The thermal dynamic simulation and microstructure characterization of micro-arc oxidation (MAO) films on magnesium AZ31 irradiated by high-intensity pulsed ion beam

Abstract

The micro-arc oxidation (MAO) film on AZ31 magnesium alloy was irradiated by High-intensity pulsed ion beam (HIPIB) at the energy density of 1–5 J/cm2 to enhance its corrosion resistance. The temperature and stress field was simulated by numerical model established by Marc.Mentat software to explore the surface modification mechanism of the irradiated MAO films. The experimental results show that the pores on the MAO film surface decreased, and obvious remelting phenomenon was observed on the irradiated film surface at 4 and 5 J/cm2. X-ray diffraction (XRD) detection indicated that HIPIB irradiation had little effect on the phase structure of the MAO films, except for grain refinement on MgO and Mg3(PO4)2. The wettability of the MAO films changed from hydrophilicity to hydrophobicity by irradiation characterized by contact angle results. From the potentiodynamic analysis, the corrosion potential of irradiated MAO films was significantly higher than that of the original ones, the maximal value of the corrosion potential was obtained at 4 J/cm2, which is increased by 57 mV compared with that of the original ones. The simulated results show that the surface temperature of MAO film increases rapidly during the irradiation process, and the maximum surface temperature reaches the boiling point of MgO 3873 K up to 4 J/cm2. At 4 J/cm2, the MAO film exhibited melting and ablation, with depths of 1.8 μm and 0.6 μm, respectively. The high temperature field and thermal stress by irradiation lead to surface melting of MAO film, which promotes the decrease of the number and dimension of the pores on the MAO film surface. The densification and less porosity of MAO film by HIPIB irradiation inhibited the infiltration of the corrosive liquid to the substrate, which is mainly responsible for the modification of MAO film corrosive performance.