A method for preparing a pipe made of aluminum-copper gradient composite material

Abstract

The present invention relates to a method for preparing a pipe of an aluminum-copper gradient composite material, which belongs to the field of metal processing technology, and specifically relates to the preparation and processing technology of high-performance, lightweight composite materials. The present invention realizes low-temperature processing and one-step forming to prepare aluminum-copper gradient composite pipes through the combined action of shear force and axial pressure generated by the rotation of the mold during the stirring friction process, which solves the technical problems such as high complexity of traditional processes, high cost of large-scale production, difficulty in regulating gradient structures, and insufficient interface bonding strength. The present invention balances the conductivity and lightweight of the composite pipe through the composition gradient design, and prepares a low-cost, high-performance, intelligent aluminum-copper composite material. The preparation process of the present invention is simple and controllable, which is convenient for industrial application.

Description

Technical Field

[0001] The invention relates to a method for preparing a pipe of an aluminum-copper gradient composite material, belongs to the technical field of metal processing, and specifically relates to a preparation and processing technology of a high-performance, lightweight composite material. Background Art

[0002] Aluminum-copper composite materials, by combining the lightweight, low-cost, and excellent processability of aluminum with the high electrical conductivity, high thermal conductivity, and corrosion resistance of copper, are widely used in electronic heat dissipation, new energy power systems, lightweight aerospace structures, high-end medical equipment, and chemical corrosion-resistant pipelines. For example, in the power battery system of new energy vehicles, aluminum-copper composite pipes are used in the liquid cooling circuit of the battery module, which not only reduces weight but also improves thermal conductivity. This is particularly important in high-energy-density batteries and fast-charging scenarios. It can effectively avoid the risk of battery thermal runaway caused by local overheating and is one of the key materials for upgrading the thermal management system of new energy vehicles. In 5G base stations, it serves as a shielding layer and heat dissipation substrate for high-frequency signal transmission, balancing signal integrity and energy consumption control. In the nuclear industry, the gradient structure takes into account both radiation protection and thermal management needs, making it an ideal material for the pursuit of high performance and economic synergy in multiple fields.

[0003] Copper alloys have high plasticity and can be processed through traditional extrusion processes at room temperature without preheating. However, traditional hot-extruded copper tubes are prone to coarse grains (>100μm in size), which affect conductivity and mechanical properties. Aluminum alloys have poor plasticity at room temperature, and hot extrusion requires heating to high temperatures (>400°C) and applying extremely high axial pressures (>400MPa). This results in high equipment costs, severe die wear, and extremely high energy consumption. High-temperature extrusion also leads to rapid grain growth, typically exceeding 50μm, which reduces material strength and ductility. Furthermore, hollow tubes require multiple processing steps such as drilling and welding, resulting in scrap rates as high as 15%-20%. These technical limitations significantly limit the further application of aluminum-copper composite tubes in applications such as electronic cooling, new energy power systems, lightweight aerospace structures, high-end medical equipment, and corrosion-resistant chemical piping.

[0004] At present, the preparation processes of aluminum-copper composite pipes mainly include extrusion molding, explosive compounding, hot pressing welding, powder metallurgy, etc. However, these processes generally face many technical problems and it is difficult to take into account the coordinated optimization of electrical conductivity, thermal conductivity and mechanical properties. Due to the large difference in the melting points of aluminum and copper in extrusion molding, complete metallurgical bonding cannot be achieved during extrusion. The interface bonding of the prepared pipe is weak and requires reliance on diffusion layer or brazing reinforcement. In addition, the mold design is complex, the dual extruder heads need to be precisely synchronized, and the mold must be resistant to high temperature and high pressure. The process of explosive compounding is highly complex and requires precise control of explosion parameters such as the amount of explosives, detonation point, and gap distance. Otherwise, stratification or local unbonding is likely to occur. The equipment cost of hot pressing welding is high, and it requires high-temperature and high-pressure molds, high-precision temperature control systems, and vacuum or inert gas protection. In addition, the production efficiency is low, the welding of single pieces takes a long time, and continuous production is difficult. The powder metallurgy preparation process is cumbersome and requires multiple steps of sintering and densification, which is not suitable for rapid mass production. These processes are still unable to meet the requirements of social development for high-performance, low-cost, and large-scale preparation of aluminum-copper composite materials. Therefore, there is an urgent need to explore new technical and process ideas to promote the efficient and green development of high-performance aluminum-copper composite materials in my country. Summary of the Invention

