TIG welding aka Heli-Arc process and GTAW
There aren't many metals, either ferrous or non-ferrous that cannot be welded with the TIG- Tungsten Inert Gas, An inert gas is non-flammable, Argon and Helium- an non-inert, such as Hydrogen (read Hindenberg 1937 Big Bang theory here) is flammable. The inert gas shields the welding arc from oxygen, in both TIG and MIG (Metallic Inert Gas) welding processes, much as the gas produced from the arc shield from the flux that is burned and consumed in the "stick" welding process. I'll pass on welding aluminum (100% pure Tungsten electrode, end "balled" and on AC high freq- and stick with ferrous, such as hardened steels used in mfg. firearms. Pre-heat and inter pass temps. are critical, as post heat and wrap, annealing the area prior to the welding process is critical on Air, Water and Oil hardened alloy steels- DC straight polarity (80% of the amperage (heat) is in the parent metal in this polarity setting, 1 or 2 % thoria tungsten (thorium prevents the electrode, which is NOT consumed in the TIG process from breaking down, ground to a flat tip- amperage, open circuit voltage, size of cup, torch, tungsten and flow of shielding gas all basically depend on ther thickness and mass of the piece(s) to be welded. Most, but not all TIG welding is done on a bench in the downhand position- wind must be contained in TIG and MIG, to prevent a breeze from blowing the shielding gas away from the welding zone and the resulting HAZ- Heat Affected Zone. Hope I got it right- TIG welding is like brain surgery- not a real "do it your-self-er" in my book.