Compréhension des mécanismes de colmatage des couches anodisées sur alliages d’aluminium aéronautiques et développement de nouvelles formulations de colmatage

Abstract : Aluminium alloys are very used in the aircraft industry as structural materials because of their low density and their good mechanical properties. They have a polyphase microstructure that is causing electrochemical discontinuities and increasing sensitivity to corrosion. A system of protective coatings containing chromate Cr(+VI) is traditionally formed at the surface of these alloys. However, the REACH environmental guidelines impose Cr(+VI) surface treatments replacement because of chromate carcinogenicity. The aim of the thesis work has been the development of a new surface treatment constituted of a sulfuric acid anodizing (SAA) and a sulfate chromium and fluorozirconate salts sealing (Cr3+/ ZrF62-). The study of the SAA electrochemical process linked the alloys microstructure and the anodic layer porous morphology developed at their surface. The Cr3+ / ZrF62- sealing treatment is realized by a simple immersion of the anodized alloy in the solution. It is demonstrated that the sealing is caused by a local alkalinization of the anodized coating surface that leads to the precipitation of the Cr3+ and ZrF62- salts. These ones are forming a sealing film of about 300 nm thick, very covering of the nanometric pores. The anodic layers sealing greatly improves the corrosion resistance of the anodized alloys by forming an additional barrier against corrosive agents and by healing the corrosion initiation. The developed treatment allows both to achieve Cr(+VI) treatments performance over a wide range of alloys and to satisfy the environmental requirements.
Document type :
Theses
File URL :
http://docnum.univ-lorraine.fr/prive/DDOC_T_2015_0318_CHAHBOUN.pdf
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https://hal.univ-lorraine.fr/tel-01754616
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Submitted on : Friday, March 30, 2018 - 9:55:12 AM
Last modification on : Tuesday, December 11, 2018 - 10:33:27 AM

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  • HAL Id : tel-01754616, version 1

Citation

Najat Chahboun. Compréhension des mécanismes de colmatage des couches anodisées sur alliages d’aluminium aéronautiques et développement de nouvelles formulations de colmatage. Autre. Université de Lorraine, 2015. Français. ⟨NNT : 2015LORR0318⟩. ⟨tel-01754616⟩

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