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topic 4287

Electroplated Zinc-Iron


(2000)

Could anyone tell me why electroplated zinc-iron isn't used more often in the aerospace industry? This coating outperforms cadmium in the salt spray chamber by an order of magnitude. I know the lubricity is a key concern, but aren't there additives now which can take care of that problem?

Marc Pepi
US Army Research Lab - APG, Maryland, USA


(2000)

Electrical conductivity is the main drawback to Zn-Fe for the aerospace industry. In order to provide the required corrosion resistance in NSS testing, a chromate film must be applied (usually black). This chromate film seals and protects the Zn-Fe, but also insulates it as well.

Victor Waldman
Modern Metal Finishing, Inc. - Naugatuck, Connecticut


(2000)

The biggest reason is the same as the military. It takes a lot of convincing to change a mil spec because if it turns out wrong for any reason, the guy that made the change is going to be hung out to dry. The next reason is every single part has to be looked at as to what the optimum replacement is. Aerospace has a great deal more liability than the military ever thought about. Lawyers have a field day with changes. There is always an expert witness, somewhere, that will badmouth anything for a buck.

No, additives will not equal the same lubricity over time and use.

Zinc-tin is probably the overall best GENERAL substitute, but it has not found much favor. My suspect is that it is very hard to control. Some formulations are cyanide and everybody is trying to get away from that.

James Watts
- Navarre, Florida


(2000)

Zn-Fe is probably a good replacement system of cadmium. But what about the volume of the corrosion products. I know that the low volume of the corrosion products is a important advantage of cadmium when you have to dismantle parts. I am not sure that Zn-Fe has this advantage.

The copper top boy, Laurent

Laurent Schuster
CRIF - BELGIUM



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