[0005] In response to the above problems, the present invention develops a preparation method for aluminum-copper gradient composite materials suitable for high-performance requirements based on a novel stir friction extrusion process. Stir friction extrusion is an innovative solid-state technology that can directly produce metal powder or solid billets into large pipes and rods. This technology is mainly based on the conventional extrusion process, and utilizes the relative rotation friction between the billet and the extrusion head to generate heat to achieve a new severe plastic deformation preparation process for efficient material processing and forming. During the preparation process, heat is generated between the billet and the extrusion head due to friction. The friction heat is mainly concentrated at the mold / blank interface, and the interface metal softens. The uniaxial extrusion force applied at the same time is combined with the rotational motion of the mold, resulting in severe plastic deformation of the billet at the interface. The softened metal layer diffuses and recrystallizes under the thermal-mechanical coupling of stirring and extrusion. Its essence is a process in which a metal material continuously forms a dense and reliable ultrafine-grained material under dynamic thermal equilibrium and pressure conditions. Compared with the processing and preparation process of traditional materials, the stir friction extrusion process gives the alloy structure and performance control more degrees of freedom. Compared to processes involving remelting, friction stir extrusion (FSE) can save approximately 50% of energy due to its efficient, short process flow. The FSE process combines the shear force and axial pressure generated by die rotation with a spiral rolling die design and low-temperature processing strategies to significantly reduce extrusion pressure (<50 MPa), refine grain size (1-10 μm), and achieve one-step hollow tube formation. This, in turn, reduces oxidation risk and equipment costs, providing a breakthrough solution for the efficient and precise forming of lightweight, highly integrated aluminum-copper gradient composites.

[0006] The present invention realizes low-temperature processing and one-step forming to prepare aluminum-copper gradient composite pipes through the combined effect of shear force and axial pressure generated by mold rotation during stir friction, which solves technical difficulties such as high complexity of traditional processes, high cost of large-scale production, difficulty in controlling gradient structures, and insufficient interface bonding strength. Through the composition gradient design, the conductivity and lightweight of the composite pipe are balanced to prepare low-cost, high-performance, intelligent aluminum-copper composite materials, which has become a material preparation and processing technology supporting the global green economy and high-end manufacturing industry.

[0007] The present invention provides a method for preparing a pipe of an aluminum-copper gradient composite material, comprising the following steps:

[0008] Step 1

[0009] A blank is prepared according to the designed composition; in the blank, the copper content of at least two regions differs by more than 1wt%;

[0010] Step 2

[0011] The obtained billet is added into a silo and an aluminum-copper gradient composite material is prepared by a friction stir extrusion process;

[0012] When using the friction stir extrusion process to prepare aluminum-copper gradient composite materials, the initial speed of the grinding head is set to 30-50 rpm / min. After contacting the raw materials in the hopper, the speed is maintained to gradually increase the temperature of the grinding head to A°C. During the grinding head preheating stage, the pressure applied by the hydraulic system is 0.3-0.8 MPa to ensure that the initial pressure when the grinding head contacts the raw materials is moderate to avoid premature deformation or extrusion of the material. The value of A is 180-220. When the grinding head preheating temperature reaches A°C, the staged heating begins.

[0013] During the first stage of heating, the grinding head speed is increased to 100~120 rpm / min, the temperature is raised to 350~400℃ (the recrystallization temperature of aluminum is about 270℃), and the hydraulic pressure is maintained at 0.5~1.0 MPa to maintain plastic fluidity; in the second stage, the speed is further increased to 150~180 rpm / min, and the temperature is raised to 450~550℃ (lower than the recrystallization temperature of copper but higher than the softening temperature of the aluminum layer). During the implementation of the second stage, the hydraulic pressure is controlled and gradually increased to 1.5~3.0 MPa to promote diffusion at the copper-aluminum interface and compensate for the low plasticity of aluminum.

