Large-scale prepared superhydrophobic HDTMS-modified diatomite/epoxy resin composite coatings for high-performance corrosion protection of magnesium alloys

Superhydrophobic coatings have great potential applications in protecting metallic substrates due to their excellent water-repellency and high corrosion resistance, however, most of their preparation processes are complicated, expensive and difficult to scale up for practical applications. Herein, we reported a facile, low-cost and large-scale-preparation method to fabricate superhydrophobic coatings on the magnesium alloy, of which superhydrophobic hexadecyltrimethoxysilane (HDTMS)-modified diatomite powder was first synthesized by electrochemical deposition method, and subsequent spray coating of the epoxy resin and superhydrophobic diatomite mixture was performed to form superhydrophobic composite coatings on the alloy substrates. The influencing factors of surface wettability of the modified diatomite were comprehensively investigated. Under the optimized synthesis condition of a current density of 0.033 A·cm⁻² and electrodeposition time of 2.5 h, the superhydrophobic diatomite powder had an approximately 260 % (in mass fraction) production yield. The spray-coated composite coating delivered superior superhydrophobicity with water contact angle of circa 157° and self-cleaning ability. Such superhydrophobic coating also exhibited a high corrosion protection efficiency of circa 99.8 % and excellent anti-icing performance, and was demonstrated to own ISO grade 1 adhesion and good chemical stability to bear 90 days of immersion in a 3.5 wt% NaCl solution and 20 days of salt spray testing without corrosion. In addition, the superhydrophobic composite coating exhibited great robustness against water impact and sand impact. Therefore, this diatomite/epoxy resin-based superhydrophobic coating can be effectively used for Mg alloy anti-corrosion and has the potential in large-scale production for practical applications.