High-performance thin-wall micro-pipe for magnesium alloy vascular stent and preparation method thereof

Abstract

The application discloses a kind of high-performance thin-wall microtubes for magnesium alloy blood vessel stent, high-performance thin-wall microtubes are prepared from magnesium alloy, magnesium alloy includes the following mass percentage content combination: Zn content is 1-3%, Mn content is 0.2-2%, the rest is Mg.The application also discloses the preparation method of the above-mentioned thin-wall microtube, including the following steps: in protective atmosphere, ultrasonic smelting is used to obtain magnesium alloy ingot, then the preparation of high plasticity microtube extrusion blank is carried out by the composite extrusion process of extrusion-roughing-extrusion, the formability and stability of extruded microtube are improved, after mechanical processing and perforation, hot extrusion is carried out, and ultra-long hollow pipe blank is prepared, and magnesium alloy thin-wall tube is prepared by replacing traditional multi-pass cold drawing process with single-pass hot rolling microtube forming.The beneficial effects of the application are that the prepared magnesium alloy thin-wall microtube has high strength, excellent plasticity and corrosion resistance, and good physiological tolerance, and can meet the mechanical property requirements of blood vessel stent forming and balloon expansion.

Description

Technical Field

[0001] This invention relates to the field of biomedical metal material processing technology, and in particular to a high-performance thin-walled microtube for magnesium alloy vascular stents and its preparation method. Background Technology

[0002] Coronary intervention has evolved from balloon angioplasty and bare-metal stents to drug-eluting stents, significantly improving clinical outcomes for cardiovascular patients. However, mounting evidence suggests that permanent retention of drug-eluting stents is associated with complications such as late in-stent thrombosis, chronic inflammation, and vasomotor dysfunction. Bioresorbable stents are gradually becoming a major advancement in cardiovascular innovation, offering a fundamental solution to these problems associated with permanent stents.

[0003] Among bioresorbable scaffold materials, magnesium alloys offer several significant advantages for vascular stent applications. For instance, the magnesium ions and hydrogen molecules released during magnesium alloy degradation have repairing effects on vascular lesions, and magnesium alloys also exhibit good biocompatibility, making them a promising candidate for clinical application. However, the hexagonal close-packed crystal structure and high chemical reactivity of magnesium alloys limit the plastic processing and corrosion resistance improvement of thin-walled tubing. This leads to complex manufacturing processes, low yield rates, and issues such as scaffold ribs being prone to breakage during expansion and deformation, insufficient support, and inadequate durability after implantation. Therefore, improving the plasticity and corrosion resistance of magnesium alloy thin-walled tubing is a primary and urgent problem to be solved.

[0004] Microstructure is the main factor determining the properties of magnesium alloys. Although microtubes can usually be prepared by cold drawing, the tubes are subjected to tensile stress during the cold drawing process. Therefore, multiple intermediate annealings are required to eliminate residual stress, and the risk of cracking induced by tensile stress increases, which further limits the preparation of thin-walled magnesium alloy tubes. The elongation of thin-walled magnesium alloy tubes prepared by conventional drawing process is only about 10%, which is difficult to meet the requirements of the harsh plastic deformation of vascular stents on the plastic performance of the tubes.

[0005] Current magnesium alloy vascular stent fabrication typically involves adding rare earth elements or aluminum to simultaneously enhance the material's strength, ductility, and corrosion resistance. This ensures sufficient mechanical reliability during microtubule formation and stent loading into balloons and subsequent in vivo expansion to support diseased blood vessels, while also extending effective support time. However, studies have shown that rare earth elements may induce or exacerbate local inflammatory responses; aluminum possesses potential neurotoxicity, and excessive accumulation is associated with adverse effects on the central nervous system, digestive system, brain, liver, bones, kidneys, and hematopoietic and immune functions. Given the stringent safety requirements for implantable devices, there is an urgent need to develop novel magnesium alloy microtubule and stent fabrication technologies that do not contain rare earth elements or aluminum, but primarily utilize elements abundant in the human body and physiologically well-tolerated. Furthermore, these technologies should balance stent delivery, expansion, and long-term support performance during extrusion. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance thin-walled microtube for magnesium alloy vascular stents and its preparation method, and to provide a thin-walled microtube for magnesium alloy vascular stents that simultaneously possesses high strength, excellent plasticity and corrosion resistance, as well as a method for preparing the thin-walled microtube.

[0007] The objective of this invention is achieved through the following technical solution: A high-performance thin-walled microtube for magnesium alloy vascular stents, wherein the high-performance thin-walled microtube is made of magnesium alloy, and the magnesium alloy comprises the following combination of mass percentages: Zn content of 1-3%, Mn content of 0.2-2%, and the remainder being Mg.

