Besides having excellent corrosion protective properties, cadmium has many useful engineering properties including natural lubricity.
Cadmium also has excellent electrical conductivity, low contact resistance, good solderability and excellent ductility properties.
The obvious downside of cadmium plating is its toxicity, health, safety and environmental concerns. There have been many attempts to replace cadmium, and some have been successful with certain properties, but none have incorporated all of its unique capabilities.
Many specifications have various classes and types defining thickness and dichromate post treatments. Typical thickness ranges are 0.0001” to 0.0006” per surface. Dichromate post treatments do not add to thickness but must be performed after hydrogen embrittlement baking.
Heat treated steels, particularly those plated and used at 35 HRC or greater are susceptible to hydrogen embrittlement. Pre-plating stress relief and post process embrittlement relief baking may be required for parts with a hardness of 35 HRC or greater. Each cadmium process specification is has different requirements. Be cautious and thorough about defining requirements on a contract or purchase order. Caution: An omitted or time-delayed embrittlement relief bake can have catastrophic results!
Racking of detailed machined parts can be challenging in throwing cadmium into deep bores requiring complex conforming anode fixturing.
Barrel cadmium plating can be utilized on small, non-critical parts when allowed by specification. Barrel rotational speed is limited to 7 RPM leaving the parts free of rack marks, nicks and dings.