Soluble magnesium alloy rod capable of enhancing elongation and preparation method of soluble magnesium alloy rod

Abstract

The invention belongs to the technical field of soluble magnesium alloy rods, and discloses a soluble magnesium alloy rod with enhanced elongation, and the magnesium alloy rod comprises the following chemical components in percentage by mass: 1.5%-14.5% of Gd element, 0.5%-4.0% of Y element, 0.1%-2.5% of Zn element, 0.2%-0.5% of Zr element, 0.01%-0.5% of Li element, 0.01%-0.6% of Ni element, 0.01%-0.5% of Ga element, 0.01%-0.5% of In element, 0.1%-2.0% of Cu element and the balance of Mg element. In component design, various elements are scientifically proportioned, the proportion of Gd to Y and the proportion of Zn to Zr are just right, specific elements are added to form a composite structure, the ductility is improved, the dissolution rate and strength are balanced by means of the Cu element, in the performance aspect, dissolution is accelerated at the high temperature of 200 DEG C, the dissolution rate is increased by 10%-15% compared with the room temperature, the degradation period can be shortened, a dissolved product is fine and uniform, and the degradation rate is high. The biocompatibility and environmental friendliness are excellent, the application field is wide, and degradable medical instruments are covered.

Description

Technical Field

[0001] This invention belongs to the technical field of soluble magnesium alloy rods, specifically a soluble magnesium alloy rod with enhanced elongation and its preparation method. Background Technology

[0002] A method using magnesium as a matrix, through specific alloying design (such as adding rare earth elements, low-melting-point metals, or micro-alloying elements) and microstructure control (such as nanocrystals or bimodal grain structures), maintains a controllable dissolution rate (typically greater than or equal to 0.5 g / (cm³)) in an aqueous medium. 2 While simultaneously increasing elongation to 1.5-3 times that of traditional magnesium alloys (greater than or equal to 25%-40%), rod-shaped materials are produced. Currently, the preparation of soluble magnesium alloy rods with enhanced elongation faces multiple challenges: In material design, while rare earth elements can increase elongation, they reduce the dissolution rate; low alloying makes it difficult to achieve uniform and refined grains; and the synergistic effect of multiple elements lacks a quantitative model, relying on trial and error optimization. In process control, heat treatment parameters are sensitive; homogenization treatment easily leads to grain coarsening; aging treatment has a narrow window; deformation processes such as extrusion deformation are prone to cracking; differential rolling equipment is complex and easily leads to plate warping; and there is an inverse correlation between dissolution performance and mechanical properties. Regarding equipment compatibility, oxidation control in smelting equipment conflicts with environmental protection requirements; heat treatment equipment lacks uniformity; and deformation equipment has limited tonnage and short die life, resulting in high costs. Furthermore, existing standards only focus on static mechanical properties and lack dynamic evaluation systems for indicators such as dissolution rate and corrosion uniformity, leading to discrepancies between laboratory performance and actual service behavior, increasing the risk of industrial applications. Summary of the Invention

[0003] The purpose of this invention is to provide a soluble magnesium alloy rod with enhanced elongation and its preparation method, so as to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a soluble magnesium alloy rod with enhanced elongation, wherein the chemical composition of the magnesium alloy rod comprises, by mass percentage: 1.5%–14.5% Gd, 0.5%–4.0% Y, 0.1%–2.5% Zn, 0.2%–0.5% Zr, 0.01%–0.5% Li, 0.01%–0.6% Ni, 0.01%–0.5% Ga, 0.01%–0.5% In, 0.1%–2.0% Cu, with the balance being Mg. Preferably, the mass ratio of Gd to Y is 2:1 to 5:1, and the mass ratio of Zn to Zr is 1:1 to 5:1; the total mass percentage of Li, Ni, Ga, and In is no more than 1.5%, and the mass ratio of Ni:Ga:In is 2:1:1 to 4:1:1; the Cu element is used to regulate the balance between dissolution rate and strength.

[0005] Preferably, the microstructure of the magnesium alloy rod is characterized by: equiaxed grains with a size of 10-20 μm; uniform distribution of the Gd / Y solid solution phase in the matrix; and nanoscale Ni / Ga / In low-melting-point eutectic phase, discontinuously distributed at the grain boundaries, accounting for 2%-5% of the total volume, forming a composite structure of "intragranular strengthening + grain boundary weakening".

