ASTM B766 specification covers the requirements for Electrodeposited Cadmium coatings on products of iron, steel, and other metals.
The coating is provided in various thicknesses up to and including 25 µm either as electrodeposited or with supplementary finishes.
Cadmium coatings are used for corrosion resistance and for corrosion prevention of the basis metal part. The asdeposited coating (Type I) is useful for the lowest cost protection in a mild or noncorrosive environment where early formation of white corrosion products is not detrimental or harmful to the function of a component. The prime purpose of the supplementary chromate finishes (Types II and III) on the electroplated cadmium is to increase corrosion resistance. Chromating will retard or prevent the formation of white corrosion products on surfaces exposed to various environmental conditions as well as delay the appearance of corrosion from the basis metal.
Cadmium plating is used to minimize bi-metallic corrosion between high-strength steel fasteners and aluminum in the aerospace industry. Undercutting of threads on fastener parts is not necessary as the cadmium coating has a low coefficient of friction that reduces the tightening torque required and allows repetitive dismantling.