Preparation method of nanometer aluminum oxide particle in-situ reinforced aluminum-based composite material

Abstract

The invention discloses a preparation method of a nanometer aluminum oxide particle in-situ reinforced aluminum-based composite material, and Mg element and La2O3 powder are introduced into a reaction system to synergistically realize refining and uniform dispersion of Al2O3 particles. After the mixed powder is added into an aluminum melt, heat preservation is conducted at the temperature of 800-900 DEG C, stirring is conducted at the speed of 300-450 r / min, it is ensured that particles are evenly dispersed and the reaction is fully conducted, meanwhile, Zn volatilization heat absorption temperature control and residual Zn solid solution strengthening are utilized, and finally the composite material with 50-100 nm Al2O3 evenly distributed is obtained. The bonding force between Al2O3 particles and a matrix interface is high, meanwhile, a small amount of Zn element is dissolved in a matrix in a solid mode to participate in aging strengthening, and the hardness of the material reaches 72-75 HV and is remarkably improved compared with pure aluminum. The method is high in process stability, low in cost and excellent in material mechanical property.

Description

Technical Field

[0001] This invention belongs to the technical field of ceramic particle reinforced aluminum matrix composites, specifically relating to the preparation method of in-situ reinforced aluminum matrix composites with nano-alumina particles, particularly to the regulation of aluminothermic reaction based on the ZnO-Al system, and the preparation process of in-situ reinforced aluminum matrix composites with nano-Al2O3 particles. Background Technology

[0002] Particle-reinforced aluminum matrix composites are novel materials that improve the mechanical properties of materials by introducing second-phase particles (such as ceramic particles) into an aluminum matrix and utilizing the "second-phase strengthening" effect. Based on the method of adding the reinforcing particles, they are mainly divided into two categories: external addition and in-situ addition. External addition involves directly adding the particle reinforcing phase to the alloy melt and dispersing it through mechanical stirring, ultrasonic stirring, or other methods. This method is simple, and the morphology, size, and type of the reinforcing phase can be artificially controlled, but it has significant drawbacks: poor wettability at the particle-melt interface, easily leading to interfacial gaps; easy contamination of the particle surface, resulting in the introduction of impurities and defects into the melt; excessive reaction or weak bonding at the particle-aluminum matrix interface; and difficulty in uniform dispersion of the reinforcing phase during stirring, severely affecting the final mechanical properties of the material. In-situ addition involves reacting an external modifier with the alloy melt to generate reinforcing particles within the melt. Compared to external addition, in-situ addition offers advantages such as clean reinforcing particle surfaces, good wettability at the melt interface, easy dispersion, high bonding strength with the matrix interface, simple operation, and lower cost. However, conventional in-situ methods still have problems such as difficulty in controlling the size and morphology of reinforcing particles; some reaction systems react violently, which can easily lead to melt splashing, resulting in increased porosity and decreased density of the material; and insufficient control over the reaction kinetics process, resulting in poor product performance consistency.

[0003] M. Tavoosi et al. (Bulk Al–Zn / Al2O3 nanocomposite prepared by reactive milling and hot pressing methods) used commercial aluminum powder and zinc oxide powder (and aluminum powder and zinc powder for comparison) as raw materials to study the process of preparing bulk Al-13.8wt% Zn / 5vol% Al2O3 metal matrix nanocomposite by mechanical milling for different times (focusing on 60h) using a planetary ball mill combined with hot pressing with specific parameters (400℃ / 500℃, 400MPa). However, ball milling for 60h easily causes powder oxidation, and the quantitative relationship between the Zn content and the material hardness and thermal stability is not clear. 13.8% Zn dissolved in the aluminum matrix will lower the melting point of the Al matrix and may form a low-melting-point eutectic phase at the grain boundaries, which will weaken the material properties and strength. At the same time, the hot pressing sintering method requires expensive hot pressing molds and high-pressure equipment, resulting in low raw material utilization, long process, and complex operation, which is not suitable for industrial mass production.