[0008] Zinc (Zn) and manganese (Mn) are essential trace elements for the human body. Using magnesium alloys containing Zn and Mn is expected to further improve the biocompatibility and biodegradability of the material while maintaining necessary mechanical properties, especially when Zn ≤ 3 wt.%, Zn can be completely dissolved into the matrix after solution treatment; the addition of a small amount of Mn is beneficial for purifying the melt and removing impurities. Therefore, low-alloyed Mg-Zn-Mn alloys are usually single-phase solid solutions, which can achieve complete and uniform degradation in vivo, exhibiting high biosafety and biocompatibility. However, traditional processing techniques cannot achieve the thin-walled tube processing of the above-mentioned magnesium alloys, and it is also difficult to guarantee the plasticity, strength, and corrosion resistance of the microtubes. Therefore, this invention also provides a method for preparing the above-mentioned high-performance thin-walled microtubes for magnesium alloy vascular stents, including the following steps: S1. Preparation of magnesium alloy ingots: Magnesium alloy is melted under a protective atmosphere and ultrasonically cast to obtain ingots. The ingots are then solution treated and cooled for later use. S2. Preparation of superplastic magnesium alloy blanks: The ingot is preheated with the extrusion-upsetting-extrusion composite mold. The preheated ingot is loaded into the extrusion-upsetting-extrusion composite mold and extruded into blanks with a diameter of 5-25 mm by an extruder. S3. Preparation of magnesium alloy blank tube: First, mechanically open the blank bar, and then hot extrude the opened blank bar to make a blank tube with an outer diameter of 2-4mm and an inner diameter of 1.1-3.1mm. S4. Preparation of magnesium alloy thin-walled tubes: The blank tube is hot-rolled in a single pass into finished thin-walled tubes with an outer diameter of 1-3 mm and a wall thickness of 0.11-0.3 mm.

[0009] Traditional processing methods for preparing thin-walled magnesium alloy tubes often involve multiple cold drawing passes and frequent intermediate annealing, which still result in uneven wall thickness, tensile stress-induced cracking, and poor corrosion resistance. This application addresses these issues by using ultrasonic melting in a protective atmosphere to obtain magnesium alloy ingots. Subsequently, a composite extrusion process of extrusion-upsetting-extrusion is employed to prepare microtube extrusion blanks with high plasticity, improving the formability and stability of the extruded microtubes. After machining and piercing, hot extrusion is performed to obtain ultra-long hollow tube blanks. A single-pass hot rolling microtube forming process replaces the traditional multi-pass cold drawing process. Benefiting from the recrystallization induced by thermal deformation during hot rolling, post-rolling stress relief or recrystallization annealing is unnecessary. Radial compressive stress is applied during hot rolling, while axial tensile stress is not borne, significantly improving wall thickness uniformity and reducing the risk of tensile stress-induced cracking. Simultaneously, texture control during hot rolling ensures that the {0001} basal plane of the grains is approximately parallel to the tube wall. Through the synergistic effect of orientation optimization and grain refinement, the plasticity and corrosion resistance of the tube are significantly improved.

[0010] Furthermore, in step S1, the melting and casting temperature is 700-750℃, the solution treatment temperature is 400-500℃, and the holding time is 12-24h.

[0011] Furthermore, in step S2, the preheating temperature is 250-400℃, the preheating time is 2h, and the extrusion speed of the extruder is 0.1-3mm / s.

[0012] Furthermore, in step S3, the hot extrusion temperature is 200-400℃ and the extrusion speed is 0.1-3mm / s.

[0013] Furthermore, in step S4, hot rolling is performed using a single-pass hot rolling mill, with the hot rolling temperature controlled at 100-300℃.

[0014] Furthermore, the extrusion-upsetting-extrusion composite mold includes an upper mold and a lower mold, which together form an extrusion-upsetting-extrusion composite cavity. The extrusion-upsetting-extrusion composite cavity includes a first extrusion cavity located in the upper mold and an upsetting cavity and a second extrusion cavity located in the lower mold. The end of the first extrusion cavity is provided with a first smooth transition cavity communicating with the upsetting cavity, and the end of the upsetting cavity is provided with a second smooth transition cavity communicating with the second extrusion cavity. The diameter of the upsetting cavity is larger than the diameter of the first extrusion cavity, and the diameter of the first extrusion cavity is larger than the diameter of the second extrusion cavity.

[0015] Furthermore, the upper mold is provided with a flared feeding chamber connected to the first extrusion chamber, the diameter of the small end of the flared feeding chamber being the same as the diameter of the first extrusion chamber, and the lower mold is provided with a discharge chamber connected to the second extrusion chamber, the diameter of the discharge chamber being larger than the diameter of the second extrusion chamber.

[0016] Furthermore, the tube rolling mill is a cold tube rolling mill, and a shower box is installed on the tube rolling mechanism of the cold tube rolling mill. A shower screen is provided in the shower box above the tube rolling mechanism. The shower box is connected to an oil inlet pipe and an oil return pipe. The oil inlet pipe is located above the shower screen, and the oil return pipe is located below the tube rolling mechanism.

[0017] The hot rolling process adds a heating unit, circulation system, temperature control unit and shower mechanism to the cold rolling mill. It can achieve uniform heating of rolled pipe and precise control of rolling temperature without large-scale replacement of main equipment. It can also reduce the diameter and thin the extruded pipe, realize the single-pass hot rolling process, and obtain high-strength, corrosion-resistant thin-walled pipe.

