Preparation method of medical pure magnesium bar with strength and plasticity

Abstract

The invention discloses a preparation method of a medical pure magnesium bar with both strength and plasticity, which specifically comprises the following steps: carrying out room temperature extrusion treatment on a pure magnesium ingot, and carrying out rapid cooling treatment on the bar obtained after extrusion to obtain the pure magnesium bar, wherein the temperature of an extrusion container in the extrusion equipment is set to be higher than 150 DEG C, and the temperature of the pure magnesium ingot and the temperature of the die before extrusion are both room temperature; the medium temperature for cooling treatment is 0-5 DEG C;

Description

Technical Field

[0001] The invention relates to the technical field of biomedical materials, and in particular to a method for preparing a medical strong-plastic pure magnesium rod. Background Art

[0002] At present, degradable biomaterials are becoming a research hotspot for biomedical materials, and the new generation of degradable medical metal materials represented by magnesium and its alloys have attracted the attention of researchers. As biometal materials, magnesium and its alloys have shown several significant advantages over other traditional biometal materials such as stainless steel, titanium alloys, and cobalt-chromium alloys: 1. Biodegradability; 2. Mechanical properties similar to human bones; 3. Good biocompatibility; 4. Good processing performance. However, the degradation rate of magnesium and its alloys is too fast, which will cause the mechanical support effect of degradable magnesium alloy implants to decay too quickly, and fail before the bone tissue is fully healed, thereby affecting the treatment effect. Therefore, from the perspective of existing technology, the control of the degradation rate of magnesium and magnesium alloys in a physiological electrolyte environment (especially the controllable degradation of materials) is still the main bottleneck problem in the application of biological magnesium alloys.

[0003] In addition to its natural characteristics (the surface of magnesium alloys cannot spontaneously form a dense surface film), another key reason for the easy corrosion of magnesium alloys is the micro-galvanic corrosion caused by the addition of alloying elements. In addition, the grain boundary regions in magnesium alloys are often enriched with impurity elements such as Fe, Ni, and Cu. These elements have significant cathode activity and accelerate the formation of micro-battery structures on the surface of magnesium alloys. What is particularly critical is that the second phase in magnesium alloys is usually not susceptible to corrosion due to its extremely strong cathode characteristics and is randomly distributed in the alloy. This characteristic, if there are larger second phase particles, may also induce potential adverse physiological reactions such as thrombosis, thus becoming another important consideration and challenge faced by bio-magnesium alloy materials in the field of medical applications.

[0004] The currently reported research has deeply revealed the unique advantages of high-purity magnesium (whose purity standard is strictly set at 99.99% and above) in the field of biomedical applications. High-purity magnesium has shown remarkable performance advantages over the modified Mg-Ca, Mg-Zn, Mg-Ca-Zn, and Mg-Y-Nd-Sm-Zr alloys widely used internationally. High-purity magnesium effectively inhibits the galvanic corrosion caused by impurities and second phases by strictly controlling the impurity content and reducing the number and distribution of second phases in the alloy. It also avoids elements with neurotoxicity and cytotoxicity, has better biocompatibility, and reduces the risk of immune response and rejection reaction with human tissues. In addition, its more excellent degradability and controllable degradation rate can further regulate its degradation rate to meet the needs of different application scenarios.

[0005] However, researchers must also face up to a technical problem that needs to be solved urgently: high-purity magnesium obtained through traditional preparation processes often has deficiencies in mechanical properties. Especially for high-purity magnesium in hot extrusion, its strength and plasticity are generally low, and its tensile strength is often difficult to break through 180MPa. At the same time, its plasticity is less than 20%, which means that when it is subjected to complex stress environments in the body, it cannot better adapt to the mechanical changes of human bones and has a higher risk of stress concentration and fracture. This performance bottleneck directly restricts the widespread application of high-purity magnesium in biodegradable implants that require both strength and plasticity. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing a medical strong and plastic pure magnesium rod, so as to solve the problem that the high-purity magnesium prepared by the prior art has deficiencies in mechanical properties and it is difficult to improve its mechanical properties while maintaining the excellent biosafety of high-purity magnesium. The present application utilizes the excellent biocompatibility of high-purity magnesium and the uniform and controllable degradation rate to obtain a strong and plastic degradable high-purity magnesium rod through two-step continuous plastic deformation processing, which meets the dual requirements of biodegradable implant devices for mechanics and degradation.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A method for preparing a medical strong-plastic pure magnesium rod, comprising the following steps:

[0009] The pure magnesium ingot is subjected to room temperature extrusion treatment, and the rod obtained after extrusion is subjected to rapid cooling treatment to obtain the pure magnesium rod; wherein the temperature of the extrusion barrel in the extrusion equipment is set to ≥150°C, and the temperatures of the pure magnesium ingot and the mold before extrusion are both room temperature; and the temperature of the cooling medium is 0-5°C.

[0010] Preferably, the pure magnesium rod can be subjected to a multi-pass rotary forging deformation treatment at room temperature.

[0011] Preferably, the temperature of the rotary forging deformation treatment is 0-40°C.

[0012] Preferably, the diameter of the rod is reduced by 0.2 to 1.0 mm during each rotary forging deformation process.

[0013] Preferably, the feeding speed of the rotary forging deformation process is ≤10 m / min.

[0014] Preferably, in the pure magnesium ingot, calculated by mass percentage, the content of Mg is greater than 99.99%, and the total content of the three impurity elements Fe, Ni and Cu in the pure magnesium ingot is ≤50 ppm.

[0015] Preferably, the cross-sectional diameter of the pure magnesium ingot is 60-80 mm, and the height does not exceed 60 mm.

[0016] Preferably, during the extrusion process, the extrusion ratio is 10 to 50, and the cooling process is a water cooling process.

[0017] Preferably, the pure magnesium rod has an axial length of 300 to 1500 mm and a cross-sectional diameter of 10 to 25 mm.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention adopts high-purity magnesium (Mg content> 99.99%), eliminating the problem of accelerated degradation caused by galvanic corrosion caused by impurity elements such as Fe, Ni, Cu (total content ≤ 50ppm) and the second phase in the alloy, as well as potential biological problems of alloying element addition. Therefore, the rod of the present invention has better biosafety and corrosion resistance; at the same time, the present invention prepares pure magnesium rods through two-step continuous plastic processing, so that the pure magnesium rod structure is refined and uniform, and its corrosion failure mode is transformed from local corrosion of magnesium alloy to uniform corrosion of pure magnesium, further improving the controllability of the degradation rate of magnesium-based implant materials, thereby solving the problem of premature failure of mechanical support caused by excessive degradation of magnesium alloy implant devices. The degradation rate of the pure magnesium rod of the present invention in simulated body fluid is ≤0.3mm / year.

[0020] 2. After in-depth research on the preparation process of pure magnesium rods, the present invention found that by raising the temperature of the extrusion barrel in the extrusion equipment and keeping the temperature of the pure magnesium ingot and the mold at room temperature before extrusion, most of the energy consumed in the closed mold for deforming pure magnesium will be converted into heat energy, resulting in an increase in the temperature of the pure magnesium, and then dynamic recrystallization will occur. Then, through subsequent rapid cooling, the obtained pure magnesium rods will obtain fine recrystallized structures, and the strength of the pure magnesium rods will be significantly improved while maintaining excellent plasticity, thereby improving the comprehensive mechanical properties of the material. In the method described in the present invention, the room temperature extrusion billet and the mold do not need to be heated, which can significantly reduce energy consumption, further shorten the preparation process, reduce production costs, and the prepared rods have high surface quality and good precision.

[0021] 3. The present invention also found that the pure magnesium rod obtained by room temperature extrusion is then subjected to rotary forging deformation. Since it has been previously subjected to room temperature extrusion and rapid cooling, a material with ultrafine grain structure and excellent mechanical properties can be provided for the rotary forging deformation process. At the same time, the rotary forging deformation process of the present invention reduces the grain growth tendency of high-purity magnesium by combining a small deformation amount with rapid water cooling, and can well achieve large plastic deformation at room temperature. It also increases the dislocation density and twin density of the material by a high strain rate, and induces the formation of nano-grains inside the pure magnesium rod, thereby increasing the strength of the material. The high-purity magnesium rod with both strength and plasticity prepared by the present invention has a room temperature tensile strength of ≥250MPa, and an elongation of more than 14%, which is comparable to the performance of the degradable bio-magnesium alloy in the prior art.