[0004] Liu et al. used Al powder (100μm), nano ZnO powder (<100nm), and Al-Zn-Cu alloy as raw materials. They ball-milled the Al powder and ZnO powder, cold-pressed them into preforms at 400MPa, and then added Al-Zn-Cu melt at 720℃ for in-situ reaction. After hot rolling (420℃, 6 passes) and solution treatment (460℃ / 1h) + aging (170℃ / 24h), they prepared nano Al2O3 / Al-Zn-Cu composite materials. However, experiments have shown that the compressed block is a solid structure, and it only has surface contact with the Al-Zn-Cu melt. The internal temperature rise depends on heat conduction, which makes it difficult to reach the reaction temperature quickly due to uneven heat conduction. The reaction is difficult to start, and there are also hidden dangers in the completeness of the reaction. Cold pressing may leave behind tiny pores or cause nano-ZnO agglomeration. The encapsulated powder may not be able to fully contact the melt, which can easily form "reaction dead zones". This leads to uneven crushing of the compressed block during the reaction, and the nano-Al2O3 generated in situ is prone to local enrichment.

[0005] In existing technologies, neither the external addition method nor the conventional in-situ method can simultaneously meet the requirements of uniform dispersion of the reinforcing phase, excellent interfacial bonding, controllable reaction process, and low preparation cost, which limits the industrial application of nano-alumina reinforced aluminum matrix composites. Summary of the Invention

[0006] To address the limitations on material properties caused by the agglomeration and large size of Al2O3 particles in traditional Al-ZnO in-situ reaction systems, this invention aims to provide a method for preparing in-situ reinforced aluminum matrix composites using nano-alumina particles. More specifically, it is a method for preparing in-situ reinforced aluminum matrix composites using nano-alumina particles based on the synergistic regulation of Mg and La2O3. By introducing Mg and La2O3 powder into the reaction system, the synergistic effect of the two is utilized to achieve the refinement and uniform dispersion of Al2O3 particles. Simultaneously, process parameters are optimized to achieve precise control over the size (50-100 nm) and distribution of nano-Al2O3 particles, improving the thermal stability of the second phase. Finally, through multi-component synergistic (Mg, La2O3) and Zn element aging strengthening, material strength is balanced, preparation costs are reduced, and process repeatability and product performance consistency are improved.

[0007] This invention provides a method for preparing an in-situ reinforced aluminum-based composite material using nano-alumina particles, the specific steps of which are as follows: (1) Ball milling: Add ZnO powder, Al powder, La2O3 powder and stearic acid-ethanol solution to the ball mill jar of the planetary ball mill, add stainless steel balls (ball-to-material ratio 10:1), close the ball mill jar, and purge the air with argon gas to avoid powder oxidation; ball mill parameters: speed 250-400 rpm, preferably 300 rpm; ball milling time 8-10 h.

[0008] The mass ratio of ZnO powder, Al powder, and La2O3 powder is 100:30:0.5-1.5. An appropriate excess of Al powder drives the complete conversion of ZnO, preventing unreacted ZnO particles from remaining in the composite material, thus ensuring material purity and mechanical properties.

[0009] The amount of stearic acid used is 1% of the total mass of ZnO powder and Al powder, and the concentration of the stearic acid-ethanol solution is 2.5-8 mg / mL. Preparation of the stearic acid-ethanol solution: Add stearic acid to anhydrous ethanol and stir in a constant temperature water bath at 60℃ until completely dissolved. During ball milling, ethanol and stearic acid act as dispersants. Stearic acid can form a coating layer on the powder surface, further inhibiting agglomeration; this step can improve the dispersibility of stearic acid in the mixed powder and enhance its anti-agglomeration effect.

[0010] (2) Removal of ethanol and stearic acid: Transfer the ball-milled powder into a vacuum drying oven, set the temperature to 200-300℃, and the vacuum degree to ≤10. -3 Pa, dry for 1-3 hours to remove alcohol and stearic acid residues, and obtain dry, pure ZnO-Al-La2O3 mixed powder.

[0011] (3) Aluminum liquid preparation and refining: Under argon protection, aluminum blocks and AlMg alloy ingots are placed in a graphite crucible and heated in a resistance furnace to 800-900℃. After complete melting, a refining agent is added. After refining, the slag is removed and the oxide slag on the surface of the aluminum liquid is skimmed off. The temperature of the alloy liquid is kept stable at 845-855℃.

