A high-toughness Zn-Mg-Ca-Sr zinc alloy, a preparation method and application thereof

Abstract

The application discloses a high-toughness Zn-Mg-Ca-Sr zinc alloy and a preparation method and application thereof, and is characterized in that: a homogenization treatment is conducted on a cast-state Zn-Mg-Ca-Sr zinc alloy, a boron nitride lubricant is sprayed on the surface of the cast-state Zn-Mg-Ca-Sr zinc alloy and the surface of an inner cavity of a mold, the cast-state Zn-Mg-Ca-Sr zinc alloy is placed in the mold and heated, the extrusion speed of a reciprocating extrusion is controlled in stages, 1-8 pass stepwise variable-flow-speed reciprocating extrusion is realized, and a high-toughness Zn-Mg-Ca-Sr zinc alloy in a stepwise variable-flow-speed control reciprocating extrusion state is obtained. After 8 passes of the variable-flow-speed control reciprocating extrusion, the grain size is reduced by 300% compared with that in the case of constant extrusion speed extrusion, the recrystallized grains are refined to 0.5 microns, the recrystallized grains are round and uniform, the shape of the strengthening phase is round and the distribution is uniform, the tensile strength of the zinc alloy is increased to more than 340 MPa, and the elongation rate is as high as 12%.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable human tissue implant materials technology, specifically relating to a high-strength and tough Zn-Mg-Ca-Sr zinc alloy, its preparation method, and its application. Background Technology

[0002] With advancements in medical technology, medical implants play an indispensable role in treating many diseases. However, traditional implants, such as those made of stainless steel, cobalt alloys, titanium alloys, and polymers, suffer from problems such as requiring secondary surgery for removal or insufficient support strength, negatively impacting patients' physical and mental well-being. Research on biodegradable metallic materials can significantly improve these issues. Among the three most studied biodegradable metals—Fe, Zn, and Mg—pure Zn's standard electrode potential (-0.76V) falls between that of Mg (-2.37V) and Fe (-0.44V), making its degradation rate more suitable for use as a biodegradable implant material. Furthermore, its degradation products can be absorbed or metabolized and excreted by the body, making it a promising biodegradable material. However, cast pure zinc has a tensile strength of only 33.6 MPa and an elongation of 1.2%, exhibiting low mechanical properties that limit its application as a biodegradable implant material. By alloying with different alloying elements, the strength of zinc can be improved while simultaneously altering its corrosion rate.

[0003] Considering the corrosiveness, mechanical properties, and biocompatibility of elements to zinc, the most widely studied alloying elements currently include Mg, Li, Cu, Ca, Sr, and Mn. Under the premise of meeting clinical requirements, Zn-Mg, Zn-Li, and Zn-Cu alloys show the most significant improvement in mechanical properties. Among these, Mg, Ca, and Sr, as essential nutrients for the human body, are the preferred alloying elements. However, alloying typically does not improve the ductility of zinc alloys, and the strength increase is limited. The strength under as-cast conditions does not exceed 200 MPa, and the elongation is often less than 5%, sometimes even leading to a significant decrease in ductility.

