Preparation And Corrosion Resistance Of Ce Micro-arc Oxidized Coating On AZ91D Surface

Magnesium alloys have good mechanical and physical properties and are widely used in aerospace,automotive electronics and many other industries.However,magnesium alloys are prone to corrosion damage during service.Aiming at this problem,this paper aims to introduce the rare earth Ce element into the micro-arc oxidation layer,and investigate the influence of various parameters on the surface morphology,element content and corrosion resistance of rare earth composite micro-arc oxidation layer by various characterization methods,improving the corrosion resistance of matrix magnesium alloy and analyze the corrosion resistance mechanism of coating.The results show that the chemical conversion,cathodic electrodeposition and micro-arc oxidation process parameters have a significant effect on the microstructure and corrosion resistance of the coating.The three ceramics are prepared by micro-arc oxidation.The optimum process parameters can be obtained by various characterizations:taking the cathode electrodeposition as the rare earth introduction process,which current density is 0.2mA/dm²,H₂O₂ concentration is 0.03mol/L,deposition time is 6 or 8min,the micro-arc oxidation parameter is 300V for 5min,the coating corrosion resistance is improved.Among them,when the deposition time is6min,the sustainable protection matrix reaches 168h,while the deposition current is8min,the corrosion current can be reduced by 2³ orders of magnitude,which pitting potential is increased to 2V or more,and the corrosion resistance is significantly improved.In the silane electrodeposition composite process,whether it is silane immersion after electrodeposition or silane is added to the electrolyte solution,the corrosion resistance of the MAO coating can be improved.Compared with the same process coating without adding silane,the silane was added to the electrolyte solution to protect the substrate for 213 hours,and the durability was further improved on the basis of168h.When the micro-arc oxidation parameter is 400V for 5min and 450V for 5min,according to the analysis of surface cross-section,line scan energy spectrum,XRD and polarization curve,the composite performance of the coating after the MAO layer is sealed for 8 min is better,and the corrosion current is lower than other coatings.Moreover,the pitting potential is also greatly improved,the sealing effect is the most significant,and the corrosion resistance is most improved.Comparing the morphology,phase composition,functional group,roughness and corrosion resistance of the micro-arc oxidation layer before and after sealing,it is shown that the main form of bismuth in the coating after 8 min sealing is CeO₂,and the corrosion current can be reduced by two orders of magnitude.The pitting potential is greatly improved,soaking in NaCl solution can resist corrosion damage up to 360h.