High-strength corrosion-resistant magnesium alloy rod and preparation method thereof

Abstract

The present application aims at the problems of low absolute strength and poor corrosion resistance of magnesium alloy, and provides a high-strength corrosion-resistant magnesium alloy rod and a preparation method thereof.The magnesium alloy rod (Silicate Coatings-Gr@MgZnMnGdY) is composed of a material matrix (Gr@MgZnMnGdY) and a surface coating (Silicate Coatings): the matrix takes zinc (Zn), manganese (Mn), gadolinium (Gd) and yttrium (Y) as alloying elements, and takes graphene (Gr) as a composite component; and the coating is a silicate-based ceramic coating.The preparation method comprises mechanical ball milling, hot isostatic pressing sintering, hot extrusion, post-heat treatment and micro-arc oxidation.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, specifically relating to a high-strength corrosion-resistant magnesium alloy rod and its preparation method. Background Technology

[0002] As an important lightweight structural metal, magnesium alloys have broad application prospects in aerospace, transportation, and electronics. Furthermore, as a functional metal, magnesium alloys possess biodegradable properties, making them a promising candidate for applications in the biomedical field. However, the current application scale of magnesium alloys is limited, primarily due to their relatively low absolute strength and poor corrosion resistance, which restricts their use in high-load, corrosive environments. Therefore, it is necessary to develop new high-strength, corrosion-resistant magnesium alloys to expand their application.

[0003] Alloying and composite are common means of strengthening metal materials, and surface modification is an effective technology for protecting metal materials from corrosion. Combining alloying, composite and surface modification can produce new high-strength and corrosion-resistant magnesium alloys. In practical applications, rods are a widely used type of material. In the field of mechanical manufacturing, they can be used to produce bearings, gears, screws, etc. In the field of aircraft, train and automobile parts, they can be used to produce wheel axles, steering rods, crankshafts, connecting rods, etc. In the field of biomedicine, they can be used to produce bone nails, interface screws, etc. It can be seen that there is a huge demand for high-strength and corrosion-resistant magnesium alloy rods. The commonly used preparation processes for magnesium alloy rods are mainly divided into two categories: extrusion and casting. (1) Extrusion is a process in which magnesium alloy billets are formed into rods of different specifications under pressure through a mold. This process can make the material obtain a fine grain structure, thereby improving its mechanical properties; however, the extrusion process consumes a lot of energy, the cost of mold manufacturing and maintenance is high, and the degree of grain refinement is limited. (2) Casting is a process in which molten magnesium alloy is poured into a pre-prepared rod-shaped mold, and then cooled and solidified to form rods of different specifications. This process is simple and low-cost, but it suffers from problems such as coarse grains and uneven microstructure, which are detrimental to mechanical properties. In summary, there is an urgent need to develop new magnesium alloy rods and corresponding preparation methods to overcome the limitations of existing technologies.

[0004] Studies have shown that for magnesium alloys, zinc (Zn) and manganese (Mn) elements can refine grains, improving the mechanical properties of the material through grain refinement strengthening and solid solution strengthening, while also improving the corrosion behavior. Rare earth elements (REs), such as gadolinium (Gd) and yttrium (Y), can also refine grains and form strengthening phases at grain boundaries and within grains, improving the mechanical properties through precipitation strengthening or sedimentation strengthening, and forming a uniform and dense oxide film on the material surface to enhance corrosion resistance. Graphene (Gr) possesses excellent physical properties (such as high thermal conductivity and high electrical conductivity), mechanical properties, and corrosion resistance; adding a certain amount of Gr to the magnesium alloy matrix can improve its overall performance. Therefore, using Zn, Mn, Gd, and Y as alloying elements and Gr as a composite component holds promise for preparing novel high-performance magnesium alloy rods (Gr@MgZnMnGdY). Designing and developing suitable preparation methods is crucial. As is well known, mechanical ball milling involves adding spherical abrasive and powdered raw materials to a rotating container. The high-speed rotation of the container causes the abrasive and powder to roll, collide, and mix thoroughly. This process effectively achieves the refinement and uniform mixing of different types of powders. Hot isostatic pressing (HIP) sintering places the mixed powder in a high-temperature and high-pressure environment and holds it for a certain period of time. This process can achieve the compaction and densification of the mixed powder, obtaining extruded billets with a certain shape and porosity. Hot extrusion is a high-temperature plastic deformation processing method. It causes large plastic deformation of porous billets under certain temperature and pressure through a mold with a specific structure, which helps to reduce the porosity of porous billets and obtain high-density rods. Post-heat treatment involves holding the rods at a specific temperature for a certain period of time, which can effectively eliminate the internal stress accumulated in the material during plastic deformation. At the same time, a second phase precipitates in the matrix, improving the mechanical properties of the material through precipitation strengthening or sedimentation strengthening. Micro-arc oxidation, by applying a high voltage to the material immersed in an electrolyte, can generate a hard, wear-resistant, and corrosion-resistant ceramic oxide layer on the material surface, which is a commonly used technology for surface corrosion protection. Among the many different micro-arc oxidation coating systems, silicate-based ceramic coatings are characterized by simple and efficient preparation processes, good repeatability, and both low cost and high performance.

[0005] Therefore, this invention proposes a high-strength corrosion-resistant magnesium alloy rod and its preparation method. High-purity powders (Mg, Zn, Mn, Gd, Y, Gr) are selected as raw materials. Mixed powders of different compositions are obtained by mechanical ball milling. Magnesium alloy extrusion billets are prepared by hot isostatic pressing sintering. Magnesium alloy rods (Gr@MgZnMnGdY) are prepared by hot extrusion. The internal stress of the magnesium alloy rods is reduced and its mechanical properties are improved by post-heat treatment. Silicate coatings are prepared by micro-arc oxidation. Finally, high-strength corrosion-resistant magnesium alloy rods (Silicate Coatings-Gr@MgZnMnGdY) are obtained. Summary of the Invention

[0006] This invention addresses the problems of low absolute strength and poor corrosion resistance in magnesium alloys by proposing a high-strength, corrosion-resistant magnesium alloy rod and its preparation method. The magnesium alloy rod uses Zn, Mn, Gd, and Y as alloying elements, Gr as a composite component, and Silicate Coatings as a surface coating. The preparation method includes mechanical ball milling, hot isostatic pressing sintering, hot extrusion, post-heat treatment, and micro-arc oxidation.

