A method and device for warm drawing magnesium alloy thin-walled micro-tube

Abstract

The application discloses a magnesium alloy thin-wall micro-tube warm drawing preparation method and device. The device comprises a quartz tube, a quartz plate placed in the quartz tube, a heating belt wound outside the quartz tube, a slidable rack for placing the quartz tube, a die holder concentric with the quartz tube in the same horizontal line, a drawing die placed in the die holder, a heating coil wound outside the die holder, and a control power supply for supplying power to the heating belt and the heating coil. The magnesium alloy tube blank is subjected to cold drawing, annealing, warm drawing and annealing by using the device. The device realizes a double heating mode, so that the magnesium alloy tube and the drawing die temperature field are consistent. Meanwhile, the cold drawing and hot drawing are combined, so that the magnesium alloy tube precision and plastic processing capacity are effectively improved. The warm drawing preparation method by using the device can more efficiently produce the thin-wall micro-magnesium alloy tube with high size precision and excellent performance.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy processing, specifically a method and apparatus for the heated drawing of thin-walled micro-tubes made of magnesium alloy. Background Technology

[0002] Thin-walled micro-magnesium alloy tubing has broad application prospects in the biomedical field, making the efficient preparation of high-quality thin-walled micro-magnesium alloy tubing a research hotspot in the magnesium alloy processing field. Currently, multi-pass cold drawing of the tube blank is the mainstream process for preparing bio-magnesium alloy microtubes. However, due to the close-packed hexagonal structure of magnesium, only basal slip and two twinning modes are activated at room temperature and lower temperatures, which cannot meet the requirement of five independent slip systems for plastic deformation. The poor deformation capacity at room temperature leads to a lengthy cold drawing process, and multiple heat treatments between passes are not conducive to the control of the microstructure and properties of the tubing. In addition, bio-magnesium alloy tubing is prone to cracking due to the large axial tensile stress during cold drawing. Increasing the temperature can activate the conical and cylindrical slip systems, improve the deformation capacity of magnesium alloy, increase the shrinkage per pass, and reduce the initiation of microcracks. However, this method is difficult to achieve a uniform temperature field due to the skin effect, resulting in temperature imbalance between the tube surface and the long mandrel, and it is also difficult to heat the drawing die. Therefore, it is urgent to explore ways to incorporate uniform heating of the microtubes and drawing die during the drawing process to form the tube. Summary of the Invention

[0003] To address the aforementioned problems, this invention first provides an apparatus for preparing thin-walled microtubes of magnesium alloy by heated drawing. This apparatus achieves dual heating, ensuring consistency in the temperature field between the magnesium alloy tube and the drawing die. Furthermore, by combining cold drawing and hot drawing, it effectively improves the precision and plastic processing capability of the magnesium alloy tube.

[0004] The present invention also provides a method for preparing thin-walled micro-tubes of magnesium alloy by heated drawing. The method uses the above-mentioned apparatus to produce thin-walled micro-tubes of magnesium alloy with high dimensional accuracy and excellent performance more efficiently through heated drawing.

[0005] This invention is achieved through the following technical solution: An apparatus for preparing thin-walled microtubes of magnesium alloy by heated drawing, the apparatus comprising a quartz tube (7), a quartz plate (11) placed inside the quartz tube (7), a heating band (9) wound around the outside of the quartz tube (7), a sliding frame (13) for placing the quartz tube (7), a mold base (4) concentric with the quartz tube (7) on the same horizontal line, a drawing die (6) placed inside the mold base (4), a heating coil (3) wound around the outside of the mold base (4), and a control power supply (12) for supplying power to the heating band (9) and the heating coil (3); The right end of the quartz tube (7) can slide and fit against the left end of the mold base (4) through the sliding frame (13); The inner diameter on the left side of the die base (4) matches the outer diameter of the drawing die (6); The width of the quartz plate (11) matches the inner diameter of the quartz tube (7), and it is inserted into the quartz tube (7) to ensure that it is at the same level as the mold base (4); a thermocouple (10) for measuring the temperature of the outer wall of the tube blank is provided on the quartz tube (7); a lubrication hole (8) for dripping lubricant is opened on the quartz tube. The die holder (4) is equipped with a temperature measuring device (2) for measuring the temperature of the drawing die; A pulling trolley (5) is provided at the same horizontal level as the outlet of the mold base (4).

