Preparation Of Mg-Zn-Sr Biomaterials And Research For Its Performance

Research into various magnesium alloys as a biodegradable implant material is gaining increasing attention due to their resemblance to cortical bone, degradability and perfect biocompatibility of corrosion products. However, the high degradation rate of Mg in physiological conditions leads to losses of strength and toughness, and thus limits their clinical application. Element alloying is one of the most effective methods to improve corrosion resistance as well as mechanical properties of magnesium.In this study, Mg-xZn (x=0,1,5,7wt.%) and Mg-4Zn-xSr (x=0,0.1,0.4,1.0wt.%) alloys were fabricated by a clean melting process. The effects of Zn and Sr on the microstructure, mechanical property and corrosion behavior of the as-cast Mg-Zn-Sr alloys were studied using direct observations (OM, SEM, XRD), tensile tests, compression test and immersion tests (weight loss test, pH curves, hydrogen evolution test) and electrochemical measurements (potentiodynamic polarization, electrochemical impedance spectra EIS) in simulated body fluid (SBF) to find the best additive amount of Zn and Sr. The results are summarized as follows:1) OM, SEM and XRD patterns showed, the addition of Zn and Sr elements can greatly refined the grain size of the alloys. Meanwhile, plenty of second phase, MgZn and Mg17Sr2, precipitated along grain boundary.2) The results of tensile tests and compression tests showed, appropriate amount of Zn and Sr elements can improve the mechanical property of magnesium alloys by fine-grain strengthening, solution strengthening and second-phase precipitation strengthening.3) The results of immersion tests showed, appropriate amount of Zn and Sr elements can improve the corrosion resistance of Mg alloys. The corrosion rate of Mg-5wt.%Zn alloy was the lowest in Mg-Zn binary alloys. While, Mg-Zn-0.1wt.%Sr alloy had the lowest corrosion rate among all of the magnesium alloys. So the anti-corrosion property of Mg-Zn-0.1wt.%Sr was the best. 4) Polarization test indicated that Zn and Sr elements can improve the potential of a-Mg phase. Both the anodic polarization curve and EIS plots had shown the beneficial effect of Zn element on the formation of a protective film on the surface of alloys, and the improvement of Sr element on the stability of passive film strengthed its protection to Mg basement.5) Excessive Zn and Sr can lead to a large number of MgZn and Mg17Sr2phase precipitated along grain boundary which accelerated galvanic corrosion of anode a-Mg phase, and thus reduced the corrosion resistance of magnesium alloys.