Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Specs for Chromate/Zinc Coatings
(2002)
Q. I am in need of as much information as I can get about the chemical composition of coatings. Specifically for the following coatings:
Zinc Plating plus Yellow Chromate coating [on steel (SAE J81)]
Zinc Plate and Yellow Zinc DiChromate coating [to meet Ford WSB-M10P10-A3 and WSD-M1P85-A2 (on AISI 12L14 steel)]
Olive Drab Chromate coating [to meet WSB-M10P10-A5 (on Zinc Alloy ASTM AC41A to meet ASTM B86)]
Zinc Plate and Black DiChromate coating [to meet WSD-M1P85-A2 and WSB-M10P10-A2 and any other(s) similar or relevant. I know they contain Chromium and/or Zinc, but do they contain anything else? And I need to know whether it is Hexavalent or Trivalent Chromium. Any knowledge would be greatly appreciated!
- Lakeland, Florida, U.S.A.
A. All of the finishes you listed are zinc plating followed by some form of hexavalent chromium passivation. As far as you need to be concerned, the terms "chromate" and "dichromate" are pretty much the same thing. These different dichromates have slightly different formulations to get the different colors, but all are very similar. I am very certain that all of your current zinc or zinc-alloy platings are chock-full of hex chrome and are slated to be banned as soon as the EU and the OEMs can give us a firm date.
Since you seem to be in the automotive industry, you should be looking at using trivalent chromate passivation instead of hexavalent. Start talking to your plating supplier(s) about this, and they should be able to explain more.
Tim Neveau
Rochester Hills, Michigan
2002
Q. For the EU directive, does Clear Chromate contain hexavalent chrome? Does anyone know of a good educational site for this topic? Finally what specification can be referenced when specifying a clear chromate?
John Loui- Concord, New Hampshire
2002
A. Your current clear chromate is most likely hexavalent chrome and eventually needs to be replaced. There are plenty of new specifications in the automotive industry. Chrysler, GM, and Ford all have new specs released. Just look for a new revision of the previous spec. For those not in the automotive industry, I have no idea.
One good website to go to is www.gmw3059.com, the only GM spec with its own website!
Tim Neveau
Rochester Hills, Michigan
2002
Q. How can I get from a Zinc Plate per WSD-M1P85-A1 with a yellow chromate per WSB-M10P10-A3 part to a finish WSS-M21P17-B1? Is it possible? Can I get the same characteristics with an e-coating?
Tere Garcia- Mexico
September 5, 2012
A. Hi Tere. I think you will find that the newer spec you mentioned is for trivalent chromates whereas as the older, superseded, spec might have gotten you hexavalent chromates because it did not specify the need for RoHS-compatible chromate. The change should not be a problem for you unless I misunderstand the question or your situation.
An e-coating is not a substitute for zinc plating & chromating for a bunch of reasons, including the fact that zinc plating offers cathodic protection, and metallic coatings like zinc are less likely to chip away in some types of service. This is not to imply that e-coating is inferior to electroplating, but that you need to look at the particular part and decide what an appropriate finish is. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 6, 2012
November 20, 2012
Q. In order to be ROHS compliant, we are planning to use the following note to replace an existing yellow zinc plate note from an earlier B633 revision:
RoHS COMPLIANT TRIVALENT CHROME PLATE, CLEAR, PER ASTM B633, LATEST REV. SERVICE CONDITION, SC 2 (.0003-.0005 THICKNESS). TYPE II, 96-HR MIN SALT SPRAY.
I think this note covers all of the requirements, it has all of the details wee need. The problem is that I have a plating supplier who insists that the TYPE II is incorrect and should be TYPE V. I have no way of confirming his statement, the B633 seems a bit vague.
So my question is (3 part);
What is the difference between Type II and V?
Can I use Type II and still be ROHS Compliant?
And what specifically is a passivate treatment? I know what passivation is with relation to iron contamination of stainless steel, but I think this is different.
Thanks for your help
- Burlington, North Carolina
A. Dear Matthew,
Type II uses hexavalent chrome in the conversion coating, Type V uses only trivalent.
You cannot use Type II and be RoHS compliant, you would be using hexavalent chrome!
A passivate treatment is the chromate conversion coating, there are some specs that use that word instead of "conversion coating".
Hope I could answer your questions!
Regards,
- Cañuelas, Buenos Aires, Argentina
November 22, 2012
Q. Our customer is asking for a Zinc plate with CR3 black chromate to ASTM B117 48hr to white rust. Appearance is important. Our manufacturers are not positive that they can achieve this. Is CR3 black chromate able to meet the above or do I need to look for an additional sealer/topcoat? If so, any suggestions?
Paul RussellFastener Distribution - New Berlin, Wisconsin, USA
February 8, 2013
A. Hello Paul,
There are many CR3 black chromates in the market that can achieve that corrosion resistance by ASTM B117. Usually the CR3 black chromate process has two steps: first coloring, second sealing. There are two products so the part can achieve more than 144 hours salt spray to white rust.
There are more products for alkaline zinc plating than for acid zinc plating. I would suggest some vendors, but you can try google them instead ;)
Regards!
- Cañuelas, Buenos Aires, Argentina
March 5, 2013
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