A method for controlling the grain boundary network structure of a Cu-Ti alloy foil based on annealing twinning

Abstract

The application discloses a method for controlling Cu-Ti alloy foil crystal boundary network structure based on annealing twin, and belongs to the technical field of Cu-Ti alloy production. The application comprises the following steps: performing stress relief annealing treatment on Cu-Ti alloy foil, and performing air cooling to room temperature after heat preservation is completed; performing multi-pass cross asynchronous rolling treatment on the foil after the stress relief annealing treatment, and controlling the speed ratio w 1 / w 2 to be 1.12-1.13; and performing high-temperature short-time recrystallization annealing treatment on the foil after the rolling treatment. The application introduces multi-directional composite shear deformation through cross asynchronous rolling, completely homogenizes the whole energy storage of the matrix cold rolling, and cooperates with accurate recrystallization annealing system to directionally induce the generation of annealing twins, reconstructs the stable and uniform crystal boundary network topology, weakens the anisotropy of the structure and the electron scattering effect, and thus comprehensively improves the plastic deformation capacity, the conductivity and the structure service stability of the foil.

Description

Technical Field

[0001] This invention belongs to the field of Cu-Ti alloy production technology, and more specifically, relates to a method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealing twins. Background Technology

[0002] Cu-Ti alloys, with their excellent elastic properties, moderate strength, and good machinability, are widely used in high-end precision electronic connectors, miniature elastic foils, and precision sensing components. As electronic components iterate towards thinner, smaller, and more reliable designs, more stringent requirements are placed on the plastic deformation coordination, bending fatigue performance, and conductivity stability of Cu-Ti alloy foils. Cracking failures, conductivity fluctuations, and elastic decay during the service life of these foils have become core bottlenecks restricting their high-end applications.

[0003] Grain boundary engineering (GBE) is a process that uses deformation heat treatment to control the grain boundary character distribution (GBCD) of a material. This involves increasing the proportion of special grain boundaries in the low Σ coincidence site lattice (CSL) and improving the connectivity of the random large angle grain boundary (RHAGB) network, thereby enhancing the material's properties.

[0004] Current grain boundary control processes for Cu-Ti alloy foils mainly employ a conventional synchronous rolling + intermediate annealing system. In conventional synchronous rolling, the upper and lower rolls rotate at completely identical speeds, and the foil only undergoes single-axis compressive deformation without additional shearing. This results in a singular activation of the internal slip system within the grains, and the energy stored during cold rolling deformation exhibits significant local aggregation characteristics, leading to extremely strong microstructural anisotropy. During subsequent recrystallization annealing, the uneven matrix energy storage leads to a high nucleation barrier for annealing twins, resulting in numerous microstructural defects in the final alloy: a high number of residual low-angle subgrain boundaries, a low proportion of Σ3 annealing twins and special grain boundaries, and strong continuity of random high-energy, large-angle grain boundary networks.

[0005] The aforementioned grain boundary structural defects lead to two major technical problems: First, the continuous and interconnected random grain boundary network and a large number of low-energy subgrain boundaries result in insufficient coordination of grain deformation. When the foil is subjected to stress deformation, local stress concentration is likely to occur, and microcracks are likely to propagate rapidly along the continuous grain boundaries, significantly reducing the material's elongation and bending plasticity, and resulting in poor service stability. Second, a large number of disordered high-energy grain boundaries, residual dislocations, and lattice distortions form dense electron scattering centers, which severely hinder the transport of free electrons, resulting in low alloy conductivity and poor performance uniformity.

[0006] Conventional processes can only slightly improve alloy strength by refining grains, but due to technical limitations such as uneven energy storage, disordered grain boundary networks, and poor plasticity and conductivity, they cannot fundamentally optimize the grain boundary topology. Therefore, developing a control method that can uniformly deform the matrix for energy storage, directionally induce annealing twin formation, and optimize the grain boundary network structure to achieve a synergistic improvement in the plasticity and conductivity of Cu-Ti alloy foils is of great significance. Summary of the Invention

[0007] This invention aims to provide a method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twins, thereby solving the technical problems of excessive low-angle grain boundary residue, insufficient number of annealed twins and Σ3 special grain boundaries, and excessively strong connectivity of random high-angle grain boundary networks in existing conventional Cu-Ti alloy foil preparation processes, which result in poor grain deformation coordination, low plastic elongation, and poor alloy electrical conductivity.

