Sum,
When you TIG the aluminum it will be anealed around the weld, not like alloy steel that will get hard. Another thing to watch out for is if you happen to dip your tungsten into the aluminum puddle ( I know we're not supposed to! but I am so "ham handed" that I do it on occasion.) well when you do dip it the tungsten will pick up some aluminum on it and then your weld will turn to crap! So keep the tungsten clean! Also you might want to think about a water cooled torch if you don't have one. I have found that weld quality with an air cooled degrades as you do longer welds.
Mkilger, I can remeber when I was in the aerospace tooling business Miller was developing their "pulse" type welder, at the time it was called "keyhole" welding becasue when you started welding you would blow a hole thru the metal and there would be a hole in front of the weld puddle and you would weld it shut as you progressed across the plates that you were welding together. We were doing 3/4 thick 2014 Al plate, butt welded, no bevel or prep, 100 % penatration and perfect welds. Looks like they have developed that for us common guys! I have been thinking about replacing my old Airco TIG maybe this is what I should look at.
Rex