A heat treatment method for preparing high-strength and high-conductivity copper alloys

Abstract

This invention relates to a heat treatment method for preparing high-strength, high-conductivity copper alloys, belonging to the field of high-strength, high-conductivity electronic device fabrication technology. The preparation process includes: solidifying alloy layers with different texture directions layer by layer using directional solidification technology to form a monolithic alloy material stacked according to soft and hard orientations; after low-temperature rolling, obtaining gradient density twins through a cyclic "rapid heating + slow cooling" heat treatment method, thereby obtaining a high-strength, high-conductivity copper alloy. The gradient twin copper alloy prepared by this method can effectively improve the conductivity of the alloy while increasing its strength. This design and preparation method for high-strength, high-conductivity copper alloys has significant guiding significance for adapting to the development of industries such as electronics and information, future transportation, and aerospace, and has very good industrial application prospects.

Description

Technical Field

[0001] This invention relates to a heat treatment method for preparing high-strength, high-conductivity copper alloys, belonging to the field of high-strength, high-conductivity electronic device fabrication technology. Background Technology

[0002] High-strength, high-conductivity copper alloys are not only fundamental materials for national economic development but also key materials in numerous high-tech fields, widely used in new energy vehicles, aerospace, high-speed rail, and electronic information. These fields require copper and copper alloys to possess sufficient strength and hardness, as well as good electrical conductivity. To meet the requirements of high strength and high conductivity in copper alloys, alloy strengthening methods have been continuously evolving. The alloying method involves creating microscopic defects within the material. This process is mature and simple to operate, but the presence of microscopic defects slows down the number of electrons moving directionally within the crystal, resulting in a conductivity generally <60% IACS. Composite material methods significantly improve material strength, but the process is complex, production costs are high, and industrial production is difficult.

[0003] Patent CN113337747B discloses a method for preparing a high-strength, high-conductivity copper alloy, comprising the following steps: Step 1: precursor preparation; Step 2: calcination and reduction; Step 3: spark plasma sintering. This method prepares a composite powder with Y₂O₃ dispersed on the surface of copper powder, which, after sintering, yields a dense bulk. The uniform distribution of Y₂O₃ refines the copper grains, resulting in a dense copper-based composite material with dispersed Y₂O₃. The conductivity of this copper-based composite material can reach an extremely high level of approximately 95% IACS, but its strength is only 251.1 MPa to 303.9 MPa. Patent CN116987927A discloses a high-strength, high-conductivity copper-iron in-situ composite strip and its preparation method. This method utilizes the characteristics of materials subjected to uniaxial and biaxial tensile stress during drawing deformation processing, employing a combination of drawing and rolling deformation processing to process the copper-iron alloy. Furthermore, cold drawing deformation is dominant during the processing, accounting for approximately 60% of the total strain. Therefore, the Fe phase is subjected to uniaxial tensile stress and biaxial compressive stress during a significant portion of the deformation process, thereby optimizing the deformation of the Fe phase and achieving a more ideal degree of fibrous and nano-sized Fe phase. The results of the embodiments show that the high-strength, high-conductivity copper-iron in-situ composite strip prepared using the method provided by this invention can achieve a tensile strength of over 1000 MPa, but its conductivity is less than 40% IACS.

[0004] The copper alloy material obtained by the above process has extremely low tensile strength while improving the conductivity of the copper alloy, and extremely low conductivity while improving the tensile strength of the copper alloy. It is impossible to simultaneously achieve both strength and conductivity, and cannot meet the requirements of future production for high-strength and high-conductivity copper alloys.

[0005] Therefore, it is necessary to provide a preparation method that can simultaneously improve the strength and conductivity of copper alloys, to meet the future development requirements of high-strength and high-conductivity copper alloys, and to further expand the application of high-strength and high-conductivity copper alloy materials in various industries. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the present invention aims to provide a heat treatment method for preparing high-strength and high-conductivity copper alloys. The method is characterized by using directional solidification technology to solidify alloy plates with different texture directions layer by layer, forming a monolithic alloy material stacked according to a soft-hard orientation rule. After rolling, the gradient twinned copper alloy is prepared through cyclic heat treatment. This method can effectively improve the conductivity of the copper alloy while increasing its strength, thereby achieving the processing goal of simultaneously considering both the mechanical and electrical properties of the copper alloy.

