Gas Choices and Selections for MIG Welding Various Metals
Gas for MIG welding is what makes MIG welding possible. The name informs us of this; “Metal Inert Gas welding". The gasses used are what shield the weld from the air. When Carbon Dioxide or Oxygen is added to the mixture, MIG welding is not technically MIG welding anymore. This is due to the fact that both Carbon Dioxide and Oxygen are not inert gasses. The process then becomes GMAW or Gas Metal Arc Welding.
The type of gas uses also determines:
- How deep the weld penetrates the metal welded
- The characteristics of the welding arc
- The mechanical properties of the weld
When choosing the type of gas to be used, it is best to seek input from a welding supply store. The store will recommend the proper gas to match the welding wire to be used. Or, one may utilize the welding wire manufacturer’s recommendation. Typically, the manufacturer will provide a few choices ranging from the best choice, to something that will provide the minimum acceptable results. The final choice in the type of gas, is based on cost.
The four most common gasses used are:
CO2 / Carbon Dioxide
O2 / Oxygen
Helium (the least common)
Most of the times these gasses are used in a mixture form, typically consisting of carbon dioxide, and Argon or Oxygen. Oxygen is what causes most weld defects, however, in small percentages, mixed with other gasses, it improves the arc characteristics. Argon and Carbon Dioxide can be used by themselves. In some case there is tri-mix shielding gas containing Argon, Carbon dioxide, and Helium, or, Argon, Carbon dioxide, and Oxygen. I recently used this last mixture, when taking my 3G MIG Welder Certification.
The more common mixtures and gasses are.
- C2 or 2% Carbon Dioxide and 98% Argon
- C25 or 25% Carbon Dioxide and 95% Argon
- 100% Carbon Dioxide
- 100% Argon
Some basic guidelines for choosing the proper gas are as follows:
Welding of carbon steel can be done with Carbon Dioxide alone and it produces the deepest penetration, the most smoke and the roughest weld. The most widely used mixture is called C25 and that is 25% Carbon Dioxide and 75% Argon gas. There are other mixtures that work well depending on the type of welding that will be done. Most of these are designed by welding gas supply stores and chains. A common mixture is a combination of Argon, Carbon Dioxide and Oxygen.
Welding of stainless steel is typically done with C2 or 2% Carbon Dioxide and 98% Argon. In some cases there is tri-mix shielding gas containing 90% Helium, 7.5% Argon, and 2.5%Carbon dioxide. Again many welding supply stores carry their own mixture that can improve the weld quality and ease of welding on stainless steel.
Welding of aluminum is typically done with Argon alone, with one exception. If the aluminum being welded is thicker then ½ of an inch there may be Helium added to the mix.
Argon gas by itself works well on most exotic metals like:
- Copper Alloys
- Nickel Alloys