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Chrome plating onto aluminum

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Q. Hi, I own a metal finishing company in FL. I'm looking in to getting into chrome plating onto aluminum. A lot of people are telling me that it is a big thing. I've done chrome plating on steel and brass only. Will appreciate any suggestion.

Tony P [last name deleted for privacy by Editor]
polishing shop - Miami, Florida


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A. Hi Tony. Aluminum immediately forms a passive film onto which it is not possible to electroplate. Therefore the first step is to apply a zincate coating.

Once the zincate finish is in place you either start with cyanide copper before acid copper-nickel-chrome plating or start with alkaline electroless nickel plating before copper-nickel-chrome instead. The process vendors will be able to give you reprints of shop write-ups from the trade journals. Good luck,

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Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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A. Years ago I was involved in plating aluminum pistons. We double zincated the parts and used Enthone's alkaline EN at a much lower temp than recommended. It has a very strong ammonia smell. If you try it, buy a gal of stabilizer because it will plate out in a week or so at Miami ambient temp. They can tell you how to use it and it sure is not in the ops sheet. You might even want to put a layer of regular nickel on it because you will have to re-rack, clean and activate unless you are using tank anodes in your chrome. If you find a way to get all of the chrome off of the racks, please tell me because it always seemed to find a spot that contaminated another tank. It takes some getting used to, but plating on aluminum is not all that bad and the EN strike made it a lot better.

James Watts
- Navarre, Florida


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A. I found 2 ways would work on aluminum, one was after double zincate to use EN strike for parts with deep recesses (such as rims). The other was a cyanide copper strike. Both of these were followed by plating the parts in acid copper, then nickel-chrome.

Ray Salchow
metal finishing shop - Cincinnati, Ohio



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Q. Dear All,

Can anyone advise me regarding the hydrogen embrittlement of chrome plated aluminium? I'd like to know how it works and how it can be avoided or solved. Any help you can give will be much appreciated.

Ben B [last name deleted for privacy by Editor]
research - Cambridge, UK


A. Sorry Ben, I'm not really familiar with hydrogen embrittlement of aluminum, but see letter 55684, which addresses the subject in some detail.

Regards,

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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


October 19, 2012

Q. DEAR SIRS,

We are manufacturing aluminum cylinder block and pistons for small Two stroke I. C. engine, we want to know all process of aluminum hard chrome process.

Regards,
himmat

himmat yadav
- Pune, Maharashtra, India


October 19, 2012

A. Hi Himmat. No single book covers the whole process exhaustively, but "Hard Chromium Plating" [link is to info about book at Amazon] by Guffie says aluminum is usually zinc or tin plated first, although castings are sometimes directly plated. Wernick, Pinner and Sheasby has a little over 3 pages on hard chrome plating of aluminum =>

Hard chrome plating of aluminum is not a terribly common application because aluminum is so soft that you probably need a thick plating or the item will be subject to easy eggshell cracking.

Regards,

Pinner & Sheasby
Surface Treatment & Finishing of Aluminium and Its Alloys

pic of Ted Mooney   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
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