I have never primed aluminum siding, a good quality acrylic paint is all you really need. I have never had any bonding problems, just pressure wash the chaulk off and start painting. I normally give a 5 year warranty on an aluminum siding job, I have never been called back to fix anything on one. I have never even been called back to repaint one, it just doesnt fail.
IMO aluminum siding is the best thing in the world to paint, minimal prep, easy to spray, no sanding, no primer, just wash and spray and cash your check.
I did notice that the house next door to my parents is aluminum and peeling, I have never actually seen it peel before. I figure they either didnt wash it before painting or they used really cheap paint. I would go offer my services to them, but the owner is so cheap he wont even use a gas powered mower, he uses the old style push mower on his 1/2 acre of yard.