Aniline-based silane as a primer for corrosion inhibition of Al alloys

D.O. FLAMINI; M. TRUEBA; S.P. TRASATTI

Mons

Workshop; International workshop Application of Electrochemical Techniques to Organic Coatings AETOC 2011; 2011

University of Mons

An our previous study dealing with a pyrrole-based silane as a pre-treatment for Al alloys indicated that protective properties of polysiloxane-based coatings can be improved if silane molecule is functionalized with a monomer of a conducting polymer [1]. In order to confirm these results, as-received wrought Al alloys AA1050-H24, AA2024-T3, AA5083-H111, AA6082-T6 and AA7075-T6 were similarly modified by using an  aniline-based silane (N-(3-trimethoxysililpropyl)aniline (AniSi). Surface modification was carried out following the same steps, i.e. immersion and curing, reported for PySi [1]. In addition, 10-days aged AniSi solution presenting pink coloration was also used. AniSi molecule structure, AniSi-based solution composition and deposited film characteristics were studied by different spectroscopic techniques. Coating morphology was investigated by SEM/EDX. Several corrosion tests were used for the evaluation of the AniSi coating performance in near neutral 0.6M NaCl solution: anodic and cathodic polarizations, open circuit potential monitoring and current monitoring at the pitting potential of the bare alloys. Long-term immersion (one month) and SEM examination at the end of the exposure were also carried out. Despite the differences in microstructure and composition of Al substrates, AniSi pre-treatment provides an hybrid structure with very good protection, improved morphology and adhesion, thus supporting previous findings [1]. Below the much lower current responses obtained for AniSi-coated AA1050 and AA5083, in comparison to bare alloys (inset), when polarized at -700 and -741 mV vs SCE, respectively, are illustrated. The surface treatment performed in pink-colored AniSi solution that contains oxidized aniline units as indicated in UV-Vis. spectra (and thus partially doped), suggests possible specific interactions at the metal/coating interface, probably stimulated by local pH changes occurring during corrosion processes [2].  [1] (a) M. Trueba, S.P. Trasatti, Prog. Org. Coat. 66 (2009) 254; (b) ibid 265. [2] L. Cecchetto et al., Corr. Sci. 49 (2007) 818.