[0006] Preferably, the magnesium alloy rod exhibits excellent accelerated dissolution characteristics at a high temperature of 200℃, with a dissolution rate 10% to 15% higher than that at room temperature, effectively shortening the degradation cycle under high-temperature conditions. The dissolution products are mainly composite oxides of Mg(OH)2, Gd2O3, Y2O3, NiO, Ga2O3, and In2O3, with fine and uniform particles and a median particle size D50 of less than or equal to 50μm, which can avoid the deposition of large particles and improve biocompatibility or environmental friendliness.

[0007] Preferably, the magnesium alloy rod is used in biodegradable medical devices, temporary structural components, or 3C product casings; wherein, biodegradable medical devices include cardiovascular stents and bone fixation devices, temporary structural components include oil extraction tools and geological exploration equipment, and 3C product casings include mobile phone frames and computer frames.

[0008] Preferably, the specific steps of this preparation method are as follows: S1: Raw material pretreatment: Pure Mg, pure Zn, Mg-Gd master alloy, Mg-Y master alloy, and Mg-Zr master alloy are preheated at 120–150℃ for 4 hours under dry air or nitrogen protection to remove moisture and adsorbed gases; after preheating, the surface finish Ra of the raw materials is less than or equal to 0.8 μm, and the ratio error between the elemental metal and the master alloy is less than or equal to ±0.5 wt.%. S2: Melting: Under the protection of a mixed gas with a CO2 to SF5 volume ratio of 150:1, the pretreated raw materials are added in batches to a crucible resistance furnace and heated to 730 to 760°C at a rate of 10 to 15°C / min for 60 min. During the melting process, the mixture is mechanically stirred at a speed of 50 to 100 r / min for 10 min, with the stirring direction alternating between clockwise and counterclockwise to ensure compositional uniformity. The melt temperature is monitored in real time during the melting process, and the fluctuation range is less than or equal to ±5°C. S3: Refining: Add covering agent and refining agent, and let stand at 760℃ for 40 min; during the standing period, use an argon degassing device to blow the melt, with an argon flow rate of 5-10 L / min, to remove inclusions and hydrogen; after refining, the hydrogen content in the melt is less than or equal to 0.15 mL / 100 g, and the inclusion size is less than or equal to 20 μm; S4: Casting: The refined melt is poured at 700℃ into a steel mold preheated to 200-300℃. The inner wall of the steel mold is coated with boron nitride release agent. The casting process adopts a semi-continuous casting process, with a billet pulling speed of 50-100mm / min and a cooling water flow rate of 20-50L / min, forming a semi-continuous ingot with a diameter of 100-200mm. The ingot surface is free of cold shuts and cracks, and the microstructure density is greater than or equal to 99.5%. S5: Homogenization treatment: Place the ingot in a box-type resistance furnace and hold it at 400-520℃ for 24-72 hours. During the holding period, turn the ingot over every 12 hours to promote temperature uniformity. After the holding period, quench it with water or air to room temperature. The quenching transfer time is less than or equal to 15 seconds. After homogenization treatment, the dendrite spacing of the ingot is less than or equal to 10 μm and the elemental segregation is less than or equal to 1.2. S6: Hot extrusion forming: After homogenization, the ingot is stripped of its outer skin, and the end defects are removed. The ingot is then cut to the required length. The billet and the extrusion die are heated simultaneously to 350–450℃ and held for 30–60 min. Forward extrusion is carried out under the conditions of an extrusion ratio of 8–25:1 and an extrusion speed of 0.1–20 m / min. The extrusion barrel temperature is 300–400℃, and the die preheating temperature is 250–350℃. The diameter of the extruded bar is 10–50 mm, the surface roughness Ra is less than or equal to 0.4 μm, and the straightness error is less than or equal to 0.5 mm / m. S7: Aging treatment: Place the extruded bar in an aging furnace and keep it at 175℃ for 64 hours. During the aging process, dry air is circulated to prevent oxidation. After aging, the tensile strength of the bar increases by 10% to 15%, the elongation decreases by no more than 5%, and the hardness value is stable at HV80 to 100.

[0009] Preferably, the covering agent is a MgCl2-KCl-NaCl system, wherein MgCl2 accounts for 40%–60%, KCl accounts for 20%–40%, and NaCl accounts for 10%–30%; the refining agent is a MgCl2-BaC2-CaF2 system, wherein MgCl2 accounts for 50%–70%, BaC2 accounts for 20%–30%, and CaF2 accounts for 10%–20%.

[0010] Preferably, in the hot extrusion molding step S6, the billet and the mold are heated simultaneously to 350-450°C, the extrusion ratio is 12:1-20:1, and the extrusion speed is 1-10 m / min; the diameter of the extruded bar is 10-50 mm, and the surface roughness Ra is less than or equal to 0.8 μm.

