A method for preparing a large-size nano-reinforced aluminum-based powder metallurgy ingot

Abstract

This invention discloses a method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots, relating to the field of metallurgical preparation technology, comprising the following steps: S1, preparing composite powder: uniformly compounding aluminum-based powder with nano-reinforcing phase to prepare nano-reinforced aluminum-based composite powder; S2, pre-pressing: pre-pressing the nano-reinforced aluminum-based composite powder into ingots; S3, encasing and sealing: encasing and sealing the ingots; S4, heating and degassing: heating and degassing the encased and sealed ingots; S5, vacuum sintering: heating the heated and degassed ingots to a predetermined sintering temperature and performing vacuum sintering; S6, hot pressing and repressing: immediately after sintering, using the residual heat of the vacuum-sintered ingots, hot pressing and repressing the ingots; S7, post-treatment: removing the encasing from the hot-pressed and repressed ingots to obtain densified ingots. This method effectively solves the problem of densification in large ingots, and does not rely on equipment such as vacuum sintering furnaces or hot pressing furnaces, but can be achieved using general-purpose presses and muffle furnaces, facilitating low-cost, large-scale mass production.

Description

Technical Field

[0001] This invention relates to the field of metallurgical preparation technology, and in particular to a method for preparing large-scale nano-reinforced aluminum-based powder metallurgy ingots. Background Technology

[0002] Nano-reinforced aluminum matrix composites, relying on the multi-scale synergistic strengthening effect of nanoscale reinforcing phases, can significantly improve the comprehensive mechanical properties and thermal stability of materials, effectively solving the bottleneck problems of strength-plasticity imbalance and insufficient high-temperature performance in traditional systems. This has become an important development direction for next-generation lightweight structural materials, showing significant application potential in key components of high-end equipment. Currently, the preparation of large-size ingots faces multiple technical challenges. Generally, large-size ingots have diameters of 200-1000 mm. Compared with traditional melting and casting methods, powder metallurgy is often used to prevent harmful interfacial reactions between the nano-reinforcing phase and the aluminum matrix at high temperatures, which can lead to the formation of brittle phases. However, during the densification process in powder metallurgy, the degree of densification is often inconsistent at different locations, especially the core and edges, leading to deformation and local fluctuations in microstructure and properties. Therefore, the preparation of large ingots is difficult. Furthermore, powder metallurgy is highly dependent on equipment such as vacuum hot pressing, vacuum sintering, and hot isostatic pressing, and its production costs are high. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots, which solves the problems existing in the prior art and effectively solves the difficulties in the densification process of large ingots. At the same time, it does not rely on equipment such as vacuum sintering furnaces and hot pressing sintering furnaces, but can be achieved with general-purpose presses and muffle furnaces, which facilitates low-cost and large-scale mass production.

[0004] To achieve the above objectives, the present invention provides the following solution: The present invention provides a method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots, comprising the following steps: S1. Preparation of composite powder: The aluminum-based powder is uniformly compounded with the nano-reinforcing phase to prepare nano-reinforced aluminum-based composite powder; S2. Pre-pressing: The nano-reinforced aluminum-based composite powder is pre-pressed into an ingot; S3. Encasing and sealing: Encasing and sealing the ingot blank; S4. Heating and degassing: The ingot blank after being sealed with a sleeve is subjected to heating and degassing treatment; S5. Vacuum sintering: The ingot blank after heating and degassing is heated to a predetermined sintering temperature and then vacuum sintered. S6. Hot pressing and repressing: After sintering, the ingot blank is then hot-pressed and repressed using the residual heat from vacuum sintering. S7. Post-processing: Remove the outer casing from the hot-pressed billet to obtain a densified billet.

[0005] Optionally, in step S1, the nano-reinforcing phase includes at least one of carbon nanotubes, graphene, graphene nanosheets, carbon nanotube onion spheres, carbon nanosheets, SiC, Al2O3, B4C, TiC, TiB, TiB2, AlN, and TiN.

