Study On Microstructure And Properties Of Biomedical Mg-Sn-Zn-Mn Alloy

At present, a large-scale used biomedical magnesium alloys mainly include AZ31、WE43etc. However, the Al element may cause dialysis encephalopathy syndrome, alzheimer’sdisease and other degenerative neurological diseases, which is considered as a non-essentialtrace element of low toxicity. As reported in previous investigation, the hemolysis rate of theMg-Zn alloys is high, so it is not suitable for direct contact with the blood. Hence we make aneffort to develop a new series of Mg-Sn-Zn-Mn alloys, which have high potential as apossible biodegradable magnesium implant materials, and exhibit non-toxic, controlleddegradation and high strength and toughness. The phase constituents, microstructures,mechanical properties and corrosion resistance of the alloys were investigated by means ofX-ray diffraction （XRD） analysis, optical microscopy （OM） analysis, tensile test, scanningelectron micropy （SEM） and electrochemical device.The results show that the microstructures of the as-cast alloy consist of coarse dentriteswhile grains of the as-solution treated alloys are equiaxed irregularly, and the grains of theas-rolled alloy are more uniform and finer. The as-cast alloy consists of-Mg，Mg₂Sn andMgZn phases. After solution heat treatment, the second phases have dissolved into-Mgmatrix, resulting in the formation of the solid solution consisting only of the single-Mgphase. However, the second phases precipitated again after hot rolling, and thus the as-rolledMg-Sn-Mn alloy still consists of-Mg，Mg₂Sn and MgZn phases.After holding at400℃and450℃for different times, phase constituents and combinedmechanical properties of the Mg-Sn-Mn alloy have been investigated, the results show thatthe optimum parameters used for solution heat treatment: holding for24h at400℃for TZ31and24h,450℃for TZM310respectively, followed by water quenching.The microhardness （HV） and strain data reveal that the combined mechanical propertiesof as-solution treated alloy are best, the HV reaches between57.86, the tensile strength to217.3MPa and the elongation of27.8%is achieved, respectively. The main mechanisms areattributed to solid-solution strengthening and improved ductility induced by twinning. Thesethree states of the alloy are ranked according to the degree of corrosion resistance, from highto low: as-solution treated, as-rolled, followed by as-cast. Because of the grains become finer and the second phases distribute more uniformly, as-rolled alloy has higher corrosionresistance; On the contrary, corrosion resistance of the as-solution treated alloy is best due toreduced grain boundary areas and dissolution of the second phases. The addition of Mn canremove the influence of harmful ion on the corrosion resistance. The hemolysis rate ofTZM310alloy completely meets the requirements of biomedical materials（less than5%）.Because high corrosion resistance of the alloy reduced the concentration of Mg²⁺ in blood.Compared with the combined mechanical properties of two alloys in different states, it’sfound that Mg-3Sn-1Zn-0.5Mn have the best combined mechanical properties and corrosionresistance after rolled, which is expected to be used for the new biodegradable stent materials.