Corrosion Resistance and Durability of Superhydrophobic Coating on AZ31 Mg Alloy via One-Step Electrodeposition

To enhance durability and adhesion of superhydrophobic surface, an integrated superhydrophobic calcium myristate (Ca[CH3(CH2)12COO]2) coating with excellent corrosion resistance was fabricated on AZ31 magnesium (Mg) alloy via one-step electrodeposition process. Field-emission scanning electron microscopy, Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy as well as X-ray diffraction were employed to investigate the surface characteristics (morphology, composition and structure) of the coatings. Hydrophobicity of the coating was evaluated by means of contact and sliding angles. Additionally, potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution tests were conducted to characterize the corrosion resistance. Results indicated that the coating exhibited super-hydrophobicity with large static water contact angle (CA) and small sliding angle of 155.2° ± 1.5° and 6.0° ± 0.5°, respectively, owing to spherical rough structure and low surface energy (7.01 mJ m−2). The average hydrogen evolution rate (HERa) and corrosion current density (icorr) of the coated sample were 5.3 μL cm−2 h−1 and 5.60 × 10−9 A cm−2, about one and four orders of magnitude lower than that of AZ31 substrate, respectively, implying the excellent corrosion resistance. The CA of the coating remained 155.6° ± 0.9° after soaking for 13 days, showing the super-hydrophobicity and stability of the coating. Simultaneously, the large critical load (5004 mN) for the coating designated the outstanding adhesion to the substrate by nano-scratch test.