[0018] The present invention has the following advantages: 1. The prepared magnesium alloy thin-walled microtubes have high strength, excellent plasticity and corrosion resistance, and good physiological tolerance; 2. Introducing ultrasonic oscillation during the melting / casting stage, utilizing the synergistic effect of acoustic cavitation and acoustic flow, effectively eliminates defects such as porosity formed during the casting process, and, combined with rapid cooling, significantly suppresses macro / micro component segregation.

[0019] 3. By using a composite die and forming path of extrusion-upsetting-extrusion to precisely control the crystal orientation, the material has a higher Schmidt factor during axial deformation, which improves the plastic deformation capacity of the initial billet and produces magnesium alloy billets with fine grains, uniform distribution and high plasticity, providing a high comprehensive mechanical property basis for subsequent pipe extrusion and hot rolling.

[0020] 4. Replacing the traditional multi-pass cold drawing thinning process with single-pass hot rolling reduces the risk of pipe cracking, significantly simplifies the manufacturing process of thin-walled pipes, reduces production costs, and promotes the preferred orientation of the {0001} base plane parallel to the pipe wall. The combined effect of grain refinement and the texture of the base plane parallel to the pipe wall results in magnesium alloy thin-walled pipes with excellent strength and plasticity, good corrosion resistance, and high surface quality. Attached Figure Description

[0021] Figure 1 This is a schematic diagram showing the morphology and wall thickness of the microtubes prepared in Example 1.

[0022] Figure 2 This is a microstructure diagram of the microtubes prepared in Example 1.

[0023] Figure 3 This is a schematic diagram of the structure of a composite extrusion-upsetting-extrusion die.

[0024] Figure 4 This is a schematic diagram of material deformation during the extrusion of magnesium alloy using a combined extrusion-upsetting-extrusion die.

[0025] Figure 5 Stress-strain curves for billets prepared by traditional extrusion and extrusion-upsetting-extrusion composite extrusion.

[0026] Figure 6 Microstructure of billets prepared by traditional extrusion and extrusion-topping-extrusion composite extrusion.

[0027] Figure 7 Crystal orientation distribution, grain size distribution, and {0001} pole figure of billets prepared by traditional extrusion and extrusion-topping-extrusion composite extrusion.

[0028] Figure 8 A schematic diagram of the mold assembly for preparing the blank tube.

[0029] Figure 9 This is a schematic diagram of the tube rolling mechanism and the shower box.

[0030] Figure 10 The diagram shows the crystal orientation information, grain size distribution, and {0001} pole figure of the microtubes prepared in Example 1.

[0031] Figure 11 This is a schematic diagram showing the crystal orientation distribution of conventionally machined tubing and the tubing processed in this application.

[0032] Figure 12 Stress-strain diagrams of conventionally machined pipes and pipes processed according to this application are shown.

[0033] Figure 13 The images show the corrosion morphology of microtubes processed by conventional machining and microtubes processed according to this application after dynamic corrosion in SBF solution for 48 hours.

[0034] Figure 14 The minimum stent-balloon size that allows vascular stents prepared from conventionally machined tubing and the microtubes processed in this application to expand without breaking when compressed onto a 2.75 mm diameter balloon.

[0035] Figure 15 Micro-CT image of a vascular stent prepared using microtubes for this application implanted into the intracranial artery of a beagle.

[0036] In the diagram, 1-upper mold, 2-lower mold, 3-first extrusion chamber, 301-first smooth transition chamber, 4-building chamber, 401-second smooth transition chamber, 5-second extrusion chamber, 6-flared inlet chamber, 7-outlet chamber, 8-mold lifting hole, 9-mold extrusion rod, 10-centering mandrel, 11-perforated blank bar, 12-lower extrusion mold, 13-upper mold limit block, 14-lower mold limit block, 15-rolling tube mechanism, 16-shower box, 17-shower net, 18-oil inlet pipe, 19-oil return pipe. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0040] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0041] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0042] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0043] Example 1

[0044] This embodiment provides a high-performance thin-walled microtube for magnesium alloy vascular stents. The high-performance thin-walled microtube is made of magnesium alloy, which includes the following mass percentages: Zn content of 2.11%, Mn content of 0.23%, and the remainder being Mg.

[0045] A method for fabricating high-performance thin-walled microtubes for magnesium alloy vascular stents includes the following steps: S1. Preparation of magnesium alloy ingots: First, the vacuum induction melting furnace is evacuated to 1×10-2 Pa atmospheric pressure, and then high-purity argon gas is introduced. The ingots are then cast at 730℃. During the casting process, ultrasonic vibration is used to eliminate defects such as bubbles generated during casting. The ingots are then rapidly cooled by a cooling system. The ingots are then solution treated at 450℃ for 24 hours and cooled for later use.