[0007] The functions of each component in magnesium alloy rods are as follows: (1) Zn, Mn, Gd, and Y are commonly used alloying elements in magnesium alloys. Zn can be used as a grain inhibitor to improve the microstructure of the material by refining the grains, thereby improving its mechanical properties. At the same time, the solid solution of Zn can also improve the corrosion resistance of magnesium alloys. Mn can effectively refine the grains of magnesium alloys and purify the magnesium alloy melt, thereby improving the processing performance of magnesium alloys. Gd and Y, as rare earth elements, can form a dispersed strengthening phase in the magnesium matrix and refine the grains, greatly improving the mechanical properties of magnesium alloys. At the same time, they can improve the stability of the passivation film on the surface of magnesium alloys, thereby improving their corrosion resistance. (2) Gr is a single-layer two-dimensional honeycomb lattice structure material with excellent comprehensive performance. Adding it as a composite component to the magnesium alloy matrix can significantly improve its mechanical properties and corrosion resistance. (3) Silicate Coatings prepared by micro-arc oxidation have the characteristics of dense inner layer and porous outer layer. The inner layer can effectively prevent the contact between the corrosive medium and the substrate, thus providing a better corrosion protection effect. The porous structure of the outer layer can improve the surface roughness to a certain extent and provide a suitable surface for cell adhesion and migration, which is conducive to improving cell compatibility and promoting the application of magnesium alloy rods in the biomedical field.

[0008] The functions of each process in the preparation method are as follows: (1) Mechanical ball milling can refine the powder raw materials by subjecting them to greater mechanical shearing and collision, which helps to increase the surface area of ​​the powder and improve its reactivity. This process can also remove impurities and contaminants adsorbed on the surface of the powder raw materials, thereby improving the purity of the raw materials to a certain extent. After mechanical ball milling, a uniformly mixed powder can be obtained, which is the basis for subsequent preparation processes. (2) Hot isostatic pressing sintering can prepare relatively dense and uniformly composed extruded billets with fine structure. Due to its certain porosity, the billet can produce greater macroscopic plastic deformation, which is beneficial for subsequent hot extrusion. (3) Hot extrusion can cause significant plastic deformation of the extruded billet, obtaining bars of different specifications. It can reduce the porosity of the billet, increase its density, refine the grains, and improve its strength and plasticity. (4) Post-heat treatment can eliminate or reduce the internal stress accumulated in the bar during the extrusion deformation process. Under appropriate temperature and holding time, a uniform, fine, and dispersed second phase will precipitate inside the bar, which helps to further improve the mechanical properties of the material. (5) Micro-arc oxidation is a common process for preparing Silicate Coatings. This process has the advantages of low cost, simple operation, good controllability and high repeatability. The Silicate Coatings prepared are of excellent quality and can significantly improve the corrosion behavior of the rod, thereby improving its corrosion resistance.

[0009] The technical solution of this invention is as follows:

[0010] A high-strength, corrosion-resistant magnesium alloy rod, wherein the magnesium alloy rod uses Zn, Mn, Gd, and Y as alloying elements, Gr as a composite component, and Silicate Coatings as a surface coating; the preparation method includes mechanical ball milling, hot isostatic pressing sintering, hot extrusion, post-heat treatment, and micro-arc oxidation.

[0011] A method for preparing a high-strength, corrosion-resistant magnesium alloy rod includes the following steps:

[0012] Step 1: Mechanical ball milling to prepare mixed powder

[0013] Prepare the powdered raw materials: high-purity Mg powder (99.99%) with a mass fraction of 95%–79%, high-purity Zn powder (99.99%) with a mass fraction of 1%–3%, high-purity Mn powder (99.98%) with a mass fraction of 1%–3%, high-purity Gd powder (99.90%) with a mass fraction of 1%–5%, high-purity Y powder (99.99%) with a mass fraction of 1%–5%, and high-purity Gr powder (99.99%) with a mass fraction of 1%–5%. Place the powdered raw materials into a planetary ball mill for mechanical ball milling, adding alcohol as a cooling medium. The abrasive is stainless steel balls with a diameter of 20–60 mm. The weight ratio of stainless steel balls to powdered raw materials is 5:1–15:1. The ball milling speed is 150–250 r / min, and the total ball milling time is 8–16 h. During the process, pause for 15 min after every 30 min of ball milling for heat dissipation and cooling, and then dry with cold air for later use.

[0014] Preferably, the high-purity Mg powder (99.99%) has a mass fraction of 91%–83%, the high-purity Zn powder (99.99%) has a mass fraction of 1.5%–2.5%, the high-purity Mn powder (99.98%) has a mass fraction of 1.5%–2.5%, the high-purity Gd powder (99.90%) has a mass fraction of 2%–4%, the high-purity Y powder (99.99%) has a mass fraction of 2%–4%, the high-purity Gr powder (99.99%) has a mass fraction of 2%–4%, the stainless steel ball diameter is 30–50 mm, the weight ratio of stainless steel ball to powder raw material is 8:1–12:1, the ball mill speed is 180–220 r / min, and the total ball milling time is 10–14 h.