[0007] The technical solution of the present invention is as follows: a heat treatment method for preparing high-strength and high-conductivity copper alloys, the specific steps of which are as follows:

[0008] (1) Pour the molten copper alloy into a directional solidification furnace with different texture orientations, control the solidification rate and temperature gradient, and make the molten alloy solidify in a direction along the orientation direction of the seed crystals to obtain an alloy layer with a texture orientation.

[0009] (2) After the alloy layer in step (1) is initially solidified, another alloy layer with a different texture direction is obtained on top of it by directional solidification technology. This process is repeated, and solidification is carried out layer by layer by directional solidification. Each layer has the same thickness, resulting in materials with different texture directions, forming an integral alloy material stacked according to the soft and hard orientation rule.

[0010] (3) Homogenize the overall alloy material in step (2), and then perform low-temperature large deformation hot rolling on the homogenized overall alloy material.

[0011] (4) The material after low-temperature large deformation hot rolling is heat-treated by a cyclic "rapid heating + slow cooling" heat treatment method. This expands the anisotropy of the material, resulting in different twin contents in different texture layers, producing a gradient twin structure, thereby simultaneously improving the material's strength and conductivity.

[0012] Preferably, the rolling temperature of the low-temperature large deformation hot rolling treatment in step (3) is 350℃-400℃, and the hot rolling deformation is 90%-95%.

[0013] Preferably, in step (4), the number of heat treatment cycles is no less than 3, the heating rate increases gradually, the cooling rate decreases gradually, the heat treatment heating temperature increases gradually, the final temperature is 800℃-900℃, and the temperature is cooled to room temperature. After each heating, the temperature is maintained for 1-2 hours.

[0014] Preferably, the heating rate increases by 5℃ / s-10℃ / s, the cooling rate decreases by 5℃ / min-10℃ / min, and the heat treatment heating temperature increases by 100℃-150℃.

[0015] Preferably, the alloy has at least two alloy layers with different texture orientations. Each alloy layer with different texture orientations exhibits different anisotropy; soft orientation promotes high conductivity, while hard orientation promotes high strength. The integral molding of twinned alloy materials with different texture orientations forms a monolithic alloy material, avoiding delamination and peeling of layered materials, improving the bonding strength and transition smoothness between textured layers, thereby improving the mechanical and electrical properties of the material.

[0016] Preferably, the copper alloy melt is a C7035 copper alloy melt.

[0017] The principle of this invention:

[0018] Directional solidification is a commonly used method for controlling the solid-state phase transformation process of metals. It allows for the formation of a uniform crystal orientation, or texture, in the alloy during solidification by controlling the temperature gradient and solidification rate. This method is mainly used to prepare alloy materials with specific properties, such as high-temperature alloys and hard alloys. This invention uses directional solidification technology to first prepare an integral alloy material with layers stacked according to a soft-hard orientation, achieving the integral forming of twinned alloy materials with different texture directions. This avoids the delamination and peeling phenomena of layered materials, improves the bonding strength and transition smoothness between textured layers, and also obtains materials with different texture directions, expanding the material's anisotropy and thus improving the material's mechanical and electrical properties. In the subsequent heat treatment, due to the different anisotropy of the alloy's different textured layers, the microstructure of each layer changes differently, resulting in a gradient change in twin density, thus forming a copper alloy with gradient density twins. The cyclic "rapid heating + slow cooling" also has a significant impact on twin formation, with "rapid heating" having a certain influence on twin formation. Rapid heating can introduce annealing twins into nanocrystalline copper, achieving "thermal relaxation" at the nanocrystalline grain boundaries and improving the thermal stability of the nanocrystals. Rapid heating avoids grain growth while generating growth twins; "slow cooling" allows for the formation of a more stable internal structure with larger grain sizes and fewer lattice defects in the unit cells, improving crystal integrity and homogeneity, reducing stress and distortion, and enhancing crystal quality and performance. Therefore, by cyclically applying "rapid heating + slow cooling" heat treatment, the anisotropy of the material can be expanded, resulting in and stabilizing gradient twins. Introducing high-density nanotwin interfaces into copper alloys can increase their strength by an order of magnitude while maintaining extremely high electrical conductivity. This is because the twin interfaces are at the nanometer scale, having minimal impact on electron scattering and thus not significantly reducing the material's conductivity. Furthermore, the gradient twin structure effectively suppresses strain concentration, achieving strain delocalization. Its tensile plasticity is superior to that of ordinary coarse-grained structures; copper alloys with gradient twin structures have twice the strength of ordinary coarse-grained copper alloys. Therefore, the use of one-piece molding and a cyclic "rapid heating + slow cooling" heat treatment method can achieve the goal of having both high strength and high conductivity copper alloy.

