Electrochemical corrosion behavior of modified MAO film on magnesium alloy AZ31 irradiated by high-intensity pulsed ion beam

Abstract

Micro-arc oxidation (MAO) films on AZ31 magnesium alloy were modified by high-intensity pulsed ion beam(HIPIB) irradiation with ion energy of 300keV at 200A/cm2 with 1–10 shots. A compact and solidified layer was prepared on the irradiated MAO films. The electrochemical impedance spectrum (EIS) of the MAO films in 3.5% NaCl solution was measured with varying the immersion time. The Nyquist plots for EIS showed typical capacitive arc and inductive loop. The diameters for capacitive arc and inductive loop are both increased and then decreased with increasing irradiation shot number, the maximal value for diameters obtained at 200A/cm2 with 5 shots at immersion time of 5h achieved to 6×107Ω and 1.5×105Ω, respectively. With immersion time augment, the diameters for capacitive arc and inductive loop of Nyquist plots both decreased. Based on the results of EIS measurements, appropriate equivalent circuits for the modified layers were proposed to fit the EIS for MAO films. It is found that the enhancement in corrosion property of ablated MAO films is mainly caused by improvement of continuity and compaction of films irradiated by HIPIB, which suppressed the corrosion process by holding back the transfer of electrolyte through the modified films to magnesium substrate during immersion.