[0006] Optionally, in step S2, molding or cold isostatic pressing is used to pre-press the nano-reinforced aluminum-based composite powder into the ingot.

[0007] Optionally, in step S2, the density of the pre-pressed billet is ≤80%.

[0008] Optionally, the ingot's sheath is a double-layer hollow heat-insulating structure.

[0009] Optionally, the sheath is connected to a vacuum pumping mechanism via a pipe to perform vacuum degassing on the ingot after it is sealed by the sheath.

[0010] Optionally, in step S4, while vacuuming, the ingot after being sealed is subjected to a stepped heating process.

[0011] Optionally, the step-by-step heating process includes: first heating the sealed ingot to 150~250℃ and holding it at that temperature for 30~120 minutes, then heating the sealed ingot to 350~450℃ and holding it at that temperature for 60~300 minutes.

[0012] Optionally, in step S2, the pressing pressure for pre-pressing the nano-reinforced aluminum-based composite powder is 5~200MPa.

[0013] Optionally, in step S5, the temperature range for vacuum sintering the ingot is 450~655℃.

[0014] Optionally, in step S6, the temperature range of hot pressing is 380℃~600℃, and the pressure range is 100~500MPa.

[0015] The present invention achieves the following technical effects compared to the prior art: This invention discloses a method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots. After obtaining the nano-reinforced aluminum-based composite powder, it first performs pre-pressing to make the powder particles initially dense and uniformly distributed. This effectively eliminates problems such as uneven filling and density gradients in the loose state of the nano-reinforced aluminum-based composite powder, providing a stable and uniform green structure for subsequent sintering. Then, after sintering, while the ingot is in a high-temperature plastic state, it is immediately re-pressed. At this time, the ingot has good plasticity, and cracks are not easily generated during re-pressing. This allows for simultaneous densification and dimensional correction of the ingot, enabling uniform release of internal stress. This significantly improves problems such as deformation, warping, and dimensional deviations caused by uneven sintering temperature field and inconsistent cooling shrinkage in large-size ingots, thus achieving densification of the ingot in a hot state.

[0016] Furthermore, vacuuming after the pre-pressing and encapsulation sealing steps can effectively reduce the oxidation of the ingot during the subsequent high-temperature process. This allows vacuum sintering to be achieved using general-purpose presses and muffle furnaces without relying on equipment such as vacuum sintering furnaces or hot pressing furnaces, facilitating low-cost and large-scale mass production. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is an overall process flow diagram in one example disclosed in this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The purpose of this invention is to provide a method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots, which solves the problems existing in the prior art and effectively solves the difficulties in the densification process of large ingots. At the same time, it does not rely on equipment such as vacuum sintering furnaces and hot pressing sintering furnaces, but can be achieved with general-purpose presses and muffle furnaces, which facilitates low-cost and large-scale mass production.

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] like Figure 1 As shown, this invention provides a method for preparing large-scale nano-reinforced aluminum-based powder metallurgy ingots, comprising the following steps: S1. Preparation of composite powder: Aluminum-based powder is uniformly compounded with nano-reinforcing phase to prepare nano-reinforced aluminum-based composite powder. In some specific examples, aluminum-based powder and the required nano-reinforcing phase are first mixed according to a preset mass ratio. It is understood that the type of aluminum-based powder selected will vary for the preparation of different composite materials, and the preparation of the same composite material is not limited to a single aluminum-based powder, but can be a mixture of multiple powders. Then, the aluminum-based powder and the nano-reinforcing phase are uniformly compounded to prepare nano-reinforced aluminum-based composite powder. Of course, it is not limited to the above examples.

[0023] S2. Pre-pressing: The nano-reinforced aluminum-based composite powder is pre-pressed into an ingot. For pre-pressing, a customized pre-pressing mold can be used to pre-press the nano-reinforced aluminum-based composite powder into an ingot. It is understood that the pressing pressure for pre-pressing can be adjusted according to different materials and working conditions. The pressing pressure range for pre-pressing nano-reinforced aluminum-based composite powder is controlled between 5 and 200 MPa.

