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What process for 400 Hours of Red Rust protection on fasteners

I have a new customer who is requiring 400 hours of salt spray to red rust. They need to come into ROHS compliance with all of their fasteners. They are trying to do this at the lowest impact to cost possible as they are currently using zinc yellow. Any ideas?

Dave Black
Buyer - Elmhurst, NY, US
September 11, 2008

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A good, thick coating of gamma phase zinc/nickel, topped with a gold hex chrome conversion coating.

Dave Wichern
Consultant - The Bronx, New York
September 12, 2008

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Hex chrome conversion coatings are NOT RoHS compliant.

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


September 22, 2008

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It is true that a zinc/nickel finish will meet the 400 hr requirement even with a trivalent passivation. However zinc/nickel is expensive when compared to the zinc rich dip/spin finishes. There are several different dip/spin finishes that will meet both your salt spray and environmental requirements with ease.

David J. Wolf
Medina, Ohio
September 24, 2008

Zn-Ni alloy deposition is not the only solution for this case. You can meet 400 h using the following sequence: pure alkaline zinc 12 micron mimimum, modern thick trivalent passivation and organo-mineral sealer. Experienced local supplier should design the sequence, make tests and propose to you the right solution.

Janusz LABEDZ
- Warsaw, Poland
October 12, 2008

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If zinc-nickel is chosen, the nickel content should be between 9 and 10%. Higher than 10% reduces the ability to receive a conversion coating, below 9% the corrosion protection is less.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
October 14, 2008

Nickel (4-7 tens) Cadmium (2 tens) will be in compliance for the test required

Carlos Carrera
- MIAMI, Florida, USA
October 15, 2008

One of my past positions involved some testing of screws and other types of fasteners in salt spray. The straight zinc plated would last maybe 96 hours. Zinc passivated with chrome would be good for approximately 500 hours. Hopes this helps.

Ron Zeeman
Coil Coating - Brampton, ON, Canada
October 16, 2008