The authoritative public forum
  for Metal Finishing since 1989
-----

Trivalent zinc plating composition

2005

I need to know exactly (by percentage) what is in standard zinc trivalent plating (ASTM B633 )
Can anyone help?

Thanks,

Alan Ifft
hardware - Highland, Illinois

---

I doubt that anyone can answer that, Alan. Trivalent chromates are all proprietary, come in different thicknesses and formulations, with and without topcoats of various types. Please try to phrase the question in terms of your actual situation, and additional help may be available on that. Thanks.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

Does trivalent chrome conversion coatings on electroplated zinc exhibit the same or similar "HEALING EFFECTS" as hexavalent chrome when the plating is scratched to the base metal,steel?

RICH KIOLBASA
- Des Plaines, Illinois
2006

---

In some cases I know for sure that they don't, Rich. But trivalent chrome conversion coatings are highly proprietary and based on at least 3 different general technologies, so there may not really be a final answer to your question.

You may wish to ask an individual vendor that question about a particular product. But seeing as 'self healing" seems to have completely left the lexicon about the same time that trivalent coatings started gaining popularity, my guess is that they'll all say "no" :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

---

The sacrificial part of the finish is underneath the yellow or clear chromate (chromate is actually a misnomer for clear) which is the zinc. How quickly the sacrificial zinc is used up depends on the porosity of the chromate. When the ASTM specification was originally written, Plain tri- is/was more porous than plain hex- As indicated in the above response, the proprietary part now comes with what is added with these and on top of these.
Coatings/passivates are to my knowledge non-conductive. Low porosity typically yields better corrosion resistance. But higher porosity yields better conductivity which matters in my industry.

Marc Soubliere
Communications - Belleville, Ont, Canada
April 29, 2011