Highly reliable double-layer coatings on magnesium alloy surfaces for robust superhydrophobicity, chemical durability and electrical property

The long application life and reliable performance of magnesium alloys have been putting forward strict requirements for both better chemical stability and functional characteristics of protective coating. Herein, a highly reliable superhydrophobic double-layer coating on AZ31 Mg with excellent anti-corrosion and electrical protection was achieved by assembling modified SiO2-based organic-inorganic hybrid films on Plasma Electrolytic Oxidation (PEO) ceramic bottom layer. The coating exhibits preferable antiwater surfaces with a barrier layer isolating the underlying substrate from the external environment, rendering a long-term active corrosion protection for the multilayer covered magnesium alloy. Remarkably, the coating achieves high electric insulation with volume resistivity of 1.7 × 1012 Ω cm, breakdown voltage of 1405.2 ± 117.1 V and dielectric strength of 40.2 ± 3.3 V/μm. Simultaneously, its dielectric properties with a low dielectric constant (ε ≈ 3.75) and a low dielectric loss (tan δ ≈ 0.0058) outperform those of some current dielectric coatings with similar components. Moreover, the superhydrophobic coating displays strong mechanical robustness undergoing 50th linear abrasion, superior environmental stability (thermal shock, prolonged solution immersion, salt-spray corrosion and UV irradiation), and high adhesion strength. The excellent multifunction benefits from the introduction of ceramic bottom layer, the assembly of compact nanocomposite films, and the synergistic effect of organic-inorganic components. This study provides a new inspiration for designing advanced protective coating with a great potential for the applications of sensitive electronic devices.