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Anodized parts fail salt spray test if dyed

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Q. We are doing Type I & Type II Class 2 anodizing using Black dye as per MIL-A-8625 / MIL-PRF-8625 [on DLA] on AA2024 T3 sheets. The specimens are failing in Salt Spray test as per ASTM B117 after 48-50 hrs. instead of 336 hrs.

The Class 1 (Non-dyed) specimens are passing the salt spray test.

1. What can be the reason? Shall we use different parameter for class 2 than class 1?

2. If dye may not be suitable, can any one suggest the dye specification which can withstand 336 hrs salt spray test?

Biren Desai
Manufacturing - Mumbai, India
2006

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A. The dye has nothing to do with it. Anodize at a proper temperature, a proper voltage/amperage and long enough to get an adequate thickness to pass more than the minimum weight loss criteria and finally, seal it with a cobalt or nickel seal-HOT not this room temperature stuff. If you have proper cleaning, etch desmut deoxidize rinses, then it should pass.
Finally, are you using parts or coupons for the salt spray.

James Watts
- Navarre, Florida

A. Are you sealing the parts after dyeing? If not that is more than likely your problem, dyeing is not a replacement for sealing.

Brian Terry
Aerospace - Yeovil, Somerset, UK

A. Use an anodizing dye from a reputable supplier, and follow their application instructions. Textile dyes may contain high salt content or operate at a low pH damaging to the anodize. MIL-A-8625F merely states "The dyes and pigments used shall not be damaging to the anodic coatings."

What are the sealing solution, time and temperature?

Ken Vlach [deceased]
- Goleta, California

Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
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A. The most likely cause of failure has been mentioned. You lack proper sealing after dye coloring. Check the sealing process for temperature and time.

Kas Amadi
- Dayton, Ohio

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