[0004] Therefore, one of the most effective methods to simultaneously improve the strength and ductility of alloys is grain refinement. Severe Plastic Deformation (SPD) technology, by introducing large plastic strain into the metal, can achieve nanoscale grain refinement. Techniques such as equal channel angle extrusion, high-pressure torsion, reciprocating extrusion, and laminated rolling have been proven to produce submicron or nanoscale grains in the forming of various metals and alloys. Among these, reciprocating extrusion can effectively eliminate various defects in the original microstructure of the material, improve the distribution and shape of reinforcements, form a uniform equiaxed fine-grained structure, and allow for continuous repeated deformation. As the number of reciprocating extrusion passes increases, the grains in the alloy gradually become finer. As the deformation resistance of the alloy gradually increases, if continuous multi-pass extrusion is performed at a fixed extrusion rate, the flow stress of the alloy becomes large, making deformation through the die increasingly difficult, and subsequent deformation will exacerbate damage to the die. While modular die structures offer flexibility and adaptability, they also present drawbacks such as increased die contact surfaces and difficulty in completely eliminating die gaps. As the number of reciprocating extrusion passes increases, material inevitably flows, accumulates, and is extruded along the die contact surfaces, resulting in surface defects such as "flashes," "burrs," and "cracks" in the extruded parts. Furthermore, severe material flow and accumulation can damage the die, leading to difficulties in reciprocating extrusion forming, significant internal frictional losses, and a substantial increase in forming force. This results in a significant reduction in yield and die lifespan, and may even cause die failure. Studies on the reciprocating extrusion of AZ31 and WE43 magnesium alloys have also revealed that higher extrusion speeds lead to more uneven temperature distribution during deformation, affecting the uniformity of the deformed microstructure. Therefore, in the reciprocating extrusion process, as the number of extrusion passes increases, the material microstructure becomes denser and finer. If a constant extrusion speed is continuously used to obtain a larger cumulative strain, the extrusion pressure will inevitably increase in subsequent reciprocating extrusion processes, making the extrusion process increasingly difficult. This not only increases the forming difficulty but also increases the risk of die damage. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy, its preparation method and application, to solve the technical problems of difficult reciprocating extrusion multi-pass forming of biodegradable zinc alloys, poor uniformity of reciprocating extrusion structure, difficulty in controlling recrystallization grain size, low yield of extruded parts, and limited strength and toughness of extruded structure.

[0006] The present invention adopts the following technical solution:

[0007] A method for preparing a high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy includes the following steps:

[0008] The as-cast Zn-Mg-Ca-Sr zinc alloy is homogenized, and boron nitride lubricant is sprayed on the surface of the as-cast Zn-Mg-Ca-Sr zinc alloy and the inner surface of the mold cavity. The as-cast Zn-Mg-Ca-Sr zinc alloy is placed in the mold and heated. The extrusion speed of the reciprocating extrusion is controlled in stages to achieve 1 to 8 passes of stepped variable flow rate reciprocating extrusion, so as to obtain a high-strength and tough Zn-Mg-Ca-Sr zinc alloy in the stepped variable flow rate controlled reciprocating extrusion state.

[0009] Preferably, the specific steps for 1-8 passes of stepped variable flow rate reciprocating extrusion are as follows:

[0010] The first stage consists of 1 to 3 passes, with the extrusion speed controlled at 0.065 to 0.080 mm / s;

[0011] The second stage consists of 4 to 6 passes, with the extrusion speed controlled at 0.0275 to 0.040 mm / s;

[0012] The third stage consists of 7 to 8 passes, with the extrusion speed controlled at 0.008 to 0.015 mm / s.

[0013] More preferably, the hydraulic press pressure is 80~90T.

[0014] More preferably, after each extrusion, the mold is rotated 180° and kept warm for 10-20 minutes.

[0015] Preferably, the homogenization treatment temperature is 200~220℃, and the holding time is 2.5~3.5h.

[0016] Preferably, the thickness of the boron nitride lubricant is 15~30μm.

[0017] Preferably, the heating temperature is 250~280℃ and the holding time is 0.5~1h.

[0018] Another technical solution of the present invention is a high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy, wherein, by mass percentage, Mg accounts for 0.95%~1.30%, Ca accounts for 0.15%~0.20%, Sr accounts for 0.08%~0.12%, and the remainder is Zn.

[0019] Preferably, the high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy has a strength of 300~350MPa and an elongation of 10%~15%.