[0011] Preferably, in the aging treatment step S7, the aging temperature is 175℃ and the aging time is 64 hours; after aging, the tensile strength of the bar increases by 10% to 15%, and the elongation decreases by no more than 5%. The beneficial effects of this invention are as follows: 1. This invention achieves its goals through a scientifically designed composition with a perfect balance of Gd and Y, and Zn and Zr ratios. The addition of specific elements creates a composite structure that enhances elongation. Furthermore, Cu is used to balance the dissolution rate and strength. In terms of performance, it accelerates dissolution at 200°C, improving performance by 10%-15% compared to room temperature, shortening the degradation cycle. The dissolved products are fine and uniform, exhibiting excellent biocompatibility and environmental friendliness. Its applications are wide-ranging, covering biodegradable medical devices, temporary structural components, and 3C product casings. The manufacturing process is also highly refined, with strict raw material pretreatment and precise control of parameters in melting and refining steps to ensure uniform composition and structure. 2. This invention achieves precise removal of moisture and gases during raw material pretreatment by preheating at specific temperatures and environments, ensuring surface smoothness and proportioning accuracy, thus laying the foundation for high-quality alloys. In the smelting process, under the protection of a specific mixed gas, the heating rate, temperature, and stirring method are strictly controlled to ensure uniform composition and stable temperature. During refining, specific reagents are added and argon gas is used to effectively remove inclusions and hydrogen, improving melt purity. The casting process employs a semi-continuous casting technique, precisely controlling temperature, speed, and flow rate to ensure high ingot quality. Homogenization treatment, through reasonable heat preservation, turning, and rapid quenching, improves the ingot microstructure. Hot extrusion molding precisely controls heating and extrusion parameters, resulting in high dimensional accuracy and good surface quality in the bars. Aging treatment, performed under specific conditions, significantly improves the tensile strength of the bars while controlling the reduction in elongation and stabilizing hardness values, meeting the stringent performance requirements of alloy bars in various fields. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the preparation method of the soluble magnesium alloy rod of the present invention. Detailed Implementation

[0013] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] like Figure 1 As shown, this embodiment of the invention provides a soluble magnesium alloy rod with enhanced elongation. The chemical composition of the magnesium alloy rod, by mass percentage, includes: 1.5%–14.5% Gd, 0.5%–4.0% Y, 0.1%–2.5% Zn, 0.2%–0.5% Zr, 0.01%–0.5% Li, 0.01%–0.6% Ni, 0.01%–0.5% Ga, 0.01%–0.5% In, 0.1%–2.0% Cu, with the balance being Mg. The magnesium alloy rod has an elongation of ≥20%, a tensile strength of ≥300 MPa, and a dissolution rate of ≥50 mg / (cm³) in a 1 wt.% KCl solution at room temperature. 2 ·h), the elongation retention rate at 200℃ is greater than or equal to 80%.

[0015] The mass ratio of Gd to Y is 2:1 to 5:1, and the mass ratio of Zn to Zr is 1:1 to 5:1. The total mass percentage of Li, Ni, Ga, and In is no more than 1.5%, and the mass ratio of Ni:Ga:In is 2:1:1 to 4:1:1. Cu is used to regulate the balance between dissolution rate and strength.

[0016] The microstructure of the magnesium alloy rod is characterized by: equiaxed grains with a size of 10-20 μm; uniform distribution of Gd / Y solid solution phase in the matrix; and nanoscale (50-200 nm) Ni / Ga / In low-melting-point eutectic phase distributed discontinuously at grain boundaries, accounting for 2%-5% of the total volume, forming a composite structure of "intragranular strengthening + grain boundary weakening".

[0017] The equiaxed grains are of moderate size, which improves the strength and toughness of the material; the Gd / Y solid solution phase is evenly distributed, which strengthens the matrix; the nanoscale low-melting-point eutectic phase is discontinuously distributed at the grain boundaries, forming a "grain boundary strengthening + grain boundary weakening" structure, which not only enhances the material properties, but also optimizes its processing and performance.

[0018] The magnesium alloy rod exhibits excellent accelerated dissolution characteristics at a high temperature of 200℃, with a dissolution rate 10% to 15% higher than that at room temperature. This effectively shortens the degradation cycle under high-temperature conditions. The dissolution products are mainly composite oxides of Mg(OH)2, Gd2O3, Y2O3, NiO, Ga2O3, and In2O3. The particles are fine and uniform, with a median particle size D50 of less than or equal to 50μm, which can avoid the deposition of large particles and improve biocompatibility and environmental friendliness.

