Low-density high-modulus ultrahigh-strength magnesium-based composite material and preparation method thereof

Abstract

The invention relates to the technical field of magnesium alloys, in particular to a low-density, high-modulus and ultrahigh-strength magnesium-based composite material and a preparation method thereof.The preparation method comprises the steps that SiC reinforcement particles are pretreated; the raw materials are proportioned according to the mass percent of the components of the magnesium alloy; melting pure magnesium, sequentially adding alloy elements, uniformly stirring, cooling to a semi-solid temperature interval, adding the pretreated SiC reinforcement particles, and casting in a preheating mold to solidify, so as to obtain a magnesium-based composite material cast ingot; the cast ingot is sequentially subjected to solution treatment and extrusion forming; carrying out secondary solution treatment on the magnesium-based composite material bar subjected to extrusion forming; and performing rotary swaging deformation and intermediate annealing treatment on the magnesium-based composite material bar subjected to secondary solution treatment to obtain the ultrahigh-strength magnesium-based composite material. Therefore, the problems that in the prior art, magnesium alloy is insufficient in strength and modulus, a magnesium-based composite material easily generates casting defects and is difficult to deform at room temperature, and the performance of the material is weakened due to grain growth during high-temperature deformation are solved.

Description

Technical Field

[0001] This application relates to the field of magnesium alloy technology, and in particular to a low-density, high-modulus, ultra-high-strength magnesium-based composite material and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest structural metal materials, exhibit broad application prospects in aerospace, automotive, and 3C fields due to their low density, high specific stiffness and strength, easy recyclability, and good damping and electromagnetic shielding properties. Compared with currently widely used aluminum alloys and alloy steels, magnesium alloys have significant resource and density advantages, which are of great importance for energy conservation, emission reduction, and lightweight design of modern industrial products. However, the low absolute strength and insufficient elastic modulus of currently commercially available magnesium alloys limit their application as structural components under extreme conditions, which is a key factor restricting the further promotion and use of magnesium alloys.

[0003] Composite materials are an effective way to improve the strength and modulus of magnesium alloys. By adding high-hardness, high-modulus reinforcing particles to magnesium alloys, not only can the as-cast strength and modulus be improved, but their wear resistance and thermal stability can also be significantly enhanced. However, in actual production, magnesium-based composites often suffer from casting defects such as porosity and segregation in the as-cast state, which need to be eliminated through deformation to further improve mechanical properties. However, stress concentration easily occurs at the interface between the reinforcing material and the matrix alloy, especially at high reinforcing material contents. Plastic deformation can induce more severe stress concentration, leading to cracking and failure of the composite material during deformation. Therefore, magnesium-based composites usually need to be hot-deformed at high temperatures. However, excessively high deformation temperatures can lead to internal grain growth, weakening the grain refinement effect and accelerating the release of dislocations and stored energy, making it difficult to achieve the desired strengthening effect on the alloy matrix. Summary of the Invention

[0004] This application provides a low-density, high-modulus, ultra-high-strength magnesium-based composite material and its preparation method, in order to solve the problems of insufficient strength and modulus of magnesium alloys, easy casting defects in magnesium-based composite materials, difficulty in room temperature deformation, and grain growth weakening material properties during high-temperature deformation.

[0005] This application provides a low-density, high-modulus, ultra-high-strength magnesium-based composite material and its preparation method, comprising the following steps: pre-treating the reinforcing particles; proportioning the raw materials according to the composition of the magnesium alloy by mass percentage; melting pure magnesium and sequentially adding alloying elements, stirring evenly, cooling to the semi-solid temperature range, adding the pre-treated reinforcing particles, and casting into a preheated mold to solidify the mixed melt under pressure to obtain a magnesium-based composite material ingot; sequentially performing solution treatment and rod extrusion forming on the ingot; performing a secondary solution treatment on the extruded magnesium-based composite material rod; and performing rotary forging and intermediate annealing on the secondary solution-treated magnesium-based composite material rod to obtain a low-density, high-modulus, ultra-high-strength magnesium-based composite material.

