Surface composition and corrosion behavior of an Al-Cu alloy

Abstract : In this work, Al-Cu model alloy samples were heated in ultra high vacuum (UHV), and it was found that the Al oxide grew and Cu percentage increased as a function of exposure to the O2 owing to the preferential oxidation of Al. Then samples were annealed at 540 °C in high vacuum and aged at 300 °C in air, and corroded in short time in the neutral electrolyte and the alkaline electrolyte containing Cl- ion using the three-electrode system, respectively. After immersion in the neutral electrolyte, corrosion morphologies (trenching on the polished sample vs. hollow pits on the aged sample) are distinguished due to the different distributions of Cu-rich intermetallics in the polished sample (distributed homogeneously) and the aged sample (mostly beneath the oxide layer). However, in alkaline electrolyte, corrosion went at two stages owing to the dissolution of aluminium and aluminium oxide in an alkaline solution: firstly, Al oxide and the Al matrix were dissolved generally, resulting in Cu-rich intermetallics being left isolatedly on the surface; secondly, general corrosion went on accompanied with the preferential dissolution of substrate surrounding Cu-rich intermetallics resulting in trenching around particles. Formation of mixed Al-Cu oxides/hydroxides layer rich in Cu2O and CuO deposits were found on the corroded surface. Furthermore, Al-Cu samples covered with Al2O3 coatings deposited by ALD process on the surface were corroded under similar conditions. As expected, a significant improvement of corrosion resistance of the coated alloy samples was observed, but the ALD layer in alkaline electrolyte is not as stable as in neutral electrolytes, and undergoes dissolution.
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Jun Tao. Surface composition and corrosion behavior of an Al-Cu alloy. Chemical Physics [physics.chem-ph]. Université Pierre et Marie Curie - Paris VI, 2016. English. ⟨NNT : 2016PA066159⟩. ⟨tel-01412882⟩

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