Layered grain structure biomedical magnesium alloy and preparation method and application thereof

Abstract

The application provides a layered grain structure biomedical magnesium alloy and a preparation method and application thereof, and relates to the technical field of biomedical magnesium alloys.The layered grain structure biomedical magnesium alloy is prepared through raw material pretreatment, alloy smelting, ingot preparation, double-stage solid solution treatment and lining plate rolling forming; the magnesium alloy comprises Ca 0.4% and the balance of magnesium and inevitable impurities in terms of mass percentage; and the RD-ND plane of the magnesium alloy presents a layered grain structure in which fine equiaxed grains and coarse equiaxed grains are alternately distributed.The magnesium alloy prepared by regulating the content of calcium elements and wrapping the upper and lower surfaces of the blank with 304 stainless steel plates and then performing single-pass large reduction rolling presents a layered grain structure in which fine equiaxed grains and coarse equiaxed grains are alternately distributed on the RD-ND plane, has excellent strength and toughness synergy and good physiological corrosion resistance, and has good industrialization potential.

Description

Technical Field

[0001] This invention relates to the field of biomedical magnesium alloy technology, and in particular to a layered grain structure biomedical magnesium alloy, its preparation method, and its application. Background Technology

[0002] Magnesium alloys, as a novel biodegradable biomedical metallic material, possess density and elastic modulus similar to human bone tissue, effectively avoiding stress shielding effects. Furthermore, they can naturally degrade within the human physiological environment, eliminating the need for secondary surgical removal, thus demonstrating broad application prospects in the field of orthopedic implants. However, magnesium alloys are chemically reactive and corrode rapidly in physiological environments. Excessive degradation can lead to premature implant failure and the generation of large amounts of hydrogen gas locally, affecting bone tissue healing. Therefore, effectively controlling the corrosion rate while ensuring mechanical properties is one of the core challenges in current research on biomedical magnesium alloys.

[0003] Alloying is one of the effective means to improve the overall performance of magnesium alloys. Calcium, as an important component of human bones, has good biocompatibility. Appropriate addition of calcium can form a reinforcing phase in the magnesium matrix, refine the grains, and thus improve the mechanical properties of the alloy. Simultaneously, the addition of calcium helps to form a relatively dense corrosion product layer on the alloy surface, which to some extent slows down the corrosion process. However, when the calcium content is too high, coarse second phases are easily formed at the grain boundaries, becoming preferential channels for corrosion and leading to a synergistic deterioration of both mechanical properties and corrosion resistance. Therefore, precise control of the calcium content is crucial for obtaining biomedical magnesium alloys with balanced performance.

[0004] In terms of processing technology, rolling deformation is a common method for preparing magnesium alloy sheets, which can significantly improve the mechanical properties of the alloy by introducing dislocations and refining grains. However, magnesium alloy sheets prepared by traditional rolling processes usually exhibit a uniform grain structure, making it difficult to achieve a synergistic improvement in both strength and plasticity. Summary of the Invention

[0005] In view of this, the present invention provides a layered grain structure biomedical magnesium alloy, its preparation method, and its applications. By precisely controlling the calcium content and combining a two-stage solution treatment with a liner rolling process, the present invention achieves the controllable preparation of a layered grain structure biomedical magnesium alloy, which has good prospects for industrial application.

[0006] The first aspect of the present invention provides a layered grain structure biomedical magnesium alloy, comprising, by mass percentage: 0.4% Ca, with the balance being magnesium and unavoidable impurities; The RD-ND surface of the magnesium alloy exhibits a layered grain structure with alternating distribution of fine and coarse equiaxed grains; the average grain size of the surface layer is 18.9±1.2 μm, and the average grain size of the central layer is 28.2±2.9 μm.

[0007] Preferably, the layered grain structure biomedical magnesium alloy has a yield strength ≥197 MPa, a tensile strength ≥300 MPa, and an elongation ≥25% at room temperature.

