An ultra-high-strength corrosion-resistant multi-element low-alloyed magnesium alloy and a preparation method thereof

Abstract

A high-strength, corrosion-resistant, multi-element low-alloy magnesium alloy and its preparation method are disclosed. The alloy's chemical composition (mass percentage) is: Cu 0.2–1.8%, Zn 0.3–2.0%, Ca 0.15–0.7%, Mn 0.2–0.8%, impurity content ≤0.05%, and the balance being Mg, wherein the Zn content is not less than the Cu content. Through multi-element micro-alloying, combined with melting, heat treatment, and deformation processing, a large number of in-situ endogenous nanophases are introduced into the magnesium matrix, constructing segregated structures formed by one or more elements selected from Ca, Cu, Mn, and Zn at grain boundaries and subgrain boundaries. Zn and Ca elements are dissolved in the matrix. The prepared magnesium alloy material has low cost, simple processing technology, and a minimum corrosion rate as low as 0.5 mL / cm². 2 / d, the tensile yield strength can reach 545MPa, while the elongation is about 10%.

Description

Technical Field

[0001] This invention relates to the field of metallic materials and metallic material processing, and in particular to the preparation technology of ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloys. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials currently available for engineering applications, possess advantages such as high specific strength and specific stiffness, good resistance to magnetic interference, excellent damping and vibration reduction performance, high thermal conductivity, and easy recyclability and environmental friendliness. They have enormous application prospects in aerospace, military equipment, transportation equipment manufacturing, 3C products, and biomedicine, and have become one of the most promising metallic materials of the 21st century. Among them, ultra-high strength magnesium alloys are gradually becoming advanced basic materials supporting the continuous upgrading and development of high-end equipment such as aviation, aerospace, next-generation weaponry, high-speed trains, and new energy vehicles. my country is at the forefront of the world in the research and application of ultra-high strength wrought magnesium alloys. Ultra-high strength magnesium alloy materials and their strengthening and toughening deformation processing technology are the main directions of development in the magnesium alloy field. It is estimated that by 2035, ultra-high strength magnesium alloys will replace more than 20% of similar ordinary materials. However, from the perspective of further expanding the application of magnesium alloy materials, existing high-strength magnesium alloy materials still have significant shortcomings in terms of specific strength, specific stiffness, fracture toughness, and corrosion resistance. This severely restricts the application of magnesium alloy materials in these fields and hinders the improvement of the competitiveness of their end products, which is a pressing development problem that needs to be solved. Developing and utilizing ultra-high-strength corrosion-resistant magnesium alloys is highly attractive, but it also presents enormous challenges.

[0003] In recent years, numerous research efforts have focused on preparing high-strength, corrosion-resistant magnesium alloys using various methods, including the addition of large amounts of rare earth elements and special processing techniques such as powder metallurgy or large plastic deformation. Several high-strength magnesium alloys have been gradually developed domestically. For example, Chinese patent CN111254333A discloses a multi-element high-strength, corrosion-resistant wrought magnesium alloy and its preparation method. The mass percentage of each component element in this wrought magnesium alloy is as follows: Sn 2.8–4.8%, Zn 0.8–2.2%, Zr 0.3–1.0%, RE (rare earth metals) 0.2–2.2%, Mn 0.05–0.15%, impurity content ≤0.2%, and the balance being Mg. Its room temperature tensile strength is 322–372 MPa, yield strength is 243–318 MPa, and elongation is 16.82–26.15%. The corrosion rate of this magnesium alloy is 0.181–0.332 mg·cm⁻¹. -2 ·d -1The alloy of this invention has a high overall alloying element content and contains relatively valuable Zr and rare earth elements. However, its strength is still relatively low, with a yield strength of less than 320 MPa, far from reaching the ultra-high strength level. Chinese patent CN114395667A discloses a high-strength corrosion-resistant magnesium alloy and its preparation method based on coherent precipitate control. This magnesium alloy, by mass percentage, contains: Al 1.3–2.9%, Zn 0–0.8%, Ca 0.1–0.8%, Mn 0.3–0.6%, unavoidable impurities <0.02%, and the balance being magnesium. The magnesium alloy sheet prepared using this method has a tensile strength ≥280 MPa and a corrosion rate ≤6 mm / year, achieving a simultaneous improvement in corrosion resistance and high strength. Although it has good corrosion resistance, the overall strength level it can achieve is relatively low, far from reaching the level of high-strength or ultra-high-strength magnesium alloys. Chinese patent CN114525437A discloses a low-alloy-content corrosion-resistant high-performance magnesium alloy and its preparation method. The magnesium alloy composition by mass percentage is: Al 0.15-0.55%, Mn 0.01-0.5%, Ca 0.03-0.1%, with the remainder being magnesium, additives, and unavoidable impurities. The additives are one or a combination of tin, zinc, gadolinium, and yttrium, added in the following percentages: Sn 0-0.4%, Zn 0-0.5%, Gd 0-0.35%, Y 0-0.35%. The total alloy element content is ≤2.8%. The heat treatment process before and after extrusion is simple and time-efficient. The extrusion speed of the profile can reach 4-50 m / min, effectively saving production time and costs, making it suitable for large-scale production applications. The extruded profile has a yield strength of 200-250 MPa, a tensile strength of 275-290 MPa, an elongation of 7-16%, and a corrosion rate of 0.86-3.6 mL / cm² in a 3.5% sodium chloride solution. 2 / d, significantly lower than the hydrogen evolution rate of AZ31 alloy under the same conditions (8.67 mL / cm² after immersion in 3.5% sodium chloride solution for 3 days). 2While achieving a certain degree of simultaneous improvement in corrosion resistance and ductility, the strength and ductility of this alloy remain relatively low, far below the mechanical properties of commercially available high-strength magnesium alloys such as AZ80 and ZK60, and far from reaching ultra-high strength levels. Chinese patent CN114540683A discloses a micro-alloyed corrosion-resistant, low-cost magnesium alloy and its preparation method. The magnesium alloy composition by mass percentage is: Al 0.55~1.2%, Mn 0.5~0.65%, Zn 0~0.4%, Ca 0.01~0.03%, with the remainder being magnesium, additives, and unavoidable impurities; the additives are one or a combination of samarium and lanthanum, with the following mass percentages: Sm 0.01~0.2%, La 0.01~0.2%. The average hydrogen evolution rate of the alloy after immersion in a 3.5% sodium chloride solution for 3 days is 2.27-4.5 mL / cm³. 2 / d. Mechanical properties: average yield strength of 208-215 MPa, tensile strength of 270-279 MPa, and elongation of 9.8-10.9%. Although the alloy in this invention exhibits better corrosion resistance than the AZ31 alloy, its corrosion rate is still relatively high, and its corrosion resistance is insufficient. Simultaneously, the strength and plasticity of this alloy are also relatively low, far below the mechanical properties of commercially available high-strength magnesium alloys such as AZ80 and ZK60, and it is still far from reaching the ultra-high strength level. Chinese patent CN115466890A discloses a rapidly degradable high-strength and tough Cu-containing magnesium alloy material and its preparation method. The raw materials, calculated by mass percentage, include: Al 2~10 wt%, Cu 0.1~5.0 wt%, Mn 0.1~5.0 wt%; the balance being magnesium and unavoidable impurity elements. The room temperature tensile strength of this alloy is 318-377 MPa, and the elongation is 12-21%. The strength is still low, and due to the presence of the MgAlCu ternary phase, the corrosion resistance is very poor, making it impossible to produce alloy materials with good corrosion resistance.

