Low-alloyed medical heterogeneous magnesium alloy, and preparation method and application thereof

Abstract

This invention discloses a low-alloy medical-grade heterogeneous magnesium alloy, its preparation method, and its applications. The preparation method includes: melting a magnesium matrix under a protective atmosphere to obtain a melt; maintaining a constant temperature and under stirring conditions, adding an alloying element to the melt for smelting to obtain an alloy melt; lowering the temperature of the alloy melt, removing slag to obtain a melt to be cast, then casting it into a mold and air-cooling it to obtain an alloy ingot; holding the alloy ingot in an oxygen-free environment and water-quenching it to obtain a solid solution alloy billet; removing the oxide layer from the surface of the solid solution alloy billet, preheating it at 330~380℃ for 1~1.5h, and then hot-extruded it at 330~380℃, followed by air cooling to obtain a low-alloy medical-grade heterogeneous magnesium alloy. This invention introduces an alloying element into the magnesium matrix and further optimizes the hot extrusion temperature and extrusion ratio to obtain a low-alloy medical-grade heterogeneous magnesium alloy with a heterogeneous structure.

Description

Technical Field

[0001] This invention belongs to the field of medical biodegradable metal materials technology, specifically relating to a low-alloy medical heterogeneous magnesium alloy, its preparation method and application. Background Technology

[0002] Magnesium alloys possess excellent biocompatibility and biodegradability, with densities and elastic moduli close to those of human bone tissue. Furthermore, magnesium, as an essential nutrient element for the human body, promotes osteoblast proliferation and differentiation, and accelerates bone healing. Based on these characteristics, magnesium alloys offer significant advantages in fracture and bone defect repair. However, in current clinical applications, medical magnesium alloys are limited to bone screws and various scaffold products in non-load-bearing areas. In applications involving load-bearing areas of internal fixation for fractures or craniofacial plate and screw systems, existing medical magnesium alloys cannot simultaneously meet the requirements of a yield strength higher than 300 MPa, an elongation greater than 10%, and an annual corrosion rate lower than 0.5 mm / y, resulting in the absence of compliant plate and screw systems on the market. Therefore, developing a medical magnesium alloy that combines high strength and toughness (high strength and high plasticity) with excellent corrosion resistance is of great significance for promoting the clinical application of plate and screw systems.

[0003] Zinc (Zn) is an essential trace element for the human body, exhibiting good biocompatibility. Its maximum solubility in magnesium is 6.2 wt%. Adding it to magnesium alloys allows for the formation of a MgZn2 phase (second phase) distributed along grain boundaries through a eutectic reaction. Furthermore, the addition of Zn provides solid solution strengthening and precipitation strengthening effects, thereby improving the corrosion resistance and ductility of magnesium alloys. Calcium (Ca) is also essential for maintaining normal human metabolism and is a major component of bones. Adding appropriate amounts of Ca helps bone formation and growth, improves bone healing, and demonstrates good biocompatibility. Adding Ca to magnesium alloys also forms a second phase (Mg2Ca phase) through a eutectic reaction. The formation of this second phase helps refine the alloy microstructure, thereby enhancing the mechanical properties of magnesium alloys. Therefore, by adjusting the Ca content, the microstructure and properties of magnesium alloys can be effectively controlled. Existing research has shown that adding small amounts of rare earth elements to medical magnesium alloys can improve the fluidity of the magnesium alloy, refine the grains, and significantly improve the strength of the magnesium alloy through solid solution strengthening of the matrix and the formation of dispersed intermetallic compounds. Therefore, adding rare earth elements can improve the mechanical properties of magnesium alloys while also enhancing their corrosion resistance.

[0004] However, while adding elements such as zinc and calcium to medical magnesium alloys can form abundant second phases to improve performance, it also introduces corrosion risks. In corrosive solutions, the second phase and the magnesium matrix form corrosion microcells, which may trigger severe microgalvanic corrosion, leading to excessively rapid and uneven degradation of the medical magnesium alloy. Previous studies have shown that using a low-alloying strategy (total alloy element content <3 wt.%) can effectively suppress microgalvanic corrosion, thereby significantly improving the corrosion resistance of magnesium alloys. However, with the reduction of the second phase, the strength of the magnesium alloy will decrease significantly. According to the Hall-Petch equation, grain refinement can improve the mechanical properties of magnesium alloys, but due to the limited dislocation-accommodating capacity of the fine-grained structure, its elongation is often low, resulting in an inverse relationship between the strength, plasticity, and corrosion resistance of magnesium alloys. Therefore, developing low-alloy medical magnesium alloys with high strength, toughness, and corrosion resistance is of great significance.

[0005] In recent years, inspired by the heterogeneous structure of biological shells in nature, constructing heterogeneous structures (also known as heterostructures) in metallic materials has proven to be an effective way to achieve a coexistence of high strength and toughness. When the grain structure of metallic materials is refined to the ultrafine or nanocrystalline scale, the grain boundary strengthening effect can make its yield strength several times that of coarse-grained samples. However, during deformation of ultrafine or nanocrystalline metallic materials, dislocations are often generated only at the grain boundaries and quickly disappear through grain slip, making it difficult for them to accumulate effectively inside the grains. This results in low strain hardening capacity and extremely low plasticity. Conversely, by designing a non-uniform distribution of grains of different sizes in space to form a cross-scale grain structure, the coordinated role of fine-grained and coarse-grained regions during deformation can be achieved. The fine-grained region provides high strength, while the coarse-grained region maintains good ductility, thereby synergistically improving the strength and plasticity of the metallic material.

