In this work, a novel stearic acid modified nickel-based (NiSA) superhydrophobic composite coating with good anti-corrosion properties was prepared on magnesium alloy AZ31 surface through electroless nickel-phosphorus plating, electrodeposition of porous nickel, and decoration with stearic acid. Surface topography, chemical groups, and structural compositions of the NiSA coating were characterized through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD), respectively. Adhesion of the NiSA coating was evaluated by a tape test method, and corresponding water contact angle (WCA) and water sliding angle (WSA) were tested by a contact angle meter. Results indicate that WCA value of the NiSA coating was 154.6° ± 3.7°, and WSA value was 5.9° ± 1.7°, indicating a high superhydrophobicity. Electrochemical impedance spectroscopy (EIS) and Tafel fitting reveal that the corrosion current density of the coating ( j corr = 1.41 × 10 −8 A cm −2 ) was three orders of magnitude lower than that of the bare magnesium alloy, and the corresponding low-frequency impedance modulus (| Z | f = 0.01 Hz = 554.65 kΩ cm 2 ) increased by three orders of magnitude, verifying high corrosion resistance. Moreover, all contact angles (CA) of common liquid stains in life were higher than 150°, indicating the good anti-fouling capability of the NiSA coating.
A strategy based on chelating agent addition was used to assist the in-situ growth of MgAl-layered double hydroxides (LDHs) films on magnesium alloy AZ31 in a relatively mild condition. The growth behavior of MgAl-LDH films was studied on the magnesium alloy AZ31 substrate as the sole source of Al 3+ and/or adding aluminum compounds as a supplementary source of respective ions. The composition, structure, corrosion resistance , and formation mechanism of LDH films were investigated and discussed. Results showed that the LDH-coated samples could effectively retard the corrosion of magnesium alloy. A thicker Mg (OH) 2 /MgAl-LDH composite film with larger flake size was formed without additional aluminum source. MgAl-LDH film fabricated with moderate additional Al 3+ concentrations showed better corrosion resistance and an interesting stable network structure on a flat surface both covered/consisting of very fine LDH flakes.
Magnesium alloys are widely used in aerospace and automobile industries because of their lightweight and high strength properties . However, the occurrence of surface corrosion limits their application. Among the protection methods of magnesium alloys, the sol-gel method has received a growing attention recently because of its green economy, high efficiency, and stability. However, the sol-gel method cannot provide corrosion protection for an extended duration in saline solutions. In this study, a novel sol-gel coating via catechol/lysine (CA/Lys) polymerization has been prepared via a facile method and systematically investigated. The CA/Lys co-deposition process was studied by ultraviolet-visible (UV-Vis) spectroscopy. Corrosion performances of the coating were evaluated in aqueous 0.1 M NaCl by electrochemical impedance spectroscopy (EIS) and hydrogen evolution measurements. The experimental results showed that the CA/Lys-modified sol-gel coating provided corrosion protection for up to 18 days, while the unmodified sol-gel coating failed after only 3 days of testing. The polymerized CA/Lys was adsorbed by and then diffused into the sol-gel coating by filling in the macropores or nanopores and the nano-SiO 2 cross-linked network, greatly improving the compactness of the coating. In addition, albeit the thickness of CA/Lys modified coating being only 9 µm, this material was able to provide a long-lasting corrosion protection. This study introduced a novel approach to greatly improve the corrosion resistance of the sol-gel film for magnesium alloys by adopting phenolamines to modify the sol-gel for anticorrosion. This approach can provide a new strategy for Mg alloy corrosion protection.
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