Preparation And Corrosion Behavior Of Biodegradable Mg-Zn-Mn-Ca Alloys

Magnesium and its alloys have attracted extensive attention from all walks of life due to their low density,high specific strength,and high specific stiffness.In attention,Magnesium alloy also has good biocompatibility.It has the elastic modulus similar to human skeleton,which can promote the formation of human endoskeleton.The characteristics of Mg alloy,such as biocompatibility,non-toxicity and in vivo degradation,make it have a wide application prospected and important significance in biomedical field.However,fast degradation rate and poor corrosion resistance limit the further development of Mg alloy in the biomedical field.In this research,Zn,Mn and Ca which are harmless to human body,are chosen as alloying elements in Mg alloy.The effect of Ca and Mn on the microstructure and corrosion properties of Mg alloy are studied.Optical microstructure（OM）and X-ray diffractometer（XRD）are used to observe the microstructure and phase analysis of the alloys with different compositions.The corrosion morphology of Mg alloy samples was analyzed by scanning electron microscopy（SEM）.The corrosion mechanism of Mg-Zn-Mn-Ca alloy with different components in simulated body fluid（SBF）solution was analyzed by weight loss method and electrochemical test.The results show that the corrosion resistance of Mg-4Zn alloy is improved by inducing x Mn（x=0,0.2,0.5,1 wt.%）and x Ca（x=0,0.2,0.5,1 wt.%）elements into the alloy,and that the Mg-4Zn alloy with 0.2 wt.%Ca and 1 wt.%Mn has the best corrosion resistance in SBF solution.The effect of extrusion deformation on the microstructure and corrosion properties of the alloy was also studied.The as-cast alloy was extruded into bars with a diameter of 10 mm at 260℃,6 mm/min and the extrusion ratio of 16:1.It is found that the microstructure of the extruded alloy is refined.However,due to the incomplete dynamic recrystallization,there are still many unrefined grains in the alloy and the corrosion resistance of the extruded alloy is lower than that of the as-cast alloy.The grains and the second phase were refined by subsequently muti-pass ECAP.Results show that the microstructure of alloys after 8 passes of ECAP deformation is refined and more uniform than that of the extruded alloy.The corrosion resistance in SBF solution by electrochemical testing technology,immersion test and the observation of microstructure and morphology of corrosion products.The relationship between microstructure characteristics,Mg matrix behavior and corrosion product performance was revealed.The results show that the microstructure of the alloy is refined and the corrosion resistance is improved with the increase of extrusion passes in SBF solution.The corrosion resistance of Mg alloy after 8 passes ECAP deformation is the best,which shows smaller I_corr and larger R_ct R_f values.With the extension of immersion time,passive film will be formed on the surface of the alloy,so as to protect the matrix and avoid further corrosion of the alloy.The surface corrosion is mainly pitting corrosion,indicating that Ca²⁺,HCO^3-and HPO₄^2-in SBF reduced the corrosion rate of Mg alloys.