Bilayer diatomite-based composite coatings with superhydrophobic and self-healing properties for enhanced anticorrosion of AZ31B magnesium alloys

Magnesium (Mg) alloys have shown great promise as engineering materials due to their unique properties. However, their high chemical reactivity limits their wide application. Herein, a novel bilayer diatomite-based composite coating was fabricated by spraying coating AZ31B Mg alloy with a bottom layer of benzotriazole (BTA)-loaded diatomite/epoxy resin for providing self-healing properties and a top layer of hexadecyltrimethoxysilane (HDTMS)-modified diatomite/epoxy resin for contributing superhydrophobic properties. The resulting bilayer composite coating (BTA@DME-12 %) exhibited exceptional stability and maintained its superhydrophobicity in a temperature range of 0–160 °C. The coating also delivered good adhesion and physical stability in tape-peeling and frictional testing. Electrochemical study results demonstrated that the BTA@DME-12 % coating exhibited lower corrosion tendencies and corrosion rates compared to the BTA@DME-free coatings. After immersing in 3.5 wt% NaCl solution for 21 days, the bilayer composite coating still achieved an impressive anti-corrosion efficiency of 99.6 %. This work not only provides a scalable and simple method to prepare self-healing and superhydrophobic bifunctional coatings for corrosion protection of Mg alloy, but also presents a novel multifunctional coating strategy by utilizing diatomite with a hierarchical structure.