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How to spec zinc plating with trivalent iridescent yellow chromate

Q. We are used to working with hexavalent zinc yellow coatings such as A2C according to ISO 4042 in our products and right now, due to customer requirements, we have to change to a trivalent coating.

We have a proposal to use a trivalent zinc plated with a slightly yellow iridescent colouration and the question is: Which code following some international standards such as ISO or DIN we could use to explain that coating?

Would the code Fe/Zn5/Cn/T0 according to DIN 50979 be suitable for that slightly yellow iridescent zinc plating?

On the other hand, is there any other zinc plate and code which could fit better for a A2C zinc plated free of Cr6+?

Jirka Dvorak
Product designer - Barcelona, Spain
April 8, 2011

A. I know this is an old topic, but here's the info.

For zinc trivalent plating we use the spec:
ASTM B633-13 Type V

Alain Bouthillier
- Granby, QC, Canada
January 20, 2014

A. ASTM B633 is for general zinc plating whereas ISO 4042 is for electroplating of fasteners. ASTM F1941/F1941M-16 would be appropriate as it is designed for zinc plating on fasteners.

The expected corrosion values between the two standards may vary as the IISO 4042 and the ASTM F1941/F1941M-16 in front of me have different expectations for white / red rust.

Sorry for bringing up an old topic, just wanted to make sure that the correct references are used for future readers.

Erick Leong
- Buffalo Grove, Illinois
January 7, 2016

Thanks for the update, Erick!

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 2016

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