[0006] Optionally, the pretreatment of the reinforcing particles includes: washing the reinforcing particles multiple times with a 0.3%-2% hydrofluoric acid aqueous solution to remove impurities, followed by washing with deionized water until the supernatant reaches neutrality; drying the reinforcing particles at a preset temperature; and making the size of the reinforcing particles uniform by passing them through a sieve with a predetermined aperture.

[0007] Optionally, the reinforcing particles are SiC with an average particle size of 1-20 micrometers and a mass percentage of 5%-30%.

[0008] Optionally, the raw materials are proportioned according to the composition of the magnesium alloy by mass percentage, and the raw materials include: Al: 4.97%-9.04%; Zn: 0.96%-5.03%; the remainder is Mg; the combined mass of Al and Zn accounts for 6%-12% of the total mass of the alloy, with Al content being higher than Zn content.

[0009] Optionally, pure magnesium is melted and alloying elements are added sequentially. After stirring evenly, the mixture is cooled to a semi-solid temperature range, pretreated reinforcing particles are added, and the mixture is cast into a preheated mold to solidify under pressure. This process includes: melting pure magnesium in a resistance furnace at 760-800℃; cooling to 740-750℃, removing the oxide film from the melt surface, adding pure Al, stirring thoroughly, and allowing it to stand for 5-20 minutes. min; then cool to 710-730℃, add pure Zn, and stir evenly; after standing for 10-30 minutes, cool the melt to the semi-solid temperature range (570-630℃) to make the melt a semi-solid slurry state, and add and start the stirring paddle to form a stable vortex in the center of the melt; then add the pretreated reinforcing particles to the center of the vortex, and after the addition is completed, stir the mixed melt clockwise for 8-15 minutes and counterclockwise for 5-8 minutes under mechanical stirring; after stirring, remove the stirring paddle, heat the mixed melt to 710-730℃, and then pour the melt into a mold with a preheated temperature of 350-450℃, and solidify under a pressure of 50-200MPa to obtain a magnesium-based composite material ingot.

[0010] Optionally, the process of smelting magnesium-based composite ingots is carried out under the protection of a mixture of CO2 and SF6 gas.

[0011] Optionally, the solution treatment temperature is 360-420°C, the solution treatment time is 6-24 hours, followed by immediate water quenching.

[0012] Optionally, the extrusion die is a magnesium alloy bar extrusion die, and the extrusion ratio is not less than 4:1. The extrusion temperature is 250-400℃, and the solution-treated billet is kept warm for 0.5-2 hours before extrusion. The inlet velocity during extrusion is 0.01-1mm / s.

[0013] Optionally, the temperature of the secondary solution treatment is 350-400℃, the secondary solution treatment time is 8-12 hours, and the solution is immediately cooled by water quenching after the secondary solution treatment.

[0014] Optionally, the rotary forging deformation includes multi-pass rotary forging deformation and single-pass rotary forging deformation, with an effective strain of 0-20% and a preheating temperature of 25-300℃ for the rotary forging bar; the annealing temperature is 200-450℃ and the annealing time is 15-120 minutes.

[0015] Therefore, this application has at least the following beneficial effects: (1) This invention utilizes the solid solution and precipitation strengthening effects of Al and Zn alloying elements on the matrix by designing the composition and content of magnesium alloys, while not weakening the deformability of the matrix and ensuring the formability of the matrix. The selection of SiC as a heteropolymer not only has excellent wettability with the matrix, but also has low density, high hardness and high modulus, which has a beneficial effect on the low density and high modulus of magnesium-based composite materials.

[0016] (2) This invention employs a semi-solid stirring casting method to add SiC to the matrix alloy, and finally solidifies the mixed melt under pressure. On the one hand, this ensures the uniform distribution of SiC particles in the matrix during mechanical stirring. On the other hand, solidification under pressure allows the trapped gas during stirring to be expelled, reducing porosity. Simultaneously, it enables the magnesium-based composite ingot to solidify rapidly, preventing uneven particle dispersion due to interface migration during solidification. Furthermore, solidification under pressure provides a greater driving force for grain nucleation during solidification, which is beneficial for grain refinement in the ingot.