[0008] To achieve the above objectives, the technical solution provided by the present invention is as follows: This invention provides a method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning, comprising the following steps: The Cu-Ti alloy foil is subjected to stress-relief annealing at a temperature of 400-410 ℃ for 50-70 min, followed by air cooling to room temperature. For example, the annealing temperature can be 400 ℃, 402 ℃, 404 ℃, 405 ℃, 408 ℃, or 410 ℃, and the holding time can be 50 min, 55 min, 58 min, 60 min, 65 min, or 70 min, etc.

[0009] The foil material after stress-relief annealing is subjected to multi-pass cross-asynchronous rolling. During the rolling process, the main rolling direction is kept constant, and the speed ratio is controlled. w 1 / w 2. With the numerical values ​​unchanged, the rotational speeds of the upper and lower rolls in adjacent passes are exchanged, resulting in a speed ratio. w 1 / w The value of 2 can be between 1.12 and 1.13, for example, it can be 1.12 or 1.13.

[0010] The rolled foil is subjected to high-temperature short-time recrystallization annealing, and then air-cooled to room temperature after annealing. The annealing temperature is 580~620 ℃, such as 580 ℃, 590 ℃, 595 ℃, 600 ℃, 610 ℃ or 620 ℃, and the annealing holding time is 15~25 min, and the specific holding time can be 15 min, 17 min, 20 min, 23 min, 25 min, etc.

[0011] To address the technical problems in existing conventional Cu-Ti alloy foil manufacturing processes, such as excessive low-angle grain boundary residue, insufficient annealing twins and Σ3 special grain boundaries, and excessively strong connectivity of random high-angle grain boundary networks, which easily lead to poor grain deformation coordination, low plastic elongation, and poor alloy electrical conductivity, this invention employs multi-pass cross-asynchronous rolling processing combined with high-temperature short-time recrystallization annealing, while controlling the main rolling direction and the rate ratio. w 1 / w 2. With the numerical value unchanged, the rotational speeds of the upper and lower rolls in adjacent passes are exchanged, thereby directionally inducing the formation of annealing twins and increasing the proportion of Σ3 special grain boundaries. This effectively cuts the continuous random high-energy grain boundary network and weakens the topological connectivity of grain boundaries, thus significantly improving the deformation coordination of alloy grains, reducing local stress concentration and microcrack initiation during plastic deformation, and greatly improving the elongation and bending fatigue performance of foil.

[0012] Specifically, the multi-pass cross-asynchronous rolling process provides a stable energy and structural basis for the uniform nucleation and growth of annealing twins throughout the subsequent high-temperature short-time annealing process. High-temperature short-time recrystallization annealing drives the static recrystallization of the alloy matrix after rolling deformation, eliminating the high-density dislocations and residual distortions introduced by rolling, breaking up the elongated deformed grains in the rolled state, and forming some uniform and regular equiaxed recrystallized grains. At the same time, relying on the uniform energy storage substrate constructed by cross-asynchronous rolling, the nucleation barrier of Σ3 annealing twins is significantly reduced, and a large number of annealing twins are induced to form in the grain boundaries and inside the grains, enriching low-energy special grain boundaries, effectively cutting the continuous random grain boundary network, realizing the precise reconstruction of the grain boundary topology, and obtaining the desired grain boundary network state.

[0013] It should be noted that the all-speed ratio w 1 / w The value of 2 and the temperature of the recrystallization annealing are crucial to ensuring the grain boundary control effect. Specifically, when the velocity ratio is too large, the microstructure is prone to delamination after heat treatment, the grain boundary angle distribution is uneven, the proportion of special grain boundaries decreases, and the grain boundary network fragmentation occurs; when the velocity ratio is too small, the shear strain is insufficient, resulting in a low recrystallization nucleation rate after heat treatment and a poor grain boundary engineering effect; the optimal velocity ratio is... w 1 / w 2 is 1.13.

[0014] As the recrystallization annealing temperature increases, the material hardness continuously decreases while the degree of recrystallization continuously increases. When the temperature reaches 600 °C, the decrease in hardness tends to stabilize, indicating that the material has undergone sufficient recrystallization. However, when the temperature is too high, although the hardness further decreases, there is a tendency for grain growth, which is detrimental to the stability of the grain boundary network. This application further preferably controls the recrystallization annealing temperature to be 590~610 °C, and even more preferably 595~605 °C.

