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Finishing Process for Zamak

Quickstart:
'Zamak' or 'Zamac' is a series of zinc-based metal alloys used for diecast ⇦ huh? parts. Typical finishing processes include chromate conversion coating as a final finish, chromate conversion coating followed by painting or powder coating, or zinc plating followed by chromate conversion coating.

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Q. Hello!
I am being asked to start finishing on AC41A Zamac 5. The called out finishing is Trivalent Chromate Type III per ASTM B633. Looking for experience with this process, or if there are other recommendations for finishes on this material.

Emily Freiss
Sr Engineer - Warrendale, PA
February 9, 2026

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A. Hi Emily

It is possible to apply a chromate conversion coating directly to Zamac die castings, and it is alternately possible to zinc electroplate them first and then chromate conversion coat the plating.

ASTM B633 is a specification for zinc electroplating, so I'm not totally certain whether you are intending to zinc plate the castings before chromating or not.

The advantages of not plating them them first include economy and simplicity, and probably less likelihood of minor defects like cold-shuts ⇦ huh? being amplified by the plating.

The advantages of plating them first would be more consistent aesthetics, and the fact that most commercial chromating processes are optimized for application to zinc plated surfaces. Luck & Regards,

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