[0019] The beneficial effects of this invention are:

[0020] The beneficial effects of this invention are mainly reflected in the fact that, through the above-described processing technology, gradient density twins are generated in the material, which improves the material's strength while ensuring its high conductivity. It can improve the material's performance by altering its microstructure and grain orientation without changing its chemical composition.

[0021] In summary, the invention principle and superior effects of this patent are mainly reflected in its unique processing technology and structural design, which enable the material to maintain high strength while also possessing good electrical conductivity, thereby greatly improving the material's performance. This undoubtedly opens up new possibilities for the research and application of copper alloy materials. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the gradient twinning described in this invention.

[0023] Figure 2 This is a schematic diagram of the texture of C7035 copper alloy and its elastic modulus diagram for its main crystal orientations. Detailed Implementation

[0024] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below in conjunction with specific embodiments; however, the scope of protection of this invention is not limited to the content described.

[0025] In this embodiment of the invention, C7035 copper alloy melt with the composition shown in Table 1 was used for the experiment.

[0026] Table 1. Chemical composition (wt%) of the copper alloy described in this invention.

[0027]

[0028] Example 1

[0029] The preparation method of the high-strength, high-conductivity copper alloy described in this embodiment specifically includes the following steps:

[0030] (1) Pour the C7035 copper alloy melt into a directional solidification furnace with seed crystals of different orientations, control the solidification rate and temperature gradient, and make the melt directional solidify along the orientation direction of the seed crystals to obtain an alloy layer with a texture direction of (111).

[0031] (2) After the alloy layer with a texture direction of (111) is initially solidified, another alloy layer with a texture direction of (221) is obtained on top of it by directional solidification technology. In this way, layer by layer solidification is carried out by directional solidification method to obtain a material with seven different texture directions (111), (221), (211), (110), (210), (310) and (100), forming an integral alloy material containing layers with different texture directions.

[0032] (3) The overall alloy material is homogenized and then subjected to low-temperature large deformation hot rolling. The rolling temperature is 350℃ and the hot rolling deformation is 90%.

[0033] (4) The material after low-temperature large deformation hot rolling is subjected to cyclic "rapid heating + slow cooling" heat treatment. The hot-rolled material is heated to 600℃ at a rate of 15℃ / s and held for 1h. The material is then slowly cooled to room temperature at a rate of 15℃ / min. The material is then heated to 700℃ at a rate of 20℃ / s and held for 1h. The material is then slowly cooled to room temperature at a rate of 10℃ / min. The material is then heated to 800℃ at a rate of 25℃ / s and held for 1h. The material is then slowly cooled to room temperature at a rate of 5℃ / min to complete the preparation of gradient twins.

[0034] The tensile strength and electrical conductivity of the final high-strength, high-conductivity copper alloy are shown in Table 2.

[0035] Table 2. Performance test results of copper alloy in specific embodiment 1 of the present invention.

[0036]

[0037] Example 2

[0038] The preparation method of the high-strength, high-conductivity copper alloy described in this embodiment specifically includes the following steps:

[0039] (1) Pour the C7035 copper alloy melt into a directional solidification furnace with seed crystals of different orientations, control the solidification rate and temperature gradient, and make the melt directional solidify along the orientation direction of the seed crystals to obtain an alloy layer with a texture direction of (111).