[0019] The magnesium alloy rod exhibits significant advantages at 200℃. Its accelerated dissolution characteristics are excellent, with a dissolution rate 10%-15% higher than at room temperature, significantly shortening the degradation cycle under high-temperature conditions and meeting the time-sensitive requirements of specific scenarios. Furthermore, the dissolution products are multiple composite oxides with fine and uniform particles, and a median particle size D50 of less than or equal to 50μm. This characteristic effectively prevents the deposition of large particles, significantly improving biocompatibility and environmental friendliness whether applied in the biomedical field or in the natural environment, reducing potential adverse impacts on organisms or the ecological environment, demonstrating promising application prospects and practical value.

[0020] The magnesium alloy rod is used in biodegradable medical devices, temporary structural components, or 3C product casings; the biodegradable medical devices include cardiovascular stents and bone fixation devices, the temporary structural components include oil extraction tools and geological exploration equipment, and the 3C product casings include mobile phone frames and computer frames.

[0021] In the field of biodegradable medical devices, they are used in cardiovascular stents and bone fixators, whose biodegradable properties can avoid secondary surgery for removal and reduce patient suffering; as temporary structural components, they are used in oil extraction tools and geological exploration equipment, which can naturally degrade after completing their mission, reducing long-term occupation and pollution of the environment; in the 3C product field, they are made into the frames of mobile phones and computers, which not only have a certain strength, but can also naturally degrade after the product is scrapped, reducing the difficulty of electronic waste disposal, balancing performance and environmental protection, and providing high-quality and sustainable material solutions for multiple industries.

[0022] The specific steps of this preparation method are as follows: S1: Raw material pretreatment: Pure Mg (purity ≥ 99.95%), pure Zn (purity ≥ 99.99%), Mg-Gd master alloy (Gd content 20%–30%), Mg-Y master alloy (Y content 15%–25%), and Mg-Zr master alloy (Zr content 30%–50%) are preheated at 120–150℃ for 4 hours under dry air or nitrogen protection to remove moisture and adsorbed gases; after preheating, the surface finish Ra of the raw materials is less than or equal to 0.8 μm, and the ratio error between the elemental metal and the master alloy is less than or equal to ±0.5 wt.%. S2: Melting: Under the protection of a mixed gas with a CO2 to SF5 volume ratio of 150:1, the pretreated raw materials are added in batches to a crucible resistance furnace and heated to 730 to 760°C at a rate of 10 to 15°C / min for 60 min. During the melting process, the mixture is mechanically stirred at a speed of 50 to 100 r / min for 10 min, with the stirring direction alternating between clockwise and counterclockwise to ensure compositional uniformity. The melt temperature is monitored in real time during the melting process, and the fluctuation range is less than or equal to ±5°C. S3: Refining: Add covering agent (MgCl2Cl5 or MgCO3, amount is 0.5%~1.0% of the total mass of melt), let stand at 760℃ for 40min; during the standing period, use an argon degassing device to blow the melt, the argon flow rate is 5~10L / min, to remove inclusions and hydrogen; after refining, the hydrogen content in the melt is less than or equal to 0.15mL / 100g, and the inclusion size is less than or equal to 20μm; 2-KCl-NaCl system, mass ratio 4:3:3) and refining agent (C S4: Casting: The refined melt is poured at 700℃ into a steel mold preheated to 200-300℃. The inner wall of the steel mold is coated with boron nitride release agent. The casting process adopts a semi-continuous casting process, with a billet pulling speed of 50-100mm / min and a cooling water flow rate of 20-50L / min, forming a semi-continuous ingot with a diameter of 100-200mm. The ingot surface is free of cold shuts and cracks, and the microstructure density is greater than or equal to 99.5%. S5: Homogenization treatment: Place the ingot in a box-type resistance furnace and hold it at 400-520℃ for 24-72 hours. During the holding period, turn the ingot over every 12 hours to promote temperature uniformity. After the holding period, quench it with water (water temperature 20-30℃) or air cool it (air speed 5-10m / s) to room temperature. The quenching transfer time should be less than or equal to 15 seconds. After homogenization treatment, the dendrite spacing of the ingot should be less than or equal to 10μm and the elemental segregation should be less than or equal to 1.2. S6: Hot extrusion forming: After homogenization, the ingot is stripped of its outer skin, and the end defects are removed. The ingot is then cut to the required length. The billet and the extrusion die are heated simultaneously to 350–450℃ and held for 30–60 min. Forward extrusion is carried out under the conditions of an extrusion ratio of 8–25:1 and an extrusion speed of 0.1–20 m / min. The extrusion barrel temperature is 300–400℃, and the die preheating temperature is 250–350℃. The diameter of the extruded bar is 10–50 mm, the surface roughness Ra is less than or equal to 0.4 μm, and the straightness error is less than or equal to 0.5 mm / m. S7: Aging treatment: Place the extruded bar in an aging furnace and keep it at 175℃ for 64 hours. During the aging process, dry air is circulated to prevent oxidation. After aging, the tensile strength of the bar increases by 10% to 15%, the elongation decreases by no more than 5%, and the hardness value is stable at HV80 to 100.

