A biodegradable magnesium alloy of Mg-Nd-Gd-Zn-Sm and its preparation method

Abstract

A Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy and its preparation method are disclosed. The magnesium alloy has the following composition by mass percentage: Nd: 2.4-3.0%, Gd: 1.2-2.0%, Zn: 1.0-1.5%, Sm: 0.5-1.0%, other unavoidable impurities ≤0.1%, and the remainder being Mg. Preparation steps: Pure magnesium, Mg-Nd master alloy, Mg-Gd master alloy, Mg-Zn master alloy, and Mg-Sm master alloy are used as raw materials for batching and drying before smelting; pure magnesium is placed in a medium-frequency induction furnace and filled with protective gas; heated to 670℃~800℃ until the magnesium ingot is completely melted; the temperature is raised to 800~900℃, other raw materials are added, and after complete melting, the temperature is held for 30~60 minutes; the temperature is lowered to 800℃~820℃, refining agent is added, and after refining, it is allowed to stand for 30~50 minutes; the temperature is lowered to 750℃~790℃, and the ingot is cast and cooled to obtain a magnesium alloy ingot; annealing and homogenization are performed; extrusion treatment is then carried out. The biodegradable magnesium alloy of this invention has good mechanical properties and corrosion resistance, the degradation rate is controllable and it is harmless to the human body, and the preparation process is simple and low in cost.

Description

Technical Field

[0001] This invention relates to a biomedical metallic material, specifically to a Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy and its preparation method. Background Technology

[0002] Biomedical materials are used to diagnose, treat, repair, or replace damaged tissues and organs, or enhance their function in living organisms. They form the foundation for research into artificial organs and medical devices, encompassing biomedical metallic materials, biomedical organic materials (primarily organic polymers), biomedical inorganic non-metallic materials (primarily bioceramics, bioglasses, and carbon materials), and biomedical composite materials (metal-based ceramic coating systems, etc.). Among these, biomedical metallic materials possess superior mechanical properties compared to other medical materials—high strength, good toughness, high flexural fatigue strength, excellent processing performance, and good biocompatibility—and are primarily used as load-bearing materials in medical applications. 316L stainless steel is used for medical artificial joints; it is inexpensive but prone to crevice corrosion, friction corrosion, and fatigue corrosion cracking. Cobalt-based alloys (Co-Cr) have good biocompatibility but are expensive; however, Co and Ni elements can cause severe sensitization. Precious metals (gold, silver, platinum) and metalloids (tantalum, niobium, zirconium, etc.) have good biocompatibility, good chemical stability, and corrosion resistance, but are expensive. Titanium-based alloys are non-toxic, lightweight, high-strength, biocompatible, corrosion-resistant, and widely used. However, they contain aluminum (Al), which can cause organ damage, leading to osteomalacia, anemia, and neurological disorders. Magnesium-based alloys have high specific strength and specific stiffness, good machinability, and an elastic modulus (45 GPa) closer to that of human bone (7-25 GPa), reducing stress shielding. Their density is 1.7 g / cm³. 3 ) and human bone mineral density (1.75g / cm³) 3 It is close to and meets the requirements of an ideal bone plate, has a very low standard electrode potential (-2.37V), poor corrosion resistance, and is biodegradable.

[0003] Magnesium is one of the most abundant cations in the human body, participating in almost all metabolic processes and playing a positive role in maintaining normal physiological functions. It participates in protein synthesis, promotes neuromuscular transmission, maintains a normal heart rate, and also has a blood pressure-lowering effect for patients with hypertension. Furthermore, magnesium plays a positive role in bone remodeling. However, current magnesium alloy materials suffer from rapid degradation and poor uniformity, hindering their clinical application. Under the premise of good biocompatibility, improving the mechanical properties and corrosion resistance of magnesium alloys could make them a promising biodegradable material for clinical applications in orthopedic supports and vascular stents. Traditional vascular stent materials, such as 316L stainless steel, cobalt-chromium alloys, and titanium alloys, are not biodegradable, posing a risk of requiring secondary surgery.

