Difference between MIL-C-5541 Class 1a and MIL-DTL-5541 Type 2 Class 1a

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 and check out some excellent trivalent chromium base conversion coats (Henkel, Surtec, Macdermid, Luster On ) which can, incidentally be classified as Type II.

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.

A. Hi Cheah. I think the confusion is that there are RoHS compliant trivalent conversion coatings which are yellow (through the addition of dye) -- but they are not compliant with MIL-DTL-5541. So it probably isn't correct to call them Type II ... just call them yellow and RoHS-compliant :-)

Regards,

A. Hi Thomas. We appended your question to thread where Cheah Sin Kooi had answered the question: RoHS-compliant, Type II coatings did not exist in the old Mil-C-5541 standards. Good luck.

Regards,

A. Hi Senthil. We appended your question to a thread which answers it. No, Mil-C-5541E, class 1A is NOT RoHS compliant. Good luck.

Regards,

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 of their RoHS compliance.

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

"...hazardous in any way?" is a loaded and qualitative question which I don't think anyone can authoritatively answer. A former governor of NJ once remarked that " 'toxic' is a matter of statute, not opinion", and I think we can look at the word 'hazardous' the same way. Good luck.

Regards,

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".

A. Hi Gary. Yes, there are several -- Mil-QPD-81706 [link is to free spec at Defense Logistics Agency, dla.mil] lists them. Good luck.

Regards,