Study On Corrosion Behavior Of Magnesium Alloy By Continuous Variable Cross-section Direct Extrusion

At present,magnesium alloys are considered as the most potential"green material"in the 21st century because of low density and high specific strength.In the fields of aerospace and military applications,magnesium alloys are also more and more popular.However,the standard electrode potential of magnesium alloys is low,so magnesium alloys are prone to corrosion,which limits their application greatly.Therefore,it is very important to study the corrosion resistance of magnesium alloys.For metals,most of the corrosion is electrochemical corrosion.Therefore,electrochemical method is one of the most important methods to study the metal corrosion process.However,the magnesium alloy extruded by the continuous variable cross-section direct extrusion receives strong shear stress during the extrusion process,thereby significantly refining the grains,which can effectively improve the mechanical properties of the magnesium alloy component.The electrochemical corrosion properties of the extruded magnesium alloy are evaluated by the electrochemical method,which can more comprehensively understand the effect of the continuous variable cross-section direct extrusion process on the comprehensive properties of the magnesium alloy.Therefore,it is necessary to detect the electrochemical corrosion behavior of extruded magnesium alloy.This paper studies the microstructure and corrosion behavior of AZ31magnesium alloy after continuous variable cross-section direct extrusion by means of electrochemical workstation,optical microscope?OM?,scanning electron microscope?SEM?,electron backscatter?EBSD?and transmission electron microscope?TEM?.The results show that electrochemical corrosion is an irreversible process.The charge transfer process and the material transfer and diffusion are the two main factors affecting the corrosion rate,which determine the total rate of electrochemical reaction,and the homogeneity of grain size can make the corrosion potential move towards the positive potential direction.In addition,the change of impedance diagram with time can be divided into two stages:the gradual formation of corrosion film and the thickening of corrosion layer.The main factor affecting two different directions is the thickness of the Mg O/Mg?OH?₂ corrosion layer.For the extruded magnesium alloy sheet,the corrosion in the ED-ND direction is more inclined to develop in the depth direction than the TD-ND direction,so it is easier to form pitting corrosion.The grain size is the main factor affecting its corrosion properties.Twins are a secondary factor,and the increase in the number of twins can correspondingly reduce the corrosion resistance of magnesium alloy sheets.In conclusion,the study of the influence of continuous variable cross-section direct extrusion process on the corrosion properties of magnesium alloys after extrusion can help us to better understand the comprehensive properties of extruded magnesium alloy,so that it can be better applied to a wider range of field.