Doctoral Dissertations

Abstract

"The aim of the work presented in this dissertation is to investigate the corrosion protection mechanism of cerium-based conversion coatings ( CeCCs) used in the corrosion protection of high strength aluminum alloys. The corrosion resistance of CeCCs involves two general mechanisms; barrier and active. The barrier protection mechanism was influenced by processing parameters, specifically surface preparation, post-treatment, and the use of gelatin. Post-treatment and the addition of gelatin to the coating solution resulted in fewer cracks and transformation of the coating to CeP0₄, which increased the corrosion resistance by improving the barrier aspect of CeCCs. CeCCs were found to best act as barriers when crack size was limited and CeP0₄ was present in the coating.

CeCCs were found to protect areas of the substrate that were exposed in the coating, indicating that the coatings were more than simple barriers. CeCCs contained large cracks, underneath which subsurface crevices were connected to the surface by the cracks. Despite the observation that no cerium was present in crevices, coatings with crevices exhibited significant corrosion protection. The impedance of post-treated coatings with crevices increased during salt spray exposure. The increase in impedance was associated with the formation of protective oxides / hydroxides; however, crevice-free coatings also exhibited active protection leading to the conclusion that the formation of interfacial layers between the CeCC and the substrate also contributed to the active protection. Based on the overall results of the study, the optimal corrosion protection of CeCCs occurred when processing conditions produced coatings with morphologies and compositions that facilitated both the barrier and active protection mechanisms"--Abstract, page iv.

Advisor(s)

OKeefe, Matt
Fahrenholtz, William

Committee Member(s)

Miller, F. Scott, 1956-
Stoffer, James O.
Schlesinger, Mark E.

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Materials Science and Engineering

Sponsor(s)

Strategic Environmental Research and Development Program (U.S.)

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2010

Journal article titles appearing in thesis/dissertation

  • Effects of acid and alkaline based surface preparations on spray deposited cerium-based conversion coatings on Al 2024-T3
  • Effect of gelatin additions on the corrosion resistance of cerium-based conversion coatings spray deposited on Al 2024-T3
  • Formation of subsurface crevices in aluminum alloy 2024-T3 during deposition of cerium-based conversion coatings
  • Electrochemical and structural changes in cerium-based conversion coatings during exposure to salt spray
  • Corrosion protection of cerium-based conversion coatings with subsurface crevices

Pagination

xiii, 195 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2010 William Ross Pinc, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Subject Headings

Aluminum alloysCeriumCorrosion resistant alloys -- TestingProtective coatings -- Corrosion

Thesis Number

T 9655

Print OCLC #

749903727

Electronic OCLC #

908949575

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