| At present,the static immersion experiments are mostly used to study the degradation behavior of medical magnesium alloy and its coatings in vitro.There are few reports on the effects of physiological flow field environment in human body and biological macromolecules represented by proteins on their degradation behavior.In this study,the effects of simulated physiological flow field,protein(BSA)and their synergistic effects on the degradation behavior of WE43 magnesium alloy were studied using Hank’s balanced salt solution(HBSS)as corrosion medium.On this basis,micro-arc oxidation(MAO)and polylactic acid(PLA)sealing processes were used to prepare the MAO coating and the composite coating on magnesium alloys,respectively.The corrosion mechanisms of the two coatings in static and dynamic environments containing BSA were compared.The main conclusions are as follows:The effect of flow velocity on the corrosion rate of WE43 magnesium alloy is timedependent.After 7 days of immersion,the flow velocity showed a positive correlation with the corrosion rate of magnesium alloy.With the increase of flow velocity,the corrosion type of magnesium alloy surface changed from local corrosion to uniform corrosion,and the integrity of surface degradation products gradually decreased.In addition,the corrosion rate of magnesium alloy in low flow rate(0.13 cm/s)for 48-96 h and high flow rate(5.33 cm/s)for 24 h is slower than that in static environment.Adding protein into the corrosion solution in static environment can accelerate the degradation of magnesium alloy.The higher the protein concentration is,the more significant the acceleration effect is,which is related to the inhibitory effect of protein on the Ca-P phase deposition on the surface of magnesium alloy.Under the synergistic effect of flow field and protein,the corrosion rate of magnesium alloy surface is slower during soaking for 12 hours,and the lower the flow rate and the lower the concentration of BSA,the slower the corrosion rate of magnesium alloy surface.After soaking for 7 days,the synergistic effect of the two can accelerate the corrosion of magnesium alloy,and its corrosion current density is much higher than that of the flow field at the same velocity or the single effect of protein at the same concentration.At low flow rate(0.13 cm/s),the influence of protein concentration on the corrosion rate of magnesium alloy is greater.At high flow rate(1.33 cm/s),the effect of flow field on corrosion rate of magnesium alloy plays a dominant role.The cracking of magnesium alloy surface coating was promoted by flow field environment.In the flow field environment,soaking for 6 hours,the corrosion rate of the magnesium alloy treated by micro-arc oxidation is slower than that of the static magnesium alloy,and the protein content adsorbed on its surface is higher.After that,the flow field inhibited the deposition of degradation products on the magnesium alloy surface and accelerated the cracking of the magnesium oxide coating.The protective effect of micro-arc oxidation coating on magnesium alloy matrix disappeared after soaking in static solution for 48 hours,while the protective time was 24 hours earlier in dynamic environment.The corrosion resistance of magnesium alloy surface can be improved by using PLA to seal the holes of micro-arc oxidation coating.In the static environment,a large number of degradation products were deposited on the surface of the composite coating,which inhibited the degradation rate of the coating.In the dynamic environment,the damage of the composite coating was more serious,and obvious pitting pits appeared.After soaking for 120 hours,the composite coating could no longer protect the matrix. |
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