A Guide to Shielding Gases

Mastering the Art of TIG Welding: A Comprehensive Guide to Shielding Gases

Beginning your TIG welding journey can be both exciting and challenging. Especially when it comes to choosing the right shielding gas. In this post, we aim to explain the process and equip you with the knowledge needed to confidently select the ideal gas for your TIG welding projects, considering your specific materials and applications.

The Crucial Role of Shielding Gases in TIG Welding:

TIG welding, or Gas Tungsten Arc Welding, stands out as a precise and clean welding method. It is perfect for thin materials and widely used in industries like aerospace and automotive. The key to achieving flawless welds lies in the shielding gas, which creates a protective atmosphere around the weld area. This shield prevents contaminants like oxygen from entering the weld pool. Additionally it  ensures the integrity of the weld and avoids issues like porosity and cracking. Meanwhile, Shielded Metal Arc Welding, Submerged Arc Welding, Plasma Arc Welding, Flux Core Arc Welding, etc., use welding flux for shielding.

Illustrative image showing the how tig welding works internally
Commonly Used Shielding Gases in TIG Welding:

Argon takes the lead as the most widely used shielding gas in TIG welding due to its inert nature and effectiveness in producing high-quality welds. Helium, another noble gas, is employed to enhance heat and penetration, particularly in thicker materials. While reactive gases like nitrogen and hydrogen are generally avoided, small amounts can be beneficial for specific applications, such as welding stainless steel. 

Argon in TIG Welding:

Argon, a noble gas, serves as the primary shielding gas in TIG welding. Its effectiveness lies in creating a protective atmosphere, preventing contamination and defects. 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. However, its density somewhat limits its use to a flat position since gravity can displace it in vertical or out-of-position welding. While pure argon is versatile and suitable for various materials, including mild steel, stainless steel, aluminium, and copper, it may lack the heat and penetration required for thicker materials.

Image of a sheet of metal welded at the left-hand side with argon written on the sheet
Helium TIG Shielding Gas:

Like argon, helium does not react chemically with other elements, including tungsten, weld metals, or the atmosphere. However, compared to argon, helium gas has higher thermal conductivity, which means higher heat input.As a result, helium is widely used when TIG welding thicker materials, and it somewhat reminds of CO2 in MIG welding. Another difference with argon is that pure helium is rarely used in manual TIG welding, mainly because it is not cost-effective for all applications.

Helium is lighter than air, so you must increase the gas flow rate to get proper shielding gas coverage. However, low weight can be helpful in overhead welding. Knowing that helium is pricier than most shielding gases for TIG welding, it is clear why 100% helium is rare choice. To deal with the issue, most welders use an argon/helium mixture. While pure helium is less common due to cost considerations, a blend of argon and helium combines the benefits of both gases, providing a stable arc and excellent shielding coverage.

Image of a metal cylinder being welded to a metal box using helium gas
Reactive Gases in TIG Welding:

Reactive gases, as their name states, can react chemically with other elements and are, therefore, unsuitable for shielding in TIG welding. In addition, interacting with the molten pool and electrode can cause defects such as porosity or cracking. However, in specific applications, small amounts of hydrogen and nitrogen can be added to increase the properties of the weld.

  • Hydrogen, in addition to up to 5%, can increase the penetration and weld fluidity, therefore, welding speed when dealing with austenitic stainless steel and nickel alloy. In this case, hydrogen cleans surface oxides, stabilises the arc, and creates deep, broad penetration. However, even the slightest additions of hydrogen can cause porosity or hydrogen cracking in welding aluminium, martensitic, ferritic, or duplex stainless or mild steel and steel alloys.
  • Nitrogen plays the same role as hydrogen but is only used to weld duplex or super-duplex stainless steel. Like hydrogen, it shouldn’t be used when welding steel, austenitic stainless steels, or exotic metals.
Image of a welder welding pieces of scrap metal together using hydrogen gas
Can You Use Carbon Dioxide in TIG welding?

While you can use inert gases for both MIG and TIG welding processes, you shouldn’t use CO2 in TIG welding. CO2 is a semi-reactive gas that breaks the molten metal’s surface tension and quickly burns the non-consumable tungsten. As a result, you get weld contamination, significantly reducing weld quality, which is crucial in TIG welding.

In addition to contamination, CO2 causes highly unable arc; you notice sparks and fumes all around the weld. You can also see cracks, holes, and overall poor quality weld. If you are looking for similar results to a C25 mixture (75% argon/25% Co2) in TIG welding, that’s the 75% Argon/ 25% Helium blend, but we will talk about mixtures in the following section.

TIG Welding Gas Mixtures

Since most shielding gases don’t perform exceptionally well when used as pure, welders started using mixtures. The mixture of two gases get the best out of each gas and surpasses the cons of each gas individually. In TIG welding, the most common gas mixtures are:

Argon/Helium: is a versatile and effective shielding gas mixture that can be used for a wide range of materials and produce high-quality welds. Argon and helium mix in 50-75% percent of each, but welders usually opt for 75% argon and 25% helium. Combining these two gases gives you a more stable arc, good penetration, high welding speed, and excellent shielding gas coverage. In addition, you deal with each gas’s cons individually, which present in lower penetration of argon and high price and somewhat less stable arc of helium. You can also tweak the amount of each gas to get even better results.

Image of a metal sheet that has been welded on the left-hand side with the argon and helium gas values written on the top of the sheet

Argon/Hydrogen: is a more specialized mixture used to TIG weld austenitic stainless steel and nickel alloys. The 5% hydrogen added to 95% argon helps stabilize the arc, increase heat, and weld fluidity in these applications, but it shouldn’t be used with other types of stainless steel, aluminum, or steel alloys.

