The synergistic effect of trace Sr and Zr on the microstructure and properties of a biodegradable Mg-Zn-Zr-Sr alloy

To further improve the mechanical properties and corrosion resistance of the biodegradable magnesium (Mg) alloy, the Mg-Zn-Zr-Sr (MZZS) alloy was smelted in vacuum under the protection of inert gas, and the bar material with dimensions of 8 mm diameter was then obtained through a hot-extrusion process. The synergistic effect of trace Sr and Zr addition on the microstructure and the crystallization of the as-cast Mg-Zn-Sr (MZS) and Mg-Zn-Zr alloy (MZZ) were analyzed by XRD and SEM-EDS. The mechanical properties and corrosion behavior of the as-extruded MZS, MZZ and MZZS alloys were tested by electronic universal and immersion test in vitro, respectively. The grains in as-cast MZZS alloys were significantly refined and its average grain size (19.6 μm) was only one-third of as-cast MZS and MZZ alloys. Yield tensile strength (YTS) of 322.363 ± 4.547 MPa and ultimate tensile strength (UTS) of 376.400 ± 7.526 MPa were obtained for the Mg-3.2Zn-0.8Zr-0.3Sr alloy; these values were much higher than those of the other two types alloy with the same extrusion ratio and extrusion process. According to immersion tests in vitro, the corrosion rate of the MZZ alloy increased from 4.07 ± 0.71 mm/y to 5.357 ± 0.75 mm/y after the addition of Sr. Moreover, the in vitro cytotoxicity test showed that the MZZS alloy had good cytocompatibility and could hence aid in the proliferation of cell.