tig welding gas

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What gas do you use for welding aluminum? I have used  ARGON then a guy at airgas my supplier said to try a 25% ARGON 75% HELIUM mix which seems to work well. so now started using an airgas thats closer to home and this guy is telling me to use 90% HELIUM 7.2 ARGON 2.4 CARBON DIOXIDE mix . I am new at this so give the ins & outs on this gas thing PLEASE.
Reply:Sounds like your Airgas rep is trying to make some extra cash at your expense.  Unless your welder is undersized for the work being done, there is no reason to use anything other than 100% argon.  Everything I've seen seems to suggest that Helium will provide a hotter arc at any given power level, though it may be more difficult to strike an arc.  That said, helium is much more expensive than argon.  Also, I have no idea where the suggestion to use a mix with carbon dioxide came from.  Seems like that would lead to all sorts of problems.
Reply:If you do a search here, you'll find lots of threads about what gases to use, beyond what I can quickly type here.For TIG welding Aluminum, you need a 100% inert gas, meaning No CO2 in the mix. Usually pure Argon is used, but for thicker material with greater penetration needed, Helium is added because it has a higher ionization voltage so imparts more heat at the same amperage setting.Helium is more expensive and because it has smaller molecules, it 'drifts' away faster and upward too, so more is needed to give good coverage.
Reply:Argon, or Argon, for most stuff Argon.Disclaimer; "I am just an a$$hole welder, don't take it personally ."
Reply:Argon.  It's that simple.TurkeyLincoln Idealarc 250Millermatic 250Miller Synchrowave 250 Miller Synchrowave 350Thermal Arc PlasmaHH140Miller Diversion
Reply:most any noble gas will work like Krypton
Reply:Thanks for all the input guys. I am running a Syncrowave 350 LX so i don't think under sized  is a problem. One of them things where someone is just trying to sell me some sh!# I don"t need.