[0022] 4. The preparation method of the biodegradable high-purity magnesium rod of the present invention can be carried out on a large scale, and can prepare high-purity magnesium rods with a diameter of 10 to 25 mm and a length of 300 to 1500 mm, solving the problems of long multi-step continuous plastic processing process, high energy consumption, high equipment requirements, high production cost, and high requirements for rod accuracy and shape. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Distribution diagram of large and small angle grain boundaries and bright field image of the embodiment.

[0024] Figure 2 Macroscopic morphology of extruded rods of Example and Comparative Example.

[0025] Figure 3 Macroscopic morphology of comparative example 3.

[0026] Figure 4 Room temperature tensile mechanical properties diagram. DETAILED DESCRIPTION

[0027] The present invention will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the present invention belong to the scope of protection of the present invention.

[0028] Unless otherwise indicated in specific cases in the present invention, the numerical ranges listed herein include the upper and lower limits, and all integers and fractions within the range, and are not limited to the specific values ​​listed when defining the range.

[0029] 1. A method for preparing a pure magnesium rod with both strong plasticity and medical properties

[0030] The pure magnesium ingot is subjected to room temperature extrusion treatment, and the rod obtained after extrusion is subjected to rapid cooling treatment to obtain the pure magnesium rod; wherein the temperature of the extrusion barrel in the extrusion equipment is set to ≥150°C, and the temperatures of the pure magnesium ingot and the mold before extrusion are both room temperature; and the temperature of the cooling medium is 0-5°C.

[0031] After conducting an in-depth study of the prior art, the present invention found that in order to improve the deficiencies of pure magnesium materials in mechanical properties, the prior art generally adopts the addition of other alloying elements to form a second phase with magnesium in the alloy, so as to improve the mechanical properties of the alloy material to a certain extent. For example, modified Mg-Ca, Mg-Zn, Mg-Ca-Zn, and Mg-Y-Nd-Sm-Zr alloys have shown remarkable mechanical performance advantages. However, due to the formation of a second phase in the alloy, galvanic corrosion will occur in the second phase. This corrosion process usually accelerates the degradation of the alloy material, causing the degradation rate of the alloy material to be too fast, which not only affects the long-term stability of the implant, but also may cause a series of adverse biological reactions, such as local inflammatory reactions, tissue damage and even rejection reactions. Based on this, the present invention contemplates the use of high-purity magnesium as a raw material, strictly controlling the impurity content and thoroughly reducing the number and distribution of the second phase in the alloy, thereby effectively inhibiting this galvanic corrosion phenomenon. However, the pure magnesium obtained by the traditional preparation process still needs to face the problem of insufficient mechanical properties, especially for the high-purity magnesium material prepared by hot deformation, its strength and plasticity are generally low, and the tensile strength is often difficult to break through 180MPa, and the plasticity is difficult to exceed 20%. Therefore, the present invention starts with the preparation method and makes improvements and finds that the pure magnesium rod is first extruded at room temperature, and then rapidly cooled, so that the grain of the pure magnesium rod can be significantly refined, and the plasticity of the pure magnesium rod can also be improved. The dislocation density in the pure magnesium rod is increased by a high strain rate, and the high-density dislocation induces a large number of nano-scale substructures to form inside the pure magnesium, and finally, while retaining the medium plasticity of the pure magnesium, the strength of the prepared pure magnesium rod is improved, thereby making up for the shortcomings of the high-purity magnesium prepared by the prior art in mechanical properties. Therefore, in the method described in the present invention, the temperature of the extrusion barrel in the extrusion equipment is set at above 150°C, and the pure magnesium ingot and the mold are kept at room temperature before extrusion, and no special heating treatment is performed on them. At the same time, after the pure magnesium ingot is placed in the extrusion cylinder, it is directly extruded. The outer surface of the pure magnesium ingot is in contact with the extrusion cylinder, and under contact, the temperature of the pure magnesium ingot from the surface to the core has a gradient distribution. In this state, the pure magnesium ingot is rapidly extruded, and a large amount of deformation work is converted into heat, which causes the temperature of the billet to further increase. Dynamic recrystallization occurs during the extrusion deformation process, followed by rapid cooling. The pure magnesium rod obtained in this way has excellent plasticity of pure magnesium, and its mechanical properties are also significantly improved, thereby making up for the shortcomings of the mechanical properties of high-purity magnesium prepared by the prior art.