[0004] Therefore, in order to better meet the requirements of transportation, aerospace, electronics, electrical appliances, weaponry and other fields for high-strength magnesium alloys that are low-cost, easy to process and high-performance, it is urgent to develop ultra-high-strength corrosion-resistant magnesium alloys and their preparation methods using simple and continuous production processes. This is of great significance for improving the application of wrought magnesium alloys. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of poor corrosion resistance, insufficient strength, difficulty in achieving both corrosion resistance and high mechanical properties, and high cost in existing high-strength magnesium alloys.

[0006] This invention relates to an ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy and its preparation method. The ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy has the following mass percentages of each component: Cu 0.2-1.8%, Zn 0.3-2.0%, Ca 0.15-0.7%, Mn 0.2-0.8%, impurity content ≤0.05%, and the balance being Mg, wherein the Zn content is not less than the Cu content.

[0007] The preparation method of the ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy of the present invention includes the following steps:

[0008] Step (1) Raw material preparation: Pure Mg ingots, pure Cu or Mg-Cu master alloy, pure Zn blocks, pure Ca or Mg-Ca master alloy and Mg-Mn master alloy are used as raw materials. After surface pretreatment, the materials are prepared according to the mass percentage of the magnesium alloy composition.

[0009] Step (2) Melting: Place pure Mg ingots into the crucible of the melting furnace, set the furnace temperature to 700~800℃ and maintain it. After melting, add pure Ca or Mg-Ca master alloy, pure Cu or Mg-Cu master alloy, pure Zn block and Mg-Mn master alloy preheated to 50~200℃ to the magnesium melt in sequence. Hold the temperature for 5~50 minutes. After the master alloy melts, stir for 1~7 minutes, remove the slag and then cool down to 680~750℃, refine for 1~20 minutes, remove the slag again and then hold at 680~730℃ for 10~80 minutes to obtain a uniform alloy melt, ready for casting. The melting, stirring and holding of the alloy are carried out under the protection of a protective solvent or protective atmosphere.

[0010] Step (3) Casting: The uniformly smelted magnesium alloy melt is cast using sand casting, metal mold casting or semi-continuous casting under a protective atmosphere to obtain a cast billet;

[0011] Step (4) Heat treatment: The alloy ingot obtained in step (3) is heat treated in a heat treatment furnace at a temperature of 380~530℃ for 2~48 hours, and then cooled to room temperature by air cooling or water cooling.

[0012] Step (5) Machining: Cut the heat-treated billet into the corresponding specifications and remove the surface oxide scale;

[0013] Step (6) Deformation processing: The de-oxidized blank obtained in step (5) is heated to 200~450 ℃, and then placed in a deformation mold for hot deformation processing with a deformation strain rate of 0.01s. -1 -4s -1 Between these conditions, the cumulative deformation is greater than 0.8 mm. After deformation, the material is cooled to obtain the ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy.

[0014] Compared with the prior art, the significant advancements and advantages of the present invention are as follows:

[0015] 1) The novel Mg-Cu-Zn-Ca-Mn magnesium alloy of this invention successfully introduces a large number of low-potential in-situ endogenous nanoparticle reinforcing phases into the magnesium alloy through a simple alloying method. These phases are dispersed on the matrix, overcoming the limitation that the size of precipitated reinforcing phases in magnesium alloys is generally large (above 100 nm). Moreover, they are generated in situ with good interfacial bonding. The large number of nano-reinforcing phases can effectively pin grain boundaries and dislocation movement, exerting a strengthening effect. On the other hand, they can control the deformation and recrystallization process of the matrix, generating a large number of ultrafine grain structures in the matrix. At the same time, due to the low potential difference between them and the matrix, they will not cause obvious microgalvanic corrosion. Their uniform dispersion characteristics can make the corrosion process more slight and uniform, avoiding the occurrence of severe local point potentials.

