A medical BXM2 magnesium alloy with self-repairing film forming ability and a preparation method thereof

Abstract

The application relates to the technical field of magnesium alloys and discloses a medical BXM2 magnesium alloy with self-repairing film forming capacity and a preparation method thereof, the magnesium alloy comprises, in mass percentage, Nd: 2.0-6.0 wt.%; Y: 0.5-3.0 wt.%; Zr: 0.3-1.0 wt.%; and the balance of Mg and inevitable impurity elements; Fe, Cu, Ni and Si in the impurity elements are all less than or equal to 0.005 wt.%, and the total content of the impurity elements is less than or equal to 0.02 wt.%. When a surface film layer of the magnesium alloy is partially damaged due to mechanical damage, newly released Nd 3+ and Y 3+ can rapidly enrich at the damaged position and react with the medium again to generate new rare earth compounds to deposit and actively repair the film layer gap.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy technology, and more specifically, to a medical-grade BXM2 magnesium alloy with self-healing film-forming ability and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials currently available, possess significant potential for application in the field of biodegradable biomedical implants (such as bone screws, bone plates, and cardiovascular stents) due to their high specific strength, excellent biocompatibility, and density (approximately 1.74 g / cm³) and elastic modulus (Mg's elastic modulus is approximately 45 GPa) similar to human bone. Their ability to gradually degrade and be absorbed within the body avoids the need for secondary removal surgery, representing an important development direction for orthopedic internal fixation materials. However, their clinical application remains constrained by a fundamental contradiction: achieving both the required mechanical properties as a structural material and controllable, uniform degradation behavior in a physiological environment is difficult.

[0003] From the perspective of corrosion thermodynamics and kinetics, this contradiction stems from the inherent properties of magnesium. Magnesium has the lowest standard electrode potential of all structural metals (-2.37 V vs. SHE), exhibiting an extremely high tendency to corrode. More critically, the Pilling-Bedworth ratio (PBR) of its naturally formed oxide film (MgO) is approximately 0.81 (<1), meaning that the film is loose and non-dense, unable to provide effective protection for the substrate. In physiological fluids rich in corrosive components such as chloride ions, this film is easily damaged, inducing severe localized corrosion (such as pitting and intergranular corrosion). Localized corrosion not only leads to premature failure of the implant's mechanical properties but also affects tissue healing due to a sharp increase in local pH and rapid accumulation of hydrogen, even causing complications such as emphysema. Studies have shown that although ultrapure magnesium has relatively good corrosion resistance, its yield strength is extremely low (approximately 20 MPa), completely failing to meet the mechanical load-bearing requirements of implants.

[0004] Alloying is an essential approach to improving mechanical properties. However, this often introduces new corrosion problems. Traditional commercial magnesium alloys (such as AZ91) or alloys with large amounts of rare earth elements added to achieve high strength (such as some Mg-Gd-Y-Zr alloys) typically have electrode potentials higher than the magnesium matrix for the added alloying elements (such as Al, Zn, Mn, and some rare earth elements). This causes the formed second phase to become the cathode phase, forming a micro-couple with the magnesium matrix, which in turn exacerbates micro-couple corrosion and deteriorates corrosion resistance. For example, Chinese patent application (publication number CN116694943A) optimized the mechanical properties and biocompatibility of Mg-Zn-Mn-Zr alloys by adding Sr, but its corrosion resistance foundation remains weak. While high-aluminum-content Mg-Y-Al alloys disclosed in CN111304510B have certain corrosion resistance, the long-term biocompatibility of aluminum is questionable. Therefore, existing technical solutions often fall into a dilemma: pursuing mechanical properties sacrifices corrosion resistance and biocompatibility, while avoiding harmful elements may lead to insufficient performance. Currently, applying external coatings (such as polymer coatings or calcium phosphate coatings) to isolate the substrate is the mainstream method to improve corrosion resistance. However, coatings have the risk of weak adhesion to the substrate, easy peeling and failure in dynamic physiological environments, and complex processes. Summary of the Invention

[0005] In view of this, the present invention provides a medical BXM2 magnesium alloy with self-healing film-forming ability and its preparation method, aiming to solve the above problems.

