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Phosphoric acid anodize testing
We are just starting phosphoric acid anodizing, we're not sure we have a good coating. The light test described in the ASTM spec is inconclusive. Are there some other definitive tests to determine the quality of the coating?
Steve Peters - Stanton, California, USA
Wedge Crack extension tests will provide the best indication of whether the coating is fit for purpose but the coating is normally fairly easy to see. Bright light at right angles and look along the edge of the part. Those pretty interference colours like oil or petrol on water. A photographic filter aids but is rarely required. Colour varies with alloy type. 2024 usually gives a nice colour.
Ciaron Murphy - Great Britain
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