Summary for anodizing blisters Discussion
Blisters found on sulfuric acid anodizing parts are reported on large 2024 and 6061 aluminum parts anodized to MIL-A-8625 Type II, with the defects appearing after sealing as un-anodized spots deeper than 0.002 in. Han Lin Yap says the blisters tend to show up about 45 degrees from the jigging points, sometimes on the opposite side, and only on horizontal or top surfaces, never on vertical or bottom surfaces. The poster says the material seems sound and that changing chemicals did not eliminate the issue. The thread excerpt provided contains only the question, so no named answerer or diagnosis is available here. The key problem is a recurring surface defect that cannot be covered by anodizing and appears linked to part orientation, fixturing, or process conditions during anodizing/sealing.
August 16, 2013
Q. We are facing some problem in sulfuric acid anodizing 2024 and 6061 AL materials using MIL-A-8625 Type II recently.
Our part is 1.7 m in diameter with 4 jigging points. We revealed some blisters on the surface after sealing process as per attached pictures:
Those un-anodized blisters seem to be more than 0.002″ deep and can’t cover by anodizing. They usually happen 45 deg away from the jigging points but not necessarily the same area at all times, and it appeared on opposite side as well. In addition, those small blisters only appeared on the horizontal and top surfaces of the part but it never appeared on the vertical or bottom surfaces ever.
We need valuable advise on this issue since we found no problem with the materials and also we have tried changing the new chemical but it still appeared. Thank you.
Han Lin Yap
Operation – Baya Lepas, Penang, Malaysia