AC (Alternating Current) TIG welding is used for the welding of Aluminum and Magnesium. TIG welding primarily utilizes a 100% argon gas as a sheilding gas. In some cases Helium may be used when welding thick materials. TIG welding (AC and DC) is one of the cleanest processes with no sparks or spatter. TIG welding offers the most control of any welding, which is why it is preffered for precision jobs like aerospace and racing.
DC (Direct Current) TIG welding is used with all metals other than Aluminum and Magnesium.