POTENTIAL USE OF HYBRID SOL-GEL COATINGS AS AN ALTERNATIVE APPROACH FOR CORROSION PROTECTION OF LIGHT ALLOYS

Abstract

The aim of this work was to show the preliminary results related to the synthesis of hybrid sol-gel coatings for corrosion protection of the commercial AZ31 and AZ91D magnesium alloys, and the AA2124-T4 and AA2050-T8 aluminium alloys. For this purpose, hybrid sols  were  prepared  from  a  mixture  of  the  inorganic  precursor  tetraethylorthosilicate  (TEOS)  and  the  organics  precursors glycidoxypropyltriethoxysilane  (GPTMS)  and  3-aminopropyltriethoxysilane  (APTES).  Two  experimental  variables  were  fixed:  the molar ratio APTES:GPTMS (from 0,15:1 to 0,25:1) and the aging time (from 10 to 60 minutes). Later, sol-gel coatings were obtained by deposition of these sols following the dip-coating route. Coatings were characterized using Scanning Electron Microscopy (SEM) while Fourier Transform Infrared (FTIR) Spectroscopy and rheological tests were used to analyze the sol properties. On the other hand, corrosion resistance was evaluated by potentiodynamic anodic polarization test in aerated 0.1 M NaCl solution. The experimental results showed that, under some specific experimental conditions, it was possible to obtain homogeneous and uniform coatings with excellent corrosion resistance with regard to the parent alloy. The precursor APTES was confirmed as a key variable during the gelation process. Its properties substantially modified the sol viscosity, affecting the morphological features and the corrosion protection of the coatings.