Study On Hot Drawing Process And Microstructure And Properties Of Agnesium Alloy Tubes

At present, the stent materials used in blood vessel are non-degradable materials. Asbiological material, the degradable feature of magnesium alloy is the biggest selling point.Although the degradation process of magnesium alloy needs further discussion, as thenecessary element for the human body, with the development of science, magnesiumwould be applied in biomedicine as biomaterials certainly. Based on the trend ofapplication of magnesium alloy in medicine, this paper mainly studies on the hot drawingforming process of AZ31magnesium alloy tubes combined with simulation,metallographic analysis. Finally, the thin wall tubes with better comprehensivemechanical properties are obtained successfully, which lay the foundations for theapplication of magnesium alloy in medicine.This paper uses the numerical simulation software to analyze the hot drawingprocess of AZ31magnesium alloy, then the bearing width of the drawing die and thedrawing process parameters are optimized. The simulation results show that: the drawingforce is minimum when the bearing width is2.5mm; the drawing force increases withdrawing speed increased, when the drawing speed is0.25mm/s, the drawing force isrelatively small and the change is stable; the minimum total strain is obtained when thereducing of the tube diameter is1mm, and the wall thickness variation of tube is moreevenly, therefore, it suitable for the tubes with diameter size are7~14mm to choose1mmas the best deformation.The AZ31magnesium alloy tubes with the size Φ4×0.2mm are obtained by thedrawing process, which adopt three passes non-mandrel drawing and eleven passesmandrel drawing. By analyzing the thickness change of the drawing process, the resultshows that: with the non-mandrel drawing speed of0.25mm/s, the wall thickness of thetubes is more uniform, meanwhile, it good for rectifying eccentric; when mandreldrawing with the speed of0.3mm/s, the wall thickness decreases linearly. By analyzing the microstructure and properties of drawing, its show that: with theincrease of deformation degree, the grain size of magnesium alloy refines significantly,and the mechanical property is improved, too. When the deformation reaches to95.4%,the grain size is about8μm. The tensile strength reaches to247.3MPa, compared withthe extruded, it increases about10%, while the elongation is improved to16.8%.After solution treatment of AZ31magnesium alloys, the twins produced by drawingdisappear, β-Mg17Al12phase mainly integrates into Mg matrix, the plasticity ofmagnesium alloy improves significantly. Between the non-mandrel drawing and mandreldrawing, solution treatment is adopt to prevent the pipe breaking phenomenon duringdrawing process, the pipe has better comprehensive mechanical properties at420℃for4h, the elongation is17.5%, the strength is235.4MPa.