Mil-DTL-5541 / Mil-C-5541 testing per ASTM B117

Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert

Also available in Spanish

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A. There are several factors that affect the successful processing of panels that will pass the corrosion resistance test. The first place to look is the cleaning process. If the aluminum is not properly prepared, there may be discontinuities in the conversion coating. The second place to look would be the Chromate itself. Is there contamination? Is the process being performed in accordance with the manufacturers recommendations? Finally, I have had experiences with poor quality test panels. Another potential cause would be if the salt spray test is being applied to the panels at 15 degrees (As specified in ASTM B117) or at 6 degrees (As specified in MIL-C-5541). It is imperative to understand that the Class 3 coating is not going to be as corrosion resistant as a Class 1A coating. I hope this gives you some insight into solving your problem.

Best of Luck.

A. We had the same problem before, tried to figure out what was wrong for about a year but without luck. Until I read repeatedly the technical brochure of the product we were using (Alodine).

There was a mention of post treatment. We inquired and asked for sample which they sent. It was a liquid that is supposed to be mixed with the final rinse. We had 100% passing mark ever since!

A. Hi Gary,
MIL-DTL-5541 is very prescriptive; test pieces must be run with a production lot. It is sometimes impractical and, if it is greater 35 days since your last production run you will either have to run at risk or wait the 35 days. Even then, because of the way the specification is written you will need to process parts at risk with the test pieces, as we come back to the need to process with a production run.

What you could do is ask for a deviation from MIL-DTL-5541 to allow you to run the test pieces separately and within the 35 day window, meaning that production can be continued.

A. I'm looking over MIL-DTL-5541. It seems to be done with continuous production in mind, with the monthly (not exceeding 35 days between) testing. If anything fails a test, all "traceable and retrievable" parts produced since the previous round of testing are rejected. If the line has not been in production for over a month, then you are starting with a blank slate and perform the first round of testing immediately ("at the restart of production", not "prior to production").

You don't give much info on your situation, other than it's impractical to include the test specimens during the production run for the order. If you get this order, would you be starting up the line after over a month of shutdown? Would the order itself take more than 35 days to complete? Why are you unable to send a batch of test specimens through in between batches of the actual parts?

I don't see anything that actually says you have to wait the one week for the salt spray test results before doing anything else, only that if the results come back as a failure, you have to collect everything you can that was processed and scrap them. This is what Brian referred to as "running at risk", but the standard seems to be entirely designed for that, no part is ever run without risk since even with a continuous production, any "traceable and retrievable" part at any time can be rejected if the next testing cycle produces a failure.

I also don't see anything that actually says the test specimens must be run in the same batch as production parts, only that they must go through all the same processes as the actual production parts. It seems to be the general expectation that they will be run separately, though sequentially or concurrent, with the production parts.

You may have to be more specific about what your actual difficulty here is.

Hi Michael. As you see, we appended your question to a thread on the subject and we have dozens other such threads. Yes, hundreds of our readers are familiar with the topic. You should probably be using MIL-DTL-5541 these days. What is your situation and your question?

Regards,