Are you guys serious? Clearly you don't know a great deal about what a good coded welder can do. Someone who know's what they're doing with a TIG torch can weld aluminium foil to the side of a ship. The problems with welding different materials come from their different melting points, so if you try to weld steel and aluminium with a MIG kit, the aluminium is gone before the steel melts. A TIG torch allows you to regulate both the position of the torch, the position/progression of the filler, AND the amount of current to the torch (this can be changed on the fly with a footpedal). This allows a skilled welder to join materials of different thicknesses, or different materials. It's absolutely possible.