Research On Process And Mechanisms Of Micro-arc Oxidation On Aluminum And Titanium

Ceramic coating is prepared on the surface of aluminum and titanium by the method of Micro-arc Oxidation (MAO). Coating composition, surface appearance and microstructure are determined by Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). The ceramic coating tribological behavior is investigated by abrasion test machine. Mechanism of micro-arc oxidation and growth progress of ceramic coating is opened up. The effect of conductance, oxidation time, the addition of Na₂WO₄ on the microstructure and surface appearance of Al₂O₃ ceramic coating, the effect of the electrolyte, the time and the additive of Na₂Mo₇O₂₄ on the TiO₂ ceramic coating are mainly discussed.The research on the aluminous micro-arc oxidation indicates that the ceramic coating mainly consists of α-Al₂O₃ and Y-Al₂O₃, the coating created in the electrolyte of Na₂SiO₃ and Na₂CO₃ possesses smooth surface, high micro-hardness, and good adhesion with the aluminum substrate. Thickness and surface roughness of the ceramic coating increases with the time of micro-arc oxidation. The surface roughness of the ceramic coating created in the electrolyte of Na₂B₄O₇,NaH₂PO₄,Na₂CO₃,Na₂SiO₃ is the smallest. The property of the ceramic coating becomes better with the conductance increase. The content of α-Al₂O₃ decreases with increase of the concent of Na₂WO₄.The research on titanic micro-arc oxidation indicates that the ceramic coating in acid electrolyte is mainly composed of anatase TiO₂. The content of anatase TiO₂ increases with decrease of pH of the electrolyte. There are lots of micro-holes on the ceramic coating surface. The ceramic coating created in approximate neutral electrolyte is composed of anatase TiO₂ and rutile TiO₂. The ceramic coating is mainly composed of rutile TiO₂ and a small quantity of anatase TiO₂ in the alkalescency electrolyte. The content of rutile TiO₂ increases as pH of the electrolyte increases. The ceramic coating becomes smooth and has a better cohesion with the substrate. The content of rutile TiO₂ increases while the Na₂Mo₇O₂₄ additive concentration increases.