Process description: Plating cadmium

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Cadmium plating

Cadmium is mainly used to protect parts made of steel, and aluminium or titanium alloys. It has particular properties: a low risk of hydrogen embrittlement, a low friction coefficient and constant torque for fasteners, and has better throwing power and penetration as well as better corrosion resistance than zinc. It’s toxicity has resulted in it being restricted to specific vital technical uses where it is difficult to replace in aviation and aerospace, military equipment, mining and nuclear industries and some safety critical electrical contacts.

Cadmium plating can be performed in acidic as well as alkaline cyanide baths. The pretreatment is the same as for zinc plating. After plating the coating is often given a passivation treatment in chromic acid. High strength steel parts are heat treated to minimise the hydrogen uptake and then activated in diluted acid before chromating. Cadmium covering layers can be chromate plated.

Electrolytes may be based on cyanide, fluoroborate, sulphate or chloride:

  • electrolyte based on cyanide:

NaOH: 20 g/l; NaCN: 120 g/l; cadmium: 20 – 30 g/l; temperature: 20 – 35 °C

  • electrolyte based on fluoroborate:

Cadmium fluoroborate: 250 g/l; ammonium fluoroborate: 60 g/l; boric acid: 25 g/l; temperature: 20 – 35°C

  • electrolyte based on sulphate:

Cadmium sulphate: 52 – 85 g/l; sulphuric acid: 50 – 120 g; temperature: 18 – 30°C

  • electrolyte based on chloride:

Cadmium chloride: 114 g/l; ammonium chloride: 112 g/l; complexing agent (EDTA, NTA): 180 g/l


Source: BAT Surface Treatment of Metals and Plastic, Aug. 2006.



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