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Abstract :
[en] Aluminum alloys, such as AA 2524, are widely used in the aerospace industry due to their lightweight, high specific strength and durability. However, these alloys are particularly sensitive to localized corrosion in chloride environments and need to be protected by coating system.
The usual protective system consists of an anodic layer formed by anodizing process and serving as anchoring layer for an organic coating.. Due to its high protective efficiency against corrosion, chromium based anodizing has been widely employed. Nevertheless, as the chromate compounds are toxic for health and the environment, these baths will be prohibited in aerospace industry in a near future. Tartaric-sulfuric acid (TSA) anodizing is a promising alternative which is already used at industrial level with appropriate paint adhesion. However, the corrosion performance of this system needs to be improved in order to avoid the water boiling sealing of the anodizing layer which reduces strongly the compatibility with organic coatings.
This study aims at proposing a sol-gel treatment after anodizing in order to improve the corrosion resistance while maintaining the compatibility with organic coatings. In this study, different anodizing voltages were applied in order to modify the morphology of the anodic layer (thickness, pore size and size distribution, tortuosity ...) formed onAA2524 specimens...
After the anodizing step, the specimens were either sealed with boiling water or coated with a hybrid organic-inorganic sol-gel. The sol-gel coating was prepared using a solution with high water content (58 %v/v) and obtained by the hydrolysis and condensation of tetraethoxysilane (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS). The morphology of the top surface and cross section was characterized before and after sol-gel deposition by SEM-FEG analyses.
The corrosion behavior was evaluated in 0.1 M NaCl by EIS measurements versus immersion time. The EIS results were fitted and interpreted using electrical equivalent circuits and considering SEM-FEG information.