[0020] Another technical solution of the present invention is the application of high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy in biodegradable human tissue implant materials.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] A method for preparing high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy employs a "fast-then-slow" extrusion speed distribution. The as-cast Zn-Mg-Ca-Sr zinc alloy undergoes staged variable-flow-rate controlled reciprocating extrusion, resulting in reciprocating extrusion at different speeds in different passes. Through a technical approach where the recrystallized structure of the billet during multi-pass extrusion exhibits a "gradually finer and more fluid" structure according to the number of passes, a gradient extrusion speed distribution with progressively decreasing speeds is achieved. This not only facilitates the effective and complete deformation of the difficult-to-deform biodegradable zinc alloy but also protects the multi-pass reciprocating extrusion die, thereby improving the overall yield and die lifespan. The multi-pass variable-flow-rate controlled reciprocating extrusion deformation technology... The reciprocating extrusion process, characterized by a gradient decrease in speed according to the gradual densification of the extruded billet, causes dynamic recrystallization of the alloy, forming a large number of distortion-free equiaxed crystals. This significantly refines the recrystallized grains to below the micrometer level, resulting in a streamlined distribution of the overall microstructure parallel to the extrusion direction. The original lamellar eutectic structure disappears and transforms into a solid solution state and a secondary phase dispersed within the grains. The secondary reinforcing phase breaks down and distributes along the extrusion direction, with sharp corners becoming rounded. This effectively improves the strength and elongation of the zinc alloy, significantly refines the grain size of the Zn-Mg-Ca-Sr zinc alloy, and improves the size, shape, and distribution of the reinforcing phase. It plays a dual role in grain refinement and secondary phase reinforcement, providing new research ideas for the further development of biodegradable materials applicable to clinical medicine.

[0023] Furthermore, staged reciprocating extrusion speed control was implemented, allowing for reciprocating extrusion at different speeds in different passes. This resulted in a gradient distribution of extrusion speed with progressively decreasing speeds. Specifically, the extrusion speeds for passes 1-3 were controlled at 0.065-0.080 mm / s, for passes 4-6 at 0.0275-0.040 mm / s, and for passes 7-8 at 0.008-0.015 mm / s. This improved the overall extrusion yield by 96% and increased the die life by 150%.

[0024] Furthermore, after completing one extrusion pass, the mold is rotated 180° and kept at a temperature for 10-20 minutes to perform multiple reciprocating extrusion passes, which fully deforms the alloy, effectively improving the grain refinement effect and improving the shape, size and distribution of the reinforcing phase.

[0025] Furthermore, homogenization treatment can eliminate compositional segregation in the microstructure of as-cast Zn-Mg-Ca-Sr zinc alloys and improve the uniformity of the alloy microstructure.

[0026] Furthermore, before placing the as-cast Zn-Mg-Ca-Sr zinc alloy into the mold, spraying a 15-30 μm thick layer of boron nitride lubricant onto the surfaces of the sample and the inner cavity of the mold can prevent adhesion and reduce friction during deformation. Compared with the sample and mold surfaces without lubricant, the lubrication and protection effect is significant.

[0027] Furthermore, Zn has an HCP crystal structure. Heating to 250℃~280℃ and holding for 0.5h~1h can effectively improve the ductility of Zn alloy and prevent cracking of the material during reciprocating extrusion. The melting point of the cast Zn-Mg-Ca-Sr zinc alloy is 362℃. Setting the extrusion temperature to 250℃~280℃ allows α-Zn to undergo dynamic recrystallization during extrusion to form distorted equiaxed crystals, thereby improving the strength and ductility of the alloy.

[0028] A high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy, according to the Zn-Mg, Zn-Ca, and Zn-Sr phase diagrams, will generate α-Zn dendrites and lamellar structures (Zn+Mg2Zn) during solidification. 11 Eutectic structure, massive (Ca,Sr)Zn 13 Intermetallic compounds. When the Mg content is set to 0.95%~1.30%, (Zn + Mg₂Zn) is formed. 11 Eutectic structures can significantly improve the strength and hardness of alloys. The addition of Ca and Sr can refine the grains through modification treatment, further improving the strength of the alloy.

[0029] In summary, the alloy composition, reciprocating extrusion pressure, extrusion temperature, extrusion speed, and coating of this invention are appropriate. Furthermore, the use of variable flow rate controlled extrusion for multi-pass reciprocating extrusion deformation results in a 300% reduction in grain size compared to constant extrusion speed after 8 passes. The recrystallized grains are refined to 0.5 μm, and the recrystallized grains are round and uniform. The strengthening phase is round and uniformly distributed, increasing the tensile strength of the zinc alloy to over 340 MPa and the elongation to as high as 12%.

