| Zn and it alloys have become a highly valuable orthopedic implant material due to its excellent biocompatibility as well as moderate degradation rate among biodegradable biomedical metal materials.A large number of research have been conducted on Mg,Fe,and alloy materials.However,the degradation rate of Mg based alloys is too fast,while the degradation rate of Fe based alloys is too slow,which limits the clinical application of Mg based alloys and Fe based alloys.The standard electrochemical potential of Zn based alloys is between the Mg based alloys and Fe based alloys,and the corrosion rate of Zn based alloys meets the requirements of clinical implant materials.However,the ultimate tensile strength（UTS）and elongation（EL）of existing biodegradable Zn alloys cannot meet the requirements of biodegradable materials such as cardiovascular stents and human bone nails,which limits the development of biodegradable Zn alloys.Research has shown that ultrasonic treatment can effectively refine the microstructure of alloys and further improve their mechanical properties.In this paper,degradable Zn-0.5Sr and Zn-2Sn-0.5Sr alloys were prepared by adding Sn and Sr elements（2%and 0.5%）to further optimize the mechanical properties of Zn alloys and meet the corrosion rate requirements of biomedical materials.Ultrasonic treatment was applied to Zn-0.5Sr and Zn-2Sn-0.5Sr alloys to study the effects of ultrasonic vibration on the microstructure,mechanical properties,and corrosion rate of Zn-0.5Sr and Zn-2Sn-0.5Sr alloys,and the strengthening mechanisms and corrosion behavior of Zn-0.5Sr and Zn-2Sn-0.5Sr alloys were studied.Through analysis,the following conclusions can be drawn:（1）The primaryα-Zn in the Zn-0.5Sr alloy is gradually refined into equiaxed crystals when the ultrasonic power is 600W,and its average size is decreased to80.84μm.Meanwhile,the average size of Sr Zn13 phase is reduced to 34.60μm.The UTS and EL of Zn-0.5Sr alloy are increased to 117.67MPa and 1.29%when the ultrasonic power is 600W.The electrochemical experimental results indicate that the corrosion rate of Zn-0.5Sr alloy gradually increased with the increase of ultrasonic power.When the ultrasonic power reaches 600W,the corrosion rate of the alloy increases from 2.078±0.141mm/a to 5.747±0.390mm/a.The as-cast Zn-0.5Sr alloy treated by different ultrasonic power was immersed in Hank’s solution for 15 and 30days,respectively.The experiment results show within the same time（15days）,the corrosion rate of Zn-0.5Sr alloy without ultrasonic treatment was lower than that of the ultrasonic treated alloy,and the corrosion rate of Zn-0.5Sr alloy treated with 600W ultrasonic power increased from 0.048mm±0.0015/a to 0.090±0.0021mm/a.Moreover,the corrosion rate of the alloy treated with the same ultrasonic power（600W）increased from 0.038±0.0013mm/a to 0.074±0.0019mm/a with the immersion experiment time increased to 30 days.（2）The results of ultrasonic treatment of Zn-0.5Sr alloy for 0 min,2min,5min and 8min show that the second phase sizes of the primaryα-Zn and Sr Zn13 phase are reduced to 87.24μm and 35.01μm when the ultrasonic time is 5min.Meanwhile,the UTS and EL of the alloys are increased to 118.93MPa and 1.32%.The results show that the corrosion rate of the Zn-0.5Sr alloy without ultrasonic treatment is the lowest,which is 0.046±0.0017mm/a,and the corrosion rate of the alloy increases to0.085±0.0031mm/a when the ultrasonic time was 5min.In the electrochemical corrosion experiment,the analysis results of potentiodynamic polarization curve and electrochemical impedance spectroscopy show that the corrosion rate of Zn-0.5Sr alloy increased from 2.340±0.159mm/a to 5.207±0.354mm/a when ultrasonic time was 5min.（3）The study on the microstructure of Zn-2Sn-0.5Sr alloy shows that ultrasonic treatment can refine the microstructure.The primaryα-Zn gradually changes from columnar crystals to equiaxed crystals with the increase of ultrasonic power,and the morphology of Sr Zn13 phase changes from irregular polygon to small massive.The average grain size of primaryα-Zn and Sr Zn13 phase in the alloy are reduced to43.63μm and 19.18μm when the ultrasonic power is 600W.The UTS and EL of Zn-2Sn-0.5Sr alloy increase first and then decreased with the increase of ultrasonic power.The UTS of Zn-2Sn-0.5Sr alloy is increased by 39.4%from 71MPa to 99MPa,and the elongation is increased by 396%from 0.25%to 1.24%when the ultrasonic power is600W.The electrochemical analysis results of Zn-2Sn-0.5Sr alloy in Hank’s solution show that the corrosion rate of Zn-2Sn-0.5Sr alloy is increased from 4.772±0.318 mm/a to 7.438±0.517mm/a when the ultrasonic power was increased from 0W to 600W;and the corrosion rates of Zn-2Sn-0.5Sr alloy immersed in Hank’s solution for one month increase and then decrease with the increase of ultrasonic power.The corrosion rates of Zn-2Sn-0.5Sr alloy with different ultrasonic power are as follows:600W（0.079±0.0018mm/a）>300W（0.062±0.0017mm/a）>900W(0.052±0.0014mm/a>0W（0.042±0.0012mm/a）,respectively. |
