Metal finishing Q&As since 1989

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Why the black spots after thermal cycling of electroless nickel plating on aluminum

January 4, 2011

We are carrying out Electroless Nickel plating with 25 microns with High phosphorous.
When the plated article is tested for thermal cycling , we observed black spots on the top of the plated surfaces.
How to rectify the defects?
why we get this black spots?
Pl advice us with suitable remedy.
Thanks.
with warm regards,

Chandramani Pg
Ex. Manager in Plating & Painting - Bangalore, Karnataka, India

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January 4, 2011

I never had the problem, but we did not do a full blown thermal cycling (more than one cycle).
There is no reason for it with the limited amount of information given.
My guess is that it is from your oven. Take a spotted part and manually polish it with wet fine pumice. Check frequently to see if the spot goes away. If it does, it is a surface problem that is either from your oven and quite possibly with wet or damp parts Or your final rinse is too contaminated. Rinse a rack of parts with a bottle of distilled water.

Do not use tap water for the makeup of your EN tank.

James Watts
- Navarre, Florida

You said high phosphorous plating, that means you are using an alkaline bath, that could be the source of your problem. There could be localised dissolution of aluminium forming hydroxides, which probably shows up on thermal cycling.

Palaniappa M
- Hyderabad, AP, India
January 7, 2011

The high phos EN bath that I used in 2 different places were both acid, so it is not absolutely an alkaline bath.

James Watts
- Navarre, Florida
January 7, 2011