Directional solidification preparation method of degradable high-hardness zinc alloy material

Abstract

The invention provides a directional solidification preparation method of a degradable high-hardness zinc alloy material. The preparation method of the zinc alloy material comprises the machining processes of vacuum induction melting, vacuum directional solidification melting and the like, through the preparation method, growth of Zn + Mg2Zn11 trilobal eutectic and Zn + MgZn2 spiral eutectic is regulated and controlled, microscopic structures are arranged in the specific direction, fine and uniform structure morphology is formed, and the corrosion resistance and the mechanical property of the alloy are improved. The Zn-Mg series alloy prepared by the preparation method disclosed by the invention shows excellent microhardness (181.19 to 243.10 HV). Besides, the corrosion rate of the ideal degradable bone implant is within the range of 0.1 mm / y to 0.5 mm / y, and the corrosion rate of the degradable medical Zn-Mg alloy bone implant material is within the range of 0.0316 mm / y to 0.2280 mm / y, so that the requirement on the corrosion rate in the bone repair process is met; and after the Cu element is added on the basis of Zn-3% Mg, the microhardness of the Zn-3% Mg-Cu-Cu alloy material is improved to about 200HV, and the advantages in the aspect of mechanical support are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical degradable alloys, and relates to a method for directionally solidifying a degradable high-hardness zinc alloy material. Background Art

[0002] As a new type of medical material, biodegradable metals are driving technological innovation in the medical field with their excellent biocompatibility and suitable degradation characteristics. Different from traditional permanent implants, biodegradable metals can naturally degrade in the human body environment after completing their support and repair functions, without the need for a second surgery to remove them. This not only significantly reduces the pain and surgical risks of patients, but also greatly reduces medical costs. These characteristics make them known as biomedically decisive metal materials and show great potential to become the next-generation implant materials.

[0003] Currently, the research on biodegradable metals mainly focuses on three categories of materials: magnesium-based alloys, iron-based alloys, and zinc-based alloys. From the perspectives of materials science and electrochemistry, the corrosion rate of a metal is closely related to its standard electrode potential, showing an obvious inverse relationship - the lower the electrode potential, the faster the corrosion rate. The standard electrode potential of magnesium is -2.372V, and its corrosion rate is relatively fast. Although rapid degradation is beneficial in some cases, it is clearly not ideal for maintaining the long-term mechanical support of implants. The standard electrode potential of iron is -0.447V, and its corrosion rate is relatively slow. Its degradation products can form a dense protective layer on the material surface, further delaying the degradation process. However, this characteristic may hinder the functional recovery and regeneration of human tissues. Especially in cases where synchronous degradation and tissue growth are required, the application range of iron-based alloys is somewhat limited. In comparison, the standard electrode potential of zinc is -0.763V, which is between magnesium and iron. Therefore, its corrosion rate is moderate, and it can achieve a better balance between mechanical support and tissue repair. In recent years, in order to obtain alloy materials with excellent properties, researchers have focused on the preparation and research and development of zinc-based biodegradable biomaterials for biomedical applications.

