Thank you for the comment Plasma56 - I am an 'outside the box' thinker, I am often invited to sit in on discussions and strategy meetings for that quality alone. It's not always a great trait, sometimes it results in me complicating things for people, but I've learned to keep my mouth shut and filter through some of the thoughts before talking.
I stopped by the school yesterday and we discussed the procedure for a little bit; the blunt tungsten tip was one idea that surfaced in addition to slightly faster travel speeds, an improved cleaning process, and no preheat. A CWI previously working with them told them to keep the Al temp between 250ºF and 350ºF for the duration of the weld-out. I also found out that they had been given some 3/8" material to use, so they were welding 3/8", then machining it down to 1/4" or 3/16" after welding and prior to mechanical testing. ??? Don't ask me..... :) I suspect that in addition to everything else that might have gone wrong they were probably having issues accessing the joint resulting in a long arc at the root pass(es) - it appeared to me that the root was the initial point of failure when I look at the coupons.
Based on my research and your guy's help I think I'm going to be able to help them solve this problem fairly easily. There are still a few unknowns I'll admit, but I have a much better understanding of what I'm looking for now.
Thanks guys I appreciate the help.
BJ