[0006] On one hand, the present invention provides a medical-grade BXM2 magnesium alloy with self-healing film-forming capability, comprising, by weight percentage: Nd: 2.0-6.0 wt.%; Y: 0.5-3.0 wt.%; Zr: 0.3-1.0 wt.%; And the remainder of Mg and unavoidable impurity elements; The impurity elements are Fe ≤ 0.005 wt.%, Cu ≤ 0.005 wt.%, Ni ≤ 0.005 wt.%, and Si ≤ 0.005 wt.%, with a total impurity element content ≤ 0.02 wt.%. After T6 heat treatment, the magnesium alloy has a multiphase structure. The matrix is ​​an α-Mg solid solution with a close-packed hexagonal crystal structure. Second phase particles are dispersed in the α-Mg solid solution. The second phase particles are intermetallic compounds containing Nd and Y. The average size of the second phase particles is 50-200 nm. The average grain size of the magnesium alloy is 10-50 μm.

[0007] Preferably, the average size of the second phase is ≤100nm, and the average grain size of the alloy is ≤20μm.

[0008] On the other hand, the present invention also provides a method for preparing a medical-grade BXM2 magnesium alloy with self-healing film-forming ability, comprising the following steps: (1) Raw material pretreatment: Preheat pure magnesium ingots, Mg-Nd master alloy, Mg-Y master alloy and Mg-Zr master alloy in an oven at 150-200℃ for 1-2 hours; (2) Melting: Pure magnesium ingots are melted at 680-700℃ under a mixed protective gas atmosphere of CO2 and SF6. The temperature is raised to 720-740℃ and Mg-Nd master alloy and Mg-Y master alloy are added. The mixture is stirred until completely melted. The temperature is then raised to 740-760℃ and Mg-Zr master alloy is added. The mixture is stirred and held at this temperature for 10-20 minutes to obtain magnesium alloy melt. (3) Melt purification and casting: At 740-750℃, add 1.0-1.5% of the total mass of the magnesium alloy melt to the magnesium alloy melt, stir mechanically for 15-25 minutes, then let it stand at 730-740℃ for 30-40 minutes, adjust the temperature of the magnesium alloy melt to 690-705℃, pour it into a metal mold preheated to 180-220℃, and cool to obtain a magnesium alloy ingot; (4) Solution treatment: Place the magnesium alloy ingot in an atmosphere-protected or vacuum heat treatment furnace and hold it at 500-525℃ for 8-12 hours. After the holding is completed, transfer it to hot water at a temperature not lower than 60℃ for quenching. (5) Aging treatment: The magnesium alloy ingot after solution quenching is kept at 200-220℃ for 16-40h. After the heat treatment is completed, it is taken out and cooled to room temperature in the air to obtain magnesium alloy.

[0009] Preferably, the aging process in step (5) is to keep warm at 210°C for 24 hours.

[0010] Preferably, the volume ratio of the mixed protective gas in step (2) is CO2:SF6=1:(9-10).

[0011] Preferably, it further includes: Magnesium alloy billets after aging treatment can be hot extruded or rolled at 300-350℃, with the deformation controlled at 30-70%.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This application employs a Mg-Nd-Y-Zr alloy system. By controlling the contents of Nd, Y, and Zr, the alloy composition is designed without introducing Al. Nd and Y participate in solid solution strengthening and second-phase formation, and can enter the corrosion product film during alloy corrosion. Zr plays a grain-refining role during solidification, which is beneficial to improving the uniformity of the microstructure. By controlling the individual contents of Fe, Cu, Ni, and Si to below 0.005 wt.%, and controlling the total content of unavoidable impurities to below 0.02 wt.%, the possibility of forming local microcouples between impurity phases and the magnesium matrix is ​​reduced, thereby reducing the tendency for localized corrosion caused by impurities.

[0013] 2) This application employs a T6 heat treatment regime combining solution treatment and artificial aging treatment. Solution treatment promotes the incorporation of Nd and Y into the magnesium matrix, followed by aging treatment at 200℃~220℃, causing the Nd and Y-containing intermetallic compound second phase to precipitate from the magnesium matrix. By controlling the average size and distribution of the second phase particles, the second phase exerts a precipitation strengthening effect and reduces the tendency for localized corrosion caused by the continuous distribution of coarse second phases, thereby balancing the mechanical properties and corrosion uniformity of the alloy.