[0016] 2) The novel Mg-Cu-Al-Ca-Mn magnesium alloy of the present invention has a large number of solute segregation structures at the grain boundaries of recrystallized grains and the subgrain boundaries of deformed grains. These structures work synergistically with the above-mentioned nanoprecipitates to significantly refine the grains and thus greatly improve the mechanical properties of the alloy. In addition, a dense oxide film is formed during the corrosion process to enhance the corrosion resistance of the alloy.

[0017] 3) The alloy system of this invention has a low content of elements, with the maximum content of each alloying element not exceeding 2wt%. Combined with the control of the processing and preparation process, the size of the micron-sized second phase in the alloy is also relatively small. While optimizing the alloy structure and improving the mechanical properties of the alloy, it will not cause obvious rupture to the matrix and will also avoid the occurrence of severe local pitting corrosion, thereby improving the corrosion resistance of the alloy.

[0018] 4) Through the synergistic regulation of alloy composition and processing technology, a large number of ultrafine grain structures with a size of less than 500 nm were successfully constructed in the alloy of this invention. At the same time, a small number of strongly textured deformed grains also exist in the alloy. This synergistic effect of multi-scale microstructure significantly improves the strength and toughness of the alloy. In addition, the large number of ultrafine grains in the alloy microstructure provides a large number of grain boundaries, which makes the small amount of impurity elements more diluted and dispersed. These effects can also make the corrosion process more slight and uniform, and weaken the adverse effects of trace impurity elements on the corrosion resistance of the alloy.

[0019] 5) The alloy of this invention exhibits excellent mechanical properties. Currently, the yield strength of commercially available high-strength magnesium alloy AZ31 under the same extrusion conditions is only around 213 MPa, while the alloy of this invention can achieve a minimum corrosion rate as low as 0.5 mL / cm. 2With a tensile yield strength of up to 545 MPa and an elongation of about 10%, it exhibits excellent strength and plasticity matching, achieving a level of toughness comparable to ultra-high strength aluminum alloys. Furthermore, it possesses excellent corrosion resistance, making it significant for the development and industrial application of ultra-high performance structural and functional integrated magnesium alloys and their products.

[0020] 6) The alloy of this invention exhibits relatively uniform and stable melting. Due to the good flame-retardant properties of Ca in the magnesium alloy, the melt is also relatively stable. Simultaneously, since Zn, Ca, and Cu, one of the main alloying elements, readily react with the magnesium melt and melt, the intermediate alloy has a low melting point, easily resulting in a uniform alloy melt. Furthermore, some Zn, Ca, and Mn elements can react with impurity elements in the melt, reducing the adverse effects of impurity elements on the alloy's microstructure and properties, further weakening their harmful effects.

[0021] 7) The total content of alloying elements in the alloy of the present invention does not exceed 5 wt%, and the second phase in the alloy has high thermal stability, which makes the alloy have excellent plastic processing performance. It can be hot-processed and deformed in a wide temperature range, thereby reducing the resistance to hot deformation and improving processing or production efficiency.

[0022] 8) The novel high-strength magnesium alloy of this invention does not contain any rare earth elements or high-valence alloying elements. The corresponding element resources are abundant and the raw materials are widely available. The prices of metallic Mg, Zn, pure Cu, Mg-Cu master alloy, pure Ca, Mg-Ca master alloy and Mg-Mn master alloy are low, which can reduce the production cost of the alloy.

[0023] 9) The magnesium alloy composition design of this invention adopts the principle of multi-element trace alloying, giving full play to the role of each element. At the same time, there is no mutual reduction effect between them, but rather a mutual promotion effect. The total amount of alloying elements is low, the solidus temperature of the alloy is higher, and the higher alloying magnesium alloy will be closer to the melting point of pure magnesium. At the same time, the solute segregation structure at the grain boundary will further improve the strength of the grain boundary, which is expected to be a material for high-strength heat-resistant magnesium alloy parts.

[0024] 10) The Cu element in the magnesium alloy of this invention also has a bactericidal effect, and Zn and Ca are elements that promote bone healing, which can be used as potential materials for biomedical devices.

[0025] 11) The magnesium alloy preparation process of this invention is simple and breaks through the limitations of special processing methods such as large plastic deformation required by most high-strength magnesium alloys. At the same time, it can achieve ultra-high strength, good plasticity and corrosion resistance without special heat treatment after deformation processing. Existing magnesium alloy extrusion equipment, rolling equipment and forging equipment can all continuously process and produce it without additional modifications, and the requirements for production equipment are low. Attached Figure Description

[0026] Figure 1 This is a typical tensile stress-strain curve of the magnesium alloy in Example 2. Figure 2 The image shows the SEM microstructure of the deformed and recrystallized regions of the magnesium alloy in Example 2. Figure 3 The image shows the SEM microstructure of the recrystallization region of the magnesium alloy in Example 2. Figure 4 This is a TEM bright-field image of the magnesium alloy from Example 2. Figure 5 This is a high-angle annular dark-field image of the magnesium alloy from Example 2. Figure 6 This is a typical tensile stress-strain curve for the magnesium alloy in Example 3. Implementation

[0027] This invention relates to an ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy and its preparation method. The ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy has the following mass percentages of each component: Cu 0.2-1.8%, Zn 0.3-2.0%, Ca 0.15-0.7%, Mn 0.2-0.8%, impurity content ≤0.05%, and the balance being Mg, wherein the Zn content is not less than the Cu content.