[0004] An investigation revealed that the existing Chinese invention patent ZL201910743108.2, entitled "A Mg-Y-Nd-(La+Ce)-Zr Biodegradable Magnesium Alloy," discloses a Mg-Y-Nd-(La+Ce)-Zr biodegradable magnesium alloy. The mass percentages of each element are: Y: 3.0–4.5%, Nd: 2.0–3.5%, Zr: 0.3–1.0%, lanthanum-cerium composite rare earth: 0.05–0.5%, with the remainder being magnesium and unavoidable impurities, the impurity content being ≤0.1%. This magnesium alloy exhibits good mechanical properties and a uniform and controllable degradation rate. However, the rare earth elements La and Ce are cytotoxic, and although their content is low, implantation into the human body poses certain safety risks.

[0005] Furthermore, Chinese invention patent CN104120320B, entitled "A Biodegradable Rare Earth Magnesium Alloy Medical Biomaterial and its Preparation Method," discloses a biodegradable rare earth magnesium alloy with the following mass percentages of elements: Y 0.5-2%, Dy 0.1-0.5%, Zn 0.8-1.2%, Zr 0.35-0.55%, and the balance being magnesium. However, this magnesium alloy exhibits poor mechanical properties and lacks research on its corrosion resistance.

[0006] Therefore, it is of great significance to study a biodegradable magnesium alloy material with good mechanical properties, controllable degradation rate and no harm to the human body, in light of existing biodegradable magnesium alloy materials. Summary of the Invention

[0007] The first technical problem to be solved by the present invention is to provide a Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy with good comprehensive mechanical properties, controllable degradation rate in the human body and no harm to the human body.

[0008] The second technical problem to be solved by the present invention is to provide a method for preparing Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy, which has the characteristics of simple process and low cost.

[0009] The technical solution adopted by the present invention to solve the first technical problem mentioned above is: a Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy, characterized in that: the biodegradable magnesium alloy is composed of the following components in mass percentage: Nd: 2.4-3.0%, Gd: 1.2-2.0%, Zn: 1.0-1.5%, Sm: 0.5-1.0%, other unavoidable impurities ≤0.1%, and the remainder is Mg.

[0010] The biodegradable magnesium alloy has a tensile strength of 320–370 MPa, a yield strength of 250–285 MPa, a Vickers hardness of 88–96, an elongation greater than 30%, and an average corrosion rate of 0.08–0.15 mg / (cm²) over 96 hours. 2 ·h).

[0011] The technical solution adopted by this invention to solve the second technical problem mentioned above is: a method for preparing the above-mentioned Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy, characterized by comprising the following steps:

[0012] 1) Using pure magnesium, Mg-Nd master alloy, Mg-Gd master alloy, Mg-Zn master alloy and Mg-Sm master alloy as raw materials, the raw materials are proportioned according to the mass percentage of each component of the biodegradable magnesium alloy, and dried before smelting.

[0013] 2) Place pure magnesium into a medium-frequency induction furnace and fill it with protective gas for smelting;

[0014] 3) Heat to 670℃~800℃ until the magnesium ingot is completely melted;

[0015] 4) Continue heating to 800-900℃, add Mg-Nd master alloy, Mg-Gd master alloy, Mg-Zn master alloy and Mg-Sm master alloy, and hold for 30-60 minutes after complete melting.

[0016] 5) Lower the temperature to 800℃~820℃, add 3~5wt% magnesium ingot content refining agent (use 92wt% RJ-2 flux and 8wt% CaF2 as refining agent), let it stand for 30~50 minutes after refining, then lower the temperature to 750℃~790℃, pour the magnesium alloy melt into the preheated mold, and cool to obtain magnesium alloy ingot;

[0017] 6) The smelted cast magnesium alloy is annealed and homogenized;

[0018] 7) Finally, the cast magnesium alloy is subjected to extrusion treatment.