[0024] S3, Encasing and Sealing: Encasing and sealing the billet.

[0025] S4. Heating and degassing: Heating and degassing the ingot after it has been sealed.

[0026] S5. Vacuum sintering: The ingot after heating and degassing is heated to the predetermined sintering temperature and then vacuum sintered; it is understood that the sintering temperature can be adjusted according to different materials and working conditions; the temperature control range for sintering nano-reinforced aluminum-based composite powder is 450~655℃.

[0027] S6. Hot Pressing and Re-pressing: After sintering, the residual heat of the vacuum-sintered ingot is used to hot press and re-press the ingot. The hot pressing and re-pressing of the sintered ingot can be performed using a press, etc., to transfer the vacuum-sintered ingot to the press's worktable for hot pressing and re-pressing. It is understood that the temperature for hot pressing and re-pressing can be adjusted according to different materials and working conditions, and the temperature range for hot pressing and re-pressing is controlled between 380℃ and 600℃, and the pressure range is controlled between 100 and 500 MPa. It should be noted that, under normal circumstances, after sintering, the ingot needs to be cooled to room temperature. If it is to be repressed, it needs to be reheated. In this invention, the residual heat is used immediately after vacuum sintering for repressing. The high-temperature residual heat of the ingot is used for vacuum repressing, eliminating the need for additional heating, saving energy and reducing production costs. In addition, the presence of the sheath makes it more difficult for heat to dissipate. The synergistic effect of high-temperature vacuum sintering and residual heat repressing enables the ingot to form a uniform and fine microstructure, significantly improving the tensile strength, hardness, and other mechanical properties of the ingot, thus meeting the high-performance requirements of high-end equipment. Specifically, high-temperature vacuum sintering provides a uniform microstructure and suitable plasticity temperature, while residual heat repressing utilizes this temperature condition to further close the residual pores inside the ingot, achieve more complete particle interface bonding, and compact and homogenize the microstructure. This inhibits abnormal grain boundary growth, ultimately forming a fine, uniform, and highly dense microstructure. Furthermore, the present invention utilizes residual heat immediately after sintering for repressing, which is a continuous process with a simple flow and no need for complex equipment. Compared with hot isostatic pressing, it reduces equipment investment. At the same time, the use of residual heat from sintering for repressing saves energy consumption, shortens the production cycle, enables mass production of large-size ingots, and reduces production costs. S7. Post-processing: Remove the outer casing from the hot-pressed billet to obtain a densified billet.

[0028] Furthermore, the method for preparing large-scale nano-reinforced aluminum-based powder metallurgy ingots according to the present invention yields ingots with a density of 95% to 99.9%.

[0029] In the above embodiments, after the pre-pressing step, the ingot is sealed with a sleeve to improve the degassing effect on the ingot, thereby facilitating rapid heating and degassing of the sealed ingot. Heating and degassing after sleeve sealing, combined with the pre-pressing step, can effectively reduce the oxidation of materials in subsequent high-temperature processes. Moreover, it can be achieved without relying on equipment such as vacuum sintering furnaces and hot pressing sintering furnaces, using general-purpose presses and muffle furnaces, which is conducive to low-cost and large-scale mass production.

[0030] In summary, the method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots disclosed in this invention involves mixing aluminum-based powder with nano-reinforcement to obtain nano-reinforced aluminum-based composite powder. Pre-pressing is then performed to initially densify and uniformly distribute the powder particles, effectively eliminating problems such as uneven filling and density gradients in the loose state of the nano-reinforced aluminum-based composite powder, thus providing a stable and uniform green structure for subsequent sintering. After sintering, while the ingot is in a high-temperature plastic state, it is immediately re-pressed. At this point, the ingot has good plasticity, and cracks are less likely to occur during re-pressing. This allows for simultaneous densification and dimensional correction of the ingot, resulting in uniform release of internal stress. This significantly improves problems such as deformation, warping, and dimensional deviations caused by uneven sintering temperature fields and inconsistent cooling shrinkage in large-size ingots, thus achieving densification of the ingot in a hot state.

