Why Cadmium Plating?

Cadmium plating has a long history of use in all industries, but is becoming rare as concerns over the metal's toxicity and carcinogenicity outweigh its engineering effectiveness. Cadmium provides galvanic protection to steel, meaning that in the presence of moisture, it corrodes instead of the steel. Zinc, a much more benign metal, protects via the same mechanism, so what's so special about cadmium that it persists in critical applications such as aerospace? The corrosion products--the powdery residue that is formed as the metal corrodes--from cadmium are less significant than from zinc. Zinc's corrosion products can contribute to the premature failure of moving parts or cause galling in applications where repeated dis-assembly/reassembly is necessary (which is the case with aerospace components that are on maintenance schedules). Additionally, Cadmium has a sufficiently low coefficent of friction to facilitate repeated maintenance, and its corrosion products are relatively benign.

Cadmium is also a mainstay in the aerospace industry because of its position on the galvanic scale relative to aluminum and stainless steel. Before the introduction of composites, airframes were primarily aluminum. Where stainless steel components interface with aluminum, they are often coated with cadmium. This provides an intermediate galvanic layer the minimizes the possibility of corrosion cells forming. The industry has moved toward zinc-nickel alloy as a replacement in this application. The substitution of zinc-nickel for cadmium presents less of a challenge than replacement in corrosion protection applications, as its tribological properties are not relevant.

Cadmium is not used in space applications because of its tendency to sublimate, or transition directly from a solid to a gas, in high vacuum.

Before its health risks were recognized, cadmium was used on automobiles, retail hardware and almost every application where corrosion protection was required. Today, it is used only in a handful of specialized applications. If you are working in one of these areas where the finish is still required and need the support of a premium cadmium plating provider, contact Chem Processing.

For more information on cadmium plating, visit Chem Processing's cadmium page.