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Zinc electroplating in salt spray test

We are currently researching various coatings for some of our products. We would like to have a basis of comparison to how some of these coatings are performing in a salt spray test. As a general guideline, how many hours in a salt spray test does each mil of zinc electroplating last, with steel as the base metal? Thank you.

Lisa McGurty
R&D Engineer - Pleasanton, California, USA
2007

A. A lot of it has to do with the type of chromate coating that is applied in the post-plate.

Dave Wichern
Consultant - The Bronx, New York
2007

A. Hi Lisa. Please see ASTM B633 for this subject, andr see if you can get a copy of the booklet "Quality Metal Finishing Guide: Zinc & Cadmium Coatings" from nasf.org for an explanation.

Dave is correct that satisfactory salt spray performance depends more on the chromate employed than the zinc plating thickness. Zinc is a sacrificial coating which is consumed over time, and the plating thickness should be based on the real world exposure (mild, moderate, severe, very severe) not on salt spray results. Good luck.

Regards,

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

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