[0046] S2. Preparation of superplastic magnesium alloy blanks: The ingot and the extrusion-upsetting-extrusion composite die are placed in a heat treatment furnace at 300℃ and held for 2 hours. Then, the surface is coated with a lubricant and placed into the extrusion cylinder of an extruder. The ingot is then extruded into a blank with a diameter of 16mm using the extrusion-upsetting-extrusion composite die at an extrusion speed of 0.1mm / s.

[0047] S3. Preparation of magnesium alloy blank tube: First, mechanically pierce the blank bar to form an open blank bar with an outer diameter of 10mm and an inner diameter of 1.9mm. Then, use a tube extrusion die with a centering mandrel to extrude it into a blank tube with an outer diameter of 2.3mm and an inner diameter of 1.85mm at 250℃. The extrusion speed is 0.1mm / s.

[0048] S4. Preparation of magnesium alloy thin-walled tubes: The blank tube is inserted into the mandrel of the tube rolling mill, and the rolling temperature is controlled at 220℃. The blank tube is hot rolled in a single pass to obtain a thin-walled tube with an outer diameter of 2.22mm and a wall thickness of 0.22mm.

[0049] The prepared thin-walled tube can be further cut and polished to produce a magnesium alloy vascular stent.

[0050] Specifically, to achieve the composite extrusion in step S2, such as Figure 3As shown, the extrusion-upsetting-extrusion composite mold includes an upper mold 1 and a lower mold 2. The upper mold 1 and the lower mold 2 form an extrusion-upsetting-extrusion composite cavity. The extrusion-upsetting-extrusion composite cavity includes a first extrusion cavity 3 located in the upper mold and an upsetting cavity 4 and a second extrusion cavity 5 located in the lower mold. The end of the first extrusion cavity 3 is provided with a first smooth transition cavity 301 that connects to the upsetting cavity 4. The end of the upsetting cavity 4 is provided with a second smooth transition cavity 401 that connects to the second extrusion cavity 5. The diameter of the upsetting cavity 4 is larger than the diameter of the first extrusion cavity 3, and the diameter of the first extrusion cavity 3 is larger than the diameter of the second extrusion cavity 5.

[0051] The upper mold 1 is provided with a flared feeding chamber 6 connected to the first extrusion chamber 3. The diameter of the small end of the flared feeding chamber 6 is the same as the diameter of the first extrusion chamber 3. The lower mold 2 is provided with a discharge chamber 7 connected to the second extrusion chamber 5. The diameter of the discharge chamber 7 is larger than the diameter of the second extrusion chamber 5.

[0052] To facilitate the hoisting of the mold, hoisting holes 8 are provided on the side walls of the upper mold 1 and the lower mold.

[0053] like Figure 4 The diagram illustrates the material deformation. Under extrusion pressure, the magnesium alloy first passes through the first extrusion chamber 3 (D1) of the die, and then enters the upsetting chamber 4 (D2). When the material tip touches the first smooth transition chamber 301, because the aperture of D1 is smaller than that of D2, the material undergoes upsetting deformation first. During this stage, the crystal orientation in the material gradually shifts from the {0001} basal plane parallel to the extrusion direction to the {0001} basal plane perpendicular to the extrusion direction. When the material fills the upsetting chamber 4, and pressure continues to be applied, the magnesium alloy is extruded through the second extrusion chamber 5 (D3). At this time, the orientation of the {0001} basal plane perpendicular to the extrusion direction in the upsetting part shifts, resulting in grain refinement and crystal orientation control. Ultimately, an orientation of approximately 67° between the {0001} basal plane and the extrusion direction is obtained, thereby increasing the Schmidt factor of basal slip. Simultaneously, through the synergistic effect of grain refinement, the plasticity of the material is significantly increased.

[0054] like Figure 5 As shown, under the condition of using the same raw materials, the stress-strain curves of the blank bar prepared by traditional extrusion and the blank bar prepared in step S2 are shown. It can be seen that after extrusion-upsetting-extrusion composite processing, the plasticity of the magnesium alloy is significantly increased to 44%, which is much higher than that of the blank bar prepared by traditional extrusion. Extrusion-upsetting-extrusion composite processing lays the foundation for subsequent processing formability, stability and microtube performance improvement.

[0055] like Figure 6As shown, when using the same raw materials, the microstructure of the blank prepared by conventional extrusion and the blank prepared in step S2 are compared. Figure 6 A represents the traditional extrusion process. Figure 6 B represents the composite extrusion process in step S2. It can be seen that the grain size after the extrusion-upsetting-extrusion composite processing is significantly reduced compared to the traditional process, indicating that the composite processing has a significant grain refinement capability. like Figure 7 As shown, when using the same raw materials, the crystal orientation distribution, grain size distribution, and {0001} pole figure of the blank rod prepared by conventional extrusion and the blank rod of step S2 are compared. Figure 7 A, 7B, and 7C represent traditional extrusion processes. Figure 7 D, 7E, and 7F represent the composite extrusion process in step S2. Figure 7 A and C indicate that traditional extrusion resulted in a strong texture where the {0001} basal plane is parallel to the extrusion direction, meaning that the c-axis of most grains forms an angle of approximately 90° with the extrusion direction. Figure 7 D and F indicate that the orientation of the {0001} basal plane deviates after the "extrusion-upsetting-extrusion" composite processing. Most grains form an angle of about 67° with the extrusion direction, which is conducive to improving the Schmidt factor, thereby promoting basal slip and improving the plasticity of the extruded billet. Figure 7 The grain size distribution results of B and 7E also show that the magnesium alloy billet prepared by traditional extrusion has a larger grain size distribution range and an average grain size of 6.47±3.86 μm, while the magnesium alloy billet prepared by "extrusion-upsetting-extrusion" has a smaller grain size distribution range and an average grain size of 3.36±1.95 μm, proving the significant grain refinement capability of the extrusion-upsetting-extrusion composite process.

