Testing and Implementation of Non-Chromium Sealer for U.S. Air Force Anodizing Operations

Ogden Air Logistics Center (OO-ALC), Utah, is the primary facility within the United States Air Force for maintaining and overhauling aircraft landing gear. Aluminum landing gear components are anodized at OO-ALC to provide enhanced corrosion resistance, paint adhesion, and wear resistance; a sodium dichromate sealing operation usually completes the anodizing process. However, this sealer contains hexavalent chromium, which is listed on the Environmental Protection Agency's list of industrial toxic chemicals that are targeted for voluntary reduction or elimination. While the specification that outlines the sodium dichromate sealing process delineates other sealing processes (specifically, boiling deionized water and solutions containing cobalt or nickel acetate) that are approved for use, these alternatives have not been successful for all OO-ALC applications. Because the specification also allows the consideration of other, less traditional non-chromium sealers, the Air Force Research Laboratory Energy and Environment Team tasked Concurrent Technologies Corporation to identify viable alternatives to the sodium dichromate sealer, conduct testing on these alternatives, and initiate implementation of the most-promising sealer(s) based on the test results. This presentation will describe test results for several alternative non-chromium sealing technologies. Based on these results, a commercial-off-the shelf permanganate-based sealer was recommended because it can be used on both 2024 and 7075 aluminum alloys for wheels and struts processed at OO-ALC. This sealer was subsequently approved for use by OO-ALC on these materials after a thorough engineering review. OO-ALC's plans to use the new sealer will also be described.