Study On The Preparation And Performance Of Al-Zn Coatings And Micro-arc Oxidation Ceramic Membrane

In this thesis, the Al–Zn coatings were electrodeposited on Q235steel surface fromAlCl₃-NaCl-KCl molten salts in which the different contents of ZnCl₂were added. Theinfluence of the atomic mole ratio of Al to Zn of the coatings on the properties of coatingswas studied. The surface morphology、components and structure of the coatings wereinvestigated by scanning electron microscopy （SEM）, energy dispersive spectroscopy（EDS）, and X-ray diffraction （XRD）. The polarization curves、electrochemical impedancespectroscopy、corrosion weight gain and corrosion time were performed in3.5wt%NaClsolution aiming to evaluate the corrosion resistance of the coatings. The results show thatwhen ZnCl₂was added in the molten salts, the even surface morphology of the coatingscan be obtained. The coating elements are mainly composed of Al、Zn and Fe, however thealuminum and zinc haven’t formed Al-Zn alloy but with eutectic body in the coatings.Theatom mole ratio plays an important role in the corrosion resistance of the coatings. Thethickness and hardness are perfect and corrosion resistance of the coating is excellentwhen the atomic mole ratio of Al to Zn is33.53:1.The coatings were transformed into ceramic membrane by the micro-arc oxidation.The concentration of sodium silicate、oxide voltage and oxide time on the properties ofceramic membrane were tested aiming to find the best processing parameters. The effectof the atom mole ratio and some additives on the ceramic membrane were studied. Thesurface morphology and structure of the ceramic membrane were tested by SEM and XRD.The polarization curves、electrochemical impedance spectroscopy and corrosion weightgain were investigated in3.5wt%NaCl solution to evaluate the corrosion resistance of theceramic membrane. The results show that the even surface morphology of the ceramicmembrane can be obtained at the correct processing parameters. The ceramic membrane ismainly composed of Al、Fe、Al₂O₃and Al_0.403Zn_0.597,aluminum and zinc exists in the formof Al-Zn alloy. The ceramic membrane has the best corrosion resistance、thickness andhardness when the atom mole ratio is33.53:1. That NaOH、Na₂WO₄、KMnO₄、（NH₄）₂MoO₄、NaF、rare earth added in the sodium silicate electrolyte havn’t improved thecorrosion resistance of the ceramic membrane.