A low-anisotropy degradable zinc alloy and a preparation method and application thereof

Abstract

This invention relates to a low-anisotropy biodegradable zinc alloy, its preparation method, and its applications, relating to the field of biomedical materials, and particularly to the field of zinc alloys. The zinc alloy composition includes: Cu content of 0.4%-1.0%, Mg content of 0.01%-0.1%, microalloying element X content of 0.15%-0.6%, and the remainder being Zn. Through Cu, Mg, Ca, and Sr multi-element alloying, and the synergistic use of low-temperature four-dimensional forging and asynchronous shearing and skew rolling (45°) processes, the zinc alloy prepared achieves a balance of high strength, high plasticity, and extremely low anisotropy. The obtained zinc alloy has a tensile strength of 300-350 MPa and an elongation >45%. The low anisotropy ensures stable and reliable mechanical properties of implantable devices within the body. Combined with the inherent biodegradability of zinc alloys, it has broad application prospects in the field of medical devices.

Description

Technical Field

[0001] This invention belongs to the field of biomedical materials, particularly the field of zinc alloys, and specifically relates to a low anisotropy biodegradable zinc alloy, its preparation method, and its application. Background Technology

[0002] Zinc and its alloys are promising biodegradable implant materials due to their suitable degradation rate, excellent biocompatibility, and good osteogenic capacity. However, zinc and its alloys have a hexagonal close-packed (HCP) crystal structure with a c / a ratio (axial length ratio) of approximately 1.856, which is much higher than the ideal HCP structure of 1.633 and also significantly higher than the c / a ratio of magnesium alloys (approximately 1.624). This high c / a ratio leads to basal slip in zinc alloys. <1120> Easier to activate, while cylindrical slip {1010} <1120> and conical surface slip {1122} <1123> The difference between the critical shear stress (CRSS) and the basal slip is even greater. During conventional rolling, extrusion and other plastic processing, strong basal texture is easily formed (i.e., the (0001) crystal plane of the grain tends to be parallel to the rolling surface).

[0003] Zinc alloys and magnesium alloys exhibit fundamentally different anisotropy. For conventionally rolled pure zinc or high-alloy zinc alloy sheets, the strength in the transverse (TD) direction is typically much higher than that in the rolling (RD) direction; while for magnesium alloys, the strength in the rolling (RD) direction is typically much higher than that in the transverse (TD) direction. This difference stems from the different texture types resulting from the different c / a values. This anisotropy can lead to reduced predictability of the mechanical response of medical devices (such as bone plates) made from sheet metal after implantation. Under complex and variable physiological loads, they may fail prematurely due to weakness in one direction, or cause uneven stress on the repair site, affecting the treatment outcome.

[0004] To reduce the anisotropy of HCP structural metals, Chinese patent CN 116640974 B discloses a method for preparing large structural components with low anisotropy magnesium alloys and a short process. This method achieves reduced anisotropy of magnesium alloys by optimizing alloy composition (elements such as Gd, Y, and Zr) and ring rolling / die forging processes. Chinese patent CN 119120965 B discloses a method for preparing high-strength deformable magnesium alloy sheets with low anisotropy at room temperature. This method achieves low anisotropy of magnesium alloy sheets through hot extrusion and room temperature rolling processes. Chinese patent (ZL202511824523.2) discloses a Zn-Cu-Mg-Ca-Sr alloy system. This system prepares high-strength zinc alloys by adding elements such as Cu (0.3-0.8%), Mg (0.01-0.05%), Ca (0.05-0.1%), and Sr (0.05-0.1%) and using anisotropic rolling processes (0° / 90° reversal). However, it has limitations: firstly, the Ca / Sr content is low (usually <0.15%), making it impossible to form a sufficiently dense second-phase particle (CaZn) during deformation. 13 / SrZn 13 One approach is to effectively pin grain boundaries and control texture; the other is to use only traditional 0° / 90° reversing rolling, which introduces insufficient shear strain to activate non-basal planes in zinc alloys that are usually difficult to initiate.<c+a> Slip system. Summary of the Invention

[0005] The purpose of this invention is to provide a low-anisotropic biodegradable zinc alloy, its preparation method, and its application. Addressing the problem of strong basal plane texture caused by the high c / a value (approximately 1.856) of zinc alloys, this invention employs a synergistic process of low-temperature four-directional cyclic forging and multi-pass composite directional asynchronous rolling to precisely control the microstructure of the zinc alloy. This results in a high-strength deformable zinc alloy with a non-basal plane bimodal texture, ultrafine grain structure, and near isotropy, thus solving the technical problems of high anisotropy and uneven mechanical properties in existing technologies.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A method for preparing a low-anisotropic biodegradable zinc alloy, wherein the zinc alloy comprises Zn, Cu, Mg, and a microalloying element X, wherein the Cu content is 0.4%-1.0%, the Mg content is 0.01%-0.1%, the microalloying element X content is 0.15%-0.6%, X is Ca, Sr, or a mixture of both, and the remainder is Zn; the preparation method includes the following steps:

[0008] (1) Pure zinc ingots, zinc-copper master alloys, zinc-magnesium master alloys, and microalloying element master alloys are smelted under an inert atmosphere to obtain zinc alloy ingots.