[0004] CN104212998A discloses a Zn-Mg series zinc alloy, its preparation method and applications. The invented zinc alloy includes Zn and Mg; by weight percentage, the mass percentage of Mg in the zinc alloy is 0% to 20%, but does not include 0. The preparation process of this alloy is as follows: first, the alloy is subjected to vacuum melting, and then processed by at least one of different processing methods, including rolling, forging, rapid solidification and extrusion, to obtain the mechanical properties of the alloy as follows: tensile strength 90.37 - 316.65 MPa, yield strength 63.43 - 257.42 MPa, elongation 0.521% - 12.858%. However, the composition range of this alloy is relatively wide, with Mg being 0% to 20%. Although it helps for flexible applications under different requirements, the best composition ratio is not clearly recommended, and different ratios may lead to differences in the alloy's mechanics. CN108588484A discloses a high-strength and high-ductility degradable Zn-Mn-Mg zinc alloy and its preparation method, in which it is disclosed that by composition in mass percentage: Mn: 0.02% - 0.49%, Mg: 0.001% - 0.3%. Mn is the main alloying element, and Mg is the secondary alloying element. The Mn content in the alloy is not less than the Mg content. The basic preparation process flow of this alloy is: vacuum directional solidification → extrusion; on this basis, at least one of the following methods is selected for further processing: double-stage heat treatment, extrusion, rolling, drawing and annealing treatment. However, the preparation process adopted by this method is relatively traditional. Secondly, the room-temperature tensile mechanical properties of the obtained alloy are: yield strength 260 - 430 MPa, tensile strength 305 - 580 MPa, elongation 18% - 55%. However, the preparation method has cumbersome steps and it is difficult to achieve the preparation of customized implantable devices. CN114182138A discloses a biodegradable Zn-Mg-Bi zinc alloy and its preparation method. The composition (mass percentage) of this alloy material is: 1.10% - 1.20% of Mg, 0.50% - 2.50% of Bi, and the balance is Zn; in an inert atmosphere, magnesium is heated to melting to obtain a magnesium melt, then bismuth particles are added and stirred, and after heat preservation, a magnesium-bismuth alloy melt is obtained. After standing, refining and skimming the slag, a Mg-50wt.% Bi alloy ingot is obtained by casting and demolding; then zinc is heated to melting, the Mg-50wt.% Bi alloy ingot and pure magnesium or pure bismuth are added, and after heating, stirring and heat preservation, a Zn-MgBi alloy melt is obtained; finally, after standing, refining and skimming the slag, a biodegradable Zn-Mg-Bi zinc alloy is obtained by casting and demolding. In this patent, not only the alloy element content is high, but also the hardness of this alloy material is relatively low, and its Vickers hardness is only 36.75 - 70.35 HV.

[0005] In summary, the current methods for improving the mechanical properties of zinc alloys mainly include optimizing the preparation process and alloying. For example, single extrusion, drawing, rolling, forging, or a combination of plastic deformation processes and heat treatment processes. The processes of these preparation methods are relatively complex. Alloying is an important way to improve the strength of zinc alloys. However, highly alloyed zinc alloys contain more second phases, which are prone to local corrosion. In addition, the stress field between the second phase and the Zn matrix easily leads to stress concentration and crack initiation, exacerbating local corrosion, which becomes the key reason for the premature failure of the device during service. Therefore, how to break through the limitations of the existing design ideas and explore innovation in the preparation process to improve the performance of zinc alloys is the current research focus. Summary of the Invention

[0006] The purpose of the present invention is to find a directional solidification preparation method for degradable high-hardness zinc alloy materials, to solve the problem of large performance differences in zinc alloys prepared by conventional casting methods in different directions; and to obtain materials with uniform corrosion resistance at the same time.

[0007] The present invention relates to a degradable medical zinc alloy material. The alloy is composed of Zn, Mg, Cu elements and inevitable impurity elements. The components are calculated by mass percentage: 3% - 4.5% of Mg element, 0 - 1% of Cu element, and the balance is Zn and inevitable impurities; the zinc alloy material is first prepared into an alloy ingot by vacuum induction melting, and then a bar is cut from the ingot and placed in a directional solidification device to prepare a zinc alloy with significant corrosion resistance.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A directional solidification preparation method for degradable high-hardness zinc alloy materials, comprising the following steps:

[0009] S1. Weigh the raw materials according to the mass percentages, place them in a high-temperature resistant quartz tube, put the quartz tube into a vacuum high-frequency induction melting furnace, evacuate to 5×10 -3 MPa, then introduce argon gas with a pressure of 20 - 30 Pa into the furnace, start melting, and obtain a zinc alloy ingot after cooling and solidification;

[0010] S2. Cut the obtained zinc alloy ingot into alloy bars, and polish and clean the alloy bars;

[0011] S3. Place the alloy bars in an alumina ceramic tube, then fix the ceramic tube on the draw bar of a vacuum directional solidification furnace, evacuate, introduce argon gas with a pressure of 20 - 30 Pa, then heat and keep warm, and then pull them into a Ga-In-Sn coolant at a set draw rate to complete the preparation of the degradable high-hardness zinc alloy.

[0012] Preferably, in step S1, a zinc alloy system composed of Zn and Mg elements is used. The mass percentage of the Mg element is 3-4.5%, the total content of impurity elements is ≤0.1%, and the balance is Zn; the purity of pure zinc is above 99.99%, and the purity of pure magnesium is above 99.99%.

