Stearic acid modified porous nickel-based coating on magnesium alloy AZ31 for high superhydrophobicity and corrosion resistance

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 (jcorr = 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 cm2) 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.