[0040] (2) After the alloy layer with a texture direction of (111) is initially solidified, another alloy layer with a texture direction of (221) is obtained on top of it by directional solidification technology. In this way, layer by layer solidification is carried out by directional solidification method to obtain a material with seven different texture directions (111), (221), (211), (110), (210), (310) and (100), forming an integral alloy material containing layers with different texture directions.

[0041] (3) The overall alloy material is homogenized and then subjected to low-temperature large deformation hot rolling. The rolling temperature is 400℃ and the hot rolling deformation is 95%.

[0042] (4) The material after low-temperature large deformation hot rolling is subjected to a cyclic "rapid heating + slow cooling" heat treatment method. The hot-rolled material is heated to 600℃ at a rate of 20℃ / s and held for 2 hours. The material is then slowly cooled to room temperature at a rate of 25℃ / min. The material is then heated to 750℃ at a rate of 30℃ / s and held for 2 hours. The material is then slowly cooled to room temperature at a rate of 15℃ / min. The material is then heated to 900℃ at a rate of 40℃ / s and held for 2 hours. The material is then slowly cooled to room temperature at a rate of 5℃ / min. Finally, the gradient twin is prepared.

[0043] The tensile strength and electrical conductivity of the final high-strength, high-conductivity copper alloy are shown in Table 3.

[0044] Table 3. Performance test results of copper alloy in specific embodiment 2 of the present invention.

[0045]

[0046] Example 3

[0047] The preparation method of the high-strength, high-conductivity copper alloy described in this embodiment specifically includes the following steps:

[0048] (1) Pour the C7035 copper alloy melt into a directional solidification furnace with seed crystals of different orientations, control the solidification rate and temperature gradient, and make the melt directional solidify along the orientation direction of the seed crystals to obtain an alloy layer with a texture direction of (111).

[0049] (2) After the alloy layer with a texture direction of (111) is initially solidified, another alloy layer with a texture direction of (221) is obtained on top of it by directional solidification technology. In this way, layer by layer solidification is carried out by directional solidification method to obtain a material with seven different texture directions (111), (221), (211), (110), (210), (310) and (100), forming an integral alloy material containing layers with different texture directions.

[0050] (3) The overall alloy material is homogenized and then subjected to low-temperature large deformation hot rolling. The rolling temperature is 380℃ and the hot rolling deformation is 92%.

[0051] (4) The material after low-temperature large deformation hot rolling is subjected to a cyclic "rapid heating + slow cooling" heat treatment method. The hot-rolled material is heated to 600℃ at a rate of 20℃ / s and held for 1.5h. The material is then slowly cooled to room temperature at a rate of 25℃ / min. The material is then heated to 720℃ at a rate of 28℃ / s and held for 1.5h. The material is then slowly cooled to room temperature at a rate of 17℃ / min. The material is then heated to 840℃ at a rate of 36℃ / s and held for 1.5h. The material is then slowly cooled to room temperature at a rate of 9℃ / min. Finally, the gradient twin is prepared.

[0052] The tensile strength and electrical conductivity of the final high-strength, high-conductivity copper alloy are shown in Table 3.

[0053] Table 3. Performance test results of copper alloy in specific embodiment 2 of the present invention.

[0054]

[0055] Comparative Example 1

[0056] This comparative example uses the same method as Example 1 to prepare copper alloy, the difference being that: in step (2), multiple plates with different textures of the same thickness are obtained by directional solidification technology, and the plates with different textures are cut into the same size and not randomly stacked according to the soft and hard orientation to form copper alloy.

[0057] The tensile strength and electrical conductivity of the final copper alloy are shown in Table 5.

[0058] Table 5. Performance test results of copper alloy in specific comparative examples of the present invention.

