ASTM B-449 and other specs for Chromating Aluminum Q&A's

A. Greg, it sure looks like it is available from ASTM at:

www.astm.org/cgi-bin/SoftCart.exe/STORE/filtrexx40.cgi?U+mystore+llav2649+-L+B449+/usr6/htdocs/astm.org/DATABASE.CART/PAGES/B449.htm^ ^{Ed note March 2021: that link is broken, try https://www.astm.org/Standards/B449.htm}

for a mere $25. [Ed. note: $52 at last viewing  ].

I can vouch that their pdf delivery works well (at least on my computer, it did...)

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Ed. note: Thanks, Lee! Readers, are certainly welcome to purchase their specs from ASTM, but Finishing.com appreciates when readers get their specs from Techstreet, a clearing house which carries ASTM and many other specs, and here's why:
Websites constantly change their organization, creating broken links. Techstreet pays finishing.com a small commission to keep their links current across our quarter million postings going back to 1989, whereas when ASTM and other spec suppliers change their URLs (with no notice to us of course), it's quite the whack-a-mole battle for us to try to keep this large & long-running site free of broken links :-(

A. Hi, Karl. Those specs are somewhat similar, but I do not think there is any claim that they are "technically equivalent". ASTM B449 is, however, "technically equivalent" to ISO 10546 [link is to spec at Amazon] if you have that one on hand. Certainly no one wants to spend money on specs simply out of general curiosity, but I'd strongly suggest that people not quote or certify compliance to specs which they don't have. Good luck.

Regards,

A. Hi again Karl. Yes, a rough correspondence between what comprises class 2 vs. other classes in old specs probably does hold; but with MIL-DTL-5541 [on DLA] having replaced MIL-C-5541 in 2006, class 2 coatings not being recognized in the MIL spec for a long time, RoHS requirements becoming common, and a nearly universal migration to hex-free Type II coatings, relying on an old copy of MIL-C-5541 for anything other than compliance with a very old drawing calling for that specific coating sounds problematical.

Luck and regards,

A. Hi Mike,
Most of conversion coating that we do here, the customers drawing specifies MIL-DTL-5541F. I don't see why MIL-DTL-5541F cannot be used as an international specification. It is clear, precise and easy to understand. Foreign suppliers like me do not have a problem to abide.

A. I don't believe coating wt. is a requirement in either of those specs. I believe some OEM specs such as Boeing's may have a requirement but I am not certain of this. We test coating wt. so that in the event it should be required by an OEM we would have records on file showing we meet the requirement. 40 mg/sq. ft. for chem film on aluminum per is our minimum.

A. Nancy

MIL-DTL-5541F makes no reference to coating weight.

ASTM B449 has a coating weight requirement in Section 7.5, referencing Table 1 for the 4 different classes and their respective coating weight ranges. It might be worth getting your customers to waive or except the requirement in writing, assuming your coupons are passing the SS test.

A. MIL-DTL-5541 F does not specify coating weight; it does however reference that material shall be compliant with MIL-DTL-81706 B, and MIL-DTL-81706 par 3.6 requires that coating weight shall not be less than 40 Mg's/ft2 for class 1A coatings.

A. Hi Nick!
I'm pretty sure I have a few of those expensive orange hi-lighters in my lab. It's hard to resist temptation to use them on certain bits of paper that come across my desk! Per my last email, (highlighted in hex),...

Can they? Sure! They work great and I've spent many happy hours explaining why they can't go in the trash when they dry out. Ahh. I love consumer packaging:)

Can they, but OFFICIALLY? Well, that is a more formal can o worms!

Write to your Henkel tech rep for a statement on official letterhead for that one! I'm sure they already have a prepared document for it.

If you still have doubts or feel you are in a situation where you are finding insufficient or conflicting instructions, be prepared to set up a test to send out for salt spray so you can have evidence that, despite touchup, the coating (s) passed the destructive testing required by the spec.

A. (add on answer to Rachel Mackintosh's answer)

chemically speaking tri chrome and hex chrome are very different, and while my copy of ASTM may be out of date, the spec is not really geared to a non-hexavalent chromium solution. The tri chrome have fluorozirconate and trivalent chromium as the main ingredients and each company's proprietary blend of wetting agents, so in general the coatings won't have any zinc or phosphorous.

Also MIL-DTL-81706, which is what the pens are actually qualified for, only requires 168 hours in ASTM B117 not the 120-336 hr range in ASTM 449. Also the paint adhesion test for touch up pens in MIL-81706 is a tough one as well, and while failure of that part of the spec disqualifies it for the Mil spec, the ASTM defaults to ASTM D3359 for organic coatings which in my opinion is easier to pass.

Now as for the conductivity requirements, those are quite different between the ATM and the MIL spec. In short I would say if a tri chrome pen is on the QPL for MIL-DTL-81706 it probably would pass the spirit of the rules for ASTM 449 but it would not pass the letter.