Nickel Chrome Plating on Aluminum Castins

Can you please describe your entire process to us?  I have a feeling that your first coating is not adhereing to the surface of the aluminum and allowing the chrome solution to get underneath and attack the substrate. 

First, I would recommend that you check your pretreatment steps.  A good cleaner is required to remove any dirt and oils.  A good etch will give you greatly better adhesion once removed with a good de-smut/de-ox in the nest step.  It could be that you are not in the de-ox long enough, or that the bath is not strong enough to remove the etch-oxide very well.

You didn't state what kind of strike you are using (Watts nickel, sulfamate nickel, alkaline cyanide/non-cyanide copper?).  I hope that you are using one.

Also, rinsing is key in aluminum processes.  A single stage rinse between steps will often lead to failure.  2- or 3-stage rinsing  is required.  And the rinses must be clean.  Especially with casting, which can be porous, you can trap solution in the pores and this can easily lead to failure.

Are the blisters small or large?  Are they over the entire surface or only in certain areas?

Thank you for your response. We have been electroplating products made in brass, and this is our first time electroplating a product made in Aluminum. Our process is as under- Buffing & Polishing on bench polishers - degreasing in an ultrasonic machine using trichloroethylene - soak cleaning in zictane 73  ( for 1 minute )- single water rinse - dip in Alzincate D ( for 1/2 a minute ) - single water rinse - bright nickel bath ( 20 minutes ) - nickel drag out - double water rinse - chrome bath ( for 2 minutes ) - chrome drag out - double water rinse - hot water rinse.

I am quite certain that we have not followed a proper procedure, and would request you to suggest the proper procedure and chemicals to be used.

Thanks Yogesh Modi.