Effect Of Sr On Microstructure And Properties Of Commercial Zn-4Al Alloy For Biomedical Applications

The biomedical metal materials have been recognized as the most potential biomedical materials due to its good biocompatibility and mechanical properties.During the last decade,iron(Fe),magnesium(Mg)and their alloys have been widely studied as biodegradable metals.However,Fe-based biodegradable metals degrade at a slow rate which is similar to permanent implants while Mg-based biodegradable metals display a rapid corrosion rate without effective support after being implanted in the body.Zn and Zn-based alloys have more appropriate degradation rates that are close to clinical requirements because their standard potential is between that of Mg and Fe.But,pure Zn has poor mechanical strength and will have local corrosion in the human body,which must be improved to satisfy the requirements for clinical applications.So in this study,the aim of our research is to develop a new kind of Zn based alloy with good mechanical and corrosion properties that can basically satisfy the clinical implant requirement.Five group of Zn-4Al-xSr alloys with different Sr content(0 wt.%?0.03 wt.%?0.06 wt.%?0.1 wt.%and 0.15 wt.%,respectively)were melted in the experiment.Then,the microstructure characterization and mechanical properties test were conducted.It found that the size of primary ?-Zn phase and the distance of lamellar(?+?)phase changed significant with increasing Sr content.When the Sr content is 0.1 wt.%,the size of primary ?-Zn phase and the distance of lamellar(?+?)phase is the smallest.So the Zn-4Al-0.1Sr alloy shows the best mechanical properties,the tensile strength,elongation,impact toughness and Brinell hardness of Zn-4Al-0.1 Sr alloy were 238 MPa,5.70%,74.6 J·cm-1 and 105 HB,respectively.The corrosion test of five groups Zn-4Al-xSr alloys was conducted by weight loss experiment and polarization curve in the Hank's solution with a temperature of 37 ?.The results showed that the weight loss and corrosion rate of five samples reduced first and then increased.When the Sr content is 0.1 wt.%,the weight loss and corrosion rate reach to minimum,so the Zn-4Al-0.1Sr alloy displayed the best corrosion resistance.This is because increasing Sr addition progressively decreased the volume fraction of primary ?-Zn phase and progressively increased the(?+?)lamellar eutectic morphology and SrZn13 phase.On the one hand,the Zn-4Al-0.1Sr alloy exhibited a more uniform corrosion mode due to(?+?)lamellar eutectic morphology the in Hanks' solution,which could reduce stress concentration and rapid reduction in the mechanical integrity.On the other hand,the discontinuous SrZn13 phase acts as a sacrificial anode sites that can protect the basic alloys from the invasion of the corrosion medium.