| Magnesium is a necessary nutrient for the human body.Magnesium alloy and the human body has a good biocompatibility.And because it is formed in the human body corrosion products non-toxic harmless,so magnesium alloy is often used as a biomaterial in medicine.For example,magnesium alloy as a common material of vascular stent,magnesium alloy implanted in the human body,in the human body environment slow degradation,and ultimately replaced by the newly generated bone tissue.This eliminates the patient's secondary surgery to remove the implanted stent pain,and reduce the medical expenses.However,the magnesium alloy in the electrolytic water environment corrosion rate is too fast,leading to the patient has not yet completely cured before the implant on the loss of complete mechanical properties.This shortcoming limits the wide application of magnesium alloy as an implant material in medicine.In this paper,Gd,Zn and Zr with good biocompatibility were selected as alloy materials to study the effect of Gd on the mechanicalproperties and corrosion properties of Mg-Zn-Zr alloy and to determine the optimal alloy composition.The effect of extrusion temperature on the properties of the alloy was studied and the optimum extrusion temperature was determined.The results are as follows:(1)The grain size of the alloy decreases with the increase of the content of gadolinium in the Mg-4Zn-xGd-0.4Zr alloy with different Gd content(0wt%,1wt%,2wt%,3wt%).After the addition of the Gd element,the composition of the pHase in the magnesium alloy also changes.Mg-4Zn-0.4Zr alloy consists of magnesium matrix and Mg0.97Zn0.03 binary pHase.Mg-4Zn-0.4Zr-1Gd,Mg-4Zn-0.4Zr-2Gd and Mg-4Zn-0.4Zr-3Gd are mainly composed of Mg matrix,Mg0.97Zn0.03 pHase and Mg3 Gdp Hase after adding Gd element,and Mg3 Gd.The volume fraction of the Mg3 Gd pHase increases with increasing Gd content.In the range of 0-3wt% Gd,the more Gd content,the finer the grain structure,the better the mechanical properties,and the Mg-4Zn-0.4Zr-3Gd showed the best mechanical properties.(2)The refinement of the grains in the alloy can enhance the corrosion resistance.The presence of an appropriate amount of Mg3 Gd also enhances the corrosion resistance,but the excess Mg3 Gdp Hase weakens the corrosion resistance of the magnesium alloy.Therefore,Mg-4Zn-0.4Zr-1Gd alloy has a relatively fine grain size and the existenceof a small amount of Mg3 Gd pHase,under the combined effect of the best performance.(3)Extrusion process can effectively refine the grain.Low bar temperature can effectively inhibit the growth of grain,250 ? alloy grain size minimum.After the extrusion there is a pHenomenon of uneven microstructure.(4)When the extrusion temperature is 250 ?,the second pHase crushing is obvious,the second pHase of the granular form is more and the particles are smaller.When the temperature rises to 350 ° C,the degree of breakage of the second pHase is gradually reduced,and the second pHase volume fraction decreases.Compared with the as-cast,the extrusion temperature does not change the composition of the alloy p Hase,the alloy is still by the ?-Mg,Mg0.97Zn0.03 and a small amount of Mg3 Gd pHase composition.(5)Extruded alloy in the early immersion,the corrosion rate will suddenly increase,and then slowly become stable and stable.As the temperature increases,the lower the corrosion rate of the alloy,the better the corrosion resistance.When the extrusion temperature is 350 ?,the alloy exhibits the best corrosion resistance.The average corrosion rate is0.42 mm / a.(6)In the electrochemical corrosion test,when the extrusion temperature is 250?,the corrosion potential is-1.62 V,the extrusiontemperature is 300?,the corrosion potential is-1.54 V,the extrusion temperature is 350?,the corrosion potential is-1.52 V.As the extrusion temperature increases,the corrosion potential of the alloy becomes more positive.When the temperature is 350 ?,the alloy has the best corrosion resistance,the results consistent with the results of weightlessness experiments. |
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