[0009] (2) The zinc alloy ingot is homogenized and then air-cooled to room temperature;

[0010] (3) After the homogenization treatment, the zinc alloy ingot is preheated and then subjected to low-temperature four-way cyclic forging. The low-temperature condition is 150-200℃. The four-way cyclic forging is a four-way cyclic deformation mode of 0°, 90°, 45° and 135° to obtain a slab of a set thickness.

[0011] (4) The slab is subjected to multi-pass asynchronous rolling with a reversing direction. The asynchronous rolling process is adopted, wherein the rolling path adopts a cyclic reversing mode of 0°, 90°, 45° and 135° in sequence.

[0012] (5) The rolled sheet is subjected to stress-relief annealing and air-cooled to room temperature to obtain the biodegradable zinc alloy.

[0013] As a further optimization of the above invention, when the microalloying element X is a mixture of Ca and Sr, the Ca content is 0.1%-0.4% and the Sr content is 0.05%-0.2%.

[0014] As a further optimization of the above invention, in step (1), the melting temperature is 520-570℃, the holding time is 3-8 min, the electromagnetic stirring frequency is 800-1200 Hz, the casting temperature is 480-520℃, and the mold preheating temperature is 200-250℃.

[0015] As a further optimization of the above invention, in step (2), homogenization is carried out at 280-320℃ and the heat preservation time is 6-16 h.

[0016] As a further optimization of the above invention, in step (3), the reduction amount in each pass of the four-way cyclic forging is 10-25%, and the cumulative deformation amount is 70-95%.

[0017] As a further optimization of the above invention, in step (4), the speed ratio in the asynchronous rolling process is 1.2-1.5.

[0018] As a further optimization of the above invention, in the asynchronous rolling process, the single-pass reduction is 0.2-0.5mm, the plate is rotated cyclically according to the angle after every 2-4 passes of rolling, and after every 20-40% cumulative deformation, an intermediate annealing treatment is performed at 180-200℃ for 15-25 minutes.

[0019] As a further optimization of the above invention, in step (5), stress-relief annealing is performed at 120-160℃ for 0.2-1 h.

[0020] The present invention also provides a low anisotropy biodegradable zinc alloy, which is prepared by the above preparation method.

[0021] The present invention also provides the application of the above-mentioned low anisotropy biodegradable zinc alloy in the preparation of bioactive medical implants, including orthopedic internal fixation devices, oral implants and implantable stents.

[0022] The beneficial effects of this invention are as follows:

[0023] (1) This invention addresses the high c / a value of zinc alloys by using Cu, Mg, Ca, and Sr multi-element alloying to change the axial length ratio and stacking fault energy, thereby promoting the activation of non-basal plane slip systems and effectively suppressing the formation of strong basal plane textures. Solid solution strengthening is achieved through the solid solution of Cu and trace amounts of Mg. Ca and Sr elements form dispersed second-phase particles (CaZn). 13 、SrZn 13 ), which regulates texture evolution through a particle-induced dynamic recrystallization mechanism.

[0024] (2) This invention introduces multi-oriented twins through low-temperature four-way forging, and combines asynchronous shearing with skew rolling (45°) to achieve dual forced activation.<c+a> The slip system makes the mechanical properties of the material almost identical in the rolling direction RD and the transverse direction TD (IPA<2%), which solves the inherent anisotropy problem of HCP zinc alloy. Low-temperature four-directional cyclic forging is carried out at 150-200℃, which inhibits dynamic recrystallization and promotes deformation-induced grain refinement. Combined with subsequent rolling, an ultrafine grain structure of 0.1-4μm is obtained.

[0025] (3) Through the synergy of the above components and processes, the zinc alloy sheet prepared by the present invention achieves a unity of high strength, high plasticity and extremely low anisotropy; the tensile strength of the zinc alloy obtained by the present invention can reach 300-350MPa, and the elongation is >45%. Its anisotropy index IPA value can be less than 2%, exhibiting near isotropic mechanical behavior.