[0008] A second aspect of the present invention is to provide a method for preparing the above-mentioned layered grain structure biomedical magnesium alloy, comprising the following steps: S1. Raw material pretreatment: Weigh magnesium metal blocks and magnesium-calcium intermediate alloy according to the weight parts, remove the oxide layer on their surface by grinding wheel and dry at 200℃ to obtain metal raw materials; S2. Alloy smelting: 75-90% of the magnesium metal blocks are placed in a smelting furnace under a protective atmosphere. After holding at the first temperature, magnesium-calcium master alloy and the remaining magnesium metal blocks are added. After holding at the second temperature, the alloy liquid is obtained. S3. Ingot preparation: Add refining agent to the alloy liquid and stir, heat preservation, cooling and casting in sequence to obtain ingot; S4. Two-stage solution treatment: The ingot is subjected to two-stage solution treatment to obtain a solution-treated ingot. S5. Liner plate rolling: After removing the oxide layer from the solution-treated ingot, it is cut into square billets, and the upper and lower surfaces are wrapped with 304 stainless steel plates. Then, the liner plate is rolled to obtain a layered grain structure biomedical magnesium alloy.

[0009] Preferably, in step S1, the metal raw material is composed of the following parts by weight: 620-630 parts of magnesium metal block and 9.1-9.3 parts of magnesium-calcium master alloy; the magnesium-calcium mass ratio of the magnesium-calcium master alloy is 7:3.

[0010] Preferably, in step S2, the protective atmosphere is a mixture of SF6 and CO2 at a volume ratio of 1:40; the first temperature is 710±5℃ and the holding time is 25±2 min; the second temperature is 750±5℃ and the holding time is 20±2 min.

[0011] Preferably, in step S3, the amount of refining agent used is 1-2 wt.% of the alloy liquid; the refining agent is composed of the following raw materials by weight percentage: MgCl2 46-51%, KCl 40-45%, BaCl2 8-10%, CaF2 5-7%, and the sum of all components is 100%; the stirring time is 3-6 min; the holding temperature is 740±5℃, and the holding time is 20±2 min; the temperature after cooling is 710±5℃.

[0012] Preferably, in step S4, the two-stage solution treatment is carried out under an argon protective atmosphere. The first-stage solution treatment temperature is 320℃ and the first-stage solution treatment time is 1±0.5 h. The second-stage solution treatment temperature is 500℃ and the second-stage solution treatment time is 5±2 h. After the heat preservation is completed, water quenching is performed immediately to obtain a solution-treated ingot.

[0013] Preferably, in step S5, the liner rolling process is as follows: the billet is placed in an electric resistance furnace and heated to 350±5℃, held for 60±5 min, and then rolled in a single pass to produce an alloy plate with a thickness of 2.5 mm through a total reduction rate of 75%; the 304 stainless steel plate has a thickness of 2±0.5 mm, a length of 250±2 mm, and a width of 120±2 mm.

[0014] A third aspect of the present invention is to provide the application of the above-mentioned layered grain structure biomedical magnesium alloy in the preparation of biodegradable biomedical implant materials, wherein the biodegradable biomedical implant materials are used for bone tissue regeneration and repair.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The magnesium alloy RD-ND surface prepared by this invention exhibits a layered grain structure with alternating distribution of fine and coarse equiaxed grains. This structure can effectively coordinate the strain distribution in different regions of the alloy during deformation, enabling the alloy to maintain good plastic deformation capacity while obtaining high strength, thus achieving a synergistic improvement in strength and toughness. This overcomes the shortcomings of traditional uniform grain structure magnesium alloys, which have difficulty in achieving both strength and toughness.

[0016] This invention employs a two-stage solution treatment process, combining low-temperature pretreatment with high-temperature homogenization to ensure that alloying elements are fully dissolved and uniformly distributed in the matrix. This effectively eliminates segregation defects in the as-cast structure, providing a good microstructure basis for subsequent rolling deformation and helping to further improve the overall mechanical properties of the alloy.

[0017] This invention selects calcium as the sole alloying element. Calcium is non-toxic to the human body, participates in bone metabolism, and exhibits excellent biocompatibility. The alloy degrades at a controllable rate in physiological environments, and the corrosion products are harmless to the human body, meeting the biosafety requirements of biodegradable orthopedic implant materials and possessing good potential for clinical translation.

