Research On Corrosion Behavior And Service Performance Of Biomedical Magnesium Alloy

Magnesium alloys have the potential to be developed into a new generation of degradable biomaterials due to their good biocompatibility and mechanical properties.It has received the attention of many researchers in the fields of materials science and medicine.Magnesium alloy as a human implant material has a density and modulus of elasticity similar to that of human bone and avoids stress masking effects when implanted in the human body.Magnesium alloys as human implant materials have a density and modulus of elasticity similar to that of human bone,so magnesium alloys can avoid stress masking effects during human service.Once implanted in the body,magnesium alloys can degrade and disappear within the patient's body,avoiding secondary surgery and reducing medical costs.The degradation of magnesium alloys results in the formation of Mg2+ in the organism's fluid environment.Mg2+ affects the effects of a variety of biological enzymes in the organism and is also involved in the organism's nervous system and muscle activity.Excess Mg2+ is eventually excreted from the body by participating in metabolism.It can be seen that magnesium alloys are biocompatible as implant materials and are not harmful to humans.However,the current commercial magnesium alloys contain a large number of elements that are harmful to the human body,such as Al,Ni and Pb.The degradation products of commercial magnesium alloys as implant materials in the biological fluid environment can cause adverse reactions to the human body,which greatly hinders the promotion and application of biomedical magnesium alloys.Therefore,the comprehensive properties of magnesium alloys need to be optimised,elements that are harmless to humans are preferred as alloying elements,and the mechanical properties and corrosion rates of the alloys need to be regulated by improving the microstructure,weave and deformability of magnesium alloys through heat treatment and deformation treatment.In this paper,Mg,Mg-0.8Ca and Mg-2.0Zn-1.6Ca were used as research objects.Mechanical property tests,electrochemical tests and corrosion product analysis were carried out on the three cast materials,and the overall performance of the cast materials was found to be poor.In view of this,the properties of magnesium alloys are enhanced through alloy melting,solid solution treatment and extrusion strengthening.The electrochemical corrosion behaviour of different materials in simulated body fluids was investigated by weightlessness tests and electrochemical tests(open circuit potential scans,dynamic potential scans,impedance tests).The grain size,structure and grain orientation of the extruded alloy were analysed by EBSD and the effect of changes in extrusion temperature on the internal weave was investigated.Finally the material with the best corrosion resistance and tensile strength was subjected to a microwear test and a screw pull-out force test to investigate the changes in the service performance of the magnesium alloy in the SBF simulated body fluid.A study of the mechanical properties and corrosion resistance of the cast materials revealed that the cast Mg,Mg-0.8Ca and Mg-2.0Zn-1.6Ca have coarse grains and poor mechanical properties and corrosion resistance,which cannot meet the service requirements of biological implant materials.The best corrosion resistance of the three cast materials is Mg,followed by Mg-0.8Ca and the worst is Mg-2.0Zn-1.6Ca.On the other hand Mg-2.0Zn-1.6Ca has the best overall mechanical properties and Mg has the worst overall mechanical properties.It shows that alloying can improve the hardness,tensile and flexural properties of magnesium alloys,but alloying creates a second phase,which forms a primary cell between the second phase and the magnesium matrix,making the magnesium alloy less resistant to corrosion.After extrusion,the alloy grain is obviously refined,the tensile strength is obviously increased,the lower the extrusion temperature the higher the tensile strength of magnesium alloy.The best tensile strength was Mg-2.0Zn-1.6Ca at 300? extrusion at 393.96 MPa,which was a 490.65% increase over the acquired cast Mg-2.0Zn-1.6Ca.This was followed by Mg-0.8Ca under extrusion at 250? with a tensile strength of 332.9628 MPa,which is an increase of 471.53% over the acquired as-cast Mg-0.8Ca.It shows that hot extrusion makes the internal grains appear to be preferentially oriented and the weaving strengthening effect is obvious.The corrosion resistance of Mg-0.8Ca decreases with increasing extrusion temperature,but that of Mg-2.0Zn-1.6Ca increases with increasing extrusion temperature.Microwear tests were carried out on Mg-2.0Zn-1.6Ca-300?,the alloy with the best tensile properties after extrusion,and Mg-0.8Ca-250?,the alloy with the best corrosion resistance.The coefficient of friction under the dry friction test was found to be smaller than under the test with the addition of SBF simulating body fluid,which indicates that the SBF simulating body fluid corrodes the substrate surface and increases the coefficient of friction.Mg-2.0Zn-1.6Ca-300? and Mg-0.8Ca-250? were machined into screws to create a bone-screw model.The model was immersed in SBF simulating body fluid and screw pull-out force tests were performed after removal every five days and it was found that the screw pull-out force of Mg-0.8Ca-250? showed little variation and good service performance.Therefore Mg-0.8Ca-250? is an ideal choice for biomedical magnesium alloys.