[0026] (5) The alloying element Cu has antibacterial properties, while Mg, Ca, and Sr are essential elements for the human body and can promote bone formation. Low anisotropy ensures that the mechanical properties of the implanted device are stable and reliable in the body. Combined with the inherent biodegradability of zinc alloy, it has broad application prospects in the fields of orthopedic fixation, oral repair membranes, and cardiovascular stents. Attached Figure Description

[0027] Figure 1 The pole figure and inverse pole figure of the rolled zinc alloy sheet in Example 1 show a non-basal plane bimodal texture, with the peak value deviating from ND by about 25°;

[0028] Figure 2 The diagram shows the Schmidt factor distribution of the rolled zinc alloy sheet in Example 1 when stretched along the RD and TD directions.

[0029] Figure 3 This is a diagram showing the distribution of elastic modulus of the rolled zinc alloy sheet under tension along the RD and TD directions in Example 1.

[0030] Figure 4 The pole figure and inverse pole figure of the rolled zinc alloy sheet in Comparative Example 1 show the strong basal texture characteristics.

[0031] Figure 5 This is the phase diagram for a Zn-Ca binary alloy. Detailed Implementation

[0032] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0033] I. Explanation

[0034] At least one embodiment of the present invention discloses a low-anisotropy, high-strength, deformable, biodegradable zinc alloy comprising the following components in weight percentage:

[0035] Cu: 0.4%-1.0%; Mg: 0.01%-0.1%; Microalloying element X: 0.15%-0.6% (X is selected from Ca, Sr or a mixture of the two), of which Ca: 0.1%-0.4%, Sr: 0.05%-0.2% (when the two are mixed); balance Zn.

[0036] At least one embodiment of the present invention discloses a method for preparing a high-strength, deformable, biodegradable zinc alloy with low anisotropy, comprising the following steps:

[0037] S1. Melting and Casting: According to the alloy composition design, each raw material is prepared, and pure zinc ingots, zinc-copper master alloy, zinc-magnesium master alloy, zinc-calcium master alloy and zinc-strontium master alloy are melted under an inert atmosphere. The melting temperature is 520-570℃, the holding time is 3-8min, the electromagnetic stirring frequency is 800-1200Hz, the casting temperature is 480-520℃, and the mold preheating temperature is 200-250℃ to obtain zinc alloy ingots.

[0038] S2. Homogenization treatment: The zinc alloy ingot obtained in S1 is homogenized at 280-320℃ for 6-16 hours, and then air-cooled to room temperature;

[0039] S3. Low-temperature four-way cyclic forging: The zinc alloy ingot treated by S2 is preheated at 150-200℃ for 1-3 hours, and then subjected to low-temperature four-way cyclic forging. This low-temperature condition is conducive to suppressing dynamic recrystallization and promoting twin formation. At the same time, the four-way cyclic deformation mode of 0°→90°→45°→135° is adopted. The reduction of each pass is controlled at 10-25%, and the cumulative deformation reaches 70-95%, finally obtaining a slab with a thickness of 8-12mm.

[0040] S4. Multi-pass reversing asynchronous rolling: The pre-rolled plate obtained in S3 is subjected to multi-pass reversing asynchronous rolling. This step adopts an asynchronous rolling process with a speed ratio of 1.2-1.5. Shear stress field is generated by the difference in speed between the upper and lower rolls. At the same time, the rolling path adopts a cyclic reversing mode of 0°→90°→45°→135°. The single-pass reduction is controlled within the range of 0.2-0.5mm. After every 2-4 passes, the plate is rotated cyclically according to the above angle. During the rolling process, the initial rolling temperature is maintained at 180-220℃, and the final rolling temperature is controlled at 150-180℃. After every 20-40% cumulative deformation, an intermediate annealing treatment is performed at 180-200℃ for 15-25 minutes.

[0041] S5 stress-relief annealing: The S4 rolled sheet is subjected to stress-relief annealing at 120-160℃ for 0.2-1h, and then air-cooled to room temperature to obtain a high-strength, deformable, biodegradable zinc alloy sheet with low anisotropy.

[0042] The present invention also provides the application of the above-mentioned low anisotropy biodegradable zinc alloy in the preparation of bioactive medical implants, including orthopedic internal fixation devices, oral implants and implantable stents.

[0043] Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products, and all instruments used are conventional instruments known to those skilled in the art.

[0044] II. Methods

[0045] Example 1

[0046] The zinc alloy Zn-0.6Cu-0.03Mg-0.2Ca-0.1Sr in this embodiment has the following elemental mass fractions: Cu 0.6%, Mg 0.03%, Ca 0.2%, Sr 0.1%, with the balance being Zn. The preparation method includes the following steps:

[0047] S1: Melting and Casting: Place the raw material in the graphite crucible of the vacuum induction melting furnace and evacuate to 5×10⁻⁶. -2After Pa, high-purity argon gas is introduced to 0.05 MPa, and the mixture is heated to 560°C to completely melt the raw material. The temperature is maintained for 8 minutes, and a medium-frequency electromagnetic stirrer is started with a frequency of 1000 Hz and stirred for 5 minutes. The melt is then cooled to 500°C and poured into a graphite cylindrical mold (Φ120mm×200mm) preheated to 230°C. The mold is then air-cooled to room temperature to obtain an ingot.

