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Formulation d'un nouveau traitement de conversion chimique sans chrome pour la protection anticorrosion d'alliages d'aluminium aéronautiques

Abstract : In the current aeronautical context, corrosion is a major problem and this is why surface treatments are necessary. Conversion treatments are widely used but currently use hexavalent or trivalent chromium. However, an environmental regulation (REACh), which will come into effect in 2024, aims to prohibit the use of hexavalent chromium substances that are toxic. In order to develop a sustainable solution, industrial actors are working to completely avoid chromium for this kind of application. This thesis work is part of this framework and focuses on the formulation of new solutions for 2024-T3 aluminum alloy conversion treatments as well as the associated parametric study. Several corrosion inhibitors known to CIRIMAT or listed in the literature have been studied such as cerium, tungstates and molybdates. The first study consisted in discriminating these inhibitors by comparing their electrochemical properties, mainly by chronopotentiometry and electrochemical impedance spectroscopy, and their microstructure, the reference layer remaining that based on trivalent chromium. Two conversion layers (based on Ce3+ and WO4 2-) were selected and were the subject of extensive microscopic characterization as well as exhaustive analysis by electrochemical impedance spectroscopy via the use of equivalent electrical circuits. The results demonstrated that there is a good correlation between the conversion coating structure (interfacial layer, inner layer and outer layer) and its electrochemical properties. Thus, the interfacial layer gives the system the best resistance to corrosion with a very pronounced barrier effect. The inner layer protects this interfacial layer from the electrolyte by forming a passivating layer. Finally, the outer layer acts as a reservoir of corrosion inhibitor that can heal the system during a local defect. Finally, for reasons of implementation on an industrial scale, the tungstate-based conversion layer has been privileged. In order to optimize its anticorrosion performance, the influence of parameters such as inhibitor concentration, conversion time, pH and storage time was evaluated. The optimized solution was then completed with post-treatment and demonstrated good anticorrosion properties after electrochemical analysis. These results led to a second step, which is the transfer to pilot scale at the industrial company, Mécaprotec Industries, the coordinator of the NEPAL FUI project in which several manufacturers are partners.
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Submitted on : Friday, February 28, 2020 - 4:54:09 PM
Last modification on : Saturday, February 29, 2020 - 1:35:43 AM
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  • HAL Id : tel-02494420, version 1



Quentin Boyer. Formulation d'un nouveau traitement de conversion chimique sans chrome pour la protection anticorrosion d'alliages d'aluminium aéronautiques. Matériaux. Université Paul Sabatier - Toulouse III, 2018. Français. ⟨NNT : 2018TOU30364⟩. ⟨tel-02494420⟩



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