Optimizing Fabrication of Plasma‐Driven <scp>CuO</scp> Shell Over Porous <scp> Al ₂ O ₃ </scp> Substrate to Meet Coating Issues

ABSTRACT A plasma‐driven in situ conversion strategy was developed in which Cu 2 O nanoparticles introduced into an alkaline phosphate–hydroxide electrolyte undergo oxidative transformation to CuO within plasma micro‐discharge channels during plasma electrolytic oxidation (PEO) of AA6061 aluminum alloy. The positive duty cycle was systematically varied from 10% to 40% under constant mean current density to regulate dielectric breakdown behavior, discharge energy input, and interfacial oxidation conditions. Voltage transient analysis, X‐ray diffraction, field emission scanning electron microscopy, and scratch adhesion testing were employed to correlate discharge characteristics with phase evolution and coating integrity. A progressive increase in the duty cycle was found to reduce the dielectric breakdown transition voltage, promote more spatially distributed microdischarges, and facilitate charge‐transfer‐driven oxidation of Cu 2 O to CuO within the active oxide growth zone. This plasma‐assisted redox mechanism enables CuO to form co‐spatially with Al 2 O 3 melting and rapid re‐solidification, producing a CuO shell structure distributed over the porous alumina matrix rather than as a passively entrapped particulate phase. The resulting microstructural densification suppresses discharge‐crater porosity, reduces surface roughness, and improves coating–substrate adhesion by nearly twofold relative to particle‐free PEO coatings. These findings establish that duty‐cycle‐controlled discharge behavior provides a mechanistically grounded and dispersant‐free route for fabricating CuO‐modified oxide coatings with enhanced structural integration and interfacial adhesion on aluminum alloys.