[rahtreelimbs]

From a technical standpoint why is aluminum mig used with spray transfer instead of short circuit?

[Farmwelding]

I am no expert on the matter, but from what I have found, it has a cleaner weld and no spatter which I assume is bad for aluminum because spatter on aluminum has issues that I dont know very well. Also it may have to do with heat and cutting through the oxide layer that melts at a higher temperature. It can also be run with pulse mig which is probably for the same reasons.

[Rupes]

Mig is reverse polarity. So electrode positive. That's the same polarity that cleans oxides off on tig welds.

I'll take a stab at why its done in spray transfer. Only because I made a mess of some aluminium when I tried out a mig ages ago. It was because it was in short circuit, voltage too low and was probably the ugliest thing I've ever welded.

Mig isn't known for being a high penetration process and not especially hot. Spray on the other hand is very hot and definitely no penetration issues. I think its mostly likely that the aluminium being welded is especially good at transferring heat and short circuit ends up with little to no penetration due to lack of heat. The constant stream of molten droplets you get with spray probably helps with the cleaning action. Electrode positive cleans but in short circuit I think it would be a bit intermittent.

Again I'm guessing, that's how it felt to me when I did it.