Study On Preparation Technology,Microstructure And Properties Of Magnesium Alloy Microtubes

With the deepening of research on magnesium alloy stents and the advancement of clinical applications,fully degradable magnesium alloy stents have a huge market prospect because of their high support strength and biodegradable absorption characteristics.However,the hexagonal close packed(HCP)structure of magnesium alloy has poor plastic deformation ability,and it is difficult to prepare high-quality micro-tubes through simple processing.Therefore,the preparation of magnesium alloy thin-walled micro-tubes has become an urgent problem to be solved.In this paper,the process of "electromagnetic stirring ingot casting-large extrusion ratio deformation preparation of bar material-extrusion forming tube blank" is used to prepare AZ31 magnesium alloy tube blank with a diameter of 6.12 mm and a wall thickness of 1.02 mm.The study found that the alloy grain size is greatly refined after plastic deformation.The average grain size of the electromagnetic stirring ingot is 112?m;the extruded tube billet has uniformly fine grains,and the average grain size is 2.78?m,which is compared with the electromagnetic stirring ingot The grain size has been refined by 97.52%.Analyzing the evolution of the texture of the ingot-bar-tube blank: the ingot grain has no preferred orientation;the extruded bar has a strong <10-10>-<11-20> dual-fiber texture;the extruded tube blank The(0001)base surface is parallel to the extrusion direction,which is a typical(0001)base surface fiber texture.Based on the successful preparation of extruded tube blanks,rotary forging was used to further reduce the size of the tube,and the influence of rotary forging on the forming of the extruded tube blank at room temperature was explored.Numerical simulation of rotary forging at room temperature was carried out by ABAQUS finite element software,and the technological parameters of rotary forging were optimized by orthogonal experiment.The study found that the forging pressure first decreases and then increases with the decrease of the forging die cavity entrance diameter.The axial feed speed of the pipe and the hammering frequency of the forging die have the greatest influence on the surface strain uniformity of the pipe material,and there is an interaction;It has the lowest effect on the surface strain uniformity,which mainly affects the maximum principal strain distribution at the end of the tube blank.The optimal process parameters of rotary forging in this experiment are: axial feed rate 0.9mm/s,forging die hammer frequency 20 Hz,reduction amount 0.05 mm.This parameter is used to perform spin forging of AZ31 magnesium alloy microtube.After 9 passes of rotary forging the extruded tube,the final diameter of the tube is 5.0mm and the wall thickness is 0.79 mm.The actual test results show that at room temperature,rotary forging has a poor effect on the thickness reduction of the tube blank,but it greatly improves the uniformity of the tube blank wall thickness.This paper proposes to use the fixed-length acid etching process to rapidly form magnesium alloy microtubes.Through the exploration of the fixed-length acid etching process of nitric acid and phosphoric acid combined with sodium citrate corrosion inhibitors,the effect of the abovementioned inorganic acid solution on the wall thickness of AZ31 magnesium alloy tube blanks is studied.Impact.Through the orthogonal test of phosphate-based solution and nitric acid-based solution,it is found that the(size reduction)phosphoric acid-based solution makes the surface of the tube billet easy to produce pitting pits,which is not conducive to controlling the surface roughness.The optimal surface roughness parameter is only 13.315 ?m.The nitric acid-based solution gives the tube blank a metallic luster,which is easy to control the surface roughness.Parameters optimized by range analysis are nitric acid concentration 50ml/L,acid etching time7 min,sodium citrate corrosion inhibitor 2g/L,tube billet surface roughness is 5.201?m,and only weak intergranular corrosion occurs.Tests have found that fixed-length acid etching is beneficial to quickly and uniformly reduce the geometric dimensions of the wall thickness of magnesium alloy pipes.