[0019] Preferably, the protective gas in step 1) is CO2.

[0020] Furthermore, the annealing temperature in step 6) is 610–630°C, and the holding time is 2.5–3.5 hours.

[0021] Finally, in step 7), the extrusion temperature is 180–350°C and the extrusion speed is 0.6–1.2 m / min.

[0022] Compared with existing technologies, the advantages of this invention are: the material composition is scientifically and rationally designed, adopting the principle of multi-element, low-volume alloying, which effectively improves its mechanical properties and corrosion resistance; at the same time, the degradation rate is uniform and controllable, it has good biocompatibility, is harmless to the human body, and the average corrosion rate in simulated human body fluids is 0.08–0.15 mg / (cm³) after 96 hours. 2 (h) After being implanted in the human body for a certain period of time, it can completely degrade, avoiding the need for secondary surgery. The biodegradable magnesium alloy of this invention has good mechanical properties and corrosion resistance. The mechanical properties can reach: tensile strength 320-370MPa, yield strength 250-285MPa, Vickers hardness 88-96, elongation greater than 30%. At the same time, the degradation rate is controllable and harmless to the human body. Moreover, the preparation process is simple and low cost. It can be used to prepare medical implant devices, providing a material basis for solving the current situation of magnesium alloys as medical materials with excessively fast degradation rate and poor uniformity when implanted in the human body, and has good application prospects. Attached Figure Description

[0023] Figure 1 This is a microstructure image of Example 1 of the present invention after soaking in a modified SBF solution for 60 days. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] The compositional designs of the Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloys in Examples 1-4 are shown in Table 1:

[0026] Table 1. Composition (wt%) of Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloys in Examples 1-4

[0027] Example Nd Gd Zn Sm Mg Example 1 2.5 1.4 1.5 0.9 margin Example 2 2.5 1.4 1.3 0.8 margin Example 3 2.6 1.6 1.3 0.6 margin Example 4 2.7 1.8 1.0 0.5 margin

[0028] Example 1

[0029] A method for preparing a Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy is as follows:

[0030] 1) Using pure magnesium, Mg-Nd master alloy, Mg-Gd master alloy, Mg-Zn master alloy and Mg-Sm master alloy as raw materials, the raw materials are batched according to the composition ratio in Table 1, and dried before smelting.

[0031] 2) First, put pure magnesium into a medium-frequency induction furnace and fill it with protective gas CO2 for smelting;

[0032] 3) Heat to 670℃~800℃ until the magnesium ingot is completely melted;

[0033] 4) Continue heating to 800-900℃, add Mg-Nd master alloy, Mg-Gd master alloy, Mg-Zn master alloy and Mg-Sm master alloy, and hold for 30-60 minutes after complete melting.

[0034] 5) Lower the temperature to 800℃~820℃, add a refining agent with 4wt% magnesium ingot content (use 92wt% RJ-2 flux and 8wt% CaF2 as the refining agent), let it stand for 30~50 minutes after refining, then lower the temperature to 750℃~790℃, pour the magnesium alloy melt into the preheated mold, and cool to obtain magnesium alloy ingot;

[0035] 6) The smelted cast magnesium alloy is annealed to homogenize it and eliminate segregation in the ingot. The annealing temperature is 620℃ and the holding time is 3 hours.

[0036] 7) Extrusion treatment of cast magnesium alloy at an extrusion temperature of 180-350℃ and an extrusion speed of 0.6-1.2m / min.

[0037] Example 2:

[0038] The only difference between this embodiment and the above embodiment 1 is: 1. The ingredients are different, as shown in Table 1. The performance of this embodiment is shown in Table 2.