[0006] In recent years, heterogeneous materials have attracted widespread attention in the industry due to their excellent strength and toughness (high strength and high plasticity). However, constructing stable heterogeneous structures in low-alloy medical magnesium alloys still faces significant challenges, mainly due to the low recrystallization temperature of magnesium alloys and the rapid grain growth during hot deformation. Meanwhile, for medical magnesium alloys, while a finely dispersed second phase helps improve their corrosion resistance, the cross-scale grain inhomogeneity caused by the heterogeneous structure often leads to the formation of high-energy micro-regions and defects, resulting in severe pitting corrosion and causing localized and unstable corrosion behavior. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing low-alloy medical heterogeneous magnesium alloy.

[0008] Another object of the present invention is to provide a low-alloy medical heterogeneous magnesium alloy obtained by the above preparation method.

[0009] Another object of the present invention is to provide the application of the above-mentioned low-alloy medical heterogeneous magnesium alloy in bone graft implants.

[0010] The objective of this invention is achieved through the following technical solution.

[0011] A method for preparing a low-alloy medical-grade isomeric magnesium alloy includes the following steps:

[0012] Step 1): Under a protective atmosphere, the magnesium matrix is ​​melted at 740-760℃ to obtain a melt. While maintaining a constant temperature, the introduced element alloy is added to the melt under stirring to obtain a uniformly mixed alloy melt. The temperature of the alloy melt is lowered to 720-730℃, slag is removed, and a casting melt is obtained. The casting melt at 720-730℃ is poured into a mold at 150-200℃ and air-cooled to obtain an alloy ingot. The introduced element alloy includes Zn, Ca, RE, and Mg, where RE is yttrium (Y), neodymium (Nd), or samarium (Sm). By mass percentage, the alloy melt includes: 0.5-1.5% Zn, 0.05-0.5% Ca, 0.05-0.6% RE, unavoidable impurities, and the balance Mg.

[0013] In step 1), the protective atmosphere comprises sulfur hexafluoride (SF6) and nitrogen (N2), with the ratio of sulfur hexafluoride to nitrogen being (0.1~0.4):(99.9~99.6) by volume.

[0014] In step 1), the introduced elemental alloys include: zinc ingots, magnesium-calcium master alloy (Mg-Ca master alloy) and magnesium-rare earth master alloy (Mg-RE master alloy). The magnesium-calcium master alloy is an alloy of magnesium and calcium, and the magnesium-rare earth master alloy is an alloy of magnesium and RE.

[0015] In the above technical solution, the Ca content in the magnesium-calcium master alloy is 25~30wt%, and the RE content in the magnesium-rare earth master alloy is 25~30wt%.

[0016] In step 1), the magnesium matrix and the alloy of introduced elements are pretreated before use to remove impurities and oxide layers from their surfaces. The pretreatment process includes: polishing the surface, immersing it in alcohol for 2-3 minutes, and drying.

[0017] In step 1), the magnesium matrix is ​​heated to 740-760°C at a rate of 5-8°C / min.

[0018] In step 1), the melting temperature is 740~760℃ and the melting time is 25~30min.

[0019] Step 2), the alloy ingot is held at 480~510℃ for 2~4 hours in an oxygen-free environment and then water-quenched to obtain a solid solution alloy billet;

[0020] In step 2), the oxygen-free environment is achieved through an antioxidant treatment. The antioxidant treatment method includes covering the alloy ingot with graphite powder to isolate it from air or introducing an inert gas.

[0021] In the above technical solution, the inert gas includes nitrogen or argon.

[0022] Step 3) Remove the oxide layer on the surface of the solid solution alloy billet, preheat at 330~380℃ for 1~1.5h, and then hot extrude at 330~380℃ and air cool to obtain a low alloy medical heterogeneous magnesium alloy, wherein the extrusion ratio of the hot extrusion is (10~50):1 and the hot extrusion speed is 0.2~1mm / s.

[0023] In the above technical solution, the diameter of the low-alloy medical heterogeneous magnesium alloy is 7~10mm.

[0024] The low-alloy medical heterogeneous magnesium alloy obtained by the above preparation method.

[0025] Application of the above-mentioned low-alloy medical isomeric magnesium alloys in bone graft implants

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. In the preparation method of the present invention, a magnesium matrix is ​​used as the matrix, and an alloy containing trace amounts of rare earth elements (RE) is added to the magnesium matrix to allow the rare earth elements to slowly diffuse and precipitate for strengthening. The microalloying of rare earth elements delays grain boundary migration, thereby hindering recrystallization and grain growth, and refining the recrystallized grains. Furthermore, the parameters such as the hot extrusion temperature and extrusion ratio are optimized to promote the formation of heterogeneous structures, resulting in a low-alloy medical heterogeneous magnesium alloy with heterogeneous structures.

[0028] 2. In the preparation method of the present invention, by optimizing the ratio of alloying elements, a low-alloy medical heterogeneous magnesium alloy with a low total content of alloying elements is obtained.