[0028] The preparation method of the ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy of the present invention includes the following steps:

[0029] Step (1) Raw material preparation: Pure Mg ingots, pure Cu or Mg-Cu master alloy, pure Zn blocks, pure Ca or Mg-Ca master alloy and Mg-Mn master alloy are used as raw materials. After surface pretreatment, the materials are prepared according to the mass percentage of the magnesium alloy composition.

[0030] Step (2) Melting: Place pure Mg ingots into the crucible of the melting furnace, set the furnace temperature to 700~800℃ and maintain it. After melting, add pure Ca or Mg-Ca master alloy, pure Cu or Mg-Cu master alloy, pure Zn block and Mg-Mn master alloy preheated to 50~200℃ to the magnesium melt in sequence. Hold the temperature for 5~50 minutes. After the master alloy melts, stir for 1~7 minutes, remove the slag and then cool down to 680~750℃, refine for 1~20 minutes, remove the slag again and then hold at 680~750℃ for 10~80 minutes to obtain a uniform alloy melt, ready for casting. The melting, stirring and holding of the alloy are carried out under the protection of a protective solvent or protective atmosphere.

[0031] Step (3) Casting: The uniformly smelted magnesium alloy melt is cast using sand casting, metal mold casting or semi-continuous casting under a protective atmosphere to obtain a cast billet;

[0032] Step (4) Heat treatment: The alloy ingot obtained in step (3) is heat treated in a heat treatment furnace at a temperature of 380~530℃ for 2~48 hours, and then cooled to room temperature by air cooling or water cooling.

[0033] Step (5) Machining: Cut the heat-treated billet into the corresponding specifications and remove the surface oxide scale;

[0034] Step (6) Deformation processing: The de-oxidized blank obtained in step (5) is heated to 200~450 ℃, and then placed in a deformation mold for hot deformation processing with a deformation strain rate of 0.01s. -1 -4s -1 Between these conditions, the cumulative deformation is greater than 0.8 mm. After deformation, the material is cooled to obtain the high-strength, corrosion-resistant, multi-element low-alloy magnesium alloy.

[0035] The preparation methods described above include the Mg-Ca master alloy Mg-20Ca master alloy, Mg-Mn master alloy Mg-5Mn master alloy, and Mg-Cu master alloy Mg-30Cu mentioned in step (1).

[0036] In the preparation method described above, the stirring in step (2) is mechanical stirring, gas blowing stirring, electromagnetic stirring, or a combination thereof.

[0037] In the preparation method described above, the protective solvent in step (2) is preferably RJ-5.

[0038] In the preparation method described above, the protective atmosphere in step (2) is preferably a mixed gas with a volume ratio of CO2:SF6 = 50~100:1.

[0039] In the preparation method described above, the protective atmosphere in step (3) is preferably a mixed gas with a volume ratio of CO2:SF6 = 50~100:1.

[0040] The preparation method described above, the heat treatment in step (4) is a single-stage heat treatment or a double-stage heat treatment. The single-stage heat treatment is to hold at a constant temperature between 410 and 500°C for 2 to 48 hours and then cool. The double-stage heat treatment is to first heat treat at a constant temperature between 380 and 430°C for 2 to 24 hours and then heat to a temperature between 460 and 530°C for 1 to 24 hours.

[0041] The above-described preparation method, in step (6), the deformation process can be extrusion deformation, rolling deformation, forging, or a combination thereof.

[0042] The preparation method described above, the mold in step (6) is a mold used to form plates, rods, pipes, wires, profiles, or cylindrical parts.

[0043] The essential features of this invention are:

[0044] Obtaining a high proportion of ultrafine grain structure, dispersed distribution of various low-potential nano-precipitates, and corresponding solute agglomerates are important measures to endow alloys with excellent strength and corrosion resistance. However, it is generally difficult to construct such microstructures in magnesium alloys. At the same time, by controlling the type of second phase in the alloy, the solute agglomerates at the interface, and the content of solid solution atoms and impurities in the matrix, magnesium alloys with excellent corrosion resistance can be obtained. Under normal conditions, the introduction of Cu into magnesium alloys severely deteriorates their corrosion resistance. This invention, through comprehensive control of alloy composition and processing technology, enables Zn and Cu elements in the alloy to form 5-100 nm nanoscale MgZnCu in situ with Mg, avoiding the formation of Mg2Cu with higher potential and reducing the potential difference between the second phase and the matrix. By controlling the preparation process, the content of impurity elements in the alloy is reduced, thereby minimizing the damage of impurity elements and their compounds to the alloy's corrosion resistance. In addition, a large number of fine Mn particles are induced in the alloy matrix, while solute segregation clusters of Zn, Ca, and Mn atoms are constructed at grain boundaries and phase boundaries, inhibiting microgalvanic corrosion. Finally, the synergistic effect of Cu, Zn, Ca, and Mn elements enhances the compactness of corrosion products, thereby further increasing the alloy's corrosion resistance.

