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Anodized aluminum has microscopic black dots on its surface

August 30, 2021

Q. Hi, I am a student studying aluminum anodizing.

I've got a question about my anodizing.
My anodizing condition is 15V 25°C 25-45 min anodizing on AL1050 (sulfuric acid 2M).

I don't know the reason but when I look under a microscope(450x) it seems uneven (not a clean white or grey). It has grey background and black dots on it.
(The dots are invisible to the naked eye. It can only be observed through a microscope with a magnification of 3000 or less.)

61317-1

This has always been there and I don't think it's a problem, but I'd like to know what these black dots are and how to get rid of them.

yoonhee kim
- si-heung Gyeonggi-do

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