[0029] 3. The low-alloy medical-grade heterogeneous magnesium alloy of this invention can effectively reduce microgalvanic corrosion and significantly improve corrosion resistance, with a minimum annual corrosion rate of 0.21 mm / y after immersion in Hank's solution for 14 days. This is because, in the early stages of corrosion, the fine grains in the heterogeneous structure help form a dense corrosion product layer on the magnesium matrix surface, preventing further erosion of the magnesium matrix. Furthermore, trace amounts of rare earth elements also contribute to increasing the density of the corrosion products.

[0030] 4. The low-alloy medical heterogeneous magnesium alloy of the present invention has good mechanical properties, exhibiting high strength, toughness and yield strength, with a yield strength of 345.1 MPa and an elongation of 16.1%. Attached Figure Description

[0031] Figure 1 Metallographic images of the low-alloy medical magnesium alloy obtained in Example 1, the low-alloy medical isomeric magnesium alloys obtained in Examples 2-4, and the high-alloy medical magnesium alloy obtained in Example 7;

[0032] Figure 2 These are electron backscatter diffraction (EBSD) grain distribution images of the low-alloy medical magnesium alloy obtained in Example 1 and the low-alloy medical isomeric magnesium alloys obtained in Examples 2-4.

[0033] Figure 3 Corrosion rate diagrams of the low-alloy medical magnesium alloy obtained in Example 1, the low-alloy medical heterogeneous magnesium alloys obtained in Examples 2-4, and the high-alloy medical magnesium alloy obtained in Example 7;

[0034] Figure 4 (a) The stress-strain curves of the low-alloy medical magnesium alloy obtained in Example 1, the low-alloy medical heterogeneous magnesium alloy obtained in Examples 2-4, and the high-alloy medical magnesium alloy obtained in Example 7 under tensile testing; (b) The stress cycle curves of the low-alloy medical magnesium alloy obtained in Example 1 and the low-alloy medical heterogeneous magnesium alloy obtained in Example 2 under loading-unloading cycle testing; (c) The back stress and effective stress of the low-alloy medical magnesium alloy obtained in Example 1; (d) The back stress and effective stress of the low-alloy medical heterogeneous magnesium alloy obtained in Example 2.

[0035] Figure 5 The graph shows a comparison of the mechanical properties of the low-alloyed medical magnesium alloy obtained in Example 1, the low-alloyed medical heterogeneous magnesium alloys obtained in Examples 2-4, and the high-alloyed medical magnesium alloy obtained in Example 7 with alloys reported in existing technical literature.

[0036] Figure 6 The corrosion cross-section SEM images and elemental distribution diagrams of the low-alloy medical magnesium alloy obtained in Example 1 and the low-alloy medical heterogeneous magnesium alloys obtained in Examples 2-4 are shown. Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0038] This invention uses a magnesium matrix as the base and incorporates an alloy containing trace amounts of rare earth elements (RE) into the magnesium matrix to allow the rare earth elements to slowly diffuse and precipitate for strengthening. By adding trace amounts of rare earth elements and further optimizing parameters such as hot extrusion temperature and extrusion ratio, the formation of heterogeneous structures is promoted, resulting in a low-alloy medical heterogeneous magnesium alloy with heterogeneous structures (heterogeneous characteristics). This achieves the goal of simultaneously improving high strength, toughness, and corrosion resistance, and is expected to meet the performance requirements of plate and nail systems for internal fixation of fractures.

[0039] The sources of materials used in the following embodiments are:

[0040] The pure Mg ingots (high-purity Mg ingots) were purchased from Fengfeng Longhai Magnesium Metal Processing Co., Ltd., with dimensions of 50×15×8cm. 3 The purity is 99.95 wt%.

[0041] The pure Zn ingots (high-purity Zn ingots) were purchased from Ganzhou Feiteng Light Alloy Co., Ltd., with dimensions of 50×15×8cm. 3 The purity is 99.95 wt%.

[0042] The magnesium-calcium master alloy (Mg-Ca master alloy) was purchased from Ganzhou Feiteng Light Alloy Co., Ltd., and its dimensions are 50×15×8cm. 3 The magnesium-calcium master alloy contains 30 wt% Ca and 70 wt% Mg.

[0043] The magnesium rare earth master alloy (Mg-RE master alloy) was purchased from Ganzhou Feiteng Light Alloy Co., Ltd., with dimensions of 50×15×8cm. 3 The magnesium rare earth master alloy contains 25 wt% RE and 75 wt% Mg; RE is one of yttrium (Y), neodymium (Nd) or samarium (Sm).

[0044] The equipment used for hot extrusion is an extrusion press, model LXCJ550, purchased from Wuxi Linlian Machinery Co., Ltd.