[0032] In some embodiments of the present invention, the pure magnesium rod can be subjected to a multi-pass rotary forging deformation treatment with a small deformation amount at room temperature. After further in-depth research on the preparation process of pure magnesium rods, the present invention found that due to the room temperature extrusion and rapid cooling in the early stage, a material with refined grain structure and excellent plasticity is provided for the rotary forging deformation treatment, which prevents the grain growth of the rod during the rotary forging process. The next step of the rotary forging deformation treatment is to perform a small deformation on the pure magnesium rod combined with rapid water cooling to further refine the ultrafine grain structure of the pure magnesium rod and achieve large plastic deformation at room temperature. The pure magnesium rod prepared by this two-step continuous plastic processing method has a refined internal structure and produces a large number of twins and dislocations. The pure magnesium rod is transformed from local corrosion in the magnesium alloy material to uniform corrosion when it fails due to corrosion, which improves the controllability of the corrosion process of the pure magnesium rod, and makes the degradation rate of the pure magnesium rod of the present invention in simulated body fluids ≤0.3mm / year, thereby solving the problem of premature failure of mechanical properties due to excessive degradation of magnesium implant devices in the prior art.

[0033] In some embodiments, in step 1, the temperature of the extrusion barrel in the extrusion equipment is adjusted to at least 150°C, but before entering the extrusion barrel, the temperature of the pure magnesium ingot and the mold are kept at room temperature, so that during the extrusion process, the internal temperature of the pure magnesium ingot is in a gradient state, and the temperature from the surface of the pure magnesium ingot to the vicinity of its axis gradually decreases. The temperature of the mold barrel is higher than that of the pure magnesium ingot, and a large amount of deformation work is converted into heat, resulting in a further increase in the temperature of the billet, and dynamic recrystallization occurs during the extrusion deformation process. At the same time, rapid cooling is required immediately after the extrusion is completed to provide an extruded rod with ultrafine grain structure and excellent plasticity for the rotary forging deformation process, so as to prevent the rod from heating up in large quantities during the rotary forging process, resulting in grain growth. The temperature of the cooling medium used for the cooling treatment is 0 to 5°C, and the cooling treatment is preferably a water cooling treatment, so as to achieve the effect of rapid cooling.

[0034] In some embodiments, the pure magnesium ingot has a Mg content of >99.99% calculated by mass percentage, and the total content of the three impurity elements Fe, Ni, and Cu in the pure magnesium ingot is ≤50ppm. The present invention strictly controls the content of impurity elements in the pure magnesium ingot, eliminates the problem of accelerated degradation caused by galvanic corrosion caused by impurity elements such as Fe, Ni, and Cu (total content ≤50ppm) and the second phase in the alloy, and also eliminates potential biological problems caused by the addition of alloying elements. Therefore, the rod of the present invention has better biological safety and corrosion resistance.

[0035] In some embodiments, before extrusion, the cross-sectional diameter of the pure magnesium ingot is 60 to 80 mm, and the height does not exceed 60 mm. The cross-sectional area of ​​the pure magnesium ingot is directly controlled within a certain range. Too thin or too thick is not conducive to the subsequent process. The cross-sectional diameter of the pure magnesium ingot can be 60 mm, 70 mm, 80 mm, etc., and all ranges and sub-ranges between the above values. It should be understood that in the embodiment, any of the above ranges can be combined with any other ranges.