[0039] Example 3:

[0040] The only difference between this embodiment and the above embodiment 1 is: 1. The ingredients are different, as shown in Table 1. The performance of this embodiment is shown in Table 2.

[0041] Example 4:

[0042] The only difference between this embodiment and the above embodiment 1 is: 1. The ingredients are different, as shown in Table 1. The performance of this embodiment is shown in Table 2.

[0043] The composition design of the biodegradable magnesium alloy of the present invention will be described below:

[0044] Rare earth elements (REEs) have a similar crystal structure to magnesium, exhibiting a hexagonal close-packed (hcp) structure. They possess high solid solubility in magnesium alloys, with Nd reaching a maximum solubility of 3.6%. During solidification, a binary phase (Mg12Nd) forms, refining the as-cast microstructure of the magnesium alloy and improving its mechanical properties. The hardness of the magnesium alloy increases with increasing Nd content, and its room temperature tensile strength also increases. However, when the Nd content exceeds 3.0%, the room temperature tensile strength of the magnesium alloy decreases, while the grain size increases. Therefore, an Nd content of 2.0–3.5% in the magnesium alloy of this invention is suitable.

[0045] Rare earth element Gd has a significant effect on refining the grain size of magnesium alloys. An appropriate amount of Gd can essentially eliminate the as-cast dendrites in magnesium alloys, resulting in a significant reduction in grain size after homogenization. Dynamic recrystallization occurs after extrusion, and the dynamically precipitated β-phase is distributed along the grain boundaries of the recrystallized grains. Adding approximately 1.8% Gd allows the precipitated phase to inhibit recrystallized grain growth, while the particle-induced nucleation and recrystallization work together to achieve a grain-refining strengthening effect. However, as the Gd content exceeds 2%, β-phase precipitation decreases, rare earth phase particles become larger, weakening the dynamic recrystallization effect, leading to stress concentration and a decrease in strength. Therefore, a Gd content of 1.2–2.0% in the magnesium alloy of this invention is relatively suitable.

[0046] Zinc has a maximum solid solubility of 6.2% in magnesium, making it another highly effective alloying element besides aluminum. It possesses both solid solution strengthening and age-hardening properties. Furthermore, zinc's structure is similar to that of rare earth elements, forming high-strength precipitation-strength magnesium alloys. Increasing the Zn content significantly enhances the texture strength of recrystallized grains, deformed grains, and subgrains in magnesium alloys. However, excessive Zn content or the formation of large-sized second phases can disrupt the compatibility of different grain boundaries, hindering basal slip. Therefore, a Zn content of 1.0–1.5% in the magnesium alloy of this invention is suitable.

[0047] The light rare earth element Sm has an atomic size close to that of magnesium and a maximum solid solubility of 5.8% in magnesium. It has good solid solution strengthening and precipitation strengthening effects. The precipitate Mg24Sm5 formed by Sm and Mg is completely dissolved back into the matrix during the solid solution treatment to form a supersaturated solid solution. After aging, the hardness is greatly improved.

[0048] Next, mechanical and corrosion resistance tests were conducted on the Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy. The simulated body fluid used in the corrosion resistance test was designed to closely resemble the environment of human blood. Table 3 shows a comparison of the components of several representative simulated body fluids. Comparatively, the modified SBF solution best matches the composition of human blood plasma; therefore, the modified SBF solution was used in the corrosion test, according to the ASTM G1-03 immersion test standard. The microstructure of the Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy prepared in Example 1 after immersion in the modified SBF solution for 60 days is as follows: Figure 1 As shown, the surface corrosion is uniform, with no obvious corrosion pits appearing in any localized areas. The test results of the mechanical properties and corrosion resistance of the Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy are shown in Table 2 below.

[0049] Table 2. Mechanical properties and corrosion resistance of Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloys in Examples 1-4

[0050]

[0051] As shown in Table 2, the Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy of the present invention has good mechanical properties and strong corrosion resistance, meeting the requirements for implantation into the human body as a biomedical metal material.