[0012] The main function of the AlMg alloy ingot is to provide magnesium (Mg). Mg can be adsorbed on the surface of Al2O3 particles, reducing the interfacial tension between the particles and the molten aluminum, improving wettability, and forming the MgAl2O4 spinel phase with Al2O3, strengthening interfacial bonding and inhibiting crack propagation. Adding Mg in the form of an Al-Mg50 alloy avoids oxidation and burn-off compared to directly adding Mg powder, preventing Mg powder with large density differences from floating on the surface of the molten aluminum, making it difficult to disperse during stirring and forming localized Mg-rich zones. Furthermore, the AlMg alloy ingot is added at a Mg content of 1-2% of the aluminum block mass. Preferably, the AlMg alloy ingot is an Al-Mg50 alloy ingot.

[0013] The amount of refining agent added is 0.1% - 0.3% of the mass of the aluminum block. The preferred refining agent is C2Cl6.

[0014] Furthermore, using a graphite bell jar preheated to 100°C, the refining agent C2Cl6 is pressed into the molten aluminum and stirred for 5-10 minutes to perform refining, degassing, and impurity removal.

[0015] (4) In-situ reaction: Insert a graphite stir bar (the surface is polished to avoid introducing impurities) into the alloy liquid, set the stirring speed to 300-450 r / min, and start stirring; then add the mixed powder obtained in step (2) into the alloy liquid at a rate of 1.5-2.5 g / min through a feeding funnel, control the reaction rate between the powder and the alloy liquid, and avoid excessive local reaction; after the powder is completely added, keep stirring, raise the temperature of the aluminum liquid to 800-900℃, and keep it at that temperature for 10-30 min to ensure that the aluminothermic reaction between ZnO and Al is complete.

[0016] The amount of mixed powder added is calculated based on the theoretical yield of Al2O3 being 1% to 6% of the mass of molten aluminum.

[0017] The aluminothermic reaction between ZnO and Al is: 3ZnO + 2Al = +Zn↑. The generated Zn partially volatilizes and absorbs heat, inhibiting a sudden rise in reaction temperature, and partially dissolves in the aluminum matrix. At the same time, Mg and La2O3 can improve the wettability of Al2O3 particles with aluminum liquid and inhibit the agglomeration and growth of Al2O3 particles.

[0018] The aluminothermic reaction temperature is 800-900℃ and held for 10-30 minutes. This ensures the aluminothermic reaction is complete and prevents excessive growth of Al2O3 particles, ensuring that the particle size is stable at 50-100nm. At the same time, at a temperature close to the boiling point of Zn (850-900℃), Zn will volatilize significantly. This endothermic process balances the exothermic reaction and prevents splashing. The residual 10%-30% Zn solid solution strengthening is an innovative design that takes into account both process safety and material performance.

[0019] The stirring rate, controlled at 300-450 r / min, provides sufficient shear force to effectively break up particle agglomerates, ensuring that the generated 50-100 nm Al2O3 particles are uniformly dispersed in the aluminum matrix. Simultaneously, it promotes the migration of liquid Zn to the aluminum melt surface, allowing it to escape via high vapor pressure. If the stirring rate is below 300 r / min, insufficient shear force leads to particle agglomeration, forming large aggregates and weakening the "second-phase strengthening" effect. If the stirring rate is above 450 r / min, excessive stirring may entrain too much gas into the aluminum melt, increasing melt porosity, or exacerbate aluminum melt oxidation due to localized turbulence, thus negatively impacting the material's density and mechanical properties.

[0020] (5) Casting and cooling: After the reaction is completed, stop stirring and skim off the reaction residue and oxide residue on the surface of the aluminum liquid; then, under the protection of argon, quickly cast the aluminum liquid into a preheated copper mold and cool it naturally to room temperature to obtain an in-situ reinforced aluminum matrix composite material of nano-alumina particles.

[0021] As one of the preferred methods for preparing the above-mentioned in-situ reinforced aluminum matrix composite material using nano-alumina particles, the following components are selected: nano-ZnO powder with a purity of 99.9% and a particle size of 100-200 nm; Al powder with a purity of 99.75% and a particle size of 200-300 mesh; and La2O3 powder with a purity of 99.9% and a particle size of 100-200 nm. The ZnO powder with a particle size of 100-200 nm has a much larger specific surface area than micron-sized ZnO, resulting in more surface active sites. This significantly reduces the activation energy of the aluminothermic reaction and shortens the reaction induction period. Furthermore, it belongs to the conventional nanoscale and can be mass-produced using sol-gel and vapor deposition methods at a lower cost. The Al powder with a particle size of 200-300 mesh acts as a "dispersion medium" during ball milling, preventing the ZnO nanoparticles from agglomerating due to their small particle size. La2O3 can refine the Al2O3 particle size and, in conjunction with Mg, improve its wettability with molten aluminum, inhibiting particle agglomeration.

