One-step hydrothermal method for long-term anti-corrosion lanthanum-based superhydrophobic coating on Mg alloy

The superhydrophobic coating was created on the surface of AZ31B using a one-step hydrothermal method. Various characterisation techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), contact angle goniometer, and electrochemical workstation, were employed to characterise its morphology, composition, hydrophobicity and corrosion resistance. The prepared coating from a 5-hour hydrothermal reaction exhibited a double-layer structure with a dense inner oxide layer and an outer layer of needle-like micro-nano structures. Achieving a water contact angle (WCA) as high as 159°, the superhydrophobic coating demonstrated low water adhesion and excellent self-cleaning properties. In a 3.5 wt-% NaCl aqueous solution, its corrosion rate was 5 orders of magnitude lower than that of the bare Mg alloy. Furthermore, the coating maintained a high impedance modulus value at 0.01 Hz (∼6.85 × 10 6 Ω cm 2 ) after immersion in 3.5 wt-% NaCl solution for 25 days, which was attributed to the synergistic effect of the inner and outer layers. This study introduces a strategy for preparing long-term corrosion-resistant superhydrophobic coating on Mg alloy.