Blisters and peeling in Cu-Ni-Cr

A. It is difficult to hazard a guess, but remember that chromic acid is a wonderfully effective passivation agent :-)

If your rack coatings are poor, or housekeeping is a problem, chromic acid will get into your cleaners and copper plating tanks and ruin adhesion.

Q. You had not answered my question. I'm asking about the compatibility of acids to be used in activation prior to copper and nickel plating respectively.

A. I'd suggest sulfuric acid for both.

A. Use sulfuric acid 10-15% by volume in both cases and do electro degreasing properly.

A. But I think cause of the problem is another thing, as you said Cu plate is one that peeled-off, I think the electroless reaction between copper ions and brass elements is the main reason of this phenomena. We have had such problem during Cu plating on lead bronze alloy.

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! Mahdi, your comment about poor adhesion of copper to leaded bronze is interesting. The reason for the poor adhesion is "lead smear" which is caused by the lead in the bronze smudging or smearing during the machining process. This is a common problem with metals where lead has been added to enhance the machining capabilities. I think the best way of overcoming it is to use a copper fluoborate bath as this should adhere to the lead.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004

A. If your brass items are leaded brass and soldered assemblies, I recommend the following process flow: Degreasing > Electrodegreasing > rinse > Acid dip in 10% by vol. fluoboric acid for 5-15s at RT > rinse > dip in a 30g/LNaCN solution > rinse > Copper strike plating > rinse > acid dip in 5% by vol. sulfuric acid >rinse > Nickel plating>acid dip in 10%-15%vol. sulfuric acid > rinse > chrome plating > rinse > hot rinse > dry

A. We encounter the same problem in our line. Yes basically copper plating adhesion on your base metal is weak. Both acids you mentioned will do. Try to consider the oil removing capability of your degreaser first before jumping ahead on your process. You could also improve your rinsing process.

A. Better to use Iron activation prior to Cu plating and Sulfuric Acid prior to Ni plating...

A. Hi Rongmei. This nickel-cobalt alloy will be very passive and unreceptive to plating. Please try starting with a Wood's Nickel Strike, and then, almost immediately, doing the copper plating. Good luck.

Regards,

Q. Dear Ted,

Thanks for your answer. you are right, it is really hard to plate on Ni-Co alloy with well bonding, even using Wood's Nickel strike.

A. Hi. ASM Metals Handbook Vol. 5, "Surface Engineering" has a chapter on prepping refractory metals for plating with very aggressive activation sequences. You could review whether parts of those powerful processes are applicable ... and then follow them with the Wood's Nickel. Good luck.

Regards,