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

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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 employed during its manufacture (other directives like REACH may regulate the use of hazardous materials in the manufacturing process).

An 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 [on DLA] has been expanded from earlier -5541 releases to now cover both types.

Q. When it states in a DFAR Clause on a Contract:
252.223-7008 Prohibition of Hexavalent Chromium.
(1) Unless otherwise specified by the Contracting Officer, the Contractor shall not provide any deliverable or construction material under this contract that:
(i) Contains hexavalent chromium in a concentration greater than 0.1 percent by weight in any homogenous material.

The spec on the drawing notes to Conversion Coat per MIL-DTL-5561 ^ 5541 Cl 1A.

I read in the spec that Type I applies if nothing is noted but I don't know how to figure out if the coating weight would exceed the 0.1 percent by weight of the part.

Mary Richard
Quality Assurance / Contract Review - Belmont, NH
October 9, 2023

Ed. note: "5561" was a typo; it should be "5541".

A. Hi Mary,

In MIL-DTL-5541 [on DLA] conversion coating, "Class" has to do with electrical conductivity (which in turn involves coating weight), but in addition to "Classes" there are also "Types" which have to do with the presence or absence of hexavalent chromium.

Type II are "Compositions containing no hexavalent chromium". I think that once that DFAR requirement for minimal hexavalent coating weight has been made, something very important has been "noted" and the situation of "if nothing is noted" no longer applies. You should specify and do 'Type II' conversion coating to comply with the requirement you speak of.

Luck & Regards,

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

Q. Hi Ted,
Since the Drawing only states CL 1A and the Spec states Type I would apply if no type is specified I still don't know if I would be within the .1% by part weight. I read somewhere that a part would rarely exceed .07% by part weight which would be within the limits of the 0.1%.

Mary Richard
- Belmont, New Hampshire
October 19, 2023

A. Hi again.
I can't intelligently critique an article that you read somewhere, but I haven't read, that says hexavalent chromium rarely exceeds 0.07% of the part weight. But I can warn you that 'homogeneous' material doesn't necessarily mean what you might expect it to mean -- it means what the European Parliament wants it to mean, and they want it to mean "don't use hexavalent chromium" :-)

I am 99.44% confident that DFAR wants you to use Type 2, non-chromate, conversion coating and I fear that even if you tested and proved that the hex chrome was less than 0.1% of the part weight you still won't be safe but would be a target. Luck & Regards,

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

⇩ Related postings, oldest first ⇩

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 [on DLA] for yellow hex. Please let me know. Thank you.

Mike Logan
plating shop employee - Minneapolis, Minnesota
January 28, 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 [on 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 ^ 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
February 4, 2008

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

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

SK Cheah
MST - Penang Malaysia
February 28, 2008

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

Q. Can anyone tell me what are the differences in the new standards (MIL-DTL-5541 [on DLA]F) as compared to the old.

Thomas Joseph
Precision Metal Fabricator - Singapore
August 27, 2009

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

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

Senthil Kumar
- Bangalore, India
December 6, 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,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
December 9, 2013

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 26, 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,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
September 2014

Q. Is MIL-DTL-5541 [on 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 8, 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
June 16, 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 13, 2016

A. Hi Gary_. Yes, there are several -- MIL-DTL-81706 [on 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 - Pine Beach, New Jersey
October 2016

Q. Is that possible that MIL-DTL-5541 [on DLA] type II class 1a or type I class 3 coating processes on Aluminum alloys?

ender toprak
- Ankara, Turkey
December 13, 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 - Pine Beach, New Jersey
December 2020

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 19, 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 - Pine Beach, New Jersey
June 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
June 18, 2021

Q. a customer drawing : AMSC5541 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 [fictitious]
August 5, 2021

A. Hi Kasen.

What you heard is incorrect but it has a seed of truth. In the old days trivalent chromates weren't as corrosion resistant as hexavalent ones, but these days they are -- 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 1A and yellow and RoHS compliant.

sidebar Postings are very welcome from anyone anywhere in the world, but this site is a place of camaraderie since 1989, and small dishonesties can be a kiss of death to the aloha. When readers need help understanding environmental regs in NYC and ask you a question, we hope you don't tell them you can't help because you're from Guangzhou :-)

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
August 2021

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 13, 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 - Pine Beach, New Jersey

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