Carbon nanotube reinforced magnesium alloy composite material and preparation method thereof

Abstract

The invention relates to a carbon nanotube reinforced magnesium alloy composite material and a preparation method thereof, and relates to the technical field of magnesium alloy composite materials. According to the main technical scheme, the preparation method comprises the following steps: carrying out ball-milling mixing treatment on aluminum powder and carbon nanotubes to obtain composite powder; then, the composite powder is sequentially subjected to cold pressing treatment and hot pressing sintering treatment, and the aluminum-based composite material is obtained; under the protective atmosphere, the aluminum-based composite material is added into molten magnesium liquid, and after stirring treatment, casting is conducted to form a cast ingot; and the cast ingot is subjected to hot extrusion treatment, and the carbon nano tube reinforced magnesium alloy composite material is obtained. The method is mainly used for improving the distribution uniformity of the carbon nanotubes in the magnesium alloy composite material, and the uniform distribution of the carbon nanotubes can ensure a dispersion strengthening mechanism, so that the performance of the composite material is ensured.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy composite materials technology, and in particular to a carbon nanotube reinforced magnesium alloy composite material and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials, are renowned for their high specific strength, specific stiffness, excellent damping properties, and biocompatibility, making them a promising lightweight structural metal material. Their lightweight advantage (density 1.74 g / cm³) is a key factor. 3 Magnesium alloys have shown significant value in the automotive and aerospace fields—a 10% reduction in car weight can reduce fuel consumption by 6–8%, and a 15% reduction in aircraft weight can increase range by 20%. However, their inherent defects, such as low absolute strength, poor corrosion resistance, and insufficient high-temperature creep performance, limit their engineering applications to some extent.

[0003] Carbon nanotubes (CNTs), as one-dimensional nanoreinforcements, are considered ideal for overcoming the performance bottlenecks of magnesium alloys due to their exceptional tensile strength (50-150 GPa), elastic modulus (1 TPa), and thermal conductivity (0.1–6600 W / mK). Theoretical calculations show that adding 1.5 vol.% CNTs can increase the strength of AZ91 by 80%, and their tubular structure can serve as a heterogeneous nucleation core for the α-Mg phase, refining the grain size to <10 μm (>50 μm without CNTs). However, CNTs are difficult to uniformly disperse in metal matrix composites. The large aspect ratio of CNTs makes them prone to entanglement, coupled with the strong agglomeration effect of the nanoreinforcement phase and the low interfacial bonding strength caused by the difficulty of metals forming stable compounds with carbon, ultimately resulting in a much lower-than-expected strengthening and toughening effect in the composite material (measured strength <350 MPa, elongation <8%). With the increasing demand for lightweight high-end equipment, the development of a magnesium alloy composite material preparation technology that can achieve uniform dispersion of CNTs has become an urgent need in fields such as lightweight load-bearing components for aerospace and high-precision medical implants. During the preparation process, precisely controlling the introduction of carbon nanotubes and ensuring their dispersion are key issues.

[0004] The main technologies related to magnesium alloy composites with carbon nanotubes as the reinforcing phase are as follows:

[0005] (1) The first technology discloses a method for preparing carbon nanotube-reinforced AZ91 alloy. The main technical solution described therein is: under an argon atmosphere, a certain proportion of pure Mg, Al, Zn and Mn metal powders are mixed in an ethanol solvent using a mechanical stirrer. At the same time, carbon nanotubes are ultrasonically dispersed in ethanol for 2 hours. Then, the two suspensions are mixed together, mechanically stirred for 1 hour, and vacuum dried to obtain a composite mixture. Finally, the carbon nanotube-reinforced AZ91 rod is obtained by hydraulic pressure, sintering and hot extrusion.

[0006] (2) The second technology discloses a method for preparing carbon nanotube-reinforced AZ31 alloy, the main technical solution of which is as follows:

[0007] A certain proportion of carbon nanotubes were dissolved in ethanol for 1 hour using ultrasonic treatment. At the same time, magnesium, aluminum and zinc powders were mixed in ethanol in proportion using a stirrer. The carbon nanotube solution was added dropwise to AZ31 alloy powder slurry. The composite mixture was further mixed for 0.5 hours and then dried to obtain carbon nanotube-AZ31 composite powder. The powder was then ball-milled to improve its dispersibility, then cold-pressed into blocks, sintered, and finally hot-extruded to obtain carbon nanotube-reinforced AZ31 rods.

