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"MIL-C-5541 Type 1 & 2, and Class 1A & 3 -- understand the differences"



FAQS & TUTORIAL:

RoHS = short for the European Parliament's directives on "Reduction of Hazardous Substances".

This particular directive is concerned with the constitution of the end-product item in question, not the materials used in its manufacture (although other directives like REACH may regulate the use of hazardous materials in the manufacturing process).

Example of the distinction: hexavalent chrome is used both in some chromate conversion coatings for zinc plating and for aluminum (some of the Alodines and Iridites) and in most chrome electroplating. Articles which have a hexavalent chromate conversion coating contain hexavalent chromium as shipped & as used, and may therefore release it, and are thus a RoHS concern; but chrome electroplating produces a coating of zero valence metal and is therefore not a RoHS concern.

Back to the chromate conversion processes: In the old days, until a few years into this century, the main alternative to hexavalent chromate coatings was trivalent chromate coatings and they were vastly inferior to hexavalent, especially in corrosion resistance. These days some trivalent coatings are equal (at least in corrosion resistance) to hexavalent.

Consequently, Mil-DTL-5541 [link is to free spec at Defense Logistics Agency, dla.mil] has been expanded from earlier -5541 releases to now cover both types.

Current question and answers:

June 19, 2021

Q. Is there any evidence of incompatibility between a Class I and a Class II chem film if these are in the same electrical bonding interface?

Ted Laurvik
EMC engineer - Centennial
^


June 2021

A. Hi Ted. I think you have a typo because to my knowledge there is no 'Class II'. There is Class 1A and Class 3. There is also a Type I (hex chrome) and a Type II (non-hex chrome) though.

Sometimes the same chemical is used for the Class 1A and Class 3 needs, and I believe the spec tells you to ignore the chromate in calculating galvanic compatibility, so I wouldn't foresee any between the various combinations.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


June 18, 2021

thumbs up sign Bravo! I read a lot of quite valid answers to good questions hre. The only thing that puzzled me was what RoHS was. I have been around the MIL-DTL 5541 and MIL-DTL-81706 world for a few decades. I was happy to see the 81706 answer for Ender. Typically I see people confusing the process spec (5541) with the material spec (81706).

Ted Laurvik
- Centennial Colorado
^



August 5, 2021

Q. a customer drawing : AMS-C-5541 1A YELLOW (ROHS) 168H sst.
But my supplier told me : yellow conversion coating needing to pass 168 hours salt spray must be Hexavalent chromium, and cannot pass ROHS. Non chromium treatment cannot pass 168H sst -- is it right ?

Kasen Kwong
- NYC NY
^


August 2021

A. Hi Kasen.

What you heard is incorrect but it may have a seed of truth. Trivalent chromates are just as corrosion resistant these days as hexavalent ones, so a 168 hour salt spray test should not be a challenge. But it might be true that there is no chromate which is acceptable to AMS-C-5541 and yellow and RoHS compliant.

sidebar Your posting came from Guangzhou, so Welcome to New York! Some large companies have presence in both cities, which can explain such IP routing, but posters should please appreciate that, while postings are highly welcome from anyone anywhere, this site relies heavily on camaraderie, and a small dishonesty can be the kiss of death to that welcome. When readers need help understanding environmental regs in NYC I'll be counting on you; I hope I won't be disappointed.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^




Closely related historical postings, oldest first:

January 28, 2008

Q. What is the difference between these two mil standards? Is one for a clear RoHS compliant and the other for a yellow RoHS compliant? Or is the Mil-C-5541 for clear RoHS and Mil-DTL-5541 [link is to free spec at Defense Logistics Agency, dla.mil] for yellow hex. Please let me know. Thank you.

Mike Logan
plating shop employee - Minneapolis, Minnesota
^


February 4, 2008

A. Mike, Hi.
Type I - Compositions containing Hex Chrome
Type II - Compositions containing no Hex Chrome
Class 1A - For maximum protection against corrosion, painted or unpainted.

Mil-C-5541 did not mention Type I or II whereas Mil-DTL-5541 [link is to free spec at Defense Logistics Agency, dla.mil] does. Class 1A is the same for both standards. For Mil-DTL-5541, it is very clear when Type II is mentioned, the conversion coating shall not contain Hexavalent Chrome, hence, RoHS compliant. When Type I is mentioned, the conversion coat contains Hexavalent Chrome but it may not necessarily be yellow. There are clear conversion coatings out there which are Hexavalent chromium based. As far as I am concerned, there is no yellow conversion coat (yellow chromate if you prefer) that is Type II. If you have time check out http://assist.daps.dla.mil ^ quicksearch.dla.mil and check out some excellent trivalent chromium base conversion coats (Henkel, Surtec, Macdermid, Luster On ) which can, incidentally be classified as Type II.