[0017] (3) The embodiments of this application significantly improved the modulus of the material by adding hard SiC particles. At the same time, the multi-stage heat treatment and deformation process played a role in promoting the recrystallization of the matrix by SiC particles during the deformation process, which improved the microstructure of the material, refined the matrix grains, increased the dislocation density inside the material, and achieved a significant improvement in mechanical properties. (4) The embodiments of this application further eliminate casting defects, regulate microstructure, improve particle distribution, refine matrix precipitates and significantly improve the strength of the material by using a coupled process of hot deformation, cold deformation and heat treatment; (5) The hard SiC reinforcement used in the embodiments of this application has extremely low production cost and significant reinforcement effect; the alloy raw materials used do not depend on rare earth elements, and low-cost alloy elements can meet the requirements. (6) The preparation method in the embodiments of this application is applicable to a variety of common magnesium alloy systems. The type, size and content of the reinforcement can be selected according to actual needs, while meeting the mechanical properties and functional requirements of the application scenario. At the same time, the process is not highly dependent on equipment, and existing equipment can achieve continuous production.

[0018] This solves the technical problems in existing technologies, such as insufficient strength and modulus, easy casting defects in magnesium-based composite materials, difficulty in room temperature deformation, and grain growth that weakens material properties during high-temperature deformation.

[0019] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0020] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a flowchart of a method for preparing a low-density, high-modulus, ultra-high-strength magnesium-based composite material according to an embodiment of this application; Figure 2 This is an electron scanning morphology image of a low-density, high-modulus, ultra-high-strength magnesium-based composite material provided according to an embodiment of this application; Figure 3 This is a room temperature quasi-static tensile stress-strain curve of a low-density, high-modulus, ultra-high-strength magnesium matrix composite material provided according to an embodiment of this application. Figure 4 The room temperature compressive stress-strain curve of a low-density, high-modulus, ultra-high-strength magnesium matrix composite material provided according to an embodiment of this application. Detailed Implementation

[0021] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0022] In the embodiments of this application, unless otherwise specified, the raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0023] The following description, with reference to the accompanying drawings, illustrates an embodiment of a low-density, high-modulus, ultra-high-strength magnesium-based composite material and its preparation method. Addressing the issues of low absolute strength and modulus of magnesium alloys and insufficient strength of magnesium-based composite materials after high-temperature plastic deformation mentioned in the background art, this application provides a low-density, high-modulus, ultra-high-strength magnesium-based composite material. By introducing a high content of hard reinforcing particles into the magnesium alloy and combining hot deformation, cold deformation, and heat treatment processes, a magnesium-based composite material with low density, high modulus, and ultra-high strength is successfully prepared. This method effectively eliminates casting defects, regulates the microstructure, refines the matrix grains, improves the particle distribution, and refines the precipitates in the matrix, thereby significantly improving the overall performance of the material. Thus, it solves the problems of insufficient strength and modulus, easy casting defects in magnesium-based composite materials, and grain growth weakening material properties during high-temperature deformation in the prior art.

[0024] Example 1 This application provides a low-density, high-modulus, ultra-high-strength magnesium-based composite material and its preparation method, such as... Figure 1 As shown, it includes the following steps: S101. Pretreatment of the reinforcing particles.

[0025] The reinforcing particles can be SiC particles with an average particle size of 5 micrometers, and their mass percentage is 30%.

[0026] It is understood that the embodiments of this application, by pre-treating the reinforcing particles, effectively improve their wettability and interfacial bonding with the magnesium alloy matrix, reduce casting defects, optimize particle distribution, and thus significantly improve the strength, modulus and overall performance of magnesium-based composite materials.

[0027] In this embodiment, the pretreatment of the reinforcing particles includes: washing the reinforcing particles multiple times with hydrofluoric acid aqueous solution to remove impurities, then washing the particles with deionized water until the supernatant reaches neutrality; drying the reinforcing particles at a preset temperature; and using a sieve to make the reinforcing particles uniform in size.