[0014] Step 3

[0015] When the temperature of the grinding head rises to 450~550℃, the hydraulic pressure is adjusted according to the wall thickness of the pipe and the grinding head speed is controlled at 150~200 rpm. The mold is preheated to 300~400℃. At the same time, gradient speed control (reducing the speed at the outlet end) is used to prevent interface peeling; the specific operating steps of gradient speed control are as follows: gradient speed control specifically refers to the grinding head inlet speed being 150~200 rpm, and the outlet speed being reduced by 5%~15% (135~170 rpm), and the speed decreasing distribution is achieved through the axial displacement of the spiral rolling mold.

[0016] Adjust the hydraulic pressure according to the pipe wall thickness during specific operation. When the wall thickness is 1-3mm, the hydraulic pressure is set to 2~4 MPa. When the wall thickness is greater than 3mm and less than or equal to 7mm, it is set to 4~6 MPa.

[0017] Step 4

[0018] The pipe prepared by the friction stir extrusion process is cooled to 50-80°C at a cooling rate greater than 100K / s to obtain the product.

[0019] The present invention provides a method for preparing a tube of an aluminum-copper gradient composite material. In step 1, the density of the blank is ≥95% of the theoretical density.

[0020] In practical applications, the blank may include at least three parts, namely a high copper area, a medium copper area, and a low copper area; and the medium copper area is located between the high copper area and the low copper area, the copper content of the high copper area is greater than that of the medium copper area and the low copper area, and the copper content of the medium copper area is greater than that of the low copper area.

[0021] In practical applications, the copper content in the low copper area is greater than or equal to 50%.

[0022] Preferably, the copper content of the middle copper zone is greater than or equal to 70%.

[0023] In practical applications, the high copper area, the medium copper area, and the low copper area are composed of copper and aluminum or a copper and aluminum alloy.

[0024] In industrial applications, the raw materials used in preparing billets are A1060 aluminum alloy powder with a purity of ≥99.0% and a particle size of 20-50μm. Fine powder is used to improve the density of the billet; C1100 electrolytic copper powder with a purity of ≥99.5% and a spherical fine powder with a particle size of 20-50μm is used to improve the conductivity of the material, improve powder fluidity, and reduce powder segregation.

[0025] The present invention provides a method for preparing a pipe of an aluminum-copper gradient composite material, wherein the aluminum content in the high-copper region is less than or equal to 10%.

[0026] The present invention provides a method for preparing a pipe of an aluminum-copper gradient composite material, wherein the aluminum content in the medium copper zone is less than or equal to 30%, but greater than the aluminum content in the high copper zone.

[0027] The present invention provides a method for preparing a tube of an aluminum-copper gradient composite material, wherein the aluminum content in the low copper zone is less than or equal to 50%, but greater than the aluminum content in the medium copper zone.

[0028] The invention discloses a method for preparing a pipe of an aluminum-copper gradient composite material. When mixing raw material powder in a high-copper region, a three-dimensional motion powder mixer is used, and the rotation speed is controlled to be 200 rpm / min and the mixing time is 2 hours.

[0029] The invention discloses a method for preparing a pipe of an aluminum-copper gradient composite material. When mixing raw material powder in a middle copper zone, a three-dimensional motion powder mixer is used, and the rotation speed is controlled to be 150 rpm / min and the mixing time is 4 hours.

[0030] The invention discloses a method for preparing a pipe of an aluminum-copper gradient composite material. When mixing raw material powder in a low-copper region, a three-dimensional motion powder mixer is used, and the rotation speed is controlled to be 100 rpm / min and the mixing time is 6 hours.

[0031] In addition to mechanical ball milling, the present invention can also use air flow mixing, wet mixing or electrostatic mixing to mix powders.

[0032] The present invention discloses a method for preparing a pipe of an aluminum-copper gradient composite material. The method comprises the following steps: laying evenly mixed high-copper region raw material powder according to a set thickness, and then laying evenly mixed high-copper region raw material powder again according to the set thickness; obtaining a high-copper region raw material powder layer; then laying a medium-copper region raw material powder layer on the high-copper region raw material powder layer, and then laying a low-copper region raw material powder layer on the medium-copper region raw material powder layer; and then pressing to obtain a preform, wherein the density of the preform is greater than or equal to 95% of the theoretical density.

