Preparation method of high-toughness and high-corrosion-resistance magnesium alloy bar for intraosseous implant

Abstract

The invention discloses a preparation method of a high-toughness and high-corrosion-resistance magnesium alloy bar for an intraosseous implant. The preparation method comprises the following steps: S1, performing eccentric extrusion on a magnesium alloy blank to obtain an extruded bar; s2, the bar is subjected to single-pass high-temperature drawing, and a drawn bar is obtained; and S3, the drawn bar is subjected to aging treatment, and the aluminum alloy bar is obtained. According to the method, the technology of combining eccentric extrusion and single-pass near-phase transition temperature drawing is adopted for tissue regulation and control, high grain refinement, high-density second-phase dispersed distribution and formation of a weak (near) basal texture are achieved, and the problems that in the prior art, magnesium alloy is limited to be used as an intraosseous implant, namely, the toughness coordination capacity is low, the corrosion resistance is poor, and the service life of the magnesium alloy is prolonged are solved. And the magnesium alloy bar for the degradable intraosseous implant, which has high toughness and high corrosion resistance, is prepared.

Description

Technical Field

[0001] This invention belongs to the field of material processing and preparation technology for intraosseous implants, and relates to a method for preparing magnesium alloy rods for intraosseous implants with high strength, toughness and high corrosion resistance. Background Technology

[0002] In recent years, the frequent occurrence of bone trauma due to accidents or diseases, as well as age-related osteoporosis, has led to a sharp increase in the demand for intraosseous implants. Common intraosseous implants mainly include bone screws and bone plates, which are placed on or within the bone to fix the injured bone and prevent deformation. Currently, commercially available permanent metal implant materials mainly include titanium, stainless steel, and cobalt-chromium alloys. However, these traditional medical metal materials face challenges in intraosseous implant applications due to their significant difference in modulus compared to bone and their inert and non-degradable nature in the body, namely, stress shielding and secondary surgical intervention. Stress shielding can cause metal implants with higher modulus to become the main load-bearing component, affecting bone healing or causing osteoporosis and secondary fractures; secondary surgical intervention aims to prevent or alleviate negative tissue reactions such as inflammation caused by inert and non-degradable metal implants in the body.

[0003] Although magnesium and magnesium alloys exhibit significant advantages over other implant materials, such as biodegradability, high biocompatibility, good tissue compatibility, and low cost, their relatively low strength and deformability lead to difficulties in implant fabrication, easy breakage during implantation, and insufficient service life, limiting their large-scale application. Specifically: 1) Magnesium alloys have a low-symmetry hexagonal structure, resulting in poor deformation coordination and low toughness, which may cause defects such as cracks during implant fabrication or make it difficult to achieve relatively fine structures. 2) When magnesium is used to make bone nail implants, it needs to have sufficient strength to prevent failure during screwing. 3) After implantation, insufficient initial strength or degradation over time leads to a continuous loss of mechanical strength, thus failing to achieve a good healing effect, i.e., failing to help new bone form stably and reach a certain strength; simultaneously, while the implant plays a fixing role in the body, it also needs a certain degree of toughness to ensure it does not crack and fail during service. Furthermore, magnesium alloy implants also need to overcome their rapid degradation and poor corrosion resistance. Due to the potential difference between the second-phase particles and the magnesium matrix in wrought alloys, galvanic corrosion occurs when the alloy is immersed in a corrosive medium, accelerating the corrosion and degradation of the magnesium matrix. Therefore, the rapid degradation of magnesium alloy implants in the body can prematurely destroy the mechanical integrity of the implant, making it unable to support subsequent repair of the damaged site.

