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"Zinc Clear over Nickel Plated Brass - Salt Spray Test Failure"
April 23, 2010
Sorry for the Zinc 101 question I am way out of my field. I have a brass tube which has been nickel plated and then a clear Zinc over it for corrosion protection. After a 96 hour 5% salt spray test I was surprised that the parts came out very white and dull - I guess the zinc was in the process of giving up! Is that normal? I would have thought that after 96 hours of SS at 5% the part should still look good. Have I misinterpreted the specification or the end result!
Operations - Director - Ottawa, Canada
First of two simultaneous responses -- April 26, 2010
A clear chromate on the zinc very probably will not last for 96 hours as it is very thin. You may have to put a clear coat "paint" over it.
One option would be to use a heavy nickel coat and skip the zinc.
- Navarre, Florida
Second of two simultaneous responses -- April 27, 2010
Clear passivation on zinc does not guarantee 96 hours in NSST.
Hexavalent clear chromate gives max 24 hours.
Trivalent passivation is better but still in order to make sure that the corrosion resistance will be 96 hours, you need a sealer which follows the passivation.
chemical process supplier - Tel-Aviv, Israel