I worked in an aluminum extrusion plant over the summers of 1996 & 1997, so I believe my opinion may count for something here, though I am by absolutely no means an expert on the subject.
Aluminum oxidizes very quickly. To give an idea of just how fast it happens, a billet of aluminum takes about a minute to press through a die; the leading end of the extrusion has oxidized before the tail end is clipped off. The oxidization is very hard, and transparent. Unless you knew it was there, you wouldn't know it was there, you know?
This oxide layer, being - as Mr. Disco's pointed out - a self-limiting one, prevents corrosion. Al doesn't corrode unless exposed to some corrosive agent, like an acid or alkaline etchant, extreme heat, years (literally years) of direct sunlight, etc.
Anodization doesn't prevent the oxide layer from forming, since it's the oxide layer that takes & holds (most of) the colour. Painting just buries the oxide layer under some paint. (Incidentally, aluminum doesn't paint very well - dish soap and a Scotch-Brite pad will strip most paints from aluminum.)
Why would you want to stop the oxide layer from forming? I'm confused!
Edit: Can't think of anyplace off the top of my head for a source, unless you want industrial-sized billets, in huge amounts. In that case, contact Alcan.
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Never laugh at live dragons, Bilbo you fool!
JRR Tolkien
[This message has been edited by willOthewisp (edited 02-06-2001).]
