Effects Of Voltages On The Structure And Corrosion Resistance Of Rare Earth Magnesium Alloy Micro-arc Oxidation Coatings

Rare earth alloying is one of the effective ways to improve the performance of magnesium alloys,but the second phase of rare earth usually forms a micro electric couple with the magnesium matrix,thereby inducing local corrosion of magnesium alloys.The preparation of ceramic coatings on rare earth magnesium alloys by micro arc oxidation(MAO)technology can significantly improve their corrosion resistance.When the composition and concentration of electrolyte are constant,voltage is the main factor affecting the morphology of the coatings.Therefore,studying the influence of voltage parameters on the growth and discharge of MAO coatings can provide theoretical guidance for the optimization of corrosion resistance of the coatings.In this paper,Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy was taken as the research object.By changing the voltage parameters,the rare earth magnesium alloy was treated with one-step MAO and two-step MAO in silicate and silicate+aluminate electrolyte systems,respectively,to prepare MAO films.The effects of voltage on the growth process,microstructure,element distribution,phase composition,and corrosion resistance of MAO film layers were studied using current time curves,scanning electron microscopy,X-ray diffraction,and electrochemical workstations.The main work of this article is as follows:(1)In a silicate electrolyte composed of 10g/L Na2 Si O3 and 2g/L Na OH,a one-step micro arc oxidation process was used to increase the voltage to 283.5V,304 V,352V,405 V,and 452.5V at a rate of 6.75V/s,respectively.Then,the rare earth magnesium alloy was subjected to constant voltage treatment for 5 minutes to prepare a MAO film layer.Through the analysis of the spark morphology,microstructure,phase composition,corrosion resistance,and growth mechanism of five sets of samples,it was found that when the chemical composition and concentration of the electrolyte are constant,changing the voltage parameters of one-step micro arc oxidation cannot prepare MAO film layers with large thickness,good density,and high corrosion resistance,which cannot meet the needs of practical applications.Therefore,further research is needed on the micro arc oxidation process of rare earth magnesium alloys.(2)To address the above issues,a two-step micro arc oxidation treatment was performed on rare earth magnesium alloys.During the experiment,the one-step micro arc oxidation coating was prepared as the base sample at 304 V voltage,and then the sample was subjected to the second micro arc oxidation treatment in the aluminate electrolyte composed of 10g/L Na Al O2 and 2g/L Na OH by changing the voltage parameters,and the two-step MAO coating was prepared.Through the study of the micro morphology,elements,phase,and electrochemical performance of the MAO film layer,it was found that the twostep micro arc oxidation process increased the thickness of the film layer,which to some extent improved the corrosion resistance of the MAO film layer;By analyzing the experimental results,the influence of voltage on the structure and corrosion resistance of the two-step MAO film was summarized.Among them,when the voltage is 304 V and452.5V respectively,the MAO film layer has a larger thickness,good density,and high corrosion resistance.