Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Randy Taylor, Advanced Tooling Corporation.
Hard Chrome Over Electroless Nickel
Q. I have tried to improve the corrosive
resistance of hard chrome plating by plating electroless nickel underneath. However, I have experienced peeling of the hard chrome layers. Please advise.
A. In general,
nickel tends to passivate and must be activated. There are various methods
to accomplish this. Be sure your nickel is properly cleaned and ready for
chemical processing, including solvent cleaning and a hot soak electro
Most common method for activation of nickel plating, 1.) 1 minute-forward /
30 secs - reverse / 2 minutes - forward, electrolytic activation in dilute,
ambient, 5-15% HCL by volume with water (hydrochloric acid), or preferred,
2.) same fwd/rev/fwd process in 5%-15% H2SO4 by volume with water, (sulfuric
acid), rinse thoroughly, keeping part(s) wet, then enter the chrome plating
bath quickly with rectifier current on at 2-2.5 DC Volts, cathodize (forward
current) for 1-2 minutes, then step voltage .2 volt/each 10 seconds until at
full plating current. Make sure you are in good proximity to your anode
source to encourage even current distribution and gassing.(if SCR ACC/ACV
controls, set rectifier by Volt pot for both activation & plating).
Electroless nickel is tougher to chrome plate than electrolytic nickels, but
it can be done. If your E-nickel is high-phos., or the e-nickel has been
heat treated before chrome, you may have to hand polish with a fine scotch
brite buff pad to burnish the nickel coating to enhance the surface