Characterization Of MAO Ceramic Coatings On The Surface Of ZAlSi12Cu2Mg1in The Electrolyte Of NaOH-mSiO₂·nH₂O

ZAlSi12Cu2Mg1is multielement alloy with aluminum, silicon, magnesium andmanganese; it is widely used due to better casting performance, smaller thermal expansioncoefficient and higher thermal performance. But it is easy to form concentrated shrinkagecavity, poor wear resistance and hardness, which cannot be directly used for friction parts.The characteristics can be improved with Al2O3coatings formed on its surface by MAOtechnique and expand its serviceable fields. Highlight problem of common silicate electrolyteis coating growth rate increasing with quality of Na2SiO3concentration, thus results inrougher surface and lower quality. Hence, developing a new formula for electrolyte will playan important part in theory and engineering.In this work, ceramic coatings were fabricated on ZAlSi12Cu2Mg1alloy by micro-arcoxidation power, type WHD-30, in NaOH-mSiO₂·nH₂O electrolyte system. The basiscompositions were selected by characterization of coatings with variation of NaOH andmSiO2nH2O content. Ceramic coatings with vary properties were obtained by adjusting theparameters of power supply, the performance test and organization analysis were applied toresearch variation of characteristics.The results show that the thickness of ceramic coating rises with the content ofmSiO2nH2O in the electrolyte increasing from0.5g/L to2.5g/L, and ceramic coating hasbeen obtained in electrolyte with compositions of2.0g/LmSiO2nH2O+2.75g/L NaOH+2g/LNa2EDTA by MAO at420/120V forward/reverse voltage and100Hz power frequency treatedfor50min. Spherical particles with uniform size on the surface of ceramic coating have beengrown completely. Both pores and micro-cracks on this coating surface were less than that ofany other oxide coatings. The ceramic coating was mainly composed of mullite, γ-Al2O3phase and Al2O3with crystal structure of rhombohedral, but no diffraction peaks of matrixelement Al and Si have been found in the spectrum, which indicated that the density of thefirm was better.The characteristics of the ceramic coating obtained in base electrolyte with differentforward voltage, reverse voltage and power frequency have been investigated. The thicknessof ceramic coatings and the average size of particle were increased slightly while forwardvoltage varied from390V to430V and reverse voltage was120V. However, the thickness andthe number of particles on the firm was increased, hole diameter reduced and quantity was bigger while reverse voltage varied from60V to80V and forward voltage was420V. With theincreasing of power frequency, thickness declined gradually but film qualities got better. Theceramic coating was also mainly composed of mullite, γ-Al2O3phase and Al2O3with crystalstructure of rhombohedral.