In-situ hydrothermal Mg(OH)2-SiO2-Al(OH)3 composite coatings on AZ91D magnesium alloy with enhanced corrosion properties

Abstract

A one-step in-situ hydrothermal method (HT) was performed on magnesium alloys to prepare Mg(OH)2-SiO2-Al(OH)3 (MSA) composite coatings with strong corrosion resistance. In this study, the aluminum-rich Mg(OH)2 was used as the bottom layer, and SiO2-Al(OH)3 microsphere particles generated by self-assembly of strip monomers were the top layers, which together prevented the penetration of corrosive ions (Cl−) into the AZ91D surface. Due to the in-situ growth process, the adhesion between the film and the substrate stays strong, and the generation of silicate during HT further enhanced the stability of the coating, which improved its potential for practical application. Electrochemical experiments showed that the MSA composite multilayer film strengthened the corrosion resistance of AZ91D, and the corrosion current density decreased by about five orders of magnitude. The connection between particle morphology and different preparation conditions was also discussed. MAS composite coatings provide a new approach to corrosion protection of metal substrates.