Characteristics Of Micro-arc Oxidation Ceramic Coating Formed In The Electrolyte Containing Potassium Permanganat On The Surface Of Alloy AZ91D

Micro-arc oxidation,which were the reactions on production of metal surface and free oxygen,need free oxygen.So,the free oxygen had a major impact on the rate of reaction and the formation of film.Silicate system,which was short of free oxygen,was one of the best widely electrolyte by used.the electrolyte containing potassium permanganat was a reliable method.Hence,study on the influences in the electrolyte containing potassium permanganat,analyse the morphology of surface of specimen,will be of great importance in high performance.In this way,ceramic coatings were obtained on the surface of AZ91D by multifunction micro-arc oxidation power supply,by controlling oxidation time or the content of KMnO₄.Their thickness,micro-hardness,wear-resisting property and corrosion resistance were measured and the phase compositions,the element of oxidation coatings and surface morphology were analyzed by XRD,SEM and EDS.The results show that the thickness and hardness of micro-arc oxide,which the positive and negative voltage are constant,film thickness and hardness increased with the increase of oxidation time.There are many holes and cracks distributed on the surface of oxidation coating,which are depletion in numbers and increased in size.There are more melting materials around the hole.Abrasion resistance and corrosion resistance are enhancement.The growth rate of oxidation coatings reduce and then decreases with the content of KMnO₄ increasing when the KMnO₄ additives are added into electrolyte.In addition,the content of KMnO₄ obviously effects on the thickness and micro-hardness of oxidation coating.The microarc oxide film layer is mainly composed of loose layer and dense layer.The layer of microarc oxide film is more uniform and the proportion of the entire film layer increases with the content of KMnO₄ increasing.The rare earth KMnO₄ in electrolyte not only enhances the electrical conductivity but also participates in the oxidation process of the oxidation coating.There is MnO₂ in the microarc oxide film,which is new phase.