[0014] 3) After the corrosion product film on the magnesium alloy surface is locally damaged, the exposed magnesium alloy substrate in the damaged area continues to corrode and releases Nd³⁺. + and Y³ + Nd³ + and Y³ + The magnesium alloy reacts with phosphate and carbonate ions in simulated body fluids to form corrosion products containing Nd and Y, which are then deposited on the damaged area, causing the damaged area to be re-covered by the corrosion products. Therefore, the magnesium alloy of this application can utilize alloying elements to participate in the re-film formation of the damaged area without the need for an external coating.

[0015] 4) This application employs a Mg-Nd-Y-Zr alloy system. Raw materials include pure magnesium ingots, Mg-Nd master alloys, Mg-Y master alloys, and Mg-Zr master alloys. The preparation process includes raw material pretreatment, smelting, melt purification, casting, solution treatment, and aging treatment. These processes can be implemented using existing magnesium alloy smelting and heat treatment equipment. The process parameters have clearly defined temperature and time ranges, facilitating control of alloy composition and heat treatment microstructure. By controlling the addition amounts of Nd and Y, this application achieves both mechanical properties and corrosion film-forming properties while avoiding reliance on external coatings to form a protective layer, thus simplifying the preparation process of medical magnesium alloy materials. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The SEM image provided in Embodiment 1 of the present invention; Figure 2 The XRD pattern provided in Embodiment 2 of the present invention; Figure 3 This is a SEM image provided in Embodiment 3 of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] This invention is based on the Mg-Nd-Y-Zr alloy system. By controlling the contents of Nd, Y, and Zr, and combining solution treatment and aging treatment, a dispersed intermetallic compound second phase containing Nd and Y is formed in the α-Mg solid solution. This second phase improves the mechanical properties and corrosion uniformity of the alloy. In physiological environments or simulated body fluids, magnesium alloys corrode and release Nd³⁺. + and Y³ + Nd³ + and Y³ + It can react with phosphate and carbonate ions in the medium to form a composite corrosion product film containing Nd and Y. When the corrosion product film is locally damaged, the exposed magnesium alloy substrate in the damaged area continues to release Nd³⁺. + and Y³ + This promotes the redeposition of Nd and Y-containing corrosion products in the damaged area, thereby re-covering the damaged area with corrosion products. In this embodiment of the invention, the magnesium alloy composition (chemical composition and dosage) is as follows: This magnesium alloy, by mass percentage (wt.%), consists of the following components: Main alloying elements: Neodymium (Nd): 2.0-6.0 wt.%, with a preferred range of 3.0-5.0 wt.% and a most preferred range of 4.0 wt.%.

[0021] Yttrium (Y): 0.5-3.0 wt.%, with a preferred range of 1.0-2.0 wt.%, and the most preferred value of 1.5 wt.%.

[0022] Zirconium (Zr): 0.3-1.0 wt.%, preferably 0.4-0.8 wt.%, most preferably 0.6 wt.

[0023] Matrix element: Magnesium (Mg): Balance

[0024] Impurity control: For unavoidable impurity elements, such as iron (Fe), copper (Cu), nickel (Ni), and silicon (Si), the content of each impurity is ≤0.005 wt.%, and the total content of impurity elements is ≤0.02 wt.%.

[0025] The structure (microscopic organization) is as follows: This alloy has a multiphase structure, and its core structural feature lies in the microstructure formed after specific heat treatment: Matrix: α-Mg solid solution with a hexagonal close-packed (HCP) crystal structure.

[0026] The key second phase: Nanoscale and submicron-sized rare-earth-containing second-phase particles are uniformly and dispersedly distributed within the magnesium matrix. These particles are primarily Nd and Y-rich intermetallic compounds, such as Mg... 12 Nd-type phase, Mg 24 Y5 type phase or its composite phase. The average size of these precipitated phases is 50-200 nm, preferably ≤100 nm.

[0027] Grain structure: Due to the grain-refining effect of Zr and subsequent processing, the average grain size of the alloy is 10-50 μm, preferably ≤20 μm.

