Which shielding gases are typically used for welding nonferrous metals in MIG welding?

The use of argon and helium as shielding gases in MIG (Metal Inert Gas) welding for nonferrous metals is instrumental due to their unique properties. Argon, being an inert gas, provides a stable arc and excellent coverage by displacing air, which prevents oxidation and contamination during the welding process. This is particularly important for nonferrous metals like aluminum and copper, which can be sensitive to atmospheric conditions.

Helium is also used in combination with argon to enhance the heat of the arc. It has a higher thermal conductivity and can result in deeper penetration and a smoother bead finish. The combination of these gases allows for better control over the welding process, which is necessary when working with the lighter and often more challenging-to-weld nonferrous materials.

The other options involve gases that either do not provide the necessary inert environment or are not suitable for achieving high-quality welds in nonferrous metals. Thus, the effectiveness and characteristics of argon and helium make them the preferred shielding gases in this specific welding application.