Home /
Search 🔍
the Site
pub Where the world gathers for
plating, anodizing, & finishing Q&As since 1989


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

adv.    pri_imageonline


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 in some chromate conversion coatings for aluminum (some of the Alodines and Iridites) but also 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. But these days some trivalent coatings are equal (at least in corrosion resistance) to hexavalent.

Consequently, MIL-DTL-5541 [affil. link or DLA] has been expanded from earlier -5541 releases to now cover both types.

Current question and answers:

April 13, 2022

How are you, my name is DAVE.L; I am from/in China Now I have problems.
Alodine Type 2 Class 1A, MIL-C-5541: Will It Work On Copper? Alodine Type 2 Class 1A, MIL-C-5541: What is the maximum temperature that the surface coating can withstand with no damage to coating characteristics?

Look Forward To Your Reply.

R & D Engineer - Suzhou, China

April 2022

A. Hi Dave. You can apply Alodine and similar chemicals to copper and it will offer some tarnish resistance and corrosion resistance. However, it cannot be called MIL-C-5541 because that is a specification for surface treatment of aluminum, not copper. The temperature resistance is generally thought to be 140 °F.

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 [affil. link or DLA] 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 [affil. link or DLA] 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.

SK Cheah
- 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 :-)


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 [affil. link or DLA]F) as compared to the old.

Thomas Joseph
Precision Metal Fabricator - Singapore

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


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 might be based on non-compliant hexavalent chrome. Good luck.


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.


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 [affil. link or DLA] 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 [affil. link or DLA] lists them. Type II in actual effect essentially means "doesn't contain hex chrome". Good luck.


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 [affil. link or DLA] 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

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 here. 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 : AMSC5541 [withdrawn / affil. link] 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

August 2021

A. Hi Kasen.

What you heard is incorrect but it has 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 AMSC5541 [withdrawn / affil. link] 1A and yellow and RoHS compliant.

sidebar Postings are welcome from anyone anywhere, but this site is a place of camaraderie, and small dishonesties can be the kiss of death to the aloha. When readers need help understanding environmental regs in NYC they'll be counting on you ... we hope you won't tell them you don't know because you're actually in Guangzhou :-)

Luck & Regards,

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

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Chemicals &
Consult'g, Train'g
& Software

About/Contact    -    Privacy Policy    -    ©1995-2023 finishing.com, Pine Beach, New Jersey, USA