Study On Plastic Forming Modification Of High Toughness Mg-Sc-Yb-Mn-Zr Alloy And Its Mechanical Properties And Biodegradation

Biomedical magnesium alloys have received extensive attention in the field of medical materials due to their good mechanical compatibility,biocompatibility and biodegradability.However,the difficulties in precise formation of implanted devices,excessive degradation rate in vivo,and insufficient mechanical strength of magnesium alloys have restricted the application of magnesium alloys in the field of biomedical.Therefore,improving the mechanical properties and corrosion resistance of biomedical magnesium alloys has become one of the research hotspots of scientists.In response to this problem,this article takes the rare earth magnesium alloy with Mg-6Sc-3Yb-1Mn-0.5Zr as the research object.The magnesium alloys in different states have prepared by metal mold casting,homogenization heat treatment,equal channel extrusion composite deformation,rolling and post-rolling annealing processing.The effects of different treatment processes on the structure and properties of biomedical magnesium alloy were studied and analyzed by optical microscope(OM),scanning electron microscope(SEM),X-ray diffractometer(XRD),universal tensile testing machine,and electrochemical workstation.At the same time,the effect of equal channel extrusion composite deformation on the grain orientation and texture of the alloy were analyzed by the electron backscattering technology(EBSD).The ideas and methods for improving the ductility and corrosion resistance of biomedical magnesium alloy materials are discussed.Through a series of studies,the following conclusions have been reached:1.After the heat treatment,the toughness of the alloy is obviously enhance d,but the strength and corrosion resistance have decreased.First,the toughness is greatly enhanced,and the yield strength has decreased.After heat treatment,the elongation of the alloy reached 28%,an increase of 15%,but the yield strength and tensile strength fell to 69 MPa and 151 MPa,respectively,a decrease of 32%and 2%.Second,corrosion resistance has decreased,after heat treatment,the corrosion current density increased from 0.463 mA/cm~2 to 0.866 mA/cm~2.2.Equal channel extrusion composite deformation significantly improves the mechanical properties and corrosion resistance of the alloy.After the compound deformation of equal channel extrusion,the microstructure of the alloy is more uniform and fine,the strength is significantly improved,and the corrosion resistance is enhanced.The average grain size of the alloy was reduced from 50μm to about 3μm;the yield strength and tensile strength of the alloy increased to about 200 MPa and 280 MPa on average,which were 208%and 88.5%higher than that of the homogeneous alloy,but the average elongation reduced to about 15%;corrosion current density decreased by 38%on average.Among them,the alloy with forward extrusion+375℃ECAP composite deformation has the best mechanical properties and corrosion resistance,with yield strength,tensile strength and elongation reachin g 250MPa,307 MPa and 14.6%respectively.3.After ECAP,grain orientation and texture has also changed significantly.The EBSD experimental results show that,compared with normal extrusion,most of the grain orientation changed from?to?and??,and the alloy texture component changed from*+?and*?+to*+?silk texture and*+??rare earth texture,in which the strength of the silk texture decreased significantly.Therefore,ECAP deformation not only changes the texture composition,but also significantly weakens the silk texture.4.Rolling at different temperatures has a significant effect on the strength and corrosion resistance of the alloy.First,the rolling significantly improved the alloy strength and corrosion resistance,but the alloy elongation decreased.After rolling,the yield strength and tensile strength of the alloy increased by an average of 183%and 55%,the elongation decreased by an average of 82%,and the corrosion current density decreased by an average of 34%.Second,with the rolling temperature increased,the alloy strength increased,orrosion resistance decreases,elongation is almost unchanged.Among the 350℃,400℃,and 450℃rolling temperature of homogeneous alloys,after 450℃rolling,the alloys have the highest strength,and the yield strength and tensile strength reach 218 MPa and 250 MPa,respectively,which are 210%and 65%higher than homogeneous alloys.After 350℃rolling,the corrosion resistance of the alloy is the best,and the corrosion rate is 1.98 mm/a.In summary,increasing the rolling temperature can enhance the strength of the alloy,but reduces the corrosion resistance of the alloy.5.Annealing at different temperatures has a significant effect on the strength and corrosion resistance of the alloy.Studies have shown that with the annealing temperature increases,alloy strength decreases,alloy toughness increase,and corrosion resistance decreases first and then increases.Among the annealing treatments at 250℃,300℃,and 350℃for 1 hour,the alloy,after 250℃annealing treatment for 1 hour,has the highest strength,and the yield strength and tensile strength are 229 MPa and 280 MPa,which are 15.6%and 18.1%higher than those of the rolled alloy.The alloy,after 350℃annealing treatment for 1h,has the best toughness and corrosion,elongation is 12%,which is 5.5%higher than that of rolled alloy,and the corrosion rate is 1.26 mm/a.In summary,annealing at a suitable temperature can improve both mechanical properties and corrosion resistance,but excessively high annealing temperatures actually reduce mechanical properties.