A method for improving the process plasticity and toughness of particle reinforced aluminum matrix composite materials

Abstract

This invention discloses a method for improving the process plasticity and toughness of particle-reinforced aluminum matrix composites. The method involves obtaining an initial particle-reinforced aluminum matrix composite ingot through hot isostatic pressing or mechanical hot pressing, followed by high-temperature, low-deformation, multi-directional cyclic deformation. This improves the process plasticity and toughness of the material, while also enhancing the uniformity of the microstructure and overall performance of the final part. This method overcomes the limitations of large extrusion equipment and specialized tooling dies, successfully achieving the process on general-purpose forging equipment using general-purpose free forging tooling dies. This enables the forming of large and complex parts while ensuring uniform microstructure and performance, reducing material scrap due to forging cracks, significantly improving material utilization, and lowering manufacturing costs.

Description

Technical Field

[0001] This invention discloses a method for improving the process plasticity and toughness of particle-reinforced aluminum matrix composites, belonging to the field of aluminum alloy hot working processes. Background Technology

[0002] With the increasing demands on equipment technology, the performance requirements for basic materials are becoming more stringent. Where traditional metallic materials cannot meet these requirements, metal matrix composites have become irreplaceable strategic new materials. Aluminum matrix composites possess high specific strength, specific modulus, good electrical and thermal conductivity, and high-temperature performance, leading to their increasingly widespread application in aerospace, aviation, and electronics. Powder metallurgy is the most commonly used process for preparing aluminum matrix composites. However, particle-reinforced aluminum matrix composite ingots prepared by powder metallurgy exhibit low process plasticity and toughness, are difficult to forge, and suffer from uneven internal properties and high dispersion. For small parts, hot extrusion is typically performed before forging to improve the material's process plasticity and toughness. However, hot extrusion is not feasible for large, complex components and ingots with high reinforcement content. If the billet is used directly for forging production, it will place high demands on the forging tooling and molds. At the same time, it is easy to cause problems such as small deformation, uneven deformation, large deformation dead zone, low material utilization, and large machining allowance. In addition, the defects of the original billet material, such as uneven performance and large dispersion, will also be inherited by the forging, reducing the service life and reliability of the forging. This greatly limits the application of aluminum-based composite materials. Summary of the Invention

[0003] This invention addresses the problems existing in the prior art by providing a method to improve the process plasticity and toughness of particle-reinforced aluminum matrix composites. When the billet size is large and traditional processes such as hot extrusion cannot be used to improve the billet, this method uses general-purpose equipment to perform layer-by-layer plasticizing and toughening of the particle-reinforced aluminum matrix composite billet through high-temperature, low-deformation, multi-directional cyclic reciprocating deformation. This makes the billet microstructure and properties more uniform, significantly improves the process plasticity and toughness, provides a good billet foundation for the subsequent forging of large components, and ensures the forming ability of large and complex parts and the uniformity of the final microstructure and properties.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] The steps of this method for improving the plasticity and toughness of particle-reinforced aluminum matrix composites are as follows:

[0006] Step 1: Heating:

[0007] Because forging has a slow deformation rate, small heat-affected zone, rapid cooling during forging, and small deformation per forging, common forging heating temperatures using matrix alloys are prone to cracking and abnormal grain growth. Therefore, the heating temperature should be as high as possible while ensuring that the alloy does not overheat. Through experiments, the heating temperature of the initial particle-reinforced aluminum matrix composite billet was set to be 20-30°C lower than the overheating point of the matrix material of the aluminum matrix composite billet. In this way, forging is smoother and overheating will not occur. Depending on the matrix alloy, this heating temperature is generally between 440 and 500°C.

