Aluminum-based composite material based on nanoparticle auxiliary dispersion and preparation method of aluminum-based composite material

Abstract

The invention relates to an aluminum-based composite material based on nano-particle auxiliary dispersion and a preparation method thereof, and relates to the technical field of aluminum-based composites.The preparation method comprises the steps that (1) aluminum alloy is melted to obtain liquid aluminum alloy, and the liquid aluminum alloy is stirred in the air atmosphere to obtain aluminum alloy melt containing nano-particles; (2) the reinforcement particles are added into the aluminum alloy melt containing the nano-particles to be evenly mixed, and semi-solid slurry is obtained; and (3) the semi-solid slurry is sequentially subjected to pressure casting, cooling and hot extrusion, and the aluminum-based composite material is obtained. On the basis of a semi-solid stirring casting method, the nano-particles are introduced through stirring in the air atmosphere, the viscosity of the liquid aluminum alloy is effectively improved, the problems that reinforcement particles are prone to agglomeration in an aluminum matrix, the density of a composite material is low, and meanwhile the reinforcement and matrix interface bonding is poor are solved, and the method is efficient, clean, low in cost and suitable for industrial production. The method can be applied to preparation of high-performance aluminum-based composite materials.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum matrix composites, in particular to the technical field of nanocomposites, and particularly to an aluminum matrix composite based on nanoparticle-assisted dispersion and a preparation method thereof. Background Art

[0002] By adding appropriate reinforcements to the aluminum alloy matrix, the above disadvantages of aluminum alloys are significantly improved, and the aluminum matrix composites have high specific stiffness, specific strength, good high-temperature resistance and dimensional stability. Particle-reinforced aluminum matrix composites have many advantages such as high specific strength, high specific stiffness, high wear resistance, and high damping capacity. Among them, silicon carbide particles have high hardness, good wear resistance, easy availability of raw materials, low cost, and relatively mature preparation technology, and are considered to be ideal reinforcements for developing new composite materials. It has been confirmed that incorporating silicon carbide particles into the metal matrix can produce metal matrix composites with high performance.

[0003] Currently, common preparation methods for particle-reinforced aluminum matrix composites include melt infiltration method, spray deposition method, powder metallurgy method, and stir casting method, etc. Among them, the melt infiltration method and the spray deposition method require complex process parameters to be controlled and have high preparation costs; the powder metallurgy method has low safety factor, high risk in the operation process and poor stability. The stir casting method has simple process and low risk in the operation process, is not restricted by the types of metal matrix and reinforcements, and has significant advantages. However, the wettability between reinforcements such as silicon carbide particles and the aluminum matrix is poor, and it has been difficult to effectively solve how to achieve uniform dispersion of the reinforcement particles in the aluminum matrix during the stirring process; at the same time, harmful interfacial reactions are likely to occur at the interface between silicon carbide and the aluminum matrix at high temperatures, resulting in low interfacial bonding force of the composite material. Although the traditional semi-solid stir casting method can disperse micron-sized silicon carbide reinforcement particles into the aluminum matrix, the dispersion of silicon carbide reinforcement particles is greatly affected by the melt temperature and gravity sedimentation, and the narrow semi-solid temperature range further deepens the influence of the above factors, making the silicon carbide reinforcement particles tend to sink to the bottom, resulting in uneven content of the prepared aluminum matrix composite, poor processing performance, and low surface integrity. Summary of the Invention

[0004] In order to solve one or more technical problems existing in the prior art, the present invention provides an aluminum matrix composite based on nanoparticle-assisted dispersion and a preparation method thereof, which can increase the viscosity of liquid aluminum alloy and facilitate the adjustment of the temperature range, and prepare an aluminum matrix composite with uniform dispersion, good processing performance and high surface integrity based on semi-solid stir casting.

[0005] In the first aspect, the present invention provides a preparation method for an aluminum matrix composite with nanoparticle-assisted dispersion, including:

[0006] (1) Melt the aluminum alloy to obtain molten aluminum alloy, and stir the molten aluminum alloy in an air atmosphere to obtain an aluminum alloy melt containing nano-particles;

[0007] (2) Add the reinforcing particles to the aluminum alloy melt containing nano-particles and mix them evenly to obtain a semi-solid slurry;

[0008] (3) Subject the semi-solid slurry to pressure casting, cooling, and hot extrusion in sequence to obtain the aluminum matrix composite material.

[0009] Preferably, step (1) includes:

[0010] (11) Melt the aluminum alloy at the melting temperature in a protective atmosphere to obtain molten aluminum alloy;

[0011] (12) In an air atmosphere, insert a stirring paddle into the molten aluminum alloy at the melting temperature for mechanical stirring, then gradually cool down to the semi-solid temperature range of the current system and continue mechanical stirring to obtain the aluminum alloy melt containing nano-particles.

[0012] Preferably, in step (1): Insert a stirring paddle into the molten aluminum alloy at the melting temperature for mechanical stirring at 1000 - 1800 rpm for 30 - 60 min.

[0013] More preferably, in step (1): Insert a stirring paddle into the molten aluminum alloy at the melting temperature for mechanical stirring at 1000 - 1500 rpm for 30 - 40 min.

[0014] Preferably, in step (1): Gradually cool down to the semi-solid temperature range and continue mechanical stirring at 1000 - 1800 rpm.

[0015] More preferably, the gradual cooling is to cool down 5 - 10 °C every 5 - 10 min.

[0016] More preferably, the gradual cooling is to cool down 10 °C every 10 min.

[0017] Preferably, the protective atmosphere is a gas atmosphere without oxygen and nitrogen.

[0018] More preferably, the protective atmosphere is an argon atmosphere or a helium atmosphere.

[0019] Preferably, the reinforcing particles are at least one of silicon carbide particles, titanium carbide particles, graphene particles, or pure metal titanium particles.

[0020] More preferably, the reinforcing particles are silicon carbide particles.