[0015] Step 2: Hot isostatic pressing sintering to prepare extruded billets

[0016] The mixed powder prepared in the first step is placed into the high-pressure sealed cavity of a hot isostatic press. The inner cavity of the mold has a size of Ф90mm×200mm. Sintering is carried out under argon protection at a temperature of 280~550℃, a sintering pressure of 50~100MPa, and a sintering time of 1~3h. After sintering, the temperature is controlled to decrease at a rate of 20~80℃ / min to prevent cracking caused by excessive cooling.

[0017] Preferably, the sintering temperature is 350–450℃, the sintering pressure is 70–90 MPa, the sintering time is 1.5–2.5 h, and after sintering, the temperature is controlled to decrease at a rate of 40–60℃ / min.

[0018] Step 3: Hot extrusion to prepare rods

[0019] The extruded billet obtained in the second step is machined into a Ф80mm bar. Before hot extrusion, it is preheated to 320-420℃ and held for 1-3 hours. Then it is placed in the extrusion die. The extrusion temperature is 300-400℃, the extrusion speed is 0.5-3.5mm / s, the number of extrusion passes is 3-10, and the extrusion ratio is 64, to obtain a bar with a diameter of Ф10mm.

[0020] Preferably, the material is preheated to 340–400°C before hot extrusion and held at that temperature for 1–2 hours. The extrusion temperature is 320–380°C, the extrusion speed is 1.5–2.5 mm / s, and the number of extrusion passes is 4–8.

[0021] Step 4: Post-heat treatment

[0022] The rod with a diameter of Ф10mm prepared in the third step is placed in a vacuum heating furnace, and the vacuum degree is maintained at 1×10 - 3 Pa is first held at 350–450°C for 4–12 hours, then held at 150–220°C for 8–16 hours, and then quenched in vegetable oil preheated to 50°C.

[0023] Preferably, the temperature is first kept at 380–420℃ for 8–10 hours, and then kept at 180–200℃ for 10–12 hours.

[0024] Step 5: Micro-arc oxidation to prepare silicate-based ceramic coatings

[0025] The rods that underwent post-heat treatment in the fourth step were placed in an electrolytic cell for micro-arc oxidation. The electrolyte consisted of KOH and Na2SiO3, with a KOH concentration of 8–14 g / L and a Na2SiO3 concentration of 12–18 g / L. The electrolyte was kept at 22–36°C by a circulating water cooling device. A constant voltage working mode was selected, with a voltage of 350–500 V, a treatment time of 5–15 min, a frequency of 400–1200 Hz, a pulse number of 30–80, and a duty cycle of 30%–50%. Finally, magnesium alloy rods with a silicate-based ceramic coating on the surface were obtained.

[0026] Preferably, the KOH concentration is 10-12 g / L, the Na2SiO3 concentration is 14-16 g / L, the voltage is 400-450 V, the treatment time is 8-12 min, the frequency is 600-1000 Hz, the number of pulses is 50-60, and the duty cycle is 35%-45%.

[0027] The high-strength corrosion-resistant magnesium alloy rod (Silicate Coatings-Gr@MgZnMnGdY) prepared by the above method has a matrix containing Zn, Mn, Gd, Y alloying elements and Gr composite components, and a silicate-based micro-arc oxidation coating on the surface.

[0028] The magnesium alloy rod composition is cleverly designed: (1) Adding Zn and Mn elements can refine the grains, improving the mechanical properties of magnesium alloys while improving their corrosion behavior; adding Gd and Y rare earth elements can stabilize the grain boundaries and form a uniform, fine, and dispersed second phase in the magnesium alloy matrix, while forming a dense and stable passivation film on the material surface, which helps to improve both the mechanical and corrosion properties of magnesium alloys. (2) The silicate-based micro-arc oxidation coating can undergo a metallurgical reaction with the matrix, resulting in high interfacial bonding strength. The dense inner layer can provide good corrosion protection, and the porous outer layer can be controlled to obtain appropriate pore structure and roughness, thereby improving cell compatibility by improving cell adhesion and migration, and thus promoting the application of magnesium alloys in the biomedical field.

[0029] The preparation method of the magnesium alloy rod is simple, feasible and reasonable: (1) Mechanical ball milling can refine the powder raw material, remove impurities and dirt adsorbed on the surface of the powder raw material, and obtain uniformly mixed powder, which is the basis for subsequent preparation processes. (2) Hot isostatic pressing sintering can prepare relatively dense and uniform extruded billets with fine structure. Its porous structure has good macroscopic plastic deformation ability, which is convenient for subsequent hot extrusion. (3) Hot extrusion can cause large plastic deformation of the extruded billet, which can reduce the porosity of the billet, increase its density, refine the grains, and improve its strength and plasticity. (4) Post-heat treatment is used to eliminate or reduce the internal stress accumulated in the material during large plastic deformation. By controlling the heat treatment process, a uniform, fine and dispersed second phase can be precipitated in the matrix, thereby improving the mechanical properties of the material. (5) Micro-arc oxidation is a commonly used preparation process of Silicate Coatings. It has the advantages of low cost, simple operation, good controllability and high repeatability. The resulting coating has excellent quality and is mainly used to improve the corrosion resistance of the material.

