Abstract :
[en] Aluminium alloys used in aircraft applications offer improved mechanical properties compared to pure aluminium but are strongly sensitive to corrosion. In this sector, the most classical corrosion protection systems consist in a conversion layer or an anodic layer coated with an epoxy primer filled with corrosion inhibition pigments. These different layers contain hexavalent chromate compounds which are recognized as having major health and environmental drawbacks. Alternatives systems with a lower toxicity and comparable performance are therefore required.
Alternative corrosion protection systems combining different layers have been investigated: inhibitor modified sol-gel layer as a conversion treatment and an epoxy coating as a top coat, porous oxide layers obtained from sulfo-tartaric (TSA) with sealing by sol-gel in order to replace the boiling water sealing and finally the replacement of epoxy resins by benzoxazine ones. Benzoxazine resins display high thermal, mechanical and chemical resistance, which can overtake classical epoxy resins. Two laboratory-synthesized benzoxazines have been studied: Phenol-para-Phenylene DiAmine (P-pPDA) [1] and 4-Ethyl (Phenol-para-PhenyleDiAmine (4EP-pPDA).
It will be shown that Electrochemical Impedance Spectroscopy (EIS) is a very useful tool to investigate the corrosion protection mechanisms of the different proposed alternative systems.
The following examples will be presented:
- Selection of the more efficient inhibitive species and study of the reversibility of formed inhibitive film [2]
- Release of an inhibitor from nanocontainers during immersion in an aggressive solution
- Effect of the inhibitor or nanocontainer addition on the sol-gel corrosion performance [3]
- Influence of electrical parameters and bath composition during anodizing process on the sealing of an oxide layer by a hybrid sol-gel layer. These parameters modify the thickness, pore size and size distribution, tortuosity ... formed on AA2xxx specimens [4]
- Optimization of the synthesis and deposition parameters during the development of new resins: solvent content, curing process and temperature, resin viscosity, role of the anodic layer.
In this field of research, it will also be emphasized that EIS results need to be supported by using complementary tools such as SEM-FEG, GD-OES analysis, DEA technique, UV-visible determination, ....
References
[1] A. Renaud, M. Poorteman, J. Escobar, L. Dumas, Y. Paint, L. Bonnaud, Ph. Dubois, M.-G. Olivier, Progress in Organic Coatings 112 (2017) 278-287
[2] I. Recloux, A. Francesco, M.-E. Druart, L. Bertolucci Coelho, C. Cepek, D. Cossement, F. Lorenzo, M.-G. Olivier, Journal of Alloys & Compounds 735 (2018) 2512-2522
[3] M.-E. Druart, I. Recloux, T. T. Thai, S. Ershov, R. Snyders, M.-G. Olivier, 'Impact of the addition of cerium salts (Ce(III) and Ce(IV)) on formation and ageing of a silica sol-gel layer' Surface & Coatings Technology 304 (2016) 40-50
[4] H. Costenaro, A. Lanzutti, Y. Paint, L. Fedrizzi, M. Terada, H. Gomes de Melo, M.-G. Olivier, Surface & Coatings Technology 324 (2017) 438-450
