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Finishes and passivation questions

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We have had a request regarding ZN 6 Passivate Blue. What does the 6 mean?
Why Blue over gold or clear?

Also what is passivate bi-chromatic?

Are there any links to good websites describing the finishes and passivation processs?

David Lovegrove
Product Design - Christchurch, New Zealand

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David,

ZN6 passivate blue is zinc plating with blue passivation using hexavalent chrome.
Now since hexavalent chrome is being phased out,blue passivation with trivalent chrome process is commercially available which is superior to dichronate type hexavalent chromium process. The neutral salt spay life before white rust as well as the finish is better than the latter.

However,yellow iridescent passivation (what you are referring to as "gold")has better corrosion resistance than blue passivation ("clear.")

K.V.Phadnis
- Mumbai, India

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Zn6 is 6 microns of zinc

John Martin
- Wales

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I have read your question and read the answers. I must admit both could be correct. I think you need to go back to your customer and ask him exac. what he wants. It is a problem in the plating game when a customer gives a "spec" like that ( internal spec ) that is not clearly understood by the plater.

Gary Joseph
- Johannesburg, South Africa