[0030] The beneficial effects of this invention are as follows:

[0031] (1) The inventors, through extensive experimentation and by comprehensively utilizing mechanical ball milling, hot isostatic pressing sintering, hot extrusion, post-heat treatment, and micro-arc oxidation, prepared high-strength corrosion-resistant magnesium alloy rods and summarized the optimal range of process parameters: for mechanical ball milling, the mass fraction of high-purity Mg powder (99.99%) was 91%–83%, the mass fraction of high-purity Zn powder (99.99%) was 1.5%–2.5%, and the mass fraction of high-purity Mn powder (99.98%) was… The raw materials contain 1.5% to 2.5% high-purity Gd powder (99.90%), 2% to 4% high-purity Y powder (99.99%), 2% to 4% high-purity Gr powder (99.99%), 30 to 50 mm diameter stainless steel balls, a weight ratio of stainless steel balls to raw powder of 8:1 to 12:1, a ball milling speed of 180 to 220 r / min, and a total ball milling time of 10 to 14 h. For hot isostatic pressing (HIP), the sintering temperature is 350–450℃, the sintering pressure is 70–90 MPa, and the sintering time is 1.5–2.5 h. After sintering, the temperature is controlled to decrease at a rate of 40–60℃ / min. For hot extrusion, preheating is performed to 340–400℃ and held for 1–2 h. The extrusion temperature is 320–380℃, the extrusion speed is 1.5–2.5 mm / s, and the number of extrusion passes is 4–8. For post-hot pressing... The treatment involves first holding the material at 380–420℃ for 8–10 hours, followed by holding it at 180–200℃ for 10–12 hours. For micro-arc oxidation, the KOH concentration is 10–12 g / L, the Na₂SiO₃ concentration is 14–16 g / L, the voltage is 400–450 V, the treatment time is 8–12 minutes, the frequency is 600–1000 Hz, the number of pulses is 50–60, and the duty cycle is 35%–45%. Using this combination of process parameters, a new type of high-strength, corrosion-resistant magnesium alloy rod can be obtained.

[0032] (2) The inventors used a preferred combination of process parameters to prepare high-strength, corrosion-resistant magnesium alloy rods with a silicate-based ceramic coating on the surface. Microstructure and performance analysis showed that the average grain size of the magnesium alloy rods was 25.5–20.2 μm, the coating thickness was 15.7–18.2 μm, the adhesion was grade 5B, the tensile strength was 405–445 MPa, the self-corrosion potential was -1.24–-0.86 V / SCE, and the self-corrosion current density was 5.2 × 10⁻⁶. -8 ~7.4×10 -9 A / cm 2 Compared with ZK60 magnesium alloy bars, which have better corrosion resistance, its strength is increased by 14.4% to 25.7%, its self-corrosion potential is increased by 16.8% to 42.3%, and its self-corrosion current density is reduced by 80.8 to 567.6 times. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the cross-sectional structure of the magnesium alloy rod in Example 1.

[0034] Figure 2 The image shows the surface microstructure of the magnesium alloy rod in Example 1.

[0035] Figure 3 This is a comparison of the mechanical strength of the magnesium alloy rod in Example 1 with that of common commercial magnesium alloys.

[0036] Figure 4 This is a comparison of the corrosion resistance of the magnesium alloy rod in Example 1 with that of common commercial magnesium alloys. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0038] The present invention discloses a high-strength corrosion-resistant magnesium alloy rod and its preparation method. The specific implementation of the preparation method includes the following steps:

[0039] Step 1: Mechanical ball milling to prepare mixed powder

[0040] Prepare powdered raw materials: high-purity Mg powder (99.99%) with a mass fraction of 95%–79%, preferably 91%–83%; high-purity Zn powder (99.99%) with a mass fraction of 1%–3%, preferably 1.5%–2.5%; high-purity Mn powder (99.98%) with a mass fraction of 1%–3%, preferably 1.5%–2.5%; high-purity Gd powder (99.90%) with a mass fraction of 1%–5%, preferably 2%–4%; high-purity Y powder (99.99%) with a mass fraction of 1%–5%, preferably 2%–4%; and high-purity Gr powder (99.99%) with a mass fraction of 1%–5%. The powdered raw material is placed in a planetary ball mill for mechanical ball milling. Alcohol is added as a cooling medium. The abrasive is stainless steel balls with a diameter of 20-60 mm, preferably 30-50 mm. The weight ratio of stainless steel balls to powdered raw material is 5:1-15:1, preferably 8:1-12:1. The ball milling speed is 150-250 r / min, preferably 180-220 r / min. The total ball milling time is 8-16 h, preferably 10-14 h. During the process, the ball milling is paused for 15 minutes after every 30 minutes for heat dissipation and cooling. Then, the powdered raw material is dried with cold air and ready for use.

[0041] Step 2: Hot isostatic pressing sintering to prepare extruded billets

[0042] The mixed powder prepared in the first step is placed into the high-pressure sealed cavity of a hot isostatic press. The inner cavity of the mold has a size of Ф90mm×200mm. Sintering is carried out under argon protection. The sintering temperature is 280~550℃, preferably 350~450℃, the sintering pressure is 50~100MPa, preferably 70~90MPa, and the sintering time is 1~3h, preferably 1.5~2.5h. After sintering, the temperature is controlled to decrease at a rate of 20~80℃ / min, preferably 40~60℃ / min, to prevent cracking caused by excessively rapid cooling.

[0043] Step 3: Hot extrusion to prepare rods

[0044] The extruded billet obtained in the second step is machined into a Ф80mm bar. Before hot extrusion, it is preheated to 320-420℃, preferably 340-400℃, and held for 1-3 hours, preferably 1-2 hours. Then it is placed in an extrusion die, and the extrusion temperature is 300-400℃, preferably 320-380℃, the extrusion speed is 0.5-3.5mm / s, preferably 1.5-2.5mm / s, the number of extrusion passes is 3-10, preferably 4-8, and the extrusion ratio is 64 to obtain a bar with a diameter of Ф10mm.

[0045] Step 4: Post-heat treatment

[0046] The rod with a diameter of Ф10mm prepared in the third step is placed in a vacuum heating furnace, and the vacuum degree is maintained at 1×10 - 3 Pa is first held at 350–450°C for 4–12 hours, preferably at 380–420°C for 8–10 hours, then held at 150–220°C for 8–16 hours, preferably at 180–200°C for 10–12 hours, and then quenched in vegetable oil preheated to 50°C.

