Metal finishing Q&As since 1989

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Coating mass/weight for ASTM B449 colorless

Q. Heya Guys, Gals, and intergalactic travelers!

I cannot for the life of me pass ASTM B449 CL3 coating mass, despite SPOTLESS salt fog. HALP!

Ive been happily running hex chromate to the MIL-DTL-5541 [on DLA] specs for years, and testing to ASTM B449 for salt fog as well. It has been fine; salt fog and adhesion are pretty predictable.

Ive recently been asked to check coating mass for the ASTM B449 cl3 "colorless", and... it has surprised me. In a bad way. Its... too high?! How??

I'm consistent in passing adhesion and salt fog for both related specs. The B449 cl3 120h salt fog is typically 0/0/0.

I ran tests at 30, 15, and 5 sec immersion, with associated salt fog panels; too much weight. Despite being perfectly clear.

Every single associated salt fog specimen passed 0 pits.

Prep is:
Mild alkaline cleaner 140 °F
Rinse city water <200 ppm tds
Flash etch hot caustic... like, DIP.
Rinse <2000 tds neutralization tank, cuz who cares, its going into...
DeOx macD-enthone Isoprep 184 til smutless
Rinse <1000 ppm city
DI rinse <10ppm /max 120'f
Iridite 14-2 83 °F, factory targets met for conc/pH, dead nuts.
Still rinse full of Iridite, 1300 ppm currently, drip off over bath.
Recirc DI, 85 °F, soak til colorless. This bath never goes over 8 ppm TDS NaCl equivalents.

I can't get less than 0.35 mg/m3 mg/m2 g/m2. Its supposed to be <0.1.

Are any of you ancient platers able to hit this? And if so, how?

I'm desperate. 99.9% of what I need to confirm good is 5541 work. I really am terrified to attempt any uncompensated R&D work on a known-good 5541 line ... like messing with pH or temp or conc.

Short of racking the parts and waving them in the fumes coming off my well behaved Iridite tank... has anyone tried to pass this test? Even if you failed, I'm really curious as to your experience.

I did reach out secondhand through a trusted contact, and only got; "are you SURE she's running that, you know it's strictly military?"

I am; as the kids say, ded.

If anyone would be so kind as to share weight loss tricks to a sturdy middle aged lady (chromate, silly!!!)... I'd be much obliged.

Cheers from the Great Green North.

Rachel Mackintosh
- Greenfield, Vermont
June 14, 2023

Oh my goodness, yes. You're absolutely right. And I did not seriously intend to put CUBIC meters. Thank you for catching that.

Rachel Mackintosh
- Greenfield, Vermont

I'm: a bit embarrassed ;)
June 23, 2023

Hi William!

Thanks for "weighing" in ;D

My usual protocol is to run chromate on a Friday, let it hang over the weekend, then unrack and package on Monday. It's an interesting thought though -- that we might be artificially high due to not fully dehydrating?

This alone makes me even more issue with the wording of the spec. By that logic, the panels should be placed in a desiccator at the lab to verify no weight change prior to going into test, right?

And then, there are 3 methods: "fresh" defined by <3h out of process, "aged" which gives no defined wait time, and a general one with no time mentioned at all.

If a 48h aging is basic good practice, it would be nice to see that included in the spec.

I am under the understanding that there is some discussion within the guidance committee about how to make this test more useful -- including the time question. We shall see how that goes.

As an aside, I had a nice chat a couple days ago with a gentleman retired from a manufacturer of a particular chromate line, who is of the strong and vocal opinion that coating mass might be a useful data point for troubleshooting a process where failures are found in salt fog and/or resistivity, but not a true requirement for primary testing, and that any auditor who takes issue with the test not being done on an otherwise-good process is misinterpreting the intent of the mass test. And there's some historical anecdotes about how it ended up in there to begin with, dating back to before I was born...

I'll be honest, I read it the same way due to lacking specific information provided for other standardized tests; periodicity, specimen size and configuration, number of specimens...

I'm really looking forward to see when and if the next revision addresses some of these gaps.

Rachel Mackintosh
- Greenfield, Vermont

I'm a labrat
June 24, 2023

Yes, it is g/m2 and the red edit in my initial post still says mg; but your first reply gave the correct units.

Ted, sorry to be a bother, but could you update that edit? Thank you!

Rachel Mackintosh
- Greenfield, Vermont


June 29, 2023

Ed. note: Hopefully, we've now corrected correctly :-)