Selecting the right welding gas - Shielding gas guide for MIG and TIG welding
Selecting the right welding gas for your MIG and TIG application can make or break your project. The reason for this is simple - different metals have different properties. Metals therefore react differently to the elements in the oxygen in the air, once they begin to melt during a welding process.
A welding gas, or shielding gas, is designed to protect your metal from contamination once it begins melting and protect the integrity of your weld. Without the appropriate welding gas your metal can contaminate and, over time, your welding join can become frail.
So, with that in mind, let's talk about welding gas (or shielding gas). The appropriate welding gas for welding a particular metal will differ depending on whether you’re MIG or TIG welding. The thickness of the metal must also be taken into account.
But before we discuss the different welding gas combinations that are appropriate for different metals, it is worth getting to know some basic information about the different gases themselves.
Argon is the most commonly used welding gas for MIG and TIG applications. It can be used pure or mixed with other gases. Argon is a colourless, odorless and non-toxic gas and is 0.93% of the earth's atmosphere. It can create an oxygen and nitrogen free inert shield, making it appropriate for welding a wide range of metals and alloys. It is frequently mixed with Hydrogen (H2), Carbon Dioxide (CO2), Helium (He) and Oxygen (O2) to optimise the quality of a weld, depending on the thickness and characteristics of the metal.
Helium is an extremely light and non-flammable gas. In fact it is the second lightest gas behind hydrogen. It is odorless, non-toxic and tasteless. Its primary function as a welding gas is to provide an inert shield and prevent contamination through oxidisation for a wide range of metals. These include stainless steel, aluminum, copper and magnesium alloys.
CARBON DIOXIDE (CO2)
Carbon Dioxide is an odorless, tasteless, and nonflammable gas which is found in the earth’s atmosphere. As a welding gas it is commonly combined with argon (Ar) as an inert shield for low alloy steels, mild steels and carbon steels.
Hydrogen is non-toxic, odorless, colorless and tasteless and the lightest of welding gases. As a welding gas, hydrogen is commonly combined with Argon for high temperature metals, especially stainless steel. It is commonly used in plasma cutting processes.
Occasionally used as a welding gas, usually in combination with argon for use on duplex stainless steels. Nitrogen is colorless, odorless, and non-toxic. It is non-flammable at normal atmospheric temperatures.
Welding gases to suit different metals
Now that you know the basics about the main gases used in welding, let's talk about which ones and which combinations are appropriate for the metal you want to weld. Let’s start with MIG welding
Welding gas for MIG welding of mild steel
If you’re looking for an all-purpose mild steel welding gas, an Argon-CO2 combination is your best option. Argon-CO2 blends produce minimal spatter, and a nice bead appearance is forgiving on thinner mild steels meaning it is less likely to burn through.
As an alternative, you can use pure CO2. This will provide a deeper weld penetration, but will result in a rougher weld than if you use a Argon-CO2 mix. It is therefore worth keeping in mind depending on the project.
If you’re looking for an optimum welding gas combination depending the thickness of the mild steel, different Argon-CO2 combinations are available from specialist gas dealers. Here is our recommendation:
0-4mm Mild Steel: 93% Argon, 5% CO2, 2 % Oygen (O2)
4-12mm Mild Steel: 84-86% Argon, 14-16% Co2 (Click here)
12mm+ Mild Steel: 78%Argon, 20% CO2, 2% O2
Welding gas for MIG welding of aluminium
Argon is generally the "go to" gas for aluminium welding, whether you’re TIG welding or MIG welding. We recommend you use a pure argon shield when welding aluminium base metals less the 15mm thick.
For welding thicker metals a helium mix can be added to increase the penetration. Start at about 20-25% helium for 15mm thick and then increase the helium content as the aluminium gets thicker. Helium mixes will increase the price of the welding gas shield, in comparison to argon.
DO NOT use a welding gas containing any Carbon Dioxide or Oxygen when welding aluminium, regardless of whether you’re using MIG or TIG process, as it will contaminate the metal and affect the weld quality.
Welding gas for MIG welding of stainless steel
Stainless steel does have different properties to mild steel. These need to be taken into account when selecting your welding gas shield. However, it is far less fickle than aluminium and the welder has various shielding gas options.
An Argon-CO2 blend will provide good results on common stainless steels.
But stainless steel does contain a higher level of chromium which increases its resistance to corrosion. This contributes to a slightly higher melting point than mild, carbon-based steels. For this reason many welders opt to use a helium combination as helium conducts more heat and increases the weld penetration. Helium will increase weld speed but this won’t necessarily translate to cost savings because it is more expensive than Argon and creates higher consumption rates.
For high quality welds consider an argon-helium-CO2 blend with about 25-33% helium and 1 CO2. This will create a high travel speed, better control of distortion in thin material, and superior bead shape.
Welding gas for Mig welding of stainless steel to mild steel
Consider an Argon-Co2-helium blend containing 25-33% helium and 1% Co2.
Welding gas for TIG welding
Pure argon is generally the welding gas of choice for use as a shield when using the TIG process. TIG welding is generally suited to welding stainless steels and aluminium. When welding aluminium, a pure argon gas can be effectively used for metals up 18mm thick.
Once the aluminium base metal exceeds this width, it is worth adding a helium blend to increase weld penetration. We recommend a 75% Argon 25% helium blend for aluminium welds thicker than 18mm.
A similar principal applies when choosing a welding gas shield for TIG welding of stainless steel. Pure argon can effectively be used for a width of up to 8mm. Once the stainless steel exceeds this width add switch to an argon-helium blend.