"This thesis investigates alternative surface preparation and deposition methods for cerium-based conversion coatings (CeCC) on high strength aluminum alloys. Cerium-based conversion coatings are being investigated as a more environmentally friendly replacement for chromium-based conversion coatings. Currently, the alloys are immersed in strong alkaline and acidic solutions to prepare the aluminum surfaces for conversion coating, in which immersion may not be suitable for all situations. Alternatives to this method were investigated, including wipe application of solution, ultrasonic processing in deionized water, and abrasive blasting with alumina. AI 7075-T6 test panels were prepared using each of these methods and compared to a conventional alkaline chemical immersion process. Coatings were evaluated using Auger depth profiling, electrochemical response, and corrosion performance. A CeCC was produced by spray deposition. The chemical wipe method produced the surface most similar to the chemical immersion method. Both of these methods had an uncoated total impedance value near 4 kΩ-cm². However, the immersion panel coating was approximately 125 nm thick after one spray while the wipe prepared panel coating was approximately 75 nm thick after the spray. Both coatings provided similar protection in corrosion testing.
An alternative deposition method using a brush was investigated on AI 2024-T3. Prior to deposition, the panels were prepared using an acidic chemical immersion method. The CeCC was deposited using the brush-based method or the spray-based method. These methods were compared using coating thickness, morphology, and crystalline phases in the coating. Brush-based coatings were thinner than spray-based, but they had a similar surface morphology. Spray deposited coatings were about 400 nm thick after three deposition cycles, while brush deposited coatings were approximately 275 nm thick after five cycles. Cerium phosphate, a phase previously shown to improve corrosion resistance, was detected in spray coatings after treatment in a 85°C phosphate solution but not in brush-based coatings. Brush-based deposition provided some corrosion protection but not as much as a spray applied coating, likely due to the absence of the formation of cerium phosphate"--Abstract, page iv.
Schlesinger, Mark E.
Materials Science and Engineering
M.S. in Metallurgical Engineering
Missouri University of Science and Technology
Journal article titles appearing in thesis/dissertation
- Alternative surface preparation methods for cerium conversion coating of Al 7075-T6 substrates
- Deposition of cerium-based conversion coatings using a spontaneous brush application process
ix, 60 pages
© 2010 William J. Gammill, All rights reserved.
Thesis - Restricted Access
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Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.http://laurel.lso.missouri.edu/record=b8069056~S5
Gammill, William J., "Evaluation of alternative methods for surface preparation and deposition of cerium-based conversion coatings on aluminum alloys" (2010). Masters Theses. 114.
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