In the present work, a coating was prepared on an Al alloy substrate by plasma electrolytic oxidation (PEO). To seal the micro defects in the oxide scale, a siloxane layer was prepared on the PEO coating by sol gel method. The polymer sealant was synthesized from Tetraethoxy silane (TEOS) and methacryloxy propyl trimethoxyl silane (MPTES). The chemical structure of the polymer was studied by Fourier transform infrared spectroscopy (FTIR). The morphologies and microstructure of the PEO coating and siloxane coating were investigated by scanning electron microscopy (SEM). The results showed that siloxane formed a continuous layer on the surface and effectively sealed the micro defects. The corrosion behavior of the coatings in three different corrosion solutions (NaCl, HCl, and NaOH) was examined by electrochemical impedance spectroscopy and potentiodynamic polarization. The corrosion resistance of the sealed coatings was superior to that of the PEO coating because it prevented the penetration of corrosive solutions. The corrosion resistance of the sealed coatings was found to decrease with increasing electrolyte concentration. The work demonstrated that siloxane sealing may greatly enhance the corrosion resistance of Al-based PEO coating in acidic, neutral, and alkaline environments.

In this communication, a bis-silane prepolymer was used to modify epoxy resin, aiming to enhance the corrosion resistance of epoxy coatings on aluminum alloy substrates. The bis-silane prepolymer was prepared by tetraethoxysilane (TEOS) and γ-glycidoxypropyl trimethoxysilane (GPTMS). The corrosion behavior of silane-epoxy coatings was studied. Compared with silane monomer-modified epoxy coatings, bis-silane-modified epoxy coatings have lower coating capacitance (Cc), higher charge transfer resistances (Rdl), and lower double layer capacitance (Cdl) during long-time immersion. It indicates that bis-silane-modified epoxy coating has stronger waterproof permeability and substrate corrosion protection ability. In addition, due to the leaching of the silane component and cross-linking reaction between different silanes during the immersion process, the bis-silane-modified epoxy coatings exhibit much stronger “self-healing” ability.

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