[0006] Furthermore, the thickness of the heating part of the mold base is 10-15mm, and the wall thickness of the quartz tube is 3-5mm.

[0007] Furthermore, multiple drawing dies of different sizes can be placed inside the die holder.

[0008] Furthermore, the drawing die is made of die steel, and the die base is made of 40Cr steel.

[0009] The present invention also provides a method for preparing magnesium alloy thin-walled microtubes by heated drawing using the above-mentioned apparatus, the method comprising the following steps: S1: Take a magnesium alloy tube blank and a steel mandrel and clean the surface to remove impurities and oil stains. Then insert the steel mandrel into the magnesium alloy tube blank to obtain the assembly (1); the length of the mandrel is greater than the length of the tube blank. S2: The assembly (1) described in step S1 is placed in the above-mentioned heated drawing apparatus for preparing thin-walled microtubes of magnesium alloy for drawing, as follows: Slide the quartz tube (7) to the left side of the mold base, place a suitable drawing die (6) in the mold base, and add lubricant through the lubrication hole (8) to lubricate the outer surface of the assembly (1). Then, insert the head of the assembly (1) through the drawing die (6), pass through the mold base (4), and clamp it on the drawing carriage (5) of the drawing machine. Place the other end of the assembly (1) on the quartz plate (11) inside the quartz tube (7). Then, slide the quartz tube (7) through the sliding frame (13) so that its right end is in contact with the left end of the mold base (4). S3: Start the drawing machine and the drawing carriage to drive the assembly to run at a constant speed for cold drawing, while dripping lubricant through the lubrication hole (8); S4: Repeat steps S2 and S3 until the magnesium alloy tube blank and the steel mandrel are tightly fitted together; S5: Place the assembly obtained after cold drawing in step S4 into a tube furnace for annealing; S6: Repeat step S2 for the annealed assembly in step S5, and turn on the control power supply of the quartz tube and heating coil. Set the heating temperature to 100~300℃. After the temperature reaches the set temperature, turn on the drawing machine's drawing carriage to drive the assembly to run at a constant speed for heated drawing. At the same time, drip lubricant through the lubrication hole (8). S7: Place the assembled body after the heated drawing in step S6 into a tube furnace for annealing. S8: Repeat steps S6 and S7 for the annealed assembly in step S7 until the target outer diameter and wall thickness are achieved. Then remove the mandrel to obtain the magnesium alloy microtube.

[0010] Furthermore, the magnesium alloy tube blank mentioned in step S1 can be ZE21B magnesium alloy, ZE21C magnesium alloy, WE43C magnesium alloy, EK20M magnesium alloy, etc.; the steel mandrel material can be spring steel, mold steel or stainless steel. Further, in step S1, the surface roughness Ra of the inner and outer surfaces of the magnesium alloy tube blank is <3.2μm, the surface roughness Ra of the outer surface of the steel mandrel is <3.2μm, the outer diameter of the tube blank is 2.8~3.5mm, and the wall thickness of the tube blank is 0.2~0.3mm; the diameter of the steel mandrel is 1.95~2.7mm, and the length of the steel mandrel is not less than 1200mm.

[0011] Furthermore, the head of the assembly (1) is ground before drawing to ensure that it can pass through the drawing die (6) and be held by the drawing carriage (5); Furthermore, in step S2, the assembly, die holder, drawing die, drawing carriage, and quartz tube in the device are strictly concentric to improve the uniformity of the wall thickness of the drawn tube.

[0012] Furthermore, the drawing speed of the cold drawing in step S3 is 0.5~2mm / s, and the deformation amount of a single pass of cold drawing is not greater than 20%; the lubricant is graphene grease or high-temperature resistant lubricating oil.

[0013] Furthermore, in step S6, the deformation per pass of the heated drawing is 20-40%, and the drawing speed for each pass is 0.5-2 mm / s.

[0014] Furthermore, argon gas is introduced into the tubular furnace in both steps S5 and S7, and annealing is carried out at an annealing temperature of 260~340℃ for 30~60 minutes.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. The method of the present invention has high production efficiency, saves time and labor, and reduces production difficulty.

[0016] 2. In this invention, a dynamic recovery phenomenon occurs during the heated drawing process, which eliminates the work hardening effect and activates the cylindrical and conical slip systems, thereby improving the deformation capability of magnesium alloy microtubes.