[0045] Example 1 (for comparison)

[0046] A method for preparing a low-alloy medical magnesium alloy (Mg-1Zn-0.3Ca alloy) includes the following steps:

[0047] Step 1): Place the magnesium matrix (pure Mg ingot) in a graphite crucible in a melting furnace and heat it (at a rate of 8°C / min). When the temperature reaches 200°C, introduce a protective atmosphere and then heat it to 750°C at a rate of 8°C / min, melting the magnesium matrix at 750°C to obtain a melt. Keep the temperature constant (750°C) and, under stirring, add zinc ingots and a magnesium-calcium master alloy (Mg-Ca master alloy) to the melt. Maintain the temperature at 750°C for 30 minutes to obtain a homogeneous alloy melt. Set the melting furnace to a cooling program (cooling rate of 3°C / min) to allow the alloy melt to cool down. The temperature is lowered to 720℃, slag is removed, and the molten material to be cast is obtained. The molten material at 720℃ is poured into a mold (a steel mold with a diameter of 70mm) at 200℃ and air-cooled to obtain an alloy ingot. The alloy melt, by mass percentage, includes: 1.0% Zn, 0.3% Ca, unavoidable impurities, and the balance Mg (by mass, the ratio of magnesium matrix, zinc ingot, and magnesium-calcium master alloy is 1176:12:12); the protective atmosphere is a mixture of sulfur hexafluoride (SF6) and nitrogen (N2), and by volume, the ratio of sulfur hexafluoride to nitrogen is 0.4:99.6.

[0048] Magnesium matrix, zinc ingots, and magnesium-calcium master alloys are pretreated before use to remove impurities and oxide layers from their respective surfaces. The pretreatment process includes: cleaning impurities and oxide layers from their surfaces by mechanical grinding, then immersing them in alcohol for 2 minutes, and drying them at 200°C for 1.5 hours for later use.

[0049] Step 2), cover the alloy ingot with graphite powder to isolate it from the air, keep it at 500℃ for 2 hours, and then quench it with water to obtain a solid solution alloy billet.

[0050] Step 3) The solid solution alloy billet is machined to remove the surface oxide scale, preheated at 330℃ for 1.5h, and then hot extruded at 330℃ and air-cooled to obtain a low-alloy medical magnesium alloy (Mg-1Zn-0.3Ca alloy, bar with a diameter of 8.5mm). The hot extrusion ratio is 25:1 and the hot extrusion speed is 0.2mm / s.

[0051] Examples 2-4

[0052] A method for preparing a low-alloy medical-grade heterogeneous magnesium alloy (Mg-1Zn-0.3Ca-0.3RE alloy) includes the following steps:

[0053] Step 1): Place the magnesium matrix (pure Mg ingot) in a graphite crucible in a melting furnace and heat it (at a rate of 8°C / min). When the temperature reaches 200°C, introduce a protective atmosphere and then heat it to 750°C at a rate of 8°C / min, melting the magnesium matrix at 750°C to obtain a melt. Keep the temperature constant (750°C) and, under stirring, add the alloying element to the melt, maintaining the temperature at 750°C for 30 minutes to obtain a homogeneous alloy melt. Set the melting furnace to a cooling program (cooling rate of 3°C / min) to lower the temperature of the alloy melt to 720°C. Remove the slag to obtain the melt to be cast. Pour the 720°C melt into a 200°C mold (70mm diameter steel mold) and air cool to obtain the final product. The alloy ingots are made of zinc (pure Zn), magnesium-calcium master alloy (Mg-Ca master alloy), and magnesium rare earth master alloy (Mg-RE master alloy), where RE is yttrium (Y), neodymium (Nd), or samarium (Sm). The alloy melt comprises, by mass percentage: 1.0% Zn, 0.3% Ca, 0.3% RE, unavoidable impurities, and the balance Mg. The RE values ​​in different embodiments are shown in Table 1. The mass ratio of magnesium matrix, zinc ingot, magnesium-calcium master alloy, and magnesium rare earth master alloy is 1161.6:12:12:14.4. The protective atmosphere is a mixture of sulfur hexafluoride (SF6) and nitrogen (N2), with a volume ratio of SF6 to nitrogen of 0.4:99.6.

[0054] The magnesium matrix and the alloy of introduced elements are pretreated separately before use to remove impurities and oxide layers from their respective surfaces. The pretreatment process includes: cleaning the impurities and oxide layers from their surfaces by mechanical grinding, then immersing them in alcohol for 2 minutes, and drying them at 200°C for 1.5 hours for later use.

[0055] Step 2), cover the alloy ingot with graphite powder to isolate it from the air, keep it at 500℃ for 2 hours, and then quench it with water to obtain a solid solution alloy billet.

[0056] Step 3) The solid solution alloy billet is machined to remove the surface oxide scale, preheated at 330℃ for 1.5h, and then hot extruded at 330℃ and air-cooled to obtain a low-alloy medical heterogeneous magnesium alloy (Mg-1Zn-0.3Ca-0.3RE alloy, bar with a diameter of 8.5mm). The hot extrusion ratio is 25:1 and the hot extrusion speed is 0.2mm / s.

[0057] Table 1

[0058]

[0059] The low-alloyed medical heterogeneous magnesium alloy obtained in Example 2 is a Mg-1Zn-0.3Ca-0.3Y alloy, the low-alloyed medical heterogeneous magnesium alloy obtained in Example 3 is a Mg-1Zn-0.3Ca-0.3Nd alloy, and the low-alloyed medical heterogeneous magnesium alloy obtained in Example 4 is a Mg-1Zn-0.3Ca-0.3Sm alloy.

[0060] Example 5

[0061] The preparation method of a high-alloy medical magnesium alloy (Mg-1Zn-0.3Ca-2Sm alloy) is basically the same as the preparation method of a low-alloy medical heterogeneous magnesium alloy in Example 4, except that the amount of alloying elements introduced (alloy melt) is different.

