We have some 6061 aluminum material (0.160" thickness) that is going to be welded as square groove butt joint.  I've been playing around with DCEN TIG on aluminum because we use that polarity a lot at our shop on a lot of other aluminum parts.  We have a decent procedure for that, but we do end up with some porosity because I believe we are traveling too fast and not giving the hydrogen a chance to boil out.  However, I'd like to make a decent AC weld and compare the two in terms of strength, discontinuities, etc.  I'm looking for some recommended parameters for welding aluminum of this thickness in AC TIG mode.  I have a Miller Dynasty 700 that's hooked up to a jetline seamer, so we can accurately dial in travel speed, voltage, current, wire feed speed, etc.  Here's what I was running, and it wasn't turning out that great...

AC
Square Wave Function
EN - 225
EP - 140
Balance - 90%
Frequency - 400hz
Travel speed - 11.5ipm
Voltage 11.0
Wire feed - 38.0ipm
80%Ar, 20% UHP Helium
Flowrate: 35CFH
Backup Gas - 5CFH argon

Another point to make is that this material is clamped in place with copper along the entire length, so there is a sufficient heat sink.  However, I hooked some heating pads up to the copper in an effort to reduce the amount of amperage really needed to push through the material.

I'm having trouble dialing in a smoot running welding schedule and was looking for some suggestions for this thickness.  I'm doing bead on plate right now and I can't seem to get consistent results.  Any suggestions would be GREATLY appreciated because I've been experimenting with this for days and I'm at my wits end.

Thanks