[0008] The above are two techniques for preparing carbon nanotube-reinforced magnesium alloy composites. The main process involves separately stirring and dispersing carbon nanotubes and matrix powder in ethanol, then mixing the two solutions and stirring again, drying to obtain a mixed powder, and finally obtaining the final carbon nanotube-reinforced magnesium alloy composite material by combining cold pressing, hot pressing sintering, and hot extrusion.

[0009] In summary, the inventors of this invention have at least the following technical problems with the carbon nanotube-reinforced magnesium alloy composite material prepared as described above.

[0010] The powder is mixed using simple ethanol solution dispersion and mechanical stirring. However, when the reinforcing phase is nanoscale, the mixing becomes inhomogeneous, leading to agglomeration. Dispersion reinforcement is a crucial strengthening mechanism for magnesium-based composites. Once the reinforcing phase agglomerates significantly, forming micron-sized clusters within the matrix, localized stress concentrations occur, creating core areas for crack initiation and propagation. Furthermore, the agglomeration of the reinforcing phase drastically reduces the contact area between the reinforcing phase and the matrix, affecting effective load transfer and ultimately impacting the overall material properties. Summary of the Invention

[0011] In view of this, the present invention provides a carbon nanotube-reinforced magnesium alloy composite material and its preparation method, the main purpose of which is to improve the uniformity of carbon nanotube distribution in the magnesium alloy composite material.

[0012] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0013] On one hand, embodiments of the present invention provide a method for preparing a carbon nanotube-reinforced magnesium alloy composite material, which includes the following steps:

[0014] Pre-dispersion step: Aluminum powder and carbon nanotubes are ball-milled and mixed to obtain composite powder; then, the composite powder is subjected to cold pressing and hot pressing sintering in sequence to obtain aluminum-based composite material;

[0015] Redispersion step: Under a protective atmosphere, the aluminum-based composite material is added to molten magnesium liquid, stirred, and then cast into an ingot; the ingot is subjected to hot extrusion treatment to obtain a carbon nanotube-reinforced magnesium alloy composite material.

[0016] Preferably, in the pre-dispersion step, the mass fraction of carbon nanotubes in the composite powder is not higher than 15%.

[0017] Preferably, the ball milling process is carried out under a protective gas atmosphere; wherein the ball milling speed is not less than 200 rpm / min, preferably 350-450 rpm / min; the ball milling time is not less than 2 hours, preferably 6-8 hours; the ball-to-material ratio is not less than 5:1, preferably 15:1; and / or stearic acid needs to be added during the ball milling process to prevent the composite powder from sintering; and / or the average particle size of the aluminum powder is 30-150 μm; and / or the average diameter of the carbon nanotubes is 5-20 nm, and the average length is 5-15 μm.

[0018] Preferably, the pressure of the cold pressing process is not less than 5 MPa, and more preferably 6-10 MPa; the holding time of the cold pressing process is not less than 5 s, and more preferably 10-30 s.

[0019] Preferably, the hot pressing sintering treatment is carried out under vacuum or a protective atmosphere, and the temperature of the hot pressing sintering treatment is not lower than 540°C, preferably 540-630°C; the time of the hot pressing sintering treatment is not lower than 0.5h, preferably 0.5-1h; and the pressure of the vacuum sintering treatment is not lower than 10MPa, preferably 30-50MPa.

[0020] Preferably, before heating the cold-pressed blank after cold pressing to the temperature of hot pressing sintering under vacuum or protective atmosphere, the cold-pressed blank is first heated to a first temperature and held at the first temperature for a first time to remove stearic acid from the cold-pressed blank.

[0021] Preferably, the first temperature is not lower than 400℃, and more preferably 400-450℃;

[0022] Preferably, the time should be no less than 1 hour, and more preferably 1-2 hours.

[0023] Preferably, in the pre-dispersion step: after the hot pressing and sintering treatment, the ingot after the hot pressing and sintering treatment is further subjected to hot extrusion treatment to obtain an aluminum-based composite material; preferably, the aluminum-based composite material is an aluminum-based composite material rod or sheet; preferably, the temperature of the hot extrusion treatment is not lower than 400℃, preferably 400-500℃, and the extrusion ratio is (4-25):1, preferably (8-20):1.

[0024] Preferably, in the redispersion step: under a protective atmosphere, the aluminum-based composite material, zinc granules, and magnesium-manganese alloy blocks are added to molten magnesium liquid, stirred, and then cast into ingots.

[0025] Preferably, in the redispersing step: the melting temperature of the magnesium liquid is not lower than 700°C, preferably 760-770°C; and / or the stirring treatment is a high-shear stirring treatment, with a rotation speed of not less than 1000 rpm / min, preferably 2500-3500 rpm / min; the stirring treatment time is not less than 10 min, preferably 15-25 min; and / or the casting temperature is not lower than 730°C, preferably 730-740°C.

