Here is a link with some specific Data on 2219.
http://klabs.org/DEI/References/design_guidelines/design_series/1205msfc.pdf

After you have sifted through the Vairable Polarity Plasma, and the DCEN with Helium, you will note that the author of that article (NASA Geniuses) will for thin sections (your 0.060 material can be considered thin) fall back on GTAW AC.

Here are some tips;

Make sure your edge prep is perfect. A roughly sheared edge will blow an X-ray,

Wire brush may not be satisfactory for oxide removal, try a 120 grit 1 1/2 inch aluminum oxide disk on a 12-18 thousand rpm pnumatic 90 degree angle die grinder. If tube 120 grit flappers on a straight die grinder.

Make sure your balence control is set to provide suitable cathodic etching (I like a good 1/8 inch beyond the weld toe)

Make sure your argon is not contaminated, with adiquate surface prep prior to welding, the top of your weld bead should be perfectly clear and reflective, if anything is floating on the top or a grey skin appears you have contamination of some sort.

If all this is done and you still find a *grainy* appearence on your weld surface you may be moving too slowly. Slow travel speeds with GTAW Aluminum allow too much hydrogen to dissolve into the pool, when the pool solidifies not all the hydrogen can escape. If the porosity on your X-rays is very fine and especially dense at the ends of the weld this may be the case. Aluminum likes to be welded hot and fast. A good heat sink arrangement will help dissapate unwanted heat.

If your using Thorium electrodes stop, Thorium electrodes are the most likely to *spit* into the weld pool, when they over heat small particals of tungsten actually transfer across the arc into the pool. Cerium or Zirconium are better choices when your doing X-ray quality welds.

Forget the purge box/bag Thousands of them are sitting dusty in shop corners around the nation. You shouldn't even need backing gas.