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Effect of Aluminum Content and Carbon Dioxide on the Corrosion Behavior and Surface Film Formation on Magnesium-Aluminum Alloys: A Combined Experimental and Modeling Approach

Cantonwine, Sara
http://rave.ohiolink.edu/etdc/view?acc_num=osu161912159654409

Abstract Details

2021, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
Alloying additions are employed in magnesium (Mg) to increase its corrosion performance, formability, and strength. Widely used commercial alloys such as the AZ series use Aluminum (Al) and Zinc (Zn) as the main alloying elements. The alloys used in this research contained 3, 6, or 9 wt. % Al with around 1 wt. % Zn in each alloy. This alloy system has been characterized as showing second phases forming at grain boundaries and interdendritic regions. Heterogeneities in the microstructure can vary the electrochemical potentials of the material, making them instrumental in understanding the corrosion behavior of this alloy system. From microstructural investigation, an increase in Al content increased the volume fraction and segregation of secondary phase, β. This change in microstructure showed a clear difference in corrosion morphology among alloys. Mg and its alloys form Mg oxide films in ambient conditions and Mg hydroxide in aqueous conditions. Studies have shown an inhibiting effect when Mg is in the presence of atmospheric carbon dioxide (CO2). An increase in Al content has shown to have a positive effect on corrosion performance of Mg alloys. In laboratory conditions, most tests are done in bulk solution which can limit the access of CO2 at the surface of the alloy. A simple immersion experiment was conducted to demonstrate the effect that experimental set up can have on corrosion behavior. The amount of CO2 available at the surface of the alloy is changed by varying solution height. It was shown that the interfacial pH attained a high value due to the overwhelming effect of hydrogen evolution, while the bulk solution remained buffered by the CO2. The effect of CO2 on Mg alloys was studied by testing various AZ series alloys in the presence and absence of CO2. This study aimed to identify a possible interaction between Al content and CO2 that affects the corrosion rate. Electrochemical testing was done using electrochemical impedance spectroscopy (EIS) to understand the subtleties in the relationships of Al and CO2 on corrosion performance. EIS showed that both Al and CO2 decrease the corrosion rate of the alloy, but EIS did not provide much information on the possibility of a synergistic effect between Al and CO2. To comment on this interaction, characterization of the surface film was done using in-situ Raman infrared spectroscopy in conjunction with X-ray photoelectron spectroscopy (XPS). Surface characterization techniques have revealed the presence of carbonate (CO32−) and Al on the surface. Potentiodynamic polarization and open circuit tests were used to determine the relationship between chloride concentration in solution and the stability of a protective film. Testing different chloride concentrations showed that the Al and CO2 contributed more to localized corrosion growth rather than the breakdown of passivity. Finally, density functional theory (DFT) modeling using VASP® was employed to simulate various molecules, specifically OH− and CO32−, attaching to the Mg surface. Comparison of these free energy calculations showed that carbonate species preferentially adsorbed over hydroxide. Other useful information, such as vibrational frequencies, can be attained and compared with experimental data. Overall, both Al and CO2 help reduce the corrosion of Mg alloys. A discussion of the possible interaction between Al and CO2 with respect to film formation and breakdown of passivity will be offered
Rudolph Buchheit (Advisor)
Gerald Frankel (Advisor)
Christopher Taylor (Committee Member)
301 p.
Materials Science
magnesium, magnesium alloys, magnesium-aluminum alloys, corrosion, lightweight alloys, XPS, Raman, EIS, polarization, VASP

Recommended Citations

Citations

  • Cantonwine, S. (2021). Effect of Aluminum Content and Carbon Dioxide on the Corrosion Behavior and Surface Film Formation on Magnesium-Aluminum Alloys: A Combined Experimental and Modeling Approach [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu161912159654409

    APA Style (7th edition)

  • Cantonwine, Sara. Effect of Aluminum Content and Carbon Dioxide on the Corrosion Behavior and Surface Film Formation on Magnesium-Aluminum Alloys: A Combined Experimental and Modeling Approach. 2021. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu161912159654409.

    MLA Style (8th edition)

  • Cantonwine, Sara. "Effect of Aluminum Content and Carbon Dioxide on the Corrosion Behavior and Surface Film Formation on Magnesium-Aluminum Alloys: A Combined Experimental and Modeling Approach." Doctoral dissertation, Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu161912159654409

    Chicago Manual of Style (17th edition)

osu161912159654409
177
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