Black Power on Die Casting After Anodizing
After anodizing there is a loose, black powder that can be removed just by touch. Can you tell me why this happens and recommend a method to prevent it?
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Q. I am clear anodizing an aluminium die casting that is alloy A380. After anodizing there is a loose, black powder that can be removed just by touch. Can you tell me why this happens and recommend a method to prevent it? T.W.
- Alkaline or acid clean
- Double Rinse
- Deox/desmut (nitric acid or ferrous sulfate). Lots of good acid deoxidizers can be used. Nitric acid will work, but other stronger deoxidizers are recommended. Nitric acid is really an oxidizer not a deoxidizer.
- Double Rinse
- Anodize at approximately 15–22 amps/ft2 for 30 min. This should result in a coating thickness of about 6–10 um. Anodize by current density, not by voltage and hold current constant for the entire time.
- Double rinse
- Dilute nitric soak (1 min in 3–5% nitric by vol, 25°C)
- Double rinse
- DI rinse
- Hot DI rinse
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