[0018] This invention employs a liner rolling process, which is simple in process flow and easy to control parameters, making it suitable for large-scale production. It provides a new direction for the industrial preparation of layered grain structure biomedical magnesium alloys and has good industrialization potential. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 The X-ray diffraction intensity spectrum of the layered grain structure biomedical magnesium alloy obtained in Example 1 of this invention; Figure 2 The electron backscatter diffraction (EBSD) inverse pole figure of the RD-ND surface of the layered grain structure biomedical magnesium alloy prepared in Example 1 of this invention; Figure 3 The inverse pole figures of electron backscatter diffraction (EBSD) of the surface layer and the central layer of the layered grain structure biomedical magnesium alloy prepared in Example 1 of this invention are shown. Figure 4 This is a tensile property diagram of the layered grain structure biomedical magnesium alloy obtained in Example 1 of the present invention; Figure 5 This is a potentiodynamic polarization curve of the layered grain structure biomedical magnesium alloy obtained in Example 1 of the present invention. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] In the following embodiments and comparative examples of this invention, the crucibles, crucible tongs, and stirring rods used must be pretreated before use: a protective coating is uniformly applied to their surfaces; the protective coating is composed of zinc oxide, water, and water glass mixed in a mass-volume ratio of 45 g: 250 mL: 45 g; the magnesium-calcium mass ratio of the magnesium-calcium master alloy used is 7:3.

[0023] Unless otherwise specified, all experiments were repeated three times. Results are expressed as mean ± standard deviation, and P < 0.05 indicates a significant difference.

[0024] Example 1: A method for preparing a layered grain structure biomedical magnesium alloy, the steps of which are as follows: S1. Raw material pretreatment: The oxide layer on the surface of the metal raw material is removed by a grinding wheel and dried at 200℃, with 625 parts of magnesium metal blocks and 9.2 parts of magnesium-calcium master alloy. S2. Alloy Melting: Preheat the crucible to 300℃, place 80% of the magnesium metal blocks in the crucible, and then put them into the resistance furnace together. Introduce a protective gas consisting of a mixture of SF6 and CO2 at a volume ratio of 1:40. When the temperature reaches 710℃, hold for 25 minutes. Then add the dried magnesium-calcium master alloy and magnesium metal blocks to the crucible. Raise the furnace temperature to 750℃ and hold for 20 minutes to allow sufficient time for the alloying elements to diffuse fully in the molten magnesium alloy, thereby homogenizing the alloy composition and obtaining the alloy liquid. S3. Ingot Preparation: After the holding period, adjust the furnace temperature to 740℃, vigorously stir the alloy liquid, and slowly add the refining agent at the same time. Maintain this process for 5 minutes until a mirror-like surface appears on the alloy liquid. The refining agent is composed of the following raw materials by weight percentage: MgCl2 46%, KCl 41%, BaCl2 8%, CaF2 5%, with the sum of each component being 100%, and the amount of refining agent used is 1.5 wt.%. After refining, heat the furnace temperature to 740℃ and hold for 20 minutes. After the holding period, wait for the furnace temperature to drop to 710℃, and then begin casting into the preheated and dried metal mold (the mold preheating temperature is 200±5℃), finally casting a cylindrical ingot. S4. Two-stage solution treatment: The shrinkage cavity and bottom of the cylindrical ingot are cut off by wire cutting. Then, a two-stage solution treatment is carried out under an argon protective atmosphere. The first stage solution treatment temperature is 320℃ and the first stage solution treatment time is 1 h. The second stage solution treatment temperature is 500℃ and the second stage solution treatment time is 5 h. After the heat treatment is completed, the ingot is immediately quenched with water to obtain a solution-treated ingot.

[0025] S5. Liner Plate Rolling: First, the solution-treated ingot is cut into rectangular blanks with a length of 80 mm, a width of 60 mm, and a thickness of 10 mm. The oxide scale on the surface is removed to make the surface bright. The upper and lower surfaces are wrapped with 304 stainless steel plates with a length of 250 mm, a width of 120 mm, and a thickness of 2 mm. It is then placed in an electric resistance furnace and heated to 350℃, held for 60 min, and then rolled in a single pass. With a total reduction rate of 75%, an alloy plate with a thickness of 2.5 mm was successfully prepared.