[0004] In summary, to fully leverage the potential biomedical advantages of biodegradable magnesium alloys, it is crucial to improve the strength, toughness, and corrosion resistance of medical magnesium alloy materials. Alloying and plastic processing are common methods for enhancing the performance of magnesium alloys. Although alloying is widely proposed to achieve high strength in magnesium, the addition of alloying elements inevitably introduces a second phase, which typically exacerbates galvanic corrosion. High alloying can significantly improve its mechanical strength, but it easily introduces large-sized second phases, causing stress concentration and reducing alloy toughness; simultaneously, the presence of bulk phases also promotes localized corrosion. Therefore, adjusting the microstructure through deformation processing is more promising for preparing high-strength, high-toughness, and corrosion-resistant magnesium alloys. Grain refinement is considered to simultaneously improve the mechanical and corrosion resistance of magnesium alloy materials and is usually the main objective of microstructure control. Although the second phase causes galvanic corrosion, multiple studies have shown that dispersed, fine second-phase particles do not significantly impair corrosion resistance, and nano-sized second phases are beneficial to both strength and toughness. Furthermore, basal texture has been reported to be more beneficial to the corrosion resistance of alloys, but severe basal texture can also reduce its toughness. Therefore, controlling the microstructure to facilitate corrosion without sacrificing toughness, or simultaneously improving both corrosion resistance and toughness, can be a new strategy for preparing high-toughness and corrosion-resistant magnesium alloys. As mentioned above, to obtain the optimal combination of mechanical and corrosion properties of magnesium alloys, comprehensive microstructure control is required to maximize its advantages. Summary of the Invention

[0005] To address the problems of low strength and toughness and poor corrosion resistance of magnesium alloys in existing technologies, this invention provides a method for preparing magnesium alloy rods for high-strength, high-toughness, and high-corrosion-resistant intraosseous implants. This method aims to achieve grain refinement and dispersed precipitation of the second phase, while obtaining a weak (near) basal texture. As a result, the alloy possesses both high mechanical properties and high corrosion resistance, thus better meeting the performance requirements of magnesium alloy intraosseous implants and broadening its application range.

[0006] The innovative principle of this invention is as follows: (1) A novel extrusion process is adopted, which differs from the traditional symmetrical extrusion mode, where the feed port and discharge port are both located on the central axis of the die and collinear in the vertical direction. Instead, an asymmetrical feed area with a height of 1-2 mm is designed at the feed port. This area is a circular region with a center 2-8 mm away from the central axis of the die. This process realizes differential flow of the billet during the extrusion process, which leads to asymmetrical deformation. This asymmetrical deformation introduces severe shear deformation, promotes grain refinement and texture weakening, and is beneficial to improving the strength and toughness of the alloy. (2) Combined with a single-pass high-temperature drawing process, the introduction of large drawing strain transforms the recrystallization texture of the extruded sample into a (near) basal texture, which greatly enhances the resistance of basal grain orientation to corrosion. In addition, at high temperatures close to the phase transformation temperature (below the phase transformation temperature), severe dynamic precipitation is triggered, the second phase is densely distributed and the average size is reduced. Specifically, when deformation occurs at a temperature slightly below the secondary phase transformation temperature, the dissolution and precipitation of the second-phase particles are in a dynamic equilibrium state. The deformation temperature being slightly below the phase transformation temperature is a key factor. During deformation at this temperature, on the one hand, dynamic dissolution of particles is easy to occur, thereby increasing the supersaturation of the matrix; on the other hand, under the conditions of large deformation strain and high matrix supersaturation, a large number of lattice defects (such as dislocations and GBs) will induce severe precipitation, which leads to the widespread nucleation of particles along lattice defects. At the same time, particle diffusion and re-dissolution are still in progress, limiting the size of the particles. Meanwhile, the high density of second-phase particles inhibits grain boundary migration and prevents the growth of recrystallized grains at high temperatures. Therefore, after drawing, further refined grains and second-phase particles are obtained, which is not only beneficial to the improvement of strength and toughness, but also beneficial to corrosion resistance. (3) After deformation, aging treatment was carried out, which not only strengthened precipitation strengthening, but also achieved the steady-state transformation of the unsteady deformation structure through heat treatment.