[0008] Step 2: Insulation:

[0009] After adding reinforcing particles, the heat penetration time of the aluminum-based composite billet is longer than that of the pure aluminum alloy billet, and the heat penetration time tends to increase with the increase of particle content. Therefore, the holding time cannot be determined by referring to the traditional aluminum alloy forging parameters. So, after the aluminum-based composite billet is heated to the specified temperature, the holding time is selected as follows:

[0010] The first insulation method: when the reinforcing particle content is ≤20wt.% and the diameter of the aluminum-based composite ingot does not exceed 200mm, the insulation time is 12h; when the diameter of the aluminum-based composite ingot exceeds 200mm, the insulation time is not less than 2h + aluminum-based composite ingot diameter / 20.

[0011] The second insulation method: when the reinforcing particle content is 20wt.% to 25wt.% and the diameter of the aluminum-based composite ingot does not exceed 150mm, the insulation time is 12h; when the diameter of the aluminum-based composite ingot exceeds 150mm, the insulation time is not less than 2h + aluminum-based composite ingot diameter / 15.

[0012] Step 3, Axial Upsetting:

[0013] Because the original particle-reinforced billet has poor plasticity and fluidity, the deformation speed should not be too fast, and the forging speed should be reduced as the particle content increases. Therefore, after the heat treatment is completed, the aluminum matrix composite billet is axially upset. The axial upset is carried out in the following way:

[0014] The first axial upsetting method: when the reinforcing particle content is 15wt.% to 20wt.%, the deformation speed is controlled below 0.5mm / s;

[0015] The second type of axial upsetting method: when the reinforcing particle content is 20wt.% to 25wt.%, the deformation speed is controlled below 0.3mm / s;

[0016] Axial upsetting is performed twice, with the deformation amount controlled at 15% in each step. Between the two axial upsettings, the aluminum-based composite material billet is reheated and kept at a certain temperature. The heating temperature is the same as in step one, and the holding time is not less than 6 hours to eliminate internal stress and work hardening.

[0017] Step 4: Axial elongation:

[0018] The aluminum-based composite ingot after step three is heated and held at a constant temperature, following the same treatment process as steps one and two. Then, radial compression and axial elongation are performed, using the following methods:

[0019] The first axial upsetting method: when the reinforcing particle content is 15wt.% to 20wt.%, the deformation speed is controlled below 0.5mm / s;

[0020] The second type of axial upsetting method: when the reinforcing particle content is 20wt.% to 25wt.%, the deformation speed is controlled below 0.3mm / s;

[0021] The radial compression and axial elongation are performed four times. Between the two times, the aluminum-based composite material billet is reheated and kept at a certain temperature. The heating temperature is the same as in step one, and the holding time is not less than 6 hours.

[0022] The aluminum-based composite material ingot is stretched and deformed axially to its original length;

[0023] Step 5: Repeat steps 3 and 4 3 to 4 times;

[0024] Step Six: First Upsetting and Reverse Lengthening:

[0025] After completing step five, the aluminum-based composite material ingot is heated and kept warm. The treatment process is the same as that in steps one and two. Then, the first upsetting and reversing drawing are carried out to make the axial direction of the aluminum-based composite material ingot after this step perpendicular to the axial direction of the original billet, and its length is not less than the length of the original aluminum-based composite material ingot.

[0026] This step is completed in one go without reheating in the furnace. The deformation rate is 0.05 to 0.5 mm / s, and the deformation amount of the first upsetting and reversing elongation is 20% to 30%.

[0027] Step 7: Second upsetting and reversing elongation:

[0028] After completing step six, the aluminum-based composite material ingot is heated and kept warm. The treatment process is the same as that in steps one and two. Then, a second upsetting and reversing drawing are performed to restore the axial direction of the aluminum-based composite material ingot to be consistent with the axial direction of the original billet, and its length is not less than the length of the original aluminum-based composite material ingot.

[0029] This step is completed in one go without reheating in the furnace. The deformation rate is 0.05 to 0.5 mm / s, and the deformation amount of the first upsetting and reversing elongation is 20% to 30%.

[0030] Step 8: For the aluminum-based composite material ingots after completing Step 7, according to the requirements of the final forging, upsetting, drawing, punching, and ring forging processes can be used to provide the required billets for the subsequent final forging.

