Electrochemical corrosion behavior and mechanism of irradiated micro-arc oxidation coating on AZ31 magnesium alloy by HIPIB

Micro-arc oxidation (MAO) coating on AZ31 magnesium alloy was modified by High-intensity Pulsed Ion Beam (HIPIB) to improve its corrosion resistance at the energy density of 4 J/cm2 with 2-10 shots. The results show that a dense remelted layer of irradiated MAO coating formed at 2 shots, reducing the porosity by 14.39%. Potentiodynamic polarization results showed that the corrosion potential of the irradiated MAO coating with 2 shots increased from -1.504 V to -1.447 V, and the corrosion current density decreased from 3.59×10-6 A/cm2 to 7.89×10-7 A/cm2. Electrochemical impedance spectra(EIS) showed that the initial capacitive arc diameter of the irradiated coating (2.2×104 Ω·cm2) was twice that of the original coating, and the phase angle in the high-frequency region increased from 40° to 55°, confirming the significant enhancement in corrosion resistance. Fitting of the equivalent circuit indicated a 2.4-fold increase in the outer coating resistance, while the hydrophobicity further inhibited the penetration of simulated body fluid(SBF). It is found that the improved corrosion resistance of the MAO coating stems from the HIPIB-induced remelted layer and modified surface wettability, which synergistically inhibit the penetration of SBF into the magnesium alloy substrate.