Corrosion resistance and wetting properties of silica-based superhydrophobic coatings on AZ31B Mg alloy surfaces

A spraying method has been employed to prepare silica-based superhydrophobic coatings on AZ31B Mg alloy surfaces. Both nanometer and micrometer silica particles were used to construct the micrometer and nanometer scale binary structures, and 1H, 1H, 2H, 2H-Perfluorooctyltriethoxysilane (PFOTES) was used as the fluorine silane coupling agent. The coatings were characterized using the techniques of Field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared (FTIR) spectra. The corrosion resistance properties of the prepared superhydrophobic surfaces were checked based on polarization curves. And their wetting properties were studied for aqueous solutions of HCl, NaOH, NaCl, MgCl2, NaI, CH3COONa, C2H5OH, C17H33COONa, and sodium dodecylbenzene sulfonate, respectively, with contact angle and sliding angle as the parameters. In contrast with the bare magnesium alloy AZ31B, after coating, the corrosion current density shows a more than three-order of magnitude smaller value, and the water contact angle increases from similar to 32 degrees to over 155 degrees. Solution pH and coexisted NaCl, MgCl2, NaI, and CH3COONa salts have little effect on the wetting properties of the prepared superhydrophobic surfaces. On the contrary, coexisted C2H5OH, C17H33COONa, or sodium dodecylbenzene sulfonate has an obvious effect on the wetting properties. The differences in the wetting properties were explained by considering the interactions between the superhydrophobic surfaces and the surfaces of the solution droplets. In addition, the superhydrophobicity coating also exhibited good mechanical, chemical and environment stability in the abrasion test, immersion test, salt spray test, etc.