[0017] 3. The use of heated drawing in this invention can effectively increase the deformation per pass during the drawing process, effectively reduce the number of drawing passes and the number of heat treatments, improve drawing efficiency, and shorten the pipe processing cycle.

[0018] 4. This invention combines cold drawing with heated drawing, which can effectively improve the uniformity of tube wall thickness and surface quality, and prepare bio-magnesium alloy thin-walled microtubes with high dimensional accuracy and excellent performance.

[0019] 5. The device described in this invention achieves consistent temperature of the pipe and the mold, resulting in a significant improvement in the quality of the prepared magnesium alloy pipe, which is also uniform. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0021] Figure 1 This is a schematic diagram of the overall structure of the heated drawing forming apparatus of the present invention; Figure 2 This is a schematic diagram of the internal structure of the heated drawing forming apparatus of the present invention; Figure 3 Macroscopic images of the tubes obtained in the cold-drawing examples and Examples 2-4 of the present invention; Figure 4 Figures showing the measurement results of pipe wall thickness uniformity obtained in the cold drawing example and Examples 2-4 of the present invention; Figure 5 The figures show the straightness measurement results of the pipes obtained in the cold drawing example and Examples 2-4 of the present invention; Figure 6 Figures showing the cross-section and maximum deformation per pass of the tubes obtained in the cold drawing examples and Examples 2-4 of the present invention; Figure 7 The figures show the measurement results of microcracks on the surface of the pipes obtained in the cold drawing example and Examples 2-4 of the present invention.

[0022] Explanation of reference numerals in the attached figures: 1—Assembly; 2—Temperature measuring device; 3—Heating coil; 4—Die base; 5—Pulling carriage; 6—Pulling die; 7—Quartz tube; 8—Lubrication hole; 9—Heating belt; 10—Temperature measuring device; 11—Quartz plate; 12—Control power supply; 13—Sliding frame Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to specific embodiments, but this does not constitute a limitation on the present invention. Specific conditions not described in the following embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Example 1

[0024] This embodiment provides an apparatus for preparing magnesium alloy thin-walled microtubes by heated drawing. The apparatus includes a quartz tube (7), a quartz plate (11) placed inside the quartz tube (7), a heating band (9) wound around the outside of the quartz tube (7), a sliding frame (13) for placing the quartz tube (7), a mold base (4) concentric with the quartz tube (7) on the same horizontal line, a drawing die (6) placed inside the mold base (4), a heating coil (3) wound around the outside of the mold base (4), and a control power supply (12) for supplying power to the heating band (9) and the heating coil (3). The right end of the quartz tube (7) can slide and fit against the left end of the mold base (4) through the sliding frame (13); The inner diameter on the left side of the die base (4) matches the outer diameter of the drawing die (6); The width of the quartz plate (11) matches the inner diameter of the quartz tube (7), and it is inserted into the quartz tube (7) to ensure that it is at the same level as the mold base (4); a thermocouple (10) for measuring the temperature of the outer wall of the tube blank is provided on the quartz tube (7); a lubrication hole (8) for dripping lubricant is opened on the quartz tube. The die holder (4) is equipped with a temperature measuring device (2) for measuring the temperature of the drawing die; A pulling trolley (5) is provided at the same horizontal level as the outlet of the mold base (4).

[0025] The thickness of the heating part of the mold base (4) is any value between 10 and 15 mm, and the wall thickness of the quartz tube is any value between 3 and 5 mm.

[0026] The die holder can hold drawing dies of different sizes.

[0027] The drawing die used in this device is made of die steel, and the die base is made of 40Cr steel. Example 2