[0056] To achieve the preparation of the blank tube in step S3, such as Figure 8 The diagram shows an assembly of an extrusion die. The die extrusion rod 9 is located on the extrusion hole of the upper limit block 13 to push the centering mandrel 10 through the extrusion of the perforated blank rod 11. The end of the centering mandrel 10 is equipped with a force-bearing block adapted to the die extrusion rod 9. The perforated blank rod 11 is placed in the extrusion hole of the upper limit block 13. A lower extrusion die 12 is located below the perforated blank rod 11 within the extrusion hole. A lower die limit block 14 is used to restrict the lower extrusion die 12. The lower die limit block 14 has a through hole for the blank tube to pass through.

[0057] The upper flared structure of the extrusion die 12 ensures that the prepared blank tube has a high degree of concentricity by placing the centering mandrel 10 and the extrusion die 12 in the same cavity (extrusion hole).

[0058] To achieve the hot rolling process in step S4, this embodiment improves the cold rolling mill, such as... Figure 9 As shown, a shower box 16 is installed on the tube rolling mechanism 15 of the cold rolling mill. A shower screen 17 is located above the tube rolling mechanism 15 inside the shower box 16. The shower box 16 is connected to an oil inlet pipe 18 and an oil return pipe 19. The oil inlet pipe 18 is located above the shower screen 17, and the oil return pipe 19 is located below the tube rolling mechanism 15. Correspondingly, a heating unit, a temperature control unit, and a circulation system are also provided. The circulation system includes a heat transfer oil circulation tank, high-temperature resistant oil pipes, and a high-temperature resistant circulation pump. The heating unit includes a power supply system and electric heating elements. The temperature control unit includes thermocouples, a temperature controller, a circuit breaker, and an AC contactor. The hot oil is dimethyl silicone oil or other high-temperature resistant oil.

[0059] The heat transfer oil in the circulation tank is heated to the hot rolling temperature by a heating unit. The oil temperature is precisely controlled and stabilized by thermocouples, a temperature controller, and a circuit breaker. A high-temperature circulating pump pumps the high-temperature heat transfer oil into a shower box, where the heat transfer oil is heated via a shower screen 17. During hot rolling, the tube exhibits good lubrication and uniform heating across all parts. Single-pass hot rolling (without secondary rolling) under the conditions of horizontal reciprocating motion of the rolls and continuous tube feeding allows for tube diameter and thinning, resulting in high-strength, corrosion-resistant thin-walled microtubes. Hot rolling further refines the grains and improves the plasticity of the microtubes, such as… Figure 10 As shown, from Figure 10 As can be seen from A and 10B, it has a very uniform and fine grain size, with an average grain size of 3.38. Figure 10 As can be seen from C, the reshaping of the texture makes the {0001} basal plane approximately parallel to the tube wall, which is beneficial to the improvement of the corrosion resistance of the microtubes. This confirms that hot rolling significantly improves the corrosion resistance of microtubes through the synergistic effect of orientation optimization and fine graining.

[0060] By improving the cold rolling mill, a hot rolling process is achieved. Compared to the traditional multi-pass cold drawing process, hot rolling induces recrystallization in the microtubes through thermal deformation, eliminating the need for post-rolling stress relief or recrystallization annealing, thus simplifying the process and control. Furthermore, during tube manufacturing, primarily radial compressive stress is applied, with minimal axial tensile stress, significantly improving wall thickness uniformity and reducing the risk of tensile stress-induced cracking. This process boasts high efficiency, high yield, and low cost, making it suitable for large-scale production and clinical translation applications.

[0061] like Figure 1 As shown, Figure 1 C and D are extruded microtubules, which have a rough surface morphology similar to "orange peel". Figure 1E and F are hot-rolled microtubes. Their wall thickness and surface roughness are significantly reduced compared to extruded microtubes. The wall thickness and inner diameter of the extruded microtubes decreased from 0.23±0.02 mm and 1.85±0.03 mm, respectively, to 0.22±0.01 mm and 1.79±0.02 mm after hot rolling. This indicates that the dimensional accuracy of the hot-rolled microtubes fully meets the requirements for vascular stent cutting. Figure 2 Microscopic tissue diagrams, in which Figure 2 A represents the traditional extrusion process. Figure 2 B represents the hot rolling process in step S4. It can be seen that the grain size is significantly refined and the grain distribution is more uniform after hot rolling.