[0030] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0031] Figure 1 A schematic diagram of a reciprocating extrusion die under variable flow rate conditions;

[0032] Figure 2 A statistical chart of extrusion speed under reciprocating extrusion with variable flow rate control for different extrusion passes;

[0033] Figure 3 Microstructure morphology of Zn-Mg-Ca-Sr zinc alloy under different conditions;

[0034] Figure 4 Statistical diagrams of grain size and grain boundary distribution of Zn-Mg-Ca-Sr zinc alloy under four passes of reciprocating extrusion with variable flow rate control;

[0035] Figure 5 The room temperature tensile curve of Zn-Mg-Ca-Sr zinc alloy after four passes of reciprocating extrusion with variable flow rate control.

[0036] The components include: 1. mold base; 2. pad block; 3. buffer spring; 4. screw; 5. extrusion cylinder; 6. extrusion rod; 7. mold; and 8. fixing sleeve. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0039] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0040] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0041] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0042] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation of these numerical combinations.

[0043] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0044] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0045] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0046] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0047] This invention provides a high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy, its preparation method, and its applications. The method involves step-by-step variable-flow-rate controlled reciprocating extrusion deformation of the as-cast Zn-Mg-Ca-Sr zinc alloy, with the extrusion speed decreasing in stages and adopting a "fast-then-slow" extrusion speed distribution to obtain an ultra-fine-grained reciprocating extruded Zn-Mg-Ca-Sr zinc alloy with high strength and elongation. The as-cast microstructure reveals the presence of matrix α-Zn dendrites and a small amount of lamellar (Zn+Mg2Zn) structures. 11 Eutectic structure, with a small amount of massive (Ca,Sr)Zn 13 Intermetallic compounds, after repeated extrusion, exhibit dynamic recrystallization of the matrix α-Zn phase, resulting in significantly refined grains. The fine recrystallized grains are distributed in a streamlined pattern along the extrusion direction. The lamellar eutectic structure disappears, replaced by a solid solution or dispersed fine precipitates, with a bulk reinforcing phase (Ca,Sr)Zn. 13 The alloy exhibits breakage and rounded corners. Under the combined effects of fine-grain strengthening and second-phase strengthening, the grain size is significantly refined to a few micrometers, increasing the average tensile strength in the extruded state to 340 MPa and the elongation to 12%.

[0048] This invention discloses a method for preparing a high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy. Using as-cast Zn-Mg-Ca-Sr zinc alloy as raw material, a "fast-then-slow" extrusion speed distribution is employed. This achieves a "gradually finer and more fluid" recrystallized structure in the reciprocating extrusion billet during multiple extrusion passes, based on the number of passes. By controlling the extrusion speed in stages, a stepped variable-flow-speed reciprocating extrusion process is achieved, with 1 to 8 passes. The extrusion speed of the multi-pass variable-flow-speed reciprocating extrusion exhibits a gradient-decreasing speed according to the gradual densification process of the extruded billet. The specific steps are as follows:

[0049] S1. The as-cast Zn-Mg-Ca-Sr zinc alloy is subjected to homogenization treatment at 200~220℃ for 2.5~3.5h, and the material is machined to be the same shape as the inner cavity of the mold.

[0050] S2. Using the as-cast Zn-Mg-Ca-Sr zinc alloy obtained in step S1 as raw material, spray a 15~30μm thick boron nitride lubricant on its surface and the inner cavity of the mold, and then place it into the reciprocating extrusion mold according to the shape. Install the upper and lower cylinders of the mold, the extrusion rod, the heating coil, the fixing sleeve and connect it to the reciprocating extrusion support. Use a hydraulic press to pre-compact the reciprocating extrusion mold to eliminate the gap between the billet and the mold.

[0051] S3. Connect the heating coil, thermocouple and temperature control device, wrap the heating coil with refractory cotton, set the heating temperature to 250~280℃, and start heating;

[0052] S4. Heat to 250~280℃, hold for 0.5~1h, set the hydraulic press pressure to 80~90T, start the hydraulic press, and complete the first extrusion at a speed of 0.08mm / s.