[0036] In some embodiments, during the extrusion process, the extrusion ratio is 10 to 50, and the cooling treatment is a water cooling treatment. If the extrusion ratio is too low, it is impossible to form a sufficient amount of grain structure that is refined to a certain extent in the pure magnesium rod; if the extrusion ratio is too high, it will cause excessive deformation in the pure magnesium rod, and even cracks will form, which is not conducive to further processing of the pure magnesium rod during the rotary forging process. Therefore, the extrusion ratio can be 10, 20, 30, 40, 50, etc., as well as all ranges and sub-ranges between the above values. It should be understood that in the implementation scheme, any of the above ranges can be combined with any other ranges.

[0037] In some embodiments, in the rotary swaging deformation process, the deformation amount of each pass of the rotary swaging deformation process is as small as possible. The temperature of the bar during the rotary swaging deformation process is always at room temperature, not lower than 0°C and not higher than 40°C, ensuring that the pure magnesium bar is quickly cooled during rotary swaging, reducing the tendency of high-purity magnesium bar grain growth, thereby achieving large plastic deformation at room temperature, ensuring that the dislocation density of the pure magnesium bar can be increased, thereby inducing the formation of nano-scale substructures inside the pure magnesium, and ultimately improving the strength of the pure magnesium bar.

[0038] In some embodiments, in the rotary forging deformation process, the diameter of the rod is reduced by 0.2 to 1.0 mm for each rotary forging deformation process. The cross-sectional diameter of the high-purity magnesium rod obtained by the rotary forging deformation process is 10 to 25 mm, which is 0.2 to 5 mm less than the cross-sectional diameter of the extruded rod. The degree of each rotary forging deformation process is regulated so that the deformation process inside the rod occurs gradually. Too large or too small a reduction causes the rod to crack, and too small a reduction causes the rod to fail to produce enough dislocations and twins. In each rotary forging deformation process, the reduction in the diameter of the rod can be 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, etc., as well as all ranges and sub-ranges between the above values. It should be understood that in the implementation scheme, any of the above ranges can be combined with any other ranges.

[0039] In some embodiments, in the rotary swaging deformation process, the feed rate of the rotary swaging deformation process is ≤10m / min. The feed rate of the rotary swaging deformation process should not be too fast, and is controlled to be ≤10m / min, and can be 4m / min, 5m / min, 6m / min, 7m / min, 8m / min, etc., and all ranges and sub-ranges between the above values. It should be understood that in the embodiment, any of the above ranges can be combined with any other ranges.

[0040] In some embodiments, the pure magnesium rod has an axial length of 300 to 1500 mm and a cross-sectional diameter of 10 to 20 mm.

[0041] 2. Examples and Comparative Examples

[0042] Example 1

[0043] A high-purity magnesium ingot is selected as the raw material, wherein the Mg content is 99.99wt%, and the total content of three impurity elements, Fe, Ni and Cu, is less than 50ppm.

[0044] S1: firstly cut an extrusion billet with a cross-sectional diameter of 80 mm and a height of 50 mm from a high-purity magnesium ingot, and only set the billet barrel of the extruder at 150° C. to extrude the extrusion billet to obtain an extruded rod; wherein the temperature of the extruded billet before entering the billet barrel of the extruder and the temperature of the die are both 25° C., the extrusion ratio is 50, and the cross-sectional diameter of the extruded rod is 12.0 mm;

[0045] S2: Performing a rapid water cooling treatment on the extruded rod to obtain an extruded rod; the temperature of the medium in the water cooling treatment is 0-5°C.

[0046] Example 2

[0047] A high-purity magnesium ingot is selected as the raw material, wherein the Mg content is 99.99wt%, and the total content of three impurity elements, Fe, Ni and Cu, is less than 50ppm.

[0048] S1: firstly cut an extrusion billet with a cross-sectional diameter of 80 mm and a height of 50 mm from a high-purity magnesium ingot, and only set the billet barrel of the extruder at 150° C. to extrude the extrusion billet to obtain an extruded rod; wherein the temperature of the extruded billet before entering the billet barrel of the extruder and the temperature of the die are both 25° C., the extrusion ratio is 25, and the cross-sectional diameter of the extruded rod is 16.0 mm;

[0049] S2: Performing a rapid water cooling treatment on the extruded rod to obtain an extruded rod; the temperature of the medium in the water cooling treatment is 0-5°C.

