I just want to elaborate a bit more, since I have given this alot of thoughts (this doesn't mean I'm correct though). Alodine + zinch chromate give superior corrosion protection, but is not the industry standard. Zinc Chromate is illegal in Europe due to environmental/health reasons. Alodine is available but requires special disposal handling. The industry standard is:
* Clean/passivate with etching solution
* Non chromate wash primer (with zinc oxid)
OR
* Alodine
Then
* Strontium chromate epoxy primer
* Polyurethane top coat(s) (preferably, or some other)
On internal parts it is enough to clean/pasivate and a layer of Str Cr epoxy.
The "main ingredient" is the strontium chromate epoxy. This gives superb corrosion protection and superb strength, chemical resistance, is 100% water proof, stick like glue and act as an excellent base for top coats. It is vastly superior to zinc chromate rattle cans due to the properties of the epoxy, and strontium chromate is nowhere near as toxic as zinc chromate.
Water bourne systems have low VOC values, but is harder to apply. In industrial processes where all the fumes are captures and recycled anyway, the water based products really doesn't add any value.
But, what is a health/environmental risk in industrial processes may be insignificant in a garage shop. Also, what is a non-issue industrially may be very complicated and risky in a garage shop. No one is going to convince me that, considering I am wearing a good mask, I will run a greater health risk using zinc chromate rattle cans than I will by messing around with a two component non chromate etch primer using a spray gun.
Given the choice (if Zinc Chromate was available), I would use Zinc Chromate from rattle cans on all internal parts + alodine on all non-alclad pieces. On external parts I would use StrCr epoxy. Right now I'm using a two component wash primer for internal parts and a zinc chromate rattle can I got hold on for non-alclad pieces, but will be switching to the "industry solution" with StrCr epoxy when I get the goods.