摘要
This study investigates the micro-arc oxidation (MAO) behavior of AZ31B and Mg–8Al–4Ca (AC84) magnesium alloys, with emphasis on the role of the β–Al–Ca phase (β phase). Constant-voltage MAO treatments were performed, and the resulting coatings were characterized by SEM and TEM. At low voltage (150 V), the high conductivity of the β phase in AC84 promoted localized discharges, leading to uneven and thinner coatings compared to the more uniform coatings on AZ31B. At higher voltages (≥200 V), AC84 formed stable Mg–Ca-rich silicate/oxide phases, enhancing coating corrosion resistance. However, reduced discharge intensity in AC84 at high voltages also limited coating growth, resulting in thinner layers under identical conditions. Selective removal of surface β phases prior to MAO improved coating uniformity and thickness, yielding characteristics closer to those of AZ31B. These findings demonstrate the significant influence of β phase distribution and anodizing voltage on MAO coating evolution and performance.
•Distinct MAO behaviors observed in AZ31B and AC84 due to β-phase effects.•β–Al–Ca phase in AC84 controls discharge and stabilizes silicate formation.•Ca-containing silicates enhance corrosion resistance but limit coating growth.•Removing β–Al–Ca confirms its key role in coating thickness and evolution.