[0045] The nano-precipitates and solute segregation structures in the alloy can, on the one hand, play a strengthening role, and on the other hand, regulate the deformation and recrystallization process of the matrix. This results in a large number of ultrafine-grained structures as well as some non-recrystallized deformed structures containing residual dislocations. Furthermore, the fine micron-sized second phases that are not dissolved into the matrix during heat treatment are further broken down and dispersed in the matrix during deformation. These second phases, synergistically with the dynamically precipitated nanoparticles and grain boundary segregating elements during hot deformation, effectively promote recrystallization nucleation and inhibit recrystallized grain growth, which is also conducive to the formation of ultrafine-grained structures. Simultaneously, the smaller size of these second phases can reduce their adverse effects on corrosion resistance and provide more interfaces. These interfaces can pin dislocations in the grain boundaries and matrix when the alloy is deformed by external forces, improving the overall mechanical properties and corrosion resistance of the alloy. Through synergistic control of alloy composition and processing technology, a large number of ultrafine grains with a size below 500 nm were successfully constructed in the alloy of this invention. Simultaneously, a small number of strongly textured deformed grains also exist in the alloy. This multi-scale microstructure synergy significantly improves the strength and toughness of the alloy. Furthermore, the grain refinement provides numerous grain boundary interfaces, further reducing the density of minor impurity elements and mitigating their adverse effects on corrosion resistance. Finally, the small amounts of Cu, Zn, Ca, and Mn elements dissolved in the matrix can also exert a certain solid solution strengthening effect and improve the density of the corrosion product film. Considering all these factors, the prepared Mg-Cu-Zn-Ca-Mn alloy exhibits excellent strengthening and toughening effects and corrosion resistance.

[0046] The technical solution of the present invention will be described in detail below through specific embodiments. The following embodiments are all implemented under the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments. Example

[0047] The design selects an alloy composition of Mg-0.25Cu-0.6Zn-0.25Ca-0.35Mn (wt%) to prepare a magnesium alloy. The preparation method includes the following steps:

[0048] (1) Ingredients: Pure Mg (99.99wt%) ingots, pure Zn (99.99wt%) blocks, pure Ca (99.98wt%) granules, Mg-20Cu master alloy (actual Cu content is 20.1wt%) and Mg-10Mn master alloy (actual Mn content is 10.1wt%) are used as raw materials. After surface pretreatment (such as removing dirt, oxide scale, etc., the same in the following examples), the ingredients are prepared according to the above weight percentage of magnesium alloys.

[0049] (2) Alloy smelting: Clean and preheat the crucible. Place the magnesium ingot, preheated to 150°C, into the crucible of the smelting furnace. Set the furnace temperature to 720°C and heat the magnesium ingot. When the temperature reaches 500°C, start introducing a mixed gas of Ar:SF6 = 100:1 (volume flow ratio) to protect against combustion. After the magnesium is completely melted, add pure Ca, preheated to 60°C, to the melt. After melting, add pure Zn blocks, then add Mg-20Cu master alloy, and finally add Mg-10Mn master alloy. After melting, mechanically stir for 2 minutes, remove the surface slag, and let stand at the temperature for 35 minutes to ensure that all alloying elements are evenly distributed in the magnesium alloy melt.

[0050] (3) Casting: Skim off the slag on the surface of the melt, and then cast it into a cylindrical mold with a diameter of 60 mm under the protection of a mixed gas of CO2:SF6 = 90:1 (volume flow ratio) to obtain the cast billet;

[0051] (4) Heat treatment: After removing the riser, the alloy ingot prepared in step (3) is heated to 400°C in the furnace and held at this temperature for 24 hours for homogenization treatment. Then it is quenched in warm water and cooled to room temperature. The heating time is 60 minutes. This heat treatment process does not require gas protection.

[0052] (5) Machining: Turning is used to remove the oxide layer on the surface of the alloy ingot after heat treatment in step (4) and to process it into a bar suitable for extrusion.

[0053] (6) Plastic processing: Heat the billet for 30 minutes to reach the required extrusion temperature, put it into the extrusion cylinder of the extruder for extrusion processing, and obtain a bar with a diameter of 10mm. The main process parameters during extrusion are: billet temperature 280℃, extrusion cylinder temperature 280℃, die temperature 280℃, extrusion speed 3m / min, extrusion ratio 36, and the extruded material is cooled by air cooling, thus obtaining a low-cost non-rare earth high-strength magnesium alloy.

[0054] Alloy performance testing and microstructure analysis: A 70 mm long sample was cut from the extruded magnesium alloy rod and processed into a cylindrical tensile specimen with a gauge length of 20 mm and a gauge diameter of 4 mm. The axial direction of the cylindrical specimen was aligned with the extrusion streamline direction of the material. The tensile strength of the magnesium alloy described in this invention was measured to be 512 ± 4 MPa, the yield strength to be 503 ± 3 MPa, and the elongation to be 9.8 ± 1%. Its corrosion rate in 3.5 wt% NaCl solution was 0.5 mL / cm². 2 / d, exhibiting ultra-high strength and plasticity as well as excellent corrosion resistance. Example

[0055] The design selects an alloy composition of Mg-0.45Cu-0.65Zn-0.35Ca-0.45Mn (wt%) to prepare a magnesium alloy. The preparation method includes the following steps:

[0056] (1) Ingredients: Pure Mg (99.99wt%) ingots, pure Zn (99.99wt%) blocks, Mg-20Ca master alloy (actual Ca content is 19.98wt%), Mg-20Cu master alloy (actual Cu content is 20.1wt%) and Mg-10Mn master alloy (actual Mn content is 10.1wt%) are used as raw materials. After surface pretreatment (such as removing dirt, oxide scale, etc., the same in the following examples), the ingredients are prepared according to the above-mentioned weight percentage of magnesium alloys.

[0057] (2) Alloy smelting: Clean and preheat the crucible, place the magnesium ingot preheated to 150°C into the crucible of the smelting furnace, set the furnace temperature to 740°C to heat the magnesium ingot, and cover the surface of the magnesium alloy with RJ-5 solvent. After the magnesium is completely melted, add the pure Zn block preheated to 150°C and the Mg-20Ca master alloy to the melt in sequence. After melting, add the Mg-30Cu master alloy, and after melting, add the Mg-5Mn master alloy. After melting, mechanically stir for 2 minutes, let stand for 5 minutes, then introduce argon gas to the bottom of the melt and treat for 2 minutes. Then remove the surface slag, introduce a CO2:SF6 = 99:1 (flow ratio) mixed gas above the surface of the melt for protection, keep it at the temperature and let it stand for 25 minutes to make all alloying elements evenly distributed in the magnesium alloy melt.

