Superhydrophobic ZIF-8-Based Dual-Layer Coating for Enhanced Corrosion Protection of Mg Alloy.

Magnesium (Mg) and its alloys are regarded as the most promising engineering materials because of their unique property. However, the Mg alloys were easily corroded in humid environments, which restricted their wider applications. Herein, the superhydrophobic ZIF-8/PVDF/LDH (SZPL) double-layered coating was fabricated on Mg alloys via electrodeposition and dip-coating methods, which consisted of the underlying layered double hydroxide (LDH) transition structure and top superhydrophobic zeolitic imidazolate framework-8 (ZIF-8) layer. Besides, the LDH transition structure not only worked as a protection shield but also strengthened the binding force between the substrate and the top superhydrophobic ZIF-8 layer. The top superhydrophobic ZIF-8 layer could serve as an armor on the LDH layer to further prevent the corrosive ions from infiltrating the microporous defects. In addition, the as-prepared SZPL double-layered coating showed robust superhydrophobic and self-cleaning properties, which could block the electrolyte invasion. Furthermore, the electrochemical tests demonstrated that the SZPL coating highly enhanced the corrosion protection ability of Mg alloys. Moreover, the superhydrophobic ZIF-8-based coating could still retain excellent anticorrosion property after immersion in 3.5 wt % NaCl solution for 7 days. The enhanced anticorrosion ability was ascribed to the fact that a synergistic effect of the underlying LDH transition layer hindered the transmission of aggressive ions and the top superhydrophobic ZIF-8-based coating decreased the contact area of the substrate with corrosive solution. Therefore, such coatings offer a new strategy for fabricating excellent anticorrosive coatings with robust superhydrophobicity and self-cleaning performance on metal substrates.