Study On Directionally Solidified Porous Medical Mg-Zn Alloy

In this paper,the Bridgman type directional solidification method was used to successfully prepare the lotus root porous Mg-Zn alloy.The effects of different zinc content and hydrogen pressure on pore morphology were studied.Through theoretical calculations,the porosity of Mg-1Zn was predicted.And the prepared porous pure Mg,Mg-1Zn and Mg-2Zn alloy samples were subjected to a series of in vitro degradation tests,including macro observation analysis and scanning electron microscope observation analysis before and after the removal of corrosion products,and the change of p H value during the corrosion process Analysis,weightlessness analysis,dynamic potential polarization curve and electrochemical impedance spectroscopy test.The results show that the addition of zinc will have a significant effect on the pore structure.As the Zn content increases from 0 to 2%,the average pore size increases.As the hydrogen pressure increased from 0.1 MPa to 0.6 MPa,the porosity of the Mg-1Zn alloy decreased significantly.Based on the calculation model of the solubility of hydrogen in the multi-component molten metal,the calculation results of the porosity of the Mg-1Zn alloy ingot with a solidification height of 20 mm are in good agreement with the results of the model.By observing the structure,as the Zn content increases,the solidified structure changes from columnar crystals to equiaxed crystals.The pore formation process at different solidification stages is studied,which can provide a theoretical basis for the application of directional solidification porous Mg-Zn alloy in biomedical materials.The corrosion methods of the three porous magnesium alloys are all pitting corrosions.The difference is that the pitting pits of porous pure Mg gradually expand around and in depth to form large and deep corrosion pits,while the pitting pits of porous Mg-Zn alloy follow Slowly expand in a certain direction to form thin and shallow filamentous corrosion pits.The simulated p H of the body fluids around porous Mg-1Zn and Mg-2Zn is relatively close in amplitude and law,and it rises to a maximum value of about 9.3 after 90 hours from the initial 7.40,and then fluctuates around 9.25.The p H value of porous pure Mg The change is relatively rapid.Within the first 20 hours,it rapidly increased from 7.4 to about 9.4,and then slowly dropped to about 9.2 after 120 hours.Therefore,the implantation of porous Mg-1Zn and Mg-2Zn will not cause the p H of the implantation site the rapid change of value is conducive to maintaining the original physiological environment in the body.Porous pure Mg has the fastest weight loss rate,followed by Mg-1Zn,Mg-2Zn is the slowest,and the weight loss rate of porous Mg-Zn alloy is much smaller than that of porous pure Mg,which shows that the addition of alloying element Zn greatly improves the pure weight Corrosion resistance of Mg.Potential polarization curve and electrochemical impedance spectroscopy test results show that the hydrogen evolution overpotential of porous Mg-1Zn and Mg-2Zn is higher than that of porous Mg,that is,the cathodic hydrogen evolution reaction is more likely to proceed on the surface of porous Mg,while on the anode In the area,the polarization curves of the three alloys are also similar,that is,the anodic polarization curve changes smoothly without obvious inflection points,which indicates that the corrosion products on the surface of the alloy do not effectively protect the substrate.In the impedance spectroscopy,the radius of the capacitive reactance half-ring increases in the order of porous pure Mg,Mg-1Zn and Mg-2Zn,indicating that the corrosion resistance also increases in sequence.