[0023] The covering agent is a MgCl2-KCl-NaCl system, wherein MgCl2 accounts for 40%–60%, KCl accounts for 20%–40%, and NaCl accounts for 10%–30%; the refining agent is a MgCl2-BaC2-CaF2 system, wherein MgCl2 accounts for 50%–70%, BaC2 accounts for 20%–30%, and CaF2 accounts for 10%–20%.

[0024] In the hot extrusion molding step of S6, the billet and the mold are heated simultaneously to 350-450°C, the extrusion ratio is 12:1-20:1, and the extrusion speed is 1-10 m / min; the diameter of the extruded bar is 10-50 mm, and the surface roughness Ra is less than or equal to 0.8 μm.

[0025] Simultaneous heating of the billet and die to a suitable temperature range creates favorable conditions for extrusion. A reasonable extrusion ratio and speed ensure sufficient material deformation and uniform flow. The diameter of the extruded bar is precisely controllable, meeting diverse size requirements. Surface roughness is as low as Ra ≤ 0.8μm, with high smoothness, reducing subsequent processing steps and improving production efficiency and product quality.

[0026] In the aging process of step S7, the aging temperature is 175°C and the aging time is 64 hours. After aging, the tensile strength of the bar increases by 10% to 15%, and the elongation decreases by no more than 5%.

[0027] The aging treatment process offers significant advantages. Aging the bars at 175℃ for 64 hours allows for precise control of the material's internal microstructure. This treatment significantly increases the tensile strength of the bars by 10%-15%, enhancing load-bearing capacity and durability; simultaneously, the elongation decreases by no more than 5%, effectively optimizing mechanical properties while maintaining a certain level of plasticity, thus improving the overall product quality and reliability.

[0028] Example 1: A soluble magnesium alloy rod with enhanced elongation and its preparation Chemical composition (mass percentage) of magnesium alloy rod: 8.0% Gd, 2.0% Y (Gd:Y=4:1), 1.0% Zn, 0.3% Zr (Zn:Zr≈3.3:1), 0.2% Li, 0.2% Ni, 0.1% Ga, 0.1% In (Ni:Ga:In=2:1:1, total percentage 0.4%), 1.0% Cu, with the balance being Mg.

[0029] Microstructure characteristics: The grains are equiaxed with a size of 15 μm; the Gd / Y solid solution phase is uniformly distributed in the matrix; the Ni / Ga / In low-melting-point eutectic phase is nanoscale (average particle size 80 nm), discontinuously distributed at the grain boundaries, accounting for 3.5% of the total volume, forming a "grain strengthening + grain boundary weakening" structure.

[0030] High-temperature solubility: The solubility rate at 200℃ is 12% higher than that at room temperature; the solubility products are composite oxides of Mg(OH)2, Gd2O3, Y2O3, NiO, Ga2O3, and In2O3, with a median particle size D50 of 35μm.

[0031] Application areas: Cardiovascular stents (biodegradable medical devices).

[0032] Preparation method: S1 raw material pretreatment: pure Mg, pure Zn, Mg-Gd (25%Gd), Mg-Y (20%Y), and Mg-Zr (30%Zr) master alloys were preheated at 130℃ for 4 hours, protected with dry air, with a surface finish Ra=0.6μm and a proportioning error of ±0.3wt.%.

[0033] S2 smelting: CO2 to SF6 volume ratio 150:1, heating rate 12℃ / min to 750℃, smelting for 60min, stirring speed 80r / min (clockwise / counterclockwise alternating), temperature fluctuation ±3℃.

[0034] S3 Refining: Covering agent (MgCl2 50%, KCl 30%, NaCl 20%) and refining agent (MgCl2 60%, BaC2 25%, CaF2 15%), stand at 760℃ for 40 min, argon flow rate 8 L / min, hydrogen content less than or equal to 0.12 mL / 100 g, inclusion size less than or equal to 15 μm.

[0035] S4 casting: Pour at 700℃ into a preheated 250℃ steel mold, semi-continuous casting, billet pulling speed 80mm / min, cooling water flow rate 35L / min, ingot diameter 150mm, no surface defects, density 99.8%.