[0013] Preferably, in step S1, a zinc alloy system composed of Zn, Mg, and Cu elements is used. The mass percentage of the Mg element is 3%, the mass percentage of the Cu element is 0.5%-1%, the total content of impurity elements is ≤0.1%, and the balance is Zn; the purity of pure zinc is above 99.99%, the purity of pure magnesium is above 99.99%, and the purity of copper is above 99.99%.

[0014] Preferably, in step S1, the melting temperature of the alloy is 450°C-500°C, the holding time is 10 min, after cooling for 5 min, it is reheated, and melted repeatedly 3 times, and a zinc alloy ingot is obtained after cooling and solidification.

[0015] Preferably, in step S2, the method for grinding and cleaning the alloy rod is: first grind with sandpaper, and then put it into an alcohol solution for ultrasonic cleaning.

[0016] Preferably, in step S3, the temperature for directional solidification is 693°C, and the holding time is 30 min.

[0017] Preferably, in step S3, the drawing rate is 100 μm / s-1000 μm / s.

[0018] Preferably, an alumina ceramic tube is used as the crucible in this preparation method, a graphite sleeve and a quartz sleeve are successively sleeved as the thermal insulation layer, and carbon felts are placed at the top and bottom of the sleeve for heat insulation.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention uses the directional solidification method to prepare zinc alloys. By controlling the drawing direction to control the influence of the heat flow direction on crystal growth, the random distribution of grains is avoided, and zinc alloys with a specific orientation microstructure are prepared. By adjusting the drawing rate, the size of the structure can be adjusted to obtain a fine structure, ensuring a high microhardness, thereby enhancing the support performance, anti-deformation ability, and corrosion resistance of the material.

[0021] 2. The degradable medical Zn-Mg alloy material of the present invention selects alloy elements with good biocompatibility and is non-toxic to the human body. The Mg element in the alloy releases Mg in the human body 2+It can promote the growth, proliferation and differentiation of osteoblasts, has a good bone induction effect, and has the function of promoting bone healing. The bone implant device prepared from this alloy can continuously and slowly release Mg ions in the human body, thereby accelerating bone tissue repair and reducing the inflammatory response. Adding Cu elements to the zinc alloy can improve the mechanical properties and corrosion resistance of the material. Appropriate copper ions can improve the strength and hardness of the alloy through solid solution strengthening and the formation of intermetallic compounds. In addition, the ideal corrosion rate of the degradable bone implant is in the range of 0.1 mm / y to 0.5 mm / y. The corrosion rate of the degradable medical Zn-Mg-based alloy bone implant material of the present invention is in the range of 0.0316 mm / y to 0.2280 mm / y, meeting the requirements for the corrosion rate during bone repair; moreover, after adding Cu elements on the basis of Zn-3%Mg, its microhardness has been increased to about 200 HV, improving the advantage in mechanical support. Description of the Drawings

[0022] Figure 1 It is the metallographic structure of the Zn-3Mg alloy prepared in Example 1 of the present invention at a drawing rate of 100 μm / s.

[0023] Figure 2 It is the metallographic structure of the Zn-4.5Mg alloy prepared in Example 2 of the present invention at a drawing rate of 100 μm / s.

[0024] Figure 3 It is the metallographic structure of the Zn-4.5Mg alloy prepared in Example 3 of the present invention at a drawing rate of 1000 μm / s.

[0025] Figure 4 It is the metallographic structure of the Zn-3Mg-0.5Cu alloy prepared in Example 4 of the present invention at a drawing rate of 100 μm / s.

[0026] Figure 5 It is the metallographic structure of the Zn-3Mg-0.5Cu alloy prepared in Example 5 of the present invention at a drawing rate of 500 μm / s.

[0027] Figure 6 It is the metallographic structure of the Zn-3Mg-1Cu alloy prepared in Example 6 of the present invention at a drawing rate of 100 μm / s.

[0028] Figure 7 It is the metallographic structure of the Zn-3Mg-1Cu alloy prepared in Example 7 of the present invention at a drawing rate of 500 μm / s.

[0029] Figure 8 It is the metallographic structure of the as-cast Zn-3Mg alloy prepared in Comparative Example 1 of the present invention.

[0030] Figure 9The potentiodynamic polarization curves of the degradable Zn-Mg alloys prepared in Examples 1-7 and Comparative Example 1 of the present invention in SBF solution.

