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Oxydation thermique, comportement à la corrosion induite par intermétallique et traitement de surface de l'alliage Al-Cu-Li

Abstract : Al-Cu-Li alloys are considered as advanced materials for the aircraft manufacturing due to their high mechanical properties and low weight. However, Al-Cu-Li alloys, similarly to other Al alloys, are susceptible to corrosion due to the presence of intermetallic particles (IMP) such as Al-Cu-Fe-Mn particles, T1 phase (Al2CuLi). These IMPs can lead to different surface modifications of the alloy during the alloy treatment and/or exposure to various working conditions. The objective of this PhD thesis was to understand the surface modifications induced by thermal treatments, the corrosion behaviour of bare Al-Cu-Li alloy (AA2050) and the corrosion protection efficiency of the alloy after chemical treatments (degreasing, pickling and TCP deposition).This PhD thesis is composed of three parts. In the first part, the surface composition of the as received AA2050-T8 and the alloy surface modifications induced by thermal oxidation at 190°C, using in situ X-ray photoelectron spectroscopy (XPS), were performed. The formation of a mixed Al-Li oxide layer was demonstrated after sample exposure to oxygen at low pressure. Post mortem time-of-flight secondary ion mass spectrometry (ToF-SIMS) 3D chemical mapping and ion depth profile analyses showed Mg segregation at the grain boundaries and Ag enrichment at the oxide/metal interface. In the second part, the pitting corrosion of the AA2050-T8 alloy exposed to the aggressive chloride-based electrolytes was studied in details by ToF-SIMS 2D and 3D chemical mapping and scanning electron microscopy (SEM). The formation of an oxide-hydroxide layer with different composition and higher thickness was evidenced over the IMPs than over the alloy matrix. Moreover, the behaviour of Li in the oxide was also discussed. In the third part, the surface chemical treatments including degreasing, pickling and conversion coating (TCP) and related surface chemical modifications were studied using XPS, ToF-SIMS and SEM. An improved corrosion behaviour on TCP coated alloy was revealed. A strong influence of copper enrichment on the quality, composition and corrosion performance of the TCP was demonstrated.
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Meicheng Li. Oxydation thermique, comportement à la corrosion induite par intermétallique et traitement de surface de l'alliage Al-Cu-Li. Chimie analytique. Université Paris sciences et lettres, 2020. Français. ⟨NNT : 2020UPSLC024⟩. ⟨tel-03551222⟩

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