MICROSTRUCTURE AND GROWTH PROCESS OF Al2O3 FILM ON PURE ALUMINUM BY MICRO-ARC OXIDATION

Ceramic coatings were formed on a pure aluminum substrate in an aqueous solution of phosphate salt, using the pulsating micro-arc oxidation method. XRD indicated that the film composed of pure γ-Al2O3. SEM showed that the surface of the film was micro-porous with 1–5 μm pores. EDS gave the element distributions of the cross-section. The result indicated that elements from the electrolyte like P could be incorporated into the film during MAO process. The microhardness test showed that the film had an average hardness of 654 HV0.025. The growth process of the Al2O3 ceramic-like film was discussed on the basis of the structure analysis.