[0058] (3) Casting: Skim off the slag on the surface of the melt, and then cast it in a metal mold under the protection of a mixed gas of CO2:SF6 = 95:1 (volume flow ratio). Then, a non-rare earth magnesium alloy ingot with a diameter of 60 mm is prepared by metal mold casting.

[0059] (4) Heat treatment: After removing the riser, the alloy ingot prepared in step (3) is heated to 460℃ in the furnace and held for 36 hours, and then quenched in warm water.

[0060] (5) Machining: Turning is used to remove the oxide layer on the surface of the alloy ingot after heat treatment in step (4) and to process it into a size suitable for extrusion processing;

[0061] (6) Plastic processing: Heat the billet for 30 minutes to reach the required extrusion temperature, put it into the extrusion cylinder of the extruder for extrusion processing, and obtain a bar with a diameter of 10 mm. The main process parameters during extrusion are: billet temperature 300℃, extrusion cylinder temperature 300℃, die temperature 300℃, extrusion speed 2m / min, extrusion ratio 36, and the extruded material is cooled by air cooling, thus obtaining a low-cost non-rare earth type high-strength magnesium alloy.

[0062] Alloy performance testing and microstructure analysis: A 70mm long sample was cut from the extruded magnesium alloy rod and processed into a cylindrical tensile specimen with a gauge length of 20mm and a gauge diameter of 4mm. The axial direction of the cylindrical specimen was aligned with the extrusion flow lines of the material. The tensile strength of the magnesium alloy described in this invention was measured to be 526±4 MPa, the yield strength to be 518±3 MPa, and the elongation to be 10.3±0.5%. Its corrosion rate in 3.5wt% NaCl solution was 0.8 mL / cm². 2 / d, exhibiting ultra-high strength and ductility as well as excellent corrosion resistance. The typical tensile curve of the magnesium alloy obtained in this embodiment is shown below. Figure 1 As shown, the magnesium alloy obtained in this embodiment has both ultra-high strength and good elongation. Figure 2 The SEM microstructure of the deformed and recrystallized regions of the magnesium alloy prepared in this embodiment shows that a large number of second phases are dispersed on the deformed grains of recrystallization, and the grains in the nearby dynamic recrystallization region are extremely fine, with grain sizes all below 1 micrometer. Figure 3 The SEM microstructure of the recrystallized region of the magnesium alloy prepared in this embodiment shows that its average grain size is about 500 nm, and there are a large number of fine white precipitates on the matrix. Figure 4 This is a bright-field TEM image of the alloy in this embodiment. It shows grains with a size of more than 1 micrometer and grains with a size of less than 500 nm. There are also a large number of nano-precipitates on the matrix, with a size of about 10-50 nm. These precipitates are MgZnCu nano-precipitates, Mg2Ca nano-precipitates, and Mn nano-precipitates. Figure 5 The high-angle annular dark-field image of the alloy in this embodiment reveals significant solute segregation at the fine recrystallization grain boundaries, primarily formed by the segregation of one or more of Ca, Zn, Cu, and Mn elements. This demonstrates that the microstructure of the alloy of this invention can be specifically controlled through alloy composition and processing technology to obtain a mixed-grain structure with ultrafine grains, and to construct a microstructure containing multiple nano-precipitates and solute segregation structures, thereby obtaining an alloy billet with ultra-high strength, good plasticity, and excellent corrosion resistance. Example

[0063] The magnesium alloy was designed and prepared using an alloy composition of Mg-0.8Cu-0.9Zn-0.35Ca-0.6Mn (wt%). The preparation method includes the following steps:

[0064] (1) Ingredients: Pure Mg (99.99wt%) ingots, pure Zn (99.99wt%) blocks, Mg-20Ca master alloy (actual Ca content is 19.98wt%), Mg-20Cu master alloy (actual Cu content is 20.1wt%) and Mg-10Mn master alloy (actual Mn content is 10.1wt%) are used as raw materials. After surface pretreatment (such as removing dirt, oxide scale, etc., the same in the following examples), the ingredients are prepared according to the above-mentioned weight percentage of magnesium alloys.

[0065] (2) Alloy smelting: Clean and preheat the crucible. Place the magnesium ingot, preheated to 150°C, into the crucible of the smelting furnace. Set the furnace temperature to 720°C and heat the magnesium ingot. When the temperature reaches 500°C, start introducing a CO2:SF6 = 100:1 (flow ratio) mixed gas to protect against combustion. After all the magnesium has melted, add the Mg-20Ca master alloy, preheated to 150°C, to the melt. After melting, add pure Zn blocks, then add the Mg-30Cu master alloy, and finally add the Mg-5Mn master alloy. After melting, mechanically stir for 2 minutes, remove the surface slag, and keep it at the temperature for 20 minutes to ensure that all alloying elements are evenly distributed in the magnesium alloy melt.

[0066] (3) Casting: Skim off the slag on the surface of the melt, and then cast it into a cylindrical mold with a diameter of 60 mm under the protection of a mixed gas of CO2:SF6 = 100:1 (flow ratio) to prepare a non-rare earth magnesium alloy ingot.

[0067] (4) Heat treatment: After removing the riser, the alloy ingot prepared in step (3) is heated to 410°C in the furnace and held at this temperature for 12 hours. Then, the temperature is increased to 450°C in 10 minutes and held for 24 hours. Then, it is quenched in warm water and cooled to room temperature.

