Effect of process conditions for the preparation of a manganese-based coating on the surface of AZ31 magnesium alloy

Manganese-based coatings on AZ31 magnesium alloy with Mg(OH)₂ interlayer were prepared by hydrothermal reaction under different process conditions (temperature, time, and concentration). The harsh reaction conditions provided coatings with defects. These defects enabled the corrosive environment penetrated to the magnesium alloy which impaired the corrosion properties of AZ31 alloy. Optimal conditions included a temperature of 120 °C, 0.25 M MnCl₂, and a reaction time of 1 h. The prepared coating was mainly composed of Mn₃O₄, which consisted of nanosized crystals of polyhedral shape. Potentiodynamic polarization measurements showed that the coating had very good corrosion resistance in 0.15 M NaCl. Future work will focus on the potential use of the manganese-based coating in biomedical applications.