Silicon oxide multilayer coatings doped with carbon nanotubes and graphene nanoplatelets for corrosion protection of AZ31B magnesium alloy

Abstract

Magnesium (Mg) AZ31B alloy substrates were coated by the dip-coating method to obtain four different coating configurations. Three different sol-gels were synthesized to create different monolayer and multilayer coating configurations from two silicon alkoxides, tetraethyl orthosilicate (TEOS) and methyl-triethoxysilane (MTES). Two of these sol-gel solutions were doped with nanocharges. The final concentration of nanocharges in the coatings was 0.045 wt% and 0.046 wt% for multiwall carbon nanotubes (MWCNTs) and functionalized graphene nanoplatelets (COOH-GNPs), respectively. The anti-corrosion behaviour of these coatings was assessed by electrochemical and hydrogen evolution tests in 3.5 wt% NaCl solution. All of the coating configurations significantly improved the behaviour against corrosion compared with the bare substrate, especially the SG + SG/GNP (sol-gel + sol-gel doped with 0.046 wt% COOH-GNPs) multilayer coating system. The sol-gel synthesis combined with the dip-coating method was demonstrated to be an effective way to generate compact and homogeneous coatings for corrosion protection.