[0031] Figure 10 The macroscopic structure diagram of the Zn-3Mg-0.5Cu alloy prepared in Example 2 of the present invention at a drawing rate of 100 μm / s. Specific embodiments

[0032] The present invention will be further described below in conjunction with specific examples and comparative examples.

[0033] The performance test method of the embodiments of the present invention is as follows:

[0034] In this experiment, the microhardness of the directional solidification zone of the sample was measured by a Wilson VH1102 microhardness tester. The sample was cut into small pieces by wire cutting, and a hot embedding device was used to prepare an embedded sample to ensure the flatness of the upper and lower surfaces of the sample during the test to reduce errors. A 100 g load was selected for the test, and the loading time was 10 s. In order to reduce data errors, multiple points were punched near the same area, and the average value was taken as the hardness value of this point.

[0035] The corrosion resistance of the samples in this study was obtained by testing with an American Gamry electrochemical workstation. The three-electrode system was used for the test. The reference electrode was a saturated calomel electrode, the auxiliary electrode was a platinum sheet, and the experimental corrosion medium was SBF simulated body fluid. The working electrode was allowed to obtain a stable potential in the corrosion medium by running the open circuit potential for 1800 s; the potential range for the polarization curve test was -2 to 1 V; the scanning range selected for the AC impedance test was 10 -2 ~10 5 Hz.

[0036] The purity of the pure zinc used in the following examples is above 99.99%, the purity of the pure magnesium is above 99.99%, and the purity of the copper is above 99.99%.

[0037] Example 1

[0038] A method for directionally solidifying a degradable high-hardness zinc alloy material, comprising the following steps:

[0039] S1. Weigh 12 parts of pure magnesium particles and 388 parts of pure zinc particles by mass, place them in a high-temperature resistant quartz tube with a diameter of 50 mm and a height of 80 mm, and put the quartz tube into a vacuum high-frequency induction melting furnace;

[0040] S2. Evacuate to 5×10 -3MPa, argon gas is introduced into the furnace for protection, and this process is repeated 2 times; adjust the induction current to 10 A, melt the mixed raw materials at 450 °C, keep warm for 10 min until the sample is completely melted, cool for 5 - 10 min until the sample stops glowing red, then reheat and melt again, and repeat this heating and melting process 3 times;

[0041] S3. Cool in the furnace for 10 min, release the gas, open the furnace lid to take out the sample, and air-cool it to room temperature. After the sample solidifies, a as-cast Zn-Mg alloy is obtained;

[0042] S4. Place the obtained Zn-Mg alloy bar in an aluminum oxide ceramic tube, then fix the ceramic tube on the draw bar in the vacuum chamber of a qualitative solidification melting furnace, and then successively put on a graphite heat preservation sleeve and a quartz heat preservation sleeve outside the ceramic tube;

[0043] S5. Evacuate to 5×10 -3 MPa, argon gas is introduced into the furnace for protection, and this process is repeated 2 times: Turn on the main switch of the heating system, after preheating for 5 minutes, open the heating interface, manually set the heating power, increase the heating power in sections. For each increase of 0.5 W, it is necessary to stabilize the voltage for 15 min before increasing the voltage again. Repeat this step until the temperature rises to 693 °C, keep warm for 30 min to make the alloy melt reach a thermally stable state. Then set the directional solidification draw speed to 100 μm / s, and the alloy sample gradually enters the Ga-In-Sn coolant from the heating zone from top to bottom at the preset draw rate, so as to achieve directional growth.

[0044] The microstructure of the directional solidification zone of the alloy obtained under this process is Zn + Mg2Zn 11 three-leaf eutectic, as Figure 1 shown; the microhardness is 192.65 ± 7.71 HV, and the corrosion current density in the SBF solution is 3.9060 μA / cm 2 , and the corrosion rate is 0.0316 mm / year.