[0031] In practice, the initial particle-reinforced aluminum matrix composite ingot weighs less than 2 tons.

[0032] Furthermore, the initial particle-reinforced aluminum matrix composite ingot is obtained through hot isostatic pressing or mechanical hot pressing processes.

[0033] In practice, the matrix material composition and weight percentage of the initial particle-reinforced aluminum matrix composite ingot are as follows: Mg 0.5-3.5%, Cu 2.0-5.0%, Li 0-2.5%, Ti 0.01-0.05%, with the balance being Al.

[0034] Furthermore, the reinforcement of the initial particle-reinforced aluminum matrix composite ingot is SiC, with a reinforcement content of 15wt.% to 25wt.% and a reinforcement particle size of 5μm to 20μm.

[0035] During implementation, when the press cannot control the speed, forging is performed by manual inching.

[0036] During implementation, in step four, during radial compression and axial elongation, the amount of compression deformation each time is equal to 10% * the total height of the aluminum-based composite ingot in the compression direction.

[0037] During implementation, in step five, after each completion of steps three and four, the deformation amount increases by 5% in the next repetition.

[0038] During implementation, in steps six and seven, if the deformation resistance is abnormal during upsetting and reversing drawing, processing should be stopped immediately, and the aluminum-based composite material ingot should be reheated in the furnace. The heating temperature should be the same as in step one, and the holding time should not be less than 6 hours.

[0039] During implementation, in step six, before upsetting and reversing the drawing process, marks are made near the center points of both ends of the aluminum matrix composite billet. After completing step seven, the center points of both ends of the aluminum matrix composite billet coincide with the marks made in step six to ensure that the axial direction of the aluminum matrix composite billet after step seven is basically consistent with that of the original billet, so as to avoid flow line disorder.

[0040] This invention utilizes methods such as hot isostatic pressing or mechanical hot pressing to obtain an initial particle-reinforced aluminum matrix composite ingot, followed by high-temperature, low-deformation, multi-directional cyclic deformation. This multi-directional cyclic deformation causes the reinforcing particles to flow during deformation, reducing micro-agglomeration and resulting in a more uniform and dispersed distribution of the reinforcing particles. This improves the metallurgical quality of the ingot and reduces the number of microcrack sources. Deformation promotes the flow and breakup of high-pressure micropores formed during billet preparation, facilitating the formation of gas escape channels for dissipation at high temperatures. Simultaneously, high-temperature deformation welds the micropores, further reducing the number of microcrack sources in the billet. Deformation increases the energy stored in the ingot, and subsequent high-temperature holding helps the material recover and recrystallize around the reinforcing particles, improving the interface between the reinforcing particles and the aluminum matrix, and enhancing the microstructure of the ingot, thereby increasing the material's resistance to crack propagation. The reduction of microcrack sources and the improvement of the microstructure eliminate porosity defects and particle agglomeration in the ingot, reducing the tendency for cracking during subsequent forging. This improves the material's process toughness and plasticity, and also enhances the uniformity and overall performance of the final product.

[0041] This invention overcomes the limitations of hardware conditions such as equipment and special tooling molds. By using this process, general-purpose free forging tooling molds are used on general-purpose equipment to eliminate the non-uniformity of the microstructure and properties of particle-reinforced aluminum matrix composite billets, reduce the performance dispersion, improve the process plasticity and toughness of particle-reinforced aluminum matrix composite billets, improve the forming ability and microstructure and property uniformity of large and complex parts, improve material utilization, and reduce manufacturing costs.

[0042] The features and advantages of the technical solution of this invention are reflected in the following points:

[0043] 1. It can be completed using general hydraulic equipment and general free forging tooling molds, breaking through the limitations of equipment and special tooling molds. The process is convenient and feasible, and is easy to industrialize.