[0028] Specifically, the SiC particles were cleaned and impurities removed using a 0.5% hydrofluoric acid aqueous solution, followed by repeated washing with deionized water to remove residual hydrofluoric acid until the pH of the supernatant reached neutral. The SiC particles were then dried at 80°C and passed through a 10-micron sieve.

[0029] S102. Proportion the raw materials according to the composition of the magnesium alloy by mass percentage.

[0030] In this embodiment, the raw materials are proportioned according to the composition of the magnesium alloy by mass percentage, and the raw materials include: Al: 6.04%; Zn: 5.98%; the remainder is Mg.

[0031] S103, melt pure magnesium and add alloying elements in sequence, stir evenly and cool to the semi-solid temperature range, add pretreated reinforcing particles, and cast into a preheated mold to solidify under pressure to obtain magnesium-based composite material ingot.

[0032] In this embodiment, pure magnesium is melted and alloying elements are added sequentially. After stirring evenly, the mixture is cooled to a semi-solid temperature range. Pretreated reinforcing particles are added, and the mixture is cast into a preheated mold to solidify under pressure. The process includes: melting pure magnesium in a resistance furnace at 760-800°C; cooling to 740-750°C, removing the oxide film on the surface of the melt, adding pure Al, stirring thoroughly, and letting it stand for 5-20 minutes; cooling to 710-730°C, adding pure Zn, and stirring evenly; letting it stand for 20 minutes, cooling the melt to a semi-solid temperature range, and starting the stirring paddle to form a vortex; adding the pretreated reinforcing particles under mechanical stirring, then stirring clockwise for 8-15 minutes and counterclockwise for 5-8 minutes; removing the stirring paddle, heating the mixed melt to 710-730°C, casting the melt into a mold preheated to 350-450°C, and solidifying it under a pressure of 50-200 MPa to obtain a magnesium-based composite material ingot.

[0033] Specifically, polished pure Mg is melted in a resistance furnace at 780℃, then cooled to 740℃ to remove the oxide film on the surface of the melt. Pure Al is added, stirred evenly, and allowed to stand for 10 minutes. Then, the temperature is lowered to 720℃, and pure Zn is added and stirred evenly. After standing for 20 minutes, the melt is cooled to 590℃, and a stirring paddle is added to continuously stir the melt, forming a vortex. SiC particles are added to the semi-solid melt under mechanical stirring. The melt is stirred clockwise for 10 minutes and then counterclockwise for 5 minutes. The temperature is then raised to 710℃, and the melt is poured into a mold preheated to 400℃, allowing the melt to solidify under a pressure of 125 MPa to obtain a magnesium-based composite material ingot.

[0034] It should be noted that the process of smelting magnesium-based composite material ingots is carried out under the protection of a mixture of CO2 and SF6 gas.

[0035] S104. The ingot is subjected to solution treatment and extrusion molding in sequence.

[0036] The solution treatment temperature is 360-420℃, the solution treatment time is 6-24 hours, followed by immediate water quenching; the extrusion die is a bar extrusion die, the extrusion ratio is not less than 4:1; the extrusion forming temperature is 250-400℃, the solution-treated billet is kept warm for 0.5-2 hours before extrusion, and the inlet speed during extrusion is 0.01-1mm / s.

[0037] Specifically, the solution treatment temperature is 380℃, the solution treatment time is 12 hours, followed by water quenching; the extrusion die is a bar extrusion die, the extrusion ratio is 16:1, the extrusion forming temperature is 350℃, the pre-extrusion billet holding time is 1 hour, and the extrusion inlet speed is 0.04mm / s.

[0038] S105. Perform a secondary solution treatment on the magnesium-based composite rods after extrusion molding.

[0039] The temperature of the secondary solution treatment is 350-400℃, the time of the secondary solution treatment is 8-12 hours, and then it is immediately cooled by water quenching.

[0040] Specifically, the temperature of the secondary solution treatment is 350℃, the secondary solution treatment time is 12 hours, followed by water quenching.