[0021] Preferably, the size of the reinforcing particles is 5 - 25 μm.

[0022] More preferably, the size of the reinforcing particles is 10 - 14 μm.

[0023] Preferably, in step (2): under a protective atmosphere, by adjusting the temperature of the aluminum alloy melt containing nanoparticles, after the reinforcing particles are added to the aluminum alloy melt containing nanoparticles, they are in a semi-solid state to obtain the semi-solid slurry.

[0024] More preferably, in step (2): the rotation speed for mixing is 1000 - 1800 rpm.

[0025] Preferably, it further includes: before melting the aluminum alloy, pre-treating the aluminum alloy to remove the surface oxide layer and impurities.

[0026] Preferably, before adding the reinforcing particles to the aluminum alloy melt containing nanoparticles for mixing, pre-heat treatment is performed on the reinforcing particles.

[0027] Preferably, in step (3): the pressure for die casting is 5 - 10 MPa, and the pressure holding time is 3 - 5 min.

[0028] Preferably, in step (3): the temperature for hot extrusion is 300 - 400 °C, the speed is 0.1 - 1 mm / s, and the extrusion ratio is (8 - 20):1.

[0029] More preferably, the speed for hot extrusion is 0.4 - 0.7 mm / s, and the extrusion ratio is (12 - 16):1.

[0030] Preferably, when the aluminum alloy is 2024 aluminum alloy, step (1) includes:

[0031] (11) Melting 2024 aluminum alloy at 690 °C under a protective atmosphere to obtain a liquid aluminum alloy;

[0032] (12) In an air atmosphere, insert a stirring paddle into the liquid aluminum alloy at 690 °C for mechanical stirring, and then gradually cool down to 660 - 670 °C and continue mechanical stirring to obtain the aluminum alloy melt containing nanoparticles.

[0033] Preferably, the content of the reinforcing particles in the aluminum matrix composite is 10 - 15 vol%.

[0034] In a second aspect, the present invention also provides an aluminum matrix composite with nanoparticles assisted dispersion prepared by using any of the preparation methods in the first aspect above.

[0035] The present invention has at least the following beneficial effects compared with the prior art:

[0036] (1) By stirring the liquid aluminum alloy in an air atmosphere, the present invention enables the nitrogen, oxygen in the air to react with the liquid aluminum alloy in a gas-liquid reaction, thereby introducing nanoparticles (including nano-scale aluminum oxide and nano-scale aluminum nitride) into the liquid aluminum alloy, changing the fluidity of the liquid aluminum alloy, and creatively constructing an aluminum-nanoparticle dispersion network; at the same time, the nanoparticles can significantly increase the internal friction of the liquid aluminum alloy, and thus effectively increase the melt viscosity of the liquid aluminum alloy. On the basis of the increase in the melt viscosity of the liquid aluminum alloy, the critical rate for the viscous capture of the reinforcement particles by the solid-liquid interface is significantly reduced, so a high-temperature dispersion environment is further provided, greatly improving the problem of uneven distribution of micron-scale reinforcement particles caused by the movement of the solid-liquid interface.

[0037] (2) In the present invention, the presence of nanoparticles significantly increases the viscosity of the aluminum alloy melt, the resistance of the melt to the movement of the reinforcement particles increases, and when the reinforcement particles sink due to gravity, they will bear a stronger hindering effect from the surrounding high-viscosity melt. In this system, the density difference between the reinforcement and the surrounding melt is an important factor leading to sedimentation, but when the melt viscosity increases, even if the density difference between the two remains unchanged, the changes in the buoyancy and resistance of the melt to the reinforcement will make the driving effect of the density difference on sedimentation relatively decrease, further improving the dispersion of the reinforcement in the aluminum matrix composite.

[0038] (3) Since the interface between the reinforcement particles and the aluminum matrix is a weak phase, stress concentration and failure are prone to occur. In the present invention, the aluminum alloy melt containing nanoparticles provides a high-temperature - high-viscosity dispersion environment. When the reinforcement particles are silicon carbide particles, Al will react with the silicon carbide particles at the interface to generate Al 4 C 3 phase. At the same time, the presence of Si will inhibit the progress of the reversible reaction to ensure that the content of the Al 4 C 3 phase will not be too high. The SiO 2 on the surface of silicon carbide will also have a weak interfacial reaction with the Mg element in the aluminum alloy melt to generate MgO. These interface compounds with low content effectively improve the interfacial bonding degree between silicon carbide and the aluminum matrix, thereby increasing the interfacial strength.

[0039] (4) The aluminum matrix composite material prepared by the present invention has good formability and surface integrity. Nano-aluminum nitride and nano-aluminum oxide particles are widely distributed around the micron-sized reinforcement particles, and there will be a certain adsorption effect at high temperatures. These nano-particles can hinder the crack propagation formed between the micron-sized reinforcement particles and the aluminum matrix during forming, and improve the stress distribution near the interface. At the same time, the modification effect of the interface product on the interface at high temperatures also effectively improves the formability of the aluminum matrix composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0041] Figure 1 It is a flowchart of a preparation method of an aluminum matrix composite material assisted by nano-particles provided by an embodiment of the present invention;

[0042] Figure 2 It is a scanning electron microscope image and an element distribution map of the aluminum matrix composite material prepared in Example 1 of the present invention;

[0043] Figure 3 It is a scanning electron microscope image of the aluminum matrix composite material prepared in Comparative Example 1 of the present invention;

[0044] Figure 4 It is a stress-strain curve graph of the materials prepared in Example 1 and Comparative Example 4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0046] As Figure 1 shown, an embodiment of the present invention provides a preparation method of an aluminum matrix composite material assisted by nano-particles, and the preparation method includes:

[0047] (1) Melting the aluminum alloy to obtain a liquid aluminum alloy, and stirring the liquid aluminum alloy in an air atmosphere to obtain an aluminum alloy melt containing nano-particles;

[0048] (2) Add reinforcing particles into the aluminum alloy melt containing nanoparticles and mix them evenly to obtain semi-solid slurry;

[0049] (3) Subject the semi-solid slurry to pressure casting, cooling, and hot extrusion in sequence to obtain an aluminum matrix composite.