[0026] Preferably, in the redispersing step: the temperature of the hot extrusion treatment is not lower than 250°C, preferably 300-400°C, and the extrusion ratio is (8-30):1, preferably (15-25):1; and / or the carbon nanotube reinforced magnesium alloy composite material is a rod or a sheet.

[0027] On the other hand, embodiments of the present invention provide a carbon nanotube reinforced magnesium alloy composite material, characterized in that the carbon nanotube reinforced magnesium alloy composite material is prepared by the preparation method of the carbon nanotube reinforced magnesium alloy composite material described in any one of the above claims;

[0028] Preferably, the chemical composition of the carbon nanotube-reinforced magnesium alloy composite material, by weight percentage, includes: Al: 8.5–9.5 wt.%, Zn: 0.5–1 wt.%, Mn: 0.15–0.5 wt.%, CNTs: greater than 0 wt.% and less than or equal to 2 wt.%, with the balance being Mg;

[0029] Preferably, in the microstructure of the carbon nanotube-reinforced magnesium alloy composite material: the carbon nanotubes are uniformly dispersed within the material; preferably, the precipitated phase Al8Mn5 with an average particle size of less than 5 μm is oriented along the hot extrusion direction.

[0030] Compared with the prior art, the carbon nanotube-reinforced magnesium alloy composite material and its preparation method of the present invention have at least the following beneficial effects:

[0031] This invention provides a method for preparing a carbon nanotube-reinforced magnesium alloy composite material, comprising the following steps: ball milling aluminum powder and carbon nanotubes to obtain a composite powder; then, subjecting the composite powder to cold pressing and hot pressing sintering to obtain an aluminum-based composite material; adding the aluminum-based composite material to molten magnesium liquid under a protective atmosphere, stirring, and then casting into an ingot; and hot extruding the ingot to obtain the carbon nanotube-reinforced magnesium alloy composite material. The above method is explained as follows: By ball milling aluminum powder and carbon nanotubes, this invention aims to ensure that the carbon nanotubes are uniformly dispersed in the aluminum powder. Then, cold pressing the ball-milled composite powder into a blank can initially eliminate large-sized pores between particles, avoiding sintering deformation and cracking. Then, the cold-pressed billet is hot-pressed and sintered at a certain temperature to obtain an ingot. Under high temperature and pressure, the powder particles diffuse and combine between the particles, forming a preliminary dense structure. (Preferably, the ingot is then hot-extruded at a certain temperature to obtain an extruded part with uniformly dispersed carbon nanotubes in aluminum. This further compacts the material, improving its density and reducing defects.) The cold pressing, hot pressing and sintering, and hot extrusion processes also ensure the effective addition of carbon nanotubes. Subsequently, under a protective atmosphere, the aluminum-based composite material is added to molten magnesium, along with a certain proportion of zinc granules and magnesium-manganese alloy blocks. High-shear stirring with stainless steel is used to ensure uniform mixing, followed by casting to obtain an ingot. During the melting and casting process, the high-shear, high-speed stirring with stainless steel further ensures the uniform dispersion of carbon nanotubes. Finally, the ingot is hot-extruded at a certain temperature to obtain a carbon nanotube-reinforced magnesium alloy composite material with uniformly dispersed carbon nanotubes. The hot extrusion process further compacts the material, improving its density, reducing defects, and increasing grain boundary bonding, thereby enhancing its mechanical properties. Meanwhile, the uniform distribution of carbon nanotubes ensures a dispersion strengthening mechanism, which in turn ensures the mechanical properties of the composite material.

[0032] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0033] Figure 1 This is a microstructure diagram of the aluminum-based composite rod prepared in Example 1 of the present invention;

[0034] Figure 2 This is a tensile stress-strain curve of the carbon nanotube-reinforced AZ91 magnesium alloy composite material prepared in Example 1;

[0035] Figure 3This is a microstructure diagram of the carbon nanotube-reinforced AZ91 magnesium alloy composite material prepared in Example 1;

[0036] Figure 4 This is a tensile stress-strain curve of a carbon nanotube-reinforced AZ91 magnesium alloy composite material prepared in Example 2;

[0037] Figure 5 This is a comparison curve of tensile stress-strain of AZ91 magnesium alloy composites with different contents of carbon nanotubes prepared in Examples 1 and 2;

[0038] Figure 6 This is a microstructure diagram of the carbon nanotube-reinforced AZ91 magnesium alloy composite material prepared in Example 2. Detailed Implementation