[0053] S5. The extrusion rate for the first stage, 1 to 3 passes, is 0.065 to 0.080 mm / s (rapid extrusion, recrystallization and refinement).

[0054] After rotating the mold 180°, heating it to the specified temperature and holding it for 10-20 minutes, start the hydraulic press and complete the second extrusion at a speed of 0.070 mm / s. Then rotate the mold and hold it for 15 minutes, and complete the third extrusion at a speed of 0.065 mm / s.

[0055] S6, the extrusion rate of the second stage, 4 to 6 passes, is 0.0275 to 0.040 mm / s (medium-speed extrusion, recrystallization refinement, grain homogenization).

[0056] Repeat step S5, with the extrusion speeds for the next 4-6 passes being 0.040 mm / s, 0.030 mm / s, and 0.0275 mm / s, respectively.

[0057] S7, the extrusion rate of the third stage 7-8 passes is 0.008~0.015mm / s (slow extrusion, recrystallization and ultrafine processing).

[0058] Repeat step S5, with extrusion speeds of 0.015 mm / s and 0.008 mm / s for the next 7-8 passes, respectively.

[0059] After each extrusion pass, the mold is rotated 180° and kept warm for 10-20 minutes to complete the next reciprocating extrusion pass. The temperature and pressure control of each reciprocating extrusion pass remains consistent, meaning that the process flow of each reciprocating extrusion pass is completely equivalent.

[0060] Preferably, refractory cotton is used to keep the mold warm during the heating and extrusion process.

[0061] S8. Disassemble the reciprocating extrusion die, place the die on the sleeve, start the hydraulic press to extrude the billet, and obtain a stepped variable flow rate controlled reciprocating extruded Zn-Mg-Ca-Sr zinc alloy billet.

[0062] High-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy is obtained by reciprocating extrusion in 1 to 8 passes with stepped variable flow rate control.

[0063] The method of this invention prepares a high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy with the following chemical composition: Zn-Mg-Ca-Sr. By mass percentage, the Zn-Mg-Ca-Sr zinc alloy contains 0.95%~1.30% Mg, 0.15%~0.20% Ca, 0.08%~0.12% Sr, and the remainder is Zn.

[0064] This invention discloses a high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy prepared by a method with appropriate alloy composition, reciprocating extrusion pressure, extrusion temperature, extrusion rate, and coating. A multi-pass reciprocating extrusion deformation process with variable flow rate control is employed. After eight passes of variable flow rate controlled reciprocating extrusion, the grain size is reduced by 300% compared to extrusion at a constant extrusion rate. The recrystallized grains are refined to 0.5 μm, exhibiting round and uniform shape. The reinforcing phase is also round and uniformly distributed. The zinc alloy has a tensile strength of 300-350 MPa and an elongation of 10%-15%, showing broad application prospects in biodegradable human tissue implant materials (orthopedic implants and cardiovascular stents, etc.).

[0065] This invention employs a stepped variable flow rate controlled reciprocating extrusion method to prepare zinc alloys with both high strength and high toughness. During the reciprocating extrusion process, the extrusion speed adopts a "fast initially, then slow, fully flowing" technical approach. This not only improves the yield and forming efficiency of bio-zinc alloys but also extends the service life of the reciprocating extrusion die, thereby accelerating the application of zinc alloys in the field of clinical medical materials. To make the objectives, technical solutions, and advantages of the embodiments of this invention clearer, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. The components of the embodiments of this invention described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0066] Example 1

[0067] As-cast Zn-Mg-Ca-Sr zinc alloy was used as raw material and subjected to homogenization treatment at 210℃ for 3 hours. The alloy was then machined to the same shape as the inner cavity of the mold. A 30μm thick layer of boron nitride lubricant was sprayed onto the alloy surface and the inner cavity of the mold. The alloy was then placed into a reciprocating extrusion mold, and the reciprocating extrusion mold parts were installed and heated to 260℃ and held for 1 hour. The hydraulic press pressure was set to 82T, and the hydraulic press was started to complete the first extrusion at a speed of 0.08mm / s. The mold was then rotated 180° and held for 20 minutes. The hydraulic press was then started to complete the 2nd to 8th extrusions at speeds of 0.070mm / s, 0.065mm / s, 0.040mm / s, 0.030mm / s, 0.0275mm / s, 0.015mm / s, and 0.008mm / s, respectively. After completing the 8th extrusion, the mold was disassembled and demolded to obtain a high-strength and tough Zn-Mg-Ca-Sr zinc alloy obtained by step-variable flow rate control reciprocating extrusion for 8 passes.