[0050] It should be noted that the aluminum alloy includes, but is not limited to, aluminum alloys of the Al-Cu-Mg system, aluminum-magnesium alloys, aluminum-manganese alloys, aluminum-copper alloys, aluminum-zinc alloys, and so on.

[0051] In the present invention, by stirring the liquid aluminum alloy in an air atmosphere, a gas-liquid reaction occurs between nitrogen, oxygen in the air and the liquid aluminum alloy, generating nano-scale aluminum oxide and nano-scale aluminum nitride, thereby introducing nanoparticles into the liquid aluminum alloy and forming an aluminum-nanoparticle dispersion network; at the same time, the nanoparticles can significantly increase the internal friction of the liquid aluminum alloy, and thus effectively increase the melt viscosity of the liquid aluminum alloy. On the basis of the increase in the melt viscosity of the liquid aluminum alloy, the critical rate for the viscous capture of the reinforcing particles by the solid-liquid interface is significantly reduced, so a high-temperature dispersion environment is further provided, greatly improving the problem of uneven distribution of micron-scale reinforcing particles caused by the movement of the solid-liquid interface, and thus effectively improving the mechanical properties of the aluminum matrix composite.

[0052] According to some preferred embodiments, step (1) includes:

[0053] (11) Melt the aluminum alloy at the melting temperature in a protective atmosphere to obtain liquid aluminum alloy;

[0054] (12) In an air atmosphere, insert a stirring paddle into the liquid aluminum alloy at the melting temperature for mechanical stirring, and then gradually cool down to the semi-solid temperature range of the current system and continue mechanical stirring to obtain an aluminum alloy melt containing nanoparticles.

[0055] It should be noted that the melting time in step (11) is not specifically limited, and it is sufficient to obtain completely melted liquid aluminum alloy. The air atmosphere in step (12) is a flowing air atmosphere, that is, it is achieved by introducing air at a certain flow rate into the liquid aluminum alloy, so as to avoid the problem that when the liquid aluminum alloy is in a closed air atmosphere, the content of oxygen and nitrogen is exhausted due to the gas-liquid reaction between nitrogen, oxygen in the air and the liquid aluminum alloy.

[0056] According to some preferred embodiments, in step (12): insert a stirring paddle into the liquid aluminum alloy at the melting temperature and carry out mechanical stirring at 1000 - 1800 rpm (for example, it can be 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm or 1800 rpm) for 30 - 60 min (for example, it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min).

[0057] According to some preferred embodiments, in step (12): gradually cool down to the semi - solid temperature range of the current system and continue to carry out mechanical stirring at 1000 - 1800 rpm.

[0058] According to some preferred embodiments, in step (12): gradually cool down by 5 - 10 °C every 5 - 10 min.

[0059] According to some preferred embodiments, in step (1): the protective atmosphere is a gas atmosphere without oxygen and nitrogen.

[0060] According to some more preferred embodiments, the protective atmosphere is an argon atmosphere or a helium atmosphere.

[0061] Specifically, under the protective atmosphere, completely melt the aluminum alloy at its melting point temperature, then transfer it into the air atmosphere, insert a stirring paddle into the molten liquid aluminum alloy for mechanical stirring, control the stirring speed at 1000 - 1800 rpm, and the stirring time at 30 - 60 min. During this process, nitrogen, oxygen in the air and the aluminum melt undergo a gas - liquid reaction to generate nano - sized aluminum oxide and nano - sized aluminum nitride, obtaining a liquid aluminum alloy containing nano - particles. At the same time, through mechanical stirring, the nano - particles become more dispersed and evenly distributed. Subsequently, lower the melt temperature by 5 - 10 °C every 5 - 10 min and continue to carry out mechanical stirring in the air atmosphere until it cools down to the semi - solid temperature range of the current system, obtaining an aluminum alloy melt containing nano - particles.

[0062] In the present invention, throughout the entire process of melting and cooling aluminum alloy to semi-solid state, the aluminum alloy melt is always kept in contact with air, so that while avoiding excessive oxidation, sufficient pre-oxidation and pre-nitriding are achieved simultaneously, introducing nano-particles with good interfacial bonding with the aluminum alloy matrix. In this way, not only the phenomenon of oxidation and combustion of nano-particles is avoided, but also the rheological properties of the aluminum alloy melt are improved. Under the condition of continuous stirring at a stirring speed of 1000 - 1800 rpm, an aluminum alloy melt containing aluminum oxide and aluminum nitride is obtained, forming a dispersion framework composed of nano-particles and the aluminum alloy melt, forming a nano-dispersed phase, which lays a good foundation for the dispersion of micron-sized reinforcing particles. Moreover, in the semi-solid state, spherical fragmented grains are beneficial to the dispersion and capture of nano-particles, making the nano-particles evenly distributed in the aluminum alloy melt. At the same time, the liquid phase part of the semi-solid state can wet the nano-particles, promoting further interfacial bonding, which lays a good foundation for the dispersion of micron-sized reinforcing particles.

[0063] In the present invention, in order to avoid the reaction of aluminum alloy with oxygen in the air during the melting process, generating an aluminum oxide film, thus affecting the melting effect and product quality, it is selected to melt in a protective atmosphere excluding nitrogen and oxygen. Then, air is introduced into the liquid aluminum alloy through mechanical stirring, enabling the liquid aluminum alloy to undergo pre-oxidation and pre-nitriding, and in-situ generating nano-scale aluminum oxide and nano-scale aluminum nitride, thereby introducing nano-particles into the liquid aluminum alloy and increasing the viscosity of the current liquid aluminum alloy.

