Self-assembled monolayer and multilayer thin films on aluminum 2024-T3 substrates and their corrosion resistance study

Abstract

Aluminum alloy 2024-T3 substrates were modified with self-assembled monolayer or multilayer thin films from four different alkylsilane compounds, octadecyltrichlorosilane (C 18SiCl 3), octadecyltrimethoxysilane (C 18Si(OMe) 3), octyltrimethoxysilane (C 8Si(OMe) 3) and octadecyldimethylchlorosilane (C 18SiMe 2Cl). The water contact angle of the aluminum surface increased substantially after modification by the two trimethoxysilane compounds and trichrolosilane C 18SiCl 3, but decreased after the modification with monochlorosilane C 18SiMe 2Cl. Potentiodynamic polarization test, prohesion exposure, and electrochemical impedance spectroscopic studies revealed that the corrosion resistance of the C 18SiCl 3-modified aluminum alloy substrates improved significantly compared to the unmodified and the two trimethoxysilane-modified aluminum alloy samples. The C 18SiMe 2Cl-modified substrate also exhibited an improved corrosion resistance compared to the unmodified ones. While extensive corrosion appeared on the unmodified aluminum alloy samples after only 20–30 h of prohesion exposure, early stage corrosion was observed from C 18SiCl 3-modified samples after 150–200 h of prohesion exposure and C 18SiMe 2Cl-modified samples after 80 h of prohesion exposure. Based on the results obtained so far, it is believed that a mixed monolayer or multilayer thin film with opposite molecular orientations was formed through the self-assembling of alkylsilane molecules on the aluminum 2024-T3 surface.