| Because of its excellent mechanical properties and biodegradability,magnesium alloy has a broad application prospect in the field of cardiovascular stent,bone transplantation and other medical fields.However,the chemical properties of magnesium alloy are relatively active,and it is easy to corrode in the humoral environment,while the whole process of bone regeneration takes a long time,during which most of the magnesium alloy implants have been degraded and lost their function.In addition,with the movement of human body,the wear of magnesium alloy will occur,which will lead to the loosening between the implant and bone tissue,resulting in the failure of the operation.Like other metal materials,the instability of magnesium alloy mostly starts from the surface of the material.Therefore,controlling and improving the surface properties of the materials and obtaining better surface properties are the important guarantee for the continuous and normal work of the magnesium alloy.In recent years,it has gradually entered the field of vision to improve the overall performance of materials by preparing nano layers on the surface of materials.This method avoids the limitation of overall nano technology and reduces the difficulty of nano material preparation.Therefore,in this paper,the surface of magnesium alloy is nano treated by hammering annealing to improve the wear resistance and corrosion resistance of magnesium alloy and solve the clinical application problems.In this paper,AZ91D magnesium alloy is taken as the research object,the influence of surface nano-sized on the comprehensive mechanical properties and surface morphology of AZ91D magnesium alloy,the formation process and mechanism of surface nano-sized and the change of wear resistance and corrosion resistance of AZ91D magnesium alloy are analyzed.The main research results are as follows:(1)The influence of hammering time and annealing temperature on the surface grain size and hardness of AZ91D magnesium alloy was studied by single factor experiment.Through the analysis of the X-ray diffraction pattern,the grain size of the surface layer of the hammered sample was calculated and compared by using the Scheler formula.The results show that,in a certain range,with the increase of hammering time,the grain size of the surface layer of the sample first decreases and then remains unchanged,and the depth of the plastic deformation layer first increases and then becomes stable.At the same time,with the increase of annealing temperature,the grain size first decreases and then increases,and the grain size of the hammered sample annealed at 300 ? is the smallest.The results show that the surface hardness of AZ91D magnesium alloy increases significantly after surface nano treatment,and the relationship between the surface hardness and grain size basically meets hall Petch relationship.(2)The sliding friction behavior of hammered AZ91D magnesium alloy was studied by cmt-i friction and wear tester.The results show that the wear amount of AZ91D magnesium alloy increases with the increase of normal load and wear time,but under the same conditions,the wear resistance of AZ91D magnesium alloy after surface nanocrystallization is higher than that of the original sample.Among them,the relative wear resistance of hammered samples increased by 1.4 times after 15 minutes,and further improved after annealing.The relative wear resistance of hammered samples annealed at 300 ? increased by 3.75 times.(3)The electrochemical corrosion behavior of AZ91D Magnesium Alloy before and after surface nanocrystallization was studied by electrochemical comprehensive tester.By analyzing the polarization curve,the results show that the corrosion current density of AZ91D magnesium alloy decreases sharply and the corrosion resistance increases significantly.Compared with the original sample,the corrosion current density of AZ91D magnesium alloy sample decreased about 2 times after hammering treatment.At the same time,it is found that the corrosion current density of the annealed samples after hammering for 15 min + 300 ? is the lowest,which is about 4.5 times lower than that of the original samples. |
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