[0015] When the holding time is short, the material recrystallizes insufficiently; as the time is extended to about 20 minutes, the hardness gradually stabilizes. Further extending the holding time leads to further grain growth and coarsening of the structure, resulting in a decrease in hardness again.

[0016] Preferably, the multi-pass cross-asynchronous rolling process has 12 to 16 rolling passes, and the total reduction rate is controlled at 25% to 35%, with the single-pass reduction rate not exceeding 10%.

[0017] Preferably, the rolling force during the multi-pass cross-asynchronous rolling process is controlled to be 2.1~2.7t, and the roll tension is 38~42kg. Preferably, the Ti atomic fraction in the Cu-Ti alloy foil is 3.25 at.% to 3.30 at.%; the thickness of the Cu-Ti alloy foil before rolling is 0.1 to 0.12 mm, and the thickness of the foil after rolling is 0.065 to 0.084 mm.

[0018] Optionally, prior to the multi-pass cross-asynchronous rolling process, the following steps are also included: The Cu-Ti alloy foil after stress-relief annealing is cleaned to remove oil, dust and organic impurities from the surface of the foil. Dilute sulfuric acid is used to corrode the surface of the foil to remove the oxide scale and passivation film on the foil surface.

[0019] Optionally, the cleaning of the Cu-Ti alloy foil after stress-relief annealing is specifically performed by sequentially using anhydrous ethanol and acetone for ultrasonic cleaning, with ultrasonic cleaning times of 10 min-15 min respectively.

[0020] Preferably, after high-temperature short-time recrystallization annealing, the proportions of large-angle grain boundaries and small-angle grain boundaries in the obtained Cu-Ti alloy foil are 54%~56% and 44%~46%, respectively, and the proportion of special grain boundaries is 35%~40%.

[0021] In grain boundary engineering, special angle grain boundaries usually refer to low-energy grain boundaries such as Σ3, Σ9, and Σ27. In this application, we mainly refer to Σ3, while the contents of Σ9 and Σ27 are negligible.

[0022] Preferably, after recrystallization annealing, the average grain size of the obtained Cu-Ti alloy foil is 2.8~3.5μm, the twin-related domain size is 10~12μm, and the twin-related domain size / grain size ratio is 2.85~4.3.

[0023] Preferably, after recrystallization annealing, the proportions of J0, J1, J2, and J3 in the obtained Cu-Ti alloy foil are 5%~6%, 24%~25%, 16%~18%, and 50%~52%, respectively. J0, J1, J2, and J3 represent three-way nodes with different numbers of connections to special grain boundaries, and J2 / (1-J3) is 35%~36%.

[0024] In summary, by adopting the technical solution provided by this invention, the following beneficial effects can be achieved compared with the prior art: (1) Unlike the single deformation mode of traditional synchronous rolling, this invention introduces multi-directional composite shear deformation through cross asynchronous rolling, thoroughly homogenizes the energy storage of the matrix in the cold rolling domain, and at the same time, with the precise recrystallization annealing regime, it can directionally induce the generation of annealing twins, reconstruct a stable and uniform grain boundary network topology, weaken the anisotropy of the structure and the electron scattering effect, thereby comprehensively improving the plastic deformation capacity, conductivity and structural service stability of the foil.

[0025] (2) The present invention can effectively eliminate the strong anisotropy of the microstructure and residual lattice distortion caused by synchronous rolling, and significantly reduce the matrix defect density; at the same time, the high proportion of coherent twin interface energy is low and the lattice distortion is small. Compared with the traditional random large-angle grain boundaries, it can greatly weaken the free electron scattering effect, reduce the electron transport resistance, significantly improve the conductivity of Cu-Ti alloy foil, and achieve simultaneous optimization of plasticity and conductivity.

[0026] (3) Foil materials prepared by traditional unidirectional cold rolling process have a single grain orientation and significant anisotropy in microstructure, resulting in poor deformation compatibility between grains. Under service conditions such as bending, reciprocating elastic deformation, and micro-vibration, differences in grain orientation can lead to severe local stress concentration, which can easily cause micro-damage at grain boundaries. After long-term service, problems such as plastic decay, elastic relaxation, and fatigue cracking may occur, significantly shortening the service life of precision electronic components. This invention eliminates the microstructure directionality caused by unidirectional deformation through cross-asynchronous rolling, making the grain orientation more diversified and the deformation degree of each region of the matrix tends to be consistent. At the same time, the optimized grain boundary network can uniformly transmit and disperse external loads, weaken the stress concentration effect between grains, and improve the deformation coordination ability between multiple grains. In addition, the low-energy stable special grain boundaries can effectively resist grain boundary migration and microstructure coarsening under high temperature and alternating loads, inhibit abnormal growth of recrystallized grains, and allow Cu-Ti alloy foil to maintain stable microstructure and dimensional accuracy under long-term and repeated precision service conditions, adapting to the stringent service requirements of precision components such as high-end connectors and micro springs.

