## 3 Results and Discussion
### Corrosion Resistance Properties  
The superhydrophobic surface is in the Cassie-Baxter state, and its surface micro/nano structure can trap air, thereby increasing the contact angle with water [30]. When the superhydrophobic surface is immersed in the corrosive medium, the micro/nano structure is filled with a large amount of air, and the \"air cushion layer\" formed is similar to the dielectric between parallel plate capacitors, which can inhibit the electron transfer between the corrosive medium and the substrate. Figure 9 shows the polarization curve test results of AZ31B Mg alloy substrate and PVDF/PFOTES-SiO\({}_{2}\) superhydrophobic coatings. It can be seen from Figure 9 that fitting the Tafel line according to the experimental data, the corrosion current densities (\(I_{\text{corr}}\)) of bare AZ31B Mg alloy and superhydrophobic coatings can be obtained 9.76 \(\pm\) 1.05 \(\times\) 10\({}^{-6}\) A/cm\({}^{2}\) and 6.18 \(\pm\) 2.43 \(\times\) 10\({}^{-9}\) A/cm\({}^{2}\), respectively, the corrosion voltage (\(E_{\text{corr}}\)) is \(-\)1.54 \(\pm\) 0.05 V and \(-\)1.32 \(\pm\) 0.04 V, respectively. Figure 8: The hydrophobic performance of superhydrophobic surface after 10\(\times\) abrasion testing. However, it can be found from Figure 9a that the anode polarization curve does not show a broad Tafel area, and the anode curve has an active/passive transition, which may be the existence of the dissolution reaction and the initiation of the passivation reaction did not lead to a clear experimental anode Tafel area [31]. Compared with the polarization curve of bare AZ31B Mg alloy, the polarization curve of superhydrophobic coating (Figure 9b) is quite different. The anode curve and cathodic curve of superhydrophobic coating do not conform to [PERSON]'s law. This is maybe attribute to the air cushion between the coatings and the NaCl solution, which prevents the corrosive solution from the surface of the magnesium alloy [14]. Although the application of dynamic polarization curve to superhydrophobic surface has certain limitations, the fitting results also indicate that the superhydrophobic surface improves the corrosion resistance of Mg alloy. To better understand the influence of superhydrophobic coating on the corrosion resistance of magnesium alloys, EIS test is considered as an effective way to analyze the corrosion characterization of coated or modified metals [32]. The corrosion resistances of the as-prepared super-hydrophobic surface were further explored by the Nyquist plots. Figure 10 shows the Nyquist plots of the bare AZ31B Mg alloy substrate and as-prepared super-hydrophobic surface in 3.5 wt % NaCl solution. The results show quite different capacitive loops that can be attributed to the charge transfer resistance of the corrosion process [33]. Compared with the bare AZ31B Mg alloy, the capacitive loops of the as prepared superhydrophobic surface have a widespread trend attributed to a protective surface film. The diameter of the capacitor circuit is usually proportional to the corrosion rate, that is, the larger the diameter, the smaller the corrosion rate, which shows that the super-hydrophobic surface has better corrosion resistance. A continuous neutral salt spray test was performed in a salt spray test box following the ASTM B117 standard. The samples were taken out every 24 h to observe the macroscopic changes on the surface of the samples and photograph them with a digital camera. The surface of the sample after the salt spray experiment is shown in Figure 11. The surface of the bare AZ31B has been completely corroded after a 24 h salt spray test. The depth of surface pitting pits continues to increase as corrosion time increases. However, after the 96 h salt spray test, the PVDF/PROTES-SiO\({}_{2}\) coating gradually showed salt spray deposition and pitting corrosion on the surface. The corrosion area on the surface continues to grow as the salt spray time is extended.