Argon/Nitrogen: is another specialized mixture you are less likely to use as a hobbyist, but it can be helpful when welding duplex or super-duplex stainless steel. The 2% nitrogen to 98% argon shows similar results to hydrogen addition, but similarly, it shouldn’t be used in steel, aluminum, or exotic metal welding.

 

A table showing the different shielding gases for TIG welding on different parent metals
Choosing the Right Gas for Specific Applications:

The choice of shielding gas depends on the material being welded. However, you will likely use 100% argon in nearly 90% of your home or DIY projects. Understanding the properties of each is crucial in choosing the best gas for tig welding, so this section will summarise everything we have learned so far.

Mild steel

If most of your TIG welding projects include common or mild steel, you shouldn’t look further than 100% argon. This is an all-around choice for your everyday GTAW welding of medium-thickness mild steel, but once you feel like you need more heat, you can add helium to the mixture. However, many welders find pure argon capable and cost-effective, so they rarely add helium in home applications.

Aluminium

You can successfully TIG weld aluminium with 100% argon or argon/helium mixture. Pure argon shows excellent results when welding thin aluminium, as it provides good arc starts and stable arc at low amp AC current. In addition, limited penetration will prevent burn-through, wrapping, and distortion of sheet aluminium.

Once the thickness of the aluminium increases, you can add up to 25% of helium. Adding helium increases the penetration and welding speed while retaining good AC TIG properties of the 75% argon. Adding more than 25% helium in AC TIG aluminium welding can be used in specific applications, but it is not that common.

In highly specialised situations, seasoned welders use 100% helium to DC weld thick aluminium. The combination of high temperature, high penetration, and welding speed can be useful in full-penetration butt welds. However, mastering the technique due to low arc length is challenging and not recommended to new welders.

Stainless Steel

The biggest challenge with TIG welding stainless steel is matching the parameters and shielding gas to the given grade. Each stainless steel grade shows somewhat different properties, so you will have to be cautious. If you are unsure of the specific grade you are about to weld, you can use pure argon or an argon/helium mixture as a go-to choice.

Pure argon will work great in welding medium to thin stainless steel. Limited heat and penetration won’t cause defects or discoloration or remove the corrosion resistance. However, if the thickness increases, you will need more heat, therefore, helium addition.

When dealing with austenitic stainless steels, adding 5% hydrogen will help with arc properties, heat input, and speed. 2% nitrogen does the same with duplex and super duplex stainless steels. Minimal doses of less than 0,5% oxygen or CO2 can deal with surface-active oxygen on some stainless steel, but these are extreme cases.

Exotic metals

GTAW is known for its good results in welding exotic metals, and the shielding gas choice isn’t too different. If you are unsure what specific metal you are about to weld; you can always work with 100% argon.

Pure argon will work well with nickel, magnesium, or copper, but you might need some tweaking. Copper is an excellent heat sink, so you will need more heat input which 100% helium usually provides. Nickel alloys require 5% hydrogen to battle the porosity, and magnesium can be DC TIG welded with 100% helium.

Shielding Gas Coverage:

Achieving proper shielding gas coverage is crucial for successful TIG welding. Factors such as gas flow rate, nozzle size, and TIG torch consumables play a vital role in creating a protective atmosphere around the weld pool and tungsten electrode.

Suitable Gas Flow

The suitable gas flow will differ from the welding conditions, consumables, and shielding gas choice. Typically, flow rates are between 10 and 35 cubic feet per hour (CFH). Indoor welding will require lower rates due to a lower risk of contamination, while outdoor or welding with 100% helium will require higher rates. You can check the current rate by looking at your gas flow regulator. 

Regardless of the actual conditions, you will want to get the laminar gas flow. To accomplish that, you should use the lowest gas flow rate possible for the application and conditions. Increasing the gas flow or selecting improper torch consumables can cause turbulent gas flow. Turbulent gas flow will suck in the unwanted gases from the atmosphere. So when choosing the flow, the bigger, the better isn’t the right approach.

Image of a Single Stealth Tig Flow meter
TIG Torch Consumables

The essential TIG torch consumables include a nozzle and a collet with either a gas lens or a collet body. These can impact how shielding gas is distributed and cause issues even though you selected the suitable shielding gas for TIG. 

The collet body is a more affordable option, and it will do just fine when dealing with non-critical welds. However, the array of holes on the collet body can cause turbulent flow in specific applications, so it shouldn’t be used when high-quality welds are required.

Size and Shape of Nozzle

The size and shape of the nozzle can affect the coverage of the gas and, in turn, the quality of the weld. For example, if the nozzle is too large, it can lead to insufficient coverage of the gas, which can allow air contaminants to enter the weld area or require a higher flow rate, increasing costs. On the other hand, if the nozzle is too small, it can lead to too much gas being used, which can increase the cost of the welding process or cause turbulent flow.

Nozzles also come in different shapes, such as straight, converging, and champagne, and they can also affect gas coverage. The wanted laminar flow is usually achieved using a converging nozzle in the largest diameter and longest length practical for the job.

Image of Mega Tig Welding Kit (tig cups, gas lenses and collets)

FInal Thoughts:

In conclusion, selecting the right shielding gas is a critical aspect of TIG welding that significantly influences weld quality and integrity. By understanding the properties of different gases and considering specific application requirements, you can confidently choose the ideal gas for your TIG welding projects, ensuring success and high-quality welds.

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