[0045] Example 2

[0046] A method for preparing a degradable high-hardness zinc alloy material by directional solidification, comprising the following steps:

[0047] S1. Weigh 18 parts of pure magnesium particles and 382 parts of pure zinc particles by mass, place them in a high-temperature resistant quartz tube with a diameter of 50 mm and a height of 80 mm, and put the quartz tube into a vacuum high-frequency induction melting furnace;

[0048] S2. Evacuate to 5×10 -3MPa, argon gas is introduced into the furnace for protection, and this process is repeated 2 times; adjust the induction current to 10 A, melt the mixed raw materials at 450 °C, keep them warm for 10 min until the sample is completely melted, cool for 5 - 10 min until the sample stops glowing red, then reheat and melt again, and repeat the heating and melting process 3 times;

[0049] S3. Cool in the furnace for 10 min, release the gas, open the furnace lid to take out the sample, and air-cool it to room temperature. After the sample solidifies, a as-cast Zn-Mg alloy is obtained;

[0050] S4. Cut and prepare bars from the obtained zinc alloy ingot, place the obtained Zn-Mg alloy bars in an alumina ceramic tube, then fix the ceramic tube on the pull rod in the vacuum chamber of the qualitative solidification melting furnace, and then successively put on a graphite heat preservation sleeve and a quartz heat preservation sleeve outside the ceramic tube;

[0051] S5. Evacuate to 5×10 -3 MPa, argon gas is introduced into the furnace for protection, and this process is repeated 2 times: Turn on the main switch of the heating system, after preheating for 5 minutes, open the heating interface, manually set the heating power, increase the heating power in stages. For every 0.5 W increase, it is necessary to stabilize the voltage for 15 min before increasing the voltage again. Repeat this step until the temperature rises to 693 °C, keep it warm for 30 min to make the alloy melt reach a thermally stable state. Then set the directional solidification pulling speed to 100 μm / s, and the alloy sample gradually enters the Ga-In-Sn coolant from top to bottom in the heating zone at the preset pulling rate, so as to achieve directional growth.

[0052] The microstructure of the directional solidification zone of the alloy obtained under this process is primary MgZn2 dendrites and peritectic Mg2Zn 11 and Zn + Mg2Zn 11 trifoliate eutectic. The primary MgZn2 dendrites have various morphologies: hollow hexagonal morphology, hollow petal-like and V-shaped morphologies, as Figure 2 shown. The grains of the primary MgZn2 dendrites are relatively large at the initial stage of directional solidification. As the directional solidification progresses, their grain size gradually decreases and is distributed in a dispersed manner; Zn + Mg2Zn 11 One ridge and the tissues on both sides of the trifoliate eutectic grow along the direction of directional solidification and are distributed alternately in light and dark under macroscopic conditions, as Figure 10 shown. The microhardness is 181.19 ± 8.28 HV, and the corrosion current density in the SBF solution is 5.7331 μA / cm 2 , and the corrosion rate is 0.0464 mm / y.

[0053] Example 3

[0054] The operation method of this example is exactly the same as that of Example 2, except that the pulling rate of directional solidification is 1000 μm / s.

[0055] The microstructure of the directionally solidified zone of the alloy obtained under this process is MgZn2 dendrites and a small amount of peritectic Mg2Zn 11 and Zn + Mg2Zn 11 Trilobal eutectic, the morphology of primary MgZn2 dendrites is irregular long strip along the direction of directional solidification, and there are also a small number of primary MgZn2 dendrites with fine hollow hexagonal morphology, hollow petal-like and V-shaped morphology, as Figure 3 shown; the microhardness is 243.10 ± 14.89 HV, and the corrosion current density in SBF solution is 8.5286 μA / cm 2 , and the corrosion rate is 0.0691 mm / year.

[0056] Example 4

[0057] A method for directionally solidifying and preparing a degradable high-hardness zinc alloy material, comprising the following steps:

[0058] S1. Weigh 12 parts by mass of pure magnesium particles, 2 parts of pure copper particles, and 386 parts of pure zinc particles, place them in a high-temperature resistant quartz tube with a diameter of 50 mm and a height of 80 mm, and put the quartz tube into a vacuum high-frequency induction melting furnace;

[0059] S2. Evacuate to 5×10 -3 MPa, fill the furnace with argon for protection, and repeat this process 2 times; adjust the induction current to 10 A, melt the mixed raw materials at 500 °C, keep warm for 15 min until the sample is completely melted, cool for 5 - 10 min until the sample stops glowing red, and then reheat and melt it again. Repeat the heating and melting process 3 times;

[0060] S3. Cool in the furnace for 10 min, release the gas, open the furnace lid to take out the sample, and air-cool it to room temperature. After the sample solidifies, a as-cast Zn-Mg-Cu alloy is obtained;