[0062] In this embodiment, the amount of elemental alloy introduced is "by mass parts, the ratio of magnesium matrix, zinc ingot, magnesium-calcium master alloy and magnesium rare earth master alloy is 1080:12:12:96", and by mass percentage, the alloy melt includes: 1.0% Zn, 0.3% Ca, 2.0% Sm, unavoidable impurities and the balance Mg.

[0063] Hot extrusion failed in this preparation method, and bar stock could not be obtained.

[0064] Example 6

[0065] The preparation method of a high-alloy medical magnesium alloy (Mg-0.5Zn-2Y alloy) is basically the same as the preparation method of a low-alloy medical heterogeneous magnesium alloy in Example 2, except that the types of alloying elements introduced and the amount of alloying elements introduced (alloy melt) are different.

[0066] In this embodiment, the introduced element alloy is a zinc ingot and a magnesium rare earth master alloy (without adding a magnesium-calcium master alloy). The amount of the introduced element alloy is "by mass parts, the ratio of magnesium matrix, zinc ingot and magnesium rare earth master alloy is 1098:6:96". By mass percentage, the alloy melt includes: 0.5% Zn, 2.0% Y, unavoidable impurities and the balance Mg.

[0067] Hot extrusion failed in this preparation method, and bar stock could not be obtained.

[0068] Example 7

[0069] The preparation method of a high-alloy medical magnesium alloy (Mg-0.5Zn-2Y-380 alloy) is basically the same as the "preparation method of a high-alloy medical magnesium alloy" in Example 6, except that the hot extrusion temperature is different.

[0070] In this embodiment, the hot extrusion temperature is 380℃, that is, "preheating at 380℃ for 1.5 hours and then hot extruding at 380℃", and the hot extrusion is successful, resulting in a bar with a diameter of 8.5mm.

[0071] Optical microscopy tests were performed on the low-alloy medical magnesium alloy obtained in Example 1, the low-alloy medical isomeric magnesium alloys obtained in Examples 2-4, and the high-alloy medical magnesium alloy obtained in Example 7. The results are as follows: Figure 1 As shown. The right side is a magnified view of a portion of the left side. (From...) Figure 1 As can be seen from the metallographic images, the low-alloyed medical magnesium alloy obtained in Example 1 is almost entirely composed of fully recrystallized equiaxed grains. Figure 1 The microstructure of the low-alloyed medical heterogeneous magnesium alloys obtained in Examples 2-4 consists of fine recrystallized grains and deformed grains elongated along the extrusion direction (ED). The average grain sizes of the recrystallized grains in the low-alloyed medical heterogeneous magnesium alloys obtained in Examples 2-4 are 1.41µm, 1.62µm, and 1.78µm, respectively. The microstructure of the high-alloyed medical magnesium alloy obtained in Example 7 consists of coarse, fully recrystallized grains with an average grain size of 15.3µm. This indicates that the low-alloyed medical heterogeneous magnesium alloys obtained in Examples 2-4 have heterogeneous microstructures. This is attributed to the fact that the diffusion rate of rare earth elements at lower hot extrusion temperatures is much lower than that of elements such as Zn and Ca, which can prevent grain boundary migration (hinder recrystallization) and grain growth, thereby promoting the formation of heterogeneous microstructures.

[0072] Electron backscatter diffraction (EBSD) grain distribution images of the low-alloy medical magnesium alloy obtained in Example 1 and the low-alloy medical isomeric magnesium alloys obtained in Examples 2-4 are shown below. Figure 2 As shown. By Figure 2 It can be clearly seen that the low-alloyed medical magnesium alloy obtained in Example 1 consists almost entirely of fully recrystallized equiaxed grains. Figure 2 The "recrystallized grains" in the text are very few, and subgrains are extremely rare; while in the low-alloyed medical isomorphic magnesium alloys obtained in Examples 2-4, there are fine equiaxed grains and deformed grains distributed along the extrusion direction ( Figure 2 The blue area in the image), along with numerous small-angle grain boundaries ( Figure 2 The presence of the red line in the image suggests this. This may be attributed to the fact that the microalloying of rare earth elements slows down grain boundary migration, thereby hindering recrystallization and grain growth.