[0062] Example 2

[0063] This embodiment provides a high-performance thin-walled microtube for magnesium alloy vascular stents. The high-performance thin-walled microtube is made of magnesium alloy, which includes the following mass percentages: 1% Zn, 0.2% Mn, and the remainder Mg.

[0064] A method for fabricating high-performance thin-walled microtubes for magnesium alloy vascular stents includes the following steps: S1. Preparation of magnesium alloy ingots: First, the vacuum induction melting furnace is evacuated to 1×10-2 Pa atmospheric pressure, and then high-purity argon gas is introduced. The ingots are then cast at 700℃. During the casting process, ultrasonic vibration is used to eliminate defects such as bubbles generated during casting. The ingots are then rapidly cooled by a cooling system. The ingots are then solution treated at 400℃ for 20 hours and cooled for later use.

[0065] S2. Preparation of superplastic magnesium alloy blanks: The ingot and the extrusion-upsetting-extrusion composite die are placed in a heat treatment furnace at 250°C and held for 2 hours. Then, the surface is coated with a lubricant and placed into the extrusion cylinder of an extruder. The ingot is then extruded into a blank with a diameter of 20 mm using the extrusion-upsetting-extrusion composite die at an extrusion speed of 2 mm / s.

[0066] S3. Preparation of magnesium alloy blank tube: First, mechanically pierce the blank bar to form an open blank bar with an outer diameter of 12mm and an inner diameter of 3.5. Then, use a tube extrusion die with a centering mandrel to extrude it into a blank tube with an outer diameter of 4mm and an inner diameter of 3.1 at 200℃. The extrusion speed is 2mm / s.

[0067] S4. Preparation of magnesium alloy thin-walled tubes: The blank tube is inserted into the mandrel of the tube rolling mill, and the rolling temperature is controlled at 100℃. The blank tube is hot rolled in a single pass to obtain a thin-walled tube with an outer diameter of 3mm and a wall thickness of 0.3mm.

[0068] Since the mold assembly and usage process is the same as in Example 1, the relevant details will not be repeated. The dimensions and specifications of each mold can be adjusted according to specific circumstances.

[0069] Example 3

[0070] This embodiment provides a high-performance thin-walled microtube for magnesium alloy vascular stents. The high-performance thin-walled microtube is made of magnesium alloy, which includes the following combination of mass percentages: 3% Zn, 2% Mn, and the remainder Mg.

[0071] A method for fabricating high-performance thin-walled microtubes for magnesium alloy vascular stents includes the following steps: S1. Preparation of magnesium alloy ingots: First, the vacuum induction melting furnace is evacuated to 1×10-2 Pa atmospheric pressure, and then high-purity argon gas is introduced. The ingots are then cast at 750℃. During the casting process, ultrasonic vibration is used to eliminate defects such as bubbles generated during the casting process. The ingots are then rapidly cooled by a cooling system. The ingots are then solution treated at 500℃ for 12 hours and cooled for later use.

[0072] S2. Preparation of superplastic magnesium alloy blanks: The ingot and the extrusion-upsetting-extrusion composite die are placed in a heat treatment furnace at 400℃ and held for 2 hours. Then, the surface is coated with a lubricant and placed into the extrusion cylinder of an extruder. The ingot is then extruded into a blank with a diameter of 18mm using the extrusion-upsetting-extrusion composite die at an extrusion speed of 3mm / s.

[0073] S3. Preparation of magnesium alloy blank tube: First, mechanically pierce the blank bar to form an open blank bar with an outer diameter of 10mm and an inner diameter of 3. Then, use a tube extrusion die with a centering mandrel to extrude it into a blank tube with an outer diameter of 2mm and an inner diameter of 1.1 at 400℃. The extrusion speed is 3mm / s.

[0074] S4. Preparation of magnesium alloy thin-walled tubes: The blank tube is inserted into the mandrel of the tube rolling mill, and the rolling temperature is controlled at 300℃. The blank tube is hot rolled in a single pass to obtain a thin-walled tube with an outer diameter of 1mm and a wall thickness of 0.11mm.

[0075] Since the mold assembly and usage process is the same as in Example 1, the relevant details will not be repeated. The dimensions and specifications of each mold can be adjusted according to specific circumstances.

[0076] Example 4

[0077] This embodiment provides a high-performance thin-walled microtube for magnesium alloy vascular stents. The high-performance thin-walled microtube is made of magnesium alloy, which includes the following mass percentages: Zn content of 2.4%, Mn content of 0.3%, and the remainder being Mg.

[0078] A method for fabricating high-performance thin-walled microtubes for magnesium alloy vascular stents includes the following steps: S1. Preparation of magnesium alloy ingots: First, the vacuum induction melting furnace is evacuated to 1×10-2 Pa atmospheric pressure, and then high-purity argon gas is introduced. The ingots are then cast at 720℃. During the casting process, ultrasonic vibration is used to eliminate defects such as bubbles generated during casting. The ingots are then rapidly cooled by a cooling system. The ingots are then solution treated at 420℃ for 18 hours and cooled for later use.

