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Preparation of Mg-Zn-Ca Alloy with Y Element and Research of Its Thin-walled Tube Extruding-drawing Process

Author: HanJie
Tutor: SunHongFei
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: magnesium-rare earth alloy high ratio extrusion cold drawing thin-walledtube
CLC: TG146.22
Type: Master's thesis
Year: 2012
Downloads: 18
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Abstract


Magnesium alloy with advantages of low density, high specific strength, specificstiffness, good biocompatibility and biodegradability has broad application prospects inthe field of biological material. In this paper, the as-cast Mg-Zn-Ca alloy andMg-Zn-Ca-Y alloy ingots were prepared by smelting with protective Ar environment.The grains of the material were significantly refined by the high ratio extrusion process.Then the thin-walled magnesium tubes were fabricated by muti-pass drawing combinedannealing process, which can be used for coronary artery stent.The average grain size of as-cast ingots is150~350μm.The grain size of Mg-Zn-Caalloy is315μm while the grain sizes of three kinds of Mg-Zn-Ca-Y alloys are172μm,217μm and248μm, respectively, which reveals that Y element helps to refine grains.The grain sizes of materials were significantly refined to below3μm after two-passextrusion (the cumulate extrusion ratio is85). Especially the Mg-Zn-Ca-Y alloy afterfirst-pass extrusion at300℃and second-pass extrusion at150℃has the smallest grainsize of1.4μm. The mechanical properties of Mg-Zn-Ca-Y alloy after first-pass extrusionat300℃and second-pass extrusion at150℃are the best. The highest yield strength,ultimate tensile strength and elongation are350MPa,400MPa and25%, respectively.The mechanical properties of Mg-Zn-Ca-Y alloy are better than that of Mg-Zn-Ca alloy,which reveals that mechanical properties of magnesium alloys can be enhanced by Yelement addition.The as-extruded magnesium alloy bars were machined into Φ5×0.6mm tube billets,then annealled at250℃for15minutes. Finally, the Φ3.3×0.4mm Mg-Zn-Ca tube andΦ3.2×0.35mm Mg-Zn-Ca-Y tube were obtained by muti-pass cold drawing combinedannealing process.The yield strength, ultimate tensile strength and elongation of thefinal Mg-Zn-Ca tube are345.3MPa,366.6MPa and0.4%respectively. The yieldstrength, ultimate tensile strength and elongation of the final Mg-Zn-Ca-Y tube are296.4MPa,296.5MPa and0.7%respectively. The fracture pattern of the tubes is brittlefracture.In this paper, the best process for fabricating the thin-walled Mg-Zn-Ca alloy andMg-Zn-Ca-Y alloy tubes is as below: extrude the as-cast ingots at300℃for first passand at250℃for second pass. After anealled at250℃for15min the as-extrusion barswere drawn into thin-walled tubes by muti-pass drawing and recrystallization annealling.The best recrystallization annealling process is annealing at250℃for10min duringdrawing.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys > Magnesium
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