[0048] S2: Homogenization treatment: The ingot is machined to remove the surface oxide scale and defects, resulting in a bar with a diameter of 100mm and a height of 150mm. The bar is placed in a box-type resistance furnace and heated to 310℃ at 5℃ / min under the protection of flowing argon gas. It is held at this temperature for 14 hours and then cooled to 150℃ in the furnace before being removed from the furnace and air-cooled.

[0049] S3: Low-temperature four-directional cyclic forging: First, the bar is upset to a thickness of 60mm along the 0° direction (axial direction), then pressed down by 25% to 45mm along the 90° direction, then pressed down by 20% to 36mm along the 45° direction, and finally pressed down by 15% to 30.6mm along the 135° direction. After completing the first deformation cycle, it is held at 180℃ for 5 minutes, followed by the second round of four-directional cyclic forging: pressing down by 20% along the 0° direction... The thickness is reduced by 20% to 24.5mm, then by 20% to 19.6mm in the 90° direction, 20% to 15.7mm in the 45° direction, and 20% to 12.6mm in the 135° direction. The plate is then held at 180° for 5 minutes. Finally, the plate is forged: 12% to 11.1mm in the 0° direction and 10% to 10mm in the 90° direction, to obtain a slab with a thickness of 10mm and a width of approximately 150mm.

[0050] S4: Multi-pass reversing asynchronous rolling: Composite reversing asynchronous rolling is performed at 200℃ with a speed ratio of 1.3 (upper roll speed 30rpm, lower roll speed 39rpm). The reversing path is as follows: 1st-2nd pass 0° rolling (reduction 1.0mm / pass) → 3rd-4th pass 90° rolling (reduction 0.8mm / pass) → 5th pass 45° rolling (reduction 0.5mm) → 6th pass 135° rolling (reduction 0.5mm) → repeat the above path. After every 30% cumulative deformation, annealing is performed at 200℃ for 20 minutes. The final rolling temperature is 180℃, and the thickness is rolled to 1.0mm.

[0051] S5: Stress-relief annealing: The rolled sheet is placed in a vacuum tube furnace and held at 150°C for 1 hour for stress-relief annealing. Then it is cooled to room temperature with the furnace to obtain the final product.

[0052] The microstructure (EBSD measurement) of Example 1 shows that: the (0001) pole figure exhibits a typical non-basal bimodal texture; the (0001) crystal plane normal deviates from ND by about 25°; the maximum texture intensity is 5.7; the average grain size is 0.85 μm; and the mechanical property test results are: tensile strength in the RD direction is 312 MPa, elongation is 118%; tensile strength in the TD direction is 318 MPa, elongation is 117%; IPA=1.9%.

[0053] Example 2

[0054] In this embodiment, the zinc alloy Zn-0.7Cu-0.04Mg-0.4Ca has the following elemental mass fractions: Cu 0.7%, Mg 0.04%, Ca 0.4%, with the balance being Zn.

[0055] In the preparation method, the temperature in the S2 homogenization treatment is adjusted to 300℃ and held for 16 hours; the temperature in the S3 low-temperature four-way cyclic forging is adjusted to 170℃ and held for 5 minutes; the speed ratio in the S4 multi-pass reversing asynchronous rolling is adjusted to 1.4, and the other process steps and parameters are the same as in Example 1.

[0056] EBSD measurements show that this embodiment exhibits a non-basal bimodal texture, with the (0001) crystal plane normal deviating from ND by approximately 30°, and a maximum texture intensity of 4.1; the average grain size is 0.65 μm. Mechanical properties are as follows: tensile strength in the RD direction is 302 MPa with an elongation of 124%; tensile strength in the TD direction is 311 MPa with an elongation of 109%; IPA = 2.9%.

[0057] Example 3

[0058] In this embodiment, the zinc alloy Zn-0.5Cu-0.02Mg-0.3Sr has the following elemental mass fractions: Cu 0.5%, Mg 0.02%, Sr 0.3%, with the balance being Zn.

[0059] In the preparation method, the temperature in the S3 low-temperature four-way cyclic forging is adjusted to 190℃ and held for 5 minutes; in the S4 multi-pass reversing asynchronous rolling, the speed ratio is adjusted to 1.2, and the other process steps and parameters are the same as in Example 1.

[0060] EBSD measurements show that this embodiment exhibits a non-basal bimodal texture, with the (0001) crystal plane normal deviating from ND by approximately 22°, and a maximum texture intensity of 4.6; the average grain size is 1.3 μm. Mechanical properties are as follows: tensile strength in the RD direction is 305 MPa, with an elongation of 128%; tensile strength in the TD direction is 309 MPa, with an elongation of 114%; IPA = 1.3%.

