| As a new type of implanted medical material,magnesium alloy has good biodegradability in vivo,which can avoid the adverse effects of traditional medical materials due to stress shielding and secondary surgery.However,the rapid degradation rate of magnesium alloy limits it was large-scale use.Based on the biodegradability of magnesium alloys,the rolled Mg-Zn-Nd-Zr alloys were treated by solution treatment and surface modification.The influence of solution treatment,ultra precision polishing and micro arc oxidation coating on the biodegradability of rolled Mg-Zn-Nd-Zr alloys immersed in Hank’s solution was studied,and the basic data of new medical magnesium alloy materials were obtained.Firstly,the as-rolled Mg-Zn-Nd-Zr alloy was solution treated at different temperature/time,and the biodegradability of the alloy under different solution treatment conditions was studied.When the solution temperature is 400℃,the grain boundaries are broken,which leads to the grain size increase.The analysis of the element content of the second phase by energy spectrum shows that the increase of solution temperature and time will cause the increase of the content of zinc and neodymium in the second phase.The degradation rate of hydrogen evolution was the slowest at 400 ℃ /4h,and the surface was lamellar after 168 h.The results of electrochemical experiments show that the degradation rate of potentiodynamic polarization at 400℃/4h is the lowest.The results show that the solution treatment can improve the degradation resistance of magnesium alloy.When the solution temperature reaches 400 ℃,the degradation resistance of magnesium alloy is obviously enhanced.Secondly,the effects of surface roughness on the biodegradability of magnesium alloy were studied by ultra-precision polishing of magnesium alloy treated at 400℃for 4h.With the increase of polishing speed,the surface roughness of magnesium alloy decreases gradually.Compared with the normal polishing,the ultra-precision polished magnesium alloy shows a large amount of hydrogen release during the whole immersion process,and the p H value also increases rapidly at the beginning of immersion.After 168 h immersion,a dense layer of degradation products existed on the degraded surface of ultra-precision polishing.Electrochemical potentiodynamic polarization results show that the degradation rate of ultra-precision polished magnesium alloy is very high,and impedance experiments also show that its unfavorable degradation resistance.The results of ultra-precision polishing show that the roughness is directly proportional to the degradation resistance under ultra-precision polishing conditions.Under the condition of conventional grinding,the roughness is inversely proportional to the degradation resistance.Finally,the micro-arc oxidation(MAO)coating was applied on the surface of the normally polished solid solution 400℃/4h magnesium alloy,and the protection and influence of the MAO coating on the biodegradability of the magnesium alloy were studied.The typical discharge pore morphology of micro-arc oxidation on the surface of magnesium alloy was observed by scanning electron microscope.The results of the biodegradation experiment showed that no obvious hydrogen release phenomenon was observed during the whole process.After 168 h immersion,the discharge pores on the coating surface were covered by degradation products.The experimental results of electrochemical potentiodynamic polarization curves show that the corrosion current density of the coating is in the order of:Substrate>MAO-1.5>MAO-2.0>MAO-2.5>MAO-3.0.The results of impedance experiments showed that MAO-2.5 and MAO-3.0showed better resistance to degradation.The results of micro-arc oxidation show that the micro-arc oxidation coating has a good and long-term protective effect on the magnesium alloy substrate,and the longer the constant current discharge time,the better the anti-degradation ability. |
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