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L'électrochimie et désalliage de Zn-Mg/Al-Zn phase pures et l'importance sur la corrosion de l'alliage Zn-Al-Mg

Abstract : The objective of this Ph.D. project is to investigate the electrochemistry of the pure phases, components of the Zn-Al-Mg coating alloys. The electrochemical data was used as an input for the prediction of corrosion behavior of the multi-phase alloy coatings. To this end, a database of elemental polarization curves was established as a function of pH by using atomic emission spectroelectrochemistry (AESEC). Dealloying of the MgZn2 intermetallic and α-phase of Al-Zn (Zn-68Al) were investigated at pH=10.1 represent the extremes of Mg and Al content in the Zn-Al-Mg alloy coating, respectively. In the cathodic polarization, the Zn(0) enriched layer was formed in both cases by selective dissolution of Mg and Al, respectively. However, the influence of this layer on cathodic dealloying differed: for MgZn2, Mg selective dissolution was restrained by the dealloyed layer, whereas for Zn-68Al, Al selective dissolution was not affected by this layer. It was observed that the onset of active Zn dissolution coincided with a reduction in the Al dissolution rate, suggesting an inhibitive effect of Zn dissolution on Al dissolution. It was observed that Al dissolution in alkaline media was limited by the dissolution rate of the Al(OH)3 film, evidenced by potential independent Al dissolution. The most stable corrosion products formed by electrochemical measurements, precipitated species in the solution during titration experiment and the thermodynamic simulation were reasonably coherent with each other. Most of the precipitated species formed in the solution corresponded reasonably well to those predicted by thermodynamic database. It was in a good agreement with the corrosion products of the alloy, characterized after the electrochemical measurements. Therefore, it can be concluded that the thermodynamic database can be used to predict and eventually model the real corrosion situation.
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Junsoo Han. L'électrochimie et désalliage de Zn-Mg/Al-Zn phase pures et l'importance sur la corrosion de l'alliage Zn-Al-Mg. Autre. Université Paris sciences et lettres, 2018. Français. ⟨NNT : 2018PSLEC014⟩. ⟨tel-02860750⟩

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