[0047] Step 5: Micro-arc oxidation to prepare silicate-based ceramic coatings

[0048] The rods that underwent post-heat treatment in the fourth step were placed in an electrolytic cell for micro-arc oxidation. The electrolyte consisted of KOH and Na2SiO3, with a KOH concentration of 8–14 g / L, preferably 10–12 g / L, and a Na2SiO3 concentration of 12–18 g / L, preferably 14–16 g / L. The electrolyte was kept at 22–36°C by a circulating water cooling device. A constant voltage operating mode was selected, with a voltage of 350–500 V, preferably 400–450 V, a treatment time of 5–15 min, preferably 8–12 min, a frequency of 400–1200 Hz, preferably 600–1000 Hz, a pulse number of 30–80, preferably 50–60, and a duty cycle of 30%–50%, preferably 35%–45%. Finally, magnesium alloy rods with a silicate-based ceramic coating on the surface were obtained.

[0049] Microstructure and performance analysis of the high-strength corrosion-resistant magnesium alloy rods prepared by the method described in this invention revealed that the matrix of the material has a uniform and fine grain structure, the surface coating is well bonded to the matrix, and there are no obvious defects. Compared with traditional commercial magnesium alloy rods, its mechanical properties and corrosion resistance are significantly improved.

[0050] The following detailed description is provided through specific embodiments.

[0051] Example 1:

[0052] Step 1: Mechanical ball milling to prepare mixed powder

[0053] Prepare the powdered raw materials: 91% high-purity Mg powder (99.99%), 1.5% high-purity Zn powder (99.99%), 1.5% high-purity Mn powder (99.98%), 2% high-purity Gd powder (99.90%), 2% high-purity Y powder (99.99%), and 2% high-purity Gr powder (99.99%). Place the powdered raw materials into a planetary ball mill for mechanical ball milling, adding alcohol as a cooling medium. The abrasive is stainless steel balls with a diameter of 30 mm, and the weight ratio of stainless steel balls to powdered raw materials is 8:1. The ball milling speed is 180 r / min, and the total ball milling time is 10 hours. During the process, pause for 15 minutes after every 30 minutes of ball milling for heat dissipation and cooling, and then dry with cold air for later use.

[0054] Step 2: Hot isostatic pressing sintering to prepare extruded billets

[0055] The mixed powder prepared in the first step is placed into the high-pressure sealed cavity of a hot isostatic press. The inner cavity of the mold has a size of Ф90mm×200mm. Sintering is carried out under argon protection at a sintering temperature of 350℃, a sintering pressure of 70MPa, and a sintering time of 1.5h. After sintering, the temperature is controlled to decrease at a rate of 40℃ / min to prevent cracking caused by excessive cooling.

[0056] Step 3: Hot extrusion to prepare rods

[0057] The extruded billet obtained in the second step is machined into a Ф80mm bar. Before hot extrusion, it is preheated to 340℃ and held for 1 hour. Then it is placed in the extrusion die. The extrusion temperature is 320℃, the extrusion speed is 1.5mm / s, the extrusion passes are 4, and the extrusion ratio is 64, to obtain a bar with a diameter of Ф10mm.

[0058] Step 4: Post-heat treatment

[0059] The rod with a diameter of Ф10mm prepared in the third step is placed in a vacuum heating furnace, and the vacuum degree is maintained at 1×10 - 3Pa was first held at 380°C for 8 hours, then held at 180°C for 10 hours, and then quenched in vegetable oil preheated to 50°C.

[0060] Step 5: Micro-arc oxidation to prepare silicate-based ceramic coatings

[0061] The rods that underwent post-heat treatment in the fourth step were placed in an electrolytic cell for micro-arc oxidation. The electrolyte consisted of KOH and Na2SiO3, with a KOH concentration of 10 g / L and a Na2SiO3 concentration of 14 g / L. The electrolyte was kept at 22–36°C by a circulating water cooling device. A constant voltage working mode was selected, with a voltage of 400 V, a treatment time of 8 min, a frequency of 600 Hz, a pulse count of 50, and a duty cycle of 35%. Finally, magnesium alloy rods with a silicate-based ceramic coating on the surface were obtained.

[0062] The microstructure and properties of the samples prepared in Example 1 were analyzed:

[0063] (A) Schematic diagram of the cross-sectional structure of magnesium alloy rod

[0064] As attached Figure 1 As shown, the sample consists of a material matrix and a surface coating. The material matrix is ​​Gr@MgZnMnGdY, and the surface coating is Silicate Coatings.

[0065] (B) Surface microstructure of magnesium alloy rod

[0066] The surface microstructure of the sample was observed using a scanning electron microscope. (Attached) Figure 2 It is evident that its surface has a loose and porous morphology with appropriate porosity and pore size, and no obvious defects such as cracks or fissures. Metallographic observation revealed that the average grain size of the matrix is ​​25.5 μm, the coating thickness was measured to be 15.7 μm using a thickness gauge, and the coating adhesion was measured to be grade 5B using the cross-cut adhesion test.

[0067] (C) Comparison of mechanical strength between magnesium alloy rods and common commercial magnesium alloys

[0068] The mechanical properties of conventional commercially available AZ31, AZ91, WE43, and ZK60 magnesium alloy bars and the aforementioned magnesium alloy bars were measured using a tensile testing machine. (See attached...) Figure 3 It can be seen that the tensile strengths of AZ31, AZ91, WE43 and ZK60 magnesium alloy rods are 221MPa, 265MPa, 205MPa and 354MPa respectively, while the tensile strength of the magnesium alloy rod is 405MPa, which is 14.4% higher than that of the ZK60 magnesium alloy rod with the highest strength.

