Summary for trivalent chromate replacement Discussion
Trivalent chromate is the main practical replacement discussed for this valve manufacturer’s need to eliminate hexavalent chromate under GMW3056 while still meeting yellow zinc and olive drab finishes with 48-hour salt fog resistance. Jeffrey asked whether trivalent chromium could replace hexavalent chromate for parts made in Italy and China. Toby Padfield replied that switching to a trivalent chromate conversion coating is probably the easiest path, noting that trivalent chromates do not exactly match the old colors but can achieve 48 hours of salt spray resistance before white rust. He recommended reviewing the latest GMW3044, which covers electrodeposited zinc coatings and supplemental chromates. David McNorrill added a caution: GMW3044 requires approved suppliers, and he had not found many overseas suppliers, so his local workaround was to specify ASTM B633 or ISO 2081 with the condition that the coating meets GMW3059. A later question asked about Australian standards for trivalent finishes, and Steve Jennings said he was only aware of automotive specifications such as WX100 S…
Q. Our company has to soon be compliant with GMW3056, which restricts the use of Hexavalent Chromate on our parts. I am looking for a substitute for yellow zinc plating (per ASTM B633-85, Fe/Zn 5, Type II) and zinc part with Olive Drab Chromate. They both have to meet a 48 hours of salt fog. Is Trivalent Chromium a good replacement? The parts will be made in Italy and China.
Jeffrey L [surname deleted for privacy by Editor]
automotive valve mfg. – Florham Park, New Jersey
2003
A. Probably the easiest thing for you to do is to change the current hexavalent chromate conversion coating to a trivalent version. The trivalent chromates do not exactly reproduce the same colors as the hexavalent chromates, but they are capable of providing 48 hours of salt spray resistance before white rust. I suggest you obtain the latest version of GMW3044, which is the standard that covers electrodeposited zinc coatings (with and without supplemental chromates, lubricants, etc.). It explains the requirements for specifying zinc + chromate coatings. Global Engineering Documents is the official provider of GM standards.
Toby Padfield
Automotive module supplier – Michigan
2003
A. The hitch with GMW3044 is in section 8, it specifies: Suppliers to this specification must be approved by the respective GM Specialist Teams/TDGs … Although these approved suppliers are growing daily, I haven’t found any overseas suppliers. Additionally our local plater (who in fact could supply to this spec) doesn’t see enough Automotive business to justify the hassle of getting approved. Our ad hoc solution has been to specify as ASTM B633 or ISO 2081 with the condition that the coating meets GMW3059. Are there any standards out there that specify trivalent chromates other than GMW3044?
David McNorrill
Automotive Supplier – Aiken, South Carolina
2004
Australian Standard for Trivalent finishes like Corro Triblue + Rogard Sealant?
Q. I am currently writing an internal standard for Trivalent plating using Corro Triblue with a Rogard Surpreme Seal 500 Sealant. Is there an official Australian standard on Trivalent finishes or just the individual motor companies standards like WSS-M21P17 for FORD?
Darren Wright
automotive – Adelaide, SA, Australia
2005
A. Hi Darren,
As far as I am aware, there are only the automotive specifications at this time (WX100 S437, GMW3044, etc.)
Steve Jennings
plating – Adelaide, South Australia
2005
Need Barrel Zinc Plating to GMW3044
May 12, 2009
RFQ: Must be on GM Approved Sources list. Chicago area.
Dean B [surname deleted for privacy by Editor]
hinge mfg. – Brookfield, Illinois, USA
Ed. note: This RFQ is outdated, but technical replies are welcome, and readers are encouraged to post their own RFQs. But no public commercial suggestions please ( huh? why?).