TIG Welding Aluminum AC or DC
If you searched for "TIG welding aluminum AC or DC", you should watch this video...
The quick answer is that aluminum is tig welded using AC. (99.9% of the time)
It is possible to TIG weld aluminum using DCEN but that is an advanced technique for thicker aluminum and pure helium is needed.
This video explains why Alternating Current is used for TIG welding aluminum and why DC current is used for Tig welding steels.
Essentially, AC has a cleaning action that is needed in order to clean up the surface oxide layer so that a clean trash free puddle can be achieved.
The video explains and demonstrates all this and more.
Understanding Why AC is used for Aluminum also helps you to fully understand the AC balance setting on your TIG welder.