[0027] (4) This invention can fundamentally solve the problem of performance inversion by precisely controlling the grain boundary structure: on the one hand, the uniform and refined grains and stable twin boundaries can effectively improve the elastic limit and fatigue resistance of the foil, improve the plasticity and bending performance of the material, and solve the problems of easy brittle fracture and rapid elastic decay of precision foil; on the other hand, the low-energy stable special grain boundaries can significantly reduce grain boundary electron scattering defects, reduce electron transport resistance, avoid the conductivity loss caused by dislocation and subgrain boundary accumulation in traditional deformation processes, and improve the conductivity of the alloy. Finally, the performance of Cu-Ti alloy foil is synergistically improved and optimized in terms of elasticity, conductivity and plasticity, making it suitable for high-end applications such as high-precision electronics, micro elastic components, and high-frequency connectors.

[0028] (5) The process parameters of this invention are stable and controllable and highly repeatable. It can be achieved by relying on mature rolling and annealing equipment. There is no need for complex modification processes. The process route is simple and unique. Without sacrificing the basic strength of the alloy, it solves the industry pain points of poor plasticity, low conductivity and poor performance matching of traditional synchronous rolling Cu-Ti alloy foil, and is suitable for the service requirements of high-end precision electronic foil. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the synchronous rolling process in Comparative Example 1; Figure 2 This is a schematic diagram of the conventional asynchronous rolling process in Comparative Example 2; Figure 3 This is a schematic diagram of the cross-asynchronous rolling process in Example 1; Figure 4 The images show the IPF orientation patterns of the foils obtained in Comparative Example 1, Comparative Example 2, and Example 1. Detailed Implementation

[0030] To further understand the present invention, specific embodiments are now described in detail. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0032] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0033] Example 1 This embodiment provides a method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning, including the following steps: Step 1: First, perform low-temperature stress-relief annealing on the original Cu-Ti alloy foil (in this embodiment, the foil size is: 0.1 mm thick × 30 mm wide, and the Ti atomic fraction is 3.25 at.%). The annealing temperature is set to 400 ℃, and the holding time is 60 min. After the holding time is completed, air cool to room temperature.

[0034] Low-temperature stress-relief annealing eliminates residual internal stress, work hardening, and local distortion generated during early rolling and processing, moderately homogenizes the original grain morphology, stabilizes the initial microstructure stress state, and ensures uniform grain size. This avoids excessive differences in the original stress of the billet and grain size, which could lead to excessive differences in energy storage during subsequent rolling. It provides a consistent initial microstructure base for uniform deformation and stable energy storage distribution throughout the subsequent asynchronous rolling process.

[0035] Step 2: After stress relief annealing, the Cu-Ti alloy foil is ultrasonically cleaned sequentially with anhydrous ethanol and acetone for 10 minutes each to thoroughly remove oil, dust, and organic impurities from the foil surface. Then, it is etched with dilute sulfuric acid for 3 seconds to gently remove the thin oxide scale and passivation film on the surface. Finally, it is rinsed with deionized water and dried with cold air to ensure that the foil surface is clean, free of oxidation, scratches, and impurities before rolling. This avoids surface defects that could lead to localized stress concentration and uneven deformation during the rolling process, ensuring consistent deformation throughout the entire process.

[0036] Step 3: Use a multi-pass cross-asynchronous rolling process to control plastic deformation, rolling at room temperature throughout the process without intermediate annealing; A schematic diagram of the state of multi-pass cross asynchronous rolling is shown below. Figure 3 As shown, where, Figure 3The left side of the diagram shows the finished state of a single-pass rolling process, while the right side shows the finished state of a double-pass rolling process. While maintaining the speed ratio and rolling direction, the speeds of the upper and lower rolls are changed (the speeds of the upper and lower rolls are exchanged in adjacent passes), creating a speed difference. This causes the Cu-Ti alloy foil to undergo bidirectional cross-shear composite deformation during rolling, constructing a cross-deformation field within the grains and activating multiple sets of slip systems to move synchronously. This deformation method breaks through the limitations of traditional unidirectional deformation, eliminates the directionality of grain deformation, and ensures uniform dislocation multiplication and slip across all regions of the foil. It effectively homogenizes the energy storage in the cold-rolled matrix, providing a sufficient and uniform energy base for the nucleation and growth of annealing twins and the formation of special grain boundaries during subsequent recrystallization annealing. This allows for controllable regulation of the grain boundary structure from the process source.