[0007] The objective of this invention can be achieved through the following methods:

[0008] In a first aspect, the present invention provides a method for preparing a magnesium alloy rod for high-strength, high-toughness, and high-corrosion-resistant intraosseous implants, comprising the following steps:

[0009] S1. The magnesium alloy billet is eccentrically extruded to obtain extruded bars;

[0010] S2. Perform a single-pass high-temperature drawing on the bar to obtain the drawn bar.

[0011] S3. Aging treatment is performed on the drawn bar to obtain the final product.

[0012] As one embodiment of the present invention, in step S1, the preparation process of the magnesium alloy billet includes: casting a magnesium alloy to form a magnesium alloy ingot, performing a solution treatment on the magnesium alloy ingot, adding a lubricant and performing a preheating treatment to obtain the magnesium alloy billet.

[0013] Furthermore, the magnesium alloy includes any one of Mg-Nd-Zn-Zr alloy, Mg-Nd-Zn-Zr-Ag alloy, Mg-Y-RE alloy, Mg-Gd-Zn alloy, and Mg-Gd-Nd-Zn alloy. This invention is based on the composition design of biodegradable medical magnesium alloys, with materials prepared according to mass ratios, and then magnesium alloy ingots obtained through casting technology.

[0014] Furthermore, the solution treatment temperature is 450-550℃, and the time is 6-12 hours. A billet for subsequent deformation processing is cut from the magnesium alloy ingot, and the cut billet is subjected to solution treatment; the billet has a diameter of at least 60mm and a height of at least 100mm.

[0015] Furthermore, the lubricant includes one or more of graphite, glass, and molybdenum disulfide.

[0016] Furthermore, the preheating treatment is performed at a temperature of 300-450℃ for 1-3 hours. In this invention, the solution-treated billet is coated with a suitable lubricant and placed in a resistance furnace for preheating before extrusion.

[0017] As one embodiment of the present invention, in step S1, the extrusion temperature of the eccentric extrusion is 300-450℃, the extrusion speed is 2-6mm / s, and the extrusion ratio is 25-56.

[0018] In one embodiment of the present invention, in step S1, the height of the eccentric region (eccentric circle) of the eccentric extrusion is 1-2 mm, and the eccentricity is 2-8 mm. The eccentricity is set based on the diameter of the extruded bar, and the radius of the eccentric circle is the sum of the eccentricity and the radius of the extruded bar. That is, the eccentric circle increases with the increase of the eccentricity. When the eccentricity is small (less than 2 mm), the shear deformation introduced by the eccentric region is weak, and the effect on microstructure optimization is not obvious. When the eccentricity is large (greater than 8 mm), the shear deformation introduced by the eccentric region is large, which poses a greater challenge to the bearing capacity of the die core and is prone to die breakage during the extrusion process, which is not conducive to large-scale continuous production.

[0019] In some embodiments, the eccentric extrusion is performed using an eccentric extrusion die. The eccentric region of the eccentric extrusion die is designed at the die inlet, the height of the eccentric region is 1-2mm, and the eccentric distance is the distance between the center of the eccentric circular region and the central axis of the die, which is 2-8mm.

[0020] The present invention immediately water-cools or air-cools the eccentrically extruded bar and cuts it to an appropriate length.

[0021] In one embodiment of the present invention, in step S2, the single-pass high-temperature drawing temperature is 400-520℃, and the speed is 10-50 mm / s. The drawing temperature is set based on the phase transformation temperature of the main second-phase particles. Temperatures above the phase transformation temperature will cause the second-phase particles to dissolve in the matrix, while drawing temperatures far below the phase transformation temperature will promote the growth of existing second-phase particles rather than further precipitation from the matrix. Therefore, a temperature slightly below the phase transformation temperature is relatively suitable, as it can promote severe dynamic precipitation, resulting in fine, dispersed second phases and suppressing grain growth at high temperatures. For Mg-Y, Mg-Nd, and Mg-Gd alloys, the phase transformation temperatures of the main second phase are 565℃, 548℃, and 548℃, respectively. Therefore, a drawing temperature of 400-520℃ is more effective in promoting microstructure refinement. The reduction rate of the cross-sectional area during drawing should reach the maximum value under the current temperature and speed conditions.

