Cadmium Vs. Zinc Plating

Q. We have a recent government contract which call out a series of mil-spec fasteners, but with zinc plating. These fasteners are readily available in the usual mil-spec cadmium plate. They are to be used in an aluminum assembly. Would I be reasonable in asking the program manager to allow the cadmium fasteners in lieu of zinc plating?

A. Richard, Cadmium and zinc are both in a class known as "sacrificial coatings", which are primarily used to protect steel (ferrous) base metals. Cadmium is superior to zinc but due to its toxicity has limited use. If zinc is being called out in the aluminum assembly, cadmium would behave the same or better in that environment.

Best of luck.

Randy Taylor