[0037] Specifically, in this embodiment, the total reduction rate is controlled at 30%, and other process parameters are shown in Table 1 below.

[0038] Table 1. Cross-Asynchronous Rolling Parameter Table

[0039] The main purpose of this step is to provide a stable energy and structural basis for the uniform nucleation and growth of annealed twins throughout the entire range during the subsequent high-temperature short-time annealing process.

[0040] Key considerations for rolling: ① Use multi-pass small deformation rolling throughout the process, with a single-pass reduction rate not exceeding 10%, to avoid foil warping, edge cracking, and extreme local strain concentration caused by large deformation in a single pass; ② Maintain uniform foil feeding speed and stable micro-tension during rolling, without deviation, slippage, or wrinkles, ensuring consistent longitudinal and transverse deformation height of the entire roll of foil; ③ Polish the rolling roll surface in advance to keep it smooth, without wear, and without adhering impurities, to prevent roll surface defects from being replicated onto the foil surface, causing uneven local deformation and energy storage differences; ④ After rolling, ensure that the foil is flat without warping, has uniform cross-sectional thickness, and uniform energy storage distribution across the entire deformation area without polarization.

[0041] Step 4: Perform high-temperature short-time recrystallization annealing treatment (grain boundary control heat treatment) on the rolled sample. Specifically, in this embodiment, the rolled Cu-Ti alloy foil is placed in a vacuum heat treatment furnace to avoid high-temperature oxidation; a high-temperature short-time recrystallization annealing process is adopted, with the annealing temperature set at 600 ℃ and held at a constant temperature for 20 min. After the treatment is completed, it is air-cooled to room temperature.

[0042] High-temperature short-time annealing can drive static recrystallization of the alloy matrix after rolling deformation, eliminating the high-density dislocations and residual distortions introduced by rolling, breaking up the elongated deformed grains in the rolled state, and forming some uniform and regular equiaxed recrystallized grains. At the same time, relying on the uniform energy storage substrate constructed by cross-asynchronous rolling, the nucleation barrier of Σ3 annealing twins is significantly reduced, and a large number of annealing twins are induced to form in the grain boundaries and inside the grains, enriching low-energy special grain boundaries, effectively cutting the continuous random grain boundary network, realizing the precise reconstruction of the grain boundary topology, and obtaining the grain boundary network state we need.

[0043] Comparative Example 1 Unlike Example 1, this comparative example uses conventional synchronous rolling, as shown in the rolling diagram below. Figure 1 As shown, the upper and lower rolls rotate at the same speed with no speed difference. The foil only undergoes single axial compression deformation without shear strain. The deformation mode is singular. During multiple rolling passes, the rolling speed and tension remain unchanged. The thickness is gradually reduced by adjusting the rolling force. The specific process parameters are shown in Table 2 below.

[0044] Table 2. Parameters for Synchronous Rolling

[0045] Comparative Example 2 Unlike Example 1, this comparative example uses conventional asynchronous rolling, meaning that the rolling speed ratio and rolling direction remain constant during the rolling process, and the rotational speeds of the upper and lower rolls in adjacent passes remain constant (the high-speed roll remains constant, such as...). Figure 2 (As shown in Table 3). Specific process parameters are shown below. Table 3. Parameters for Conventional Asynchronous Rolling

[0046] Comparison of grain boundary structure and properties: IPF orientation maps are used to visually characterize the recrystallized grain morphology, grain orientation, annealing twin distribution, and overall microstructure uniformity of materials. Figure 4 As shown in (a), the alloy grains after conventional synchronous rolling and high-temperature short-time annealing have large differences in size and single orientation. The number of annealed twins in the matrix is ​​small, and the grain boundaries are mostly continuous random large-angle grain boundaries. At the same time, there are a large number of fine subgrains and residual low-angle grain boundaries, resulting in poor microstructure uniformity.

