Research On Cold-drawing Process Of Pure Magnesium Thin-wall Tube And Corrosion Behavior Of Pure Magnesium In Simulated Body Fluid

Magnesium is becoming a popular research subject in the Biomedical MaterialsField because of its outstanding biological properties. First, Mg has biocompatibilityand degradability.Second, the Young’s modulus of Mg is close to human body’sbones. However, Mg is difficult to deformation at room temperature and is corrodedrapidly in chloride containing solution, such as the human body fluid. Therefore，ifwant to prepare magnesium thin-wall tube used in the Biomedical Materials Field, itis necessary to research preparation process and Corrosion Resistance of the tube.In this paper, certain wall thickness of pure magnesium thin-walled tube wasprepared by cold drawing process combined with intermediate annealing. Changes oftissue preparation and deformation mechanism of the tube have been analyzed. Then,the factors relating the corrosion of tubes such as the grain size, texture, twin andcorrosion medium were studied.At last, The corrosion behavior of pure magnesiumthin-walled tube have been research by Immersion test.Magnesium thin-wall tube was prepared by35times cold drawing combined with4times intermediate annealing. The cumulative deformation scale is0.7395. Grain iselongated along the drawing direction, some of the grain is refined. The drawingdeformation mechanism of Mg tube was based on dislocations slip, twining and graincoordination mechanism.The effects of grain size, texture, twin and corrosion medium on corrosionresistance were studied by electrochemical tests and immersion test. It was found thatthe effect of grain size on corrosion performance exist threshold, beyond this threshold,corrosion resistance will be worsen. The surface of Mg occurred pitting corrosionwhen the grain size is small, the filiform corrosion occurred as the increases of thegrain size. Twin will worsen the corrosion resistance of pure magnesium, the corrosionmorphology changes along with the increase of twin amount. The pitting corrosionalong the grain boundary is the main corrosion morphology when the twin amount islow, the filiform corrosion and the pitting corrosion extended to the internal of thegrain occurred as the increases of the twin amount. Influence of texture on thecorrosion resistance related to the orientation of basal plane, extrusion temperaturebelow200, the corrosion resistance of basal plane is weaker than non-basal plane. Texture has no influence on the corrosion morphology, pitting corrosion is the maincorrosion morphology both on the basal plane and non-basal plane. The effect ofchemical composition in corrosion medium is great, corrosion is slow in the simulatedbody fluid. In SBF, the main corrosion is pitting corrosion, while the main corrosion isuniform corrosion in0.9%NaCl.By study the immersion test of magnesium thin-wall tube, the average corrosioncurrent (48.75μA/cm2) of the tube obtained by method of loss of weight.The corrosionoccurred on the tube in the SBF is uneven, while in0.9%NaCl is even. At last,Confirmation of the positive role of Ca2+、HCO3-、HPO42+to reduce the corrosion rateof pure magnesium.