[0033] or

[0034] The high and low copper area raw material powders are evenly mixed and laid according to a set thickness, and then the low copper area raw material powder is evenly mixed and laid according to a set thickness; a low copper area raw material powder layer is obtained, and then a medium copper area raw material powder layer is laid on the low copper area raw material powder layer, and a high copper area raw material powder layer is laid on the medium copper area raw material powder layer; and then pressing is performed to obtain a preform, wherein the density of the preform is ≥95% of the theoretical density.

[0035] In industrial applications, A1060 aluminum alloy powder with a particle size of 20-50 μm and C1100 copper powder with a particle size of 20-50 μm can be weighed in sections according to the high copper region (such as 90% Cu / 10% Al, 90 g), the medium copper region (such as 70% Cu / 30% Al, 70 g), and the low copper region (such as 50% Cu / 50% Al, 50 g), and mixed by a wet mixing method: the copper and aluminum powders are respectively added to deionized water (liquid-powder ratio 1:8~1:10), and ultrasonically vibrated for 30 minutes to form a uniform suspension; then the high, medium, and low copper region slurries are injected into the mixing cavity in turn by a peristaltic pump, and negative pressure suction (vacuum degree -0.05 MPa) is used to achieve a gradient distribution of the copper and aluminum powders; and then dried in an 80°C oven for 6 hours to obtain a gradient composite powder with a humidity of <0.5%. Subsequently, the mixed powder was loaded into a graphite mold and pressed by hot isostatic pressing (HIP) at room temperature to 450°C: in the pre-pressing stage, a pressure of 150 MPa was applied for 10 minutes to initially eliminate the gaps between the powders; in the final pressing stage, the temperature was raised to 350°C and pressurized in two stages with a gradient pressure (150→300 MPa), and the temperature was kept for 90 minutes to ensure that the density of the blank was ≥99.5% of the theoretical density.

[0036] In the present invention, the press forming is selected from at least one of cold isostatic pressing, die pressing and hot isostatic pressing.

[0037] In this invention, a mold cold pressing process involves layering high-copper, medium-copper, and low-copper raw material powders in layers and cold pressing. A wet mixing method, through staged injection, flow field control, and drying and solidification, can form a preform with a gradient copper content decreasing along the axial direction. During the pressing process, the high-density copper region maintains a stable thickness due to its low plasticity, while the low-density aluminum region is preferentially compressed due to its high plasticity. Therefore, a gradient pressure is applied during the powder pressing process. A low pressure (150 MPa) is applied initially to eliminate internal porosity in the preform. Subsequently, the pressure is gradually increased to a final value (300 MPa), promoting diffusion at the copper-aluminum interface and compensating for the aluminum's low plastic deformation capacity. Ultimately, a preform with a continuous copper-aluminum gradient distribution (gradient difference ≥ 20% Cu), uniform density (≥ 95% theoretical density), and metallurgical bonding at the interface is achieved, meeting the requirements for zoning control of electrical, thermal, and mechanical properties. The key to this process is the deep coupling of the spatial distribution of the copper and aluminum powders with process parameters (powder addition sequence, flow rate, and stirring intensity) to form a controllable gradient structure. The theoretical predictions can be subsequently verified using SEM / EDS techniques.

[0038] One of the options for press forming is to select the following parameters: pressure of 200 MPa and holding time of 2 hours. When cold isostatic pressing is used, a rubber mold is preferred.

[0039] In the present invention, the silo material is preferably hot working die steel, and more preferably H13 steel, to ensure good wear resistance and thermal stability at high temperatures.

[0040] In industrial applications, inert gas cooling (argon flow rate 50~100 L / min) combined with a water-cooled jacket is used to achieve rapid cooling (rate ≥150 K / s). The final cooling temperature is controlled at 50~80℃ to avoid residual stress, and a nitrogen curtain is used to protect the aluminum layer from oxidation.

[0041] In addition to the friction stir extrusion process, the present invention can also use hot extrusion or cold extrusion process to form the pipe.