[0047] like Figure 4 As shown in (b), conventional asynchronous rolling and high-temperature short-time annealing processes can improve the recrystallization degree of the sample to a certain extent. However, after processing with the cross-asynchronous rolling and high-temperature short-time annealing process in Example 1, as shown in (b), the recrystallization degree of the sample is improved to a certain extent. Figure 4As shown in (c), the alloy foil exhibits the highest degree of recrystallization, with significantly improved overall grain size uniformity. Regular lamellar and layered annealed twin structures appear within the matrix, with twins penetrating the recrystallized grains and Σ3 twin boundaries forming. Simultaneously, grain orientation is more dispersed, and microstructural anisotropy is greatly reduced. This visually verifies the combined deformation effect of the cross-asynchronous rolling process in the embodiments, which can effectively induce annealed twin formation, optimize the recrystallized microstructure, and improve the overall microstructure of grain boundaries.

[0048] To further quantitatively compare the grain boundary engineering effects after heat treatment under different rolling methods, Table 4 summarizes parameters such as the special grain boundary fraction, grain size, twin-related domain (TRD) size, and their size ratio ν. Table 4 shows that the heat treatment process promoted the formation of special grain boundaries in both samples, but the microstructure provided by different cold rolling paths differed. The cross-asynchronous rolling in Example 1 was more conducive to the proliferation of special grain boundaries. Since special grain boundaries are mostly related to annealing twins, this result also indicates that asynchronous rolling has a stronger ability to form annealing twins after heat treatment, accompanied by recrystallization, leading to a decrease in the proportion of low-angle grain boundaries and an increase in the proportion of high-angle grain boundaries.

[0049] The twin-related domain size and ν value results further illustrate the differences in the degree of grain boundary network optimization among different samples. The twin-related domain is a twin-related region formed by the evolution of Σ3 twin boundaries and their related boundaries, and its size reflects the spatial expansion of the annealed twin network. In Table 4, the twin-related domain size and ν value of the synchronously rolled heat-treated sample in Comparative Example 1 are smaller, indicating that its special grain boundary network is mainly limited to a single grain or local region. The TRD in the conventionally rolled heat-treated sample in Comparative Example 2 shows some development, but it is still insufficient. In contrast, the cross-asynchronous rolling sample in Example 1 exhibits a larger twin-related domain size and ν value, indicating that the twin boundaries can connect more grains and form a larger range of low-energy boundary clusters. This means that the cross-asynchronous heat-treated sample of this application not only possesses more special grain boundaries, but these special grain boundaries are also more likely to form larger-scale twin-related structural units, which is the most obvious direct manifestation of its grain boundary engineering effect. A higher ν value indicates a higher degree of optimization of the grain boundary feature distribution, and the grain boundary network is more conducive to suppressing damage propagation.

[0050] Table 4. Parameters related to grain boundary engineering

[0051] Table 4 also presents the quantitative results of the three-way grain boundary types in different cold-rolled heat-treated samples. The changes in the three-way grain boundary types can more intuitively reflect the degree of optimization of the grain boundary network topology. J0, J1, J2, and J3 represent three-way nodes connected to special grain boundaries of different numbers. The subscript indicates how many of the three grain boundaries at that point belong to "special grain boundaries." A higher proportion of J3 indicates a higher degree of special grain boundary occupancy in the network. J2 / (1-J3) is often used to evaluate the connectivity and optimization level of the special grain boundary network. As shown in Table 4, compared to Comparative Examples 1 and 2, Example 1 has the highest proportion of J3 and the lowest proportion of J0, while J2 / (1-J3) also reaches its maximum value. This indicates that in the sample of Example 1, more three-way nodes are dominated by special grain boundaries, the random grain boundary network is more effectively cut off, and the grain boundary topology is most fully optimized. That is, Example 1 not only increases the number of special grain boundaries but also changes the connection mode of the grain boundary network, making it difficult for high-energy random grain boundaries to form long-distance continuous channels.

[0052] Table 5 below shows a comparison of elongation and conductivity parameters of the samples obtained from Example 1, Comparative Example 1, and Comparative Example 2. As can be seen from Table 5, the cross-asynchronous rolling heat-treated sample of Example 1 exhibits the best performance in both elongation and conductivity. The main reason is that the cross-asynchronous rolling combined with annealing grain boundary engineering control, through multiple mechanisms such as grain refinement strengthening, twinning strengthening, and special grain boundary pinning dislocations, synergistically improves the alloy strength. At the same time, by reducing residual dislocations and lattice distortion, increasing the proportion of low-energy special grain boundaries, weakening the anisotropy of the microstructure and the scattering of local defects, the free electron scattering loss is reduced, thereby improving its conductivity.