[0050] Comparative Example 1

[0051] The adjustment is made on the basis of Example 1, except that the extrusion forming temperature of the hot extrusion treatment is 350° C. and the extrusion ratio is 50. The other steps are exactly the same as those of Example 1. The cross-sectional diameter of the high-purity magnesium rod prepared in Comparative Example 1 is 12 mm, and the axial length is 800 mm.

[0052] Comparative Example 2

[0053] The adjustment is made on the basis of Example 2, except that the extrusion forming temperature of the hot extrusion treatment is 350° C. and the extrusion ratio is 25. The other steps are exactly the same as those of Example 2. The cross-sectional diameter of the high-purity magnesium rod prepared in Comparative Example 2 is 16 mm and the axial length is 500 mm.

[0054] Comparative Example 3

[0055] The example 2 was adjusted based on the example 2, except that the extrusion barrel temperature was set to room temperature, the extrusion ratio was 25, and the mold and the billet were not heated. The other steps were exactly the same as the example 2. Under the same extrusion conditions, the comparative example 3 failed to successfully extrude the rod. The ingot sample taken out from the extrusion barrel was as follows: Figure 3 shown.

[0056] Example 3

[0057] A high-purity magnesium ingot is selected as the raw material, wherein the Mg content is 99.994wt%, and the total content of three impurity elements, Fe, Ni and Cu, is less than 50ppm.

[0058] S1: first cut an extrusion billet with a cross-sectional diameter of 80 mm and a height of 50 mm from a high-purity magnesium ingot, set only the billet barrel of the extruder at 150°C, and extrude the extrusion billet to obtain an extruded rod; wherein, the temperature of the extruded billet before entering the billet barrel of the extruder and the mold are both 25°C, the extrusion ratio is 25, and the cross-sectional diameter of the extruded rod is 16.0 mm.

[0059] S2: Performing a rapid water cooling treatment on the extruded rod to obtain an extruded rod; the temperature of the medium in the water cooling treatment is 0-5°C.

[0060] S3: performing rotary forging deformation treatment on the extruded rod to obtain the degradable high-purity magnesium rod; wherein, the temperature of the rotary forging deformation treatment is 0-40°C, and in order to avoid excessive rotary forging deformation causing the temperature of the rod to rise, the diameter reduction of each pass is controlled at 0.4mm, and the feeding speed is 5m / min.

[0061] The cross-sectional diameter of the prepared high-purity magnesium rod is 14.8 mm, which is 1.2 mm less than the cross-sectional diameter of the extruded rod, and the axial length is 500 mm.

[0062] Example 4

[0063] A high-purity magnesium ingot is selected as the raw material, wherein the Mg content is 99.99wt%, and the total content of three impurity elements, Fe, Ni and Cu, is less than 50ppm.

[0064] S1: firstly cut an extrusion billet with a cross-sectional diameter of 80 mm and a height of 50 mm from a high-purity magnesium ingot, and only set the billet barrel of the extruder at 150° C. to extrude the extrusion billet to obtain an extruded rod; wherein the temperature of the extruded billet before entering the billet barrel of the extruder and the temperature of the die are both 25° C., the extrusion ratio is 25, and the cross-sectional diameter of the extruded rod is 16 mm;

[0065] S2: Performing a rapid water cooling treatment on the extruded rod to obtain an extruded rod; the temperature of the medium in the water cooling treatment is 0-5°C.

[0066] S3: performing rotary forging deformation treatment on the extruded rod to obtain the degradable high-purity magnesium rod; wherein, the temperature of the rotary forging deformation treatment is 0-40°C, and in order to avoid excessive rotary forging deformation causing the temperature of the rod to rise, the diameter reduction of each pass is controlled at 0.4mm, and the feeding speed is 5m / min.

[0067] The cross-sectional diameter of the prepared high-purity magnesium rod is 15.6 mm, which is 0.4 mm less than the cross-sectional diameter of the extruded rod, and the axial length is 500 mm.