[0039] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0040] This invention provides a carbon nanotube-reinforced magnesium alloy composite material and its preparation method. The invention utilizes high-energy ball milling, cold pressing, hot pressing sintering, and hot extrusion techniques to uniformly disperse carbon nanotubes in an aluminum-based composite material, followed by melting, casting, and hot extrusion processes to obtain the magnesium alloy composite material. During the melting process, the physical isolation of the carbon nanotubes by the aluminum matrix, coupled with the alloying of the gradually melting Al and Mg matrix to form a diffusion layer, inhibits the agglomeration of carbon nanotubes. Simultaneously, the high-shear stirring during the melting process further improves the dispersibility of carbon nanotubes in the magnesium matrix.

[0041] The main solutions of this invention are as follows:

[0042] On one hand, embodiments of the present invention provide a method for preparing carbon nanotube-reinforced magnesium alloy composite materials, which includes the following steps:

[0043] Pre-dispersion step: Aluminum powder and carbon nanotubes are ball-milled and mixed to obtain composite powder; then, the composite powder is subjected to cold pressing and hot pressing sintering in sequence to obtain aluminum-based composite material.

[0044] Regarding the ball milling and mixing process, the following applies: the ball milling and mixing process is carried out under a protective gas atmosphere (such as argon); the ball milling speed is not less than 200 rpm / min, preferably 350-450 rpm / min; the ball milling and mixing time is not less than 2 hours, preferably 6-8 hours. The ball-to-powder ratio is not less than 5:1, preferably 15:1. Stearic acid needs to be added during the ball milling and mixing process to prevent the composite powder from sintering.

[0045] The aluminum powder has an average particle size of 30–150 μm.

[0046] The carbon nanotubes have an average diameter of 5–20 nm and an average length of 5–15 μm.

[0047] Preferably, the mass fraction of carbon nanotubes in the composite powder is no more than 15%.

[0048] The air cooling process is as follows: the pressure of the cold pressing process is not less than 5 MPa, preferably 6-10 MPa; the holding time of the cold pressing process is not less than 5 s, preferably 10-30 s.

[0049] The hot-pressing sintering process is as follows: the hot-pressing sintering process is carried out under vacuum or a protective atmosphere, and the temperature of the hot-pressing sintering process is not lower than 540℃, preferably 540-630℃; the time of the hot-pressing sintering process is not lower than 0.5h, preferably 0.5-1h; the pressure of the vacuum sintering process is not lower than 10MPa, preferably 30-50MPa.

[0050] Preferably, before heating the cold-pressed billet to the temperature for hot pressing and sintering under vacuum or a protective atmosphere, the cold-pressed billet is first heated to a first temperature and held at that first temperature for a first time to remove stearic acid from the cold-pressed billet; preferably, the first temperature is not lower than 400°C, and more preferably 400-450°C. Preferably, the first time is not less than 1 hour, and more preferably 1-2 hours.

[0051] Preferably, after the hot pressing and sintering treatment, the hot-pressed and sintered billet (sintered billet) is further subjected to hot extrusion treatment to obtain an aluminum-based composite material; preferably, the aluminum-based composite material is an aluminum-based composite material rod or plate; preferably, the temperature of the hot extrusion treatment is not lower than 400℃, preferably 400-500℃, and the extrusion ratio is (4-25):1, preferably (8-20):1.

[0052] Redispersion step: Under a protective atmosphere, the aluminum-based composite material is added to molten magnesium liquid, stirred, and then cast into an ingot; the ingot is subjected to hot extrusion treatment to obtain a carbon nanotube-reinforced magnesium alloy composite material.

[0053] Preferably, in this step, under a protective atmosphere, the aluminum-based composite material is added to molten magnesium liquid, along with a certain proportion of zinc granules and magnesium-manganese alloy blocks. The mixture is stirred using stainless steel high-shear stirring to ensure uniform mixing, and then cast into an ingot.

[0054] Preferably, the smelting temperature of the magnesium liquid is not lower than 700℃, and more preferably 760-770℃.

[0055] Preferably, the stirring process is a high-shear stirring process with a rotation speed of not less than 1000 rpm / min, preferably 2500-3500 rpm / min; and the stirring time is not less than 10 min, preferably 15-25 min.

[0056] Preferably, the casting temperature is not lower than 730℃, and more preferably 730-740℃.

[0057] Preferably, the temperature of the hot extrusion treatment is not lower than 250°C, more preferably 300-400°C, and the extrusion ratio is (8-30):1, more preferably (15-25):1.

