Breathe easy! No registration or passwords -- nothing to hack.
... and no maddening pop-up, sticky, or floating ads :-)

Home /
Search 🔍
the Site
pub Where the world gathers for
plating, anodizing, & finishing Q&As since 1989


Dichromate -passivation of zinc plated medium carbon steel

Q. Denis Moles
Is there a plating specification that covers the subject plating/passivation process? What type of coloration is expected from this procedure, can the color of the parts range from a bright zinc to a golden iridescence? Other that subjecting to corrosion testing, is there a simple test that can be performed to determine if the dichromate-passivation operation was skipped?


A. ASTM B633 [affil link] -98e1 "Standard Specification for Electrodeposited Coatings of Zinc on Iron and Steel" [except wire and sheet] gives 4 zinc plating thickness Classes. Each is available in 4 finish Types: as-plated, clear chromated, colored chromated or phosphated. Class, Type & color are customer specified (although available colors may be limited).

Per ASTM B201-80 [affil link] "Practice for Testing Chromate Coatings on Zinc and Cadmium Surfaces," corrosion resistance of chromates increase in the order: clear, clear-blue, black, yellow, olive drab. Supplemental seals and lacquers can improve corrosion resistance. 'Jobshops' below gives several New England providers of chromated zinc finishes.

B201 gives a spot test for clear chromate coatings (unless a water-repellent supplemental coating is present) using lead acetate [affil link] solution. Another spot test, for hexavalent Cr only, is given in ASTM D2092 [affil link].

Zn-rich alloys with Co, Ni, or Fe can also be electroplated (ASTM B840 [affil link], ASTM B841 [affil link], ASTM B842 [affil link], respectively) and similarly chromated. Likewise, mechanically plated Zn and Zn alloy coatings. The much thicker galvanized coatings are less frequently chromated.

Ken Vlach [deceased]
- Goleta, California

contributor of the year honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at, continue to benefit from.


thumbs up signKen
Your response is greatly appreciated - I have plenty to run with based upon your feedback.
Thanks again,

Denis Moles

(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Chemicals &
Consult'g, Train'g
& Software

About/Contact    -    Privacy Policy    -    ©1995-2023, Pine Beach, New Jersey, USA