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Discovering an Aluminium Layer after Chrome Plating Process

May 29, 2014

Q. I am now doing a test on chromic acid solution (with catalyst) that is used in a production line for study purposes. The solution is used for a quite a long time without repairing the composition.

My problem is, after electroplating, the coating layer is dull in appearance and soft. So I examine the coating layer using SEM and EDS to identify what is the coating layer. From the result, in addition to the chrome layer that forms on the substrate (carbon steel), there is also an aluminium layer formed after the chrome layer.

Does this possibly happen in a contaminated chromium bath? Or other reason?

Wong Kok Wei
Student - Malaysia

A. Hi Wong. You cannot electroplate aluminum from an aqueous bath because it is too active -- so it's not a plated layer. If the user was plating onto aluminum, or using aluminum jigs or fixtures, or an aluminum fluorosilicate catalyst, that might be the source of the aluminum.

But I do need to say that I don't think SEM/EDS should be your principal troubleshooting instrument for chrome plating. Please try to plate a test panel in a "hanging hull cell" and get back to us. If you are trying to do "benchtop" plating from a sample in a beaker, there are difficulties like the need to maintain proper temperature as well as very close current density control. Chrome plating is not like some other plating where you can go slow and use widely varying parameters, the parameters have to be right or you'll get no plating at all, or a poor plating like you got. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 2014

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