Protection against corrosion of aluminium-SiC composites by sol–gel silica coatings

Silica mono-and multilayered coatings have been obtained through a sol–gel route on aluminium matrix composites reinforced with SiC particles for their corrosion protection. Tetraethoxysilane (TEOS) was used as alcoxide precursor, and dip-coating technique of the samples was used at different extraction rates. Corrosion protection of the different coating systems have been evaluated in 3.5 wt.% NaCl at different immersion times using several electrochemical techniques including linear polarization resistance, anodic–cathodic polarization, and electrochemical impedance spectroscopy. Gravimetric tests have been also used to characterize the protective effectiveness of the coatings, using low angle X-ray diffraction to identify the corrosion products. Coatings characterization before and after corrosion tests have been carried out using Scanning Electron Microscopy and Atomic Force Microscopy, studying the mechanisms of corrosion that take part in coated and uncoated composites. A corrosion mechanism for each one of the tested materials has been proposed.