[0031] In step S1, the nano-reinforcing phase includes at least one of carbon nanotubes, graphene, graphene nanosheets, carbon nanotube onion spheres, carbon nanosheets, SiC, Al2O3, B4C, TiC, TiB, TiB2, AlN, and TiN. In other examples, a micron-reinforcing phase, or a combination of nano-reinforcing and micron-reinforcing phases, can be used and mixed with aluminum-based powder phases to effectively improve the strength and stability of the composite powder.

[0032] In order to pre-press the nano-reinforced aluminum-based composite powder into an ingot, in step S2, molding or cold isostatic pressing is used to pre-press the nano-reinforced aluminum-based composite powder into an ingot.

[0033] To balance forming and sintering, the density of the pre-pressed ingot is ≤80% in step S2. Specifically, this ensures that the ingot has sufficient strength while also providing enough space for subsequent sintering shrinkage and gas removal, thereby avoiding defects such as cracks and warping, and ultimately obtaining a product with uniform internal structure and excellent performance.

[0034] In one embodiment, the ingot's sheath is a double-layered hollow thermal insulation structure. This double-layered hollow thermal insulation structure forms a closed micro-gap between the two layers. Utilizing the characteristics of a vacuum environment—thin air and low thermal conductivity—it significantly reduces the heat transfer rate between the inside and outside of the sheath, effectively reducing radial heat dissipation and temperature fluctuations of the ingot during sintering. Simultaneously, it effectively reduces heat dissipation during the high-temperature sintering to secondary pressing process. This facilitates the use of residual sintering heat for hot pressing, saving energy consumption, shortening the production cycle, and reducing production costs.

[0035] Based on the above implementation method, the sheath is connected to a vacuum pumping mechanism via a pipeline to perform vacuum degassing on the sealed ingot. The vacuum pumping mechanism is also connected to a vacuum display mechanism to show the vacuum level.

[0036] During the vacuum degassing process of ingots, the ingots can be heated. Heating provides sufficient energy to the gas molecules adsorbed on and inside the ingot, causing them to desorb and diffuse out, thus being removed. This avoids the situation where, without heating, vacuuming only removes free air within the casing, failing to remove chemically bound moisture and gases trapped inside the ingot. These residual gases expand during subsequent high-temperature processing, leading to porosity, cracks, or oxide inclusions within the ingot, severely affecting the final ingot's density and mechanical properties.

[0037] Regarding the heating method, in step S4, while evacuating, the sealed ingot is subjected to a stepped heating and degassing process. For example, the stepped heating step includes: first heating the sealed ingot to 150~250℃ and holding it at that temperature for 30~120 minutes, then heating the sealed ingot to 350~450℃ and holding it at that temperature for 60~300 minutes.

[0038] In summary, compared with hot isostatic pressing (HIP), this invention achieves a denser ingot through a combined process of batching, compounding, pre-pressing, degassing, sintering, and re-pressing. This replaces the high-pressure, high-temperature compounding system of HIP, resulting in simpler equipment structure, smaller investment scale, lower operating and maintenance costs, and reduced overall equipment investment. Simultaneously, the process flow is shorter, production efficiency is higher, and it is more suitable for low-cost, large-scale, and industrialized production of large-sized ingots. In particular, it ensures high density of the ingot, preventing a decrease in powder compact density as the ingot mass increases, which is difficult to achieve under vacuum hot pressing sintering, mold-pressed vacuum sintering, and HIP sintering. It is especially suitable for the preparation of powder metallurgy ingots with diameters of 200-1000 mm.

