Metal finishing Q&As since 1989

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Mil-spec anodization sometimes porous sometimes not

2003

If someone specifies MIL-A-8625 / MIL-PRF-8625 [on DLA] anodizing, type I and Class 2, is that enough to control the porosity of the anodized coating? I am having issues with different porosities of supposedly the "same anodization" process.

Thank you,

Ivan Araktingi
Optics - Murrieta , California, USA

You have two items to consider. Coating thickness and pore size. Pore size is mostly controlled by tank temperature/part temperature. The warmer the solution, the larger the pore size. Coating thickness is frequently expressed as coating weight which is actually a combination of porosity and thickness. The mil spec absolute minimum is just that, a minimum and not an optimum. The warmer tank also promotes a faster attack on the oxide coating which will give a thinner coating for a given time and voltage. If you specify a not to exceed 70 °F temperature and a coating weight closer to the top of the range, I think that most of your problems will go away. Require certifications.

James Watts
- Navarre, Florida
2003