Elizabeth Berman

Alternatives to dichromate sealer in anodizing operations

Abstract Ogden Air Logistics Center (OO-ALC) 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. During sealing, the pores of the anodized (oxide) layer are hydrated, which fills the pores and provides improved corrosion resistance. However, this sealer contains hexavalent chromium, which is listed on the Environmental Protection Agencys list of industrial toxic chemicals that are targeted for voluntary reduction or elimination. The specification that outlines the sodium dichromate sealing process delineates three alternative processes that are approved for use: 1) boiling de-ionized water, 2) cobalt acetate, and 3) nickel acetate. While some research to support the use of these and other sealing processes has been gathered under past efforts, additional work must be conducted to fully integrate non-chromate sealers into OO-ALCs anodizing operations. To meet this need, the Air Force Research Laboratory tasked Concurrent Technologies Corporation to identify viable alternatives to the sodium dichromate sealer, conduct testing on these alternatives, and recommend the most promising sealer(s) for implementation based on the test results. This paper will describe the requirements for anodizing and sealing operations within OO-ALC, as well as the sealing technologies that are available and a path forward to demonstrate/validate the most promising alternatives for the specific needs and applications of OO-ALC.

Hard Chromium Replacement Candidates for Non-Line-of-Sight Landing Gear Applications

Introduction. Electroplated hard chromium (EHC) is a proven coating process, but many environmental, health, and safety (EHS) issues and regulations are associated with its use. As a result, the Department of Defense (DoD) has investigated and implemented thermal spray coatings to replace EHC in its maintenance facilities. High velocity oxygen-fuel (HVOF), a type of thermal spray process, deposition of tungsten carbide-17 percent (%) cobalt (WC-17Co) has largely replaced EHC in line-of-sight (LOS) applications; however, it has been incapable of repeatedly depositing uniform coating thicknesses on complex (i.e., non-LOS [NLOS]) geometries[1]. Therefore, the United States Air Force Research Laboratory – Advanced Power Technology Office (AFRL – APTO), in conjunction with Concurrent Technologies Corporation (CTC), sought both electroless and electrochemically deposited chromium(Cr-) free coatings that could treat NLOS parts. Most suitable candidates contained nickel (Ni), which has other health concerns, denoted in Table 1. It also is listed on the Environmental Protection Agency’s list of hazardous substances and is on the watch list as an emerging contaminant by the Office of the Deputy Under Secretary of Defense for Installations and Environment Chemical and Material Risk Management Directorate (CMRMD). As a result, Ni-based products are expected to become more heavily regulated and, thus, not suitable for midto long-term solutions. To address this problem, the team investigated non-Cr and nonNi technologies (i.e., largely cobaltbased coatings), with fewer health concerns and potentially reduced restrictions as compared to EHC (see Table 1).