Cheah Sin Kooi
- Penang, Malaysia
^

----
Ed. note: The address for the mil spec service was updated as noted since Cheah's posting


February 28, 2008

A. Mike,
Further readings on earlier posts at finishing.com, apparently, there are yellow conversion coating that is Type II - clear conversion coating with yellow dye.

SK Cheah
MST - Penang Malaysia
^


thumbs up sign Hi Cheah. I think a big point of possible confusion is that there may be RoHS compliant trivalent conversion coatings which are yellow, either through the addition of dye or because they are thick-film and naturally yellow, but which are not be on the QPL yet -- which means you're not compliant with MIL-DTL-5541 if you use them. So it probably isn't correct to call such coatings Type II ... just call them yellow and RoHS-compliant :-)

Regards,

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



August 27, 2009

Q. Can anyone tell me what are the differences in the new standards (Mil-DTL-5541 [link is to free spec at Defense Logistics Agency, dla.mil]F) as compared to the old.

Thomas Joseph
Precision Metal Fabricator - Singapore
^


A. Hi Thomas. We appended your question to a thread where Cheah Sin Kooi had answered the question: RoHS-compliant (Type II) coatings were not part of the old Mil-C-5541 standards. Good luck.

Regards,

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



December 6, 2013

Q. Is Iridite per MIL-C-5541E, class 1A compliant with RoHS?

Senthil Kumar
- Bangalore, INDIA
^


December 9, 2013

A. Hi Senthil. Iridite is a Macdermid trade name for a range of chromate conversion coating processes, some of which are surely RoHS compliant, whereas others migh be based on non-compliant hexavalent chrome. Good luck.

Regards,

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



September 26, 2014

Q. Is the part processed per type I hazardous in any way? Or just the chemical solution used in the process? We have parts processed per type I versus required type II. The customer is giving us a hard time. Thanks.

david ho
- Milford, Connecticut, usa
^


September 2014

A. Hi David. RoHS is short for the European Parliament's directives on Reduction of Hazardous Substances, and refers to the constitution of the parts, not the processes used to manufacture the parts. The situation is simply that parts processed in Type II solutions do not put hexavalent chromium on the parts, so the parts are very likely to be RoHS complaint. Processing parts per Type I does put hexavalent chromate on the parts, and they are unlikely to pass a test for RoHS compliance.

Many domestic and non-European customers are requiring RoHS compliance as well, so it is understandable that your customer is giving you a hard time -- he may not be able to use the parts.

"...hazardous in any way?" is relative and qualitative, so I don't think anyone can definitively answer. But a former governor of NJ once declared that " 'toxic' is a matter of statute, not opinion", and I think we can look at the word 'hazardous' in the same way: if you want to send them to Europe but RoHS says they're hazardous, they're hazardous. Good luck.

Regards,

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



June 8, 2016

Q. Is Mil-DTL-5541 [link is to free spec at Defense Logistics Agency, dla.mil] Class 1A Gold Alodine acceptable for the Spacex callout:
Chemical conversion coating Class 1A using Alodine 1200 or equivalent? Thanks, gs

Gary Schneider
Quality Inspector - Mtn. View, California USA
^


June 16, 2016

A. Hi Gary,

Without being a Spacex employee I cannot guarantee my answer is correct, only they can do that, but it does look like it is meant to relate to MIL-DTL-5541 Class 1A, of which Alodine 1200 is on the QPD for MIL-DTL-81706 "Chemical Conversion Materials For Coating Aluminum And Aluminum Alloys".

Brian Terry
Aerospace - Yeovil, Somerset, UK
^



October 13, 2016

Q. Is there a MIL-DTL-5541, Type II Class 1A Chem film that is doesn't contain hex chrome?

Gary Smith
- Everett, Massachusetts USA
^


October 2016

A. Hi Gary_. Yes, there are several -- Mil-DTL-81706 [link is to free spec at Defense Logistics Agency, dla.mil] lists them. Type II in actual effect essentially means "doesn't contain hex chrome". Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^



December 13, 2020

Q. Is that possible that Mil-DTL-5541 [link is to free spec at Defense Logistics Agency, dla.mil] type II class 1a or type I class 3 coating processes on Aluminum alloys?

ender toprak
- Ankara, Turkey
^


December 2020

A. Hi Ender. Yes, there are two types and two classes. If I am understanding your question correctly, the answer is that all four combinations are listed in MIL-DTL-81706 and its Qualified Products List Database (QPL).

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^

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