[0042] Beneficial effects

[0043] The present invention provides a method for preparing a pipe of an aluminum-copper gradient composite material, which has the following significant advantages over the prior art:

[0044] This invention utilizes a friction stir extrusion process, utilizing the relative rotational friction between the billet and the extrusion head to generate heat. This eliminates the need for high-temperature metal melting, reducing energy consumption from external heat sources. Compared to hot press welding, this process reduces energy consumption by 50%, significantly lowering production costs. This process can directly convert aluminum-copper powder billets into tubing in a single step. By regulating the extrusion speed, efficient and continuous production is possible, making it suitable for large-scale production applications.

[0045] The present invention prepares an aluminum-copper gradient composite material with controllable composition. By controlling the axial composition gradient of the mixed powder, multiple gradient segment combinations are set: high copper zone → medium copper zone → low copper zone. Since copper and aluminum are prone to interfacial stress due to differences in thermal expansion coefficients, the composition design can gradually transition the copper-to-aluminum ratio, reduce local stress concentration, and avoid delamination or cracking. By adjusting the stirring head speed, pressure, and the order of laying the raw materials, the copper-to-aluminum ratio can be precisely controlled along the axial direction to avoid excessive use of high-priced copper and reduce raw material costs. In addition, the stir friction extrusion process can optimize the microstructure by regulating the processing temperature, stirring head speed, and pressure, refine the grain size (1-10μm), and regulate the grain orientation, thereby balancing the electrical conductivity, thermal conductivity, and mechanical properties of the aluminum-copper composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of friction stir extrusion process;

[0047] Figure 2 This is a photo of the aluminum-copper gradient composite pipe prepared in Example 1;

[0048] Figure 3 This is a photo of the aluminum-copper gradient composite pipe prepared in Example 2. DETAILED DESCRIPTION

[0049] Example 1

[0050] A specific embodiment of the present invention is as follows: First, prepare A1060 aluminum alloy powder (particle size 20-50μm) with a purity of ≥99.0% and C1100 electrolytic copper powder (particle size 20-50μm) with a purity of ≥99.5%, and divide the powder into three gradient sections according to performance requirements: high copper zone (90% Cu, 10% Al), medium copper zone (70% Cu, 30% Al) and low copper zone (50% Cu, 50% Al). The amount of copper powder in each zone is 90g, 70g, and 50g, respectively, and the amount of aluminum powder is 10g, 30g, and 50g respectively, and the total mass is controlled at 100g / section; then, a three-dimensional motion powder mixer is used for gradient powder mixing, and the powder is uniformly dispersed by horizontal, vertical, and rotational three-axis linkage, wherein the high copper zone is mixed at a speed of 200 rpm for 2 hours, the medium copper zone is mixed at a speed of 150 rpm for 4 hours, and the low copper zone is mixed at a speed of 100 rpm for 4 hours. The powder mixture was mixed at rpm for 6 hours, with a differential speed and time combination promoting a gradient distribution of the copper and aluminum powders. Subsequently, the mixed powder was loaded into a rubber mold and pressed using a cold isostatic press at room temperature, with a pressure controlled at 200 MPa and a holding time of 2 hours. The density of the pressed blank was ≥95% of the theoretical density (the blank was divided into three regions: high copper zone, medium copper zone, and low copper zone). Next, a friction stir extruder equipped with an H13 steel silo was used for the extrusion process: first, the speed was set to 45 rpm during the preheating stage of the grinding head, and the speed was maintained after contact with the aluminum-copper raw materials in the silo, so that the temperature of the grinding head gradually increased to 180°C, and the hydraulic system applied a pressure of 0.5 MPa to avoid premature deformation or extrusion of the material; then the temperature was increased. During the first stage of heating, the speed of the grinding head was increased to 100 rpm, the temperature was increased to 350°C, and the hydraulic pressure was maintained at 1 MPa to maintain plastic fluidity; in the second stage, the speed was further increased to 150 rpm, the temperature was increased to 450°C, and the hydraulic pressure was gradually increased to 1.5 MPa to promote diffusion at the copper-aluminum interface and compensate for the low plasticity of aluminum; in the friction extrusion stage, the hydraulic pressure needed to be adjusted according to the thickness and diameter of the pipe wall (3 MPa was set for a wall thickness of 3 mm), and the speed of the grinding head was controlled at 150 rpm and preheat the mold to 300℃, and prevent interface peeling by gradient speed control (i.e., the speed at the inlet end of the grinding head is 150rpm and the speed at the outlet end is 135rpm); finally, inert gas cooling (argon flow rate 50L / min) combined with a water-cooled jacket is used to achieve rapid cooling (rate ≥150K / s), and the final cooling temperature is controlled at 80℃ to avoid residual stress, and a nitrogen curtain is used to protect the aluminum layer from oxidation.

