Letter 054

Low resistance on black coating on aluminum

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I am a consulting design engineer (Mechanical) in the electronics packaging industry. In a recent project I encountered a need for a black coating on aluminum that was electrically conductive. Alternatives such as Black Nickel, Zinc, and Chrome over a copper and/or nickel flash have been discussed however they are cost prohibitive. Recently a black (or very dark) chromate tint was proposed. Can anyone suggest parameters or specifications for the process and sources for the tint? What cosmetic quality can be expected? Assuming it is (just) a bath change for the tint, would it be a major hurdle for local sheet metal fabricators to supply or is it best done by another source? Are there other suggestions of materials and processes to pursue? Thank you for your consideration.  

Michael D. Miles, PE

Mil-C-5541 [link is to spec at TechStreet]covers chromate conversion coatings on Aluminum. For low electrical resistance, specify Class 3. This class achieves its lower rating via a thinner coating--which naturally sacrifices some corrosion resistance, and probably some of the saturation required for a dark coating.

There may be a proprietary that offers a shade dark enough to meet your needs, but I'd be surprised to find anything even approaching the saturation of a black electroplate or black anodize coating.

Ted Mooney, P.E.  finishing.com Brick, NJ

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