[0073] The corrosion resistance of the low-alloyed medical magnesium alloy obtained in Example 1, the low-alloyed medical heterogeneous magnesium alloys obtained in Examples 2-4, and the high-alloyed medical magnesium alloy obtained in Example 7 was tested (in vitro immersion test). The specific conditions for the corrosion resistance test were as follows: Prepare a circular disc with a diameter of 8 mm and a thickness of 3 mm (obtained by wire cutting). Remove the oxide layer from the surface of the disc by mechanical grinding, then ultrasonically clean it with alcohol for 2 minutes, dry it, and weigh the dried disc, recording the original weight m0. Place the dried disc into a container containing 45 mL of... Hank's solution (the method for obtaining Hank's solution is as follows: weigh 8.00g sodium chloride, 0.40g potassium chloride, 0.14g calcium chloride, 0.10g magnesium sulfate heptahydrate, 0.10g magnesium chloride hexahydrate, 0.12g disodium hydrogen phosphate dodecahydrate, 0.06g potassium dihydrogen phosphate, 0.35g sodium bicarbonate and 1g glucose (all reagents were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) into a conical test tube, add deionized water to dissolve and make up to 1L in a volumetric flask) into a plastic conical tube, and then place the plastic conical tube in a 37℃ water bath environment for 14 days. On the 14th day (the Hank's solution was changed every 24 hours during the process), take out the disc, soak the disc in a chromic acid mixed solution for 1 minute to remove the corrosion products on the surface of the disc, ultrasonically clean it in alcohol, dry it, and weigh the disc and record the weight as m1. The disc is one of the low-alloy medical magnesium alloy obtained in Example 1, the low-alloy medical isomeric magnesium alloys obtained in Examples 2-4, and the high-alloy medical magnesium alloy obtained in Example 7. The chromic acid mixed solution is a mixture of chromium trioxide, silver nitrate, barium nitrate, and deionized water. The mass ratio of chromium trioxide, silver nitrate, and barium nitrate in the chromic acid mixed solution is 200:10:10, and the concentration of chromium trioxide in the chromic acid mixed solution is 200 g / L. The annual corrosion rate of the disc is calculated using the weight loss method. The formula for calculating the annual corrosion rate is:

[0074]

[0075] Where C (mm / y) is the annual corrosion rate of the disc, and k = 8.76 × 10⁻⁶. 4 It is a constant term, ρ (g / cm³). 3 A is the density of the disc, A (cm³). 2 ) is the surface area of ​​the disc, and t(h) is the immersion time of the disc in Hank's solution. Three parallel samples were prepared for each embodiment, and the average annual corrosion rate calculated from the three parallel samples was taken as the annual corrosion rate of the disc in that embodiment.

[0076] The annual corrosion rates of the low-alloyed medical magnesium alloy obtained in Example 1, the low-alloyed medical isomeric magnesium alloys obtained in Examples 2-4, and the high-alloyed medical magnesium alloy obtained in Example 7, after immersion in Hank's solution for 14 days, are as follows: Figure 3As shown. By Figure 3 It can be seen that the annual corrosion rates of the low-alloy medical magnesium alloy obtained in Example 1, the low-alloy medical isomeric magnesium alloys obtained in Examples 2-4, and the high-alloy medical magnesium alloy obtained in Example 7 are all less than 0.5 mm / y. The annual corrosion rates of the low-alloy medical isomeric magnesium alloys obtained in Examples 2-4 are 0.21 mm / y, 0.23 mm / y, and 0.25 mm / y, respectively, while the annual corrosion rates of the low-alloy medical magnesium alloy obtained in Example 1 and the high-alloy medical magnesium alloy obtained in Example 7 are 0.28 mm / y and 0.49 mm / y, respectively. It is noteworthy that the low-alloy medical isomeric magnesium alloys obtained in Examples 2-4, which have isomeric structures, can effectively reduce microgalvanic corrosion, significantly improve corrosion resistance, have a lower annual corrosion rate, and have stronger corrosion resistance.

[0077] Tensile Testing: Tensile specimens with a diameter of 5 mm and a length of 100 mm were prepared according to the national standard GB / T 16865-2013 "Specimens and Methods for Tensile Testing of Wrought Aluminum, Magnesium and Their Alloys". At room temperature, the tensile specimens were fixed to the clamps at both ends of an electronic universal testing machine. The gauge length (dimension of the parallel section) was set to 25 mm. Tensile testing was performed at a rate of 0.5 mm / min, parallel to the extrusion direction, until the specimen fractured. The resulting stress-strain curves were recorded. The tensile specimens were one of the following: the low-alloy medical magnesium alloy obtained in Example 1, the low-alloy medical heterogeneous magnesium alloys obtained in Examples 2-4, and the high-alloy medical magnesium alloy obtained in Example 7. Each tensile specimen was tested three times independently (to ensure data reliability). The average of the three tests was taken as the final result, and the stress-strain curves were plotted as follows: Figure 4 As shown in (a). By Figure 4 As shown in the stress-strain curves in (a), the yield strengths (yield strength is the ordinate value corresponding to the intersection of the stress-strain curve and the dashed line) of the low-alloy medical magnesium alloy obtained in Example 1, the low-alloy medical heterogeneous magnesium alloy obtained in Examples 2-4, and the high-alloy medical magnesium alloy obtained in Example 7 are 249.7 MPa, 345.1 MPa, 320.6 MPa, 286.3 MPa, and 127.5 MPa, respectively, and their elongations are 15.2%, 16.1%, 16.0%, 15.6%, and 15.0%, respectively. It was found that the low-alloy medical heterogeneous magnesium alloy obtained in Examples 2-4, which has a heterogeneous structure, has higher toughness and yield strength, while its elongation is still superior to that of the low-alloy medical magnesium alloy obtained in Example 1 and the high-alloy medical magnesium alloy obtained in Example 7.

