47026

Hard chrome plating with no strike? why? [Oklahoma] 

November 14, 2007

What is the technical reason that most hard chrome plating specs, i.e. AMS-2406 [link is to spec at TechStreet], call out specifically to chrome plate directly on basis metal with no strike? Why would it be preferred to not strike when applying a nickel strike under hard chrome increases the corrosion resistance and life of the part? Yes, the engineering spec can specify a nickel strike but I want to know why the default specifically says no strike. There must be a reason or they wouldn't have mentioned it in the spec at all.

I want to decrease the corrosion/pitting occuring on the base metal under the chrome but don't want to sacrifice any of the beneficial properties of the coating such as wear resistance and hardness or the adhesion.

Art Caples
plating shop employee - Oklahoma City, OK, USA

I wasn't involved in writing the spec and can't claim to know the reason, Art. But my suspicion is that is has to do with adhesion. Hard chrome plating can exhibit "perfect adhesion" (impossible to separate the plating at the interface even with a carefully designed pull test like the Ollard test). Perfect adhesion seems unlikely in multi-layer plating. I would encourage someone who actually knows the answer to override my guess :-)

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Mostly iron parts will slightly etch in the chrome solution (giving very good adhesion) while you wait for the part to at least partially warm up before plating. Some platers will use a very slow ramp up of amps to allow the part to warm up. The coefficient of thermal expansion of chrome and iron is enough to cause problems if you do not.There are some high nickel alloy parts that have to be Woods nickel struck to get good adhesion.

James Watts
- FL