Research On Corrosion And Tribological Properties Of Biomedical Magnesium Alloy Based On Shot Peening

In order to solve the problem of excessive corrosion and keep the good biocompatibility of biomedical magnesium and magnesium alloys,the biomedical WE43 magnesium alloy was studied,and the high energy shot peening surface treatment technology was used as a strengthening method in this paper.The corrosion and friction and wear behavior of WE43 magnesium alloy samples after shot peening were explored.(1)The numerical simulation of residual stress field of the samples strengthened with different shot peening parameters was carried out,and the results showed that the projectile diameter and velocity had the greatest influence on the residual stress field and the equivalent strain of the sample,and the influence of projectile incidence angle took second place.When the diameter was 0.8mm and 1.0mm,the incident velocity was 90m/s and the incident angle was 90 o,the shot peening effect was the best.Then the samples were shot peening treated in 60 s,90s and 120 s,and the microstructure of the samples was analyzed.The results showed that the grain refinement layer of WE43 magnesium alloy was produced by shot peening,which was about 120~150?m,and the grain refinement mechanism was twinning dislocation accumulation,subgrain formation and dynamic recrystallization.The hardness of the samples was distributed from the treated surface to the heart,and the hardness of the surface was two times of the substrate hardness.The test results of residual stress were in good agreement with the results of numerical simulation,the comprehensive characteristics of the surface of 120 s sample strengthened by shot peening was better than others.(2)The simulated body fluid(SBF)immersion test and salt spray corrosion test were carried out on WE43 magnesium alloy samples.The results showed that the corrosion rate of the untreated samples was the largest when another 3 groups were similar in the SBF immersion,and the corrosion rate increased due to the failure of the strengthened layer.In the process of salt spray corrosion,the corrosion rate of the 4 groups of samples was similar,and the corrosion rate decreases gradually until it was stable.The effect of shot peening samples on the salt spray corrosion resistance was small.The solution pH value of treated samples was less than that of the untreated samples.Shot peening can effectively reduce the corrosion rate of the sample in the SBF,and the longer the shot peening time was,the better the effect was.According to the morphology of samples,the surface of the shot peening samples was better than that of untreated samples.There were phosphate deposits on the surface.In general,the corrosion performance of the SBF immersion enhanced by the shot peening was better than that of the salt spray.And the corrosion resistance of samples treated for 120 s was the best.(3)The electrochemical tests of WE43 magnesium alloy samples were carried out in the SBF and mass fraction of 3.5% NaCl.The results showed that the self corrosion potential of samples in two kinds of electrolytes was positive,and the corrosion current density decreased.The electrochemical corrosion resistance of the samples increased.The open circuit potential curve of the untreated samples was more severe than that of the treated samples.However,the electrochemical curves of the samples in NaCl solution changed smaller than that in the SBF,and the electrochemical behavior of samples in the SBF was better than that of NaCl solution.(4)The friction and wear experiments of biomedical magnesium alloys were carried out.Under the condition of constant load and speed,the dry friction coefficient and wear rate of the shot peening samples were significantly lower than that of untreated samples.The wear mechanism under dry friction was mainly abrasive wear.In the SBF lubrication,the friction coefficient of 120 s treated samples decreased obviously,and the quality loss of all samples under lubricated conditions were greater than that of dry friction.The wear mechanism under the lubrication condition was abrasive wear,corrosion wear and spalling wear.For the samples of shot peened in120 s,and under the condition of constant speed and dynamic load,results showed that the dry friction coefficient increases with the increases of load,and the lubricant friction coefficient decreased first and then increased,and the lubricant friction coefficient of samples was always smaller than the dry friction coefficient.Under the condition of constant load and dynamic speed,the friction coefficient of magnesium alloy samples at low speed was greater than that of the high speed.This was due to the fact that the asperity on the surface of the samples was not completely worn at low speed.The mass loss of all samples increased with the increase of load and speed,and the mass loss of samples under the condition of SBF lubrication was obviously greater than that of the samples under dry friction.