[0068] Example 2

[0069] As-cast Zn-Mg-Ca-Sr zinc alloy was used as raw material and subjected to homogenization treatment at 200℃ for 3.5 hours. The alloy was then machined to the same shape as the inner cavity of the mold. A 20μm thick layer of boron nitride lubricant was sprayed onto the alloy surface and the inner cavity of the mold. The alloy was then placed into a reciprocating extrusion mold, and the reciprocating extrusion mold parts were installed and heated to 280℃ and held for 30 minutes. The hydraulic press pressure was set to 80T, and the hydraulic press was started to complete the first extrusion at a speed of 0.08mm / s. The mold was then rotated 180° and held for 15 minutes. The hydraulic press was then started to complete the 2nd to 8th extrusions at speeds of 0.070mm / s, 0.065mm / s, 0.040mm / s, 0.030mm / s, 0.0275mm / s, 0.015mm / s, and 0.008mm / s, respectively. After completing the 8th extrusion, the mold was disassembled and demolded to obtain a high-strength and tough Zn-Mg-Ca-Sr zinc alloy obtained by step-variable flow rate control reciprocating extrusion for 8 passes.

[0070] Example 3

[0071] As-cast Zn-Mg-Ca-Sr zinc alloy was used as raw material and subjected to homogenization treatment at 220℃ for 2.5 hours. The alloy was then machined to the same shape as the inner cavity of the mold. A 15μm thick layer of boron nitride lubricant was sprayed onto the alloy surface and the inner cavity of the mold. The alloy was then placed into a reciprocating extrusion mold, and the reciprocating extrusion mold parts were installed and heated to 250℃ and held for 45 minutes. The hydraulic press pressure was set to 90T, and the hydraulic press was started to complete the first extrusion at a speed of 0.08mm / s. The mold was then rotated 180° and held for 10 minutes. The hydraulic press was then started to complete the 2nd to 8th extrusions at speeds of 0.070mm / s, 0.065mm / s, 0.040mm / s, 0.030mm / s, 0.0275mm / s, 0.015mm / s, and 0.008mm / s, respectively. After completing the 8th extrusion, the mold was disassembled and demolded to obtain a high-strength and tough Zn-Mg-Ca-Sr zinc alloy obtained by step-variable flow rate control reciprocating extrusion for 8 passes.

[0072] Example 4

[0073] As-cast Zn-Mg-Ca-Sr zinc alloy was used as raw material and subjected to homogenization treatment at 215℃ for 2.5h. The alloy was then machined to the same shape as the inner cavity of the mold. A 20μm thick layer of boron nitride lubricant was sprayed onto the alloy surface and the inner cavity of the mold. The alloy was then placed into a reciprocating extrusion mold, and the reciprocating extrusion mold parts were installed and heated to 275℃ and held for 50 minutes. The hydraulic press pressure was set to 84T, and the hydraulic press was started to complete the first extrusion at a speed of 0.08mm / s. The mold was then rotated 180° and held for 18 minutes. The hydraulic press was then started to complete the 2nd to 8th extrusions at speeds of 0.070mm / s, 0.065mm / s, 0.040mm / s, 0.030mm / s, 0.0275mm / s, 0.015mm / s, and 0.008mm / s, respectively. After completing the 8th extrusion, the mold was disassembled and the alloy was demolded to obtain a high-strength and tough Zn-Mg-Ca-Sr zinc alloy obtained by step-variable flow rate control reciprocating extrusion for 8 passes.