[0041] S106. The magnesium-based composite material rods after secondary solution treatment are subjected to rotary forging deformation and intermediate annealing to obtain low-density, high-modulus, ultra-high-strength magnesium-based composite materials.

[0042] Among them, rotary forging deformation includes multi-pass rotary forging deformation and single-pass rotary forging deformation, with an effective strain of 0-20%, a preheating temperature of 25-300℃ for the rotary forging bar, an annealing temperature of 200-450℃, and an annealing time of 15-120 minutes.

[0043] Specifically, such as Figure 2 As shown, the magnesium-based composite rods after secondary solution treatment underwent multi-pass rotary forging. The effective strain of the single-pass rotary forging deformation was 5%, and the rotary forging deformation temperature was room temperature. After two passes of rotary forging, the magnesium-based composite rods were annealed at 400℃ for 45 minutes. After annealing, they were water-cooled, and then the rods were subjected to two more passes of rotary forging at room temperature to finally obtain a high-modulus, ultra-high-strength magnesium-based composite material.

[0044] According to the embodiments of this application, a method for preparing a low-density, high-modulus, and ultra-high-strength magnesium-based composite material is proposed. By introducing high-content hard reinforcing particles into a magnesium alloy and combining hot deformation, cold deformation, and heat treatment processes, a magnesium-based composite material with low density, high modulus, and ultra-high strength is successfully prepared. This method effectively eliminates casting defects, regulates the microstructure, refines the matrix grains, improves the particle distribution, and refines the precipitates, thereby significantly improving the overall performance of the material. Thus, it solves the problems in the prior art such as insufficient strength and modulus of magnesium alloys, susceptibility to casting defects in magnesium-based composite materials, difficulty in forming at room temperature, and grain growth weakening material properties during high-temperature deformation.

[0045] Comparative Example 1 The comparative example has the same composition, component content, and reinforcement content as the magnesium-based composite material in Example 1. The only difference from Example 1 is that it has not undergone secondary solution treatment, rotary forging deformation, and annealing treatment.

[0046] Comparative Example 2 The comparative example uses the same preparation method as Example 1. The only difference from Example 1 is that no reinforcing particles were added to the components. The other components and their contents are the same as in Example 1.

[0047] Performance testing The low-density, high-modulus, ultra-high-strength magnesium-based composite materials prepared in Example 1 and Comparative Examples 1-2 were tested for density, modulus, and mechanical properties. The performance test results are shown in Table 1 below.

[0048] Table 1 Performance testing of low-density, high-modulus, ultra-high-strength magnesium-based composite materials

[0049] like Figure 3 and Figure 4 As shown, Example 1 of this application exhibits significantly higher strength, and subsequent rotary forging and annealing treatments achieve excellent strengthening effects on the magnesium-based composite material. Compared with Comparative Example 2, Example 1 of this application not only possesses higher strength but also a significantly improved modulus. The addition of a high content of hard SiC effectively refines the matrix structure, achieving a synergistic improvement in both strength and modulus.

[0050] According to the embodiments of this application, a method for preparing a low-density, high-modulus, and ultra-high-strength magnesium-based composite material is proposed. By introducing high-content hard reinforcing particles into a magnesium alloy and combining hot deformation, cold deformation, and heat treatment processes, a magnesium-based composite material with low density, high modulus, and ultra-high strength is successfully prepared. This method effectively eliminates casting defects, regulates the microstructure, refines the matrix grains, and improves the particle distribution, thereby significantly improving the overall performance of the material. Thus, it solves the problems in the prior art such as insufficient strength and modulus of magnesium alloys, susceptibility to casting defects in magnesium-based composite materials, difficulty in forming at room temperature, and grain growth weakening material properties during high-temperature deformation.

[0051] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

[0052] The present application and its embodiments have been described above. This description is not restrictive, and the actual application is not limited thereto. In conclusion, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the spirit of this application, such design should fall within the protection scope of this application.

