For both TIG (Gas Tungsten Arc welding or GTAW) and MIG (Gas Metal Arc
Welding or GMAW) pure argon is used for aluminum materials up to ½” thickness. Above ½” thickness, operators may add anywhere between 25 to 75 percent helium to make the arc hotter and increase weld penetration.

Argon is the best because it provides more cleaning action for the arc than helium does and it is also less expensive. Any shielding gas that contains oxygen or carbon dioxide is never used, as this will oxidize the aluminum.