On Sun, 16 Jan 2011 16:05:24 -0500, wrote:

A phosphoric acid wash never hurts either - like Aluma-Prep-33 (or
simple water softener resin cleaner - virtually the same stuff)
(Phosphoric acid and ethyl polyol)

This stuff makes a huge difference with aluminum. It completely
degreases, and leaves a surface that really holds paint. It makes any
paint wet better and flow out nice and level. Aluma-Prep 33 is made
by PPG or Ditzler and is found at places that sell paint and supplies
for auto body work.