[0061] Comparative Example 1

[0062] The zinc alloy in this comparative example, Zn-0.6Cu-0.03Mg-0.2Ca-0.1Sr, has the following elemental mass fractions: Cu 0.6%, Mg 0.03%, Ca 0.2%, Sr 0.1%, with the balance being Zn.

[0063] The difference between the preparation process parameters of Comparative Example 1 and Example 1 lies in steps S3 and S4. Specifically, step S3 of this comparative example involves conventional triaxial forging at 200°C (0° / 90° / 180°) with a cumulative deformation of 65%. Step S4 involves conventional alternating rolling at 0°↔90°, without 45° / 135° rolling. The remaining steps are the same as in Example 1.

[0064] EBSD measurements show that the (0001) pole figure indicates a predominantly basal texture, with the (0001) crystal plane normals concentrated near the ND direction, and a maximum texture intensity of 11.5; the average grain size is 2.3 μm. Mechanical properties are as follows: tensile strength in the RD direction is 281 MPa, with an elongation of 108%; tensile strength in the TD direction is 328 MPa, with an elongation of 85%; and its anisotropy index IPA = 14.3.

[0065] Comparative Example 2

[0066] The zinc alloy in this comparative example, Zn-0.6Cu-0.03Mg-0.05Ca-0.05Sr, has the following elemental mass fractions: Cu 0.6%, Mg 0.03%, Ca 0.05%, Sr 0.05%, with the balance being Zn. The preparation method is the same as in Example 1.

[0067] EBSD measurements show that the texture is weakly bimodal, but the peak value is close to the basal plane. The normal of the (0001) crystal plane deviates from ND by about 18°, and the maximum texture intensity is 12.8. The average grain size is 2.1 μm. The mechanical properties are: tensile strength in the RD direction is 282 MPa, and the elongation is 118%; tensile strength in the TD direction is 336 MPa, and the elongation is 97%; its anisotropy index IPA is 19.1%.

[0068] Comparative Example 3

[0069] The zinc alloy in this comparative example, Zn-0.6Cu-0.03Mg-0.2Ca-0.1Sr, has the following elemental mass fractions: Cu 0.6%, Mg 0.03%, Ca 0.2%, Sr 0.1%, with the balance being Zn. The preparation method involves S4 multi-pass synchronous rolling with reversing direction (speed ratio 1.0), with the reversing path the same as in Example 1, and the remaining process parameters also the same as in Example 1.

[0070] EBSD measurements show that the texture is still dominated by strong basal planes, with a maximum texture strength of 8.7; the average grain size is 1.4 μm. The mechanical properties are: tensile strength in the RD direction is 304 MPa, with an elongation of 123%; tensile strength in the TD direction is 337 MPa, with an elongation of 112%; and its anisotropy index IPA is 10.8%.

[0071] Comparative Example 4

[0072] The zinc alloy in this comparative example, Zn-0.6Cu-0.03Mg-0.2Ca-0.1Sr, has the following elemental mass fractions: Cu 0.6%, Mg 0.03%, Ca 0.2%, Sr 0.1%, with the balance being Zn.

[0073] The difference between the preparation process parameters of Comparative Example 4 and Example 1 lies in steps S3 and S4. Specifically, step S3 involves preheating the homogenized bar to 300°C and holding it there for through-firing. Deformation is then performed using a 0° / 90° / 180° orthogonal traditional three-dimensional forging method, with a total deformation of 70%. The forging temperature is controlled at 300°C throughout the process, resulting in a slab with a thickness of 10 mm and a width of approximately 150 mm. Step S4 of Comparative Example 4 involves synchronous rolling at 200°C, with a 0° / 90° reversal path, a final rolling temperature of 180°C, and rolling to a thickness of 1.0 mm. The remaining steps are the same as in Example 1.

[0074] EBSD measurements show that the texture is still dominated by strong basal planes, with a maximum texture strength of 15.7; the average grain size is 5.4 μm. Mechanical properties are as follows: tensile strength in the RD direction is 274 MPa with an elongation of 93%; tensile strength in the TD direction is 337 MPa with an elongation of 72%; and its anisotropy index IPA is 22.9%.

[0075] Comparative Example 5

[0076] The zinc alloy Zn-0.02Mg-0.2Fe in this comparative example has the following elemental mass fractions: Mg 0.02%, Fe 0.2%, and the balance Zn. The preparation method is the same as in Example 1.