[0044] 2. A dedicated heating system was developed, specifying the heating temperature and holding time, with the holding time further refined based on the different particle content;

[0045] 3. The process sequence was clarified: billet heating; axial small deformation upsetting and drawing cyclic forging; upsetting and reversing drawing; re-upsetting and reversing drawing. Multi-directional free forging of ordinary aluminum alloys mainly aims to obtain a suitable streamline direction and achieve the required forging ratio, and mostly employs upsetting and reversing drawing.

[0046] 4. A dedicated axial upsetting procedure was developed, including deformation speed, single deformation amount, number of upsetting cycles, and furnace holding time. The deformation speed was further refined according to different particle content.

[0047] 5. A standard axial elongation system was established, including the deformation sequence, speed, single deformation amount, and number of cycles. The deformation speed was also refined according to different particle contents.

[0048] 6. The relationship between the number of cycles of axial upsetting and drawing and the amount of deformation per cycle was explored, and the sequence, direction and amount of deformation of the reverse drawing were clarified. Attached Figure Description

[0049] Figure 1 The high-magnification microstructure of the cross-section of the forgings prepared by the present invention and conventional processes in Example 1 are shown, wherein: a) is the forging prepared by the method of the present invention; b) is the forging prepared by conventional processes.

[0050] Figure 2 The high-magnification microstructure of the cross-section of the forgings prepared by the present invention and conventional processes in Example 2 are shown, wherein: c) is the forging prepared by the method of the present invention; b) is the forging prepared by conventional processes. Specific implementation plan

[0051] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0052] Example 1

[0053] The method for improving the process toughness and ductility of aluminum-based composite materials involved in this invention is used to process aluminum-based composite material billets with a SiC content of 17 wt.% and a matrix material composition and weight percentage of Mg 1.63%, Cu 3.85%, Ti 0.01%, and the balance being Al. The processing procedure is as follows: the annealed aluminum-based composite material billet is held at 490℃ for 48 hours, and then upsetting is performed axially to reduce the billet height from 880 mm to 620 mm, with a total deformation of 29.5%. The billet is then reheated once in the furnace for 6 hours, with a single deformation of 16%. The billet is then reheated in the furnace and held at 490℃ for 6 hours, followed by radial compression to elongate the billet axially to the original billet length. The axial upsetting and elongation cycle is repeated three times. The billet was reheated in the furnace at 490℃ for 6 hours, then upset and stretched in a different direction to a final length of 1010mm, with the axis perpendicular to the original billet axis. It was reheated twice in the middle. The billet was then reheated in the furnace at 490℃ for 6 hours, then upset and stretched in a different direction to a final length of 950mm, with the axis direction adjusted to match the original billet axis.

[0054] The processed billet was prepared into annular die-forged billets with a minimum outer diameter circumscribed circle of 1300 mm, a maximum inner diameter circumscribed circle of 550 mm, and a thickness of 325 mm through upsetting and ring forging processes. The billets were then placed in a die forging process, followed by heat treatment to the T4 condition. Tensile and fracture properties were measured, and the microstructure was observed under high magnification. For comparison, annular die-forged billets of the same size and shape were obtained using traditional free forging upsetting and machining methods. These billets were then placed in a die forging process, followed by heat treatment to the T4 condition. Tensile and fracture properties were measured, and the microstructure was observed under high magnification.

[0055] The microstructure and properties of forgings prepared by the two processes were compared after sampling from the same location. The results are shown in Table 1. Figure 1 As shown.

[0056] It can be observed that after treatment by the method of this invention, the tensile strength and elongation of the forgings are significantly improved, the range of helical elongation is small, the anisotropy of tensile strength and elongation is significantly reduced, and the fracture toughness is significantly improved. This indicates that after treatment by this method, the material's plasticity and toughness are significantly increased, and its properties are more uniform and stable. Metallographic analysis reveals that after treatment by this invention, the SiC agglomeration phenomenon is significantly reduced, and the distribution is more uniform.

