Effect Of Zr And Nd Addition On The Mechanical Properties And Corrosion Resistance Performance Of Mg-Zn-Ca Alloy

As Mg-Zn-Ca alloy has high strength and stiffness, it’s elastic modulus is similar to thatof human bone’s and it also has good biocompatibility, becoming a hot research field ofmedical alloys nowdays. However, the mechanical properties and corrosion resistance of thisseries alloy has not yet reached the standard of application, according to related research,theaddition of Zr and Nd into magnesium alloys can significantly improve the microstructure,and improve the mechanical properties and corrosion resistance performance at the sametime.In this article, cast and soluted treated Mg-4Zn-0.5Ca-xZr and Mg-4Zn-0.5Ca-xNdalloys have been prepared, tested and analysised. Analysed the impact of alloying elementsand solution treatment on microstructure through metallographic, SEM, EDS and XRDexperiment; Analysed the impact of changes of microstructure on the mechanical propertiesthrough tensile testing and observed fracture morphology; Analysed the effect of changes ofmicrostructure on corrosion resistance performance through observing corrosion morphology,hydrogen collection experiments and electrochemical test. The main conclusions are asfollows:1) The mirostructure of as-cast Mg-4Zn-0.5Ca-xZr alloy are composed of α-Mg,Ca2Mg6Zn3phase and Zr elemental phase, with the increasing the content of Zr, grain areconstantly refined, large amount of Ca2Mg6Zn3phase from the internal and boundary ofgrain have integrated into matrix after solution treatment,small amount of Mg2Zn3phasealso appeared in the interal grains; With the increasing of the content of Zr, the mechanicalproperties of as-cast Mg-4Zn-0.5Ca-xZr alloy are continuously improved, when the contentof Zr reached0.8wt.%, yield strength reaches the maximum of126MPa, when the content ofZr reached0.5wt.%, the tensile strength and elongation rate reaches the maximum of197MPa and16%respectively,after the mechanical properties of this alloy get furtherimprovement after solution treated,when the content of Zr reached0.5wt.%,the yieldstrength and tensile strength reached the maximum of146MPa and243MPa respectively,when the content of Zr reached0.2wt.%,the longation reached the maximum of18.1%;With the increasing of the content of Zr,the corrosion resistance performance of as-castMg-4Zn-0.5Ca-xZr alloy is significantly increased,when the content of Zr reached0.5wt.%,the hydrogen evolution rate and corrosion current density reaches the minimum of0.0177 ml/cm2·h and6.18μA·cm-2respectively, the corrosion potential reaches the maximum of-1.51V, this kind of alloy has the best corrosion resistance performance,the corrosionresistance of this alloy get further improvement after solution treated, when the content of Zrreached0.5wt.%, the hydrogen evolution rate and corrosion current density reaches theminimum of0.0166ml/cm2·h and5.164μA·cm-2respectively, the corrosion potential reachesthe maximum of-1.492V.2) The microstructure as-cast Mg-4Zn-0.5Ca-xNd alloy are composed of α-Mg,Ca2Mg6Zn3phase, Mg2Zn3phase and Mg12Nd phase, with the increasing the content of Nd,rain are constantly refined, many small dendrites appered, overall microstucture changefrom dendritic to equiaxed crystal,part of Ca2Mg6Zn3phase and Mg2Zn3phase from grainboundary integrated into matrix after solution treatment,the grain boundary becomesdiscontinuous,and dendrite disappeared;With the increasing of the content of Nd, themechanical properties of as-cast Mg-4Zn-0.5Ca-xNd alloy are continuously improved, whenthe content of Nd reached2wt.%, yield strength, tensile strength and elongation rate reachesthe maximum of110MPa,192MPa and14.4%respectively, the mechanical properties ofthis alloy get further improvement after solution treated, when the content of Nd reached2wt.%, the yield strength, tensile strength and elongation rate reaches the maximum of135MPa、227MPa and16.9%;With the increasing of the content of Nd,the corrosionresistance performance of as-cast Mg-4Zn-0.5Ca-xNd alloy is significantly increased,whenthe content of Zr reached2wt.%, the hydrogen evolution rate and corrosion current densityreaches the minimum of0.0261ml/cm2·h and12.22μA·cm-2respectively, the corrosionpotential reaches the maximum of-1.462V, this kind of alloy has the best corrosionresistance performance,the corrosion resistance of this alloy get further improvement aftersolution treated, when the content of Nd reached2wt.%, the hydrogen evolution rate andcorrosion current density reaches the minimum of0.0155ml/cm2·h and10.42μA·cm-2respectively, the corrosion potential reaches the maximum of-1.338V.