[0022] As one of the preferred methods for preparing the above-mentioned in-situ reinforced aluminum matrix composite material with nano-alumina particles, the nano-ZnO powder is further subjected to vacuum calcination activation treatment: the nano-ZnO powder is placed in a vacuum box furnace, the furnace door is closed, and a vacuum is drawn (vacuum degree ≤ 10). -3 The ZnO powder is heated to 500-550℃ and held for 2-4 hours for calcination activation. After calcination, it is cooled to room temperature in the furnace and then removed for use. Vacuum calcination can remove moisture and organic impurities adsorbed on the surface of ZnO powder, while changing the crystal structure of the powder surface, increasing the surface active sites, improving the subsequent reaction activity with Al powder, and shortening the reaction induction period.

[0023] As one of the preferred methods for preparing the above-mentioned in-situ reinforced aluminum matrix composite material with nano-alumina particles, the entire preparation process is protected by argon gas. From ball milling and aluminum liquid preparation to casting, high-purity argon gas is introduced throughout the process, which can effectively isolate air, avoid oxidation of powder and aluminum liquid, and reduce the formation of oxide slag.

[0024] The technical principles and beneficial effects of this invention are as follows: This invention provides a method for preparing an in-situ reinforced aluminum-based composite material based on Mg-La2O3 synergistic regulation of nano-alumina particles. First, ZnO and other materials are ball-milled and activated. Then, the ball-milled powder is dried and calcined. Finally, it is cold-pressed, crushed into small pieces, and added to molten aluminum to react and generate an Al-based alloy with an in-situ reinforced nanophase composite structure of nano-Al2O3 particles. In this process, ZnO reacts with the original Al powder. Under conditions of holding at 800–900℃ and stirring at 300–450 r / min, nano-Al2O3 reinforcing particles and Zn phase particles are generated in-situ through an aluminothermic reaction. On the one hand, it replaces the original aluminum powder as the source of Al2O3 reinforcing particles, solving the interface problem between the reinforcing phase and the aluminum matrix, and obtaining extremely small-scale Al2O3 nanoparticles. On the other hand, the Al2O3 reinforcing particles produced by the reaction of ZnO with Al at high temperature inhibit the growth of the nearby Al-Zn phase, improving the thermal stability of the second phase, resulting in a uniformly dispersed Al2O3 particle with a scale of 50–100 nanometers in the Al matrix.

[0025] The significant synergistic effect of Mg and La2O3 in aluminum-based composites effectively solves the technical challenges of Al2O3 particle agglomeration and large size. Combined with stirring, the particles are refined and uniformly dispersed, resulting in nano-Al2O3 particles that are uniformly dispersed in the aluminum matrix, significantly improving the strength and hardness of the material. At the same time, the Zn element generated by the reaction of ZnO and Al plays a solid solution reinforcing role. Mg and La2O3 synergistically improve the interfacial wettability between aluminum liquid and Al2O3 and limit the size of Al2O3 particles, resulting in a significant increase in material hardness (the hardness reaches 74.5 HV when the Al2O3 content is 5%, which is more than 100% higher than that of pure aluminum).

[0026] By controlling process parameters such as powder feeding rate, in-situ reaction temperature of ZnO-Al system, and stirring speed, problems such as melt splashing and oxidation during the reaction are effectively avoided. During the reaction of ZnO-Al system, the endothermic effect of zinc volatilization can suppress the sudden temperature rise, and the reaction kinetics are well controllable, which improves the stability of the preparation process and the consistency of product performance.

[0027] The selected raw materials, such as ZnO, Al, and Mg, are widely available and inexpensive, eliminating the need for expensive nano-Al2O3 particles; the process is simple and easy to operate, requiring no complex equipment, making it suitable for industrial mass production; the entire process consumes little argon and emits no harmful gases, making it environmentally friendly. Attached Figure Description

[0028] Figure 1 The image shows the XRD pattern of the alumina-reinforced aluminum matrix composite material prepared in Example 5.