[0077] EBSD measurements show that the (0001) pole figure is dominated by a strong basal plane texture, with almost no obvious non-basal plane bimodal texture characteristics. The normals of the (0001) crystal plane are highly concentrated in the ND direction, deviating from the ND angle by only 10°. The texture aggregation is extremely high, with a maximum texture intensity of 17.5. The alloy lacks Ca and Sr refining and orientation-regulating elements, and Fe easily forms a coarse and brittle second phase, severely hindering recrystallization. The average grain size is 5.6 μm, with coarse grains and extremely poor microstructure uniformity. The mechanical properties are: tensile strength in the RD direction is 260 MPa, with an elongation of 32%; tensile strength in the TD direction is 368 MPa, with an elongation of 18%; its anisotropy index IPA = 41.5%.

[0078] Comparative Example 6

[0079] This comparative example is a Zn-0.6Cu-0.03Mg alloy, prepared using the same method as in Example 1.

[0080] EBSD measurements show that only a weakly oriented dispersed texture is formed, and a stable non-basal bimodal texture cannot be formed. The normal of the (0001) crystal plane deviates from the ND angle by about 19°, and the orientation segregation phenomenon is significant. The maximum texture intensity is 10.2. Limited grain refinement is achieved only by Cu and Mg, without the heterogeneous nucleation effect of Ca and Sr, resulting in insufficient grain refinement. The average grain size is 2.0 μm, and a large number of deformed substructures remain in the microstructure. The grain orientation is highly selective, and the texture anisotropy is prominent. The mechanical properties are: tensile strength in the RD direction is 334 MPa, and the elongation is 97%; tensile strength in the TD direction is 398 MPa, and the elongation is 85%; its anisotropy index IPA is 19.0%.

[0081] III. Performance

[0082] (1) Mechanical properties

[0083]

[0084] The mechanical properties of the obtained embodiments and comparative examples are shown in the table below:

[0085]

[0086] As can be seen from the data in Table 1, all three sets of examples, through low-temperature four-directional cyclic forging and multi-angle reversing asynchronous rolling processes, formed typical non-basal plane bimodal textures. The (0001) crystal plane normals deviated from the plate normal ND by 22° to 30°, the texture intensity was only 4.1 to 5.7, the grains were refined to 0.65 to 1.3 μm, and the microstructure was uniform and dense. Comparative Examples 1, 3, and 4 used traditional three-directional forging or synchronous rolling, with strong basal plane textures as the main feature. The (0001) basal plane orientation was concentrated in the ND direction, and the texture intensity increased to 8.7 to 15.7. Comparative Example 2, due to the halved content of trace elements Ca and Sr, although exhibiting weak bimodal characteristics, still had texture peaks close to the basal plane, and the texture intensity reached 12.8. Comparative Example 5 had no Cu, Ca, or Sr alloying elements, and the matrix itself easily formed a strong preferred orientation. In terms of grain size, the comparative examples were generally coarsened to 1.4 to 5.4 μm, much larger than the examples.

[0087] Example 1 uses a reasonable ratio of Cu, Ca, and Sr, resulting in low texture strength, fine grains, and basically equal tensile strength and elongation in the RD and TD directions. Example 2 increases the Cu and Ca content, resulting in a slight increase in texture deflection angle and further refinement of grains, but excessive precipitation of elements slightly increases the difference in plasticity. Example 3 appropriately reduces Cu and Mg and increases Sr content, resulting in the lowest texture strength, IPA of only 1.3%, and the best in-plane mechanical uniformity. Comparative Example 2 significantly reduced the amount of Ca and Sr added, lacking sufficient nucleation sites and grain boundary pinning effects, resulting in a significant increase in texture strength and grain coarsening. The differences in strength and plasticity between RD and TD were significantly widened. Comparative Example 5 contained only trace amounts of Mg and Fe, without the Cu-Ca-Sr composite strengthening and texture regulation effects. The grains were severely coarsened, and the basal texture was extremely strong. Not only was the overall strength matching extremely poor, but the elongation dropped sharply to 32% and 18%, respectively. The plasticity and anisotropy were the worst among all samples, proving that the synergistic addition of Cu, Ca, and Sr is a necessary condition for weakening the basal texture, refining the grains, and achieving near isotropy.

[0088] The embodiment employs a four-dimensional cyclic large deformation process at 0° / 90° / 45° / 135°, resulting in a total deformation far exceeding that of traditional processes. This multi-directional shear deformation effectively breaks down the as-cast microstructure, disrupts the preferred grain orientation, and forms a symmetrical bimodal non-basal texture, thus weakening mechanical anisotropy at its source. Comparative Examples 1 and 4, on the other hand, use conventional three-dimensional orthogonal forging at 0° / 90° / 180°, achieving only two-dimensional planar deformation. This allows for a preference for grain orientation along the direction of force, inducing a strong basal texture. Furthermore, in Comparative Example 4, the forging temperature is raised to 300°C, resulting in sufficient dynamic recrystallization and abnormal grain growth. After the superimposed effect of the strong texture, the IPA reaches as high as 22.9%, further exacerbating the directional deviation between strength and plasticity.

