Summary for chromate conversion coat zamac 3 Discussion
chromate conversion coat zamac 3 is discussed as a finish choice for diecast zinc alloy parts. Richard Lee asked whether Zamac 3 should be zinc plated first and then chromated, or whether chromate conversion coating can be applied directly. An answer from an unnamed contributor said Zamac 3 does not chromate well with trivalent chromates directly, though it does reasonably well with hexavalent chromates, and that it is much better to zinc plate before trivalent chromate. Gene Packman suggested the spec may be aiming for a chromate that does little or no chemical polishing so the existing surface polish is preserved. Ted Mooney later noted that, if answering only the exact question asked, the answer would be “YES,” while not elaborating further. The thread therefore contains some nuance: direct chromating may be possible in some cases, but zinc plating first is generally presented as the better route, especially for trivalent systems.
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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
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May 2022
⇩ Similar, related, Q&As — 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 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.”
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
Need quick confidential answers? $25
Need project assistance? $100/hr.
2007