[0064] According to some more preferred embodiments, in step (12): insert a stirring paddle into the liquid aluminum alloy at the melting temperature and conduct mechanical stirring at 1000 - 1500 rpm (for example, it can be 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm or 1500 rpm) for 30 - 40 min (for example, it can be 30 min, 32 min, 34 min, 36 min, 38 min or 40 min).

[0065] According to some more preferred embodiments, in step (12): the temperature is gradually decreased by 10 °C every 10 min. For example, during the process of gradually decreasing the temperature from 690 °C to 660 °C, the temperature is gradually decreased from 690 °C to 680 °C, and then held for 10 min; then from 680 °C to 670 °C, and then held for 10 min; from 670 °C to 660 °C, and held for 10 - 15 min.

[0066] In the present invention, through experiments, it is found that by adjusting the stirring time of the liquid aluminum alloy in an air atmosphere, the content of nano-particles in the aluminum alloy melt can be further controlled. If the mechanical stirring time with the insertion of a stirring paddle is too short or the temperature is not gradually lowered to the semi-solid temperature range for continuous mechanical stirring (i.e., the total mechanical stirring time in the air atmosphere is too short), it will affect the content and dispersion of nano-particles, and further affect the viscosity of the aluminum alloy melt, which is not conducive to the subsequent dispersion of micron-sized reinforcement particles. If the total mechanical stirring time is too long, the too-high viscosity of the aluminum alloy melt will cause poor fluidity, which is not conducive to the subsequent dispersion and processing of micron-sized reinforcement particles. Therefore, on the premise of semi-solid stirring casting, the present invention improves the viscosity of the aluminum melt by appropriate means and makes the temperature range easy to adjust, and explores a micron-reinforcement dispersion process with good surface quality control ability and suitable for the vast majority of aluminum alloy systems.

[0067] According to some preferred embodiments, it further includes: before melting the aluminum alloy, the aluminum alloy is pretreated to remove the surface oxide layer and impurities.

[0068] In the present invention, in order to remove the oxide layer and impurities on the surface of the aluminum alloy, the aluminum alloy is soaked and cleaned with a sulfuric acid solution or a hydrochloric acid solution with a concentration of 5% - 8% (for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5% or 8%).

[0069] According to some preferred embodiments, the reinforcement particles are at least one of silicon carbide particles, titanium carbide particles, graphene particles or pure metal titanium particles.

[0070] According to some more preferred embodiments, the reinforcement particles are silicon carbide particles.

[0071] It should be noted that at least one means any one or any mixture of any several in any proportion.

[0072] According to some preferred embodiments, the size of the reinforcement particles is 5 - 25 μm (for example, it can be 5 μm, 10 μm, 15 μm, 20 μm or 25 μm).

[0073] According to some preferred embodiments, the size of the reinforcement particles is 10 - 14 μm (for example, it can be 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm or 14 μm).

[0074] In the present invention, adding reinforcing particles to an aluminum alloy melt containing nanoparticles can effectively enhance the strength, hardness, wear resistance, fatigue resistance, etc. of the aluminum matrix, thereby improving the mechanical and physical properties of the aluminum matrix composite. It has been experimentally confirmed that if the size of the added reinforcing particles is greater than 25 μm, problems such as sedimentation and uneven dispersion of the reinforcing particles will occur, and even stress concentration will affect the overall performance of the aluminum matrix composite. If the size of the added reinforcing particles is too small, less than 5 μm, the reinforcing particles will be more likely to agglomerate, thereby reducing the mechanical properties and service life of the material. Therefore, the size of the reinforcing particles is limited to 5 - 25 μm.

[0075] According to some preferred embodiments, the content of the reinforcing particles in the aluminum matrix composite is 10 - 15 vol% (for example, it can be 10 vol%, 10.5 vol%, 11 vol%, 11.5 vol%, 12 vol%, 12.5 vol%, 13 vol%, 13.5 vol%, 14 vol%, 14.5 vol% or 15 vol%).

[0076] In the present invention, it has been experimentally confirmed that when the content of the reinforcing particles in the aluminum matrix composite is relatively high, the reinforcing particles are prone to agglomeration, resulting in a decrease in the density of the aluminum matrix composite, and the particle agglomeration will exacerbate the sedimentation effect, causing sedimentation and thus leading to poor dispersion of the reinforcing particles, reducing the mechanical properties and service life of the aluminum matrix composite as well as the processing performance of the material; when the content of the reinforcing particles in the aluminum matrix composite is relatively low, it is difficult to effectively improve the mechanical properties of the aluminum matrix composite.

[0077] According to some preferred embodiments, in step (2): under a protective atmosphere, by adjusting the temperature of the aluminum alloy melt containing nanoparticles, the reinforcing particles are in a semi-solid state after being added to the aluminum alloy melt containing nanoparticles, obtaining a semi-solid slurry.

[0078] According to some preferred embodiments, in step (2): at a temperature higher than the aluminum alloy semi-solid temperature range under a protective atmosphere, the reinforcing particles are added to the aluminum alloy melt containing nanoparticles and mixed at a speed of 1000 - 1800 rpm. After the addition of the reinforcing particles is completed, the aluminum alloy melt is kept at the semi-solid temperature range for 10 - 20 min.

[0079] Specifically, due to the large temperature difference between the reinforcing particles and the aluminum alloy melt, after adding the reinforcing particles to the aluminum alloy melt containing nanoparticles, the entire melt temperature of the aluminum alloy melt system will decrease and will no longer be in a semi-solid state, making it difficult to continue adding the reinforcing particles. Therefore, it is necessary to adjust the temperature of the current system in real time, and by appropriately increasing the temperature of the current system to ensure that the entire system can be in a semi-solid state during the process of adding the reinforcing particles.

