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Test panels/coupons for salt spray testing of chromate conversion coated aluminum

(-----) February 20, 2008

Q. Are aluminum test coupons with a smooth continuous protective PVC film an advantage over unprotected or poorly protected aluminum test coupons? A supplier of test coupons is trying to convince me that poorly applied/wrinkled PVC presents no problem to meeting Mil-C-5541 [link is to free spec at Defense Logistics Agency, dla.mil].

Dennis Puhalski
Plating Shop Engineer - Maumelle, Arkansas

February 21, 2008

A. Welcome to the wacky world of chromate conversion coating, where you don't test the quality of your actual parts, and you don't really test the capability of your process, you test your buying skills in finding test panels that won't fail a salt spray test -- a world where mislabeled 1xxx or 6xxx panels would comprise the best 2xxx and 7xxx test panels :-)

Seriously though, buy some samples of any test panels you can get, process them, and run them through your salt spray test. There's no point in guessing how well they will do, but there is a lot of value in finding test panels that are of substantially higher quality material than your actual parts so everyone can maintain the pretense that their actual parts are corrosion resistant :-)

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

February 23, 2008

A. Everything Ted said above PLUS: On one 2024 program I worked on we failed salt spray with three sources of panels (which you could see voids with the naked eye), and we processed with knowledgeable educated engineers. Then we got panels from a 4th source, and the labor tank hanger passed salt spray.

In old or heat treated 2000 and 7000, the copper and zinc walk (migrate) to the grain boundaries, and in some cases it is impossible to pass salt spray.

Always inspect your incoming panels with a 10X loop, discard the big holes.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

December 5, 2008

Q. Is there such a thing as "test grade panels" or does one purchase a sheet of material with pvc film on it?

Gregg Rodehaver
- Auburn, WA USA

December 7, 2008

A. Hi, Gregg. You buy special test panels. Your chemical process distributor will probably have them or be able to tell you where to get them.


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

January 14, 2014

Q. Greetings,

I've been trying to have my 2024 panels pass corrosion resistance testing for MIL-DTL-5541 Type II, CLass IA. I've read in text that adding nitrilotris (methylene) triphosphonic acid [NTMP] can assist by acting as a chelating agent. Has anyone seen success using this additive and in addition, where would one procure this additive?

Alex Chavez
- Phoenix, Arizona, USA

January 2014

A. Hi Alex. This compound appears, on a quick glance, to be covered by US Patent 7018486 issued to United Technologies. So if you get no answers here, try locating and contacting their intellectual property division for more info. Good luck.


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

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