Effects Of KMnO₄ And Substrate Crevice Morphology On The Growth And Corrosion Resistance Of Micro-arc Oxidation Coating

In this work,the influence of potassium permanganate additive?KMnO₄?on the growth and corrosion resistance of micro-arc oxidation?MAO?coating formed on AA1060 pure aluminum substrate was studied by analyzing the differences in the oxidation behavior,structure,phase composition and corrosion resistance of the coatings obtained in silicate electrolyte with and without KMnO4 under a constant current mode.Moreover,the effects of crevice morphology in the AZ31 magnesium alloy substrate on the growth and corrosion resistance of MAO coating prepared by constant current mode were also investigated by analyzing the evolutions of the structure,phase composition and corrosion resistance of the coatings with the changing of the crevice widths.Meanwhile,the effects of current density and auxiliary ultrasonic treatment on the thickness of MAO coating were explored.The investigation on the effect of KMnO₄ additive on the micro-arc oxidation coating formed on AA1060 pure aluminum shows that the addition of KMnO4 in the electrolyte can reduce the electric field intensity distributed in the coating during the MAO process;At the same time,the oxidation behavior of the coating is changed by reducing the B-type discharge intensity and promoting the establishment of the C-type discharge.As a result,the surface roughness of the coating is reduced,the density of the coating and the uniform distribution of Si elements are enhanced;The addition of KMnO₄ inhibites the formation of crystal phase and enhances the content of amorphous phase in the coating;The electrochemical test results show that KMnO4 additive can improve the corrosion resistance of the MAO coating effectively.The study on the influence of substrate crevice morphology on the micro-arc oxidation coating prepared on AZ31 magnesium alloy shows that when the crevice width is 350?m,the crevice coating has the typical morphology like the coating prepared in the traditional silicate electrolytes,and possesses the larger coating thickness and excellent corrosion resistance.When the crevice width is less than 350?m,the crevice width has a significant effect on the coatings in the structure and corrosion resistance,that is,the coatings present the characteristics of low thickness,large porosity,and more defects?which increase as the crevice width decreases?.In a short time,the corrosion resistances of the crevice coatings exceed that of the substrate when the crevice width is 200?m,250?m and 300?m.However,the crevice coating has the best corrosion resistance in a long-time corrosion test when the crevice width is 350?m.The enhancement of current density and the introduction of ultrasound treatment during the MAO process are beneficial to the growth of the coating in the crevice on the substrate.