[0036] S5 homogenization treatment: heat treatment at 450℃ for 48h, ingot flipped every 12h, water quenched (transfer time 10s), dendrite spacing 8μm, segregation 1.1.

[0037] S6 Hot Extrusion Molding: The billet and die are heated to 400℃ and held for 45 min. The extrusion ratio is 15:1, the speed is 5 m / min, the extrusion cylinder temperature is 350℃, the die is preheated to 300℃, the bar diameter is 30 mm, the surface roughness Ra=0.5 μm, and the straightness error is 0.3 mm / m.

[0038] S7 aging treatment: heat preservation at 175℃ for 64 hours, dry air circulation, tensile strength increased by 12%, elongation decreased by 3%, hardness HV90.

[0039] Example 2: A soluble magnesium alloy rod with enhanced elongation and its preparation Chemical composition of magnesium alloy rod (mass percentage): Gd 12.0%, Y 3.0% (Gd:Y=4:1), Zn 1.5%, Zr 0.4% (Zn:Zr≈3.75:1), Li 0.3%, Ni 0.3%, Ga 0.15%, In 0.15% (Ni:Ga:In=2:1:1, total percentage 0.6%), Cu 1.5%, balance Mg.

[0040] Microstructure characteristics: The grains are equiaxed with a size of 18 μm; the Gd / Y solid solution phase is uniformly distributed in the matrix; the Ni / Ga / In low-melting-point eutectic phase is nanoscale (average particle size 100 nm), discontinuously distributed at the grain boundaries, accounting for 4.0% of the total volume, forming a "grain strengthening + grain boundary weakening" structure.

[0041] High-temperature solubility: The solubility rate at 200℃ is 14% higher than that at room temperature; the solubility products are composite oxides of Mg(OH)2, Gd2O3, Y2O3, NiO, Ga2O3, and In2O3, with a median particle size D50 of 40μm.

[0042] Application areas: Oil extraction tools (temporary structural components).

[0043] Preparation method: S1 raw material pretreatment: pure Mg, pure Zn, Mg-Gd (30%Gd), Mg-Y (20%Y), and Mg-Zr (35%Zr) master alloys were preheated at 140℃ for 4 hours under nitrogen protection, with a surface finish Ra=0.7μm and a proportioning error of ±0.4wt.%.

[0044] S2 smelting: CO2 to SF6 volume ratio 150:1 protection, heating rate 14℃ / min to 760℃, smelting for 60min, stirring speed 90r / min (clockwise / counterclockwise alternating), temperature fluctuation ±4℃.

[0045] S3 Refining: Covering agent (MgCl2 55%, KCl 25%, NaCl 20%) and refining agent (MgCl2 65%, BaC2 20%, CaF2 15%), stand at 760℃ for 40 min, argon flow rate 9 L / min, hydrogen content less than or equal to 0.14 mL / 100 g, inclusion size less than or equal to 18 μm.

[0046] S4 casting: Pour at 700℃ into a preheated 280℃ steel mold, semi-continuous casting, billet pulling speed 90mm / min, cooling water flow rate 40L / min, ingot diameter 180mm, no surface defects, density 99.7%.

[0047] S5 homogenization treatment: heat preservation at 480℃ for 60h, ingot flipping every 12h, air cooling (transfer time 12s), dendrite spacing 9μm, segregation degree 1.15.

[0048] S6 Hot Extrusion Molding: The billet and die are heated to 420℃ and held for 50 min. The extrusion ratio is 18:1, the speed is 8 m / min, the extrusion cylinder temperature is 380℃, the die is preheated to 320℃, the bar diameter is 40 mm, the surface roughness Ra=0.6 μm, and the straightness error is 0.4 mm / m.

[0049] S7 aging treatment: heat preservation at 175℃ for 64 hours, dry air circulation, tensile strength increased by 13%, elongation decreased by 4%, hardness HV95.

[0050] Example 3: A soluble magnesium alloy rod with enhanced elongation and its preparation The chemical composition (mass percentage) of the magnesium alloy rod is as follows: 6.0% Gd, 1.5% Y (Gd:Y=4:1), 0.8% Zn, 0.25% Zr (Zn:Zr=3.2:1), 0.15% Li, 0.15% Ni, 0.075% Ga, 0.075% In (Ni:Ga:In=2:1:1, total percentage 0.3%), 0.8% Cu, with the balance being Mg.

[0051] Microstructure characteristics: The grains are equiaxed with a size of 12 μm; the Gd / Y solid solution phase is uniformly distributed in the matrix; the Ni / Ga / In low-melting-point eutectic phase is nanoscale (average particle size 60 nm), discontinuously distributed at the grain boundaries, accounting for 3.0% of the total volume, forming a "grain strengthening + grain boundary weakening" structure.