[0080] In the present invention, the presence of nanoparticles in the aluminum alloy melt containing nanoparticles increases the internal friction in the melt. This increase in internal friction leads to a decrease in the melt fluidity, thereby increasing the viscosity. At the same time, the nanoparticles can inhibit the shear thinning behavior of the melt, and even at high shear rates, the viscosity will not decrease significantly. Therefore, based on the increase in the melt viscosity of the liquid aluminum alloy, the critical rate of viscous capture of the reinforcement particles at the solid-liquid interface is significantly reduced. This not only provides a high-temperature dispersion environment but also greatly improves the problem of uneven distribution of micron-sized reinforcement particles caused by the movement of the solid-liquid interface. In addition, when the viscosity of the aluminum alloy melt increases, the changes in the buoyancy and resistance of the aluminum alloy melt to the reinforcement particles will also make the driving effect of the density difference on sedimentation relatively decrease, thereby further improving the dispersion of the reinforcement particles in the aluminum matrix composite material.

[0081] Since the interface between the reinforcement particles and the aluminum matrix is a weak phase, stress concentration and failure phenomena often easily occur. In the present invention, the aluminum alloy melt containing nanoparticles provides a high-temperature and high-viscosity dispersion environment. When the reinforcement particles are silicon carbide particles, Al will react with the silicon carbide particles at the interface to generate Al 4 C 3 phase. At the same time, the presence of Si will inhibit the progress of the reversible reaction to ensure that the content of the Al 4 C 3 phase is not too high. The SiO 2 on the surface of silicon carbide will also undergo a weak interface reaction with the Mg element in the aluminum alloy melt to generate MgO. These interface compounds with low content effectively improve the interface bonding degree between silicon carbide and the aluminum matrix, thereby increasing the interface strength.

[0082] According to some preferred embodiments, before adding the reinforcement particles to the aluminum alloy melt containing nanoparticles and mixing them evenly, the reinforcement particles are preheated.

[0083] In the present invention, by preheating the reinforcement particles, the temperature difference between the preheated reinforcement particles and the aluminum alloy melt is further reduced, which is more conducive to adjusting the temperature during the process of obtaining the semi-solid slurry.

[0084] According to some preferred embodiments, in step (3): the pressure of die casting is 5 - 10 MPa (for example, it can be 5 MPa, 5.5 MPa, 6 MPa, 6.5 MPa, 7 MPa, 7.5 MPa, 8 MPa, 8.5 MPa, 9 MPa, 9.5 MPa or 10 MPa), and the pressure holding time is 3 - 5 min (for example, it can be 3 min, 3.5 min, 4 min, 4.5 min or 5 min).

[0085] According to some preferred embodiments, in step (3): the temperature of hot extrusion is 300 - 400 °C (for example, it can be 300 °C, 305 °C, 310 °C, 315 °C, 320 °C, 325 °C, 330 °C, 335 °C, 340 °C, 345 °C, 350 °C, 355 °C, 360 °C, 365 °C, 370 °C, 375 °C, 380 °C, 385 °C, 390 °C, 395 °C or 400 °C), the speed is 0.1 - 1 mm / s (for example, it can be 0.1 mm / s, 0.15 mm / s, 0.2 mm / s, 0.25 mm / s, 0.3 mm / s, 0.35 mm / s, 0.4 mm / s, 0.45 mm / s, 0.5 mm / s, 0.55 mm / s, 0.6 mm / s, 0.65 mm / s, 0.7 mm / s, 0.75 mm / s, 0.8 mm / s, 0.85 mm / s, 0.9 mm / s, 0.95 mm / s or 1 mm / s), and the extrusion ratio is (8 - 20):1 (for example, it can be 8:1, 8.5:1, 9:1, 9.5:1, 10:1, 10.5:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1).

[0086] According to some preferred embodiments, in step (3): the speed of hot extrusion is 0.4 - 0.7 mm / s (for example, it can be 0.4 mm / s, 0.45 mm / s, 0.5 mm / s, 0.55 mm / s, 0.6 mm / s, 0.65 mm / s or 0.7 mm / s), and the extrusion ratio is (12 - 16):1 (for example, it can be 12:1, 12.5:1, 13:1, 13.5:1, 14:1, 14.5:1, 15:1, 15.5:1 or 16:1).

[0087] In the present invention, the prepared aluminum matrix composite material has good formability and surface integrity. Nano-sized aluminum nitride and nano-sized alumina particles are widely distributed around the micron-sized reinforcement particles, and there will be a certain adsorption effect at high temperatures. These nano-particles can hinder the crack propagation formed between the micron-sized reinforcement particles and the aluminum matrix during forming, and improve the stress distribution near the interface; at the same time, the modification effect of the interface products at high temperatures on the interface also effectively improves the formability of the composite material.

[0088] The present invention also provides a nano-particle assisted dispersion aluminum matrix composite material prepared by the above preparation method.

[0089] In the present invention, compared with directly adding nanoparticles by the external addition method, since nanoparticles are more prone to agglomeration than microparticles, it is more difficult to achieve uniform dispersion of nanoparticles in the aluminum matrix during the stirring process. Moreover, the addition of nanoparticles will also affect the system temperature of the aluminum matrix. However, in the present invention, by introducing air stirring, nanoparticles are in-situ generated in the aluminum matrix through a gas-liquid reaction. The nanoparticles are not only in-situ generated with the air stirred in, but also further dispersed with the stirring, thereby reducing the degree of agglomeration. Moreover, it does not affect the system temperature, and there is no need to pre-prepare nanoparticles in advance, thus saving material costs and eliminating the need to additionally control the addition method of nanoparticles.

[0090] In the present invention, the "and / or" appearing between multiple technical features indicates that these technical features are all connected in an "and / or" relationship, meaning that any one of these technical features can be selected, or any combination of two or more of these technical features can be selected.

[0091] Without special instructions, the various raw materials used in the present invention can be products directly purchasable on the market or synthesized by existing methods.

[0092] The present invention will be further described by way of examples below, but the protection scope of the present invention is not limited to these embodiments.