[0057] Table 1 Properties of forgings prepared by different processes

[0058]

[0059] The material utilization rate of forgings prepared by the two processes is compared, and the results are shown in Table 2. The forgings treated with the present invention show a 20 percentage point increase in material utilization. This is mainly because the ring blanks prepared by the traditional process have poor process plasticity and toughness, making the rounding process impossible during preparation. This results in poor outer roundness and large bulges, leading to a large amount of machining on the outer circle. The hole-expanding ring forging process cannot be used, and the inner hole can only be achieved by machining. However, the present invention improves the process plasticity and toughness of the material, allowing the rounding and hole-expanding ring forging processes to be used, thus greatly improving the material utilization rate.

[0060] Table 2 Material utilization rate of forgings prepared by different processes

[0061]

[0062] Example 2

[0063] The method for improving the process toughness and ductility of aluminum-based composite materials involved in this invention was used to process an aluminum-based composite material billet with a SiC content of 22 wt.% and a matrix material composition and weight percentage of Mg 1.0%, Cu 4.5%, Li 0.45%, Ti 0.02%, and the balance being Al. After processing, the billet was forged into a disc-shaped forging with a thickness of 100 mm using free forging. Another aluminum-based composite material billet of the same shape, size, and composition was directly forged into a disc-shaped forging with a thickness of 100 mm using traditional free forging upsetting. The forgings were heat-treated to T4 condition, and samples were taken from the same location to measure tensile and fracture properties. The results were observed under high magnification and compared as shown in Table 3. Figure 2 As shown

[0064] It can be observed that after treatment by the method of the present invention, the tensile strength and elongation of the forgings are significantly improved, the anisotropy of tensile strength and elongation is significantly reduced, and the fracture toughness is significantly improved. This indicates that after treatment by this method, the material's plasticity and toughness are significantly increased, and its properties are more uniform and stable. Metallographic analysis reveals that after treatment by the present invention, the SiC agglomeration phenomenon is significantly reduced, and the distribution is more uniform.

[0065] Table 3 Properties of forgings prepared by different processes

[0066]

Claims

1. A method for improving the processing plasticity and toughness of particle-reinforced aluminum matrix composites, characterized in that; The steps of this method are as follows: Step 1: Heating: The initial particle-reinforced aluminum matrix composite ingot is placed in a heating furnace and heated at a temperature 20-30°C lower than the overheating point of the matrix material of the aluminum matrix composite ingot. Step 2: Insulation: After the aluminum-based composite material ingot is heated to the specified temperature, it is held at that temperature. The holding time is selected as follows: The first insulation method: when the reinforcing particle content is ≤20wt.% and the diameter of the aluminum-based composite ingot does not exceed 200mm, the insulation time is 12h; when the diameter of the aluminum-based composite ingot exceeds 200mm, the insulation time is greater than or equal to 2 + aluminum-based composite ingot diameter / 20, in hours. The second insulation method: when the reinforcing particle content is 20wt.%~25wt.% and the diameter of the aluminum-based composite ingot does not exceed 150mm, the insulation time is 12h; when the diameter of the aluminum-based composite ingot exceeds 150mm, the insulation time is greater than or equal to 2 + aluminum-based composite ingot diameter / 15, in hours. Step 3, Axial Upsetting: After the heat preservation is completed, the aluminum-based composite material ingot is axially upset. The axial upset is carried out using the following methods: The first type of axial upsetting method: when the content of reinforcing particles is 15wt.%~20wt.%, the deformation speed is controlled below 0.5mm / S; The second type of axial upsetting method: when the content of reinforcing particles is 20wt.% to 25wt.%, the deformation speed is controlled below 0.3mm / s; Axial upsetting is performed twice, with the deformation amount controlled at 15% in each step. Between the two axial upsettings, the aluminum-based composite material billet is returned to the furnace for heating and heat preservation. The heating temperature is the same as in step one, and the heat preservation time is not less than 6 hours. Step 4: Axial elongation: The aluminum-based composite ingot after step three is heated and held at a constant temperature, following the same treatment process as steps one and two. Then, radial compression and axial elongation are performed, using the following methods: The radial compression and axial elongation are performed four times. Between the two times, the aluminum-based composite material billet is reheated and kept at a certain temperature. The heating temperature is the same as in step one, and the holding time is not less than 6 hours. The aluminum-based composite material ingot is stretched and deformed axially to its original length; Step 5: Repeat steps 3 and 4 3 to 4 times; Step Six: First Upsetting and Reverse Lengthening: After completing step five, the aluminum-based composite material ingot is heated and kept warm. The treatment process is the same as that in steps one and two. Then, the first upsetting and reversing drawing are carried out to make the axial direction of the aluminum-based composite material ingot after this step perpendicular to the axial direction of the original billet, and its length is not less than the length of the original aluminum-based composite material ingot. This step is completed in a single operation without reheating in the furnace. The deformation rate is 0.05–0.5 mm / s, and the deformation amount during the first upsetting and reversing elongation is 20%–30%. Step 7: Second upsetting and reversing elongation: After completing step six, the aluminum-based composite material ingot is heated and kept warm. The treatment process is the same as that in steps one and two. Then, a second upsetting and reversing drawing are performed to restore the axial direction of the aluminum-based composite material ingot to be consistent with the axial direction of the original billet, and its length is not less than the length of the original aluminum-based composite material ingot. This step is completed in a single operation without reheating in the furnace. The deformation rate is 0.05–0.5 mm / s, and the deformation amount during the second upsetting and reversing elongation is 20%–30%. Step 8: For the aluminum-based composite material ingots after completing Step 7, according to the requirements of the final forging, upsetting, drawing, punching, and ring forging processes can be used to provide the required billets for the subsequent final forging.

