Efficient protection of Mg alloy enabled by combination of a conventional anti-corrosion coating and a superamphiphobic coating

Magnesium (Mg) alloys have many unique properties but suffer from poor corrosion resistance. Effective anticorrosion strategies are highly desirable for widespread applications of Mg alloys. Bioinspired super anti-wetting coatings are promising for metal protection, but are limited by some issues. Here, we report a bi-layer super-amphiphobic coating for efficient protection of Mg alloy by sequentially spray-coating a conventional epoxy anti-corrosion coating and a superamphiphobic coating (perfluorodecyl polysiloxane modified SiO2). The coating showed excellent anti-corrosion performance owing to high superamphiphobicity and "synergistic effect" of the bi-layer structure. The coating retained excellent anti-corrosion performance even after 70 d immersion and 35 d neutral salt spray tests. The long-term anti-corrosion performance is superior to a superhydrophobic coating with similar initial anti-corrosion performance, and better than reported and commercial anti-corrosion coatings. This is because the coating maintained high superamphiphobicity in the corrosion tests owing to high chemical stability of the C-F groups and easy roll off of small NaCl drops. Hence, the contact area and contact time of NaCl on the coating are limited. So, the coating could effectively block diffusion of corrosive substances, providing long-lasting efficient protection. We believe that the strategy will shed a new light on designing novel anti-corrosion coatings.