Blistering problem on chrome plated aluminum

Q. Hi. Our supplier plates Ni-Cu-Ni-Cr on die cast and extruded aluminum parts. Cr surfaces were very good and shiny after plating, and we could not see any problem after 48 hours chamber test (at -25 and +70'C). But we have seen many bubbles on these shiny Cr surfaces after 15 days to 1 month. Bubble defect rate is 20%
The problem is that not all products are from same day's production. Could you inform us on below questions:

1. What is root cause of bubble problem?
2. Why the bubble problem only on some parts of same production date's products?
3. Which reliability test can catch this problem?
4. If we sort them by eye and separate the 25% problematic products, can we use the others? What is the bubble risk in future for them? Can we use them after sorting or must they be scrapped?

Thank you for your support.
Best regards

A. Hi Erdinc.

The first thing to do is to examine the underside of the blister and the metal underneath the blister to make sure what step the problem occurs at. It is probably the first layer of plating separating from the aluminum, but you must make sure. The second step, if your mission is to find out what went wrong, is to learn the processing details. If the first layer of plating has separated, you must find out if the plater uses a double zincate cycle, and what follows it (cyanide copper, or pyrophosphate copper, or alkaline electroless nickel, or what).

One you can provide those details, someone can probably suggest the next step. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted is available for instant help
or longer-term assistance.
July 25, 2012