What Are the Different Types of Cadmium Plating and how to Tell Them Apart?

A. Hi, Grant. Cadmium plating is done to give a surface corrosion resistance, cathodic protection, lubricity, compatibility with aluminum, freedom from stick-slip, and non-sticky corrosion products. Almost always there will be a chromate conversion coating after the cadmium plating; this is usually yellow, but could be green (for greatest corrosion resistance) or clear (if less corrosion resistance is okay).

Cadmium plating, like many other surface treatments, generates molecular hydrogen which can cause hydrogen embrittlement of hardened components. To battle this embrittlement, high strength parts must be baked very shortly after plating; further, cadmium plating processes may be specified which have a lower potential for hydrogen embrittlement. I believe that "LHE" stands for "low hydrogen embrittlement". And further, that ti-cad is one type of LHE coating (I believe that the codeposition of tiny particles of titanium produces porosity that is believed to allow the hydrogen to escape easier in the baking cycle.

But after this introduction, I can't really answer your question because I don't think visual identification is a practical or safe way to determine whether the plating is an LHE type, nor whether the parts have been properly baked.

Regards,

A. Grant,

Further to Ted's comments there is only one satisfactory way to tell if the embrittlement has been done and that is by embrittlement testing in accordance with ASTM F519. The majority of MIL and AMS specifications call this up as an obligatory test.

Ted is also right that you cannot rely on color standards. There are various forms of LHE (You're right Ted, it does stand for Low Hydrogen Embrittlement), some are plated at very high current density to form a porous coating, some are doped, it will all depend on the specification that they have been plated to.