[0058] Preferably, the carbon nanotube reinforced magnesium alloy composite material is a rod or a plate.

[0059] Preferably, the chemical composition of the carbon nanotube-reinforced magnesium alloy composite material, by weight percentage, includes: Al: 8.5–9.5 wt.%, Zn: 0.5–1 wt.%, Mn: 0.15–0.5 wt.%, CNTs: greater than 0 wt.% and less than or equal to 2 wt.%, with the balance being Mg;

[0060] In the microstructure of the carbon nanotube-reinforced magnesium alloy composite material: the carbon nanotubes are uniformly dispersed within the material, effectively hindering dislocation movement and enhancing the material's resistance to deformation, thereby improving the material's strength and hardness. Preferably, the precipitated phase Al8Mn5 with an average particle size of less than 5 μm is oriented along the hot extrusion direction. The interaction between the precipitated phase and the matrix material may generate back stress at the interface, hindering further dislocation movement and thus improving the material's strength.

[0061] In summary, this invention provides a carbon nanotube-reinforced magnesium alloy composite material and its preparation method. The composite material is composed of magnesium alloy and carbon nanotubes: the carbon nanotubes are uniformly distributed within the magnesium alloy; high-energy ball milling is crucial for ensuring uniform dispersion. Cold pressing, hot pressing sintering, and hot extrusion ensure the effective addition of carbon nanotubes during the melting and casting stages; high-speed stirring with high shear in stainless steel further ensures the dispersion of carbon nanotubes during melting and casting, and finally, hot extrusion yields a magnesium alloy composite material with uniformly dispersed carbon nanotubes.

[0062] The present invention will be further illustrated below with specific embodiments:

[0063] The following examples all use the same melting furnace and extruder to melt, cast and hot extrude the materials.

[0064] Example 1

[0065] This embodiment prepares a carbon nanotube-reinforced AZ91 magnesium alloy composite material. The raw materials used include: carbon nanotubes (CNTs) with an average diameter of 10 nm and an average length of 5 μm; Al powder with an average particle size of 10 μm and a purity of 99%; zinc particles with a purity of 99.9%; magnesium blocks with a purity of 99.995%; and Mg-10wt%Mn blocks with a purity of 99%. The specific preparation steps are as follows:

[0066] Ball milling and mixing: Al powder and CNTs were prepared at a mass fraction of 4.1 wt% (Al + CNTs), mixed, and then ball-milled to obtain composite powder. The ball milling speed was 400 rpm / min, the ball-to-powder ratio was 15:1, and the ball milling time was 6 hours. Stearic acid was added during the ball milling process to prevent sintering of the composite powder.

[0067] Cold pressing: The composite powder is subjected to cold pressing, wherein the pressure of cold pressing is 10MPa and the pressure is held for 30s to obtain a cold-pressed blank.

[0068] Hot pressing sintering treatment: The mold containing the cold-pressed billet is placed in a vacuum hot pressing furnace, first heated to 400°C, and then held at that temperature for 1 hour to remove stearic acid from the cold-pressed billet. Then it is heated to 540°C and vacuum hot pressing sintering treatment is carried out at 540°C and 50MPa pressure for 1 hour. The furnace is then cooled to obtain the billet.

[0069] Hot extrusion treatment: The billet is extruded at 450°C with an extrusion ratio of 16:1 to obtain aluminum-based composite rods with a CNTs mass fraction of 4.1%.

[0070] Melting and Casting: Under a protective atmosphere, 1040g of magnesium ingots were first placed in a graphite crucible and heated to 750℃ for melting. Then, 112.6g of the above-mentioned aluminum-based composite material rods, 9.6g of Zn granules, and 36g of Mg-10wt.%Mn ingots were added to the molten magnesium. The mixture was then stirred with a stainless steel high-shear stirrer at 2500rpm / min for 15min. The heating was then turned off, and the temperature was allowed to drop to 740℃ before casting to obtain an ingot.

[0071] Hot extrusion treatment: The ingot is extruded at 350℃ with an extrusion ratio of 25:1 and an extrusion diameter of 8.7mm, finally obtaining AZ91-CNTs composite material (carbon nanotube reinforced AZ91 magnesium alloy composite material) with a carbon nanotube mass fraction of 0.38%.

[0072] Figure 1 This is a microstructure diagram of the aluminum-based composite rods prepared in Example 1. From... Figure 1 It can be seen that the carbon nanotubes are evenly dispersed within it, with almost no entanglement of the carbon nanotubes.