[0061] S4. Cut and prepare a rod from the obtained zinc alloy ingot, place the obtained Zn-Mg-Cu alloy rod in an aluminum oxide ceramic tube, then fix the ceramic tube on the draw bar in the vacuum chamber of the directional solidification melting furnace, and then successively put on a graphite heat preservation sleeve and a quartz heat preservation sleeve outside the ceramic tube;

[0062] S5. Evacuate to 5×10 -3MPa, argon gas is introduced into the furnace for protection, and this process is repeated 2 times: Turn on the main switch of the heating system. After preheating for 5 minutes, open the heating interface, manually set the heating power, and increase the heating power in stages. For every 0.5 W increase, the voltage needs to be stabilized for 15 min before increasing the voltage again. Repeat this step until the temperature rises to 693 °C, and keep it at this temperature for 30 min to make the alloy melt reach a thermally stable state. Then set the pulling rate of directional solidification to 100 μm / s, and the alloy sample gradually enters the Ga-In-Sn coolant from top to bottom in the heating zone at the preset pulling rate, thus realizing directional growth.

[0063] The microstructure of the directional solidification zone of the alloy obtained under this process is Zn + Mg2Zn 11 trilobal eutectic, as Figure 4 shown; the microhardness is 199.43 ± 12.98 HV, and the corrosion current density in the SBF solution is 19.6363 μA / cm 2 , and the corrosion rate is 0.1591 mm / year.

[0064] Example 5

[0065] The operation method of this example is exactly the same as that of Example 4, except that the pulling rate of directional solidification is 500 μm / s.

[0066] The microstructure of the directional solidification zone of the alloy obtained under this process is Zn + Mg2Zn 11 trilobal eutectic, as Figure 5 shown; the microhardness is 221.10 ± 9.08 HV, and the corrosion current density in the SBF solution is 28.1343 μA / cm 2 , and the corrosion rate is 0.2280 mm / year.

[0067] Example 6

[0068] A method for preparing a degradable high-hardness zinc alloy material by directional solidification, comprising the following steps:

[0069] S1. Weigh 12 parts by mass of pure magnesium particles, 4 parts of pure copper particles, and 384 parts of pure zinc particles, place them in a high-temperature resistant quartz tube with a diameter of 50 mm and a height of 80 mm, and put the quartz tube into a vacuum high-frequency induction melting furnace;

[0070] S2. Evacuate to 5 × 10 -3 MPa, introduce argon gas into the furnace for protection, and repeat this process 2 times; adjust the induction current to 10 A, melt the mixed raw materials at 500 °C, keep it warm for 20 min until the sample is completely melted, cool for 5 - 10 min until the sample stops glowing red, and then reheat and melt it. Repeat the heating and melting process 3 times in this way;

[0071] S3. Cool the furnace interior for 10 min, release the gas, open the furnace lid to take out the sample, and air-cool it to room temperature. After the sample solidifies, a as-cast Zn-Mg alloy is obtained;

[0072] S4. Cut and prepare bars from the obtained zinc alloy ingot. Place the obtained Zn-Mg-Cu alloy bars in an aluminum oxide ceramic tube, and then fix the ceramic tube on the pull rod in the vacuum chamber of the directional solidification melting furnace. Subsequently, put on a graphite thermal insulation sleeve and a quartz thermal insulation sleeve outside the ceramic tube in sequence;

[0073] S5. Evacuate to 5×10 -3 MPa, fill the furnace with argon for protection, and repeat this process 2 times: Turn on the main switch of the heating system. After preheating for 5 minutes, open the heating interface, manually set the heating power, and increase the heating power in stages. For each increase of 0.5 W, it is necessary to stabilize the voltage for 15 min before increasing the voltage again. Repeat this step until the temperature rises to 693 °C, and keep it warm for 30 min to make the alloy melt reach a thermally stable state. Then set the directional solidification pulling speed to 100 μm / s, and the alloy sample gradually enters the Ga-In-Sn coolant from the heating zone from top to bottom at the preset pulling rate, so as to achieve directional growth.

[0074] The microstructure of the directional solidification zone of the alloy obtained under this process is Zn + Mg2Zn 11 trilobal eutectic, as Figure 6 shown; the microhardness is 219.89 ± 12.08 HV, and the corrosion current density in the SBF solution is 25.5640 μA / cm 2 , and the corrosion rate is 0.2071 mm / year.

[0075] Example 7

[0076] The operation method of this example is exactly the same as that of Example 6, except that the pulling rate of directional solidification is 500 μm / s.