[0068] Comparative Example 4

[0069] The example 3 is adjusted, and the difference is that the hot extrusion is performed in the example 4, and the extrusion forming temperature of the hot extrusion process is 350°C, and the extrusion ratio is 25; wherein the hot extrusion process refers to the process of heating the pure magnesium billet and the die to 350°C and completing the extrusion process at this temperature. The other steps are exactly the same as those in the example 3. The cross-sectional diameter of the high-purity magnesium rod prepared in the example 4 is 14.8 mm, and the axial length is 500 mm.

[0070] 3. Performance Comparison

[0071] (1) Performance testing

[0072] The room temperature tensile properties of the high-purity magnesium rods of Examples 1-4 and Comparative Examples 1-4 were tested, and the results of the tensile yield strength, tensile strength, elongation and simulated body fluid degradation rate of the high-purity magnesium rods of Examples 1-4 and Comparative Examples 1-4 are shown in Table 1. Among them, the room temperature tensile properties of the high-purity magnesium rods were tested according to GB / T 228.1-2021 "Metallic Material Tensile Test Part 1: Room Temperature Test Method" using an MTS E43.104 electronic universal testing machine.

[0073] The degradation rate of high-purity magnesium rods in simulated body fluids was carried out in accordance with ASTM-G31-72 "Laboratory immersion corrosion test of metals" in m-SBF simulated body fluids (ion concentrations are shown in Table 1) using the hydrogen evolution method. The solution volume (mL) in the experiment was set to the total surface area of ​​the sample (cm 2 ), weigh the sample before the immersion test using a high-precision balance (0.01 mg), and record the volume of hydrogen evolution during the sample immersion process. Repeat at least 3 groups of immersion tests for each sample, and take the average value of the results.

[0074] The corrosion rate of the sample can be calculated based on the hydrogen evolution result (CRHE, mm / year) as follows:

[0075]

[0076] Where Sm is the total surface area of ​​the sample (cm 2 ), Tm is the immersion time (h), ρm is the sample density (g / cm 3 ), ΔV H2 is the volume of hydrogen evolved from the sample during the immersion experiment (ml).

[0077] Table 1

[0078]

[0079] (2) Performance Analysis

[0080] Table 2

[0081] Yield strength MPa Tensile strength MPa Elongation % 5d simulated body fluid degradation rate mm / year Example 1 147 177 25 0.30 Example 2 130 180 26 0.34 Comparative Example 1 94 155 20 0.43 Comparative Example 2 83 155 16 0.37 Comparative Example 3 - - - -

[0082] It can be seen from Table 2 that:

[0083] 1) From Figure 1 From the microstructure observation of Example 1, it can be seen that the room temperature extrusion temperature is conducive to providing a finer grain size and the presence of a large number of small-angle grain boundaries. The average grain size is lower than the pure magnesium grain size reported in the literature, and a large number of dislocations and twins are introduced after room temperature rotary forging to further improve the strength.

[0084] 2) Compared with hot extrusion, the rods prepared by the method of the present invention improve the elongation of pure magnesium while significantly improving the strength of pure magnesium; for example, in Example 1 and Comparative Example 1, the extrusion molding temperature of Comparative Example 1 is 350°C, which is to heat the pure magnesium ingot to 350°C and then extrude it. Compared with Example 1, Comparative Example 1 not only has reduced strength, but also significantly deteriorated elongation; and Comparative Example 2, compared with Comparative Example 1, has a lower extrusion ratio, and can indeed obtain a relatively high elongation, but its strength is obviously insufficient. The method of the present invention can ensure that the pure magnesium rod maintains a high plasticity while improving the strength of the pure magnesium rod. Figure 2 Comparison of the data of the embodiment with the comparative example shows that the hot extrusion temperature leads to reduced material formability and reduced precision.

[0085] 3) Compared with Example 2, in Example 3, the temperature of the extrusion barrel is not controlled, which makes the pure magnesium ingot deformed and heated up internally after being placed in the extrusion barrel, and the internal temperature rise does not reach the critical temperature of extrusion deformation, resulting in the entire pure magnesium ingot having too low internal temperature and increased deformation resistance, so that the rod cannot be successfully extruded. Figure 3 This can also be proved that when the extrusion pressure is the same, the temperature of the extrusion barrel is not set in the room temperature extrusion process, resulting in failure of material extrusion molding. This also shows that it is difficult to obtain a molded pure magnesium rod without controlling the temperature of the extrusion barrel.