[0093] Example 1

[0094] (1) Silicon carbide particles with a size of 10 μm and a content of 10 vol% were configured according to the mass of 2024 aluminum alloy; 2024 aluminum alloy was soaked and cleaned with a sulfuric acid solution with a concentration of 8% to remove the surface oxide layer and impurities; the silicon carbide particles were dried at 250 °C to complete preheating and remove the moisture adsorbed on their surfaces.

[0095] (2) 2024 aluminum alloy was melted in an argon atmosphere at 690 °C. After maintaining for 20 min, liquid aluminum alloy was obtained; then it was transferred to an air atmosphere, and a stirring paddle was inserted into the liquid aluminum alloy for mechanical stirring. The stirring speed was controlled at 1500 rpm and the stirring time was 30 min. During this process, nitrogen and oxygen in the air reacted with the liquid aluminum alloy in a gas-liquid reaction to obtain a liquid aluminum alloy containing nanoparticles; then in the air atmosphere, the system temperature was reduced by 10 °C every 10 min until it was cooled to the semi-solid temperature range of 660 °C of the current system. During the cooling process, mechanical stirring was continuously carried out at a speed of 1500 rpm to obtain an aluminum alloy melt containing nanoparticles.

[0096] (3) In an argon atmosphere, heat the aluminum alloy melt containing nanoparticles to 690 °C, and then add 10 μm, 10 vol% silicon carbide particles after preheating treatment into the aluminum alloy melt while stirring (at a rotational speed of 1500 rpm) for mixing. Ensure that the temperature of the system is not lower than 670 °C by controlling the addition speed of the silicon carbide particles. After adding the silicon carbide particles, keep stirring at 660 °C for 30 min to further uniformly disperse the silicon carbide particles and obtain a semi-solid slurry;

[0097] (4) Die-cast the semi-solid slurry in a steel mold preheated to 400 °C under a pressure of 150 MPa for 4 min; obtain a composite ingot after water cooling and solidification; then perform low-speed hot extrusion on the composite ingot at 300 °C at a speed of 0.5 mm / s with an extrusion ratio of 16:1 to obtain an aluminum matrix composite.

[0098] The SEM images and element distribution maps of the aluminum matrix composite obtained in this example are respectively as Figure 2 (a) and Figure 2 (c) - (i) shown, as Figure 2 It can be seen that in the system with fine nano-sized alumina and nano-sized aluminum nitride dispersed, the micron-sized silicon carbide particles are uniformly distributed in the aluminum matrix composite, and the aluminum matrix composite has a uniform structure and excellent compactness.

[0099] Example 2

[0100] Example 2 is basically the same as Example 1, the difference is that:

[0101] In step (1), silicon carbide particles with a size of 10 - 14 μm and 15 vol% are configured according to the mass of 2024 aluminum alloy;

[0102] (2) Melt 2024 aluminum alloy in an argon atmosphere at 690 °C, keep it for 20 min to obtain a liquid aluminum alloy; then transfer it to an air atmosphere, insert the stirring paddle into the liquid aluminum alloy for mechanical stirring, control the stirring speed at 1000 rpm and the stirring time at 30 min. During this process, nitrogen and oxygen in the air react with the liquid aluminum alloy in a gas-liquid reaction to obtain a liquid aluminum alloy containing nanoparticles; then in the air atmosphere, lower the temperature of the system by 10 °C every 10 min until the temperature is lowered to the semi-solid temperature range of 670 °C of the current system. During the temperature reduction process, continuously stir mechanically at a rotational speed of 1800 rpm to obtain an aluminum alloy melt containing nanoparticles.

[0103] Example 3

[0104] Example 3 is basically the same as Example 1, the difference is that:

[0105] In step (1), silicon carbide particles with a size of 5 - 10 μm and 10 vol% are configured according to the mass of 2024 aluminum alloy;

[0106] (2) Melt 2024 aluminum alloy in an argon atmosphere at 690 °C. After maintaining for 20 min, obtain liquid aluminum alloy; then transfer it to an air atmosphere, insert a stirring paddle into the liquid aluminum alloy for mechanical stirring, control the stirring speed at 1000 rpm and the stirring time at 30 min. During this process, nitrogen and oxygen in the air react with the liquid aluminum alloy in a gas-liquid reaction to obtain a liquid aluminum alloy containing nanoparticles; thereafter, in the air atmosphere, lower the temperature of the system by 5 °C every 10 min until the temperature is lowered to the semi-solid temperature range of 670 °C of the current system. During the temperature reduction process, continuously mechanically stir at a speed of 1000 rpm to obtain an aluminum alloy melt containing nanoparticles.

[0107] Example 4

[0108] Example 4 is basically the same as Example 1, except that:

[0109] In step (1), silicon carbide particles with a size of 20 - 25 μm and 10 vol% are configured according to the mass of 2024 aluminum alloy; in step (2), lower the temperature of the system by 10 °C every 10 min until the temperature is lowered to the semi-solid temperature range of 670 °C of the current system.

[0110] Example 5

[0111] Example 5 is basically the same as Example 1, except that:

[0112] (2) Melt 2024 aluminum alloy in an argon atmosphere at 690 °C. After maintaining for 20 min, obtain liquid aluminum alloy; then transfer it to an air atmosphere, insert a stirring paddle into the liquid aluminum alloy for mechanical stirring, control the stirring speed at 1500 rpm and the stirring time at 60 min. During this process, nitrogen and oxygen in the air react with the liquid aluminum alloy in a gas-liquid reaction to obtain a liquid aluminum alloy containing nanoparticles; thereafter, in the air atmosphere, lower the temperature of the system by 10 °C every 10 min until the temperature is lowered to the semi-solid temperature range of 670 °C of the current system. During the temperature reduction process, continuously mechanically stir at a speed of 1500 rpm to obtain an aluminum alloy melt containing nanoparticles.

[0113] Example 6

[0114] Example 6 is basically the same as Example 1, except that:

[0115] (4) Die cast the semi-solid slurry in a steel mold preheated to 450 °C under a pressure of 150 MPa for 4 min; obtain a composite ingot after water cooling and solidification; then perform low-speed hot extrusion on the composite ingot at 400 °C at a speed of 0.1 mm / s with an extrusion ratio of 20:1 to obtain an aluminum matrix composite material.