[0068] (5) Machining: Turning is used to remove the oxide layer on the surface of the alloy ingot after heat treatment in step (4) and to process it into a size suitable for extrusion processing;

[0069] (6) Plastic processing: The billet is heated for 30 minutes to reach the required extrusion temperature, and then placed into the extrusion cylinder of the extruder for extrusion processing to obtain a bar with a diameter of 12 mm. The main process parameters during extrusion are: billet temperature 330℃, extrusion cylinder temperature 330℃, die temperature 330℃, extrusion speed 3m / min, extrusion ratio 25, and the extruded material is cooled by air cooling to obtain a low-cost non-rare earth high-strength magnesium alloy.

[0070] Alloy performance testing and microstructure analysis: A 50mm long sample was cut from the extruded magnesium alloy bar and processed into a round bar tensile specimen with a gauge length of 20mm and a gauge diameter of 4mm. The axial direction of the round bar specimen was aligned with the extrusion flow lines of the material. The tensile strength of the magnesium alloy described in this invention was measured to be 556±4MPa, the yield strength to be 545±2MPa, and the elongation to be 12.7±1%. The typical tensile curve of the magnesium alloy obtained in this example is shown below. Figure 6 As shown, the magnesium alloy obtained in this embodiment possesses both ultra-high strength and good elongation. Further measurements revealed its corrosion rate in a 3.5 wt% NaCl solution to be 1.4 mL / cm. 2 / d, exhibiting ultra-high strength and plasticity as well as excellent corrosion resistance. Example

[0071] The design selects an alloy composition of Mg-1.5Cu-1.6Zn-0.35Ca-0.5Mn (wt%) to prepare a magnesium alloy. The preparation method includes the following steps:

[0072] (1) Ingredients: Pure Mg (99.99wt%) ingots, pure Zn (99.99wt%) blocks, Mg-20Ca master alloy (actual Ca content is 19.98wt%), Mg-20Cu master alloy (actual Cu content is 20.1wt%) and Mg-10Mn master alloy (actual Mn content is 10.1wt%) are used as raw materials. After surface pretreatment (such as removing dirt, oxide scale, etc., the same in the following examples), the ingredients are prepared according to the above-mentioned weight percentage of magnesium alloys.

[0073] (2) Alloy smelting: Clean and preheat the crucible. Place the magnesium ingot, preheated to 150°C, into the crucible of the smelting furnace. Set the furnace temperature to 720°C and heat the magnesium ingot. When the temperature reaches 500°C, start introducing a CO2:SF6 = 100:1 (flow ratio) mixed gas to protect against combustion. After the magnesium is completely melted, add the Mg-20Ca master alloy, preheated to 150°C, to the melt. After melting, add pure Zn blocks, then add the Mg-30Cu master alloy, and finally the Mg-5Mn master alloy. After melting, mechanically stir for 2 minutes, remove the surface slag, and keep it at the temperature for 25 minutes to ensure that all alloying elements are evenly distributed in the magnesium alloy melt.

[0074] (3) Casting: Skim off the slag on the surface of the melt, and then use semi-continuous casting under the protection of CO2:SF6 =100:1 (flow ratio) mixed gas to prepare a cylindrical semi-continuous casting alloy ingot with a diameter of 70 mm through a crystallizer.

[0075] (4) Heat treatment: After removing the riser, the alloy ingot prepared in step (3) is heated to 460℃ in the furnace and held for 36 hours, and then quenched in warm water.

[0076] (5) Machining: Turning is used to remove the oxide layer on the surface of the alloy ingot after heat treatment in step (4) and to process it into a size suitable for extrusion processing;

[0077] (6) Plastic processing: The cylindrical blank with a height of 110 mm and a diameter of 65 mm obtained after machining is placed into a mold for forging deformation processing. The blank temperature is 350℃, the forging mold temperature is 350℃, and the forging is carried out with a pressing head speed of 10 mm / s. After forging, a disc-shaped sample with a height of 20 mm is obtained. Then, it is kept at 120℃ for 10 minutes and then air-cooled to room temperature to obtain a low-cost non-rare earth high-strength magnesium alloy.

[0078] Alloy performance testing and microstructure analysis: A 60mm long sample was cut from the prepared forged magnesium alloy billet and machined into a round bar-shaped tensile specimen with a gauge length of 20mm and a gauge diameter of 4mm. Tensile tests were then conducted. The tensile strength of the magnesium alloy described in this invention was measured to be 507±4MPa, the yield strength to be 488±3MPa, and the elongation to be 12.6±0.5%. Furthermore, its corrosion rate in a 3.5wt% NaCl solution was measured to be 3.0 mL / cm². 2 / d, exhibiting ultra-high strength and plasticity as well as good corrosion resistance.

[0079] Comparative Example 1

[0080] The comparative example is a currently commercially available magnesium alloy: Mg-2.9Al-0.45Zn-0.3Mn (wt%, AZ31) magnesium alloy. Using pure Mg (99.99 wt%) ingots, pure Al (99.99 wt%) blocks, pure Zn (99.99 wt%) blocks, and Mg-5Mn master alloy (actual Mn content measured to be 5.1 wt%) as raw materials, after surface pretreatment, the alloy was prepared according to the weight percentages of the comparative example magnesium alloy. The remaining processing and preparation steps were the same as in Example 1. The resulting AZ31 alloy had a tensile strength of 294 ± 3 MPa, a yield strength of 213 ± 2 MPa, and an elongation of 16.2 ± 1.5%. Furthermore, its corrosion rate in 3.5 wt% NaCl solution was measured to be 9.2 mL / cm². 2 As can be seen from the comparison, the magnesium alloy of the present invention has significantly higher strength and plasticity than the conventional commercial AZ31 magnesium alloy, achieving mechanical properties similar to ultra-high strength wrought aluminum alloys, while also having excellent corrosion resistance. It is a highly competitive ultra-high strength corrosion-resistant magnesium alloy.