[0028] Magnesium alloy thin-walled microtubes are prepared by heated drawing using the apparatus described in Example 1, as follows: 1) A tube blank made of ZE21B magnesium alloy with a diameter of 3.30mm, a wall thickness of 0.2mm, and a length of 800mm needs to be drawn with a mandrel into a tube with a diameter of 2.78mm, a wall thickness of 0.14mm, and a length of 1000mm. The mandrel has a diameter of 2.5mm and a length of 1500mm. The mandrel is inserted into the tube blank and combined to obtain the assembly (1). 2) Grind the head of the assembly (1) obtained in step 1) to ensure that it can pass through the drawing die and be clamped by the drawing carriage; 3) Select 3.10 and 2.90 mm drawing dies in sequence and place them into the die holder. Insert the head of the assembly through the drawing die and clamp it on the jig of the drawing machine through the die holder. Place the other side of the assembly on the quartz plate inside the quartz tube. Then slide the quartz tube to overlap with the left side of the right die holder. Start the drawing carriage to cold draw sequentially at a speed of 0.5 mm / s. During the cold drawing process, drip high-temperature resistant lubricating oil (about one drop per second) through the lubrication hole (8) on the quartz tube. Repeat the operation until the magnesium alloy tube blank and the steel mandrel are tightly attached. 4) The assembly drawn by the 3.10 and 2.90 mm drawing dies in step 3) is placed in an annealing furnace under argon protection for annealing at 280°C for 30 min; 5) Next, select 2.83 and 2.78 mm drawing dies in sequence and place them into the die holder. Insert the head of the assembly obtained after annealing in step 4) through the drawing die, pass through the die holder and clamp it on the drawing carriage (5) of the drawing machine. Place the other side of the assembly on the quartz plate inside the quartz tube. Then slide the quartz tube to overlap the left side of the right die holder. Start the control power supply and set the temperature to 100℃. After the temperature of the heating strip and the heating coil are both stable at 100℃, start the drawing carriage and draw the assembly sequentially at a rate of 0.5 mm / s. During the heated drawing process, drip graphene grease through the lubrication hole (8) on the quartz tube (about one drop per second). 6) Place the assembled body drawn in step 5) in an annealing furnace under argon protection and anneal at 320°C for 30 minutes; 7) Pass the tail mandrel of the assembly obtained in step 6) through a drawing die with an inner diameter of 2.60 mm in the opposite direction and place it in the die holder. Turn on the drawing trolley of the drawing machine to drive the assembly to run at a constant speed to remove the mandrel and obtain the finished magnesium alloy microtube.

[0029] Finally, a magnesium alloy tube with an outer diameter of 2.78 mm, a wall thickness of 0.14 mm, and a length of 1070 mm was obtained through the above processing technology. Example 3

[0030] Magnesium alloy thin-walled microtubes are prepared by heated drawing using the apparatus described in Example 1, as follows: 1) The tube blank made of ZE21C with a diameter of 3.50mm, a wall thickness of 0.3mm, and a length of 500mm needs to be drawn with a mandrel into a tube with a diameter of 2.78mm, a wall thickness of 0.14mm, and a length of 1000mm. The mandrel has a diameter of 2.5mm and a length of 1500mm. The mandrel is inserted into the tube blank and combined to obtain the assembly (1). 2) Grind the head of the assembly obtained in step 1) to ensure that it can pass through the drawing die and be clamped by the drawing carriage; 3) Select 3.30 and 3.10 mm drawing dies in sequence and place them in the die holder. Insert the head of the assembly through the drawing die and clamp it on the drawing carriage (5) of the drawing machine through the die holder. Place the other side of the assembly on the quartz plate inside the quartz tube. Then slide the quartz tube to overlap with the left side of the right die holder. Start the drawing carriage to cold draw sequentially at a speed of 0.5 mm / s. During the cold drawing process, drip graphene grease through the lubrication hole (8) on the quartz tube (about one drop per second). Repeat the operation until the magnesium alloy tube blank and the steel mandrel are tightly attached. 4) The assembly drawn by the 3.30 and 3.10 mm drawing dies in step 3) is placed in an annealing furnace under argon protection for annealing at 280°C for 30 minutes; 5) Then select 3.0, 2.9, 2.8 and 2.78 mm drawing dies in sequence and place them into the die holder. Insert the head of the assembly obtained after annealing in step 4) through the drawing die, pass through the die holder and clamp it on the jig of the drawing machine. Place the other side of the assembly on the quartz plate inside the quartz tube. Then slide the quartz tube to overlap the left side of the right die holder. Start the control power supply and set the temperature to 200℃. After the temperature of the heating strip and the heating coil are stable at 200℃, start the drawing carriage to draw the assembly sequentially at a rate of 0.5 mm / s. During the heated drawing process, drip graphene grease through the lubrication hole (8) on the quartz tube (about one drop per second). 6) Place the assembled body drawn in step 5) in an annealing furnace under argon protection and anneal at 320°C for 30 minutes; 7) Pass the tail mandrel of the assembly obtained in step 6) through a drawing die with an inner diameter of 2.60 mm in the opposite direction and place it in the die holder. Turn on the drawing trolley of the drawing machine to drive the assembly to run at a constant speed to remove the mandrel and obtain the finished magnesium alloy microtube.

