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Nickel-hardened gold plating on coupons pops up and cracks

I am trying to pass a salt spray test for my hard gold plating bath.it is an acid bath with a nickel based brightener. What happens is when I build up plating on the coupon (steel with e/n under coat), the center pops up and cracks. This also happens along the edge. This bath is at least 6 years old and is the only bath I am having problems with my coupon testing. Does anyone know what this is? Or ever heard or seen this problem?

Kevin Ludwig
shop employee - Andover, Massachusetts
2007

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It would be good to plate a coupon that has not been electroless nickel plated, as poor activation of the EN may be part of the problem. It sounds like huge compressive stresses, although I don't know quite why. Is it possible to plate a hull cell panel or a stress-tab panel to get a little better handle on what is going on?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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First of two simultaneous responses -- 2007

Hi Kevin,

Firstly you have to be specific with your datas.U mentioned "when I build up plating"- till what thickness you are building up gold?.What is the bath volume?
Please note that since you are using Nickel based brightener (better name it nickel based hardener), you are bound to get cracks,beyond 10 microns irrespective of what is the base plating and for that matter, if you have nickel under coat you may get cracks early.
Please let me know the percentage of Nickel in the nickel based brightener you add in your gold bath.I feel the said brightener presently is in excess in your bath.
For immediate relief,
1.stop addition of the Nickel based brightener for some time
2. increase the conc. of Gold in the bath(kevin, pl. understand we have to do a lot of guess work with out proper data from u- tell us the conc. of gold metal)
3.Do a complete carbon treatment to your bath (please tell us
what is the frequency you do this treatment!
There are lot more things to do
But first we want full history of your bath for us to proceed further
Regards,

T.K. Mohan
plating process supplier - Mumbai, India

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Second of two simultaneous responses --

Kevin

I believe that your problem is high stress in the gold solution. 6 years is a very fair life for a gold process and breakdown of the organic additives will tell even if you do not introduce any other contaminants. It is not usually practical to purify a gold solution. The best bet is to speak to your supplier who will credit the value of the gold against a new solution.
Any passivation of the EN will not change the stress but will make the flaking much more likely.

Geoff Smith
Hampshire, England
2007