[0079] S2. Preparation of superplastic magnesium alloy blanks: The ingot and the extrusion-upsetting-extrusion composite die are placed in a heat treatment furnace at 280℃ and held for 2 hours. Then, the surface is coated with a lubricant and placed into the extrusion cylinder of an extruder. The ingot is then extruded into a blank with a diameter of 15mm using the extrusion-upsetting-extrusion composite die at an extrusion speed of 0.5mm / s.

[0080] S3. Preparation of magnesium alloy blank tube: First, mechanically pierce the blank bar to form an open blank bar with an outer diameter of 16mm and an inner diameter of 3. Then, use a tube extrusion die with a centering mandrel to extrude it into a blank tube with an outer diameter of 3.3mm and an inner diameter of 2.7 at 280℃. The extrusion speed is 0.5mm / s.

[0081] S4. Preparation of magnesium alloy thin-walled tubes: The blank tube is inserted into the mandrel of the tube rolling mill, and the rolling temperature is controlled at 250℃. The blank tube is hot rolled in a single pass to obtain a thin-walled tube with an outer diameter of 1.5mm and a wall thickness of 0.2mm.

[0082] Since the mold assembly and usage process is the same as in Example 1, the relevant details will not be repeated. The dimensions and specifications of each mold can be adjusted according to specific circumstances.

[0083] Example 5

[0084] This embodiment provides a high-performance thin-walled microtube for magnesium alloy vascular stents. The high-performance thin-walled microtube is made of magnesium alloy, which includes the following mass percentages: Zn content of 2.11%, Mn content of 0.23%, and the remainder being Mg.

[0085] A method for fabricating high-performance thin-walled microtubes for magnesium alloy vascular stents includes the following steps: S1. Preparation of magnesium alloy ingots: First, the vacuum induction melting furnace is evacuated to 1×10-2 Pa atmospheric pressure, and then high-purity argon gas is introduced. The ingots are then cast at 730℃. During the casting process, ultrasonic vibration is used to eliminate defects such as bubbles generated during casting. The ingots are then rapidly cooled by a cooling system. The ingots are then solution treated at 450℃ for 24 hours and cooled for later use.

[0086] S2. Preparation of superplastic magnesium alloy blanks: The ingot and the extrusion-upsetting-extrusion composite die are placed in a heat treatment furnace at 300℃ and held for 2 hours. Then, the surface is coated with a lubricant and placed into the extrusion cylinder of an extruder. The ingot is then extruded into a blank with a diameter of 16mm using the extrusion-upsetting-extrusion composite die at an extrusion speed of 0.1mm / s.

[0087] S3. Preparation of magnesium alloy blank tube: First, mechanically pierce the blank bar to form an open blank bar with an outer diameter of 10mm and an inner diameter of 2.8. Then, use a tube extrusion die with a centering mandrel to extrude it into a blank tube with an outer diameter of 3.2mm and an inner diameter of 2.7 at 280℃. The extrusion speed is 0.1mm / s.

[0088] S4. Preparation of magnesium alloy thin-walled tubes: The blank tube is inserted into the mandrel of the tube rolling mill, and the rolling temperature is controlled at 220℃. The blank tube is hot rolled in a single pass to obtain a thin-walled tube with an outer diameter of 3mm and a wall thickness of 0.2mm.

[0089] Since the mold assembly and usage process is the same as in Example 1, the relevant details will not be repeated. The dimensions and specifications of each mold can be adjusted according to specific circumstances.

[0090] like Figure 11 The image shows a comparison of the crystal orientation distribution between traditional mechanical tubing and the tubing of this application. Figure 11 A is a schematic diagram of the crystal orientation of a conventionally machined tube. Figure 11 B is a schematic diagram of the crystal orientation of the extruded tube in step S3 and the rolled tube in step S4 of this application. It can be seen that the crystal orientation distribution is significantly different in different parts of the machined tube. In part A1, the grain basal plane is parallel to the tube wall, while in part A2, the grain basal plane is perpendicular to the tube wall. However, in the tube prepared by the process of this application, after extrusion and rolling, the {0001} basal plane of the grains in different parts is approximately parallel to the tube wall, thus giving the microtube excellent plasticity and corrosion resistance.

[0091] Figure 12 The figure shows a stress-strain comparison between conventionally machined tubing and microtubes processed in this application. It can be seen that after hot rolling, the plastic deformation capacity and tensile strength of magnesium alloy microtubes are significantly improved. The elongation of the microtubes after hot rolling reaches more than 24%, and the tensile strength is not less than 250 MPa.

[0092] Figure 13 As shown, under the condition of using the same magnesium alloy raw materials, a comparison is made of capillary microtubes prepared by conventional machining and microtubes prepared by the processing technology of this application in a dynamic corrosion experiment in SBF simulated solution. Figure 13 A represents a microtube prepared using traditional machining methods. Figure 13B is the microtube prepared in Example 1. It can be seen that the microtube prepared by the traditional method will corrode and crack after 48 hours of corrosion test. The surface corrosion of this application is uniform, the overall structure of the microtube is intact, and the corrosion resistance is significantly improved.

