Hello Chevy_welder, the majority of aluminum welding done with the GTAW process is indeed done with AC current, it also requires a hi-frequency generator to provide arc continuity and argon, helium, or an argon/helium gas mix, there is also some that is done using DC straight polarity and helium shielding gas. GTAW aluminum welding done on the cheap, requires a hi-frequency generator and an AC stick welding machine or one that is capable of producing AC current. A true GTAW aluminum capable welding machine usually has the capability to remotely vary the amperage output of the machine and also control the shielding gas via a synched solenoid and also generally has the capability to control the afterflow time of the shielding gas(this avoids burning up the tungsten). That's the short rundown, recent technological advances have expanded the capabilities of machines designed to GTAW weld aluminum and any other weldable material, an explanation of all of the different variables out there would take a whole lot of time and certainly be outside of my knowledge, yet collectively, it is likely that others on the forum could give a very complete rundown. Hope this explains a bit of what you were asking in your question. Best regards, Allan
An AC balance control, while not technically essential, sure makes aluminum work a lot more pleasant. A balanced wave results in a lot of unnecessary heat being directed to the electrode. This limits limits the maximum current levels possible for a given electrode (limiting thick aluminum performance), and also results in a wider arc and bead (limiting thin aluminum performance).
Purpose built AC/DC square wave TIG machines are really the best way to go if you can find access to one.