[0089] The examples employ asynchronous rolling with a speed ratio of 1.2–1.4, combined with cyclic reversals of 0° / 90° / 45° / 135°. The shear stress generated by the roll speed difference further optimizes grain orientation and balances the distribution of Schmidt factor and elastic modulus in different directions, resulting in highly similar RD and TD mechanical properties. Comparative Examples 3 and 4 use synchronous rolling (speed ratio 1.0), without additional shear orientation control. Even with the initial four-way forging, they cannot suppress the recovery of basal texture, with IPA rising to over 10.8%. Furthermore, Comparative Example 4 only uses 0° / 90° bidirectional reversal rolling, lacking the coordination of 45° and 135° oblique deformation, further exacerbating texture anisotropy. This demonstrates that the shear orientation control generated by asynchronous rolling, combined with a multi-angle reversal rolling path, can perpetuate the non-basal texture characteristics formed by forging and prevent the reformation of strong basal preferred orientation during rolling.

[0090] The low-temperature four-directional cyclic forging combined with a composite reversing asynchronous rolling process of this invention, along with a high Ca / Sr content (>0.3%), can significantly reduce texture strength and anisotropy index, obtaining a near-isotropic high-strength zinc alloy with ultrafine grains (0.1-1.5μm). Low-temperature four-directional forging is key to obtaining a uniform ultrafine grain structure and weakly textured forgings, while the synergy of 45° skew rolling and asynchronous rolling helps to avoid the formation of strong basal plane textures, and by activating non-basal plane slip to form non-basal plane bimodal textures, the anisotropy of the high-strength, high-ductility zinc alloy is significantly reduced.

[0091] When the total Ca / Sr content is increased from the existing <0.15% to 0.15%-0.6% according to the present invention, based on the Zn-Ca and Zn-Sr binary phase diagram (e.g. Figure 5 As shown), CaZn formed in the alloy 13 and SrZn 13 The volume fraction of the intermetallic second phase increases significantly. These hard and brittle second-phase particles become stress concentration sources during the shear deformation process of low-temperature four-directional cyclic forging and asynchronous rolling, forming local deformation zones with high orientation gradients around them and reducing the non-basal plane.<c+a> The activation threshold of the slip system. According to the particle-induced dynamic recrystallization (PSN) theory, when the particle size and spacing reach the critical conditions (typically particle size > 1 μm, particle spacing < grain size), recrystallization nuclei preferentially nucleate at the particle-matrix interface. These new dynamically recrystallized grains exhibit random orientation characteristics, thereby weakening the original strong basal plane orientation texture. Simultaneously, high-density CaZn... 13 and SrZn 13 The particles effectively pin grain boundaries and subgrain boundaries through the Zener pinning mechanism, inhibiting the growth of recrystallized grains. This ensures that the alloy can maintain an ultrafine grain structure during subsequent multi-pass reversing rolling processes, so the strength increase brought about by grain size refinement can compensate for the loss of texture strengthening contribution due to texture weakening.

[0092] In traditional metallurgical understanding, Ca and Sr are considered microalloying elements (typically <0.1%), mainly used as heterogeneous nucleating agents to refine the microstructure. This invention breaks through this content limit to 0.15%-0.6%. Although the increased volume fraction of the second phase may impair plasticity, the synergistic process of low-temperature four-dimensional forging and asynchronous rolling not only avoids excessive embrittlement but also utilizes high-density particles to achieve PSN-dominated texture randomization, reducing anisotropy by an order of magnitude (IPA <2%) with minimal strength loss (<10%). This combination of high second-phase content, weak texture, and high strength overcomes the bottleneck of balancing composition and performance in biodegradable zinc alloys.

[0093] (2) Microstructure

[0094] Example 1 successfully controlled the texture of zinc alloy sheet to a non-basal plane bimodal texture using low-temperature four-way cyclic forging and 45° / 135° multi-directional asynchronous rolling process. The basal plane normal deviated from the sheet normal (ND) by approximately ±20° and was symmetrically distributed, with a maximum texture strength of only 5.7. In contrast, Comparative Example 1 used traditional three-way forging and 0° / 90° bidirectional rolling to form a strong basal plane texture. Figure 4 The base plane normal is strongly parallel to ND, and the maximum texture strength is as high as 11.5, proving that the composite process of multi-directional forging and oblique rolling can effectively break the preferred orientation and weaken the texture strength.

[0095] The non-basal bimodal texture of Example 1 affects the Schmidt factor (SGF) in the rolling direction (RD) and transverse direction (TD). Figure 2 ) and elastic modulus ( Figure 3 The distribution of the basal plane is highly consistent, eliminating the direction dependence and ultimately exhibiting near-isotropic mechanical behavior (IPA=1.9%). The strong basal plane texture of Comparative Example 1 leads to significant differences in the Schmidt factor and elastic modulus in the RD and TD directions, and the mechanical properties show obvious anisotropy (IPA=14.3%), which clarifies that texture is the core microscopic mechanism for regulating the in-plane anisotropy of zinc alloy plates.