[0069] (D) Comparison of corrosion resistance between magnesium alloy rods and common commercial magnesium alloys

[0070] In a 0.9% (w / w) NaCl solution, the potentiodynamic polarization curves of the samples were measured using an electrochemical workstation. The working electrode, counter electrode, and reference electrode were the sample, platinum sheet, and saturated calomel electrode, respectively. This was used to evaluate the corrosion resistance of AZ31, AZ91, WE43, and ZK60 magnesium alloy rods and the aforementioned magnesium alloy rods. (See attached...) Figure 4 It can be seen that the self-corrosion potentials of AZ31, AZ91, WE43, and ZK60 magnesium alloy bars are -1.65V / SCE, -1.51V / SCE, -1.54V / SCE, and -1.49V / SCE, respectively, and the self-corrosion current densities are 9.6×10⁻⁶. -5 A / cm 2 1.3×10 -5 A / cm 2 7.7×10 -5 A / cm 2 4.2×10 -6 A / cm 2 The self-corrosion potential of the magnesium alloy rod is -1.24V / SCE, and the self-corrosion current density is 5.2×10⁻⁶. -8 A / cm 2 Compared to ZK60 magnesium alloy rods, which have the best corrosion resistance, its self-corrosion potential increased by 16.8%, and its self-corrosion current density decreased by 80.8 times.

[0071] Example 2:

[0072] Step 1: Mechanical ball milling to prepare mixed powder

[0073] Prepare the powdered raw materials: 87% high-purity Mg powder (99.99%), 2% high-purity Zn powder (99.99%), 2% high-purity Mn powder (99.98%), 3% high-purity Gd powder (99.90%), 3% high-purity Y powder (99.99%), and 3% high-purity Gr powder (99.99%). Place the powdered raw materials into a planetary ball mill for mechanical ball milling, adding alcohol as a cooling medium. The abrasive is stainless steel balls with a diameter of 40 mm. The weight ratio of stainless steel balls to powdered raw materials is 10:1. The ball milling speed is 200 r / min, and the total ball milling time is 12 hours. During the process, pause for 15 minutes after every 30 minutes of ball milling for heat dissipation and cooling, and then dry with cold air for later use.

[0074] Step 2: Hot isostatic pressing sintering to prepare extruded billets

[0075] The mixed powder prepared in the first step is placed into the high-pressure sealed cavity of a hot isostatic press. The inner cavity of the mold has a size of Ф90mm×200mm. Sintering is carried out under argon protection at a sintering temperature of 400℃, a sintering pressure of 80MPa, and a sintering time of 2h. After sintering, the temperature is controlled to decrease at a rate of 50℃ / min to prevent cracking caused by excessive cooling.

[0076] Step 3: Hot extrusion to prepare rods

[0077] The extruded billet obtained in the second step is machined into a Ф80mm bar. Before hot extrusion, it is preheated to 370℃ and held for 1.5h. Then it is placed in the extrusion die, the extrusion temperature is 350℃, the extrusion speed is 2mm / s, the extrusion passes are 6, the extrusion ratio is 64, and a bar with a diameter of Ф10mm is obtained.

[0078] Step 4: Post-heat treatment

[0079] The rod with a diameter of Ф10mm prepared in the third step is placed in a vacuum heating furnace, and the vacuum degree is maintained at 1×10 - 3 Pa was first held at 400℃ for 9 hours, then held at 190℃ for 11 hours, and then quenched in vegetable oil preheated to 50℃.

[0080] Step 5: Micro-arc oxidation to prepare silicate-based ceramic coatings

[0081] The rods that underwent post-heat treatment in the fourth step were placed in an electrolytic cell for micro-arc oxidation. The electrolyte consisted of KOH and Na2SiO3, with a KOH concentration of 11 g / L and a Na2SiO3 concentration of 15 g / L. The electrolyte was kept at 22–36°C by a circulating water cooling device. A constant voltage working mode was selected, with a voltage of 425 V, a treatment time of 10 min, a frequency of 800 Hz, a pulse count of 55, and a duty cycle of 40%. Finally, magnesium alloy rods with a silicate-based ceramic coating on the surface were obtained.

[0082] Tissue analysis and performance characterization revealed that, for the magnesium alloy rod in Example 2, the average grain size of the matrix was 23.6 μm, the coating thickness was 16.4 μm, and the adhesion was grade 5B. The magnesium alloy rod exhibited a tensile strength of 423 MPa, a self-corrosion potential of -1.06 V / SCE, and a self-corrosion current density of 1.3 × 10⁻⁶. -8 A / cm 2 Compared with the ZK60 magnesium alloy bar with the best overall performance, its tensile strength is increased by 19.5%, its self-corrosion potential is increased by 28.9%, and its self-corrosion current density is reduced by 323.1 times.

[0083] Example 3:

[0084] Step 1: Mechanical ball milling to prepare mixed powder

[0085] Prepare the powdered raw materials: 83% high-purity Mg powder (99.99%), 2.5% high-purity Zn powder (99.99%), 2.5% high-purity Mn powder (99.98%), 4% high-purity Gd powder (99.90%), 4% high-purity Y powder (99.99%), and 4% high-purity Gr powder (99.99%). Place the powdered raw materials into a planetary ball mill for mechanical ball milling, adding alcohol as a cooling medium. The abrasive is stainless steel balls with a diameter of 50 mm. The weight ratio of stainless steel balls to powdered raw materials is 12:1. The ball milling speed is 220 r / min, and the total ball milling time is 14 hours. During the process, pause for 15 minutes after every 30 minutes of ball milling for heat dissipation and cooling, and then dry with cold air for later use.

[0086] Step 2: Hot isostatic pressing sintering to prepare extruded billets

[0087] The mixed powder prepared in the first step is placed into the high-pressure sealed cavity of a hot isostatic press. The inner cavity of the mold has a size of Ф90mm×200mm. Sintering is carried out under argon protection at a sintering temperature of 450℃, a sintering pressure of 90MPa, and a sintering time of 2.5h. After sintering, the temperature is controlled to decrease at a rate of 60℃ / min to prevent cracking caused by excessive cooling.