[0022] This invention employs a single-pass high-temperature drawing process at a temperature slightly below the phase transition temperature, triggering severe dynamic precipitation, resulting in a high-density distribution of the second phase and a reduced average size. Simultaneously, the bar stock after the single-pass high-temperature drawing is immediately water-cooled or air-cooled. Furthermore, the purpose of choosing single-pass high-temperature drawing in this invention is to ensure product quality stability and production efficiency. Using multi-pass high-temperature drawing would lead to decreased product quality stability due to the increased number of processing passes; simultaneously, the increased number of passes would decrease production efficiency and increase energy consumption.

[0023] Furthermore, the diameter of the extruded rod is 8–12 mm; the diameter of the drawn rod is at least 6 mm, to facilitate the subsequent processing and fabrication of devices for intraosseous implants.

[0024] In one embodiment of the present invention, in step S3, the aging treatment temperature is 160-220℃ and the time is 2-8 hours. The aging temperature of magnesium alloys is usually between 175 and 250℃. In order to promote the nucleation of second phase particles rather than their growth, a relatively low aging temperature range of 160-220℃ is selected.

[0025] In some embodiments, the aging process is performed using an oil bath furnace or an electric resistance furnace.

[0026] The purpose of eccentric extrusion and single-pass high-temperature drawing in this invention is to obtain optimized microstructure and mechanical properties. Eccentric extrusion introduces intense shear stress to refine the grains, weaken the texture, and promote the dispersed precipitation of the second phase. The extruded bar has a grain size dGrain ≤ 10 μm, a second-phase particle size dPhase ≤ 2 μm, and a tensile yield strength Rp > 200 MPa. High-temperature single-pass drawing further introduces large plastic deformation to refine the grains, promote the precipitation of fine second phases (nanoscale), and obtain a (near) basal surface texture. After drawing, the bar has a grain size dGrain ≤ 4 μm, a second-phase particle size dPhase ≤ 500 nm, and a tensile yield strength Rp > 330 MPa.

[0027] The main purpose of the aging treatment in this invention is to further promote precipitation strengthening of the alloy material, release the internal stress introduced during deformation, and obtain stable microstructure and properties.

[0028] Secondly, the present invention provides a magnesium alloy rod obtained by the preparation method described above.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. This invention adopts a processing method that combines two deformation methods: eccentric extrusion and single-pass hot drawing. It integrates the advantages of both processes, making the processing method feasible, with fewer steps, simple operation, and low preparation cost.

[0031] 2. This invention achieves grain refinement and fine second-phase dispersion precipitation, and obtains a weak (near) basal texture through a series of processes, namely eccentric extrusion, single-pass hot drawing and aging heat treatment. This significantly improves the strength and toughness of medical biodegradable magnesium alloy. At the same time, the corrosion degradation performance is improved due to the optimization of the microstructure, thus improving the overall performance of the alloy material. The principle of microstructure and performance optimization is as follows: (1) An eccentric extrusion process is adopted. This process is different from the traditional symmetrical extrusion mode, that is, the inlet and outlet are both located on the central axis of the mold and collinear in the vertical direction. Instead, an asymmetrical inlet area with a height of 1-2 mm is designed at the inlet. This area is a circular area, and its center is 2-8 mm away from the central axis of the mold. This process realizes the differential flow of the billet during the extrusion process, which leads to asymmetrical deformation. This asymmetrical deformation introduces severe shear deformation, promotes grain refinement and texture weakening, and is beneficial to improving the strength and toughness of the alloy. (2) The single-pass high-temperature drawing process was further combined. The larger drawing strain and drawing temperature provided favorable conditions for dynamic recrystallization and dynamic precipitation, which further promoted grain refinement and second phase dispersion precipitation, further improved the alloy's strength and toughness, and weakened the adverse effects of galvanic corrosion. In addition, the drawing deformation induced grain rotation, which transformed the recrystallized texture after extrusion into a (near) basal texture, thereby improving its corrosion resistance. (3) After deformation, aging treatment was carried out, which not only strengthened precipitation strengthening, but also achieved the steady-state transformation of the unsteady deformation structure through heat treatment.

