Here's some more...

20. "Selection and Weldability of Heat- Treatable Aluminum Alloys," ASM Handbook, Vol. 6: Welding, Brazing, and Soldering, R. Martukanitz, ASM International, 1993, pp. 528-536.

http://eagar.mit.edu/3.37/H-3371-20.pdf

Respectfully,
Henry