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On the intergranular corrosion of 7xxx aluminum alloys

Huang, Tsai-Shang
http://rave.ohiolink.edu/etdc/view?acc_num=osu1133365169

Abstract Details

2005, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
High strength 7xxx aluminum alloys used widely in aircraft structure are very susceptible to intergranular corrosion (IGC). From a practical point of view, it is important to understand IGC in these alloys. Measuring the kinetics of IGC is not only a way to evaluate corrosion susceptibility, but also very useful for a predictive model for corrosion. Several AA7075 and AA7178 plates were used in this work. The foil penetration technique was used to measure the localized corrosion kinetics of the alloys in a NaCl solution and a new approach was developed to quantify the growth rates of sharp IGC fissures in a humid environment. Electrochemical properties of the alloys were studied by measuring the polarization curves. Electron microscopy and analytical techniques were used to observe the corrosion morphology and to understand the IGC mechanism. Localized corrosion kinetics were measured on several alloys with different grain aspect ratio to understand the influence of grain structure. Anisotropic corrosion kinetics were found on alloys with grain aspect ratio greater than 1. Metallographic cross-sections confirmed that the localized corrosion kinetics strongly depend on the IGC growth path, which was affected by the microstructural anisotropy of the material. It was also found that IGC morphology of AA7xxx was selective grain attack (SGA) in a NaCl solution and was sharp fissure in a humid environment. A statistical model for corrosion in AA7xxx was developed based on the grain structure of the material and the foil penetration data. Scenarios for SGA mechanism were proposed according to the statistical method and simulations. The sharp IGC fissure growth kinetics were found to be independent of the humidity from 96% to 58% RH due to little connection of the local sites to the external environment. The sharp IGC fissures were found to be filled with corrosion products that seem to drive fissure growth by an SCC mechanism.
Gerald Frankel (Advisor)
Engineering, Materials Science
corrosion; kinetics; aluminum; electrochemical; temper; humidity

Recommended Citations

Citations

  • Huang, T.-S. (2005). On the intergranular corrosion of 7xxx aluminum alloys [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1133365169

    APA Style (7th edition)

  • Huang, Tsai-Shang. On the intergranular corrosion of 7xxx aluminum alloys. 2005. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1133365169.

    MLA Style (8th edition)

  • Huang, Tsai-Shang. "On the intergranular corrosion of 7xxx aluminum alloys." Doctoral dissertation, Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1133365169

    Chicago Manual of Style (17th edition)

osu1133365169
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© 2005, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.