Study on the Structure and Corrosion Behavior of Micro‐Arc Oxidation Coatings Regulated by Unipolar/Bipolar Pulses

This study systematically investigates the influence mechanism of unipolar/bipolar pulse modes on the corrosion behavior of micro‐arc oxidation ceramic coatings on aluminum alloys in 3.5 wt.% NaCl solution. By comparing and analyzing the microstructural evolution and electrochemical response characteristics of the coatings under different pulse parameters, the regulation of plasma discharge induced by negative voltage in the bipolar pulse mode is explored. Electrochemical tests show that the corrosion current density of the bipolar pulse specimens is lower than that of the unipolar pulse specimens, the polarization resistance is improved, and the low‐frequency impedance modulus is significantly enhanced compared with the substrate. Microstructural characterization reveals that the negative pulse promotes the fluidity of molten oxides and the reconstruction of discharge channels, forming a bilayer structure that effectively blocks the penetration pathways of corrosive ions. This study clarifies the synergistic regulation law of pulse polarity on the structure–property relationship of micro‐arc oxidation coatings, providing a theoretical basis for the development of long‐term corrosion‐resistant surface protection technologies for aluminum alloys.