Study Of Microstructure And Properties On The Mg-Zn-Y-Zr Biological Magnesium Alloy

Magnesium alloy has become a promising medical metal material because of its good biocompatibility and degradability.However,its poor corrosion resistance restricts its development in the field of bioimplantable materials.At present,the research focus of biodegradable medical magnesium alloy materials is how to improve the corrosion resistance of magnesium alloy in physiological environment.In this paper,the composition of Mg-2Zn-1Y alloy was optimized by alloying.The effects of trace elements Sr,Ca and Zr on the microstructure,mechanical properties and corrosion resistance of Mg-2Zn-1Y alloy were studied,and the Mg-2Zn-1Y-0.5Zr alloy with better comprehensive properties was selected.On this basis,the microstructure,mechanical properties and corrosion resistance of Mg-2Zn-1Y-0.5Zr alloy were improved by ssolution treatment and hot extrusion.The effects of solution treatment and hot extrusion on the microstructure and properties of Mg-2Zn-1Y-0.5Zr alloy were studied by means of optical microscope(OM),scanning electron microscope(SEM),electron backscatter diffraction(EBSD),X-ray diffractometer(XRD),transmission electron microscope(TEM),laser scanning confocal microscopy(LSCM),tensile test,immersion test and electrochemical test.The results are summarized as follows:The microstructure of the as-cast Mg-2Zn-1Y basic alloy was coarse equiaxed grain with an average grain size of about 165.64?m.The microstructure of Mg-2Zn-1Y alloy was refined in different degrees with the addition of trace Sr,Ca,and Zr elements,and the grain size was 106.50?m,125.23?m,and51.30?m,respectively.The alloy with Zr element had better mechanical properties and corrosion resistance,and its UTS,YS,and EL were 178.4 MPa,80.7 MPa,and19.0%,respectively.The average corrosion rate after immersion in SBF for 120 h was0.623 mm/y.The as-cast Mg-2Zn-1Y-0.5Zr alloy was mainly composed of equiaxed?-Mg matrix and granular Mg₃Y₂Zn₃ phase.The volume fraction of the second phase in the alloy decreased gradually and the grain size increased after solution-treated at 400,420,440,460,and 480?for 10 h.There were still small granular Mg₃Y₂Zn₃ phases remained after solution treatment.After solution treatment in the range of 400-480?,the mechanical properties and corrosion resistance of the alloy increased at first and then decreased with the increase of solution temperature.When the solution temperature was at 440?,the volume fraction of the second phase of the alloy was0.02%,and the grain size was 110±2?m.The alloy had good comprehensive properties,and its UTS,YS,and EL were 189.3±4.7 MPa,93.5±0.8 MPa and23.3±0.7%,respectively.The average corrosion rate after immersion in SBF for 120 h was 0.304±0.021 mm/y,and the corrosion was dominated by filiform corrosion.After hot extrusion,the grains of solid solution Mg-2Zn-1Y-0.5Zr alloy were significantly refined.When the extrusion temperature was 440?,the alloy structure was composed of elongated?-Mg coarse grains and fine recrystallized grains with a grain size of 3.4?m.When the extrusion temperature increased from 460?to 500?,the grain size increased from 2.8?m to 4.9?m,and the grains grew significantly.The mechanical properties and corrosion resistance of the alloy increased at first and then decreased with the increase of extrusion temperature in the range of 440-500?.When the extrusion temperature was at 460?,the alloy was mainly composed of fine recrystallized grains,nano-sized granular Mg₃Y₂Zn₃ phase and massive Zn₂Zr phase,with uniform microsture and good mechanical properties and corrosion resistance.The UTS,YS and EL of the alloy were 317.1±5.5 MPa,293.9±4.9 MPa,and 16.7±1.5%,respectively.The average corrosion rate of the alloy in SBF immersion for 120 h was0.669±0.017 mm/y.The corrosion of the alloy was uniform corrosion.