2. The method for improving the process plasticity and toughness of particle-reinforced aluminum matrix composites according to claim 1, characterized in that: The initial particle-reinforced aluminum matrix composite ingot weighs less than 2 tons.

3. The method for improving the process plasticity and toughness of particle-reinforced aluminum matrix composites according to claim 1 or 2, characterized in that: The initial particle-reinforced aluminum matrix composite ingot is obtained through hot isostatic pressing or mechanical hot pressing processes.

4. The method for improving the process plasticity and toughness of particle-reinforced aluminum matrix composites according to claim 1, characterized in that: The matrix material composition and weight percentage of the initial particle-reinforced aluminum matrix composite ingot are as follows: Mg 0.5-3.5%, Cu 2.0-5.0%, Li 0-2.5%, Ti 0.01-0.05%, with the balance being Al.

5. The method for improving the process plasticity and toughness of particle-reinforced aluminum matrix composites according to claim 1 or 4, characterized in that: The initial particle-reinforced aluminum matrix composite ingot has SiC as its reinforcement, with a content of 15wt.% to 25wt.% and a particle size of 5μm to 20μm.

6. The method for improving the process plasticity and toughness of particle-reinforced aluminum matrix composites according to claim 1, characterized in that: When the press speed cannot be controlled, manual inching is used for forging.

7. The method for improving the process plasticity and toughness of particle-reinforced aluminum matrix composites according to claim 1, characterized in that: In step four, during radial compression and axial elongation, the amount of deformation during each compression is equal to 10% * the total height of the aluminum-based composite ingot in the compression direction.

8. The method for improving the process plasticity and toughness of particle-reinforced aluminum matrix composites according to claim 1, characterized in that: In step five, after each completion of steps three and four, the deformation amount increases by 5% in the next repetition.

9. The method for improving the process plasticity and toughness of particle-reinforced aluminum matrix composites according to claim 1, characterized in that: In steps six and seven, if the deformation resistance is abnormal during upsetting and reversing drawing, processing should be stopped immediately, and the aluminum-based composite material ingot should be reheated in the furnace. The heating temperature should be the same as in step one, and the holding time should not be less than 6 hours.

Images