Abstract
Mg-3Zn-0.5Sr-xCa(wt.%) (x=0, 0.2, 0.5) alloys were fabricated by casting and hot extrusion. X-ray diffraction (XRD) and optical microscopy observation showed that the microstructure of Mg-3Zn-0.5Sr-xCa alloys was composed of α-Mg matrix and Mg17Sr2 phase precipitated along grain boundaries. The tensile strength of the alloy increased from 255MPa to 305MPa with increasing Ca content from 0 to 0.5wt%, but the elongation to fracture of the alloys was 19.45%, 28.7% and 15.2% respectively, indicating that coarse precipitation increased the risk of crack initiation and propagation along the grain boundaries leading to reduced ductility of Mg alloys. The polarization curves revealed that Mg-3Zn-0.5Sr-0.2Ca has the highest corrosion potential and the lowest corrosion current density indicating the optimum corrosion resistance. In cytotoxicity test, Mg-3Zn-0.5Sr-xCa alloys were harmless to mouse osteoblastic and Mg-3Zn-0.5Sr-0.2Ca alloy exhibited optimal biocompatibility.
Highlights
Magnesium alloys have attracted extensive attention for medical applications because of their good biocompatibility, biodegradability and elastic modulus similar to natural bone as orthopaedic and cardiovascular implant[1,2,3]
X-ray diffraction (XRD) pattern (Fig. 1) show the phases of as-extruded Mg3Zn-0.5Sr-xCa alloys consisted of α-Mg matrix and Mg17Zn2 intermetallic compound phase
With the addition of the Ca content to 0.5wt%, the yield strength (YS) of the Mg alloy slightly increased from 164MPa to 185MPa, and the ultimate tensile strength (UTS) increased significantly to 305MPa, while the elongation to fracture decreased from 19% to 15%
Summary
Magnesium alloys have attracted extensive attention for medical applications because of their good biocompatibility, biodegradability and elastic modulus similar to natural bone as orthopaedic and cardiovascular implant[1,2,3]. Brar et al.[15] reported that when the addition of zinc is 2wt% or 4wt%, the Mg alloy has optimal mechanical and degradation properties. Sr could improve bone strength and density and indicated beneficial effects on corrosion resistance and deformability[16,17,18,19]. When Sr content is over 0.3wt%, the finer grains and more homogeneous precipitation of Mg alloys occurs. The front of solid-liquid interface generates constituent supercooling after adding Ca element, which could enhance nucleation rate and inhibit grain growth. Comparing to as-cast Mg alloys, finer grains and preferable properties were possessed by as-extruded Mg alloys[2,10,23]. Mg-3Zn-0.5Sr-xCa (x=0, 0.2, 0.5) alloys were fabricated through casting and hot extrusion, while the properties of the alloys were evaluated by tissue analysis, corrosion resistance and cytotoxicity tests
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