[0051] Example 2

[0052] First, prepare A1060 aluminum alloy powder (particle size 20-50μm) with a purity of ≥99.0% and C1100 electrolytic copper powder (particle size 20-50μm) with a purity of ≥99.5%. According to performance requirements, the powders are divided into three gradient sections: high copper zone (90% Cu, 10% Al), medium copper zone (70% Cu, 30% Al) and low copper zone (50% Cu, 50% Al). The amount of copper powder in each zone is 90g, 70g, and 50g, respectively, and the amount of aluminum powder is 10g, 30g, and 50g respectively. The total mass is controlled at 100g / section. Then, the airflow mixing method is used to mix the powders. The copper and aluminum powders in the high copper zone, medium copper zone, and low copper zone are respectively loaded into three independent silos. The high-speed airflow generator (wind speed 15-20 m / s) is turned on, and the rotating scraping mechanism (speed 50 rpm) is used to achieve uniform mixing of the copper and aluminum powders through turbulent action. Subsequently, the mixed powder is loaded into a graphite mold (the inner cavity size is consistent with the target tube) (the bottom layer is high copper area powder, the middle layer is medium copper area powder, and the upper layer is low copper area powder), and the mold cold pressing method is used for pressing at room temperature: 100 MPa pressure is used in the pre-pressing stage, and the pressure is maintained for 5 minutes to preliminarily eliminate the powder gap; in the final pressing stage, the pressure is gradually increased to 300 MPa and maintained for 15 minutes. The density of the pressed blank is ≥90% of the theoretical density; the pressure is slowly released to demolding at normal pressure, and the blank is taken out (the blank is divided into three areas: high copper area / medium copper area / low copper area). Friction stir extrusion (FSE) was then performed using a FSE equipped with an H13 steel hopper. During the preheating phase, the grinding head initially rotated at 50 rpm. After contact with the aluminum-copper mixture in the hopper, the head maintained steady operation, gradually raising its temperature to 200°C. This phase then entered the heating phase. In the first stage, the speed was increased to 120 rpm, the temperature to 380°C, and the hydraulic pressure was maintained at 1.0 MPa to maintain plastic flow. In the second stage, the speed was further increased to 160 rpm, the temperature reached 480°C, and the pressure was gradually increased to 2.0 MPa to accelerate atomic diffusion at the copper-aluminum interface and compensate for the lack of plasticity in the aluminum matrix. During the friction extrusion phase, the pressure parameters were dynamically adjusted based on the pipe wall thickness: 3-5 MPa for wall thicknesses of 1-3 mm and 5-7 MPa for wall thicknesses of 5-7 mm. The grinding head speed was simultaneously controlled at 160 rpm and the die was preheated to 300°C. A gradient speed design (160 rpm at the grinding head inlet and 140 rpm at the grinding head outlet) effectively suppressed interfacial delamination. Finally, a water-cooled jacket with an argon flow rate of 70 L / min was used to achieve rapid cooling (cooling rate of 180 K / s). The final cooling temperature was controlled in the 70°C range, supplemented by a nitrogen protective curtain to prevent oxidation of the aluminum layer.