[0078] Load-unloading cycle test: At room temperature, a specimen with a diameter of 5 mm, a length of 100 mm, and a parallel section length of 25 mm was fixed on the fixture of an electronic universal testing machine, ensuring that its axis was coaxial with the loading direction. An extensometer was installed on the parallel section, and 6 load-unloading cycles were performed. Each load-unloading cycle included: at a constant strain rate of 1 × 10⁻⁶. -3 s -1 Uniaxial tension was applied to the specimen until the set maximum strain of 1.8% was reached, at which point loading was stopped (load and strain were recorded in real time). After reaching 1.8% strain, the crossbeam of the electronic universal testing machine immediately moved in the opposite direction to the loading phase at the same speed, thus unloading, until the load gradually decreased to 20N, completing the unloading process. Load and strain were recorded in real time during both loading and unloading. The specimen was either the low-alloyed medical magnesium alloy obtained in Example 1 or the low-alloyed medical isomeric magnesium alloy obtained in Example 2. The results of the load-unload cycle test are as follows: Figure 4 As shown in (b), by Figure 4 As can be seen from (b), during the entire load-unload cycle test, the strength of the low-alloy medical heterogeneous magnesium alloy obtained in Example 2 with heterogeneous structure was higher than that of the low-alloy medical magnesium alloy obtained in Example 1.

[0079] according to Figure 4 In (b), the stress-strain curve is used to calculate the back stress and effective stress. Figure 4 (c) and Figure 4 Figure (d) shows the back stress and effective stress of the low-alloyed medical heterogeneous magnesium alloy obtained in Example 1 and Example 2 under different strains, respectively. As can be seen from the figure, the back stress and effective stress of the low-alloyed medical heterogeneous magnesium alloy obtained in Example 2 are both higher than those in Example 1, indicating that the heterogeneous structure significantly contributes to its strength. This may be because different microstructure regions exist in the heterogeneous structure, generating strong interfacial stress, i.e., back stress, due to strain mismatch during deformation. Back stress effectively activates plasticity mechanisms that are difficult to initiate in homogeneous structures, such as dislocations, deformation twins, and stacking faults, effectively mitigating stress concentration and thus promoting the deformation of the heterogeneous structure and enhancing its plasticity.

[0080] Figure 5This paper compares the yield strength and elongation of the low-alloyed medical magnesium alloy obtained in Example 1, the low-alloyed medical isomeric magnesium alloys obtained in Examples 2-4, and the high-alloyed medical magnesium alloy obtained in Example 7 with alloys reported in the prior art literature. The data sources for the alloys reported in the prior art literature are shown in Table 2. Compared to the content of alloying elements reported in the prior art literature, the total content of alloying elements used in this invention is lower. In the preparation method of this invention, by optimizing the ratio of alloying elements, a low-alloyed medical isomeric magnesium alloy with a lower total content of alloying elements is obtained. It is worth noting that the low-alloyed medical isomeric magnesium alloys obtained in Examples 2-4 of this invention exhibit better mechanical properties, which is attributed to the improved mechanical properties of the low-alloyed medical isomeric magnesium alloys due to the presence of isomeric structures.

[0081] Table 2

[0082]

[0083] [1] Y. Liu, J. Wen, Huan Li, J. He. Effects of extrusion parameters on the microstructure, corrosion resistance, and mechanical properties of biodegradable Mg-Zn-Gd-Y-Zr alloy, Journal of Alloys and Compounds, 891(2022) 161964.

[0084] [2] X. Qian, Z. Dong, B. Jiang, Z. Zheng, A. Zhang, C. Li, L. Vitos. Mechanism of alloying element co-segregation at the grain boundary and its influence on mechanical properties in Mg-Zn-Ca alloy, Journal of MaterialsScience & Technology, 267(2026)132-145.

[0085] [3] K. Kikuchi, T. Nakata, C. Xu, Y. Ito, L. Geng, Y. Miyashita, S.Kamado. Development of high-performance Mg-Zn-Ca-Mn alloy sheets via theformation of optimized submicron precipitates, Journal of Alloys andCompounds, 1048 (2025) 185031.

[0086] [4] M. Li, Y. Jiao, Y. Zhu, Z. Hu, J. Wang, Y. Li, Z. Hua, Peng Chen,H. Wang. Solute cluster-mediated natural age hardening in a dilute Mg-Zn-Caalloy, Scripta Materialia, 273 (2026) 117109.

[0087] [5] Z. Li, H. Jia, M. Yang, D. Ma, M. Zha. Tailoring microstructuresand enhancing mechanical properties of a Mg-Zn-Y-Ca alloy by accumulativeroll bonding and annealing, Materials Letters, 404 (2026) 139590.

[0088] [6] X. Xu, Z. Hua, C. Hu, H. Wang, M. Huang. Impact of aging-inducedprecipitate-free zones on yielding mechanisms in a low-alloyed Mg-Zn-Ca-Mn-Yalloy, Scripta Materialia, 272 (2026) 117067.

[0089] [7] JS Suh, J. Kim, HS Kim, SE Lee, J. Kim. Effect of extrusion ratio on mechanical and biodegradation behavior of Mg-Zn-Mn-Sralloy microtubes for biodegradable vascular stents, Journal of Magnesium andAlloys, In press (2025).

[0090] [8] W. Wang, C. Blawert, R. Zan, Y. Sun, H. Peng, J. Ni, P. Han, T.Suo, Y. Song, S. Zhang, ML Zheludkevich, X. Zhang. A novel lean alloy of biodegradable Mg-2Zn with nanograins, Bioactive Materials, 6(2021)4333-4341.

