100%) Argon is a go-to shielding gas choice for most aluminum applications and metal thickness of up to 1/4", regardless of the welding process (MIG or TIG welding aluminum ).

Since Argon shows its penetration drawbacks on metals thicker than 1/4", you'll need some helium. So when welding aluminum 1/4-1/2", the welders add 25% Helium to the mixture. Helium increases the overall heat and weld penetration. Once the thickness surpasses 1/2", you will need helium content up and over 50% and vice versa.

Choosing the Shielding Gas For Non-ferrous Metals

As noted, non-ferrous metals contain no or just traces of iron, so they are generally weaker than steel. However, they show other characteristics such as malleability, corrosion resistance, and thermal or electrical conductivity, etc. Still, you can weld non-ferrous metals using some of the most common arc welding techniques, including TIG and MIG.

As a hobby welder, you are likely to deal with nickel, magnesium, copper, titanium, and zirconium. So, let's see what are the shielding gas recommendations for non-ferrous metals.

Shielding Gas For Nickel

Nickel and nickel alloys show exceptional heat and corrosion resistance, which makes them highly useful in many critical applications. However, nickel is prone to porosity, cracking, contamination, and oxide inclusions, so you'll need a proper preparation and shielding gas.

You can weld nickel with both MIG or TIG welding. During the welding, you should use pure (100%) Argon shielding gas to avoid contamination.

Shielding Gas For Magnesium

Magnesium and magnesium alloys have quite similar weldability to aluminum. Alloyed with aluminum, manganese, zirconium, zinc, and rare earth metals, magnesium alloys show strength similar to steel, but with a weight closer to aluminum.

So, when welding magnesium alloys, you will need an inert shielding gas such as Argon or Helium. However, magnesium often comes in thick casting or parts. Therefore, you should use 50/50 Argon/Helium, or even 100% helium for the thickest pieces close to 1 inch.

Shielding Gas For Copper

Copper has a very high thermal and electrical conductivity and a low melting point. These properties make it suitable for critical applications but make it tricky to weld. Copper and its alloys are prone to oxidation, particularly if alloyed with aluminum. Therefore, you will need clean and inert shielding.

Due to high thermal conductivity, TIG welding copper requires a 100% helium or 75% helium and 25% argon mixture for thicker pieces. You can MIG weld thin copper alloys with 100% Argon, or Argon-rich mixtures such as 75% argon, and 25% helium.

Shielding Gas For Titanium

Titanium is almost 50% lighter than stainless steel but more than two times stronger. Like many other non-ferrous metals, titanium has a strong affinity for oxygen. So welding titanium requires exceptional shielding gas coverage and back purging.

Most welders recommend TIG welding titanium. Both shielding and purging during titanium welding require pure inert gas, typically 100% Argon.

Shielding Gas For Zirconium

Zirconium shows excellent corrosion resistance to most organic and inorganic acids, salt solutions, strong alkalis, and some molten salts. This benefit makes it widely used in pressure vessels, heat exchangers, piping, tanks, shafts, etc.

Cleanness and shielding are paramount when welding zirconium, and that's why many turn to TIG welding. TIG welding zirconium requires a high-purity inert shielding gas. We recommend 100% Argon, or Argon/Helium mixtures in thicker parts. To ensure the best protection, welders use primary (torch), secondary (trailing gas), and back purging.

Final Thoughts

Shielding gas is a crucial component of welding, as it protects the molten metal from atmospheric contamination. However, choosing the right shielding gas for the metal you are about to weld can make or break your project.

Keeping your molten welds protected from the atmosphere is the number one priority in producing sound and the highest-quality welds. In this comprehensive guide, we simplified and explained the shielding gas choices for the most metal you will encounter in your welding endeavor.

By getting out one part of the larger equation called welding, you are set for success. Thus, you can further focus on the other aspects, such as dialing in the machine, practicing technique, or cleaning.

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