[0081] Comparative Example 2

[0082] The magnesium alloy was prepared by selecting an alloy composition of Mg-1Cu-0.6Zn-0.35Ca-0.5Mn (wt%). The remaining processing and preparation steps were the same as in Example 3. The resulting comparative alloy had a tensile strength of 577±3 MPa, a yield strength of 548±2 MPa, and an elongation of 11.6±1%. Furthermore, its corrosion rate in a 3.5wt% NaCl solution was measured to be 107 mL / cm². 2 / d, as can be seen from the comparison, when the Cu content in the alloy is higher than the Zn content, the mechanical properties of the alloy do not change much, but the corrosion resistance deteriorates sharply. This is mainly due to the presence of the Mg2Cu phase in the alloy, which causes significant galvanic corrosion and leads to a decrease in the corrosion resistance of the alloy.

[0083] The raw materials and equipment used in the above embodiments are all obtained through known means, and the operating processes used are mastered by those skilled in the art.

Claims

1. A method for preparing a super-high-strength corrosion-resistant multi-element low-alloyed magnesium alloy, the mass percentage of each component being: Cu 0.2-1.8%, Zn 0.3-2.0%, Ca 0.15-0.7%, Mn 0.2-0.8%, impurity content ≤0.05%, and the balance being Mg, wherein the content of Zn is not lower than the content of Cu, characterized in that, The steps include: Step (1) batching: pure Mg ingot, pure Cu or Mg-Cu intermediate alloy, pure Zn block, pure Ca or Mg-Ca intermediate alloy and Mg-Mn intermediate alloy are used as raw materials, after surface pretreatment, the materials are prepared according to the mass percentage of the magnesium alloy composition; Step (2) melting: the pure Mg ingot is put into the crucible of the melting furnace, the furnace temperature is set to 700-800℃ and maintained, after the pure Mg ingot is melted, the preheated pure Ca or Mg-Ca intermediate alloy, pure Cu or Mg-Cu intermediate alloy, pure Zn block and Mg-Mn intermediate alloy to 50-200℃ are gradually added into the magnesium melt; after the intermediate alloy is melted, stirring is carried out for 1-7 minutes, after slagging, the temperature is reduced to 680-750℃, refining is carried out for 1-20 minutes, after slagging again, the temperature is maintained at 680-750℃ for 10-80 minutes to obtain a uniform alloy melt, ready for pouring; the melting, stirring and standing of the alloy are carried out under the protection of a protective solvent or a protective atmosphere; Step (3) pouring: the uniformly melted magnesium alloy melt is poured under the protection of a protective atmosphere by sand casting, metal mold casting or semi-continuous casting to obtain a cast blank; Step (4) heat treatment: the alloy ingot prepared in step (3) is heat treated in a heat treatment furnace, the heat treatment temperature is 380-530℃, the time is 2-48 hours, and then air cooling or water cooling is used to cool to room temperature; Step (5) machining: the heat treated blank is cut into corresponding specifications and the surface oxide skin is removed; Step (6) deformation processing: the oxide scale removed blank obtained in step (5) is heated to 200-450℃, and then is put into a deformation die to perform hot deformation processing, the deformation strain rate is 0.01s -1 -4s -1 between, the cumulative deformation is 0.8 or more, and after deformation, cooling is performed to obtain the super-high-strength corrosion-resistant multi-element low-alloyed magnesium alloy.

2. The method for preparing ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy according to claim 1, characterized in that: In step (1), the Mg-Ca intermediate alloy is Mg-20Ca intermediate alloy, the Mg-Mn intermediate alloy is Mg-5Mn intermediate alloy, and the Mg-Cu intermediate alloy is Mg-30Cu intermediate alloy.

3. The method for preparing ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy according to claim 1, characterized in that: In step (2), the stirring is mechanical stirring, gas blowing stirring, electromagnetic stirring or a combination thereof.

4. The method for preparing ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy according to claim 1, characterized in that: In step (2), the protective solvent is RJ-5.

5. The method for preparing ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy according to claim 1, characterized in that: In step (2), the protective atmosphere is a mixed gas with a volume ratio of CO2:SF6=50-100:

1.

6. The method for preparing ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy according to claim 1, characterized in that: In step (3), the protective atmosphere is a mixed gas with a volume ratio of CO2:SF6=50-100:

1.

7. The method for preparing ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy according to claim 1, characterized in that: In step (4), the heat treatment is single-stage heat treatment or two-stage heat treatment, wherein the single-stage heat treatment is heat treatment at a constant temperature of 410-500℃ for 2-48 hours, followed by cooling, and the two-stage heat treatment is first heat treatment at a constant temperature of 380-430℃ for 2-24 hours, followed by high-temperature heat treatment at a temperature of 460-530℃ for 1-24 hours.

8. The method for preparing ultra-high strength corrosion-resistant multi-element low-alloy magnesium alloy according to claim 1, characterized in that: In step (6), the deformation processing is extrusion deformation, rolling deformation, forging or a combination thereof.

9. The method of making ultra-high strength corrosion resistant multi-low alloyed magnesium alloy according to claim 1, characterized in that: In step (6), the mold is a mold for forming a plate, a rod, a pipe, a wire, a profile or a cylindrical part.

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