[0086] Table 3

[0087] Yield strength MPa Tensile strength MPa Elongation % 5d simulated body fluid degradation rate mm / year Example 3 225 251 14 0.23 Example 4 151 206 23 0.28 Comparative Example 4 210 230 10 0.33

[0088] It can be seen from Table 2 and Table 3 that:

[0089] 1) Examples 3 to 4 are based on Example 2, and the obtained pure magnesium rod is subjected to room temperature rotary forging treatment. Compared with Example 2, the pure magnesium rod obtained after room temperature rotary forging treatment has a very significant improvement in mechanical properties, while retaining the higher plasticity of the pure magnesium material.

[0090] 2) In Comparative Example 4, room temperature rotary forging is performed after hot extrusion. The parameters of hot extrusion in Comparative Example 4 are consistent with those in Comparative Example 2. However, while high strength is obtained after room temperature rotary forging, the plasticity decrease ratio of Comparative Example 4 decreases more significantly than that of Example 3. It can be seen that not all pure magnesium bars obtained by extrusion processes can maintain good plasticity through room temperature rotary forging. Room temperature extrusion can obviously improve the mechanical properties compared to hot extrusion.

[0091] 3) In Examples 3 to 4, not only the mechanical properties are improved, but also the degradation rate is further reduced. At the same time, the corrosion process of the pure magnesium rods obtained in Examples 3 to 4 is observed, and it can be found that the corrosion process of the pure magnesium rods in Examples 3 to 4 is more uniform and slow, and the local corrosion in the pure magnesium material in the prior art is transformed into uniform corrosion, which makes the corrosion process of the pure magnesium rod more controllable and more conducive to the stability of the implantation of the pure magnesium material.

[0092] 4) From Figure 4 It can be seen from the data of the embodiment and the comparative example that the combination of room temperature extrusion and room temperature rotary forging can give play to their respective advantages and produce a synergistic effect. The extrusion process provides a good initial organizational state for the rotary forging process, while the rotary forging process further refines the grains and improves the mechanical properties of the material. Room temperature extrusion combined with room temperature rotary forging can further improve the strength and plasticity of pure magnesium. Therefore, pure magnesium under this process can withstand higher loads as a biomaterial while maintaining good plastic deformation ability. Its application range in the biomedical field can be further expanded.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a pure magnesium rod having both strong plasticity and medical properties, characterized in that: The specific steps include: The pure magnesium ingot is subjected to room temperature extrusion treatment, and the rod obtained after extrusion is subjected to rapid cooling treatment to obtain the pure magnesium rod; wherein the temperature of the extrusion barrel in the extrusion equipment is set to ≥150°C, and the temperatures of the pure magnesium ingot and the mold before extrusion are both room temperature; and the temperature of the cooling medium is 0-5°C.

2. The preparation method according to claim 1, characterized in that: The pure magnesium rod can be subjected to a multi-pass rotary forging deformation treatment under room temperature conditions.

3. The preparation method according to claim 2, characterized in that: The temperature of the rotary forging deformation treatment is 0 to 40°C.

4. The preparation method according to claim 2, characterized in that: During each rotary forging deformation process, the rod diameter is reduced by 0.2 to 1.0 mm.

5. The preparation method according to claim 2, characterized in that: The feeding speed of rotary forging deformation treatment is ≤10m / min.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In the pure magnesium ingot, calculated by mass percentage, the content of Mg is greater than 99.99%, and the total content of the three impurity elements Fe, Ni and Cu in the pure magnesium ingot is ≤50ppm.

7. The preparation method according to claim 6, characterized in that: The cross-sectional diameter of the pure magnesium ingot is 60-80 mm, and the height does not exceed 60 mm.

8. The preparation method according to claim 6, characterized in that: During the extrusion process, the extrusion ratio is 10-50, and the cooling process is water cooling.

9. The preparation method according to claim 6, characterized in that: The pure magnesium rod has an axial length of 300 to 1500 mm and a cross-sectional diameter of 10 to 25 mm.

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