[0053] Although the sample of Comparative Example 2 maintained the strongest strengthening ability after heat treatment, the sample of Example 1 had slightly lower strength than that of Comparative Example 2, but its plasticity recovery was the most obvious. This was mainly due to the more uniform defect release, higher recrystallization degree and better special grain boundary network in the sample of Example 1, which together reduced local stress concentration. Therefore, while maintaining high strength, better ductility was obtained.

[0054] Table 5. Elongation and Conductivity Parameters

[0055] Elongation test: The elongation is tested by tensile test. In this embodiment, the tensile test is carried out according to the national standard GB / T228.1-2021 "Metallic materials - Tensile test" with a tensile rate of 0.18 mm / min.

[0056] Conductivity Testing: In this experiment, a DK60 eddy current conductivity meter and a QJ84A digital DC bridge were used to measure the conductivity of the samples. The conductivity used in this paper is relative to pure copper, expressed as %IACS (International Standard for Annealed Copper), which is the percentage of the material's conductivity σ20 at 20 °C to the international standard conductivity σCu of annealed pure copper.

[0057] Example 2 The method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning in this embodiment includes the following steps: Step 1: First, perform low-temperature stress-relief annealing on the original Cu-Ti alloy foil (0.1 mm thick × 30 mm wide, Ti atomic fraction of 3.25 at.%). The annealing temperature is set to 410 ℃, and the holding time is 50 min. After the holding time is completed, air cool to room temperature.

[0058] Step 2: After stress relief annealing, the Cu-Ti alloy foil is ultrasonically cleaned with anhydrous ethanol and acetone in sequence for 15 minutes each to thoroughly remove oil, dust and organic impurities from the foil surface. Then, it is corroded with dilute sulfuric acid for 5 seconds to gently remove the thin oxide scale and passivation film on the surface. Finally, it is rinsed with deionized water and dried with cold air.

[0059] Step 3: Plastic deformation is controlled using a multi-pass cross-asynchronous rolling process, with rolling at room temperature throughout and no intermediate annealing; in this embodiment, the speed ratio is controlled. w 1 / w The value of 2 is 1.12, and other parameters are the same as in Example 1.

[0060] Step 4: Perform recrystallization annealing (grain boundary control heat treatment) on the rolled sample. Specifically, in this embodiment, the rolled Cu-Ti alloy foil is placed in a vacuum heat treatment furnace to avoid high-temperature oxidation; a high-temperature short-time recrystallization annealing process is adopted, with the annealing temperature set at 580 ℃ and held at that temperature for 18 min, followed by air cooling to room temperature. In this embodiment, the proportion of special grain boundaries, elongation, and conductivity of the foil after rolling and recrystallization annealing are all effectively improved compared to Cu-Ti alloy foil produced by existing processes.

[0061] Example 3 The method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning in this embodiment includes the following steps: Step 1: First, perform low-temperature stress-relief annealing on the original Cu-Ti alloy foil (0.12 mm thick × 30 mm wide, Ti atomic fraction of 3.25 at.%). The annealing temperature is set to 406℃ and held for 70 min. After holding, air cool to room temperature.

[0062] Step 2: After stress relief annealing, the Cu-Ti alloy foil is ultrasonically cleaned with anhydrous ethanol and acetone in sequence for 12 minutes each to thoroughly remove oil, dust and organic impurities from the foil surface. Then, it is etched with dilute sulfuric acid for 4 seconds to gently remove the thin oxide scale and passivation film on the surface. Finally, it is rinsed with deionized water and dried with cold air.

[0063] Step 3: Use a multi-pass cross-asynchronous rolling process to control plastic deformation, rolling at room temperature throughout the process without intermediate annealing; Specifically, in this embodiment, the speed ratio is controlled at 1.13, the total reduction rate is 35%, the rolling passes are 16, and the thickness of the rolled sample is 78 μm.

