At work we weld the same Al assembly at two different sites. Everything is more or less the same except that one site uses pure argon and the other uses a mix (27%He, 73% Ar). The plant using the mix has problems getting the welds to meet specification, where as the one with the pure gas does not. The sections are 5xxx series and essentially a bracket is being welded to a thicker section.

Without getting into details (because that's about all I know at the moment), can anyone suggest any possible ideas why the mix might be giving problems (porosity etc) that would not occur with the pure

I think I'm about to be dumped in this one so I'd like to at least be able to sound like I might have a clue or two...

Michael