[0116] Example 7

[0117] Example 7 is basically the same as Example 1, except that:

[0118] (4) Die cast the semi-solid slurry in a steel mold preheated to 400 °C under a pressure of 150 MPa for 4 min; obtain a composite ingot after water cooling and solidification; then perform low-speed hot extrusion on the composite ingot at 300 °C at a speed of 1 mm / s with an extrusion ratio of 8:1 to obtain an aluminum matrix composite material.

[0119] Example 8

[0120] Example 8 is basically the same as Example 1, except that:

[0121] (1) Configure graphene particles with a size of 10 - 14 μm and 12 vol% according to the mass of 2024Al aluminum alloy; soak and clean the 2024 aluminum alloy with a sulfuric acid solution with a concentration of 8% to remove the surface oxide layer and impurities; dry the graphene particles at 250 °C to complete preheating and remove the moisture adsorbed on its surface.

[0122] Example 9

[0123] Example 9 is basically the same as Example 1, except that the 2024Al aluminum alloy is replaced with 6061Al aluminum alloy. Specifically, in step (2), melt the 6061 aluminum alloy in an argon atmosphere above the melting point temperature of the 6061Al aluminum alloy, hold for 20 min, and then obtain a liquid aluminum alloy; then transfer it to an air atmosphere, insert a stirring paddle into the liquid aluminum alloy for mechanical stirring, control the stirring speed at 1500 rpm and the stirring time at 30 min; then in the air atmosphere, lower the temperature of the system by 10 °C every 10 min until it cools down to the semi-solid temperature range of the current system. During the cooling process, continuously stir mechanically at a speed of 1500 rpm to obtain an aluminum alloy melt containing nanoparticles.

[0124] Comparative Example 1

[0125] Comparative Example 1 is basically the same as Example 1, except that:

[0126] (2) Melt the 2024 aluminum alloy in an argon atmosphere at 690 °C. After maintaining for 20 min, obtain the liquid aluminum alloy; then in an air atmosphere, lower the temperature of the system by 10 °C every 10 min until the temperature is lowered to 670 °C, the semi-solid temperature range of the current system. During the temperature reduction process, continuously mechanically stir at a speed of 1500 rpm to obtain an aluminum alloy melt containing nano-particles.

[0127] The SEM image of the aluminum matrix composite prepared in this comparative example is as Figure 3 shown. It can be seen from Figure 3 that for the aluminum matrix composite without pre-nitriding and pre-oxidation, the distribution of micron-sized silicon carbide has obvious segregation characteristics. Compared with Example 1, the dispersion effect uniformity of the reinforcement in Comparative Example 1 is greatly reduced.

[0128] Comparative Example 2

[0129] Comparative Example 2 is basically the same as Example 1, the difference is that:

[0130] (4) Obtain a composite material ingot after water-cooling and solidifying the semi-solid slurry in a crucible; then perform low-speed hot extrusion on the composite material ingot at 300 °C at a speed of 0.5 mm / s, and the extrusion ratio is 16:1 to obtain an aluminum matrix composite.

[0131] The aluminum matrix composite prepared in this comparative example contains uncompacted pores, and the reinforcement agglomerates to form weak zones. There are oxide layers and inclusions near the interface between the reinforcement and the aluminum matrix, which affect the interface strength and the quality of the aluminum matrix composite.

[0132] Comparative Example 3

[0133] Comparative Example 3 is basically the same as Example 1, the difference is that:

[0134] (2) Melt the 2024 aluminum alloy in an argon atmosphere at 690 °C. After maintaining for 20 min, obtain the liquid aluminum alloy;

[0135] (3) In an argon atmosphere, add the pre-heat-treated 10 μm, 10 vol% silicon carbide particles to the liquid aluminum alloy while stirring (at a speed of 1500 rpm) for mixing, and ensure that the temperature of the system is not lower than 670 °C by controlling the speed of adding the silicon carbide particles. After adding the silicon carbide particles, keep stirring at 670 °C for 30 min to further make the silicon carbide particles evenly dispersed to obtain a semi-solid slurry.

[0136] In this comparative example, it will make the addition of the reinforcement more difficult and it is difficult to achieve the effective compounding of the aluminum alloy and the reinforcement particles. Secondly, the added reinforcement particles are difficult to be captured by the solidifying solid-liquid interface front, and are pushed by the interface to form a "necklace-like" distribution along the grain boundaries, which greatly deteriorates the mechanical properties of the obtained aluminum matrix composite material.

[0137] Comparative Example 4

[0138] Comparative Example 4 is basically the same as Example 1, except that:

[0139] (1) 2024 aluminum alloy was soaked and cleaned with a sulfuric acid solution with a concentration of 8% to remove the surface oxide layer and impurities;

[0140] (2) 2024 aluminum alloy was melted in an argon atmosphere at 690 °C. After holding for 20 min, liquid aluminum alloy was obtained; in an argon atmosphere, the temperature of the system was lowered by 10 °C every 10 min until the temperature was lowered to the semi-solid temperature range of 670 °C of the current system to obtain semi-solid slurry;

[0141] (4) The semi-solid slurry was die-cast in a steel mold preheated to 400 °C under a pressure of 150 MPa for 4 min; after water cooling and solidification, an ingot was obtained; then the ingot was subjected to low-speed hot extrusion at 300 °C at a speed of 0.5 mm / s, and the extrusion ratio was 16:1 to obtain an aluminum matrix material.

[0142] The aluminum matrix materials prepared in this comparative example and the aluminum matrix composite materials prepared in Example 1 were respectively subjected to mechanical property tests, and the stress-strain curve graphs as shown in Figure 4 were obtained. As can be seen from Figure 4 , the aluminum matrix composite material prepared in Example 1 of the present invention has higher strength, better elastic modulus and more excellent yield strength. It should be noted that Figure 4 SiC / 2024Al in is the aluminum matrix composite material prepared in Example 1, and 2024Al is the aluminum matrix material prepared in Comparative Example 4.

