The Research On Corrosion Resistance Of AZ91D Micro-arc Oxidation Ceramic Membranes Prepared From Zirconium And Silicate Electrolytes

Magnesium alloys have the characteristics of low density,high specific strength,and high specific rigidity,however,the poor corrosion resistance greatly limits its application.The micro-arc oxidation technology is based on the traditional anodizing,using this technology can significantly improve the corrosion resistance of magnesium alloys.This article takes AZ91D magnesium alloy as the research object,magnesium alloys were micro-arc oxidized in selected silicate and zirconium electrolytes,respectively,obtained the growth rule of ceramic membrane with processing voltage and holding time;the micro-hardness,roughness,micro-morphology and composition of the obtained ceramic membrane were analyzed by hardness tester,surface roughness measuring instrument,scanning electron microscope and X-ray diffractometer;the corrosion resistance of micro-arc oxidation ceramic membranes with different thicknesses was discussed by spotting,soaking and electrochemical analysis.The results show that:in both electrolytes,the thickness of the ceramic membranes increases with the increase of the processing voltage,change from rapid growth to slow growth over time;The hardness and roughness of ceramic membranes increase with the thickness;The pores of the ceramic membranes?MS30?prepared in the silicate electrolyte are not uniform,the pores of the ceramic membranes?MZ30?prepared in zirconium electrolyte are uniform;The main compositions of MS are MgO?MgF₂?Mg₂SiO₄;The main compositions of MZ are MgO?MgF₂?Mg₂Zr₅O₁₂.In the drop corrosion test,the time from the reddish to the colorless change of the etching solution increases with the increase of the thickness of the MS samples,increase first and then decrease with the increase thickness of the MZ samples;In the soak corrosion test of3.5%NaCl solution show that the pitting and spalling of MS10 and MZ30 samples are the most serious;Polarization curve analysis shows that the corrosion current density of MS samples gradually decreases with increase thickness,and the polarization resistance increases gradually.The corrosion current density of MZ samples first decreases and then increases with the increase of thickness,the polarization resistance increases first and then decreases,that is,when the thickness of the ceramic film does not exceed 30?m,the corrosion resistance of the MS samples increases with increasing thickness.The corrosion resistance of MZ samples increases first and then decreases with increasing thickness.The equivalent circuit of AC impedance map can be known that the charge transfer resistor R_L and the dense layer resistance R_C in MS have a major hindrance to the etching solution.the compact layer resistance R_C in MZ has major impediment to the etching solution.