The primary function of shielding gas in GMAW welding is to protect the molten weld puddle from atmospheric contamination. These contaminants are in the form of oxygen, nitrogen and hydrogen that are contained in the atmosphere. The reaction of these elements with the weld pool can create a variety of problems, including porosity (holes within the weld bead) and excessive spatter. Different shielding gases will also influence the following:
- Arc characteristics
- Mode of metal transfer
- Penetration and weld bead profile
- Speed of welding
- Undercutting tendency
- Cleaning action
- Weld metal mechanical properties
Argon, helium, CO2, and oxygen are the most common shielding gases used in the MIG welding process. Some gases are better suited than others for the most commonly used base materials, whether it’s aluminum, carbon steels or stainless steel.
CO2 and oxygen are reactive gases, meaning they affect what’s happening in the weld pool. The electrons of these gases react with the weld pool to produce different characteristics. Argon and helium are inert gases, so they don’t react with the base material or weld pool. For example, pure CO2 provides very deep weld penetration, which is useful for welding thick material, however 100% C02 produces a less stable arc and more spatter and can only be used in a short arc mode of metal transfer. If weld quality and appearance are important, an argon/CO2 mixture can provide arc stability, weld pool control, and reduced spatter. Depending on the base material being welded the following gases and gas mixtures can be used.
You should use 100 percent argon for aluminum. An argon/helium mix works well if you require deeper penetration or a faster travel speed.
There are a variety of shielding gas options, including 100 percent CO2 or a CO2/argon mix. As the material gets thicker, adding oxygen to an argon gas can help with penetration.
Shielding gases used for this higher carbon content steel operate well with 100 percent CO2 or a CO2/argon mix. Low-alloy steel. A 98 percent argon/2 percent oxygen gas mix is well suited for this material.
Argon mixed with 2 to 5 percent CO2 is the norm. When you require extra-low carbon content in the weld, use argon with 1 to 2 percent oxygen. For the best color match on 300 series material a mixture of helium/argon/co2 can be used as well.
The shielding gas you choose can affect many welding characteristics. Once you understand which properties are most important for your application, you can select the best blend for the job. It is recommended that you consult your gas supplier or other welding professionals for the best choice.