[0028] Physical properties

[0029] X-ray diffraction (XRD) characteristics: When tested in the range of 20°-40° diffraction angle (2θ), in addition to the main diffraction peak of the α-Mg matrix, Mg-attributable peaks should appear around approximately 30.5° and approximately 36.0°. 12 Characteristic diffraction peaks of the Nd phase (or similar Nd-rich phase). The intensity and full width at half maximum (FWHM) of these characteristic peaks are important parameters for determining the content and refinement degree of the second phase.

[0030] Composition of corrosion product film: After immersion in simulated body fluid, the corrosion product film formed on the alloy surface was analyzed by X-ray photoelectron spectroscopy (XPS) or energy dispersive spectroscopy (EDS). The analysis showed that, in addition to Mg and O elements, the atomic ratio of P to Nd (P / Nd) in the film layer was between 0.8 and 1.2, and there was a significant Y element characteristic signal, confirming the formation of a composite protective film rich in rare earth phosphates.

[0031] Mechanical and corrosion properties: Under optimal heat treatment (T6) conditions, the alloy exhibits tensile strength (σb) ≥ 250 MPa, yield strength (σ0.2) ≥ 150 MPa, and elongation (δ) ≥ 5%. In 3.5 wt.% NaCl solution or simulated body fluid, its average corrosion rate is ≤ 0.30 mg / cm² / day, and it displays a uniform corrosion morphology.

[0032] In this embodiment of the invention, the magnesium alloy is prepared by the following method: Raw material types, sources, and dosages: Pure magnesium ingots: magnesium content ≥ 99.95 wt.%.

[0033] Master alloys: Mg-30Nd master alloy, Mg-30Y master alloy, Mg-30Zr master alloy (the numbers represent the nominal mass percentage of rare earth elements).

[0034] Protective gas: a mixture of carbon dioxide (CO2) and sulfur hexafluoride (SF6).

[0035] Refining agent: It is prepared by mixing potassium chloride (KCl), calcium chloride (CaCl2), barium chloride (BaCl2), calcium fluoride (CaF2) and yttrium chloride (YCl3) in a specific ratio.

[0036] Complete preparation process and parameters: Step (1) Raw material pretreatment: Preheat the pure magnesium ingot and each intermediate alloy in an oven at 150-200℃ for 1-2 hours to completely remove the surface adsorbed moisture.

[0037] Step (2) Melting: In a closed melting furnace, a protective gas mixture of CO2 and SF6 (volume ratio CO2:SF6=1:(9-10)) is introduced. Using a low-carbon steel or stainless steel crucible, the raw materials are added and melted in the following order and at the following temperatures: At 680-700℃, pure magnesium ingots are added and held at the temperature after complete melting. The temperature is raised to 720-740℃, and Mg-30Nd master alloy and Mg-30Y master alloy are added, and mechanically stirred thoroughly until completely melted. The temperature is further raised to 740-760℃, and Mg-30Zr master alloy is added, stirred, and held at this temperature for 10-20 minutes to ensure uniform alloy composition, thus obtaining a magnesium alloy melt.

[0038] Step (3) Melt purification and casting: Refining: At 740-750℃, add 1.0-1.5% of the above-mentioned refining agent (by mass of the melt) to the melt and mechanically stir for 15-25 minutes to allow the flux to fully react with the non-metallic inclusions in the melt. Settling: After stopping stirring, allow the melt to stand at 730-740℃ for 30-40 minutes to allow the reaction products and impurities to float or sink fully. Casting: Adjust the melt temperature to 700-710℃ and let it stand for 20-30 minutes, then skim off the surface slag. At a casting temperature of 690-705℃, pour the purified melt into a metal mold preheated to 180-220℃, and obtain a magnesium alloy ingot after cooling.

[0039] Step (4) Solution treatment: Place the ingot in a protective atmosphere (or vacuum) heat treatment furnace. Perform solution treatment at 500-525℃ and hold for 8-12 hours to allow the alloying elements to fully dissolve into the magnesium matrix. After holding, quickly transfer the workpiece to hot water at a temperature not lower than 60℃ for quenching.

[0040] Step (5) Aging treatment: The solution-quenched alloy is subjected to artificial aging treatment. It is held at 200-220℃ for 16-40 hours. After holding, the alloy is removed and cooled to room temperature in air. This step is crucial for forming nanoscale dispersed precipitates and endowing the alloy with self-healing film-forming capabilities. The optimal process parameters are aging at 210℃ for 24 hours.

