American Welding Society Forum
i was hoping to hear from the pros about the advantages and disadvantages and the best combination of gases for different types of materials such as chromoly 4130, mild steel, alum, titatium and stainless steel.
your post will be greatly appreciated........
the go to gas for tig welding is pure argon. this will work on anything that can be tig welded. there are, however different gas blends that will optimize the tig welding arc. for aluminum, additions of helium will provide a "hotter" arc in order to be able to increase travel speed and/or penetration. with 300 series stainless steels, 2% or 5% hydrogen in argon will greatly increase travel speed and reduce the heat effected zone. as for chrome moly and other mild steels, plain old argon is what is needed. this thread could go on for miles with all of the experience involved in this forum, so I thought I would throw my opinion in first.
Welcome to the forum!
For 99% of manual GTAW the shielding gas of choice is 100% argon.
Sparx, rightly notes that small percentages of Hydrogen are used in some cases to improve wetting and travel speed but these are almost always automated situations.
Argon and 2.5% Hydrogen is sometimes used with cast HIPed (Hot Isostatic Pressed) Inconel718 which is much more sensitive to heat input than wrought inco718. The extra boost in heat per amp is possible plus there is a desirable cleanliness in surface bead appearance which is important in multi-pass operations (inter-pass oxide removal is still required). But this is a pretty rare case as most folks don’t run into this alloy.
I have used Straight Helium and 50/50 Argon Helium mixes to do GTAW DCEP (reverse polarity) buildups on massive magnesium castings where the reverse polarity provides a wide pool with minimum penetration and heat input. Mag cannot be welded DC+ without some helium input. (better have a big water cooled tig torch and equally large tungsten)
Two good textbook resources for general gas info is Welding Principles and Applications Fifth edition by Larry Jeffus. And Modern Welding Technology 5th edition by Howard B. Cary These texts provide some data on Gasses and Mixtures including Argon Oxygen (less than 1%), Argon Helium, Argon Hydrogen.
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