Al is beyond my scope of stuff, but as for SS;
James, you should ceck out the Ar/O2, Ar/CO2 mixes 95 Ar and above. With C25, 75/25, whatever, you will probably find a fat (not PHAT), bead. Bulbus is more discriptive; fot the height or protusion, it is not as wide, which to me means it's got more metal than it needs but not enough "wetting of the edges" (those that know correct, me if I'm wrong). Whether this is not enough volts/amps, or too fast a wire speed/ slow travel speed, I cannot be the judge. but these are the directions you should look. Higher Ar gas content will help with these aspects. Which is the right mix for you is hard to determine, but just for s%!t's&GRins try 95/5 ar/co2, or 98/2 ar/02, if its not structural and your just trying to get a "hot" bead what does it cost other than the gas(which aint cheap compaired to c25). the cost, i don't think, will be that much more than normal but, "est mas". Try this on some scrap first to get a feel. but I think you'll like it better than c25. Some playing with the knobs(volts ipm/wire) will be required to dial it in.
Your results and opinions would be just more info out here for all of us.
Good Q.:)