Cadmium Plating
Cadmium coating alike zinc coating provides sacrifical protection to steel by being prefentially corroded when the coating is damaged and the portion of the steel is exposed. Cadmium coatings are applied to iron, steel, brass & aluminum to five excellent resistance to corrosion in most conditions including marine & alkaline environments.
Cadmium coatings have low coefficient of friction, good lubricity and predictacle torque characteristics, good electrical conductivity and protection from galvanic corrosion. Cadmium coatings are particularly useful in the electrical, electronic, aerospace, mining, offshore, automotive and defense industries where they are applied to bolts and other fasteners, chassis, connectors and other components. Cadmium coating is normally specified in thickness between 5 and 25 µm depending on the severity of the atmosphere. Chromate post-treatment of the coating can increase coating life.
Key Properties of Cadmium Coating
Cadmium as an electroplated metallic coating has the following advantages:
- It provides sacrificial protection to the underlying steel (as described under "background")
- The atmospheric corrosion protection of cadmium is predictable and is proportional to the thickness of the coating. Cadmium electroplating is normally specified with minimum thickness between 5 and 25 microns, depending on the severity of atmosphere. Cadmium has good resistance to rural and marine atmospheres, in alkaline conditions and detergents.
- It proves an effective barrier to prevent the galvanic/bimetallic reaction between steel and aluminium, such as where aircraft undercarriage and weaponry mechanisms are fixed to aluminium framework.
- Undercutting of threads on nuts and bolts is not necessary. The coating has a low coefficient of friction, which reduces the tightening torque and allows repetitive dismantling.
- Cadmium corrosion products have small particle volume and are adherent, so valves and delicate mechanisms will not likely to be jammed with debris.
- Thin Cadmium coatings are appropriate on threaded components where dimensional tolerances must be maintained.
- Cadmium can be formed as easily as the substrate.
- It can easily be soldered without the use of corrosive fluxes, and has a lower electrical contact resistance than zinc coated steel. These are important properties for the electrical and electronics industry.
- Cadmium can have an attractive polishable silvery finish.
- The Cadmium plating process can be applied to all ferrous materials, including malleable iron, and to brass and aluminium. The process can enable a high efficiency throwing power, i.e. the recesses are more readily coated with a reasonably even deposit.
- Cadmium plated steel is readily adhesive-bonded.
- Chromating directly after electroplating can increase the corrosion resistance of the coating, and greatly extend the coating life by preventing the sacrificial process from commencing until in service.