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Zinc plating lasted only 5 years

Q. We had supplied a part with Zinc plating (5 microns plating thickness) to a customer in USA 5 years back. Customer has now complained of discolouration and rust. Kindly advise what is the expected life of zinc plating. What is the plating we should suggest to this customer if he requires more plating life.

S. Andrews
- Chennai, Tamil Nadu, India
December 16, 2011

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5 microns is not a thick coating for corrosive environments. You will not be able to successfully advise your customer of a good solution without knowing what exposure scenarios they are facing.

For highly corrosive atmospheres you would be looking at galvanising rather than plating. For general outdoor corrosion protection, but not in a highly corrosive atmosphere you would probably have to double the plating thickness, if not even more (maybe aim for 10-20 microns?). For general indoor applications 5 microns would normally be fine, so I will assume that it is for outside use.

Brian Terry
Aerospace - Yeovil, Somerset, UK
December 19, 2011

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December 20, 2011

IN ZINC PLATING RED RUST MEANS LESS THICKNESS OF ZINC
WHITE RUST MEANS PASSIVATION PROBLEM.
IN PLATING WE ALSO HAVE VARIATION IN THICKNESS BUT LESS IN CASE OF ALKALINE ZINC.
YOU CAN HAVE ZINC 10± 5 MICRONS + TRIVALENT PASSIVATIONS+ REACTIVE SEALANT.
ZINC ALLOYS (ZN/NI , ZN/CO ,ZINC/IRON ) CAN PROVIDE HIGHER CORROSION PROTECTION.
GEOMAT COATING CAN PROVIDE HIGHEST PROTECTION (DIP SPIN + BAKING + TOP COAT ).
I WILL REQUEST YOU TO CONTACT A REPUTED CHEMICAL SUPPLIER AND DISCUSS WITH HIM YOUR PROBLEM.
REGARDS.

Ajay Raina
Ludhiana, Punjab, India

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Please understand the specifications of the customer and accordingly, the process can be decided.

May be zinc/iron alkaline process with trivalent yellow / olive green passivation followed by a top coat should help. Chemical supplier might help you to meet the requirements of your customer.

Kishore Phadnis
- Mumbai, Maha, India
January 9, 2012