Metal finishing Q&As since 1989
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"Commercial zinc plating" vs ASTM B633 standard
December 30, 2010
Q. Good Day,
I have been looking for information in regards to Commercial zinc plating vs zinc plating to the ASTM B633 standard but unable to locate any info for the Commercial zinc.
I doubt that the commercial zinc can withstand any type of salt fog test correct?
If carbon steel parts are plated with the commercial zinc plating then what would be the plating thickness?
Any feedback would help.
Thank you.
MC
Q.A. - San Carlos California USA
A. Hi, Mario. Although some plating shop managers say that "commercial zinc plating" is .0002" thick, I've heard others claim it is .00015", and still others claim that it is only "complete coverage". In my opinion the term is meaningless, a nice sounding term that sort of implies a fitness to purpose without having to actually promise it. It probably actually means "you can't reject it if it isn't rusted when you receive it" :-)
I welcome other comments on the subject, but actually I think we should retire the term from our lexicon. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 3, 2011
Q. A hardware and fastener supplier is telling me that commercial zinc plated fasteners have 3 microns of zinc and this is standard across the industry. Our company has always had 5 microns of zinc on the print.
Our Supplier has asked us to sign numerous deviations of fasteners or else require every fastener to be sent to outside plating process to get plated to 5 microns minimum.
There is not much difference between 3 microns and 5 microns for corrosion resistance, but I'm concerned that maybe the supplier simply doesn't want to be responsible for poorly plated fasteners.
I am considering simply going to all stainless and avoiding zinc fasteners altogether except for heavy bolts.
Is my supplier right about commercial zinc on fasteners? Should I be switching to stainless (I have galvanic concerns)? How does the automotive industry avoid corrosion of hardware for small hardware #4 thru #10?
- Chicago, Illinois
September 25, 2019
A. Hi Cameron. Yes, some people may feel that "Commercial thickness" is about 3 microns (or 0.00012"), but the term is actually unenforceable and meaningless. I understand that asking for a greater thickness than most plating shops are willing to do, and asking for it cheap, is a problem. Further, just because ASTM B633 starts at 5 microns doesn't mean 3 microns is totally unacceptable for anything ever. Although personally I believe in quality and in specs, I also acknowledge that the majority of zinc barrel plating shops I visited over my career plated less than 5 microns.
I think the right resolution, if the vendor says his "Commercial" zinc plating is 3 microns, and you think it's enough, is for you to specify 3 micron thickness rather than "Commercial" thickness. As for the automotive industry, however, I don't believe they accept less than 5 microns -- I'd be happy to hear from anyone claiming the contrary. Good luck.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 2019
August 20, 2020
⇦ (tip: readers rarely show interest in abstract questions;
actual situations usually prompt responses) 
Q. What is the thickness standard of Zinc plating on sheet metal parts?
Appreciate if you please tell me the standards of zinc plating metal sheet parts tests --
1) water resistance test hours?
2) Salt Spray Test hours?
3) other important tests if you recommend?
- Lahore Pakistan
A. Hi Anique. There is no one 'standard thickness'. ASTM B633 starts at 5 microns for 'mild' service. Most automotive specs seem to be for 8 microns, which corresponds with 'moderate' service. 12-13 microns is sometimes specified for 'severe' service, and the spec goes all the way to 25 microns, although that's rarely spec'd and done.
I don't think your questions can be answered in a paragraph or two (just as an example, salt spray hours depend far more on the chromating than on the zinc thickness), but I think obtaining and studying that spec will put you well on the way towards understanding the issues of thickness, corrosion testing, and other tests.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 2020
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