[0031] Finally, through the above processing technology, a pure magnesium pipe with an outer diameter of 2.78 mm, a wall thickness of 0.14 mm, and a length of 1030 mm was obtained. Example 4

[0032] Magnesium alloy thin-walled microtubes are prepared by heated drawing using the apparatus described in Example 1, as follows: 1) The material is EK20C, the diameter is 3.40mm, the wall thickness is 0.25mm and the length is 600mm. The tube blank needs to be drawn with a mandrel into a tube with a diameter of 2.78mm, a wall thickness of 0.14mm and a length of 1000mm. The mandrel has a diameter of 2.5mm and a length of 1500mm. The mandrel is inserted into the tube blank and combined to obtain the assembly (1). 2) Grind the head of the assembly obtained in step 1) to ensure that it can pass through the drawing die and be clamped by the drawing carriage; 3) Select 3.2mm and 3.0mm drawing dies in sequence and place them into the die holder. Insert the head of the assembly through the drawing die and clamp it on the drawing carriage (5) of the drawing machine through the die holder. Place the other side of the assembly on the quartz plate inside the quartz tube. Then slide the quartz tube to overlap with the left side of the right die holder. Start the drawing carriage to cold draw sequentially at a speed of 0.5mm / s. During the cold drawing process, drip graphene grease through the lubrication hole (8) on the quartz tube (about one drop per second). Repeat the operation until the magnesium alloy tube blank and the steel mandrel are tightly attached. 4) The assembly drawn by the 3.2 and 3.0 mm drawing dies in step 3) is placed in an annealing furnace under argon protection for annealing at 280°C for 30 min; 5) Next, select 2.87 and 2.78 mm drawing dies in sequence and place them into the die holder. Insert the head of the assembly obtained after annealing in step 4) through the drawing die, pass through the die holder and clamp it on the jig of the drawing machine. Place the other side of the assembly on the quartz plate inside the quartz tube. Then slide the quartz tube to overlap the left side of the right die holder. Start the control power supply and set the temperature to 300℃. After the temperature of the heating strip and the heating coil are both stable at 300℃, start the drawing carriage to draw the assembly sequentially at a rate of 0.5 mm / s. During the drawing process, drip graphene grease through the lubrication hole (8) on the quartz tube (about one drop per second). 6) Place the assembled body drawn in step 5) in an annealing furnace under argon protection and anneal at 320°C for 30 minutes; 7) Pass the tail mandrel of the assembly obtained in step 6) through a drawing die with an inner diameter of 2.60 mm in the opposite direction and place it in the die holder. Turn on the drawing trolley of the drawing machine to drive the assembly to run at a constant speed to remove the mandrel and obtain the finished magnesium alloy microtube.

[0033] Finally, a magnesium alloy tube with an outer diameter of 2.78 mm, a wall thickness of 0.14 mm, and a length of 1070 mm was obtained through the above processing technology.

[0034] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Example 5

[0035] Magnesium alloy thin-walled microtubes were fabricated using a conventional cold drawing process, as detailed below: 1) A magnesium alloy tube blank with an outer diameter of 3.30 ~ 3.50 mm and a wall thickness of 0.20 ~ 0.30 mm obtained by hot extrusion is matched with a steel mandrel with an outer diameter of 2.50 mm and a length of 1500 mm. The mandrel is inserted into the hot extruded magnesium alloy tube blank to obtain an assembly (1). 2) First cold drawing pass: Place a 3.10mm, 3.20mm, or 3.30mm drawing die into the die holder, pass the assembly (1) through the drawing die, and clamp it on the drawing carriage (5) of the drawing machine through the die holder. Place the other side of the assembly on the quartz plate inside the quartz tube, and then slide the quartz tube to overlap with the left side of the right die holder. Start the drawing carriage to perform cold drawing at a speed of 0.5mm / s. During the cold drawing process, drip graphene grease through the lubrication hole (the deformation amount of a single cold drawing pass is not greater than 10%). 3) The assembly that has undergone the first cold drawing in step 2) is annealed at 280°C for 30 minutes in an annealing furnace with argon protection; 4) Second cold drawing pass: Place a 2.90mm, 3.00mm, or 3.10mm drawing die into the die holder and repeat step 2) to obtain the cold-drawn assembly; 5) Repeat the annealing operation of step 3) on the assembly obtained in step 4) until the magnesium alloy tube blank and the steel mandrel are tightly bonded together to obtain the cold-drawn assembly.