[0088] Step 3: Hot extrusion to prepare rods

[0089] The extruded billet obtained in the second step is machined into a Ф80mm bar. Before hot extrusion, it is preheated to 400℃ and held for 2 hours. Then it is placed in the extrusion die. The extrusion temperature is 380℃, the extrusion speed is 2.5mm / s, the extrusion passes are 8, and the extrusion ratio is 64, to obtain a bar with a diameter of Ф10mm.

[0090] Step 4: Post-heat treatment

[0091] The rod with a diameter of Ф10mm prepared in the third step is placed in a vacuum heating furnace, and the vacuum degree is maintained at 1×10 - 3 Pa was first held at 420°C for 10 hours, then at 200°C for 12 hours, and then quenched in vegetable oil preheated to 50°C.

[0092] Step 5: Micro-arc oxidation to prepare silicate-based ceramic coatings

[0093] The rods that underwent post-heat treatment in the fourth step were placed in an electrolytic cell for micro-arc oxidation. The electrolyte consisted of KOH and Na2SiO3, with a KOH concentration of 12 g / L and a Na2SiO3 concentration of 16 g / L. The electrolyte was kept at 22–36 °C by a circulating water cooling device. A constant voltage working mode was selected, with a voltage of 450 V, a treatment time of 12 min, a frequency of 1000 Hz, a pulse count of 60, and a duty cycle of 45%. Finally, magnesium alloy rods with a silicate-based ceramic coating on the surface were obtained.

[0094] Tissue analysis and performance characterization revealed that, for the magnesium alloy rod in Example 3, the average grain size of the matrix was 20.2 μm, the coating thickness was 18.2 μm, and the adhesion was grade 5B. The magnesium alloy rod exhibited a tensile strength of 445 MPa, a self-corrosion potential of -0.86 V / SCE, and a self-corrosion current density of 7.4 × 10⁻⁶. -9 A / cm 2 Compared with the ZK60 magnesium alloy bar with the best overall performance, its tensile strength is increased by 25.7%, its self-corrosion potential is increased by 42.3%, and its self-corrosion current density is reduced by 567.6 times.

[0095] Comparative Example 1:

[0096] Step 1: Mechanical ball milling to prepare mixed powder

[0097] Prepare the powdered raw materials: 95% high-purity Mg powder (99.99%), 1% high-purity Zn powder (99.99%), 1% high-purity Mn powder (99.98%), 1% high-purity Gd powder (99.90%), 1% high-purity Y powder (99.99%), and 1% high-purity Gr powder (99.99%). Place the powdered raw materials into a planetary ball mill for mechanical ball milling, adding alcohol as a cooling medium. The abrasive is stainless steel balls with a diameter of 20 mm, and the weight ratio of stainless steel balls to powdered raw materials is 5:1. The ball milling speed is 150 r / min, and the total ball milling time is 8 hours. During the process, pause for 15 minutes after every 30 minutes of ball milling for heat dissipation and cooling, and then dry with cold air for later use.

[0098] Step 2: Hot isostatic pressing sintering to prepare extruded billets

[0099] The mixed powder prepared in the first step is placed into the high-pressure sealed cavity of a hot isostatic press. The inner cavity of the mold has a size of Ф90mm×200mm. Sintering is carried out under argon protection at a sintering temperature of 280℃, a sintering pressure of 50MPa, and a sintering time of 1h. After sintering, the temperature is controlled to decrease at a rate of 20℃ / min to prevent cracking caused by excessive cooling.

[0100] Step 3: Hot extrusion to prepare rods

[0101] The extruded billet obtained in the second step is machined into a Ф80mm bar. Before hot extrusion, it is preheated to 320℃ and held for 1 hour. Then it is placed in the extrusion die. The extrusion temperature is 300℃, the extrusion speed is 0.5mm / s, the extrusion passes are 3, and the extrusion ratio is 64, to obtain a bar with a diameter of Ф10mm.

[0102] Step 4: Post-heat treatment

[0103] The rod with a diameter of Ф10mm prepared in the third step is placed in a vacuum heating furnace, and the vacuum degree is maintained at 1×10 - 3 Pa was first held at 350°C for 4 hours, then held at 150°C for 8 hours, and then quenched in vegetable oil preheated to 50°C.

[0104] Step 5: Micro-arc oxidation to prepare silicate-based ceramic coatings

[0105] The rods that underwent post-heat treatment in the fourth step were placed in an electrolytic cell for micro-arc oxidation. The electrolyte consisted of KOH and Na2SiO3, with a KOH concentration of 8 g / L and a Na2SiO3 concentration of 12 g / L. The electrolyte was kept at 22–36°C by a circulating water cooling device. A constant voltage working mode was selected, with a voltage of 350 V, a treatment time of 5 min, a frequency of 400 Hz, a pulse count of 30, and a duty cycle of 30%. Finally, magnesium alloy rods with a silicate-based ceramic coating on the surface were obtained.

[0106] Microstructural analysis and performance characterization revealed that, for the magnesium alloy rod in the comparative example, the average grain size of the matrix was 28.1 μm, the coating thickness was 12.6 μm, and the adhesion was grade 4B. The magnesium alloy rod exhibited a tensile strength of 364 MPa, a self-corrosion potential of -1.31 V / SCE, and a self-corrosion current density of 8.7 × 10⁻⁶. -8 A / cm 2 Compared to the ZK60 magnesium alloy bar with the best overall performance, this comparative example showed a 2.8% increase in tensile strength, a 12.1% increase in self-corrosion potential, and a 48.3-fold decrease in self-corrosion current density. The preparation process parameters used in this comparative example are not the optimal combination. Compared to the ZK60 magnesium alloy bar with the best overall performance, this magnesium alloy bar showed a slight increase in tensile strength, a slightly increased self-corrosion potential, and a slightly decreased self-corrosion current density, but the improvement in overall performance was not as significant as that of the magnesium alloy bar prepared with the optimal parameters.

