TIG welding is suitable for all metallic materials. With TIG welding the arc burns between the component and a non-melting tungsten electrode. The filler metal is added separately, either manually or mechanically. The shielding gas has the task of protecting the electrode and melt pool from negative influences from the atmosphere. Oxygen, especially, leads to destruction of the electrode. The process can be run using either direct or alternating current. Direct current with negatively poled electrodes is usually used for welding of steels, copper, nickel alloys, titanium and zirconium. Alternating current is used for aluminium.