Electroless nickel plating on zinc die castings

A. What issues were you having? Is there a problem with the work as you have receiving it? Are you having an adhesion problem between the copper and zinc? I prefer using a low efficiency copper strike, followed by a full build, high efficiency copper plate (either copper cyanide or acid copper). If you are getting your thickness requirement and good adhesion and all that is being used is a copper strike, then you are getting what you pay for.

Q. I am having some blistering problems for Cu 8-10um, EN 10-13um on the Die-cast part (Zinc Alloy ZAMAK#5). The adhesion between the Zamak substrate and Cu; and between Cu and EN is bad. How can I prepare the Zamak part for plating with good adhesion?

A. First cover the surface junk on the die casting with electroplated zinc, then go to a 5 minute strike in alkaline electroless nickel, then top off with the heaviest thickness you can get out of a medium phos acid electroless nickel.

A. Parting line porosity is most likely the culprit. Use a heavy copper strike and fill as much as possible. Maybe try a severe "Pre Bake" to de-gas the parts prior to plate. It sounds like they are small parts so a long pre-bake in a bulk basket may be somewhat efficient.

Q. I'm using sodium cyanide, rinsing, and uniclean and rinsing for washing. after that acid etch for 30 second. follow by copper strike 30 second and copper plating and then sulfuric acid follow by nickel plating/EN plating.

A. Hello again Stewart,
I agree with Ron Duncan on the cause of your problem. If this is a recurring problem you may want to pull some parts after Cu plating, put them under magnification and inspect for any voids in the copper. As you probably know zinc die-cast should be "sealed" in copper to eliminate open pores in the die cast. If the part configuration leads to any solution entrapment issues, rinsing techniques should be watched carefully. Good Luck!

Q. We also notice this is cause by the pores from the casting. Anyhow, we are trying and thinking is there anywhere we can solve or minimize this at our plating side. Or this can only be done at casting side?

Hi Darryl. The short answer is "yes".

We appended your inquiry to a thread on the subject which introduces the issue that when it comes to industrial plating, the theoretical question of whether something "can be done" usually must yield to the bigger question of whether an adherent, fully functional coating can be applied in a robust & highly dependable fashion at a practical level of effort.

You may have to do a lot of mechanical pretreatment, and you may have to copper plate or zinc plate the casting first, and you may have to 'spark' it (do a few seconds of conventional electroplating first to build a catalytic layer on it). People who know much more about it than me are usually standing by in this forum if you can provide details of your situation. Good luck.

Regards,