[0032] 3. The magnesium alloy rods obtained by this invention have good strength and toughness coordination and high corrosion resistance. For example, after the extrusion, drawing and aging heat treatment processes of this invention, the room temperature yield strength Rp of the medical biodegradable magnesium alloy rods is ≥350MPa, the elongation after fracture A is ≥15%, and the corrosion rate CR in Hanks' simulated body fluid is ≤0.4mm / y. Attached Figure Description

[0033] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0034] Figure 1 This is a top view of the eccentric extrusion die core. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0036] Tensile mechanical properties: Refer to standard GB / T 228.1-2021 Metallic materials, tensile testing—Part 1: Test method at room temperature;

[0037] Biodegradability (corrosion rate): Refer to standard ASTM G31-21 Laboratory Immersion Corrosion Test for Metals.

[0038] Example 1

[0039] This embodiment provides a method for preparing a biodegradable magnesium alloy rod for bone implants that combines high strength, toughness, and corrosion resistance.

[0040] Step 1: Smelt a Mg-Nd-Zn-Zr alloy with the specific composition of Mg-2.8Nd-0.2Zn-0.5Zr (wt.%), and cast ingots with a diameter of ~60mm;

[0041] Step 2: Take a cast billet with a height of ~100mm and perform a solution treatment at 540℃ for 8 hours;

[0042] Step 3: Coat the solution-treated billet evenly with graphite lubricant, then place it in an electric resistance furnace for preheating at 350°C for 1 hour.

[0043] Step 4: Assemble the eccentric extrusion die core. The eccentric zone height is 1mm, the eccentric distance is 2mm, and the preset extrusion temperature is 350℃. Extrusion is performed immediately after removing the preheated billet. The extrusion speed is 2mm / s, the extrusion ratio is 56, and the extruder diameter is ~8mm. The eccentric extrusion die is attached. Figure 1 As shown. The bar stock is water-cooled immediately after extrusion.

[0044] Step 5: Cut the extrusion bar to a suitable length (the length of the bar after drawing should be within the drawing range of the drawing machine). Set the drawing temperature to 480℃. Grind or roll one end of the extrusion bar to a point for threading through the die. Then, operate the equipment to engage the front end of the bar through the die and pull out the bar at a drawing speed of 30mm / s. The diameter of the sheet after drawing is 6.6mm, meaning the drawing deformation is ~47% and the area shrinkage rate is ~32%. The bar is held at a temperature field for 1 minute before being drawn out and then air-cooled.

[0045] Step 6: Place the drawing rod in an oil bath furnace at 200℃ and age it for 2 hours.

[0046] Results: Microstructural characterization (SEM and EBSD observation and analysis) revealed that the average grain size of the rods subjected to the above-mentioned eccentric extrusion, single-pass hot drawing, and final aging treatment was ~2.6 μm. The second-phase particles were diffusely distributed with an average diameter of ~280 nm. Most grains exhibited a c-axis distribution at ~70° to the drawing direction, resulting in a near-basal texture with a maximum texture strength of ~4.8 mrd. Room temperature tensile testing showed that the yield strength Rp of the prepared rods was ~352 MPa, and the elongation after fracture A was ~15%, fully meeting the mechanical performance requirements for magnesium alloys used in bone implants (yield strength greater than 200 MPa, elongation after fracture greater than 10%). Small discs cut from the rods underwent a 21-day corrosion immersion test (in Hanks' solution), and the in vitro corrosion rate was ~0.33 mm / y.