[0039] Based on the above embodiments, taking a 500 kg 1% carbon nanotube / 2024 aluminum-based powder metallurgy ingot as an example, its preparation method includes the following steps: S1. Preparation of composite powder: Prepare 5 kg of carbon nanotubes and 495 kg of 2024 aluminum alloy powder; uniformly combine 5 kg of carbon nanotubes and 495 kg of 2024 aluminum alloy powder to prepare carbon nanotube / 2024 composite powder. S2. Pre-pressing: The composite powder is loaded into a mold and subjected to cold isostatic pressing at a pressure of 200 MPa for 30 minutes; the final billet has a diameter of 565 mm, a height of 950 mm, and a density of 75%. S3, Encasing and sealing: Encasing and sealing the billet; S4. Heating and degassing: Place the billet into the muffle furnace, connect the vacuum pump system to the pipe on the casing to evacuate to below 100Pa, turn on the heating, and degas while heating. Heat to 250℃ and hold for 120min, then heat to 450℃ and hold for 150min. S5. Vacuum sintering: The degassed cladding billet is heated to 560℃ and sintered at 560℃ for 300 minutes, with continuous vacuuming. S6. Hot pressing and repressing: The sintered billet is quickly transferred to the press worktable, and the residual heat of the billet after vacuum sintering is used to perform hot pressing and repressing. The temperature is measured to be 500℃ and the repressing pressure is 300MPa. S7. Post-processing: The ingot blank after re-pressing is machined to remove the cladding, resulting in a densified ingot blank; the final density of the ingot is 99.5%.

[0040] Any adaptive changes made according to actual needs are within the scope of protection of this invention.

[0041] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0042] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots, characterized in that, Includes the following steps: S1. Preparation of composite powder: The aluminum-based powder is uniformly compounded with the nano-reinforcing phase to prepare nano-reinforced aluminum-based composite powder; S2. Pre-pressing: The nano-reinforced aluminum-based composite powder is pre-pressed into an ingot; S3. Encasing and sealing: Encasing and sealing the ingot blank; S4. Heating and degassing: The ingot blank after being sealed with a sleeve is subjected to heating and degassing treatment; S5. Vacuum sintering: The ingot blank after heating and degassing is heated to a predetermined sintering temperature and then vacuum sintered. S6. Hot pressing and repressing: After sintering, the ingot blank is then hot-pressed and repressed using the residual heat from vacuum sintering. S7. Post-processing: Remove the outer casing from the hot-pressed billet to obtain a densified billet.

2. The method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots according to claim 1, characterized in that, In step S1, the nano-reinforcing phase includes at least one of carbon nanotubes, graphene, graphene nanosheets, carbon nanotube onion spheres, carbon nanosheets, SiC, Al2O3, B4C, TiC, TiB, TiB2, AlN, and TiN.

3. The method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots according to claim 1, characterized in that, In step S2, the nano-reinforced aluminum-based composite powder is pre-pressed into the ingot by molding or cold isostatic pressing; the density of the pre-pressed ingot is ≤80%.

4. The method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots according to claim 1, characterized in that, The ingot is encased in a double-layer hollow heat-insulating structure.

5. The method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots according to claim 4, characterized in that, The sheath is connected to a vacuum pumping mechanism via a pipe to perform vacuum degassing on the ingot after it is sealed by the sheath.

6. The method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots according to claim 5, characterized in that, In step S4, while vacuuming and degassing, the ingot blank after being sealed in a sleeve is heated in a stepwise manner.

7. The method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots according to claim 6, characterized in that, The stepwise heating process includes: first heating the sealed billet to 150~250℃ and holding it at that temperature for 30~120 minutes, then heating the sealed billet to 350~450℃ and holding it at that temperature for 60~300 minutes.

8. The method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots according to claim 1, characterized in that, In step S2, the pressing pressure for pre-pressing the nano-reinforced aluminum-based composite powder is 5~200MPa.

9. The method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots according to claim 1, characterized in that, In step S5, the temperature range for vacuum sintering the ingot is 450~655℃.

10. The method for preparing large-size nano-reinforced aluminum-based powder metallurgy ingots according to claim 1, characterized in that, In step S6, the temperature range of hot pressing is 380℃~600℃, and the pressure range is 100~500MPa.

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