[0036] The magnesium alloy thin-walled microtubes in this experiment were all prepared using the above method.

[0037] Macroscopic images of the cold-drawn bio-magnesium alloy microtubes obtained in Examples 2-4 are shown in Example 5. Figure 3 As shown. Figure 3 The images show end face images (left image) and length direction images of the bio-magnesium alloy microtubes produced in each embodiment. As can be seen from the images, the bio-magnesium alloy microtubes produced in Examples 2-4 all meet the requirements for inner and outer diameters and length.

[0038] Example 5: Cold drawing and wall thickness deviation test of the bio-magnesium alloy microtubes obtained in Examples 2-4. Figure 4 As shown. Figure 4 The results are based on the wall thickness uniformity measurements of the bio-magnesium alloy microtubes produced by cold drawing and in the various embodiments. Figure 4 It can be seen that the wall thickness uniformity of cold-drawn tubes is greater than 4%, while the wall thickness deviation of magnesium alloy microtubes produced in each embodiment is less than 4%, which can meet the wall thickness uniformity requirements.

[0039] Example 5: Cold drawing and straightness test of microtubes obtained in Examples 2-4. Figure 5 As shown. Figure 5 The results are based on the straightness test results of the magnesium alloy microtubes produced by cold drawing and in the various embodiments. Figure 5 It can be seen that the straightness deviation of the magnesium alloy microtubes produced by cold drawing and in each embodiment is less than 2 mm / m, and the straightness increases with the increase of drawing temperature.

[0040] Example 5: Cold drawing and single-pass deformation capacity test of bio-magnesium alloy microtubes obtained in Examples 2-4. Figure 6 As shown. Figure 6 The figures show bar charts for the maximum shrinkage in a single drawing pass under warm conditions and for each embodiment, as well as cross-sectional views of the microtubes before and after drawing to show the maximum shrinkage in a single drawing pass. Figure 6 (b) It can be seen that compared with the magnesium alloy microtubes in the various embodiments, the maximum shrinkage per pass of cold drawing continuously increases, indicating that as the drawing temperature increases, a dynamic recovery phenomenon occurs, which eliminates the work hardening effect and improves the single-pass deformation capability of the magnesium alloy microtubes.

[0041] Analysis of surface microcracks in bio-magnesium alloy microtubes obtained from cold drawing in Example 5 and Examples 2-4 is as follows: Figure 7 As shown. Figure 7 Types of surface microcracks generated during the drawing process of bio-magnesium alloys: transverse cracks perpendicular to the drawing direction (a) and oblique cracks at a certain angle to the drawing direction (b); and a statistical chart of the number of microcracks in 100mm microtubes and tube blanks after cold drawing and drawing with the same 17.24% single-pass deformation at the temperature of each embodiment. Figure 7 (c) It is evident that compared to cold drawing, heated drawing can reduce the generation of microcracks, and the number of microcracks continues to decrease with increasing drawing temperature. At 300℃, the number of microcracks is comparable to that on the surface of the tube blank. This indicates that heated drawing can significantly reduce stress concentration on the surface of the bio-magnesium alloy microtubes during the drawing process, thereby greatly reducing the initiation of microcracks. In summary, the heated drawing method of this invention can produce magnesium alloy tubes with an outer diameter of 2.25~3.00mm, a wall thickness of 0.12mm~0.15mm, a wall thickness deviation of <4%, a straightness of <2mm / m, and a length of over 1000mm, meeting the process parameter requirements for medical cardiovascular stents. Furthermore, it can significantly improve the deformation capacity of microtubes, reduce the deformation per pass in the drawing process, reduce the number of drawing passes, reduce the number of heat treatments, improve drawing efficiency, and reduce drawing costs, showing good application prospects in the field of bio-magnesium alloy microtube processing.