[0047] Example 2

[0048] The preparation method of this embodiment is basically the same as that of embodiment 1, except that the eccentric extrusion mold in step 4 is replaced with a mold with an eccentricity of 4mm.

[0049] Results: Due to the increased eccentricity of the eccentric extrusion die, the asymmetric shear deformation introduced during extrusion further increased, leading to further grain refinement and more intense precipitation of the second phase. SEM characterization revealed that the average grain size of the final sample was ~2.1 μm, and the average size of the second phase particles was ~210 nm. EBSD results showed that the texture of the final sample obtained in this embodiment remained near the basal plane, with a reduced maximum texture intensity of approximately 3.9 mrd. Dog-bone shaped tensile specimens were taken from the bar and subjected to at least three room-temperature tensile tests. The yield strength Rp of the bar was ~385 MPa, and the elongation after fracture A was ~18%. Due to the further refinement of the microstructure, the final corrosion rate shown in the corrosion immersion test was ~0.28 mm / y.

[0050] Example 3

[0051] The preparation method of this embodiment is basically the same as that of embodiment 1, except that the eccentric extrusion mold in step 4 is replaced with a mold with an eccentricity of 8mm.

[0052] Implementation Results: The extrusion die core used in this embodiment has a further increased eccentricity, which means a further expansion of the eccentric region, a further increase in the differential velocity of metal flow, and the introduction of more severe asymmetric shear deformation. SEM characterization and data analysis of the final sample determined that the average grain size and second-phase particle size of the sample were reduced to ~1.6 μm and ~140 nm, respectively. EBSD characterization data of the sample showed that the rods prepared in this embodiment still have a near-basal texture, and the maximum texture intensity of the {0001} pole figure was reduced to 2.9 mrd. Room temperature tensile testing of the rod samples yielded a yield strength Rp of ~433 MPa and an elongation after fracture A of ~25%. A 21-day in vitro corrosion immersion experiment showed that the sample prepared in this embodiment has a slower degradation rate of approximately 0.21 mm / y.

[0053] Example 4

[0054] The preparation method of this embodiment is basically the same as that of embodiment 2, except that the drawing temperature in step 5 is further increased to 510°C.

[0055] Implementation Results: Numerous studies have revealed that the majority of the phase in the modified Mg-2.8Nd-0.2Zn-0.5Zr (wt.%) alloy is Mg. 41 Nd5, as can be seen from the Mg-Nd binary phase diagram, Mg 41 The phase transition temperature of Nd5 is ~548℃. This embodiment further increases the high-temperature drawing temperature compared to Examples 1 and 2, bringing it closer to the 548℃ phase transition temperature, thereby triggering intense dynamic precipitation under large drawing deformation. At such high temperatures, the intense precipitation of particles is accompanied by a significant degree of partial dissolution, resulting in the formation of high-density second-phase particles that are fine and dispersed. Simultaneously, due to the pinning effect of the second-phase particles, recrystallization grain growth at high temperatures is effectively suppressed, ultimately resulting in a microstructure composed of fine grains and high-density fine precipitates. Electron microscopy characterization confirmed that the average grain size of the final sample was ~1.7 μm, and the average size of the second-phase particles was ~160 nm; the microtexture of the sample remained near the basal plane, with the maximum texture intensity reduced to ~2.7 mrd. Room temperature tensile testing of the final sample determined the yield strength Rp of the bar to be ~410 MPa, and the elongation after fracture A to be ~22%. The in vitro corrosion rate of the bar was determined to be ~0.23 mm / y through a 21-day corrosion immersion test (in Hanks' solution).