[0029] Figure 2The following are the distribution of Al2O3 matrix in the composite materials prepared under different conditions according to the present invention: (a) distribution of alumina matrix with direct addition of Al2O3 powder; (b) distribution of in-situ alumina matrix with only 1% Mg added; (c) distribution of in-situ alumina matrix with 1% Mg and 1% La2O3 added; (d) distribution of in-situ alumina matrix with 1% Mg and 1.5% La2O3 added.

[0030] Figure 3 The figures show a comparison of the hardness of aluminum matrix composites reinforced with different alumina contents in Examples 1-6. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the embodiments. The described embodiments are only some embodiments of this application, and these embodiments are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0032] Unless otherwise specified, all percentages, fractions, and ratios are calculated based on the total mass of the compositions of the present invention. The term "percentage by mass" may be expressed using the symbol "%".

[0033] The present invention will be further described in detail below with reference to preferred embodiments: The raw material components used in the following embodiments of the present invention are as follows: Al powder 45 Purity ≥ 99.75%, Mg powder 45 Purity ≥ 99.9%, La2O3 powder purity ≥ 99.9%, ZnO powder 100nm purity ≥ 99.9%, aluminum ingot purity ≥ 99.75%, Al-Mg50 alloy ingot purity ≥ 99.75%.

[0034] Nano ZnO powder activation treatment: Place the nano ZnO powder into a vacuum chamber furnace, close the furnace door, and evacuate (vacuum degree ≤ 10). - Pa), then heat to 500-550℃ and hold for 2-4 hours for calcination activation; after calcination, cool to room temperature with the furnace and remove for use.

[0035] Example 1

[0036] The preparation method of 1% alumina reinforced aluminum matrix composite material includes the following steps: (1) Weigh the raw material powder according to the mass ratio of ZnO powder to Al powder of 10:3, weigh La2O3 powder according to 1% of the mass of ZnO powder, and weigh stearic acid according to 1% of the total weight of (ZnO+Al) powder.

[0037] (2) Add stearic acid to 130 mL of anhydrous ethanol and stir in a 60 °C water bath until completely dissolved. Set aside.

[0038] (3) Add Al powder, ZnO powder, La2O3 powder and stearic acid-ethanol solution to a ball mill jar, add stainless steel balls (ball-to-material ratio 10:1), evacuate and purge with argon three times, set the speed to 300 rpm, and ball mill for 10 hours.

[0039] (4) Place the mixed powder obtained from ball milling in step (3) into a vacuum drying oven, set the temperature to 200-300℃ and the vacuum degree to ≤10. - Pa, dry for 1-3 hours to remove alcohol and stearic acid residues, to obtain a dry and pure ZnO-Al-La2O3 mixed powder.

[0040] (5) Under argon protection, 500g of aluminum block and 10g of Al-Mg50 alloy ingot were melted in a graphite crucible at 850℃, 0.5g of C2Cl6 was added for refining, and the residue was removed and the temperature was kept at 850℃.

[0041] (6) Add the powder processed in step (4) into the molten aluminum at a uniform rate (1.5-2.5 g / min), with an addition amount of about 16 g. At the same time, turn on the stirrer and stir at a speed of 450 r / min. After the powder is completely added, stir for another 30 min to promote the powder to fully react with the matrix and improve the uniformity of the distribution of in-situ generated alumina particles in the matrix.

[0042] (7) The melt obtained in step (6) is cast into a copper mold preheated at 100°C under argon protection and cooled naturally at room temperature and pressure to finally obtain an Al-based composite material reinforced with 1% Al2O3.

[0043] Example 2

[0044] The method for preparing 2% alumina-reinforced aluminum-based composite material differs from Example 1 in that step (6) involves uniformly adding the powder processed in step (5) to the molten aluminum at a rate of 1.5-2.5 g / min, with an addition amount of approximately 32 g. Simultaneously, the stirrer is turned on and stirred at a speed of 450 r / min. The powder is then completely added and stirred for another 30 min. Finally, a 2% Al2O3-reinforced Al-based composite material is obtained.

