Copper-tin welding wire
A bronze-based filler material primarily used for MIG brazing and overlay welding of galvanized sheets and wrought copper alloys. It prevents excessive heat input and base metal damage.
Copper-tin welding wire is basically a solder for MIG brazing, not a real welding filler. It melts much lower than steel and lays down as a dense, bronze-like layer on the sheet. This way you mainly join galvanized sheets or copper alloys without getting the base material hot enough to warp or burn off the zinc coating. Just make sure you don't get too much zinc into the weld – then it becomes porous and soft. The weld must wet cleanly and flow well, so don't work too cold, but don't go full throttle either. After welding, let it cool slowly, then the weld stays tight and crack-free.