[0056] Comparative Example 1

[0057] The preparation method of this comparative example is basically the same as that of Example 1, except that the extrusion die in step 4 is replaced with a common concentric die core, that is, the extrusion method is conventional extrusion.

[0058] Results: The lack of asymmetric shear deformation introduced by eccentric extrusion during the extrusion process resulted in severe recrystallization grain growth in the extruded bar, with a significant amount of large second-phase residue and low density of newly precipitated second-phase particles. Due to the influence of microstructure inheritance, the microstructure after high-temperature drawing and aging was far less refined than that prepared in Examples 1, 2, and 3. Characterization results showed that the average grain size of the final sample was ~5 μm, and the average size of the second-phase particles was ~600 nm. Room temperature tensile tests confirmed that its mechanical properties were also far inferior to those of Examples 1, 2, and 3, with a yield strength Rp of only ~315 MPa and an elongation at fracture A of ~12%. Although the deformed texture remained a near-basal texture favorable for corrosion, the increased grain size and large-sized second-phase residue exacerbated galvanic corrosion during the corrosion immersion process, resulting in a faster measured in vitro corrosion rate of ~0.39 mm / y.

[0059] Comparative Example 2

[0060] The preparation method of this comparative example is basically the same as that of Example 1, except that the eccentric extrusion die in step 4 is replaced with a die with an eccentricity of 12 mm.

[0061] Implementation Results: When the die eccentricity is 12mm, the diameter of the eccentric circle is 32mm, which is 53% of the billet diameter. This means the eccentric area is very large, introducing a significant difference in metal flow velocity, placing high demands on the extruder's performance or posing a greater challenge to the extrusion die. Successful fabrication requires extremely low extrusion speeds and very high die load-bearing capacity, which is typically difficult to achieve. In actual processing, fabrication failed, and die breakage occurred.

[0062] Comparative Example 3

[0063] The preparation method of this comparative example is basically the same as that of Example 1, except that the drawing temperature in step 5 is set to 350°C, which is much lower than that of Mg. 41 The phase transition temperature of Nd5 is ~548℃.

[0064] Results: The eccentric extrusion process in step 4 significantly broke up the bulk second phase in the as-cast microstructure and promoted the recrystallization of grains and the dynamic precipitation of the second phase, resulting in a preliminarily refined microstructure. In the subsequent heated drawing process, the reduced drawing temperature did not significantly contribute to further microstructure refinement. SEM observation revealed that the average grain size of the final sample was much larger (~7 μm) than the samples drawn at 480℃ (Examples 1, 2, 3) and 510℃ (Example 4), exhibiting elongated deformed grains rather than the isometric recrystallized grains of Examples 1, 2, 3, and 4. Although the bulk second phase in the as-cast state was broken up and refined during the eccentric extrusion process, the second phase particles inherited from the extrusion state could not undergo partial dissolution at high temperatures during the subsequent heated drawing at 350℃. Instead, they further precipitated and grew, resulting in a final bar material with an average second phase size of ~500 nm. Furthermore, analysis of the EBSD data revealed that low-temperature drawing resulted in more intense grain rotation. While the texture distribution remained near the basal plane, the maximum texture intensity increased to approximately 6.2 mrd. This indicates more pronounced texture strengthening, but the strong near-basal texture cannot guarantee sufficient deformation capacity and will compromise the material's toughness. Room temperature tensile tests showed that the bar material prepared in this comparative example had relatively low mechanical properties, with a yield strength Rp of only approximately 295 MPa and an elongation after fracture A of approximately 8%. Moreover, the non-recrystallized deformed grains imply the presence of a high density of geometrically necessary dislocations (residual local stress), which is detrimental to corrosion. Simultaneously, low grain refinement and large second-phase size both contribute to an accelerated corrosion rate. After 21 days of corrosion immersion testing, the measured in vitro corrosion rate increased to approximately 0.44 mm / y.

