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Hard anodize is washing off

We have 6061-T6 and 7075-T6 parts that are anodized to MIL-A-8625 / MIL-PRF-8625 [on DLA]-f, type iii, class 2 black. When we put them through a bath of brulin 815gd, the anodize is coming off, flaking, bubbling, etc. It doesn't happen on all the parts, but most of them. We have already had one set chem etched to remove the previous anodize and had them redone. They changed all the material in the anodize tank and started again. Still getting same results. Is the ultrasonic cleaning with brulin 815gd messing up the anodize?

Wade May
engineer - Hampton, Virginia
February 22, 2008

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While the technical data sheet for this product indicates that it's safe for aluminum, your results would make me question that statement. Seeing that the pH listed on the MSDS is 11.7 - 12.5, that level of alkalinity is extreme enough to give me concern with aluminum, much less anodized aluminum. Furthermore, the data sheet makes reference to the pH falling with continued use to the point where if < 9, there can be corrosion. Certainly the etching you've experienced could be construed as "corrosion." Lastly, do you see black dye coming out of parts rather quickly upon initial immersion? If that is the case, your parts may not be being properly sealed. The mil spec governing Type III hardcoat anodizing contains a requirement that "unless otherwise specified, Type III coatings shall be unsealed." As this leads to fading dyed parts and reduced protection, we've always interpreted this requirement as requiring sealing if the parts specify dyed. ASTM B136 is a simple test for sealing integrity.

If you'd like me to evaluate some actual hardware, please feel free.

Milt Stevenson, Jr.
Syracuse, New York
February 25, 2008