Abstract: The ceramic coatings on the Al-alloy substrate have been synthesized by means of microarc oxidation (MAO) technique. Effects of the unipolar pulse current density on the mechanical and chemical properties of the coatings have been studied via XRD, SEM, EDS, and microhardness test. The samples fabricated at high current densities consist mainly of α-Al₂O₃ phase, while the samples fabricated at low current densities are almost completely composed of γ-Al₂O₃. The content analysis on the cross-section of the coating indicates that the ratio of α-Al₂O₃ content to γ-Al₂O₃ content shows complicated changes with the variation of the film depth, which is different from the results reported from other literatures.

Key words: aluminium alloy, microarc oxidation, microhardness, unipolar pulse, ceramic film