Research On Preparation And Performance Of Biodegradable Mg-Zn-Ca(Sn) Alloys

Magnesium alloys exhibit distinctive chemical and mechanical properties,as well as good biocompatibility and biodegradability,which makes them as bio material have obvious advantages and wide potential applications.Metallic alloys with chemical composition around the deep-eutectic point would possess high glass forming ability.On the basis of the deep-eutectic principle,composition design of Mg-Zn-Ca ternary amorphous alloys was performed by phase diagram calculation using Pandat software and the thermodynamic database for Mg alloys.The master Mg-Zn-Ca alloys were prepared by medium frequency induction furnace and the ternary amorphous alloys were prepared by single copper roller melt-spinning technique.Phase composition and glass forming ability(GFA)were analyzed by X-ray diffraction and differential thermal analysis.Corrosion behavior of the studied alloys was tested through electrochemical method in simulated body fluid.Based on the research results of Mg-Zn-Ca alloys,the effect of Sn on GFA and corrosion behavior of Mg-Zn-Ca alloys were investigated.Phase diagram calculation results showed that deep-eutectic point temperature of Mg-Zn-Ca system was 257 ? with a chemical composition of Mg-33 at.%Zn-9 at.%Ca.Mg-33Zn-7Ca and Mg-33Zn-10Ca alloys were also designed to verify the calculation results.The strmp specimens of the three alloys obtained at the roller speed of 40 m/s were entirely amorphous.But when roller speed decreased to 30m/s,the phase compositions of the studied alloys were composed of amorphous matrix and tiny amount of CaZn2 crystal phase.The results of XRD and DSC,and calculation results of Gibb is free energy and Kissinger's method demonstrated that Mg-33Zn-7Ca alloy possessed the strongest GFA.The electrochemical test results showed that,for the as-cast master alloys,corrosion resistance increases with the increament of the content of Ca.The Mg-33Zn-10Ca alloy was the most corrosion resistant among the three alloys,with the corrosion potential of-1.36 V and corrosion current density of 215?A/cm2.Corrosion resistance was greatly improved by rapid solidification.The corrosion resistance of the amorphous specimens increased with the increasing amount of Ca and Mg-33Zn-10Ca amorphous specimen showed the best corrosion resistance.Corrosion potential and corrosion current density of the Mg-33Zn-10Ca amorphous specimen was-0.97 V and 9.22?A/cm2,which were enhanced by 30 tims compared to the corresponding values of the as-cast alloy.Based on the phase diagram calculation result of Mg-Zn-Ca system,different amount of Sn elements was added to the deep-eutectic alloy to investigate the effect of Sn addition on the GFA and corrosion behavior.The results showed that strip specimens obtained at the roller speed of 40 m/s were all entirely amorphous.While for the strip specimens obtained at the roller speed of 30 m/s,free Sn alloy was composed of amorphous matrix and small amount of CaZn2 crystal phase.Alloys containing Sn element were entirely amorphous,indicating that the addition of Sn enhance the GFA of Mg-Zn-Ca alloy.However,as content of Sn further rose from 0.25at%to 0.75at%,the glass-forming ability improvement was not obvious.The electrochemical test results showed that with the increase of Sn,the corrosion current density of as-cast alloys increased gradually from 268?A/cm2 of Mg-33Zn-9Ca alloy to 524?A/cm2 of(Mg-33Zn-9Ca)-0.75Sn alloy.Corrosion current density of the(Mg-33Zn-9Ca)-0.75Sn amorphous specimen was 142?A/cm2,which were enhanced by 3 tims compared to the corresponding values of the as-cast alloy.Corrosion resistance of the amorphous alloys were higher than the as-cast ones,but decreased with increasing amount of Sn element.