We supplied the wires that could be used in "mig. brazing". They were Cu. Ni. alloys normally used in the petro chemical, nuclear industries for welding "exotic" metals. A weld melts the parent metal being joined and fills in with molten metal from the filler wire or rod. During brazing the parent metal does not melt only the filler wire and a surface alloying takes place. If during brazing the parent metal melts or the brazing rod gets too hot the joint will be much weaker and zinc will boil out of the brazing rod, and this is very unhealthy for the operator, can causes metal fume fever, and can put you in hospital. The danger with mig. brazing is that the parent metal can easily melt so pointless. The amps need to be kept as low as possible to get a good joint. Zinc boiling off however is not a problem with the mig. wires as it should not have any in. We hardly sold any wire for mig brazing, the best use would be for galvanised steel. Being zinc coated any welding of it causes the zinc to boil off so its considered very dangerous and bad practice. (Galvanised products should be welded first then galvanised). By mig. brazing at the lowest poss. amps a joint can be made with minimum heat input so reduced zinc boil off. The added advantage is the joint is non rusting however the transition area will rust between the joint and the coating. When welding galvanised steel all rust protection is lost in the joint and for a fair amount both sides, so a bit pointless doing it.
I would question the brazing of "alloy" to steel if the alloy is aluminium or an aluminium alloy, you cannot use a welding or brazing wire for steel or non ferrous metals on aluminium or its alloys, nor the wires that would be used in mig. Neither would an aluminium mig wire work on steel. You can braze aluminium and some aluminium alloys, we were specialists at that, but that's a different story. If he meant alloy steels or stainless steels to mild steel yes, but better wires especially designed to weld these dissimilar steels are readily available and a far better solution.
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