[0045] Example 3

[0046] The method for preparing 3% alumina-reinforced aluminum-based composite material differs from Example 1 in that step (6) involves uniformly adding the powder processed in step (5) to the molten aluminum at a rate of 1.5-2.5 g / min, with an addition amount of approximately 48 g. Simultaneously, the stirrer is turned on and stirred at a speed of 450 r / min. The powder is then completely added and stirred for another 30 min. Finally, a 3% Al2O3-reinforced Al-based composite material is obtained.

[0047] Example 4

[0048] The method for preparing 4% alumina-reinforced aluminum-based composite material differs from Example 1 in that step (6) involves uniformly adding the powder processed in step (5) to the molten aluminum at a rate of 1.5-2.5 g / min, with an addition amount of approximately 64 g. Simultaneously, the stirrer is turned on and stirred at a speed of 450 r / min. The powder is then completely added and stirred for another 30 min. Finally, an Al-based composite material reinforced with 4% Al2O3 is obtained.

[0049] Example 5

[0050] The method for preparing 5% alumina-reinforced aluminum-based composite material differs from Example 1 in that, in step (6): the powder processed in step (5) is added to the molten aluminum at a uniform rate (1.5-2.5 g / min), with an addition amount of approximately 79 g. Simultaneously, a stirrer is turned on for stirring at a speed of 450 r / min. The powder is stirred for another 30 min after complete addition. Finally, an Al-based composite material reinforced with 5% Al2O3 is obtained.

[0051] Example 6

[0052] The method for preparing 6% alumina-reinforced aluminum-based composite material differs from Example 1 in that step (6) involves uniformly adding the powder processed in step (5) to the molten aluminum at a rate of 1.5-2.5 g / min, with an addition amount of approximately 95 g. Simultaneously, the stirrer is turned on and stirred at a speed of 450 r / min. The powder is then completely added and stirred for another 30 min. Finally, a 6% Al2O3-reinforced Al-based composite material is obtained.

[0053] Comparative Example 1

[0054] To serve as a baseline reference, this blank comparative example was set up to examine the reaction and material properties of the pure Al-ZnO system without the addition of any Mg and La2O3.

[0055] The preparation method of 5% alumina reinforced aluminum matrix composite material includes the following steps: (1) Weigh out 85g of ZnO powder and Al powder in a mass ratio of 10:3, and 0.85g of stearic acid, which is 1% of the total weight of (ZnO+Al) powder.

[0056] (2)~(4) are the same as in Example 5.

[0057] (5) Under argon protection, 500g of aluminum block was melted in a graphite crucible at 850℃, 0.5g of C2Cl6 was added for refining, and after slag removal, the temperature was kept at 850℃.

[0058] (6)~(7) Same as Example 5.

[0059] When neither Mg nor La2O3 is added to the reaction system, the reinforcing phase of Al2O3 generated solely by the in-situ reaction of Al-ZnO has poor wettability in liquid aluminum, making it difficult to disperse evenly. It attracts and fuses with each other, forming agglomerates with sizes far exceeding 100 nm or even reaching the micrometer scale. As a result, it has poor mechanical properties, with a hardness of only 45-50 HV.

[0060] Comparative Example 2

[0061] The preparation method of 5% alumina reinforced aluminum matrix composite material includes the following steps: (1) Weigh out 85g of ZnO powder and Al powder in a mass ratio of 10:3, and 0.85g of stearic acid, which is 1% of the total weight of (ZnO+Al) powder.

[0062] (2)~(7) are the same as in Example 5.

[0063] Adding magnesium (Mg) to molten aluminum significantly improved the distribution of Al2O3 particles. Mg, as a potent surface-active element, substantially reduced the interfacial energy between Al2O3 and molten aluminum, effectively improving wettability and thus inhibiting the formation of large-scale agglomerates. Simultaneously, Mg may react slightly with Al2O3 to generate a small amount of MgAl2O4 spinel phase, further strengthening interfacial bonding. At this point, the Al2O3 particle size was typically between 150-200 nm, still relatively large, but significantly smaller than in Comparative Example 1, with only a small number of small agglomerates in localized areas. Benefiting from improved wettability, the macroscopic properties of the material also improved: hardness increased to 55-60 HV. However, Mg alone is insufficient for finely controlling the surface energy of Al2O3 particles and effectively inhibiting their growth; particle size could not be further refined, and distribution uniformity needed improvement, limiting further optimization of the material's properties.