[0041] Step (6) can be a deformation process, which is suitable for implants with higher strength requirements: the aged alloy billet can be hot extruded or rolled at 300-350℃, and the deformation amount can be controlled at 30%-70% to further refine the grains and improve the mechanical properties.

[0042] Preparation method of key intermediate alloys

[0043] High-purity Mg-Nd master alloys: can be produced by vacuum distillation, with a purity ≤1×10⁻⁶. -2 At a vacuum level of Pa and a temperature of 950-1000℃, magnesium and neodymium are evaporated and condensed to synthesize, effectively avoiding the introduction of impurities such as iron.

[0044] Mg-Y master alloy: It can be produced by argon-protected co-doping melting, where pure magnesium and yttrium are melted and stirred evenly at 780-800℃ and then cast.

[0045] Mg-Zr master alloy: The salt bath method can be used to react potassium fluorozirconate (K2ZrF6) with molten magnesium at 720-750℃ to generate zirconium, which is then melted into the magnesium.

[0046] Unless otherwise specified, the general preparation process for the following examples is as follows: raw material pretreatment → melting under a protective atmosphere (CO2:SF6=1:9) → refining and settling → casting → solution treatment (515℃, 10h, water quenching at 80℃) → aging treatment → performance testing.

[0047] Examples 1-3

[0048] The purpose of this experiment was to investigate the key role of Nd content in the self-healing film-forming ability and comprehensive performance of the alloy. The test results are detailed in Table 1, with the Y content fixed at 1.5 wt.% and the Zr content at 0.6 wt.%.

[0049] Example 1: Chemical composition: Nd: 2.5 wt%, Y: 1.5 wt%, Zr: 0.6 wt%, Mg: balance; Aging process: 210℃, 24h; Figure 1 The image shown is a SEM image from this embodiment.

[0050] Example 2: Chemical composition: Nd: 4.0 wt%, Y: 1.5 wt%, Zr: 0.6 wt%, Mg: balance; Aging process: 210℃, 24h; Figure 2 As shown, the Mg matrix and the Mg12Nd second phase are visible.

[0051] Example 3: Chemical composition: Nd: 5.5 wt%, Y: 1.5 wt%, Zr: 0.6 wt%, Mg: balance; Aging process: 210℃, 24h. Figure 3 The image shown is a SEM image from this embodiment.

[0052] Table 1

[0053] Examples 4-5

[0054] This group of experiments was based on the optimized composition (Nd: 4.0 wt%, Y: 1.5 wt%, Zr: 0.6 wt%, Mg: balance), and the test results are detailed in Table 2. The study explored the regulatory effect of aging process on microstructure and properties.

[0055] Example 4: Chemical composition: Nd: 4.0 wt%, Y: 1.5 wt%, Zr: 0.6 wt%, Mg: balance; Aging process: 200℃, 24h; Example 5: Chemical composition: Nd: 4.0 wt%, Y: 1.5 wt%, Zr: 0.6 wt%, Mg: balance; Aging process: 220℃, 24h.

[0056] Table 2

[0057] Examples 6-7

[0058] In this group of experiments, the contents of Y and Zr were adjusted to verify their role in refining grains and stabilizing the film. The test results are detailed in Table 3.

[0059] Example 6: Chemical composition: Nd: 4.0 wt%, Y: 0.8 wt%, Zr: 0.6 wt%, Mg: balance; Aging process: 210℃, 24h; Example 7: Chemical composition: Nd: 4.0 wt%, Y: 1.5 wt%, Zr: 0.3 wt%, Mg: balance; Aging process: 210℃, 24h; Table 3

[0060] Comparative Example 1

[0061] Chemical composition: Nd: 1.0 wt%, Y: 1.5 wt%, Zr: 0.6 wt%, Mg: balance; Aging process: 210℃, 24h; The rest is the same as in Example 1.

[0062] SEM showed sparse and fine precipitates. Almost no obvious Mg was detected. 12 Nd phase characteristic peaks. σb: 210 MPa, σ0.2: 110 MPa, δ: 8%; hydrogen evolution rate: 0.45 mL / cm² / day; obvious pitting corrosion is visible on the surface. P / Nd atomic ratio <0.5, the film mainly consists of Mg and O elements.