Claims

1. An apparatus for hot drawing to prepare thin-walled microtubes of magnesium alloy, characterized in that, The device includes a quartz tube (7), a quartz plate (11) placed inside the quartz tube (7), a heating band (9) wound around the outside of the quartz tube (7), a sliding frame (13) for placing the quartz tube (7), a mold base (4) concentric with the quartz tube (7) on the same horizontal line, a drawing die (6) placed inside the mold base (4), a heating coil (3) wound around the outside of the mold base (4), and a control power supply (12) for supplying power to the heating band (9) and the heating coil (3); The right end of the quartz tube (7) slides and fits against the left end of the mold base (4) via a sliding frame (13); The inner diameter on the left side of the die base (4) matches the outer diameter of the drawing die (6); The width of the quartz plate (11) matches the inner diameter of the quartz tube (7), and it is inserted into the quartz tube (7) to ensure that it is at the same level as the mold base (4); a thermocouple (10) for measuring the temperature of the outer wall of the tube blank is provided on the quartz tube (7); a lubrication hole (8) for dripping lubricant is opened on the quartz tube. The die holder (4) is equipped with a temperature measuring device (2) for measuring the temperature of the drawing die; A pulling trolley (5) is provided at the same horizontal level as the outlet of the mold base (4); The thickness of the heating part of the mold base is 10-15mm, and the wall thickness of the quartz tube is 3-5mm. The die holder contains drawing dies of different sizes.

2. The apparatus according to claim 1, characterized in that, The drawing die is made of die steel, and the die base is made of 40Cr steel.

3. A method for preparing magnesium alloy thin-walled microtubes by heated drawing using the apparatus described in any one of claims 1 to 2, characterized in that, The method includes the following steps: S1: Take a magnesium alloy tube blank and a steel mandrel and clean their surfaces. Then insert the steel mandrel into the magnesium alloy tube blank to obtain an assembly (1); the length of the mandrel is greater than the length of the tube blank. S2: The assembly (1) described in step S1 is placed in a heated drawing apparatus for preparing thin-walled microtubes of magnesium alloy for drawing, as follows: Slide the quartz tube (7) to the left, place it into a suitable drawing die (6), and add lubricant through the lubrication hole (8) to lubricate the surface of the assembly (1). Then, insert the head of the assembly (1) through the drawing die (6), pass through the die holder (4), and clamp it on the drawing carriage (5) of the drawing machine. Place the other end of the assembly (1) on the quartz plate (11) inside the quartz tube (7). Then, slide the quartz tube (7) through the sliding frame (13) so that its right end is in contact with the left end of the die holder (4). S3: Start the drawing machine and the drawing carriage to drive the assembly to run at a constant speed for cold drawing, while dripping lubricant through the lubrication hole (8); S4: Repeat steps S2 and S3 until the magnesium alloy tube blank and the steel mandrel are tightly fitted together; S5: Place the assembled body after cold drawing in step S4 into a tube furnace for annealing; S6: Repeat step S2 for the annealed assembly in step S5, then turn on the control power supply of the quartz tube and heating coil, set the heating temperature to 100~300℃, and after the temperature reaches the set temperature, turn on the drawing machine to drive the assembly to run at a constant speed for heated drawing, and at the same time drip lubricant through the lubrication hole (8). S7: Place the assembled body after the heated drawing in step S6 into a tube furnace for annealing. S8: Repeat steps S6 and S7 for the annealed assembly in step S7 until the target outer diameter and wall thickness are achieved. Then remove the mandrel to obtain the magnesium alloy microtube.

4. The method according to claim 3, characterized in that, In step S1, the surface roughness Ra of the inner and outer surfaces of the magnesium alloy tube blank is <3.2μm, the surface roughness Ra of the outer surface of the mandrel is <3.2μm, the outer diameter of the tube blank is 2.8~3.5mm, and the wall thickness of the tube blank is 0.2~0.3mm; the diameter of the mandrel is 1.95~2.7mm, and the length of the mandrel is not less than 1200mm.

5. The method according to claim 3, characterized in that, The drawing speed of the cold drawing in step S3 is 0.5~2mm / s, and the deformation of a single pass of cold drawing is not greater than 20%; the lubricant is graphene grease or high-temperature resistant lubricating oil.

6. The method according to claim 3, characterized in that, The deformation amount per pass of the heated drawing in step S6 is 20-40%, and the drawing speed of each pass is 0.5-2 mm / s.

7. The method according to claim 3, characterized in that, Argon gas was introduced into the tube furnace in both steps S5 and S7, and annealing was carried out at an annealing temperature of 260~340℃ for 30~60 minutes.

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