[0064] Comparative Example 3

[0065] The preparation method of 5% alumina reinforced aluminum matrix composite material includes the following steps: (1) Weigh the raw material powder according to the mass ratio of ZnO powder to Al powder of 10:3, weigh La2O3 powder according to 0.5% of the mass of ZnO powder, and weigh stearic acid according to 1% of the total weight of (ZnO+Al) powder.

[0066] (2)~(7) are the same as in Example 5.

[0067] When Mg and 0.5% La2O3 are present in the system, the synergistic effect of Mg and La2O3 begins to emerge. Mg provides good macroscopic wettability and interfacial bonding, creating favorable conditions for the microscopic dispersion of La2O3. La2O3 can adsorb on the surface of newly formed Al2O3 particles, effectively reducing their surface energy and preventing particle fusion and growth. At this point, the Al2O3 particle size further decreases to about 100 nm, large-scale agglomeration is basically eliminated, and the hardness is significantly increased to 65-70 HV.

[0068] Comparative Example 4

[0069] The preparation method of 5% alumina reinforced aluminum matrix composite material includes the following steps: (1) Weigh the raw material powder according to the mass ratio of ZnO powder to Al powder of 10:3, weigh La2O3 powder according to 1.5% of the mass of ZnO powder, and weigh stearic acid according to 1% of the total weight of (ZnO+Al) powder.

[0070] (2)~(7) are the same as in Example 5.

[0071] When the amount of La2O3 added increases to 1.5%, new agglomeration phenomena occur in the matrix, resulting in a decrease in hardness. The excess La2O3 exceeds its saturation adsorption capacity on the surface of Al2O3 particles. The excess La2O3 itself attracts and agglomerates due to van der Waals forces and other interactions, forming larger La2O3 agglomerates. The appearance of these agglomerates disrupts the uniformity of the microstructure, becoming defects within the material.

[0072] Comparative Example 5

[0073] This comparative example uses an external addition method, directly adding nano-Al2O3 particles to the alloy melt, and then distributing the reinforcing phase within the alloy matrix through mechanical stirring. The specific steps are as follows: Al powder and nano-Al2O3 powder were weighed at a ratio of 2:1. Simultaneously, 1% Mg powder and stearic acid were weighed and mixed evenly in a ball mill jar. An appropriate amount of alcohol was added, and the mixture was evacuated and wet-milled under argon gas. The ball milling parameters were: ball-to-powder ratio 10:1, rotation speed 300 r / min, and time 5 h. The resulting powder mixture was placed in a vacuum drying oven and dried for 12 h to evaporate the alcohol. Then, it was calcined in a vacuum tube furnace at 200℃±10℃ to remove residual stearic acid. Finally, it was dried in a drying oven at 120℃. Under an argon atmosphere, 500g of aluminum block was heated and melted in a graphite crucible. After the aluminum block melted, a self-made graphite stir bar was inserted into the melt, and the temperature was raised to stabilize at 850℃.

[0074] The treated powder was added to the molten aluminum at a uniform rate (1.5-2.5 g / min), with an addition of approximately 77 g. At the same time, the stirrer was turned on and stirred at a speed of 350 r / min. After the powder was completely added, the mixture was stirred for another 30 min. The resulting melt was then cast into a preheated iron mold at 100°C under argon protection and allowed to cool naturally at room temperature and pressure to finally obtain an Al-based composite material reinforced with 5% Al2O3.

[0075] When preparing nano-Al2O3-reinforced aluminum matrix composites using the external addition method, the particles are added from outside the alloy melt, resulting in poor interfacial wettability between the particle reinforcement phase and the alloy melt. Excessive reaction occurs at the interface between the particle reinforcement phase and the aluminum matrix, leading to weak bonding. Many powder particles can be seen embedded in the matrix on the ingot surface. During stirring, the reinforcement phase particles cannot be controlled to disperse uniformly within the alloy melt, thus affecting the final mechanical properties of the alloy.