[0107] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

[0108] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing high-strength, corrosion-resistant magnesium alloy rods, characterized in that, Includes the following steps: Step 1: Mechanical ball milling to prepare mixed powder Prepare the powdered raw materials: high-purity magnesium powder with a mass fraction of 95%~79%, high-purity zinc powder with a mass fraction of 1%~3%, high-purity manganese powder with a mass fraction of 1%~3%, high-purity gadolinium powder with a mass fraction of 1%~5%, high-purity yttrium powder with a mass fraction of 1%~5%, and high-purity graphene powder with a mass fraction of 1%~5%. Place the powdered raw materials into a planetary ball mill for mechanical ball milling, add alcohol as a cooling medium, and use stainless steel balls with a diameter of 20~60 mm as the milling medium. The weight ratio of stainless steel balls to powdered raw materials is 5:1~15:

1. The ball milling speed is 150~250 r / min, and the total ball milling time is 8~16 h. During the process, pause for 15 minutes after every 30 minutes of ball milling for heat dissipation and cooling, and then dry with cold air for later use. Step 2: Hot isostatic pressing sintering to prepare extruded billets The mixed powder prepared in the first step is placed into the high-pressure sealed cavity of a hot isostatic press. The inner cavity of the mold has the dimensions of Ф90mm × 200mm. Sintering is carried out under argon protection at a temperature of 280~550 ℃, a sintering pressure of 50~100 MPa, and a sintering time of 1~3 h. After sintering, the temperature is controlled to decrease at a rate of 20~80 ℃ / min to prevent cracking caused by excessive cooling. Step 3: Hot extrusion to prepare rods The extruded billet obtained in the second step is machined into a bar with a diameter of Ф80 mm. Before hot extrusion, it is preheated to 320~420℃ and held for 1~3 h. Then it is placed in the extrusion die. The extrusion temperature is 300~400℃, the extrusion speed is 0.5~3.5 mm / s, the number of extrusion passes is 3~10, and the extrusion ratio is 64 to obtain a bar with a diameter of Ф10 mm. Step 4: Post-heat treatment The rod with a diameter of Ф10 mm prepared in the third step is placed in a vacuum heating furnace, and the vacuum level is maintained at 1×10. -3 Pa is first held at 350~450 ℃ for 4~12 h, then held at 150~220 ℃ for 8~16 h, and then quenched in vegetable oil preheated to 50 ℃. Step 5: Micro-arc oxidation to prepare silicate-based ceramic coatings The rods that underwent post-heat treatment in the fourth step were placed in an electrolytic cell for micro-arc oxidation. The electrolyte consisted of KOH and Na2SiO3, with a KOH concentration of 8-14 g / L and a Na2SiO3 concentration of 12-18 g / L. The electrolyte was kept at 22-36 ℃ by a circulating water cooling device. A constant voltage working mode was selected, with a voltage of 350-500 V, a treatment time of 5-15 min, a frequency of 400-1200 Hz, a pulse number of 30-80, and a duty cycle of 30%-50%. Finally, magnesium alloy rods with a silicate-based ceramic coating on the surface were obtained. The magnesium alloy rod uses zinc, manganese, gadolinium, and yttrium as alloying elements, graphene as a composite component, and a silicate-based ceramic coating as a surface coating. The average grain size of the magnesium alloy rod is 25.5–20.2 μm, the thickness of the surface coating is 15.7–18.2 μm, and the adhesion is grade 5B. The tensile strength of the magnesium alloy rod is 405–445 MPa, the self-corrosion potential is -1.24–-0.86 V / SCE, and the self-corrosion current density is 5.2 × 10⁻⁶ V / SCE. -8 ~7.4×10 -9 A / cm 2 .

2. The method for preparing a high-strength, corrosion-resistant magnesium alloy rod as described in claim 1, characterized in that, In the first step, the mass fraction of high-purity magnesium powder is 91%~83%, the mass fraction of high-purity zinc powder is 1.5%~2.5%, the mass fraction of high-purity manganese powder is 1.5%~2.5%, the mass fraction of high-purity gadolinium powder is 2%~4%, the mass fraction of high-purity yttrium powder is 2%~4%, the mass fraction of high-purity graphene powder is 2%~4%, the diameter of the stainless steel ball is 30~50 mm, the weight ratio of stainless steel ball to powder raw material is 8:1~12:1, the ball milling speed is 180~220 r / min, and the total ball milling time is 10~14 h.

3. The method for preparing a high-strength, corrosion-resistant magnesium alloy rod as described in claim 2, characterized in that, In the second step, the sintering temperature is 350~450 ℃, the sintering pressure is 70~90 MPa, the sintering time is 1.5~2.5 h, and after sintering, the temperature is controlled to decrease at a rate of 40~60 ℃ / min.

4. The method for preparing a high-strength, corrosion-resistant magnesium alloy rod as described in claim 2, characterized in that, In the third step, the temperature is preheated to 340~400 ℃ before hot extrusion and held for 1~2 h. The extrusion temperature is 320~380 ℃, the extrusion speed is 1.5~2.5 mm / s, and the number of extrusion passes is 4~8.

5. The method for preparing a high-strength, corrosion-resistant magnesium alloy rod as described in claim 2, characterized in that, In the fourth step, the temperature is first kept at 380~420 ℃ for 8~10 h, and then kept at 180~200 ℃ for 10~12 h.

6. The method for preparing a high-strength, corrosion-resistant magnesium alloy rod as described in claim 2, characterized in that, In the fifth step, the KOH concentration is 10~12 g / L, the Na2SiO3 concentration is 14~16 g / L, the voltage is 400~450 V, the processing time is 8~12 min, the frequency is 600~1000 Hz, the number of pulses is 50~60, and the duty cycle is 35%~45%.

7. The high-strength corrosion-resistant magnesium alloy rod as described in claim 1, characterized in that, It is used in aerospace, transportation, electronic products, and biomedical fields.

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