| The development of biodegradable materials is on rise currently,in which metal-based biodegradable materials have received widespread attention due to its excellent mechanical properties and good processing properties.Recently,most research focus on the Mg-based and iron-based alloys,The degradation rate of magnesium alloy is too fast,the degradation rate of iron-based alloy is too slow in the body fluid environment,which becoming the main factor limiting their application in medical implanted devices.The standard electrochemical potential of zinc is between that of Mg and Fe,and zinc is also an essential element of the human body,making Zn-based alloy a new kind of biodegradable material,which drawn some reseachers'attention.Because the addition of Fe element in zinc can enhance the strength of alloy and form galvanic corrosion with the matrix,accelerate and control the corrosion rate of zinc alloy to reach the ideal corrosion rate of metal-based biodegradable material.So Fe element was selected as alloying element.Their microstructure,mechanical properties and corrosion resistance in have been investigated,effect of Fe element on zinc alloy was clear.ECAP was done at the base of extrusion to research the properties above.Thus this research provides valuable basic data to the preparation of new kinds of Zn-based biodegradable material.(1)The as-cast Zn-xFe alloys(x=0,0.1,0.2,0.5wt.%)were prepared to research the effect of Fe on their microstructure and properties.A large number of needle-shaped second phase FeZn13 was formed,The tensile strength of the alloy was increased to 37.8MPa,and the elongation decreased to 23.9%.(2)The movement of dislocation will be dragged by the second-phase particles,hinder the formation of high-density dislocation region,inhibit the transition of small-angle grain boundary to the large-angle boundary.The average grain size of the as-extruded sample was refined from 46.34 ?m pure zinc to 6.23?m at 0.1 wt.%Fe and 3.7 ?m at 0.5 wt.%Fe.The tensile strength and elongation of the alloys also increased from 62.2MPa and 37.4%of pure zinc to 103.4MPa and 52.3%of 0.1 wt.%Fe,111.4MPa and 71.8%of 0.2wt.%Fe and 0.5wt.%Fe reaches 125MPa,76.8%.(3)The equiaxed grains in the original extruded state were significantly elongated and the band-shaped microstructure of the alloy was unevenly deformed during the ECAP process.With the increase of the pass,the content of small-angle grain boundaries increased,and the content of the small-angle grain boundaries decreased after the fourth pass extrusion.The tensile strength of Zn-0.5Fe alloy increased from 123.2MPa in extruded state to 147.3MPa,and the elongation decreased from 76.8%to 46.4%and dropped to 37.1%finally.(4)The corrosion resistance in PBS solution decreases due to the addition of Fe element in cast alloy.With the increase of Fe content,the corrosion resistance of the alloy first increases and then decreases,and reaches the maximum at the 0.5wt.%Fe content.(5)By comparing the corrosion resistance of as-cast and as-extruded Zn-0.2Fe alloys,we know the effect of grain size on the corrosion properties in Zn-Fe alloys.Grain refinement increases the corrosion resistance of the alloy.Because the second phase particles form galvanic corrosion with the substrate and act as the cathode,galvanic corrosion is weakened due to the refinement of the ? phase increases the surface area of the anode,decreases the area ratio of the cathode and anode.(6)With the increase of pass,the corrosion potential of the alloy first increased and then decreased,the corrosion potential reached the highest-0.950V at the second pass,showing the best corrosion resistance... |
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