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Chromate conversion coat Zamac 3 directly

adv.
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Q. Hi, I am looking for documentation to describe why it isn't an issue for the base metal (zamak 3) to change in appearance over time. I am guessing this to be a reaction between the chromate such that different components of the alloy will change slightly in color which can be seen as variations of grey through the clear chromate. I found a Chem-E doctorate paper describing this somewhat for aluminum alloys with a max zinc content of ~6% vs zamak 3 at ~96%.

Any of you folks know of published articles or studies on this?

D Brummett
- Watsonville, California
May 4, 2022

A. Hi D. Hopefully someone will answer your question directly with a literature citation. But I would say that chromating of zamac castings is a functional coating not a decorative one, so if the function has not been compromised the coating is satisfactory.

Luck & Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 2022

⇩ Closely related postings, oldest first ⇩

2005

Hello :

Product material : Zamac 3
Product Finish : Chromate conversion coating Olive Drab

My understanding of the finish process is that it should be Zinc plating first and then followed by Chromate conversion coating, but someone told me this finish does not include the Zinc plating at the beginning.

I just want to know the correct plating process for Zamac 3. Is this a suitable finish for Zamac 3 ? If not, what is the right finish?

I will greatly appreciate if anyone can help me to get the answer.

Thanks very much.

Richard Lee
- LA, California

A. Hello Mr Richard Lee,

Zamac 3 does not chromate well with Triavalent Chromates directly, although it does reasonably well with the Hexavalent Chromates. Its much better if you zinc plate before you trivalent chromate.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2005

Dull Chromate

Q. An old drawing from 1966 specifies "dull chromate" finish on Zamac 3.
No processor can explain what it is. Do you know?

Daniel Z, Petrasek
precision mechanisms - Westbury, NY, US
2007

I am guessing that the spec is looking for a chromate that does not do any or little chemical polishing and as such replicates the existing surface polish in the chromate finish.

Gene Packman
process supplier - Great Neck, New York
2007

I've always been advised by legal counsel to answer only the question that has been asked and elaborate no further. As such my answer would be "YES."

Milt Stevenson, Jr.
Syracuse, New York
2007

But this isn't a legal proceeding, Milt -- so you could probably add: "... and we can process those parts with dull chromate for you if you wish." :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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