[0064] Step 4: Perform recrystallization annealing (grain boundary control heat treatment) on the rolled sample. Specifically, in this embodiment, the rolled Cu-Ti alloy foil is placed in a vacuum heat treatment furnace to avoid high-temperature oxidation; a high-temperature short-time recrystallization annealing process is adopted, with the annealing temperature set at 620 ℃ and held at that temperature for 15 min, followed by air cooling to room temperature. In this embodiment, the proportion of special grain boundaries, elongation, and conductivity of the foil after rolling and recrystallization annealing are effectively improved compared to Cu-Ti alloy foil produced by existing processes. However, because the annealing temperature is higher than in Example 1, the grain size is slightly larger than in Example 1.

[0065] In summary, by employing the cross-asynchronous rolling + short-time high-temperature recrystallization annealing process of this invention, the resulting alloy foil forms a unique and stable microstructure: the proportion of low-angle grain boundaries is significantly reduced, the proportion of high-angle stable grain boundaries and Σ3 special twin boundaries is increased, the size of twin-related domains is increased, the originally continuous and interconnected random high-energy grain boundary network is effectively cut and fragmented by twin boundaries, the connectivity of the grain boundary network is significantly weakened, the uniformity of grain orientation is improved, and the anisotropy of the microstructure is partially eliminated, thereby ultimately achieving a simultaneous improvement in the coordination of alloy plastic deformation and electrical conductivity.

Claims

1. A method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning, characterized in that, Includes the following steps: The Cu-Ti alloy foil was subjected to stress-relief annealing at a temperature of 400~410 ℃ for 50~70 min, and then air-cooled to room temperature after the holding time was completed. The foil material after stress-relief annealing is subjected to multi-pass cross-asynchronous rolling. During the rolling process, the main rolling direction is kept constant, and the speed ratio is controlled. w 1 / w 2. With the numerical values ​​unchanged, the rotational speeds of the upper and lower rolls in adjacent passes are exchanged, resulting in a speed ratio. w 1 / w The value of 2 is between 1.12 and 1.13; The rolled foil was subjected to high-temperature short-time recrystallization annealing at a temperature of 580~620 ℃ for 15~25 min, and then air-cooled to room temperature after annealing.

2. The method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning according to claim 1, characterized in that, The multi-pass cross-asynchronous rolling process involves 12 to 16 rolling passes, with a total reduction rate controlled at 25% to 35% and a single-pass reduction rate not exceeding 10%.

3. The method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning according to claim 1, characterized in that, The rolling force during the multi-pass cross-asynchronous rolling process is controlled to be 2.1~2.7t, and the roll tension is 38~42kg.

4. The method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning according to any one of claims 1-3, characterized in that, The Ti atomic fraction in the Cu-Ti alloy foil is 3.25 at.% to 3.30 at.%; the thickness of the Cu-Ti alloy foil before rolling is 0.1 to 0.12 mm, and the thickness of the foil after rolling is 0.065 to 0.09 mm.

5. The method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning according to any one of claims 1-3, characterized in that, Prior to the multi-pass cross-asynchronous rolling process, the following is also included: The Cu-Ti alloy foil after stress-relief annealing is cleaned to remove oil, dust and organic impurities from the surface of the foil. Dilute sulfuric acid is used to corrode the surface of the foil to remove the oxide scale and passivation film on the foil surface.

6. The method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning according to claim 5, characterized in that, The process of cleaning the Cu-Ti alloy foil after stress-relief annealing involves sequential ultrasonic cleaning with anhydrous ethanol and acetone, with ultrasonic cleaning times of 10-15 minutes each.

7. The method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning according to any one of claims 1-3, characterized in that, After recrystallization annealing, the proportions of large-angle grain boundaries and small-angle grain boundaries in the obtained Cu-Ti alloy foil are 54%~56% and 44%~46%, respectively, while the proportion of special grain boundaries is 35%~40%.

8. The method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning according to any one of claims 1-3, characterized in that, After recrystallization annealing, the average grain size of the obtained Cu-Ti alloy foil is 2.8~3.5μm, the twin-related domain size is 10~12μm, and the twin-related domain size / grain size ratio is 2.85~4.

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9. The method for controlling the grain boundary network structure of Cu-Ti alloy foil based on annealed twinning according to any one of claims 1-3, characterized in that, After recrystallization annealing, the proportions of J0, J1, J2, and J3 in the obtained Cu-Ti alloy foil are 5%~6%, 24%~25%, 16%~18%, and 50%~52%, respectively. J0, J1, J2, and J3 represent three-way nodes with different numbers of connections to special grain boundaries, and J2 / (1-J3) is 35%~36%.

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