[0077] The microstructure of the directional solidification zone of the alloy obtained under this process is Zn + Mg2Zn 11 trilobal eutectic, as Figure 7 shown; the microhardness is 215.93 ± 7.19 HV, and the corrosion current density in the SBF solution is 13.0373 μA / cm 2 , and the corrosion rate is 0.1056 mm / year.

[0078] Comparative Example 1

[0079] A method for preparing an as-cast degradable high-hardness zinc alloy material, comprising the following steps:

[0080] S1. Weigh 12 parts by mass of pure magnesium particles and 388 parts of pure zinc particles, place them in a high-temperature resistant quartz tube with a diameter of 50 mm and a height of 80 mm, and put the quartz tube into a vacuum high-frequency induction melting furnace.

[0081] S2. Evacuate to 5×10 -3 MPa, fill the furnace with argon for protection, and repeat this process 2 times; adjust the induction current to 10 A, slowly heat the sample until it is completely melted, keep it warm for 10 min, cool it down until the sample stops glowing, cool for 5 min, and repeatedly heat and melt it 3 times.

[0082] S3. Cool the furnace for 10 min, release the gas, open the furnace lid to take out the sample, and air-cool it to room temperature. After the sample solidifies, a as-cast Zn-Mg alloy is obtained.

[0083] The microstructure of the alloy obtained under this process is a Zn+MgZn2 helical metastable eutectic, as Figure 8 shown; the microhardness of the alloy is 136.8±6.11 HV, and the corrosion current density in the SBF solution is 10.3766 μA / cm 2 , and the corrosion rate is 0.0841 mm / year.

[0084] Figure 9 are the potentiodynamic polarization curves of Examples 1-7 and Comparative Example 1. By extrapolating the linear part of the Tafel curve, the corrosion potential (E corr ) and the corrosion current density (I corr ) are analyzed and obtained. The corrosion rate (V corr ) is calculated according to the electrochemical test method specified in ASTM G59-97 standard. The specific values are shown in Table 1.

[0085] The experimental results of the microhardness of the degradable Zn-Mg alloy and Zn-Mg-Cu alloy prepared in Examples 1-7 and Comparative Example 1 are shown in Table 2.

[0086] Table 1 Electrochemical experimental results

[0087]

[0088] Table 2 Microhardness experimental results

[0089] Serial number Material Drawing rate (μm / s) Microhardness (HV) Example 1 Zn-3Mg 100 192.65±7.71 Example 2 Zn-4.5Mg 100 181.19±8.28 Example 3 Zn-4.5Mg 1000 243.10±14.89 Example 4 Zn-3Mg-0.5Cu 100 199.43±12.98 Example 5 Zn-3Mg-0.5Cu 500 221.10±9.08 Example 6 Zn-3Mg-1Cu 100 219.89±12.08 Example 7 Zn-3Mg-1Cu 500 215.93±7.19 Comparative example 1 Zn-3Mg - 136.8±6.11

[0090] In summary, the present invention provides a method for directionally solidifying a degradable high-hardness zinc alloy material. In the composition of the alloy material, the mass percentage of magnesium (Mg) element is 3-4.5%, and the balance is zinc (Zn) and inevitable impurities. The alloy material is a rod with a diameter of 7 mm. Its preparation method includes processes such as vacuum induction melting and vacuum directional solidification melting. By adopting the directional solidification process, the heat flow direction and the pulling direction can be effectively controlled to obtain grains growing along a specific direction. The experimental results show that as the pulling rate increases, the microstructure of the Zn-Mg alloy is refined, the hardness is improved, the corrosion rate is reduced, and the corrosion resistance is increased. When different mass percentages of copper element (0.5%-1%) are added, the microstructure of the alloy is refined and the microhardness is further improved. Due to the different 11 corrosion potentials of Zn and Mg2Zn 11 a micro-battery will be formed between them, with Zn as the cathode and Mg2Zn 11 as the anode, forming a potential difference that causes galvanic corrosion and increasing the corrosion rate of the Zn-Mg-Cu alloy. However, it can be seen from Examples 5 and 7 that the corrosion resistance can be further improved by optimizing the pulling rate and the addition ratio of copper element. It can be seen from Example 1 and Comparative Example 1 that the alloy prepared by the directional solidification method is prone to form a Zn+Mg2Zn 11 trilobal eutectic, while the alloy prepared by vacuum induction melting is prone to form a Zn+MgZn2 spiral metastable eutectic. Among them, the Zn+Mg2Zn 11 trilobal eutectic has better corrosion resistance than the Zn+MgZn2 spiral metastable eutectic. It can be seen from Table 2 that compared with Comparative Example 1, the microhardness of Examples 1-3 increased by 40.82%, 32.45% and 77.71% respectively. Examples 4-7 increased by 45.80%, 61.62%, 60.74% and 57.84% respectively. Therefore, the Zn-Mg series alloy prepared by this method can exhibit excellent microhardness (181.19-243.10 HV). The corrosion rate in simulated body fluid (SBF) is 0.0316 mm / y - 0.2280 mm / y.

