Metal Finishing Guide Book

2012-2013

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based on a review of past work [Refs. 20���23] as well as vendor surveys. The Non-Chrome Post Treatment (NCP) process was found to be promising as a non-chromium seal for anodizing. NCP is a proprietary product of the United States Naval Air Systems Command (NAVAIR). Testing was conducted by NAVAIR under past work [Ref. 20], and the results demonstrated exceptional performance in corrosion-resistance testing and adhesion testing. While these results demonstrate that the NCP sealer might be viable for the needs of OO-ALC, the process was unavailable for demonstration at the time of testing; therefore, it could not be considered. A COTS chromium- and nickel-free anodize sealer based on permanganate was identified that reportedly provides similar characteristics to those of the dichromate sealer. This solution was evaluated by the AFRL and CTC under past work [Ref. 20] and showed exceptional performance in corrosion resistance. This sealer also passed the dry tape adhesion test, but failed the wet tape adhesion test. Sealing anodized coatings by using a liquid colloidal dispersion that solidifies (e.g., sol-gel) has been demonstrated. Specimens were anodized and then immersed in a working solution at 270��C for 15 minutes; the resulting specimens reportedly demonstrated comparable corrosion resistance to dichromate sealed specimens [Ref. 22]. However, this process is more expensive and decreases the abrasion resistance and hardness of the overall coating system. The incorporation of additional materials within the sealer, such as polytetrafluoroetheylene (PTFE) has also been explored [Ref. 23]. These technologies are typically used for low friction and/or ���non-stick��� applications; sufficient data that these sealers could meet the stringent needs of military specifications could not be obtained, and so they were not considered. DEMONSTRATION/VALIDATION TESTING Based on the findings of this activity, three candidates were selected for laboratory testing: the COTS permanganate solution, the COTS low-nickel sealing solution, and a 50 ppm sodium dichromate solution that will serve as a benchmark. As mentioned previously, the COTS low-nickel seal will be considered with and without a warm water rinse after the sealing process. The currently used sodium dichromate sealer, the boiling DI water seal, and unsealed options will be evaluated as baselines for all testing conducted for this effort. The candidate test matrix is summarized in Table 3. Efforts to test aluminum alloy test panels that have been anodized and sealed with the above processes are in progress. (2 The ideal processing temperature of the NCP process is 100��F and the optimum processing time is 10 minutes. 3 The solution was made up at 10% by volume. Temperature was maintained at 170-180��F, pH was maintained between 5.0 and 8.0, and seal time was 12 to 15 minutes.) SUMMARY The overall objective of this effort was to identify alternatives to the sodium dichromate sealer used in anodizing operations. To this end, the requirements for the sodium dichromate sealer currently in use at OO-ALC were determined. Furthermore, extensive literature and vendor searches identified promising can380

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