Effect Of Gd Addition On The Corrosion Resistance Of ZM61 Magnesium Alloy

As the lightest metal structural material,magnesium alloy has many advantages,such as light weight,high specific strength and specific stiffness,unique damping and vibration reduction,and excellent casting performance,which makes it become one of the most promising new structural materials in the contemporary era.However,compared with steel,aluminum,titanium and other structural materials widely used at present,magnesium and its alloys still have a certain gap in performance.In particular,low absolute strength and poor corrosion resistance become the most important factors restricting the further development of magnesium and its alloys.At present,alloying method is often used in scientific research and industry to improve the mechanical properties of magnesium alloys.Among them,gadolinium?Gd?,as one of the most important rare earth elements,can improve the plasticity of magnesium alloys to some extent,but the effect of the addition of Gd on the corrosion resistance of magnesium alloys is still unclear.In order to explore the influence of the addition of Gd on the corrosion resistance of magnesium alloy,the ZM61-xGd magnesium alloy containing 0,0.2,1.0,3.0 and 6.0 Gd content?wt%?was prepared by adding rare earth Gd to ZM61 magnesium alloy as the matrix alloy in this study.The microstructure of ZM61-xGd magnesium alloy in different states was systematically characterized by means of OM,SEM,EDS and XRD phase analysis.At the same time,weight-loss test,hydrogen evolution test and electrochemical experchemical?Polarization Curve,OCP,EIS?were used to test the corrosion performance of the alloy.The influence mechanism of the addition of rare earth Gd on the corrosion resistance of the alloy was studied by systematically analyzing the corrosion performance of the samples and the microstructure characteristics of the surface before and after the corrosion test.The conclusions are as follows:?1?Rare earth Gd element can effectively reduce the grain size of ZM61-xGd magnesium alloy,and the grain size tends to decrease with the increase of the amount of Gd element added.At the same time,the type and amount of the second phase in the alloy also increase,and in addition to Mg₇Zn₃,the I phase?Mg₃Zn₆Gd?and W phase?Mg₃Zn₃Gd?containing Gd element begin to appear.?2?The influence of the addition of Gd elements on the corrosion resistance of as-cast ZM61-xGd magnesium alloy tends to increase first and then decrease?ZM61-1.0 Gd>ZM61-0.2 Gd>ZM61>ZM61-3.0 Gd>ZM61-6.0 Gd?.In the as-cast ZM61-xGd magnesium alloy,when the content of Gd element does not exceed 1.0wt%,the grain refinement can promote the uniform overall corrosion of the magnesium alloy to a certain extent,and the netted second phase formed on the grain boundary can effectively prevent the corrosion from continuing,so as to improve its corrosion resistance.However,when the content of Gd element exceeds 1.0wt%,the type and content of the second phase increase,and the distribution area increases,forming more areas of micro-galvanic corrosion,and the corrosion resistance decreases.?3?The addition of Gd element reduces the corrosion resistance of extruded ZM61-xGd magnesium alloy,the extrusion process can effectively prevent the meshed second phase breakage that is further corroded and distributed in the matrix along the extrusion direction.The number of corrosion couple increases,so the corrosion rate increases and the corrosion resistance decreases.ZM61>ZM61-3.0 Gd>ZM61-6.0 Gd>ZM61-0.2 Gd>ZM61-1.0 Gd.?5?The addition of Gd element reduces the corrosion resistance of ZM61-xGd magnesium alloy in two-stage aging state,and shows a certain linear relationship.During the two-stage aging process of ZM61-xGd magnesium alloy,a large number of fine and dispersed granular second phases were precipitated in the grain boundary and within the crystal,which increased the area where the micro-galvanic corrosion occurred and decreased the corrosion resistance.The corrosion resistance trend is as follows:ZM61>ZM61 0.2-Gd>ZM61-1.0Gd>ZM61-6.0 Gd>ZM61-3.0 Gd...