Claims

1. A method for preparing a low-density, high-modulus, ultra-high-strength magnesium-based composite material, characterized in that, Includes the following steps: Pretreatment of SiC reinforced particles; The raw materials are proportioned according to the composition of the magnesium alloy by mass percentage; Pure magnesium is melted and alloying elements are added sequentially. After stirring evenly, the mixture is cooled to the semi-solid temperature range. Pretreated SiC reinforcement particles are added and the mixture is cast into a preheated mold to solidify under pressure, thus obtaining a magnesium-based composite material ingot. The ingot is subjected to solution treatment and extrusion molding in sequence; The extruded magnesium-based composite rods are subjected to a secondary solution treatment. The magnesium-based composite rods after the secondary solution treatment were subjected to rotary forging and intermediate annealing to obtain a low-density, high-modulus, ultra-high-strength magnesium-based composite material.

2. The method for preparing low-density, high-modulus, ultra-high-strength magnesium-based composite material according to claim 1, characterized in that, The pretreatment of the SiC reinforced particles includes: The SiC reinforced particles were repeatedly washed with hydrofluoric acid aqueous solution to remove impurities, and then washed with deionized water until the supernatant reached neutrality. The SiC reinforced particles are dried at a preset temperature; SiC reinforcing particles are passed through a sieve with a predetermined aperture to ensure that the reinforcing particles are of uniform size.

3. The method for preparing low-density, high-modulus, ultra-high-strength magnesium-based composite materials according to claim 2, characterized in that, The reinforcing particles are SiC with an average particle size of 5 micrometers and a mass percentage of 30%.

4. The method for preparing the low-density, high-modulus, ultra-high-strength magnesium-based composite material according to claim 1, characterized in that, The raw materials are proportioned according to the composition of the magnesium alloy by mass percentage, and the raw materials include: Al: 6.04%; Zn: 5.98%; the remainder is Mg.

5. The method for preparing the low-density, high-modulus, ultra-high-strength magnesium-based composite material according to claim 1, characterized in that, Pure magnesium is melted and high-melting-point and low-melting-point alloying elements are added sequentially. After stirring until homogeneous, the mixture is cooled to a semi-solid temperature range. Pretreated reinforcing particles are then added, and the mixture is cast into a preheated mold, including: Pure magnesium is melted in a resistance furnace at 750-800℃; Cool the melt to 740-750℃, remove the oxide film on the surface of the melt, and add high-melting-point alloying elements; Cool down to 710-730℃, add low-melting-point alloying elements, and stir until homogeneous; After standing for 20 minutes, the melt is cooled to the semi-solid temperature range, and the stirring paddle is started to form a vortex; Under mechanical stirring, stir clockwise for 8-15 minutes and counterclockwise for 5-8 minutes, then add the pretreated reinforcing particles; Heat the mixture to 710-730℃ and pour the melt into a mold preheated to 250-450℃.

6. The method for preparing the low-density, high-modulus, ultra-high-strength magnesium-based composite material according to claim 5, characterized in that, The process of smelting magnesium-based composite material ingots was carried out under the protection of a mixture of CO2 and SF6 gas.

7. The method for preparing low-density, high-modulus, ultra-high-strength magnesium-based composite material according to claim 1, characterized in that, The solution treatment temperature is 360-420℃, and the solution treatment time is 6-24 hours.

8. The method for preparing low-density, high-modulus, ultra-high-strength magnesium-based composite material according to claim 1, characterized in that, The extrusion molding temperature is 250-400℃, the holding time is 0.5-2 hours, and the extrusion inlet speed is 0.01-1mm / s.

9. The method for preparing low-density, high-modulus, ultra-high-strength magnesium-based composite material according to claim 1, characterized in that, The temperature of the secondary solution treatment is 350-400℃, and the time for the secondary solution treatment is 8-12 hours.

10. The method for preparing the low-density, high-modulus, ultra-high-strength magnesium-based composite material according to claim 1, characterized in that, The rotary forging deformation includes multi-pass rotary forging deformation and single-pass rotary forging deformation, with an effective strain of 0-20%, a preheating temperature of 25-300℃ for the rotary forging bar, an annealing temperature of 200-450℃, and an annealing time of 15-120 minutes.

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