| AZ31B alloy not only has the advantages of good shock absorption,low density,high specific strength,elastic modulus similar to human bones,but also has excellent biocompatibility,mechanical properties,osteogenic properties and safety properties,which has become a rare hot material in the field of biomedical implantable materials.But the shortcoming is the wear resistance and corrosion resistance of AZ31B alloy in human body environment.However,the surface properties of magnesium alloys are poor,so improving the surface properties of magnesium alloys without changing the original excellent properties has become a research hotspot in this field.Surface nanocrystallization is one of the effective methods to improve the corrosion resistance and wear resistance of metal.In this paper,the surface nanocrystallization of AZ31B magnesium alloy was carried out by mechanical hammering and annealing.Taking AZ31B alloy as the research object,the effects of mechanical hammering time and annealing temperature on the surface nanocrystallization and microhardness of AZ31B alloy,as well as the changes of wear resistance and corrosion resistance of AZ31B alloy before and after surface nanocrystallization were studied.The main research results are as follows:(1)The XRD diffraction data,metallographic structure and microhardness of the samples before and after mechanical hammering and annealing were compared and analyzed by single factor experiment.The results show that the surface nano of AZ31B magnesium alloy is realized by mechanical hammer and annealing.In a certain range,with the increase of hammer time,the grain size on the surface of the sample decreases and the thickness of plastic deformation layer increases;with the increase of annealing temperature,the surface grain size of the sample decreases first and then increases.The average grain size and hardness of the samples were the lowest and the hardness was the highest under the annealing condition of 15 min + 300 ? by mechanical hammer,respectively,35.39 nm and 142 HV.The microhardness of AZ31B alloy was improved after nano surface,and the relationship between the hardness and the grain size was satisfied with Hall Petch.(2)The friction and wear experiments of AZ31B alloy were carried out on cmt-i testing machine,and the simulation analysis was carried out with the help of pin disk wear model.The results show that the wear loss of AZ31B alloy increases with the increase of normal load and wear time,and the wear resistance of AZ31B alloy is obviously improved by mechanical hammering and annealing treatment.The improvement of surface wear resistance is mainly attributed to the introduction of surface nanocrystallization and residual compressive stress.Among them,the relative wear resistance of the sample hammered for 15 min is increased by 1.23 times,and the wear resistance of the sample annealed at 300 ? after mechanical hammering for 15 min is the best,the relative wear resistance is increased by 2.67 times,and the friction coefficient is significantly reduced.(3)The corrosion resistance of AZ31B alloy before and after mechanical hammering and annealing was characterized by parsat 4000 and Zeiss microscope.The results show that the corrosion rate and tendency of AZ31B alloy decrease after mechanical hammering and annealing treatment,and the corrosion resistance is obviously enhanced.After mechanical hammering,the corrosion current density of the sample decreases obviously,and the corrosion potential of the sample shifts to the right after annealing.The improvement of surface corrosion resistance is mainly attributed to the enhancement of surface activity and the improvement of passive film quality.The results show that the corrosion resistance of the samples is the best under the condition of mechanical hammering for 15 min and annealing at 300 ?.The corrosion current density decreases by 94.4% and the corrosion potential shifts to the right by 0.223v. |
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