Why can't you TIG weld Aluminium with DC current? You can TIG weld it beautifully with AC, but if you turn the TIG welder to DC it doesn't work.... You don't get a nice little weld pool, the sample seems to overheat and deform and it goes all black on the outside. The welding rod just leaves circular globules on the top that don't melt to the main body. You can happily do stainless and other steels on DC, but not Aluminium. I assume that this is a Chemistry question, as I can't think of a Physics reason...... Anyone? Thanks for listening.