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Passing Salt Spray, DPS 11.05-2 Ty IIB Thin Film Anodizing

We are presently studying how best to accomplish thin film anodizing to a film thickness of 0.0001 to 0.0002 inch, in conjunction with 8 - 12 min. in dichromate seal. We have had excellent salt spray results for some years now, using 7050 T7451 bare plate, for salt spray panels, with anodize Type II Class 1 anodizing (with dichromate seal), and our success, to my thinking, is largely due to keeping alumina content of the tank below 7 g/liter. We hope to now also use this tank for thin film anodizing. We have the immersion time down pretty well, now, to achieve proper coating thickness. The coating weight is in the 900's. The 336 hour salt spray results appear to be more marginal, or difficult to consistently achieve, with thin film anodizing. Our dichromate seal has 30 ppm chloride, and the spec allows up to 200 ppm, and we have not been motivated to do a dump, since our Type II Class 1 results have been so good. But now I am looking for any parameters I can improve. Is alumina content even lower than 7 g/L going to help? Does anyone have experience with this?

David H. Duncan
- Ponderay, Idaho, USA
2006