[0073] Figure 2 This is a tensile stress-strain curve of the carbon nanotube-reinforced AZ91 magnesium alloy composite material prepared in Example 1. It can be seen that the tensile strength of the carbon nanotube-reinforced AZ91 magnesium alloy composite material prepared in this example is 336 MPa, and the elongation is 9.68%.

[0074] Figure 3 This is a microstructure diagram of the carbon nanotube-reinforced AZ91 magnesium alloy composite material prepared in Example 1. It can be seen that the precipitates Al8Mn5 produced by extrusion are oriented. The interaction between the precipitates Al8Mn5 and the matrix material may generate back stress at the interface, which hinders the further movement of dislocations and thus improves the strength of the material.

[0075] Example 2

[0076] This embodiment prepares a carbon nanotube-reinforced AZ91 magnesium alloy composite material. The raw materials used include: carbon nanotubes (CNTs) with an average diameter of 10 nm and an average length of 5 μm; Al powder with an average particle size of 10 μm and a purity of 99%; zinc particles with a purity of 99.9%; magnesium blocks with a purity of 99.995%; and Mg-10wt%Mn blocks with a purity of 99%. The specific preparation steps are as follows:

[0077] Ball milling and mixing: Al powder and CNTs were prepared at a mass fraction of 10 wt% (Al + CNTs), mixed, and then ball-milled to obtain composite powder. The ball milling speed was 500 rpm / min, the ball-to-powder ratio was 15:1, and the ball milling time was 6 hours. Stearic acid was added during the ball milling and mixing process to prevent the raw material powder from sintering.

[0078] Cold pressing: The composite powder is subjected to cold pressing at a pressure of 10 MPa for 30 seconds to obtain a cold-pressed blank.

[0079] Hot pressing sintering treatment: The mold containing the cold-pressed billet is placed in a vacuum hot press furnace. The temperature is first raised to 400℃ and held for 1 hour to remove stearic acid from the cold-pressed billet. Then, it is heated to 540℃ and vacuum hot pressing sintering is performed at 540℃ and 50MPa pressure for 1 hour, followed by furnace cooling. The billet ingot is obtained.

[0080] Hot extrusion treatment: The billet is extruded at 450°C with an extrusion ratio of 16:1 to obtain aluminum-based composite rods with a CNTs mass fraction of 10%.

[0081] Melting and casting: Under a protective atmosphere, 1035g of magnesium block is first placed in a graphite crucible and heated to 750℃. Then, 120g of the aluminum-based composite material rod prepared above, 9.6g of Zn particles and 36g of Mg-10wt%Mn block are added to the molten magnesium liquid. The mixture is then stirred with stainless steel high shear at a speed of 3000rpm / min for 20min. The heating is then turned off and the temperature is reduced to 740℃ before casting to obtain the ingot.

[0082] Hot extrusion treatment: The ingot is extruded at 350℃ with an extrusion ratio of 25:1 and an extrusion diameter of 8.7mm, finally obtaining AZ91-CNTs composite material (carbon nanotube reinforced AZ91 magnesium alloy composite material) with a carbon nanotube mass fraction of 1%.

[0083] Figure 4 This is a tensile stress-strain curve of a carbon nanotube-reinforced AZ91 magnesium alloy composite material prepared in Example 2. Figure 4 It can be seen that the tensile strength of the carbon nanotube-reinforced AZ91 magnesium alloy composite material prepared in Example 2 is 409 MPa, and the elongation is 7.59%.

[0084] Figure 5 This is a comparison curve of tensile stress-strain of AZ91 magnesium alloy composites reinforced with different contents of carbon nanotubes prepared in Examples 1 and 2. Figure 5 It can be seen that the tensile strength of the AZ91-CNTs composite material with a carbon nanotube mass fraction of 1% is increased by 73 MPa compared with that with a carbon nanotube mass fraction of 0.38%, while the plasticity is reduced, which is constrained by the inverse relationship between strength and plasticity.

[0085] Figure 6 This is a microstructure diagram of the carbon nanotube-reinforced AZ91 magnesium alloy composite material prepared in Example 2. Figure 6It can be seen that the Al8Mn5 precipitates produced by extrusion are oriented. The interaction between these Al8Mn5 precipitates and the matrix material may generate back stress at the interface, hindering further dislocation movement and thus improving the strength of the material.