[0053] Example 3

[0054] First, A1060 aluminum alloy powder with a particle size of 20-50 μm and C1100 copper powder with a particle size of 20-50 μm were weighed in sections according to the high copper region (90% Cu / 10% Al, 90 g), medium copper region (70% Cu / 30% Al, 70 g), and low copper region (50% Cu / 50% Al, 50 g), and mixed by a wet mixing method: copper and aluminum powders were added to deionized water (liquid-powder ratio 1:8-1:10) respectively, and ultrasonic vibration was applied for 30 minutes to form a uniform suspension; then, the high, medium, and low copper region slurries were injected into the mixing chamber in sequence by a peristaltic pump, and negative pressure suction (vacuum degree -0.05 MPa) was used to achieve a gradient distribution of copper and aluminum powders (the bottom layer was high copper region powder, the middle layer was medium copper region powder, and the upper layer was low copper region powder); then, the powders were dried in an 80°C oven for 6 hours to obtain a gradient composite powder with a humidity of <0.5%. Subsequently, the mixed powder was loaded into a graphite mold and pressed by hot isostatic pressing (HIP) at room temperature to 450°C: in the pre-pressing stage, a pressure of 150 MPa was applied for 10 minutes to initially eliminate the powder gaps; in the final pressing stage, the temperature was raised to 350°C and pressurized in two stages with a gradient pressure (150→300 MPa) for 90 minutes to ensure that the density of the blank was ≥99.5% of the theoretical density; then, the pressure of 300 MPa was maintained at 450°C for 30 minutes to promote the diffusion of copper and aluminum atoms to form a metallurgical bonding interface. Finally, a hot extrusion process was used to prepare the pipe: the hot isostatically pressed preform was loaded into a ceramic barrel preheated to 450°C, with a heating rate controlled at 5°C / min. The pipe was extruded through a screw extruder at a speed of 20 mm / s, and the hydraulic pressure was adjusted according to the pipe diameter (4-6 MPa for Φ2-5 mm and 8-12 MPa for Φ5-10 mm). The cooling step used a combination of water cooling and air cooling, with a cooling rate controlled at 120 K / s and a final cooling temperature controlled at 100°C to avoid thermal stress cracking.

[0055] Comparative Example 1

[0056] Other conditions were the same as in Example 1, with the following differences: during friction stir extrusion, the first stage was omitted, proceeding directly to the second stage. The rotation speed was set at 150 rpm, the temperature was raised to 450°C, and the hydraulic pressure was increased to 1.5 MPa. During the friction extrusion stage, the hydraulic pressure was adjusted according to the tube wall thickness and diameter (3 MPa for a 3 mm wall thickness). The grinding head speed was controlled at 150 rpm, and the mold was preheated to 300°C. A gradient speed control (i.e., 150 rpm at the inlet and 135 rpm at the outlet) was used to prevent interfacial delamination. Finally, inert gas cooling (argon flow rate 50 L / min) combined with a water-cooled jacket achieved rapid cooling (rate ≥150 K / s). The final cooling temperature was controlled at 80°C to avoid residual stress, and a nitrogen curtain was used to protect the aluminum layer from oxidation. The resulting product had a grain size of 100 μm.

Claims

1. A method for preparing a pipe of an aluminum-copper gradient composite material, characterized in that: The steps include: Step 1 A blank is prepared according to the designed composition; in the blank, the copper content of at least two regions differs by more than 1wt%; Step 2 The obtained billet is added into a silo, and a pipe of an aluminum-copper gradient composite material is prepared by a friction stir extrusion process; When using the friction stir extrusion process to prepare aluminum-copper gradient composite material pipes, the initial speed of the grinding head is set to 30-50 rpm. After contacting the raw materials in the silo, the speed is maintained to gradually increase the temperature of the grinding head to A°C. During the grinding head preheating stage, the pressure applied by the hydraulic system is 0.3-0.8 MPa to ensure that the initial pressure when the grinding head contacts the raw materials is moderate to avoid premature deformation or extrusion of the material. The value of A is 180-220. When the grinding head preheating temperature reaches A°C, the staged heating begins. During the first stage of heating, the grinding head speed is increased to 100-120 rpm, the temperature is raised to 350-400°C, and the hydraulic pressure is maintained at 0.5-1.0 MPa to maintain plastic fluidity; in the second stage, the speed is further increased to 150-180 rpm, and the temperature is raised to 450-550°C. During the second stage, the hydraulic pressure is gradually increased to 1.5-3.0 MPa to promote diffusion at the copper-aluminum interface and compensate for the low plasticity of aluminum. Step 3 After the grinding head temperature rises to 450-550°C, the hydraulic pressure is adjusted according to the pipe wall thickness and the grinding head speed is controlled at 150-200 rpm. The mold is preheated to 300-400°C. At the same time, a gradient speed control is used to prevent interface peeling. The gradient speed is 150-200 rpm at the grinding head inlet and reduced by 5%-15% at the outlet. The speed reduction distribution is achieved by axial displacement of the spiral rolling mold. Adjusting the hydraulic pressure according to the pipe wall thickness means: when the pipe wall thickness is 1-3mm, the hydraulic pressure is set to 2-4 MPa; when the pipe wall thickness is greater than 3mm and less than or equal to 7mm, the hydraulic pressure is set to 4-6 MPa; Step 4 The aluminum-copper gradient composite material tube prepared by the friction stir extrusion process is cooled to 50-80° C. at a cooling rate greater than 100 K / s to obtain a product.

