Abstract :
[en] Nanoporous alumina obtained by sulfo-tartaric anodizing and coated/sealed with benzoxazine thermoset resins for aluminium corrosion protection
A. Renaud1, Y. Paint2, L. Bonnaud2, M. Poorteman1, P. Dubois2, M. Olivier1,*
1 Department of Materials Science, Materials Engineering Research Center (CRIM), University of Mons, Place du Parc 20, B-7000 Mons, Belgium
2 Laboratory of Polymeric and Composite Materials, Center of Innovation and Research in Materials and Polymers (CIRMAP), Materia Nova research Center & University of Mons, Place du Parc 20, B-7000 Mons
* +32(0)65/37.44.31, marjorie.olivier@umons.ac.be
Aluminium alloys are widely used in aircraft applications, especially series 2xxx (Cu) and 7xxx (Zn). Though offering improved mechanical properties compared to pure aluminium, such kind of alloys are strongly sensitive to corrosion. In order to protect aluminium pieces from aggressive environments, different kinds of protective layers can be elaborated. Anodizing, consisting in the electrolytic growth of an oxide layer at the aluminium surface, has mainly been developed for this purpose. By using acidic electrolytes, the competition between the growth of the oxide and its dissolution leads to a nanoporous structure, with a thickness of a few microns. However, such a layer does not provide a sufficient corrosion protection. To improve the corrosion resistance of the anodized layer, organic coatings are applied on top of it, with enhanced adherence thanks to anchoring of the coating provided by the nanoporous morphology. Another approach is the sealing of the nanostructure. Several sealing processes have been developed in order to optimize the corrosion resistance of anodized substrates, such as hydrothermal sealing and impregnation with organic acids or rare earth salts. However, the nanoporosity is lost, and no more anchoring is offered to further layers.
In this work, several para-PhenyleneDiAmine based benzoxazine thermosets have been applied by spin coating on anodized (using sulfo-tartaric electrolyte) AA2024-T3 substrates. Subsequently, a thermal curing cycle has been applied in order to cross-link the benzoxazine resins. Depending on the rheological properties of the benzoxazines at high temperature, the resins can either form a consistent coating on top of the anodic layer, or impregnate and seal the oxide nanoporous structure.
These different ways of behaviour have been investigated using Scanning Electron Microscopy (SEM) combined with Energy-Dispersive X-ray spectroscopy (EDX), and Glow Discharge Optical Emission Spectroscopy (GDOES). Finally, the impact on the electrochemical properties of the obtained systems has been evaluated using Electrochemical Impedance Spectroscopy (EIS).