[0093] Figure 14 As shown, when using the same magnesium alloy raw materials, the minimum stent-balloon size that does not break after being expanded onto a 2.75 mm diameter balloon using conventionally machined tubing and hot-rolled tubing from Example 1 is: Figure 14 A represents a vascular stent corresponding to a microtube prepared by traditional machining. Figure 13 B represents the vascular stent corresponding to the microtube prepared in Example 1. It can be seen that the minimum gripping diameter for the machined tubing stent to cut without fracture is 1.559 mm, a gripping size that is difficult to meet the implantation requirements of small-sized blood vessels. However, the minimum gripping diameter for the microtube-cut stent prepared by hot rolling in this application is reduced to 0.789 mm, a gripping diameter that can meet the delivery requirements in coronary arteries and small-sized cerebral blood vessels.

[0094] Figure 15 As shown, where Figure 15 A is a Micro-CT image of a vascular stent prepared using the microtubes of this application implanted in the intracranial artery of a beagle dog one month after implantation. Figure 15 B is a Micro-CT image of the vascular stent prepared by the microtube of this application implanted in the intracranial artery of a beagle dog 4 months after implantation. It can be seen that the vascular stent prepared by the microtube of this application still has good integrity at 1 month and 4 months after implantation.

[0095] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance thin-walled microtube for magnesium alloy vascular stents, characterized in that: The high-performance thin-walled microtubes are made of magnesium alloy, which comprises the following mass percentages: Zn content 1-3%, Mn content 0.2-2%, and the remainder Mg; the preparation method includes the following steps: S1. Preparation of magnesium alloy ingots: Magnesium alloy is melted under a protective atmosphere and ultrasonically cast to obtain ingots. The ingots are then solution treated and cooled for later use. S2. Preparation of superplastic magnesium alloy blanks: The ingot is preheated with the extrusion-upsetting-extrusion composite mold. The preheated ingot is loaded into the extrusion-upsetting-extrusion composite mold and extruded into blanks with a diameter of 5-25 mm by an extruder. S3. Preparation of magnesium alloy blank tube: First, mechanically open the blank bar, and then hot extrude the opened blank bar to make a blank tube with an outer diameter of 2-4mm and an inner diameter of 1.1-3.1mm. S4. Preparation of magnesium alloy thin-walled tubes: The blank tube is hot-rolled in a single pass into finished thin-walled tubes with an outer diameter of 1-3 mm and a wall thickness of 0.11-0.3 mm; The extrusion-upsetting-extrusion composite mold includes an upper mold and a lower mold, which together form an extrusion-upsetting-extrusion composite cavity. The extrusion-upsetting-extrusion composite cavity includes a first extrusion cavity located in the upper mold and an upsetting cavity and a second extrusion cavity located in the lower mold. The end of the first extrusion cavity is provided with a first smooth transition cavity communicating with the upsetting cavity, and the end of the upsetting cavity is provided with a second smooth transition cavity communicating with the second extrusion cavity. The diameter of the upsetting cavity is larger than the diameter of the first extrusion cavity, and the diameter of the first extrusion cavity is larger than the diameter of the second extrusion cavity.

2. The method for preparing high-performance thin-walled microtubes for magnesium alloy vascular stents according to claim 1, characterized in that: In step S1, the melting and casting temperature is 700-750℃, the solution treatment temperature is 400-500℃, and the holding time is 12-24h.

3. The method for preparing high-performance thin-walled microtubes for magnesium alloy vascular stents according to claim 1, characterized in that: In step S2, the preheating temperature is 250-400℃, the preheating time is 2h, and the extrusion speed of the extruder is 0.1-3mm / s.

4. The method for preparing high-performance thin-walled microtubes for magnesium alloy vascular stents according to claim 1, characterized in that: In step S3, the temperature of hot extrusion is 200-400℃, and the extrusion speed is 0.1-3mm / s.

5. The method for preparing high-performance thin-walled microtubes for magnesium alloy vascular stents according to claim 1, characterized in that: In step S4, hot rolling is performed using a single-pass hot rolling mill, with the hot rolling temperature controlled at 100-300℃.

6. The method for preparing high-performance thin-walled microtubes for magnesium alloy vascular stents according to claim 1, characterized in that: The upper mold is provided with a flared feeding chamber connected to the first extrusion chamber. The diameter of the small end of the flared feeding chamber is the same as the diameter of the first extrusion chamber. The lower mold is provided with a discharge chamber connected to the second extrusion chamber. The diameter of the discharge chamber is larger than the diameter of the second extrusion chamber.

7. The method for preparing high-performance thin-walled microtubes for magnesium alloy vascular stents according to claim 5, characterized in that: The tube rolling mill is a cold rolling mill. A shower box is installed on the tube rolling mechanism of the cold rolling mill. A shower screen is provided in the shower box above the tube rolling mechanism. The shower box is connected to an oil inlet pipe and an oil return pipe. The oil inlet pipe is located above the shower screen, and the oil return pipe is located below the tube rolling mechanism.

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