MAG (from English Metal Active Gas) means semi-automatic welding of metals in a protective atmosphere of an active gas (the opposite of TIG welding method, when an internal protective gas is used for welding). The active gas prevents air from entering the molten metal and also becomes involved in chemical reactions in a weld pool, so it actively participates in processes that are created in a molten welded metal.
The method MAG is used for welding plain carbon steel, low-alloy steel, and high-alloy steel and building-up.