Hydrophobic Modification of Magnesium Hydroxide Coating Deposited Cathodically on Magnesium Alloy and its Corrosion Protection

摘要

In this paper, hydrophobic modification of magnesium hydroxide film prepared by cathodic deposition on ME20M Mg alloy was achieved with ethanol solution of stearic acid. The effects of solution concentration, temperature and treatment time on the surface wettability were investigated. The corrosion behaviors of typical samples were evaluated by droplet test, total immersion corrosion test as well as PDP (Potentiodynamic Polarization) and EIS (Electrochemical Impedance Spectroscopy) techniques, respectively. Adhesion of coatings to the substrate were examined by tape test. The surface morphology and chemical composition of typical coatings were characterized by SEM, FTIR and XRD respectively. The results indicate that the superhydrophobic surface with 151.5° water static contact angle and 1° sliding angle could be fabricated successfully by simple immersion in a low-concentration stearic acid solution for a short period. Compared with blank sample, the composite surface modification based on cathodic deposition (CD) plus hydrophobic treatment (HT) extended the discoloration time in droplet tests by nearly 25 fold, decreased the icorr (corrosion current density) by three orders of magnitude, and increased the characteristic impedance modulus at 0.1 Hz by nearly four orders of magnitude, indicating that the CD/HT composite surface modification could enhance the corrosion resistance of Mg alloy significantly.