[0076] The results of Examples 1-6 and Comparative Examples 1-5 show that Mg and La2O3 exhibit a significant synergistic effect in the preparation of nano-Al2O3-reinforced aluminum-based composites in the Al-ZnO system. Mg improves the interfacial wettability between Al2O3 and the aluminum matrix, creating the basic conditions for the dispersion of La2O3; while La2O3 effectively inhibits the aggregation and growth of Al2O3 particles by adsorbing onto their surface. This synergistic effect successfully solves the technical problem of easy aggregation and large size of Al2O3 particles in the traditional Al-ZnO system, achieving particle refinement and uniform dispersion. Experiments confirm that when the system contains Mg and the La2O3 addition is 1%, the composite material achieves optimal overall performance: Al2O3 particle size is refined to 50-100 nm and uniformly dispersed; the material hardness is increased to 72-75 HV, a 100% improvement compared to pure Al. Meanwhile, compared with the traditional external addition method, the Al-ZnO system for preparing nano-Al2O3-reinforced aluminum matrix composites exhibits superior controllability of reaction kinetics due to the endothermic effect of zinc volatilization, which can suppress sudden temperature rises. The generated Zn element is dissolved in the matrix and participates in age-strengthening, balancing reaction controllability with material strength and toughness. The process is stable, low-cost, and suitable for industrial production, providing technical support for the widespread application of nano-alumina-reinforced aluminum matrix composites.

[0077] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an in-situ reinforced aluminum-based composite material using nano-alumina particles, characterized in that, The specific steps are as follows: (1) Add ZnO powder, Al powder, La2O3 powder and stearic acid-ethanol solution to the ball mill jar of the planetary ball mill, add stainless steel balls, close the ball mill jar, and then introduce argon gas to replace the air for ball milling. (2) Remove ethanol and stearic acid from the powder obtained after ball milling in step (1) to obtain ZnO-Al-La2O3 mixed powder; (3) Under argon protection, aluminum blocks and AlMg alloy ingots are placed in a graphite crucible and heated to 800-900℃. After complete melting, a refining agent is added. After refining, the slag is removed and the temperature of the alloy liquid is kept stable at 845-855℃. (4) Under stirring conditions, the mixed powder obtained in step (2) is added to the alloy liquid at a uniform speed; after the powder is completely added, stirring is continued, the temperature of the alloy liquid is raised to 800-900℃ and kept at that temperature for 10-30 minutes; stirring is stopped and the slag is removed. (5) Casting under argon protection and naturally cooling to room temperature to obtain an in-situ reinforced aluminum matrix composite material with nano-alumina particles.

2. The method for preparing the in-situ reinforced aluminum matrix composite material with nano-alumina particles according to claim 1, characterized in that, In step (1), the ZnO powder is activated ZnO powder that has undergone vacuum calcination activation treatment; the mass ratio of the activated ZnO powder, Al powder and La2O3 powder is 100:30:0.5-1.

5.

3. The method for preparing in-situ reinforced aluminum-based composite materials with nano-alumina particles according to claim 2, characterized in that, ZnO powder, purity 99.9%, particle size 100-200nm; Al powder, purity 99.75%, particle size 200-300 mesh; La2O3 powder, purity 99.9%, particle size 100-200nm.

4. The method for preparing the in-situ reinforced aluminum matrix composite material with nano-alumina particles according to claim 1, characterized in that, The amount of stearic acid used is 1% of the total mass of ZnO powder and Al powder, and the concentration of the stearic acid-ethanol solution is 2.5-8 mg / mL.

5. The method for preparing the in-situ reinforced aluminum-based composite material with nano-alumina particles according to claim 1, characterized in that, The ball milling speed in step (1) is 250-400 rpm, and the ball milling time is 8-10 h.

6. The method for preparing the in-situ reinforced aluminum-based composite material with nano-alumina particles according to claim 1, characterized in that, In step (3), AlMg alloy ingots are added according to the calculation that the Mg content is 1-2% of the mass of aluminum block.

7. The method for preparing the in-situ reinforced aluminum matrix composite material with nano-alumina particles according to claim 1, characterized in that, In step (4), the amount of mixed powder added is calculated based on the theoretical yield of Al2O3 being 1% to 6% of the mass of the aluminum liquid.

8. The method for preparing the in-situ reinforced aluminum matrix composite material with nano-alumina particles according to claim 1, characterized in that, Stirring speed: 300-450 r / min.

9. The method for preparing the in-situ reinforced aluminum matrix composite material with nano-alumina particles according to claim 1, characterized in that, The addition rate of the mixed powder is 1.5-2.5 g / min.

10. The in-situ reinforced aluminum matrix composite material with nano-alumina particles prepared by the method according to any one of claims 1-9.

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