[0052] High-temperature solubility: The solubility rate at 200℃ is 11% higher than that at room temperature; the solubility products are composite oxides of Mg(OH)2, Gd2O3, Y2O3, NiO, Ga2O3, and In2O3, with a median particle size D50 of 30μm.

[0053] Application areas: Mobile phone mid-frame (3C product casing).

[0054] Preparation method: S1 raw material pretreatment: pure Mg, pure Zn, Mg-Gd (20%Gd), Mg-Y (20%Y), and Mg-Zr (30%Zr) master alloys were preheated at 125℃ for 4 hours, protected with dry air, with a surface finish Ra=0.5μm and a proportioning error of ±0.2wt.%.

[0055] S2 smelting: CO2 to SF6 volume ratio 150:1 protection, heating rate 11℃ / min to 740℃, smelting for 60min, stirring speed 70r / min (clockwise / counterclockwise alternating), temperature fluctuation ±2℃.

[0056] S3 Refining: Covering agent (MgCl2 45%, KCl 35%, NaCl 20%) and refining agent (MgCl2 55%, BaC2 30%, CaF2 15%), stand at 760℃ for 40 min, argon flow rate 7 L / min, hydrogen content less than or equal to 0.10 mL / 100 g, inclusion size less than or equal to 12 μm.

[0057] S4 casting: Pour into a preheated 220°C steel mold at 700°C, semi-continuous casting, billet pulling speed 70mm / min, cooling water flow rate 30L / min, ingot diameter 120mm, no surface defects, density 99.9%.

[0058] S5 homogenization treatment: heat treatment at 420℃ for 36 hours, ingot flipping every 12 hours, water quenching (transfer time 8s), dendrite spacing 7μm, segregation degree 1.05.

[0059] S6 Hot Extrusion Molding: The billet and die are heated to 380℃ and held for 40 minutes. The extrusion ratio is 12:1, the speed is 3m / min, the extrusion cylinder temperature is 320℃, the die is preheated to 280℃, the bar diameter is 20mm, the surface roughness Ra=0.4μm, and the straightness error is 0.2mm / m.

[0060] S7 aging treatment: heat preservation at 175℃ for 64 hours, dry air circulation, tensile strength increased by 11%, elongation decreased by 2%, hardness HV85.

[0061] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0062] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A soluble magnesium alloy rod with enhanced elongation, characterized in that: The chemical composition of the magnesium alloy rod, by mass percentage, includes: 1.5%–14.5% Gd, 0.5%–4.0% Y, 0.1%–2.5% Zn, 0.2%–0.5% Zr, 0.01%–0.5% Li, 0.01%–0.6% Ni, 0.01%–0.5% Ga, 0.01%–0.5% In, 0.1%–2.0% Cu, with the balance being Mg.

2. The soluble magnesium alloy rod with enhanced elongation according to claim 1, characterized in that: The mass ratio of Gd to Y is 2:1 to 5:1, and the mass ratio of Zn to Zr is 1:1 to 5:

1. The total mass percentage of Li, Ni, Ga, and In is no more than 1.5%, and the mass ratio of Ni:Ga:In is 2:1:1 to 4:1:

1. Cu is used to regulate the balance between dissolution rate and strength.

3. The soluble magnesium alloy rod with enhanced elongation according to claim 1, characterized in that: The microstructure of the magnesium alloy rod is characterized by: equiaxed grains with a size of 10-20 μm; uniform distribution of Gd / Y solid solution phase in the matrix; and nanoscale Ni / Ga / In low-melting-point eutectic phase, discontinuously distributed at grain boundaries, accounting for 2%-5% of the total volume, forming a composite structure of "intragranular strengthening + grain boundary weakening".

4. The soluble magnesium alloy rod with enhanced elongation according to claim 1, characterized in that: The magnesium alloy rod exhibits excellent accelerated dissolution characteristics at a high temperature of 200℃, with a dissolution rate 10% to 15% higher than that at room temperature. This effectively shortens the degradation cycle under high-temperature conditions. The dissolution products are mainly composite oxides of Mg(OH)2, Gd2O3, Y2O3, NiO, Ga2O3, and In2O3. The particles are fine and uniform, with a median particle size D50 of less than or equal to 50μm, which can avoid the deposition of large particles and improve biocompatibility and environmental friendliness.

5. A soluble magnesium alloy rod with enhanced elongation according to claim 1, characterized in that: The magnesium alloy rod is used in biodegradable medical devices, temporary structural components, or 3C product casings; wherein, biodegradable medical devices include cardiovascular stents and bone fixation devices, temporary structural components include oil extraction tools and geological exploration equipment, and 3C product casings include mobile phone frames and computer frames.

