Although it can be a tricky topic to get your head around, it’s important to develop a solid understanding of the types of gases used in welding.



Put simply, ‘shielding gases’ are necessary for a number of different welding processes as it’s required to protect the weld arc and prevent contamination.  



While gas is not needed for some welding methods, common processes including MIG Welding, TIG Welding and Metal-Cored Arc Welding all require a shielding gas.



The most widely used shielding gases in welding are Argon (Ar), Carbon Dioxide (CO2), Helium (He) and Oxygen (O2).



SHIELDING GASES



In simple terms, gases used in welding can be broken down into two categories: Inert Shielding Gases and Reactive Shielding Gases.



The two most commonly used Inert (chemically inactive) gases in welding are Argon and Helium. They are classified as inert because neither Argon or Helium will react chemically with the molten weld pool.



In contrast, Oxygen, Hydrogen, Nitrogen and Carbon Dioxide are the most widely applicable Reactive Gases used in welding. Reactive gases combine chemically with the weld pool to produce a desired effect.



INERT SHIELDING GASES



Argon – The most common inert shielding gas in welding and can be used on its own.  Nickel, copper, aluminium, titanium, and magnesium alloyed base materials use 100% argon shielding. Argon, because of its lower ionization energy, assists with arc starting. It is the main component gas used in binary (two-part) or ternary (three-part) mixes for GMAW (MIG) welding. It also increases the molten droplet transfer rate.



Helium - Commonly added to the gas mix for stainless and aluminium applications. Its thermal conductivity is very high, resulting in the broad but less deep penetration profile. Helium additions to argon are effective in reducing the dilution of base material in corrosion resistant applications. Helium/argon blends are commonly used for welding aluminium greater than 1” (25 mm) thick.




Welding Gas Bottles



REACTIVE SHIELDING GASES



Carbon Dioxide (CO2), Oxygen (O2), Hydrogen (H) and Nitrogen (N2) are reactive gases which combine chemically with the weld pool to produce a desired effect when welding.



While Argon and Helium can be used by themselves for certain applications, reactive gases are often blended with inert gases to form ‘mixed gas’.



Two-part mixed gas blends are the most common and are typically made up either argon + helium, argon + CO2, or argon + oxygen.



Three-part mixed gas blends are popular for carbon steel, stainless steel, and, in restricted cases, nickel alloys. Helium, Oxygen and Carbon Dioxide are commonly added to Argon in varying amounts depending on the application.



Each of these gases has different properties which effect how they respond under the heat of a welding arc. These include their reactivity, ionization potential and thermal conductivity. Reactivity effects whether or not a certain gas or gas mix can be used with certain materials.



COMMON GAS BLENDS



Argon + CO2 - The most commonly found binary gas blends are used for carbon steel GMAW (MIG) welding. All four traditional modes of GMAW metal transfer are used with argon/CO2 binary blends. They have also enjoyed success in pulsed GMAW applications on stainless steel where the CO2 does not exceed 4%.



Argon + Helium - Useful for welding nickel-based alloys and aluminium. The addition of helium provides more puddle fluidity and flatter bead shape. Helium promotes higher travel speeds.



Argon + Oxygen - In small additions (1-5%), with a balance of argon, it provides good arc stability and excellent weld bead appearance. Both stainless steel and carbon steel benefit from the use of argon/oxygen blends.



Argon + Hydrogen - Hydrogen (H2) in small percentages (1-5%), is added to argon for shielding stainless steel and nickel alloys. Its higher thermal conductivity produces a fluid puddle, which promotes improved toe wetting and permits the use of faster travel speeds.



Helium + Argon + CO2 – Popular for stainless steel applications. Helium additions of 55% to 90% are added to argon and 2.5% CO2 for short-circuiting transfer. They are favoured for reducing spatter, improving puddle fluidity, and for providing a flatter weld bead shape.



Argon + Oxygen + CO2 - This ternary mix is applied to short-circuiting, pulsed spray, and axial spray modes of metal transfer on carbon steel applications. The high inert gas component reduces spatter.