Coating maintaining Cassie–Baxter wetting state for sustainable protection of magnesium alloys

Background Superhydrophobic coatings can hardly sustain a Cassie–Baxter wetting state to provide durable protection for magnesium alloys under harsh conditions. Methods In this study, a three-step method comprising F/Zr chemical conversion, boiling-water sealing, and stearic-acid modification was developed to fabricate a robust coating maintaining a Cassie–Baxter wetting state on AZ31 Mg alloy for sustainable protection in harsh conditions. The integration of hierarchical micro-nano-structures and chemically bonded low-surface-energy compounds enabled the coating to achieve a Cassie–Baxter wetting state. Findings The coating exhibits superior superhydrophobicity (with a water contact angle of 160.4°), low adhesion (with a water roll-off angle of ∼1°), and dynamic impact resistance. Electrochemical measurement results reveal that the as-coated sample exhibits a high coating resistance of 11,453 Ω·cm 2 , which contributes to a reduction in corrosion current density (i corr ) from 1.380 × 10 –4 to 1.778 × 10 –6 A cm –2 , approximately two orders of magnitude lower than that of the blank sample. Importantly, the coating maintains the Cassie–Baxter wetting state and demonstrates sustainable protection for magnesium alloys under various harsh conditions, including broad chemical media (pH range of 1–14), high-temperature (100–250 °C), external forces (peeling and abrasion), natural corrosive surroundings (simulated seawater and acidic industrial atmosphere). This work provides a feasible and practical strategy for achieving sustainable protection for metallic materials in complex settings.