[0091] This alloy material has high hardness and excellent corrosion resistance, and is suitable for manufacturing a variety of intraosseous implant devices, including intraosseous fixation screws, bone plates, fusion devices, rib plates, etc., and is particularly suitable for intraosseous fixation at load-bearing sites.

[0092] The specific embodiments of the present invention have been described in detail above. However, it should be emphasized that the present invention is not limited to the above specific embodiments. Without departing from the scope of the claims of the present invention, those skilled in the art can make various deformations, improvements or adjustments according to actual needs or technological progress.

Claims

1. A method for directionally solidifying a degradable high-hardness zinc alloy material, characterized in that, The preparation method comprises the following steps: S1. Weigh the raw materials according to the mass percentage, place them in a high-temperature resistant quartz tube, put the quartz tube into a vacuum high-frequency induction melting furnace, evacuate to 5×10 -3 MPa, then introduce argon gas with a pressure of 20 - 30 Pa into the furnace, start melting, and obtain a zinc alloy ingot after cooling and solidification; S2. Cut the obtained zinc alloy ingot into alloy rods, and polish and clean the alloy rods; S3. Place the alloy rods in an alumina ceramic tube, then fix the ceramic tube on the draw bar of a vacuum directional solidification furnace. After evacuating the air, introduce argon at 20-30 Pa, then heat and keep warm, and then draw them into the Ga-In-Sn coolant at a set draw rate to complete the preparation of the degradable high-hardness zinc alloy.

2. The directional solidification preparation method of a degradable high-hardness zinc alloy material according to claim 1, characterized in that In step S1, a zinc alloy system is composed of Zn and Mg elements. The mass percentage of the Mg element is 3-4.5%, the total content of impurity elements is ≤0.1%, and the balance is Zn; the purity of pure zinc is above 99.99%, and the purity of pure magnesium is above 99.99%.

3. The directional solidification preparation method of a degradable high-hardness zinc alloy material according to claim 1, characterized in that, In step S1, a zinc alloy system is composed of Zn, Mg, and Cu elements. The mass percentage of the Mg element is 3% Mg, the mass percentage of the Cu element is 0.5%-1%, the total content of impurity elements is ≤0.1%, and the balance is Zn; the purity of pure zinc is above 99.99%, the purity of pure magnesium is above 99.99%, and the purity of copper is above 99.99%.

4. The directional solidification preparation method of a degradable high-hardness zinc alloy material according to claim 1, characterized in that In step S1, the melting temperature of the alloy is 450°C-500°C, the holding time is 10-20 min, then cool for 5-10 min, reheat, melt repeatedly 3 times, and obtain a zinc alloy ingot after cooling and solidification.

5. The directional solidification preparation method of a degradable high-hardness zinc alloy material according to claim 1, characterized in that The method for polishing and cleaning the alloy rods in step S2 is: first polish with sandpaper, and then put them into an alcohol solution for ultrasonic cleaning.

6. The directional solidification preparation method of a degradable high-hardness zinc alloy material according to claim 1, characterized in that In step S3, the temperature of directional solidification is 693°C, and the holding time is 30 min.

7. The directional solidification preparation method of a degradable high-hardness zinc alloy material according to claim 1, characterized in that, In step S3, the draw rate is 100 μm / s-1000 μm / s.

8. The directional solidification preparation method of a degradable high-hardness zinc alloy material according to claim 1, characterized in that, Use an alumina ceramic tube as the crucible, successively put on a graphite sleeve and a quartz sleeve as the heat insulation layer, and place carbon felts at the top and bottom of the sleeve for heat insulation.

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