[0026] Testing revealed that the obtained layered grain structure biomedical magnesium alloy contained 0.4 wt.% Ca, 0.05 wt.% unavoidable impurities, and the balance being magnesium.

[0027] The layered grain structure biomedical magnesium alloy obtained in Example 1 was subjected to XRD analysis, such as... Figure 1 As shown, the vertical axis represents diffraction intensity, and the horizontal axis represents diffraction angle 2θ. The layered grain structure of the biomedical magnesium alloy is mainly composed of the α-Mg phase, and no diffraction peaks of other phases were observed.

[0028] The layered grain structure of the biomedical magnesium alloy prepared in Example 1 was analyzed by microscopy, such as... Figure 2 As shown, the RD-ND surface of this alloy exhibits a layered grain structure consisting of alternating fine and coarse equiaxed grains.

[0029] The grain distribution of the layered grain structure biomedical magnesium alloy prepared in Example 1 was detected, such as... Figure 3 As shown, the surface layer of the alloy exhibits a grain structure composed of relatively fine equiaxed grains with an average grain size of 18.9 ± 1.2 μm, while the grain structure of the central layer is mainly composed of relatively coarse equiaxed grains with an average grain size of 28.2 ± 2.9 μm.

[0030] The corrosion resistance of the layered grain structure biomedical magnesium alloy prepared in Example 1 was tested, such as... Figure 5 As shown, the potentiodynamic polarization curves of the high-strength, tough, and corrosion-resistant magnesium alloy were fitted using the CorShow software with Tafel data for the cathode branch. The corrosion potential of the alloy was found to be -1.52 ± 0.014 V, and the corrosion current was 6.52 ± 0.09 μA / cm. 2 The corrosion rate is approximately 0.15 mm / y.

[0031] Example 2 The difference from Example 1 is that the amount of magnesium-calcium intermediate alloy in step S1 is adjusted so that the final layered grain structure biomedical magnesium alloy includes 0.3 wt.% Ca, 0.05 wt.% unavoidable impurities, and the balance being magnesium.

[0032] Example 3 The difference from Example 1 is that the amount of magnesium-calcium intermediate alloy in step S1 is adjusted so that the final layered grain structure biomedical magnesium alloy includes 0.5 wt.% Ca, 0.05 wt.% unavoidable impurities, and the balance is magnesium.

[0033] Test Example 1 The same mechanical and electrochemical properties were tested on Examples 1 (magnesium metal block-0.4Ca), 2 (magnesium metal block-0.3Ca), and 3 (magnesium metal block-0.5Ca), and the results are shown in Table 1.

[0034] Table 1. Test results of mechanical and electrochemical properties of each alloy

[0035] As shown in Table 1, all three alloy compositions exhibit good strength-toughness synergy and corrosion resistance. Among them, the magnesium metal block-0.4Ca alloy (Example 1) has the best overall performance, with the highest tensile strength (330.1±4.8 MPa) and yield strength (204.4±3.6 MPa), and the lowest corrosion rate (0.15 mm / y). This indicates that the mechanical properties and corrosion resistance of the alloy are best matched when the Ca content is 0.4%.

[0036] Comparative Example 1 The difference from Example 1 is that in step S5, the upper and lower surfaces of the billet are not covered with 304 stainless steel plates and are directly rolled.

[0037] Testing revealed that the obtained magnesium alloy RD-ND surface did not exhibit a layered grain structure, with an average grain size of 22±1.8 μm; tensile strength of 143±3.2 MPa, yield strength of 114±4.2 MPa, elongation of 23±1.3%, and corrosion rate of 0.45 mm / y.

[0038] Comparative Example 2 The difference from Example 1 is that in step S4, the solution treatment is changed to single-stage solution treatment with a solution parameter of 500℃×3h, and water quenching is performed immediately after the heat preservation is completed.

