ASTM-B766 › Standard Specification for Electrodeposited Coatings of Cadmium
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This specification covers the requirements for electrodeposited cadmium coatings on products of iron, steel, and other metals. Cadmium coatings are used for corrosion resistance and for corrosion prevention of the basis metal part. The as deposited 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.Electrodeposited cadmium coatings shall be classified on the basis of thickness as Class 25, 12, 8, and 5. The coating shall be essentially pure cadmium produced by electrodeposition usually from an alkaline cyanide solution. The basis metal shall be subjected to such cleaning procedures as necessary to ensure a surface satisfactory for subsequent electroplating. Cadmium shall be deposited directly on the basis metal part without an undercoat of another metal except when the part is either stainless steel or aluminum and its alloys. The plating shall be applied after all basis metal heat treatments and mechanical operations. The thickness of the coating everywhere on the significant surface shall conform to the requirements of the specified class. The cadmium coating shall be sufficiently adherent to the basis metal to pass the tests. The supplementary Type II chromate film shall be adherent, nonpowdery, and abrasion resistant. The thickness of electrodeposited cadmium coatings shall be determined by the applicable test methods.
1.1 This specification covers the requirements for electrodeposited cadmium coatings on products of iron, steel, and other metals.
Note 1: Cadmium is deposited as a coating principally on iron and steel products. It can also be electrodeposited on aluminum, brass, beryllium copper, copper, nickel, and powder metallurgy parts.
1.2 The coating is provided in various thicknesses up to and including 25 μm either as electrodeposited or with supplementary finishes.
1.3 Cadmium coatings are used for corrosion resistance and for corrosion prevention of the basis metal part. The as-deposited 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.
1.4 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.
1.5 Cadmium-coated parts can easily be soldered without the use of corrosive fluxes. Cadmium-coated steel parts have a lower electrical contact resistance than zinc-coated steel. The lubricity of cadmium plating is used on springs for doors and latches and for weaving machinery operating in high humidity. Corrosion products formed on cadmium are tightly adherent. Unlike zinc, cadmium does not build up voluminous corrosion products on the surface. This allows for proper functioning during corrosive exposure of moving parts, threaded assemblies, valves, and delicate mechanisms without jamming with debris.
â€‰cadmium; electrodeposited coatings; electrodeposited coatings; cadmium ;; ICS Number Code 25.220.40 (Metallic coatings)
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