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

At present, a large-scale used biomedical magnesium alloys mainly include AZ31,WE43 etc. However, the Al element may cause dialysis encephalopathy syndrome, alzheimer s disease and other degenerative neurological diseases, which is considered as a non-essential trace element of low toxicity. As reported in previous investigation, the hemolysis rate of Mg-Zn system alloys is high, so it is not suitable for direct contact with the blood. Hence we make an effort to develop a new Mg-Sn-Mn system, which have high potential as a possible biodegradable magnesium implant material, and exhibits non-toxic, controlled degradation and high strength and toughness. The phase constituents, microstructures, mechanical properties and corrosion resistance of the alloys were investigated by means of X-ray diffraction (XRD) analysis, optical microscopy (OM) analysis, tensile test, scanning electron micropy(SEM) and electrochemical device.The results show that the microstructure of the as-rolled Mg-Sn-Mn alloy are more uniform and finer.The as-cast Mg-Sn-Mn alloy consists of a-Mg, Mg2Sn and MnSn2 phases. After solution heat treatment, the second phases have dissolved into a-Mg matrix, resulting in the formation of the solid solution consisting only of the singleα-Mg phase.-However, the second phases precipitated again after hot rolling, and thus the as-rolled Mg-Sn-Mn alloy still consists of a-Mg, Mg2Sn and MnSn2 phases.After holding at 400℃for different times, phase constituents and combined mechanical properties have been investigated, the results show that the optimum parameters used for solution heat treatment:holding at 400℃for 24h, followed by water quenching.The combined mechanical properties of as-solution treated alloy have declined.But the combined mechanical properties of as-rolled alloy is best, and the hardness ranges between 52 and 72, the tensile strength of about 200Mpa and the elongation of 20% are achieved, respectively.The main reason is that recrystallization have occurred during rolling and the second phase uniformly distributed.These three states of the alloy are ranked according to the degree of corrosion resistance, from high to low:as-rolled, as-solution treated, followed by as-cast. The corrosion resistance of the as-cast alloy is low due to the segregation. Because of the grain boundary area reduced and the second phase disappearance, the corrosion current density of as-solution treated decrease. On the contrary, the as-rolled alloy has the best corrosion resistance due to the grain become finer and the second phase distribute more uniform.Compared with the combined mechanical properties of different alloys in different states, it s found that Mg-3Sn-0.5Mn have the best combined mechanical properties and corrosion resistance after rolled, which is expected to become the new biodegradable stent materials.The hemolysis rate of TM30 alloy completely meets the requirements of bio-medical materials(less than 5%). The absorbance value of the as-cast, as-sloution heat treated and as-rolled TM30 alloys continue to decline, but the trends is relatively gentle. The absorbance value all are higher than 0.1. The results show that no evident blood coagulation occur, the as-rolled TM30 alloy have the best anticoagulant properties.