[0143] Comparative Example 5

[0144] Comparative Example 5 is basically the same as Example 1, except that:

[0145] (2) 2024 aluminum alloy was melted in an argon atmosphere at 690 °C. After holding for 20 min, liquid aluminum alloy was obtained; then in a high-purity argon atmosphere, the temperature of the system was lowered by 10 °C every 10 min until the temperature was lowered to the semi-solid temperature range of 640 °C of 2024 aluminum alloy. During the temperature reduction process, mechanical stirring was continuously carried out at a rotation speed of 1500 rpm;

[0146] (3) In an atmosphere of high-purity argon, the aluminum alloy melt is heated to 690 °C, and then 10 μm, 10 vol% silicon carbide particles after preheat treatment are added to the aluminum alloy melt with stirring (rotation speed is 1500 rpm) for mixing, and the temperature of the system is ensured not to be lower than 640 °C by controlling the addition rate of the silicon carbide particles. After the addition of the silicon carbide particles is completed, it is kept stirring at 640 °C for 30 min to further make the silicon carbide particles uniformly dispersed, and a semi-solid slurry is obtained.

[0147] Comparative Example 5 adopts the traditional semi-solid stirring casting method. By comparing Example 1 with Comparative Example 5, it is found that the dispersion temperature of the micron-sized reinforcement particles in Example 1 is about 30 °C higher than that of the traditional semi-solid method, realizing the dispersion of micron-sized reinforcement particles at high temperature, being applicable to more aluminum alloy systems, especially pure aluminum without semi-solid state or low-alloyed aluminum alloys with an extremely narrow semi-solid temperature range, shortening the addition time of the micron-sized reinforcement particles, reducing the time cost and energy cost, and effectively improving the quality and efficiency of the preparation of aluminum matrix composites. The present invention provides a new idea for the dispersion of traditional reinforcements in metal melts such as aluminum and magnesium.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. The parts not detailed in the present invention are well-known technologies in the art.

Claims

1. A method for preparing an aluminum-based composite material assisted by nanoparticle dispersion, characterized in that: include: (1) melting an aluminum alloy to obtain a liquid aluminum alloy, and stirring the liquid aluminum alloy in an air atmosphere to obtain an aluminum alloy melt containing nanoparticles; (2) adding the reinforcement particles into the aluminum alloy melt containing the nanoparticles and mixing them to obtain a semi-solid slurry; (3) The semi-solid slurry is subjected to pressure casting, cooling and hot extrusion in sequence to obtain the aluminum-based composite material.

2. The preparation method according to claim 1, characterized in that: Step (1) comprises: (11) melting the aluminum alloy at a melting temperature in a protective atmosphere to obtain a liquid aluminum alloy; (12) In an air atmosphere, inserting a stirring paddle into the liquid aluminum alloy at the melting temperature for mechanical stirring, then gradually cooling the temperature to a semi-solid temperature range of the current system and continuing the mechanical stirring to obtain the aluminum alloy melt containing nanoparticles.

3. The preparation method according to claim 2, characterized in that: In step (1): Inserting a stirring paddle into the liquid aluminum alloy at the melting temperature and mechanically stirring at 1000-1800 rpm for 30-60 min; preferably, mechanically stirring at 1000-1500 rpm for 30-40 min; and / or, The temperature is gradually lowered to the semi-solid temperature range and mechanical stirring is continued at 1000-1800 rpm; preferably, the temperature is gradually lowered by 5-10° C. every 5-10 min, more preferably by 10° C. every 10 min; Preferably, the protective atmosphere is a gas atmosphere free of oxygen and nitrogen, more preferably an argon atmosphere or a helium atmosphere.

4. The preparation method according to claim 1, characterized in that: The reinforcement particles are at least one of silicon carbide particles, titanium carbide particles, graphene particles or pure metal titanium particles; preferably silicon carbide particles; and / or, The size of the reinforcement particles is 5 to 25 μm, preferably 10 to 14 μm.

5. The preparation method according to claim 1, characterized in that: In step (2): Under a protective atmosphere, the temperature of the aluminum alloy melt containing nanoparticles is adjusted so that the reinforcement particles are in a semi-solid state after being added to the aluminum alloy melt containing nanoparticles, thereby obtaining the semi-solid slurry; preferably, the mixing speed is 1000-1800rpm.

6. The preparation method according to claim 1, characterized in that: Also includes: Before melting the aluminum alloy, pre-treating the aluminum alloy to remove surface oxide layers and impurities; and / or, Before adding the reinforcement particles into the aluminum alloy melt containing the nanoparticles for mixing, the reinforcement particles are preheated.

7. The preparation method according to claim 1, characterized in that: In step (3): The pressure of the pressure casting is 5-10 MPa, and the holding time is 3-5 min; and / or, The temperature of the hot extrusion is 300-400° C., the speed is 0.1-1 mm / s, and the extrusion ratio is (8-20):1; preferably, the speed of the hot extrusion is 0.4-0.7 mm / s, and the extrusion ratio is (12-16):

1.

8. The preparation method according to claim 2, characterized in that: When the aluminum alloy is 2024 aluminum alloy, step (1) comprises: (11) melting the 2024 aluminum alloy at 690° C. in a protective atmosphere to obtain a liquid aluminum alloy; (12) In an air atmosphere, insert a stirring paddle into the liquid aluminum alloy at 690° C. for mechanical stirring, then gradually cool the temperature to 660-670° C. and continue mechanical stirring to obtain the aluminum alloy melt containing nanoparticles.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The content of the reinforcement particles in the aluminum-based composite material is 10-15 vol%.

10. A nanoparticle-assisted dispersed aluminum-based composite material prepared by the preparation method according to any one of claims 1 to 9.

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