In the 1970s, the "Lotus Effect" was put forward, so that the superhydrophobic materials attracted the attention of researchers in various countries. Superhydrophobic surface referred to the surface where the water contact angle (CA) was greater than 150° and the rolling angle (SA) was less than 10°. The self-cleaning, anti-fouling, anti-icing and other characteristics of superhydrophobic materials made them widely used in various fields, such as the surface protection of aluminum alloy. It could not only provide corrosion protection for aluminum alloy, but also gave aluminum substrate self-cleaning, antifouling, antibacterial and other special functions. Superhydrophobic surface colorization could make aluminum alloy better used in architectural decoration materials, shipbuilding and other fields with decorative requirements. To prepare artificial superhydrophobic surface, it was necessary to improve surface roughness and reduce surface free energy. The construction of color super hydrophobic film layer needed to add another coloring step. Specific steps included anodic oxidation, electrolytic coloring, hot water sealing and low surface energy modification. Anodic oxidation was used to preparing a layer of porous oxide film on the surface of 7A04 aluminum alloy, and then put the anodized samples into different coloring solutions for electrolytic coloring. The metal ions in the coloring solution were reduced to single substance or compound and deposited at the bottom of the porous layer, showing black (Sample H) and mustard yellow (Sample J) respectively. Hot water sealing could not only improve the color protection of color film layer, but also construct the rough structure needed for super hydrophobic surface. Finally, black (Sample S-H) and mustard yellow(Sample S-J) superhydrophobic film was successfully prepared after low surface energy modification. Scanning electron microscope (SEM) and energy spectrometer (EDS) were used to analyze the surface morphology and elements of the color film before and after modification. The static contact angle of the superhydrophobic film was characterized by the optical contact angle tester, and the self-cleaning test and atmospheric exposure test were carried out. The corrosion resistance of color superhydrophobic film was studied by electrochemical workstation. The results showed that: (1) the surface of the color film layer was covered by petal-like substances, which were the hydrated alumina generated during the hot water sealing process. A large number of hydrated alumina provided the required rough structure for the super-hydrophobic surface, and the surface structure did not change after the modification of the low-surface energy substances. (2) According to EDS detection, metal elements from the coloring solution were detected on the film surface before the modification of low surface energy, while F and Si elements from the modification solution were detected on the film surface after modification, which proved that the long chain fluoride in the modification solution was grafted to the sample surface. (3) When the droplets were in contact with the superhydrophobic surface, most of the surface area of the droplet was supported by a cushion of air provided by the coarse structure, and the droplet remains spherical on the superhydrophobic surface. The contact angles of the black and mustard yellow superhydrophobic film measured by the contact angle tester were 160° and 162.7°, respectively, showing the superhydrophobic performance. (4) During the atmospheric exposure experiment lasting up to 180 days, the static water contact angle on the color superhydrophobic surface showed an overall downward trend, but it was still greater than 150° after 180 d, indicating that the prepared color superhydrophobic film had good stability under atmospheric environment. (5) According to the self-cleaning test process recorded by high-speed digital camera, the aluminum powder on the surface carried by the droplet slided down together. The amount of aluminum powder carried by the droplet was related to the volume of the droplet. (6) According to the polarization curve, the corrosion resistance of the color superhydrophobic membrane layer at different stages showed an upward trend. The corrosion potential (Ecorr) of the aluminum alloy substrate was -0.75 V, the corrosion current density (Icorr) was 1.10×10-3 A·cm-2, Ecorr of Samples H and S-H was -0.63 and -0.31 V, and Icorr was 3.12×10-6 and 1.35×10-8 A·cm-2, respectively. Ecorr of Samples J and S-J were -0.62 and -0.18 V, and Icorr of Samples J and S-J were 4.61×10-7 and 8.27×10-9 A·cm-2, respectively. The superhydrophobic film showed excellent corrosion resistance. The fitting results of samples' electrochemical impedance spectrum also illustrated this change. Before the modified low surface energy, the impedance modulus values of the two color films reached 1×105 Ω orders of magnitude, and the modified color superhydrophobic films impedance modulus values reached more than 1×107 Ω orders of magnitude. To sum up, the black and mustard yellow superhydrophobic films with bright luster and uniform color were prepared on the surface of 7A04 aluminum alloy by combining anodic oxidation process and low surface energy modification. The contact angle was up to 160° (Sample S-H) and 162.7° (Sample S-J), respectively, and the film had good superhydrophobicity, self-cleaning property and atmospheric environment adaptability. The results of polarization curve and electrochemical impedance spectroscopy showed that the superhydrophobic modification, as one of the common surface treatment methods for aluminum alloy protection, could provide better corrosion protection performance for aluminum alloy. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.
