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Conductivity of zinc plating with chromate conversion coating




Q. Hi,
I'm an engineer involved with designing enclosures for electronics. We use EG steel sheet typically between 16 and 20 gauge. I am looking for a industry standard that I can put on my prints to call out EG steel that has an electrically conductive post treatment like trivalent chromate.
I have found ASTM A879 [affil link] that covers coating weights but need a designator for a conductive conversion coating.
Thanks!
B

B. Jordan
- Boston Massachusetts
September 28, 2021




⇩ Closely related postings, oldest first ⇩



1996

Q. Actually we have a system enclosed in a box made of steel plated with zinc and yellow chromate. After I did some testing I found that the chromate doesn't offer good conductivity. That doesn't make a good shielded box.

If we only apply zinc with no chromate the finish is very conductive but I was told that corrosion could occur rapidly. Is it right ?

I'm looking for a finish or coating that

protect steel from corrosion
could be painted ?
is very conductive
relatively low cost

Could you help me or refer me to a company.

Best Regards

Francis Pelchat


A. Did you try "blue" or "clear" chromate - it is much thinner, therefore more conductive.
You should not be afraid of corrosion - Zinc with or without chromate provides almost the same degree of protection to steel. Without chromate your finish is easily fingermarked though and will show Zinc corrosion (white powder)much sooner than with chromate.

Max Stein
captive metal finisher - Montreal, Québec, Canada
1996


A. Max is right, blue passivation is the correct answer. If blue is still not good enough, try a short dip in 0.5% nitric acid. The nitric does not improve white corrosion resistance but gives a better appearance.
Sara

sara michaeli
sara michaeli signature
Sara Michaeli
Tel-Aviv-Yafo, Israel
1996




Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)



Q. Hello:

We produce rack mounted audio/video equipment for the broadcast industry. I would like to know which has the best conductivity and to what degree are the differences, between zinc with clear chromate, yellow chromate, and black chromate. Are their any differences in the corrosion resistance of the three. We need the best electrical grounds for EMI.

Thanks
Don

Don Hudson
- Salt lake City, Ut
1998


A. Don,

Because the chromating conversion coatings are very thin, they are all conductive. However, clear chromate film has relatively low electric resistance since it is thinner than yellow and black chromate films. On the other hand, yellow and black chromate coatings offer much better corrosion resistance than clear chromate coating.

Ling

Ling Hao
- Grand Rapids, Michigan
1998


A. I agree with the statement in regards to all three chromates being conductive, but is this true for the new wave of Tri Chromates as well?

Abel Salazar
anodizing and plating - Anaheim, California, USA
February 28, 2011




Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)



Q. Hi;

We are using electrodeposited zinc coating on steel with additional chromate conversion. The process of this plating is performed according to the standard ASTM B633 [affil link] type II. This standard does not specify if this coating (yellow chromate) is conductive ( electricity point of view). Since this finish will be used for grounding purposes. So I well appreciate to have some help regarding this issue.

Thank you in advance

Abdel Ahraiba
- Quebec - Canada
2000


A. There are several grades/types of chromate ranging from clear to yellow, to bronze, to Olive Drab. In general, the biggest difference between these grades is the thickness of the chromate conversion coating (although bath recipes and procedures my differ as well); with clear cad being the thinnest and OD being the thickest.
The electrical conductivity varies as well with clear being the most conductive and OD being the least. Yellow cad is a middle of the road plating, offering a compromise between electrical conductivity and longer corrosion resistance.

Chris FitzSimons
- Lombard, Illinois
2005




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