Metal finishing Q&As since 1989

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Zinc-Nickel Electroplating of Fasteners

We are a fastener manufacturer currently plating some product zinc-nickel, 12-15% nickel content. The base material is cl.8 steel. Even though our material is c. 25 Rhc, we had them baked 3hrs following plating. Upon installation we found a portion of the fasteners demonstrated signs of hydrogen embrittlement. Three questions:

1)Can a zinc-nickel plating lead to hydrogen embrittlement (I was not aware it could). If so, under what circumstances.

2)Would the elimination of Chrome 6 as the passivator change anything. Again I did not think it would.

3)In the past we would see less than 10% nickel content. We now use 12-15% and I have heard this may be making the material more fragile. Is this true.

Any feedback will be of great interest and I will post the results of our tests once they are completed.

Best Regards,

JASON BAINES
FASTENERS - BOUCHERVILLE, QC, CANADA
2006

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I found the following article on the web on Zinc Nickel coating that may be of some help. It does mention the capacity of hydrogen embrittlement.

http://www.jcse.org/Volume7/Preprints/V7Preprint18.pdf

Milan Marshall
Electronic Parts Mfg. - Cincinnati, Ohio, USA
2006

Hydrogen embrittlement takes the blame for many problems that it does not cause. Why do you think that it is hydrogen embrittlement?

James Watts
- Navarre, Florida
2006

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It is almost impossible for a fastener of 25 Rockwell C to exhibit hydrogen embrittlement. ANY zinc electroplating process or zinc alloy process can produce hydrogen embrittlement, but generally only in fasteners over 32 Rockwell C. The post-plate chemical treatment will make no difference. James Watts is right - what makes you think it is hydrogen embrittlement? The way to tell is to obtain a photomicrograph of the fracture face. If it is hydrogen embrittlement the photograph will show 'intergranular fracture.' You can search images on the web to see what this looks like. Metallurgists call this 'rock candy.' If it doesn't look like this, it's not hydrogen embrittlement. A lot of times people who should know better think that any plated fastener that breaks is automatically hydrogen embrittlement.

Tom Rochester
CTO - Jackson, Michigan, USA
Plating Systems & Technologies, Inc.


2006