Prepping Aluminum
Both Metal Prep 79 and Alumiprep are acid washes designed to etch the surface of the aluminum. Both are diluted with water prior to use and are rinsed after application. [Note that the Spruce catalog says that Metal Prep 79 is wiped off...however, the MSDS says to rinse].
Both are normally followed by a chromate treatment process (such as Alodine).
Prekote is a newer process and is supposed to be a more environmentally friendly process: no chromates, acids, or solvents. I haven't used it so can't comment. Having said that, I have used Alumiprep, followed by Alodine, followed by Akzo epoxy primer. I've also experimented with:
Dawn dishwashing detergent rinse, followed by Akzo primer.
Coleman fuel cleaning, followed by Akzo primer.
MEK cleaning, followed by Akzo primer.
I all cases I scuffed the aluminum well and rinsed/wiped until the rags weren't picking up any oxidation.
Results: Akzo primer sticks well, regardless of method listed above. My opinion is that an etching/chromating process might be required/desired in a maritime climate, but isn't necessary for primer to stick well as long as the aluminum is scuffed to provide some "bite" and is cleaned well/has no oils/residues on the surface.
I've also had good luck with other self-etching primers, such as NAPA 7220.
YMMV.
Mike