[0074] Example 5

[0075] As-cast Zn-Mg-Ca-Sr zinc alloy was used as raw material and subjected to homogenization treatment at 205℃ for 3.5h. The alloy was then machined to the same shape as the inner cavity of the mold. A 25μm thick layer of boron nitride lubricant was sprayed onto the alloy surface and the inner cavity of the mold. The alloy was then placed into a reciprocating extrusion mold, and the reciprocating extrusion mold parts were installed and heated to 270℃ and held for 35 minutes. The hydraulic press pressure was set to 86T, and the hydraulic press was started to complete the first extrusion at a speed of 0.08mm / s. The mold was then rotated 180° and held for 12 minutes. The hydraulic press was then started to complete the 2nd to 8th extrusions at speeds of 0.070mm / s, 0.065mm / s, 0.040mm / s, 0.030mm / s, 0.0275mm / s, 0.015mm / s, and 0.008mm / s, respectively. After completing the 8th extrusion, the mold was disassembled and demolded to obtain a high-strength and tough Zn-Mg-Ca-Sr zinc alloy obtained by step-variable flow rate control reciprocating extrusion for 8 passes.

[0076] Please see Figure 1 This is a schematic diagram of a reciprocating extrusion die under variable flow rate conditions. The reciprocating extrusion die mainly consists of eight parts: a die base 1, a pad 2, a buffer spring 3, a screw 4 for securing the die support, an extrusion cylinder 5, an extrusion rod 6, the die 7, and a fixing sleeve 8. During reciprocating extrusion, the billet is first placed into the die 7 according to its shape, and the two dies are fixed by the fixing sleeve 8. Then, the extrusion rod 6 is inserted from both ends of the die and connected to the die support by screws. After connecting the extrusion rod to the die support, the screw 4 is tightened. Then, the pad 2 and the extrusion cylinder 5 are placed to complete the subsequent extrusion process.

[0077] Please see Figure 2 The extrusion speed statistics under variable flow rate extrusion with different extrusion passes show that as the number of deformation passes increases, the deformation resistance inside the material increases, and the flow stress required for material deformation decreases. Staged control of the extrusion speed can prevent wrinkling, flash, burrs, cracking, and pitting on the sample surface, avoiding severe accumulation and uneven deformation of the extruded billet in the deformation zone, resulting in extruded billets with excellent surface quality and an overall yield increase of 96%. Compared with constant extrusion speed extrusion, variable flow rate reciprocating extrusion increases extrusion efficiency by 65% ​​and also protects the die, increasing its service life by 150%. A comparison table is shown in Table 1.

[0078] Table 1. Yield and die life of constant speed extrusion and stepped speed control reciprocating extrusion.

[0079]

[0080] The improved yield and die life of stepped variable flow rate controlled reciprocating extrusion are mainly due to the following: as the number of extrusion passes increases, the internal structure of the material gradually becomes more homogeneous, defects such as shrinkage cavities and porosity gradually disappear, the matrix grains become finer and spheroidized, and the resistance of the alloy to further deformation gradually increases. At this time, the subsequent reciprocating extrusion deformation of the alloy can be achieved by increasing the extrusion pressure or decreasing the extrusion rate. Considering the labor-saving forming, uniformity of the microstructure and grain size, smaller recrystallization grain control and die life extension, and giving full play to the flow stress of high temperature deformation and the uniformity and homogeneity of recrystallization grains, a stepped variable flow rate controlled reciprocating extrusion technology with increasing extrusion passes is adopted under appropriate extrusion pressure.

[0081] Please see Figure 3 Microstructure of Zn-Mg-Ca-Sr zinc alloy in different states. The microstructure of the as-cast Zn-Mg-Ca-Sr zinc alloy includes a matrix of α-Zn dendrites and a small amount of lamellar structure (Zn+Mg2Zn). 11 Eutectic structure and irregular blocky (Ca,Sr)Zn 13 Intermetallic compounds; after extrusion at 250℃ for 4 passes, the matrix α-Zn phase underwent dynamic recrystallization, resulting in significantly refined grains. The overall structure exhibits streamlined distribution of fine recrystallized grains along the extrusion direction. The lamellar eutectic structure disappears, replaced by a solid solution or dispersed fine precipitates, with a bulk reinforcing phase (Ca,Sr)Zn. 13 The alloy breaks and sharp corners become rounded. Compared to constant-speed reciprocating extrusion, variable-speed reciprocating extrusion results in more complete alloy deformation and a more uniform microstructure distribution.

