The influence of current density on the morphology and corrosion properties of MAO coatings on AZ31B magnesium alloy

Corrosion and corrosion fatigue performances of micro‐arc oxidation coating on AZ31B cast magnesium alloy

“…For the uncoated AZ31B alloy, a low corrosion potential of −1.49 V, commonly reported for Mg alloys, [34] was obtained. This result agrees with that of the OCP measurement (Figure 4a).…”

“…Prior to the impedance measurements, the specimens were immersed in the environment for 30 min to achieve a stable OCP. Bode plots of the impedance modulus and phase angle versus frequency for the specimens are presented in Figure , together with the simulated curves using the equivalent electric circuits (Figure ) …”

“…Bode plots of the impedance modulus and phase angle versus frequency for the specimens are presented in Figure 5, together with the simulated curves using the equivalent electric circuits ( Figure 6). [34] For the uncoated AZ31B substrate, the equivalent circuit (Figure 6a) consists of the solution resistance (R s ), the electrical double-layer capacitance (Q dl ), the charge transfer resistance (R ct ) of the electrical double-layer capacitor, and the resistance (R ads ) and inductance (L ads ) of the adsorption coating. To achieve a better fit, the capacitance is represented by the parameter Q instead of a constant phase element (CPE).…”

“…[35] R ct and Q dl are related to the Faradaic processes that occur in the electrode/ solution interface, and R ads and L ads are attributed to the partially protective surface coating commonly formed on the Mg alloy. [34,36] In the impedance spectrum, the highfrequency range (10 2 -10 5 Hz) corresponds to the performance of the electrical double-layer capacitance Q dl , the middle-frequency range (10 0 -10 2 Hz) reflects the characteristics of the charge transfer resistance R c , and the properties of the adsorption coating on the surface of the AZ31B substrate are associated with the low-frequency range (<10 0 Hz). [34] For the coated specimens, the equivalent electric circuits shown in Figure 6b [37,38] were used to fit and interpret the EIS data of the coating specimens.…”

“…[12,13] Most researchers have focused on the corrosion performance of MAO coating on Mg alloys under load-free conditions, and the corrosion protective properties of MAO coatings are closely related to their quality. [14][15][16][17][18][19][20] Nevertheless, the corrosion performance of MAO-coated Mg alloy under cyclic loading has not received much attention. Nemcova et al [21] reported reductions of 38% in air and 56% in 3.5% NaCl solution for MAO coatings on AZ61 Mg alloys due to cracks in the coating, roughness of the substrate and alloy interface, and the effects of Al-Mn phase in the alloy.…”