Effects Of Pulsed Magnetic Field On The Microstructure,mechanical Properties And Corrosion Behavior Of Biomedical Magnesium And Its Alloys

As a potentially medical degradable material,magnesium and its alloys have been investigated extensively in recent years due to their excellent biocompatibility and mechanical compatibility.However,the corrosion resistance and mechanical properties of magnesium and its alloy are still not quite qualified for clinic applications.Applying pulsed magnetic field(PMF)to the solidification of metals during casting for improving microstructure and properties of materials has become one of the most promising new techniques in recent years.PMF process has several advantages such as simple equipment,easy operation,high efficiency as well as low pollution because of the non-contact with the melt.PMF was imposed during solidification of medical degradable magnesium and its alloys in order to improve their corrosion resistance and mechanical properties.The effects of PMF on the solidification microstructure,mechanical properties and corrosion behavior of pure magnesium,Mg-7Zn alloy and Mg-0.6Cu alloy were discussed in the present work.The main contents and conclusions of the dissertation are as follows:The solidification macrostructure of the pure magnesium treated by PMF was improved.With the increase of discharging voltage,the area of equiaxed crystal zone in the pure magnesium treated by PMF was further increased in general and the equiaxed grain size was gradually reduced.The ultimate tensile strength and elongation of pure magnesium were further increased with the increase of discharging voltage.When the discharging voltage increased to 300 V,both the ultimate tensile strength and elongation of pure magnesium increased a maximum.Both immersion and electrochemical experimental results indicated that the corrosion resistance of the pure magnesium treated by PMF in SBF solution at 37 oC was improved.With the increase of discharging voltage,the hydrogen evolution rate,corrosion rate and corrosion current density of pure magnesium were gradually decreased,and the corrosion potential of pure magnesium,meanwhile,gradually moved towards positive direction.The solidification microstructure of the Mg-7Zn alloy with PMF treatment was improved.With the increase of the discharging voltage,the grain size of the primary α-Mg phase was gradually decreased,the morphology of MgZn phase changed from discontinuous network to island-like and granular coexistence.Moreover,the fraction of MgZn phase in the alloy treated by PMF was also reduced.When the discharging voltage increased to 300 V,the average area fraction of MgZn phase was reduced by 61% than that of untreated alloy.The mechanical properties of the Mg-7Zn alloy with PMF treatment were improved.With increasing discharging voltage,both the ultimate tensile strength and elongation of the alloy were further increased.When the discharging voltage increased to 300 V,the tensile strength and elongation of the alloy were increased by 29% and 24.2%,respectively,than that of the untreated alloy.Both immersion and electrochemical experimental results indicated that the corrosion resistance of the Mg-7Zn alloy treated by PMF in SBF solution at 37 oC was improved.With the increase of discharging voltage,the hydrogen evolution rate,corrosion rate and corrosion current density of Mg-7Zn alloy were gradually decreased.The solidification microstructure of the Mg-0.6Cu alloy with PMF treatment was improved.With the increase of the discharging voltage,the grain size of the alloy gradually decreased and the morphology of Mg2 Cu phase gradually changed from discontinuous network to island-like and granular coexistence.Moreover,the fraction of Mg2 Cu phase in the alloy treated by PMF was also reduced.When the discharging voltage increased to 300 V,the average area fraction of the Mg2 Cu phase was reduced by 58% than that of the untreated alloy.The mechanical properties of the Mg-0.6Cu alloy treated by PMF were significantly improved.With the increase of discharging voltage,the ultimate tensile strength and elongation of the alloy were further increased.The ultimate tensile strength and elongation of the alloy treated by PMF at a discharging voltage of 300 V were increased by 32% and 40%,respectively,than that of the untreated alloy.Both immersion and electrochemical experimental results indicated that the corrosion resistance of the Mg-0.6Cu alloy treated by PMF in SBF solution at 37 oC was improved.With the increase of discharging voltage,the hydrogen evolution rate,corrosion rate and corrosion current density of Mg-0.6Cu alloy were gradually decreased,and the corrosion potential of Mg-0.6Cu alloy,meanwhile,gradually moved towards positive direction.