[0052] Table 3 Comparison of components of simulated body fluids and human blood plasma

[0053]

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy, characterized in that: This biodegradable magnesium alloy is composed of the following components by mass percentage. Composition: Nd: 2.4-3.0%, Gd: 1.2-2.0%, Zn: 1.0-1.5%, Sm: 0.5-1.0%, other unavoidable impurities ≤0.1%, the remainder is Mg; Its preparation method includes the following steps: 1) Using pure magnesium, Mg-Nd master alloy, Mg-Gd master alloy, Mg-Zn master alloy and Mg-Sm master alloy as raw materials, the raw materials are proportioned according to the mass percentage of each component of the biodegradable magnesium alloy, and dried before smelting. 2) Place pure magnesium into a medium-frequency induction furnace and fill it with protective gas for smelting; 3) Heat to 670℃~800℃ until the magnesium ingot is completely melted; 4) Continue heating to 800~900℃, add Mg-Nd master alloy, Mg-Gd master alloy, Mg-Zn master alloy and Mg-Sm master alloy, and hold for 30~60 minutes after complete melting. 5) Lower the temperature to 800℃~820℃, add a refining agent with 3~5wt% magnesium ingot content, refine and let stand for 30~50 minutes, then lower the temperature to 750℃~790℃, pour the magnesium alloy melt into the preheated mold, and cool to obtain magnesium alloy ingot. 6) The smelted cast magnesium alloy is annealed to homogenize it; the annealing temperature is 610~630℃, and the holding time is 2.5~3.5 hours; 7) Finally, the as-cast magnesium alloy is subjected to extrusion treatment; the extrusion temperature is 180~350℃ and the extrusion speed is 0.6~1.2m / min.

2. The Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy according to claim 1, characterized in that: The biodegradable magnesium alloy has a tensile strength of 320-370 MPa, a yield strength of 250-285 MPa, a Vickers hardness of 88-96, an elongation greater than 30%, and an average corrosion rate of 0.08-0.15 mg / (cm²) after 96 hours. 2 ·h).

3. A method for preparing the Mg-Nd-Gd-Zn-Sm biodegradable magnesium alloy according to claim 1 or 2, characterized in that: Includes the following steps: 1) Using pure magnesium, Mg-Nd master alloy, Mg-Gd master alloy, Mg-Zn master alloy and Mg-Sm master alloy as raw materials, the raw materials are proportioned according to the mass percentage of each component of the biodegradable magnesium alloy, and dried before smelting. 2) Place pure magnesium into a medium-frequency induction furnace and fill it with protective gas for smelting; 3) Heat to 670℃~800℃ until the magnesium ingot is completely melted; 4) Continue heating to 800~900℃, add Mg-Nd master alloy, Mg-Gd master alloy, Mg-Zn master alloy and Mg-Sm master alloy, and hold for 30~60 minutes after complete melting. 5) Lower the temperature to 800℃~820℃, add a refining agent with 3~5wt% magnesium ingot content, refine and let stand for 30~50 minutes, then lower the temperature to 750℃~790℃, pour the magnesium alloy melt into the preheated mold, and cool to obtain magnesium alloy ingot. 6) The smelted cast magnesium alloy is annealed and homogenized; 7) Finally, the as-cast magnesium alloy is subjected to extrusion treatment.

4. The preparation method according to claim 3, characterized in that: The protective gas used in step 2) is CO2.

5. The preparation method according to claim 3, characterized in that: In step 5), the refining agent is selected as 92wt% RJ-2 flux plus 8wt% CaF2.

6. The preparation method according to claim 3, characterized in that: The annealing temperature in step 6) is 610~630℃, and the holding time is 2.5~3.5 hours.

7. The preparation method according to claim 3, characterized in that: In step 7), the extrusion temperature is 180~350℃ and the extrusion speed is 0.6~1.2m / min.

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