[0082] Please see Figure 4 Grain size and grain boundary distribution of Zn-Mg-Ca-Sr zinc alloy after four passes of reciprocating extrusion are statistically analyzed. After four passes of reciprocating extrusion at 250℃, the alloy undergoes dynamic recrystallization to form equiaxed grains, with the grain size refined to an average value of 2.2 μm. Large-angle grain boundaries account for 90.1%, and small-angle grain boundaries account for 9.9%, indicating that dynamic recrystallization has occurred sufficiently.

[0083] Please see Figure 5 The room temperature tensile curve of Zn-Mg-Ca-Sr zinc alloy after four reciprocating extrusions at 250℃ is shown. After four reciprocating extrusions at 250℃, the tensile strength of the Zn-Mg-Ca-Sr zinc alloy reaches 340 MPa, and the elongation reaches 12%.

[0084] In summary, this invention provides a high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy, its preparation method, and its applications. By using a stepped variable flow rate controlled reciprocating extrusion large plastic deformation technology, the compositional segregation in the cast Zn-Mg-Ca-Sr zinc alloy can be effectively eliminated, allowing the alloy to undergo full dynamic recrystallization. The recrystallized grain size is significantly refined to submicron, forming a uniform equiaxed fine-grained structure. The strengthening phase is rounded and uniformly distributed, increasing the tensile strength of the zinc alloy to 300~350MPa and the elongation to 10%~15%.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy, characterized in that, Includes the following steps: The as-cast Zn-Mg-Ca-Sr zinc alloy is homogenized, and boron nitride lubricant is sprayed onto the surface of the as-cast Zn-Mg-Ca-Sr zinc alloy and the inner surface of the mold cavity. The as-cast Zn-Mg-Ca-Sr zinc alloy is placed in the mold and heated. The extrusion speed is controlled in stages to achieve 1 to 8 passes of stepped variable flow rate reciprocating extrusion, thereby obtaining a high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy in a stepped variable flow rate controlled reciprocating extrusion state. The specific steps for achieving 1 to 8 passes of stepped variable flow rate reciprocating extrusion are as follows: The first stage consists of 1 to 3 passes, with the extrusion speed controlled at 0.065 to 0.080 mm / s; The second stage consists of 4 to 6 passes, with the extrusion speed controlled at 0.0275 to 0.040 mm / s; The third stage consists of 7 to 8 passes, with the extrusion speed controlled at 0.008 to 0.015 mm / s.

2. The method for preparing high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy according to claim 1, characterized in that, The hydraulic press has a pressure of 80~90T.

3. The method for preparing high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy according to claim 1, characterized in that, After each extrusion cycle, rotate the mold 180° and keep it warm for 10-20 minutes.

4. The method for preparing high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy according to claim 1, characterized in that, The homogenization treatment temperature is 200~220℃, and the holding time is 2.5~3.5h.

5. The method for preparing high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy according to claim 1, characterized in that, The thickness of the boron nitride lubricant is 15~30μm.

6. The method for preparing high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy according to claim 1, characterized in that, The heating temperature is 250~280℃, and the holding time is 0.5~1h.

7. The high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy prepared by the method according to any one of claims 1 to 6, characterized in that, By mass percentage, Mg accounts for 0.95%~1.30%, Ca accounts for 0.15%~0.20%, Sr accounts for 0.08%~0.12%, and the remainder is Zn.

8. The high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy according to claim 7, characterized in that, The high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy has a strength of 300~350MPa and an elongation of 10%~15%.

9. The application of the high-strength and high-toughness Zn-Mg-Ca-Sr zinc alloy according to claim 7 in biodegradable human tissue implant materials.

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