[0059]

[0060] A comparison of Example 1 and Example 2 reveals that the integral solidification of a monolithic alloy material with different texture directions from hard to soft orientation significantly improves tensile strength and conductivity compared to a material with randomly stacked hard and soft orientations. On one hand, the integral forming of twinned alloy materials with different texture directions avoids delamination and peeling of layered materials, improving the bonding strength between textured layers. Furthermore, the gradient of the texture direction between hard and soft orientations results in a gradient change in twin density during subsequent low-temperature large-deformation hot rolling followed by cyclic "rapid heating + slow cooling" heat treatment, thus improving both strength and conductivity. On the other hand, randomly stacked copper alloy materials disrupt the anisotropic structure obtained by directional solidification, leading to disordered grain orientation. In metallic materials, different grain orientations can generate different grain boundaries, and the presence of grain boundaries hinders dislocation movement, thus affecting the material's strength. When grain orientation is random, the number and distribution of grain boundaries become irregular, leading to a decrease in material strength. In metallic materials, the movement of electrons within grains is hindered by grain boundaries and defects. Directional solidification technology can give copper alloys a preferred orientation. Preferred-orientation grains can reduce these obstacles, thereby increasing the electron mobility and thus improving conductivity. Randomly stacked copper alloys disrupt this preferred orientation, leading to disordered grain orientation. This increases the resistance to electron movement within the grains, thus reducing conductivity. Furthermore, random stacking can result in uneven grain size distribution, which can also affect the material's conductivity. Smaller grain sizes are generally beneficial for improving conductivity, but excessively small grain sizes can lead to too many grain boundaries, thus reducing conductivity. Maintaining an appropriate grain size distribution is crucial for obtaining highly conductive copper alloys. Therefore, Comparative Example 1 shows a significant decrease in both tensile strength and conductivity compared to the materials in the examples.

[0061] Comparative Example 2

[0062] This comparative example uses the same method as Example 1 to prepare copper alloy, except that: in step (4), the whole alloy material is hot rolled at a temperature of 500°C and a compression of 70%.

[0063] The tensile strength and electrical conductivity of the final copper alloy are shown in Table 6.

[0064] Table 6. Performance test results of copper alloy in specific comparative examples of the present invention, Example 2.

[0065] Table 6. Performance test results of copper alloy in specific comparative examples of the present invention, Example 2.

[0066]

[0067] A comparison of Example 2 and Example 1 reveals that low-temperature large-deformation hot rolling significantly improves the tensile strength and conductivity of the material, especially the conductivity. This is because low-temperature large-deformation hot rolling improves the microstructure of the metallic material, achieving microstructural changes such as grain refinement, dislocation density, and precipitate strengthening, thereby increasing the material's strength. Without low-temperature large-deformation hot rolling, the grain size of the copper alloy is larger, and the movement of dislocations at grain boundaries encounters less resistance, making it easier for plastic deformation to occur, thus affecting the material's strength. Furthermore, low-temperature large-deformation hot rolling improves the grain boundary state and precipitate distribution, thereby reducing electron scattering at grain boundaries and precipitates, increasing electron migration speed, and thus improving conductivity. Without low-temperature large-deformation hot rolling, the grain boundary state and precipitate distribution of the copper alloy are poor, which leads to a decrease in electron migration speed in the material, thus greatly reducing the material's conductivity. Simultaneously, the absence of low-temperature large-deformation hot rolling may affect the grain orientation in the material, further impacting its conductivity.

[0068] Comparative Example 3

[0069] This comparative example uses the same method as Example 1 to prepare copper alloy, the difference being that: in step (5), the hot-rolled material is heat-treated at a heating rate of 10℃ / min and a heating temperature of 800℃, and then air-cooled to room temperature.

[0070] Table 7. Performance test results of copper alloy in specific comparative examples of the present invention (Example 3).

[0071] Table 7. Performance test results of copper alloy in specific comparative examples of the present invention (Example 3).

[0072]

[0073] A comparison of Example 3 and Example 1 reveals that cyclic rapid heating followed by slow cooling significantly improves the tensile strength and electrical conductivity of the material. This is because cyclic rapid heating followed by slow cooling improves the microstructure of the metallic material, eliminating defects, oxides, and other impurities. During rapid heating, the grains inside the material grow rapidly, forming coarser grains. As the grains grow, the number of grain boundaries decreases, thereby improving the material's electrical conductivity. Slow cooling, on the other hand, preserves the grain structure, forming a more stable crystal structure and reducing residual stress. The lattice structure gradually stabilizes during slow cooling, forming finer, more uniform crystals, reducing the number of grain boundaries and dislocations, and improving the material's strength. Without cyclic rapid heating followed by slow cooling, the grain size of the copper alloy material would be too large, and the movement of dislocations at grain boundaries would encounter less resistance, making it prone to plastic deformation and thus affecting the material's strength. Furthermore, failure to undergo cyclic rapid heating followed by slow cooling heat treatment can lead to uneven distribution of precipitated phases and excessive structural defects in the material, which in turn causes electron scattering, thereby increasing resistance and affecting the conductivity of the material.