[0063] Comparative Example 2

[0064] Chemical composition: Nd: 4.0 wt%, Y: 1.5 wt%, Zr: 0.6 wt%, Mg: balance; Aging process: 240℃, 24h; The rest is the same as in Example 1.

[0065] The precipitated phase was significantly coarsened (>250 nm) and some of it aggregated. After soaking in the scratch for 72 hours, the repaired deposits were sparse and uneven, with a repair rate of <40%.

[0066] Comparative Example 3

[0067] Chemical composition: Nd: 4.0 wt%, Y: 1.5 wt%, Zr: 0.6 wt%, Fe: 0.015 wt%, Mg: balance; Aging process: 210℃, 24h; Corrosion rate: 0.65 mg / cm² / day, with numerous pitting corrosion marks appearing on the surface. The film composition is complex, and Fe oxide characteristics were detected.

[0068] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A medical-grade BXM2 magnesium alloy with self-healing film-forming capability, characterized in that, By weight percentage, including: Nd: 2.0-6.0 wt.%; Y: 0.5-3.0 wt.%; Zr: 0.3-1.0 wt.%; And the remainder of Mg and unavoidable impurity elements; The impurity elements are Fe ≤ 0.005 wt.%, Cu ≤ 0.005 wt.%, Ni ≤ 0.005 wt.%, and Si ≤ 0.005 wt.%, with a total impurity element content ≤ 0.02 wt.%. After T6 heat treatment, the magnesium alloy has a multiphase structure. The matrix is ​​an α-Mg solid solution with a close-packed hexagonal crystal structure. Second phase particles are dispersed in the α-Mg solid solution. The second phase particles are intermetallic compounds containing Nd and Y. The average size of the second phase particles is 50-200 nm. The average grain size of the magnesium alloy is 10-50 μm.

2. The medical-grade BXM2 magnesium alloy with self-healing film-forming ability according to claim 1, characterized in that, The average size of the second phase is ≤100nm, and the average grain size of the alloy is ≤20μm.

3. A method for preparing a medical-grade BXM2 magnesium alloy with self-healing film-forming ability as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Raw material pretreatment: Preheat pure magnesium ingots, Mg-Nd master alloy, Mg-Y master alloy and Mg-Zr master alloy in an oven at 150-200℃ for 1-2 hours; (2) Melting: Pure magnesium ingots are melted at 680-700℃ under a mixed protective gas atmosphere of CO2 and SF6. The temperature is raised to 720-740℃ and Mg-Nd master alloy and Mg-Y master alloy are added. The mixture is stirred until completely melted. The temperature is then raised to 740-760℃ and Mg-Zr master alloy is added. The mixture is stirred and held at this temperature for 10-20 minutes to obtain magnesium alloy melt. (3) Melt purification and casting: At 740-750℃, add 1.0-1.5% of the total mass of the magnesium alloy melt to the magnesium alloy melt, stir mechanically for 15-25 minutes, then let it stand at 730-740℃ for 30-40 minutes, adjust the temperature of the magnesium alloy melt to 690-705℃, pour it into a metal mold preheated to 180-220℃, and cool to obtain a magnesium alloy ingot; (4) Solution treatment: Place the magnesium alloy ingot in an atmosphere-protected or vacuum heat treatment furnace and hold it at 500-525℃ for 8-12 hours. After the holding is completed, transfer it to hot water at a temperature not lower than 60℃ for quenching. (5) Aging treatment: The magnesium alloy ingot after solution quenching is kept at 200-220℃ for 16-40h. After the heat treatment is completed, it is taken out and cooled to room temperature in the air to obtain magnesium alloy.

4. The method for preparing the medical-grade BXM2 magnesium alloy with self-healing film-forming ability according to claim 3, characterized in that, The aging process in step (5) involves holding the product at 210℃ for 24 hours.

5. The method for preparing the medical-grade BXM2 magnesium alloy with self-healing film-forming ability according to claim 3, characterized in that, In step (2), the volume ratio of the mixed protective gas is CO2:SF6 = 1:(9-10).

6. The method for preparing the medical-grade BXM2 magnesium alloy with self-healing film-forming ability according to claim 3, characterized in that, Also includes: Magnesium alloy billets after aging treatment can be hot extruded or rolled at 300-350℃, with the deformation controlled at 30-70%.

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