Study On Microstructure And Corrosion Properties Of Mg-Sr-Zr Biomedical Alloy

Magnesium and Mg alloys have attracted considerable attention as promising biodegradable implant materials for biomedical applications, as they possess advantages over traditional metallic materials, ceramics, and biodegradable polymers. Mg alloys gradually degrade in vivo and are eventually replaced by newly grown bone tissue after implantation, which eliminates the need for further surgery to remove the implant from the human body. However, the rapid degradation rate of existing Mg alloys in an electrolytic aqueous environment, which leads to a loss of mechanical integrity before the tissue has healed sufficiently and new bone tissue has adequately regenerated, restricts their wide application.Alloying is the main method to improve the biocorrosion resistance of magnesium alloys. In present work, alloying elements Sr and Zr were chosen to form binary Mg-xSr(x = 0.5, 1, 2, 3) and ternary Mg-1Sr-yZr(y = 0.5, 1, 2, 3) alloys by conventional permanent mold casting method. The degradation behaviors of novel binary and ternary alloys were systematically investigated using weight loss, hydrogen evolution, and electrochemical techniques in simulated body fluid(SBF). The microstructure and micrography of the alloys were characterized using optical microscopy, X-ray diffraction, and SEM equipped with EDS. The various tests were used to find the best additive amount of Sr and Zr. The results are summarized as follows:(1) OM, XRD and SEM showed, the addition of Sr and Zr elements can greatly refined microstructure and the grain size of the alloys. With more addition, the Mg17Sr2 phase and the fine Zr particle phase will precipitated along the grain boundary, the grain boundary become coarsen.(2) The immension tests of alloy samples showed, with appropriate amount of Sr and Zr elements, the biocorrosion resistance of studied alloys can be greatly improved. The corrosion rate of Mg-1Sr was the lowest in Mg-Sr binary alloys.The biocorrosion property of Mg-1Sr-1Zr was the best in ternary alloys.(3) The electrochemical test indicated that the Sr and Zr elements can improve the potential of ?-Mg phase.The anodic polarization cruve showed the beneficial effect of Sr and Zr elements on the formation of a protective film on the surface of alloys, and the improvement stability of passive film strengthened its protection to Mg basement.(4) Excessive Sr and Zr elements can lead to the precipitation of Mg17Sr2 phase and particle Zr phase along the grain boundary, which would form galvanic corrosion with the ?-Mg phase, then accelerated the corrosion of anode ?-Mg as they hold a higher corrosion potential than the ?-Mg phase.(5)The main components of the corrosion products on the surface of alloys were Mg(OH)2,(Ca,Mg)3(PO4)2 and a small amount of hydroxyapatite(Ca10(PO4)6(OH)2). They adhered to the surface of corroded alloy which would prevent the further corrosion into the material. The presence of hydroxyapatite could improve the biocompatibility and bone-binding capacity. The corrosion manner of the alloys was a mixed combination of pitting and uniform corrosion.