[0091] The low-alloyed medical magnesium alloy obtained in Example 1 and the low-alloyed medical isomeric magnesium alloys obtained in Examples 2-4, which were immersed in Hank's solution for 14 days during the corrosion resistance test, were taken out, dried, and then subjected to SEM and EDS tests on their corrosion sections. The morphology and energy dispersive spectroscopy results are as follows. Figure 6 As shown in the figure. The first and second rows from top to bottom are topographic images, and the third to eighth rows from top to bottom are elemental distribution maps obtained from energy dispersive spectroscopy (EDS).

[0092] Depend on Figure 6 As can be seen from the morphological images, corrosion product layers were formed on the surfaces of the low-alloyed medical magnesium alloy obtained in Example 1 and the low-alloyed medical isomeric magnesium alloys obtained in Examples 2-4. Figure 6 The part highlighted in yellow in the first row, Figure 6 (The yellow arrow in the second row indicates the location of the corrosion product layer). In Example 1, the low-alloyed medical magnesium alloy exhibited severe pitting corrosion, meaning the interface between the magnesium matrix and the corrosion product layer was serrated. In contrast, the corrosion interfaces of the low-alloyed medical isomeric magnesium alloys obtained in Examples 2-4 were relatively straight, without obvious serrations. This is because, in the early stages of corrosion, the fine grains in the isomeric structure help form a dense corrosion product layer on the magnesium matrix surface, preventing further erosion of the magnesium matrix. Furthermore, the presence of trace rare earth elements helps increase the density of the corrosion products. Figure 6As can be seen from the elemental distribution diagram, the corrosion products on the surface of the low-alloy medical magnesium alloy obtained in Example 1 and the low-alloy medical heterogeneous magnesium alloy obtained in Examples 2 to 4 are all composed of O, Ca and P elements. Among them, the corrosion product layer on the surface of the low-alloy medical heterogeneous magnesium alloy obtained in Examples 2 to 4, which have heterogeneous structures, is more dense (the darker the color, the higher the density).

[0093] In summary, the low-alloy medical heterogeneous magnesium alloys obtained in Examples 2-4 of this invention exhibit obvious heterogeneous structures, possess excellent mechanical properties and corrosion resistance, and can meet the performance requirements of internal fixation plate and nail systems for fractures, thus having potential value in practical production applications.

[0094] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a low-alloy medical-grade isomeric magnesium alloy, characterized in that, Includes the following steps: Step 1): Under a protective atmosphere, the magnesium matrix is ​​melted at 740-760℃ to obtain a melt. While maintaining a constant temperature, the introduced element alloy is added to the melt and smelted under stirring to obtain a uniformly mixed alloy melt. The temperature of the alloy melt is lowered to 720-730℃, slag is removed, and a casting melt is obtained. The casting melt at 720-730℃ is poured into a mold at 150-200℃ and air-cooled to obtain an alloy ingot. The introduced element alloy includes Zn, Ca, RE, and Mg, where RE is yttrium, neodymium, or samarium. By mass percentage, the alloy melt comprises: 0.5-1.5% Zn, 0.05-0.5% Ca, 0.05-0.6% RE, unavoidable impurities, and the balance Mg. Step 2), the alloy ingot is held at 480~510℃ for 2~4 hours in an oxygen-free environment and then water-quenched to obtain a solid solution alloy billet; Step 3) Remove the oxide layer on the surface of the solid solution alloy billet, preheat at 330~380℃ for 1~1.5h, and then hot extrude at 330~380℃ and air cool to obtain a low alloy medical heterogeneous magnesium alloy, wherein the extrusion ratio of the hot extrusion is (10~50):1 and the hot extrusion speed is 0.2~1mm / s.

2. The preparation method according to claim 1, characterized in that, In step 1), the protective atmosphere comprises sulfur hexafluoride and nitrogen, with the ratio of sulfur hexafluoride to nitrogen being (0.1~0.4):(99.9~99.6) by volume.

3. The preparation method according to claim 1, characterized in that, In step 1), the introduced elemental alloys include: zinc ingots, magnesium-calcium master alloys and magnesium-rare earth master alloys. The magnesium-calcium master alloy is an alloy of magnesium and calcium, and the magnesium-rare earth master alloy is an alloy of magnesium and RE.

4. The preparation method according to claim 3, characterized in that, In magnesium-calcium master alloys, Ca is 25-30 wt%, and in magnesium-rare earth master alloys, RE is 25-30 wt%.

5. The preparation method according to claim 1, characterized in that, In step 1), the magnesium matrix and the alloy of introduced elements are pretreated before use to remove impurities and oxide layers from their surfaces.

6. The preparation method according to claim 1, characterized in that, In step 1), the magnesium matrix is ​​heated to 740-760°C at a rate of 5-8°C / min; The melting temperature is 740~760℃, and the melting time is 25~30min.

7. The preparation method according to claim 1, characterized in that, In step 2), the oxygen-free environment is achieved through an antioxidant treatment. The antioxidant treatment method includes covering the alloy ingot with graphite powder to isolate it from air or introducing an inert gas, including nitrogen or argon.

8. The low-alloy medical heterogeneous magnesium alloy obtained by the preparation method according to any one of claims 1 to 7.

9. The diameter of the low-alloy medical heterogeneous magnesium alloy as described in claim 8 is 7~10mm.

10. The application of the low-alloy medical heterogeneous magnesium alloy as described in claim 8 in bone graft implants.

Images