Effect Of Mn And Trace Si On Corrosion Resistance Of Magnesium Alloys

Magnesium alloys have many excellent properties compared to other metals,but their poor corrosion resistance limits their application,which has caused great interest among many material researchers.Many new types of corrosion-resistant magnesium alloys containing different elements and having a surface film are also being developed.In this paper,Mg-xMn alloy and Mg-0.4Mn-0.011Fe-xSi alloy were prepared from the perspective of alloying development of corrosion-resistant magnesium alloy to study the effect of Mn and trace Si on the corrosion performance of the alloy,which is based on the impurity removal effect of Mn and considering the inevitable impurity Si in the alloy.Field emission scanning electron microscopy(SEM),transmission electron microscopy(TEM),hydrogen evolution weight loss experiments,electrochemical tests and phase diagram calculations were used to study the effects of Mn and trace Si on the microstructure and corrosion properties of magnesium alloys,and to relate the microstructure and properties to the corrosion behavior and corrosion of the alloys.The mechanism was analyzed and discussed,and the following experimental results were obtained:Corrosion test shows that the corrosion resistance of Mg-xMn(x=0,0.4,0.8,1.8,6 wt%)alloys in 3.5 wt%NaCl solution was related to Mn content.The Mn element in the alloys can change the composition of the second phase,dissolve the impurity Fe in the alloy,reduce the galvanic corrosion of the precipitated phase and the matrix,and enhance the corrosion resistance of the alloy.The corrosion resistance of Mg-0.4Mn-0.011Fe-xSi(x=0.01,0.02,0.04 wt%)alloy in 3.5 wt%NaCl solution is related to Si content,and the Si element in the alloy changes the composition of the second phase.Further,the potential difference between the second phase and the substrate is increasing,resulting in a decrease in corrosion resistance of the alloy.Microstructure observation and analysis,show that the precipitated phase in the as-cast pure Mg is mainly iron-rich particles,and the Mg-xMn(x=0.4,0.8,1.8,6 wt%)alloys were mainly composed of an ?-Mg phase and a precipitated phase of Mn(Fe).The amount and size of precipitated phase Mn(Fe)increase with the increase of Mn content,and the content of Fe dissolved in precipitated phase Mn(Fe)is different.With the increase of Si content,the main precipitation phase of Mg-0.4Mn-0.011Fe-xSi(x=0.01,0.02,0.04 wt%)alloy is transformed from Mn(Fe)phase to(Mn,Fe)Si phase.Through observation and analysis of the corrosion process of the alloys,it were found that the iron-rich particles in the as-cast pure Mg have strong ability to support hydrogen evolution,and the supporting hydrogen evolution capacity of the Mn(Fe)phase in Mg-xMn(x=0.4,0.8,1.8,6 wt%)alloy is proportional to the solid solution Fe content.The Fe content in the precipitated phase Mn(Fe)is more than 2 wt%,and the surface of the alloy forms a porous corrosion product.Conversely,a dense corrosion product is formed to inhibit alloy corrosion.The(Mn,Fe)Si phase formed by adding Si has a strong cathode activity in the Mg-0.4Mn0.011Fe-xSi(x=0.01,0.02,0.04 wt%)alloy,and the(Mn,Fe)Si phase increases in number and accelerates the corrosion of the alloy with the increase of Si content.