[0074] Comparing the examples with those of the previous ones reveals that directional solidification according to a regular soft-hard orientation into a single material avoids the delamination and peeling of layered materials, improves the bonding strength between textured layers, and the directional solidification technology gives the copper alloy material different grain orientations in various directions, thus creating anisotropy and giving the material different mechanical and electrical properties in different directions. Random stacking without following the soft-hard orientation will destroy this anisotropy, causing the material's properties to tend to be uniform in various directions, reducing the overall performance. Low-temperature large deformation hot rolling can achieve microstructural changes such as grain refinement, dislocation density, and precipitate strengthening, thereby improving the material's strength. At the same time, this treatment method can improve the grain boundary state and precipitate distribution of the material, reduce electron scattering at grain boundaries and precipitates, increase electron migration speed, and thus improve conductivity. Cyclic rapid heating + slow cooling heat treatment can improve the grain boundary state and precipitate distribution of the material, thereby reducing electron scattering at grain boundaries and precipitates, increasing electron migration speed, and thus improving conductivity. At the same time, this heat treatment method can also promote grain refinement and dislocation density, further improving the strength of the material.

[0075] In summary, the process method of this invention is easy to operate and can effectively improve the twinning characteristics in the copper alloy matrix, obtaining copper alloy plates with heterogeneous density twinning layers. While ensuring that the strength of the copper alloy meets the alloy performance requirements, it improves the conductivity of the copper alloy, making it suitable for industrial applications. It provides a practical and feasible technical solution for the preparation of high-strength and high-conductivity copper alloy materials for industries such as aerospace, microelectronic conductive components, rail transportation, and communications.

[0076] Finally, it should be noted that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

Claims

1. A heat treatment method for preparing high-strength, high-conductivity copper alloys, characterized in that, The application discloses a method for preparing high-strength and high-conductivity copper alloy by using directional solidification technology to layer by layer solidify alloy plates with different texture directions, forming a whole alloy material stacked according to the soft and hard orientation rules, and obtaining the high-strength and high-conductivity copper alloy through cyclic heat treatment after rolling. The method comprises the following steps: (1) pouring the melt of the copper alloy into a directional solidification furnace with different texture orientations, controlling the solidification speed and temperature gradient, and making the melt directional solidification along the orientation direction of the crystal seed to obtain an alloy layer with a texture direction; (2) after the preliminary solidification of the alloy layer in the step (1), obtaining an alloy layer with a different texture direction through the directional solidification technology above the alloy layer, and iteratively layer by layer solidification through the directional solidification method, so as to obtain a material with different texture directions and form a whole alloy material stacked according to the soft and hard orientation rules; (3) performing homogenization treatment on the whole alloy material in the step (2), and performing low-temperature and large-deformation hot rolling treatment on the whole alloy material after the homogenization treatment; The rolling temperature of the low-temperature and large-deformation hot rolling treatment is 350-400 DEG C, and the hot rolling deformation is 90-95 %; (4) performing heat treatment on the material after the low-temperature and large-deformation hot rolling treatment in a cyclic heat treatment mode of "rapid heating + slow cooling"; The heat treatment cycle is not less than 3 times, the heating speed is increased gradually, the cooling speed is decreased gradually, the heat treatment heating temperature is increased gradually, the final temperature is 800-900 DEG C, the temperature is decreased to room temperature, and the heat treatment after each heating is preserved for 1-2 hours; 2. The heat treatment method for preparing high-strength and high-conductivity copper alloy according to claim 1, characterized in that: The gradually increased value of the heating speed is 5-10 DEG C / s, the gradually decreased value of the cooling speed is 5-10 DEG C / min, and the gradually increased value of the heat treatment heating temperature is 100-150 DEG C. The number of the alloy layers with different texture directions is not less than 2.

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