-Purchased my PowerTig 200-DX-d about a year ago and have used it for a few projects using the SMAW function. Very happy with the machine.

-This weekend I finally got around to getting my Argon bottle and tried testing it out on TIG AC, as I would like to practice tig welding aluminum.
-I wanted to test the machine on a piece of clean 3/8 aluminum plate(all i had available at the time), set the machine around 160 amps.

Welder settings:plugged into 240V

Pulse:off
Tried using 2T and 4T
AC
HF start
No pre or post flow
Frequency:20
Balance:30

Torch was plugged in negative.
Argon flow I varied from 10 to 20L(I forgot the regs that are supplied are not gauged in CFH)

So can any of you experienced guys tell me where i may have gone horrible wrong>?, because as soon as i hit the switch on the torch, the arc seemed extremely violent and rough...and almost seemed to be gouging the aluminum at times...leaving black marks around the beads.
I did not do much more experimenting in case I had a chance of doing any damage due to improper settings so any advice to lead me in the right direction would be great!

Thanks