Preparation And Performance Research Of Biomedical Mg-2Zn-0.2Mn Magnesium Alloy

Mechanical strength and biological inertia are no longer the most important focus for Biomedical materials.While substitute the tissues and organs and play the functions,induce tissue repairing and regeneration,the implant should gradually degrade and absorb in the process of tissue repair,which has become a new trend in the research and development of regenerated tissues.Magnesium alloys have been considered as suitable regenerative material,however the limitation of magnesium alloy is that the corrosion rate is too fast and the strength and plasticity are not enough to meet the requirement of mechanical properties of implants.Extrusion deformation can effectively improve the microstructure,mechanical properties and corrosion resistance of magnesium alloy.The effects of extrusion temperature and extrusion ratio on the microstructure and properties of Mg-2Zn-0.2Mn magnesium alloy are studied in this paper.When the extrusion ratio is low,the microstructure of magnesium alloy is bimodal structure with coarse banded deformation grains and fine recrystallized grains,resulting in poor plasticity.With the increase of extrusion ratio,the degree of grain recrystallization in magnesium alloy increases.Plasticity of magnesium alloy is effectively improved with the grain homogenization and random orientation of recrystallized grains.With the increase of extrusion temperature,some recrystallized grains grow abnormally and reduce the microstructure uniformity,the plasticity and strength of the alloy are reduced.The magnesium alloy bar extruded at extrusion ratio λ=17.6 temperature T=300℃ has the best comprehensive properties,and the average grain size is about 6 μ m.The tensile strength is266 MPa and the elongation is 32.3%.The magnesium alloy bar extruded at extrusion ratio λ=17.6,extrusion temperature T=300℃ was subjected to secondary extrusion,and its microstructure,mechanical properties and corrosion properties were studied by microstructure observation,tensile test,electrochemical test and in vitro simulated body fluid degradation test.The secondary extrusion further refined the microstructure of magnesium alloy,the strength and corrosion resistance of magnesium alloy with the fine and uniform grains are effectively improved.The tensile strength of Mg-2Zn-0.2Mn alloy extruded at extrusion ratio λ=4,extrusion temperature T=250℃ is increased to 327 MPa and the elongation is 14.8%.The average corrosion rate was1.72 mm/y after immersion in simulated body fluid for 168 h.The secondary extrusion of Mg-2Zn-0.2Mn alloy extruded at extrusion ratio λ=4extrusion temperature T= 250℃ can effectively eliminate a large number of dislocations and residual stresses caused by extrusion deformation after annealing at 160℃ for 8h.While the strength decreased slightly,the corrosion resistance of magnesium alloy was further improved.Mg-2Zn-0.2Mn magnesium alloy material with tensile strength of 315 MPa,elongation of17%,average corrosion rate of 1.39 mm/y after immersion in vitro for 168 h and was obtained.The cytotoxicity experiment of the prepared magnesium alloy material showed that the cells showed very mild cytotoxicity when cultured in 75% and 50% concentration extract for 3 days,but the cytotoxicity disappeared with the extension of culture time,and the extract below 75%concentration can promote the growth of cells.