I'm unearthing a couple of nice cast aluminum bits on my old wagon and as I clean them of the 45 years of oil that's encrusting them, they're almost immediately starting to have that white aluminum powder oxidation that I hate. How do I keep this from happening?
Oh man.... i need to bounce my brain around this one. I seem to remember a thread on this subject a few years back and someone was talking about some sort of oil-based treatment.
I'll try to dig it up.
As for what i'd do.... i'd bake some clear powdercoat over it.
Lemme guess, you're using some kind of solvent?
I know xylene causes instant oxidation...but if it's not happening immediately, the least you could do is wipe it down with WD-40.
I'm using purple power cleaner stuff.
Leave them oily and grease? 
mazdeuce wrote: I'm using purple power cleaner stuff.
That is your problem. Do not use that. It is corrosive to aluminum.
ditchdigger wrote:mazdeuce wrote: I'm using purple power cleaner stuff.That is your problem. Do not use that. It is corrosive to aluminum.
This.
mazdeuce wrote: I'm using purple power cleaner stuff.
Unless you're using Purple Power's specific Aluminum cleaner, which I have no experience with just know it exists, Purple Power Cleaner Degreaser WILL corrode Aluminum.
Some kind of Aluminum specific cleaner, elbow grease, and maybe a clear coat on the final product.
Crap, how do I get it off and fix what I've done?
Are the parts off the car? You can put them in a shaker rig with walnut shells after a good cleaning?
When I oxidized the letters on an aluminum valve cover, I took it off with a felt wheel.
Nyalic. Google it.
Polish it off with a polishing compound
Roger, will do.
Just when you think you know something, you find out that you're an idiot about something else.
Somewhere out there I remember reading that a 5% solution of oxalic acid in water will brighten plain non-anodized cast aluminum parts. The part needs to be rinsed thoroughly afterwards and it will oxidize again pretty quickly so it neds to be coated. It will also screw up/strip anodizing.
Eagle One Mag Cleaner will clean aluminum pretty nicely. It is a acid based etching solution. However you need to be careful around painted surfaces. Aluminum oxidizes fairly quick and it is that thin layer of oxidation that actually protects the aluminum from continuing to oxidize/corrode. Of course nothing beats the look of freshly sand blasted or glass beading cast aluminum.
mazdeuce wrote: Just when you think you know something, you find out that you're an idiot about something else.
Truer words were never spoken.
I've found that using Purple Power immediately followed by this blue stuff that is used to clean the wheels on airliners will pretty much clean the aluminum and stop the oxidation dead in its tracks.
mazdeuce wrote: Crap, how do I get it off and fix what I've done?
IIRC Purple Power is a strong base. If I had Al that had been exposed to it, I'd rinse it with a mild acid (vinegar), then flood with water.
For cleaning bare AL, 00, 000, 0000 steel wool + mineral spirits/WD40, then a buffing wheel.
Leave bare if you can stand going over it w/ Flitz or Simichrome now and then. Shoot with Nyalac or clear coat - I like DuPont ChromaClear if it needs to stay shiny, but it doesn't look like real polished AL anymore once it's cleared.
If you're trying to bring the 'brightness' back from soaked in oil and stuff on the parts, the mag cleaner or a chrome wheel cleaner does a pretty good job.
Absolute best thing is media blast, but that's not always an option. If you're going to polish the part i would polish and then clearcoat over them. If you want to keep the cast look i would use a matte clear. You'll be able to tell it's there but you wont have to mess with the part every 3 weeks to keep it looking good.
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