[0039] The obtained layered grain structure biomedical magnesium alloy was tested and found to have a tensile strength of 167±2.1 MPa, a yield strength of 138±4.7 MPa, an elongation of 22±1.9%, and a corrosion rate of 0.43 mm / y.

[0040] Comparative Example 3 The difference from Example 1 is that in step S5, the total reduction rate is adjusted to 50%, and an alloy plate with a thickness of 5 mm is prepared.

[0041] Testing revealed that the RD-ND alloy exhibited a layered grain structure with an average grain size of 22±1.4 μm on the surface layer and 27±2.2 μm on the central layer. The tensile strength was 200.2±4.2 MPa, the yield strength was 173±1.2 MPa, the elongation was 24.6±1.3%, and the corrosion rate was 0.29 mm / y.

[0042] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A layered grain structure biomedical magnesium alloy, characterized in that, It is manufactured through raw material pretreatment, alloy smelting, ingot preparation, two-stage solution treatment, and liner rolling. The magnesium alloy comprises, by mass percentage: 0.4% Ca, with the balance being magnesium and unavoidable impurities; The RD-ND surface of the magnesium alloy exhibits a layered grain structure consisting of alternating fine and coarse equiaxed grains.

2. A method for preparing a layered grain structure biomedical magnesium alloy, characterized in that, Includes the following steps: S1. Raw material pretreatment: Weigh magnesium metal blocks and magnesium-calcium master alloy according to the weight parts, then remove the surface oxide layer and dry to obtain metal raw materials; S2. Alloy smelting: 75-90% of the magnesium metal blocks are placed in a smelting furnace under a protective atmosphere. After holding at the first temperature, magnesium-calcium master alloy and the remaining magnesium metal blocks are added. After holding at the second temperature, the alloy liquid is obtained. S3. Ingot preparation: Add refining agent to the alloy liquid and stir, heat preservation, cooling and casting in sequence to obtain ingot; S4. Two-stage solution treatment: The ingot is subjected to two-stage solution treatment to obtain a solution-treated ingot. S5. Liner plate rolling: After removing the oxide layer from the solution-treated ingot, it is cut into square billets, and the upper and lower surfaces are wrapped with 304 stainless steel plates. Then, the liner plate is rolled to obtain a layered grain structure biomedical magnesium alloy.

3. The preparation method according to claim 2, characterized in that, In step S1, the metal raw materials include 620-630 parts by weight of magnesium metal blocks and 9.1-9.3 parts by weight of magnesium-calcium master alloy.

4. The preparation method according to claim 3, characterized in that, The magnesium-calcium mass ratio of the magnesium-calcium master alloy is 7:

3.

5. The preparation method according to claim 2, characterized in that, In step S2, the protective atmosphere is formed by mixing SF6 and CO2 at a volume ratio of 1:

40.

6. The preparation method according to claim 2, characterized in that, In step S2, the first temperature is 710±5℃ and the holding time is 25±2 min; the second temperature is 750±5℃ and the holding time is 20±2 min.

7. The preparation method according to claim 2, characterized in that, In step S3, the amount of refining agent used is 1~2 wt.% of the alloy liquid; the stirring time is 3~6 min; the holding temperature is 740±5℃ and the holding time is 20±2 min; the temperature after cooling is 710±5℃.

8. The preparation method according to claim 2, characterized in that, In step S4, the solution treatment method is as follows: the two-stage solution treatment is carried out under an argon protective atmosphere. The first-stage solution treatment temperature is 320℃ and the first-stage solution treatment time is 1±0.5 h. The second-stage solution treatment temperature is 500℃ and the second-stage solution treatment time is 5±2 h. After the heat preservation is completed, water quenching is performed immediately to obtain a solution-treated ingot.

9. The preparation method according to claim 2, characterized in that, In step S5, the liner rolling process is as follows: the billet is placed in an electric resistance furnace and heated to 350±5℃, held for 60±5 min, and then rolled in a single pass to produce an alloy plate with a thickness of 2.5 mm through a total reduction rate of 75%.

10. The application of the layered grain structure biomedical magnesium alloy of claim 1 in the preparation of biodegradable biomedical implant materials.

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