[0086] Comparative Example 1

[0087] The prior art discloses a method for preparing carbon nanotube-reinforced AZ91 alloy. The main technical scheme described is as follows: Under an argon atmosphere, a certain proportion of pure Mg, Al, Zn and Mn metal powders are mixed in an ethanol solvent using a mechanical stirrer. At the same time, carbon nanotubes are ultrasonically dispersed in the ethanol for 2 hours. Then, the two suspensions are mixed together, mechanically stirred for 1 hour, and vacuum dried to obtain a composite mixture. Finally, a composite material containing 1 wt.% CNTs-reinforced AZ91 is obtained through hydraulic pressure, sintering and hot extrusion.

[0088] In Comparative Example 1, the composite material prepared had a tensile strength of approximately 230 MPa and an elongation of 7.5%. Compared to Comparative Example 1, the reinforced magnesium alloy composite material with a CNT content of 1 wt% prepared in Example 2 of this invention showed an increase in tensile strength of approximately 77.8% while maintaining almost the same elongation. This is because the carbon nanotubes in the material prepared in Comparative Example 1 exhibited poor dispersion, leading to agglomeration and other defects, which easily resulted in stress concentration and impaired the overall performance of the material.

[0089] Comparative Example 2

[0090] Comparative Example 2 prepared a carbon nanotube-reinforced AZ91 magnesium alloy composite material. The raw materials used included: carbon nanotubes (CNTs) with an average diameter of 10 nm and an average length of 5 μm; Al powder with an average particle size of 10 μm and a purity of 99%; zinc particles with a purity of 99.9%; magnesium blocks with a purity of 99.995%; and Mg-10wt%Mn blocks with a purity of 99%. The specific preparation steps are as follows:

[0091] Ball milling and mixing: Al powder and CNTs were prepared at a mass fraction of 10 wt% (Al + CNTs), mixed, and then ball-milled to obtain composite powder. The ball milling speed was 500 rpm / min, the ball-to-powder ratio was 15:1, and the ball milling time was 6 hours. Stearic acid was added during the ball milling and mixing process to prevent the raw material powder from sintering.

[0092] Cold pressing: The composite powder is subjected to cold pressing at a pressure of 10 MPa for 30 seconds to obtain a cold-pressed blank.

[0093] Hot pressing sintering treatment: The mold containing the cold-pressed billet is placed in a vacuum hot press furnace. The temperature is first raised to 400℃ and held for 1 hour to remove stearic acid from the cold-pressed billet. Then, it is heated to 540℃ and vacuum hot pressing sintering is performed at 540℃ and 50MPa pressure for 1 hour, followed by furnace cooling. The billet ingot is obtained.

[0094] Melting and casting: Under a protective atmosphere, 1035g of magnesium block is first placed in a graphite crucible and heated to 750℃. Then, 120g of the above-prepared billet, 9.6g of Zn granules and 36g of Mg-10wt%Mn block are placed into the molten magnesium liquid. The mixture is then stirred with a stainless steel high-shear stirrer at 3000rpm / min for 20min. The heating is then turned off and the temperature is reduced to 740℃ before casting to obtain the ingot.

[0095] Compared to Example 2, Comparative Example 2 mainly lacks the hot extrusion step. By comparing the properties of the magnesium-based composite material prepared from the ingot of Comparative Example 2 and the hot-extruded material of Example 2, significant differences in mechanical properties can be found. Example 2, due to the use of hot extrusion, exhibits higher density and a more uniform grain structure, which helps improve its strength, hardness, and toughness. The hot extrusion process, through high-temperature deformation and pressure, refines the grains, improves interfacial bonding, and enhances particle dispersion, thereby improving the overall mechanical properties of the composite material. In contrast, Comparative Example 2, lacking the hot extrusion step, produces an ingot material with problems such as porosity, grain coarsening, and uneven particle distribution, resulting in lower strength and plasticity.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a carbon nanotube-reinforced magnesium alloy composite material, characterized in that, It comprises the following steps: Pre-dispersion step: ball-milling mixing treatment is performed on aluminum powder and carbon nanotubes to obtain a composite powder; then, the composite powder is subjected to cold pressing treatment and hot-pressing sintering treatment in sequence to obtain an aluminum-based composite material; Redispersion step: the aluminum-based composite material is added into molten magnesium liquid under a protective atmosphere, and after stirring treatment, the aluminum-based composite material is cast into an ingot; the ingot is subjected to hot extrusion treatment to obtain a carbon nanotube reinforced magnesium alloy composite material.

2. The method for preparing carbon nanotube-reinforced magnesium alloy composite material according to claim 1, characterized in that, In the pre-dispersion step: the mass fraction of carbon nanotubes in the composite powder is not higher than 15%.