2. The method for preparing a pipe of an aluminum-copper gradient composite material according to claim 1, characterized in that: The density of the blank in step 1 is ≥ 95% of the theoretical density.

3. The method for preparing a pipe of an aluminum-copper gradient composite material according to claim 1, characterized in that: The blank comprises at least three parts, namely a high copper region, a medium copper region, and a low copper region; the medium copper region is located between the high copper region and the low copper region, the copper content of the high copper region is greater than that of the medium copper region and the low copper region, and the copper content of the medium copper region is greater than that of the low copper region.

4. The method for preparing a tube of an aluminum-copper gradient composite material according to claim 3, characterized in that: The copper content in the low copper zone is greater than or equal to 50%; the copper content in the medium copper zone is greater than or equal to 70%.

5. The method for preparing a tube of an aluminum-copper gradient composite material according to claim 3, characterized in that: The high copper area, medium copper area, and low copper area are composed of copper and aluminum; or Made of copper and aluminum alloy.

6. The method for preparing a tube of an aluminum-copper gradient composite material according to claim 3, characterized in that: When preparing the blank, the raw materials used are A1060 aluminum alloy powder and C1100 electrolytic copper powder. The purity of the A1060 aluminum alloy powder is ≥99.0%, the particle size is 20-50μm, and fine powder is used to improve the density of the blank; the C1100 electrolytic copper powder is a spherical fine powder with a purity of ≥99.5% and a particle size of 20-50μm, which is used to improve the conductivity of the material, improve the powder fluidity, and reduce powder segregation.

7. The method for preparing a tube of an aluminum-copper gradient composite material according to claim 3, characterized in that: In the high copper area, the aluminum content is less than or equal to 10%; In the medium copper zone, the aluminum content is less than or equal to 30%, but greater than the aluminum content in the high copper zone; In the low copper zone, the aluminum content is less than or equal to 50%, but greater than the aluminum content in the medium copper zone.

8. The method for preparing a tube of an aluminum-copper gradient composite material according to claim 3, characterized in that: When mixing the raw material powder in the high copper area, a three-dimensional motion powder mixer is used, and the speed is controlled at 200 rpm and the time is 2 hours; When mixing the raw material powder in the middle copper area, a three-dimensional motion powder mixer is used, and the speed is controlled at 150rpm and the time is 4 hours; When mixing the raw material powder in the low copper area, a three-dimensional motion powder mixer is used, and the speed is controlled at 100 rpm and the time is 6 hours.

9. The method for preparing a tube of an aluminum-copper gradient composite material according to claim 8, characterized in that: Laying evenly mixed high copper area raw material powder according to a set thickness to obtain a high copper area raw material powder layer, then laying a medium copper area raw material powder layer on the high copper area raw material powder layer, and then laying a low copper area raw material powder layer on the medium copper area raw material powder layer; then pressing to obtain a preform, wherein the density of the preform is ≥95% of the theoretical density; or The low copper region raw material powder is evenly mixed and laid according to a set thickness to obtain a low copper region raw material powder layer, and then a medium copper region raw material powder layer is laid on the low copper region raw material powder layer, and then a high copper region raw material powder layer is laid on the medium copper region raw material powder layer; and then pressing is performed to obtain a preform, wherein the density of the preform is ≥95% of the theoretical density.

10. The method for preparing a tube of an aluminum-copper gradient composite material according to claim 9, characterized in that: During the pressing process, the pressure was controlled at 200 MPa and the holding time was 2 hours.

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