PEO sounds pretty cool. Maybe even within the the capabilities of our production level.
Granted I've basically just read the short wiki page on it, but it doesn't sound too complicated like an actual plasma process, unless that is occurring on the low level. Most things with plasma oxidation that I've seen involve placing the object in a chamber where oxidized radicals of various gases are bombared on the object. Those are expensive. But can do things like covalently bond a silicone polymer to glass (awesome!!).
From the wiki page, it made it sound as simple as electrolysis, with a high voltage, and with using that high voltage to penetrate the initial oxide layer. As I typed this, however, I realize that applying 200 volts could not be applied to some simple liquid because other things in solution would be effected. I also don't see how the oxygen penetrates the metal unless oxygen penetrates Alu the same way carbon penetrates iron (Alu's small radius compared to Fe makes me think there's no room in the structure to fit oxygen.) So where is the oxygen coming from? Does it just diffuse through the oxide layer? Wikipedia listed a few papers by a cambridge professor, probably worth reading. The thing is, 200V is not hard to produce with a used gel electrophoresis psu, which are quite cheap on ebay. And it sounds like the depth of the oxide layer would be largely controlled by voltage.
Anyway, I'd like to hear back from people who actually know what they're talking about (not me.) I apologize for rambling.
New to endless-sphere? Notice a lot of signatures recommending Ebike.ca? That's because it's the best place for a quality and manageable, (but still 'real'), first build. Justin is a solid supporter of electric bike development, and a good source of equipment.
My hat off a thousand times to the green people that effectively run this forum. The ES Mods are superb.