HELP! White haze when degreasing polished aluminum!

[davidh90046]

I hope someone out there can help....

I have a number of small polished aluminum parts that I wish to clearcoat. I've tried a number of degreasers and am running into the same problem with each: the piece has a perfect, mirror finish ... until I drop it in the degreaser! It then forms (depending on the degreaser used) an all-over haziness, or a bizarro pattern of lighter splotches.

A post on finishing.com said that aluminum is porous, and needs a thorough degreasing for good coating adhesion. The author recommended a 15-min soak in a water-based degreaser with a heated ultrasonic cleaner.

Well, I've now tried this process with Simple Green, Zep Citrus Degreaser, 409, Zep 505, and even liquid hand soap and Goof Off -- and I keep getting variants of the white haze.

(NOTE: An interesting and someday useful side-effect: Zep Citrus Degreaser in a heated ultrasonic cleaner gives you a bey-ooo-tee-ful, perfect satin finish in about 10min - a definite chemical reaction going on there - the entire surface releases tiny bubbles, and a cloud of something or other forms around the piece; but it sucks when you're shooting for a mirror-shine!)

The "splotchy" (somewhere between an inkblot and a crystalline formation) white areas seem to correspond to areas where bubbles form on the surface of the polished piece when in the ultrasonic cleaner - could there be impurities in the aluminum that are reacting strangely?

I've tried the ultrasonic cleaner with distilled water only, but it doesn't do anything but agitate some air bubbles out of the metal - no visible release of "grease".

I've tried soaking the pieces in the various degreasers (no ultrasonic), and still, the haze forms.

The only thing that seems to work OK is a quick dip-and-wipe, but I'm concerned that the aluminum isn't degreased well.

I've looked at the discolored areas under a stereo scope, but can't quite figure out what I'm seeing - sometimes it looks like the areas are pitted, sometimes it looks like tiny crystals have formed on the surface. I could spend all day going blind, trying to get to the bottom of the phenomena, but I'd rather just find out what will work, and be done with it.

Can anyone recommend a SAFE degreaser or degreasing process for polished aluminum, or tell me what I'm doing wrong?

Thanks,
David

[mcaswell]

Oxide Layer on Aluminum

More than likely the hazy layer you describe in a normal oxide layer that forms over aluminum when exposed to air. It forms within seconds and there's very little you can do about it.

When plating the aluminum, we supply a product called Zincate which prevents the layer forming. The zincate layer is dissolved away when the part is inserted into the plating bath.

Our customers have been clearcoating aluminum for years, and this is the first time that someone has mentioned a problem. Have you actually tried clearcoating a part? I think you'll find that the haze isn't an issue when you apply the clearcoat layer.

[davidh90046]

nope, not normal oxidation....

Actually, the white stuff forms while the piece is still IN the solution! Weird.

But it looks like I have a product that's OK - the new liquid-based Goof Off 2 works nicely, with no blotches or haze.

If I can, I'll snap a couple of pics to demonstrate what I'm talking about - it's really odd.

David