[0096] Comparing the texture strength and anisotropy coefficient of Example 1 and Comparative Example 1, it can be seen that the texture strength is positively correlated with the IPA value (texture strength of Example 1: 5.7 → IPA = 1.9%; texture strength of Comparative Example 1: 11.5 → IPA = 14.3%). This indicates that transforming the texture type from a strong basal plane texture to a low-strength non-basal plane bimodal texture through process optimization is a key technical path for zinc alloy sheets to obtain near-isotropic mechanical properties.

[0097] This conclusion further verifies the process principle of introducing complex stress states through multi-directional deformation to suppress the formation of single textures: Four-directional forging and 45° / 135° rolling, by applying uniform plastic deformation in three-dimensional space, break the preferred growth trend of textures in traditional bidirectional rolling, so that the grain orientation presents a symmetrical distribution, thereby achieving the directional homogenization of micromechanical parameters such as Schmidt factor and elastic modulus, and ultimately manifesting as near isotropic macromechanical properties.

[0098] The embodiments described above are merely examples 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 present invention. 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 modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a low-anisotropic biodegradable zinc alloy, characterized in that, The zinc alloy composition includes Zn, Cu, Mg, and microalloying element X, wherein the Cu content is 0.4%-1.0%, the Mg content is 0.01%-0.1%, the microalloying element X content is 0.15%-0.6%, X is Ca, Sr, or a mixture of both, and the remainder is Zn; the preparation method includes the following steps: (1) Pure zinc ingots, zinc-copper master alloys, zinc-magnesium master alloys, and microalloying element master alloys are smelted under an inert atmosphere to obtain zinc alloy ingots. (2) The zinc alloy ingot is homogenized and then air-cooled to room temperature; (3) After the homogenization treatment, the zinc alloy ingot is preheated and then subjected to low-temperature four-way cyclic forging. The low-temperature condition is 150-200℃. The four-way cyclic forging is a four-way cyclic deformation mode of 0°, 90°, 45° and 135° to obtain a slab of a set thickness. (4) The slab is subjected to multi-pass asynchronous rolling with a reversing direction. The asynchronous rolling process is adopted, wherein the rolling path adopts a cyclic reversing mode of 0°, 90°, 45° and 135° in sequence. (5) The rolled sheet is subjected to stress-relief annealing and air-cooled to room temperature to obtain the biodegradable zinc alloy.

2. The method for preparing a low-anisotropic biodegradable zinc alloy according to claim 1, characterized in that, When the microalloying element X is a mixture of Ca and Sr, the Ca content is 0.1%-0.4% and the Sr content is 0.05%-0.2%.

3. The method for preparing a low-anisotropic biodegradable zinc alloy according to claim 1, characterized in that, In step (1), the melting temperature is 520-570℃, the holding time is 3-8 min, the electromagnetic stirring frequency is 800-1200 Hz, the casting temperature is 480-520℃, and the mold preheating temperature is 200-250℃.

4. The method for preparing a low-anisotropic biodegradable zinc alloy according to claim 1, characterized in that, In step (2), homogenization is carried out at 280-320℃ for 6-16 h.

5. The method for preparing a low-anisotropic biodegradable zinc alloy according to claim 1, characterized in that, In step (3), the reduction in each pass of the four-way cyclic forging is 10-25%, and the cumulative deformation is 70-95%.

6. The method for preparing a low-anisotropic biodegradable zinc alloy according to claim 1, characterized in that, In step (4), the asynchronous rolling process has a speed ratio of 1.2-1.

5.

7. The method for preparing a low-anisotropic biodegradable zinc alloy according to claim 6, characterized in that, In the asynchronous rolling process, the reduction per pass is 0.2-0.5 mm. After every 2-4 passes of rolling, the plate is rotated cyclically at an angle. After every 20-40% cumulative deformation, an intermediate annealing treatment is performed at 180-200℃ for 15-25 minutes.

8. The method for preparing a low-anisotropic biodegradable zinc alloy according to claim 1, characterized in that, In step (5), stress-relief annealing is carried out at 120-160℃ for 0.2-1 h.

9. A biodegradable zinc alloy with low anisotropy, characterized in that, It is prepared by the method for preparing low anisotropy biodegradable zinc alloy as described in any one of claims 1-8.

10. The application of the low anisotropy biodegradable zinc alloy as described in claim 9 in the preparation of bioactive medical implantable devices, including orthopedic internal fixation devices, oral implantable devices, and implantable stent devices.

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