Formation of Subsurface Crevices in Aluminum Alloy 2024-T3 During Deposition of Cerium-based Conversion Coatings
The processing variables that contributed to the formation of subsurface crevices under cerium-based conversion coatings on AA 2024-T3 were investigated. Focused ion beam milling revealed the presence of subsurface crevices underneath a small fraction ( 10%) of coated areas, typically in areas with large cracks through the coatings. A solution of sodium chloride and H2O2 etched AA 2024-T3 and produced features similar to subsurface crevices, which confirmed that crevices formed during deposition due to the composition of the coating solution. Using sodium nitrate in place of sodium chloride resulted in no etching of the substrate. Thus, coatings free of subsurface crevices could be produced by using cerium nitrate instead of cerium chloride in the coating solution. Electrodeposited coatings, even those deposited from solutions containing chloride ions and H2O2, were also free of subsurface crevices. As a result, subsurface crevices are not inherent to cerium-based conversion coatings, but rather were formed due to certain process parameters, specifically the presence of chloride ions and hydrogen peroxide in the coating solution.
W. R. Pinc et al., "Formation of Subsurface Crevices in Aluminum Alloy 2024-T3 During Deposition of Cerium-based Conversion Coatings," Surface and Coatings Technology, Elsevier, Sep 2010.
The definitive version is available at http://dx.doi.org/10.1016/j.surfcoat.2010.05.039
Materials Science and Engineering
Strategic Environmental Research and Development Program (U.S.)
Keywords and Phrases
2024-T3; Aluminum Alloy; Cerium Conversion Coating; Corrosion; Subsurface Crevices
Article - Journal
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