[0065] Comparative Example 4

[0066] The preparation method of this comparative example is basically the same as that of Example 1, except that the drawing temperature in step 5 is set to 550°C, that is, the drawing temperature is higher than that of Mg. 41 The phase transition temperature of Nd5 is ~548℃.

[0067] Results: Although the eccentric extrusion treatment before drawing significantly refined the microstructure of the bar, the subsequent high-temperature drawing process (550℃) rapidly coarsens the microstructure. At this drawing temperature, the second-phase particles (Mg...) 41The Nd5 phase undergoes solid solution; under high heat transfer, the grains possess significant growth energy, rapidly coarsening and growing. Furthermore, the dissolution of the second-phase particles removes their pinning effect on grain boundary migration, further promoting grain size increase. SEM results show that the final sample obtained in this embodiment has an average grain size of ~22 μm, with very little of the granular second phase (Mg-Nd phase) remaining, leaving only some larger strip-shaped Zn-Zr phases. EBSD results indicate that the sample still exhibits a near-basal texture, but the texture strength is significantly increased, approximately 12.6 mrd. Room temperature tensile testing results show that the yield strength Rp of the bar obtained in this embodiment is reduced to ~260 MPa, and the elongation after fracture is ~18%. It can be seen that although the strength decreases, the magnitude is not large. This is because although grain boundary strengthening and precipitation strengthening weaken, solid solution strengthening and texture strengthening are simultaneously enhanced. The increase in elongation after fracture is mainly due to the release of some internal stress during high-temperature deformation and the increased alloy strength due to the dissolution of rare earth elements.<c+a> Dislocation activity. The corrosion rate of the sample was measured to be ~0.5 mm / y through Hanks' immersion test. Although texture strengthening is beneficial to the corrosion performance of the bar, the significant coarsening of the grains promotes corrosion overall, and a small amount of large-sized Zn-Zr phase can cause localized corrosion. Therefore, the prepared bar exhibits greater corrosion resistance.

[0068] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a magnesium alloy rod for high-strength, high-toughness, and high-corrosion-resistant intraosseous implants, characterized in that, Includes the following steps: S1. The magnesium alloy billet is eccentrically extruded to obtain extruded bars; S2. Perform a single-pass high-temperature drawing on the bar to obtain the drawn bar. S3. Aging treatment is performed on the drawn bar to obtain the final product.

2. The preparation method according to claim 1, characterized in that, In step S1, the preparation process of the magnesium alloy billet includes: casting a magnesium alloy into a magnesium alloy ingot, performing a solution treatment on the magnesium alloy ingot, adding a lubricant and preheating it to obtain the magnesium alloy billet.

3. The preparation method according to claim 2, characterized in that, The magnesium alloy includes any one of Mg-Nd-Zn-Zr alloy, Mg-Nd-Zn-Zr-Ag alloy, Mg-Y-RE alloy, Mg-Gd-Zn alloy, and Mg-Gd-Nd-Zn alloy.

4. The preparation method according to claim 2, characterized in that, The solution treatment is performed at a temperature of 450-550℃ for 6-12 hours.

5. The preparation method according to claim 2, characterized in that, The lubricant includes one or more of graphite, glass, and molybdenum disulfide; the preheating treatment is performed at a temperature of 300-450°C for 1-3 hours.

6. The preparation method according to claim 1, characterized in that, In step S1, the eccentric extrusion temperature is 300-450℃, the extrusion speed is 2-6mm / s, and the extrusion ratio is 25-56.

7. The preparation method according to claim 1, characterized in that, In step S1, the height of the eccentric zone of the eccentric extrusion is 1-2 mm, and the eccentric distance is 2-8 mm.

8. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the single-pass high-temperature drawing is 400-520℃, and the speed is 10-50mm / s.

9. The preparation method according to claim 1, characterized in that, The diameter of the extruded bar is 8-12 mm; the diameter of the drawn bar is at least 6 mm.

10. A magnesium alloy rod obtained by the preparation method according to any one of claims 1-9.

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