6. A method for preparing a soluble magnesium alloy rod with enhanced elongation, characterized in that: The specific steps of this preparation method are as follows: S1: Raw material pretreatment: Pure Mg, pure Zn, Mg-Gd master alloy, Mg-Y master alloy, and Mg-Zr master alloy are preheated at 120–150℃ for 4 hours under dry air or nitrogen protection to remove moisture and adsorbed gases; after preheating, the surface finish Ra of the raw materials is less than or equal to 0.8 μm, and the ratio error between the elemental metal and the master alloy is less than or equal to ±0.5 wt.%. S2: Melting: Under the protection of a mixed gas with a CO2 to SF5 volume ratio of 150:1, the pretreated raw materials are added in batches to a crucible resistance furnace and heated to 730 to 760°C at a rate of 10 to 15°C / min for 60 min. During the melting process, the mixture is mechanically stirred at a speed of 50 to 100 r / min for 10 min, with the stirring direction alternating between clockwise and counterclockwise to ensure compositional uniformity. The melt temperature is monitored in real time during the melting process, and the fluctuation range is less than or equal to ±5°C. S3: Refining: Add covering agent and refining agent, and let stand at 760℃ for 40 min; during the standing period, use an argon degassing device to blow the melt, with an argon flow rate of 5-10 L / min, to remove inclusions and hydrogen; after refining, the hydrogen content in the melt is less than or equal to 0.15 mL / 100 g, and the inclusion size is less than or equal to 20 μm; S4: Casting: The refined melt is poured at 700℃ into a steel mold preheated to 200-300℃. The inner wall of the steel mold is coated with boron nitride release agent. The casting process adopts a semi-continuous casting process, with a billet pulling speed of 50-100mm / min and a cooling water flow rate of 20-50L / min, forming a semi-continuous ingot with a diameter of 100-200mm. The ingot surface is free of cold shuts and cracks, and the microstructure density is greater than or equal to 99.5%. S5: Homogenization treatment: Place the ingot in a box-type resistance furnace and hold it at 400-520℃ for 24-72 hours. During the holding period, turn the ingot over every 12 hours to promote temperature uniformity. After the holding period, quench it with water or air to room temperature. The quenching transfer time is less than or equal to 15 seconds. After homogenization treatment, the dendrite spacing of the ingot is less than or equal to 10 μm and the elemental segregation is less than or equal to 1.

2. S6: Hot extrusion forming: After homogenization, the ingot is stripped of its outer skin, and the end defects are removed. The ingot is then cut to the required length. The billet and the extrusion die are heated simultaneously to 350–450℃ and held for 30–60 min. Forward extrusion is carried out under the conditions of an extrusion ratio of 8–25:1 and an extrusion speed of 0.1–20 m / min. The extrusion barrel temperature is 300–400℃, and the die preheating temperature is 250–350℃. The diameter of the extruded bar is 10–50 mm, the surface roughness Ra is less than or equal to 0.4 μm, and the straightness error is less than or equal to 0.5 mm / m. S7: Aging treatment: Place the extruded bar in an aging furnace and keep it at 175℃ for 64 hours. During the aging process, dry air is circulated to prevent oxidation. After aging, the tensile strength of the bar increases by 10% to 15%, the elongation decreases by no more than 5%, and the hardness value is stable at HV80 to 100.

7. The method for preparing a soluble magnesium alloy rod with enhanced elongation according to claim 6, characterized in that: The covering agent is a MgCl2-KCl-NaCl system, wherein MgCl2 accounts for 40%–60%, KCl accounts for 20%–40%, and NaCl accounts for 10%–30%; the refining agent is a MgCl2-BaC2-CaF2 system, wherein MgCl2 accounts for 50%–70%, BaC2 accounts for 20%–30%, and CaF2 accounts for 10%–20%.

8. The method for preparing a soluble magnesium alloy rod with enhanced elongation according to claim 6, characterized in that: In the hot extrusion molding step of S6, the billet and the mold are heated simultaneously to 350-450°C, the extrusion ratio is 12:1-20:1, and the extrusion speed is 1-10 m / min; the diameter of the extruded bar is 10-50 mm, and the surface roughness Ra is less than or equal to 0.8 μm.

9. The method for preparing a soluble magnesium alloy rod with enhanced elongation according to claim 6, characterized in that: In the aging treatment step of S7, the aging temperature is 175℃ and the aging time is 64h; after aging, the tensile strength of the bar increases by 10% to 15%, and the elongation decreases by no more than 5%.

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