Improve Hard Chrome Plating Corrosion Resistance

A. The more cracks, the smaller the corrosion battery is. Yours is definitely in that range. Increasing thickness of plate will help, but not as much as you want. In the thirties, chrome bumpers were more than .010" and formed long cracks that lead to peeling. Copper underplate cut the amount of chrome in half and adding two layers nickel cut it to tenths with longer life. If you are going to do quality work, it will require an underplate or cheating and waxing before CASS. But cheating poor product would put that company out of business in a few years.

A. You fail to say wether your plating solution is the old type (a thousandth per hour @ 2 Amps per sq in ), or the more modern high speed hard chrome that runs hotter with higher current densities? I have hard chromed parts for hot rod and bike enthusiasts of decorative nature. Differential housings, tappet covers, fork leg tubes, nuts and bolts and even plain wheel rims. Firstly, the parts are polished as normal. Any stopping off is done using a combination of rubber or wooden plugs. Sometimes disc thieves, as on differential ends. Threads are taped up and secured with s/s wire. After masking and etching, current is slowly increased to three times calculated for ten minutes, then reduced to normal for 12 hours, overnight. Remove trees, and finish polish. Good forever! The cost is Astronomical! But they pay.

A. Dear Jayakrishnan:

Use an underplate of nickel of at least 25 microns before chrome. This is top class of plating and should have no problems passing your tests.

Bye,

A. Marek, frankly I don't think hobbyists should ever attempt hard chrome plating because the plating solution and its mists are carcinogenic and highly toxic; but maybe there was a misunderstanding about the word "hobbyist" and you are an industrialist "tinkering" with possible solutions to your situation?

While chrome plating offers a little bit of corrosion resistance, it is not anodic to steel so it doesn't offer sacrificial protection, and it is always cracked or porous, so it doesn't offer barrier layer protection either. So it is not a practical coating for an application that requires significant corrosion resistance.

With an under layer of electrolytic or electroless nickel, thick enough to be pinhole-free and non porous, you can obtain very good corrosion resistance. If you search the site for "electroless nickel hard chrome" you will find several threads where this combination coating is discussed. Letter 1686 is probably the best introduction to HVOF as an alternative to hard chrome plating. Good luck.

A. Chrome is resistant to caustic soda [affil links] solutions. BUT, add in a small voltage and chrome is stripped very efficiently and is one of the two most common ways for stripping chrome in the industry. Possibly, you had it in a metal bucket/can or you had a very moderately dissimilar other metal in the bucket or? In short, you somehow managed to have a battery.

A. Are you also using anodic DC current to clean the parts? If so you are stripping the chrome from the steel.

Hi Fred. One final comment on the test that you described: You said that the hard chrome did not corrode during your test, but please remember that the uncoated steel area was anodic to the chrome plating and offered cathodic protection, not unlike the way a zinc anode protects a ship's steel hull. The results might have been different if you had masked the exposed steel.

Regards,