The Preparation And Property Of Micro-arc Oxide Films On Aluminum

Through the unilateralism pulse power,the ceramic coatings were fabricated by micro-arcoxidation on aluminum. By means of the micro-arc oxidation technique,ceramic coatings withstrong adhesion,high micro-hardness,high corrosion resistance and wear resistance can befabricated.The effect of the electrolyte and electric parameters on mechanism and properties of thecoatings was investigated by means of XRD,SEM,micro-hardness test,thicknesstest,roughness test,electrochemical methods and dropping corrosion experiment.Oxidation coating of aluminum was prepared in electrolyte with Na₂SiO₃ and NaAlO₂.The coatings prepared in the two kinds of solution consist ofα-Al₂O₃ andγ-Al₂O₃,the contentofα-Al₂O₃ prepared in sodium silicate solution is more;Many crater-mouth like productsformed by the plasma discharge and discharge channels were observed on the coatingssurface,and the discharge channels formed in sodium silicate solution closed better;Thepotentiodynamic polarization results indicate that the ceramic coatings possess excellentcorrosion resistance property and the coating prepared in sodium silicate solution has bettercorrosion-resistance.The effect of current density, duty ratio and frequency on structure and properties ofaluminum oxide coating was investigated. The coating's hardness,surface roughness and thecontent ofα-Al₂O₃ andγ-Al₂O₃ increased with the increase of current density.The thicknessand corrosion- resistance increased first and then decreased.with the increase of currentdensity.With the increase of duty ratio,the ceramic coating's thickness,hardness and surfaceroughness increased.When the duty ratio less than 0.3,the corrosion time increased with theincrease of the duty ratio.But when the duty ratio more than 0.3,the corrosion timedecreased.When the duty ratio was 0.3,the ceramic coating had best corrosion resistance.Theinfluence of frequency on the coating's hardness and roughness was little.When the frequencywas 5000 Hz,the coating had best thickness and corrosion resistance.The parameters was optimized by means of orthogonal design.The optimal parameterwas that the current density was 10 A/dm²,the frequency was 5000Hz,the duty ratio was60%,the concentration of Na₂SiO₃ was 12g/L.