3. The method of producing a carbon nanotube-reinforced magnesium alloy composite material according to claim 1 or 2, characterized by, The ball-milling mixing treatment is performed under a protective gas atmosphere; wherein the rotation speed of the ball-milling mixing treatment is not less than 200 rpm / min, and is preferably 350-450 rpm / min; the ball-milling mixing treatment time is not less than 2 h, and is preferably 6-8 h; the ball-to-powder ratio is not less than 5:1, and is preferably 15:1; and / or When the ball-milling mixing treatment is performed, stearic acid needs to be added to prevent sintering of the composite powder; and / or The average particle size of the aluminum powder is 30-150 μm; and / or The average diameter of the carbon nanotubes is 5-20 nm, and the average length is 5-15 μm.

4. The method of producing a carbon nanotube reinforced magnesium alloy composite material according to any one of claims 1 to 3, characterized by, The pressure of the cold pressing treatment is not less than 5 MPa, and is preferably 6-10 MPa; the pressure holding time of the cold pressing treatment is not less than 5 s, and is preferably 10-30 s.

5. The method of producing a carbon nanotube reinforced magnesium alloy composite material according to any one of claims 1 to 4, characterized by, The hot-pressing sintering treatment is performed under vacuum or a protective atmosphere, and the temperature of the hot-pressing sintering treatment is not less than 540 ℃, and is preferably 540-630 ℃; the time of the hot-pressing sintering treatment is not less than 0.5 h, and is preferably 0.5-1 h; the pressure of the vacuum sintering treatment is not less than 10 MPa, and is preferably 30-50 MPa; Preferably, before the cold-pressed compact after the cold pressing treatment is heated to the temperature of the hot-pressing sintering treatment, the cold-pressed compact is heated to a first temperature and is kept at the first temperature for a first time under vacuum or a protective atmosphere to remove stearic acid in the cold-pressed compact; Preferably, the first temperature is not less than 400 ℃, and is preferably 400-450 ℃; Preferably, the first time is not less than 1 h, and is preferably 1-2 h.

6. The method of producing a carbon nanotube reinforced magnesium alloy composite material according to any one of claims 1 to 5, characterized by, In the pre-dispersion step: After the hot-pressing sintering treatment, the ingot after the hot-pressing sintering treatment is also subjected to hot extrusion treatment to obtain an aluminum-based composite material; Preferably, the aluminum-based composite material is an aluminum-based composite material rod or plate; Preferably, the temperature of the hot extrusion treatment is not less than 400 ℃, and is preferably 400-500 ℃, and the extrusion ratio is (4-25):1, and is preferably (8-20):

1.

7. The method of producing a carbon nanotube reinforced magnesium alloy composite material according to any one of claims 1 to 6, characterized by, In the redispersion step: The aluminum-based composite material, zinc particles and magnesium-manganese alloy blocks are added into molten magnesium liquid under a protective atmosphere, and after stirring treatment, the aluminum-based composite material is cast into an ingot.

8. The method of producing a carbon nanotube reinforced magnesium alloy composite material according to any one of claims 1 to 7, characterized by, In the redispersion step: The melting temperature of the magnesium liquid is not less than 700 ℃, and is preferably 760-770 ℃; and / or The stirring treatment is high-shear stirring treatment, and the rotation speed is not less than 1000 rpm / min, and is preferably 2500-3500 rpm / min; the stirring treatment time is not less than 10 min, and is preferably 15-25 min; and / or The temperature of the casting is not less than 730 DEG C, preferably 730-740 DEG C.

9. The method of producing a carbon nanotube reinforced magnesium alloy composite material according to any one of claims 1 to 8, characterized by, In the step of re-dispersing: The temperature of the hot extrusion is not less than 250 DEG C, preferably 300-400 DEG C, and the extrusion ratio is (8-30):1, preferably (15-25):1; and / or The carbon nanotube reinforced magnesium alloy composite material is a rod or a plate.

10. A carbon nanotube reinforced magnesium alloy composite material, characterized by, The carbon nanotube reinforced magnesium alloy composite material is prepared by the method of any one of claims 1-9. Preferably, the carbon nanotube reinforced magnesium alloy composite material comprises, in terms of weight percentage: Al: 8.5-9.5 wt.%, Zn: 0.5-1 wt.%, Mn: 0.15-0.5 wt.%, CNTs: more than 0 wt.% and less than or equal to 2 wt.%, and the balance being Mg. Preferably, in the microstructure of the carbon nanotube reinforced magnesium alloy composite material: the carbon nanotubes are uniformly dispersed in the material; and preferably, the precipitated phase Al8Mn5 with an average particle size of less than 5 μm is arranged in the direction of hot extrusion.

Images