A Cu-Ti alloy strip resistant to impact fatigue, its preparation method and application

Abstract

This invention discloses a Cu-Ti alloy strip resistant to impact fatigue, with a mass percentage composition of Ti: 2.0–6.0 wt%, and the balance being Cu and unavoidable impurities. In the microstructure of the cross-section of this Cu-Ti alloy strip, the ratio of the major diameter L1 to the minor diameter L2 of the second-phase particles with a diameter greater than 100 nm satisfies 1.1 ≤ L1 / L2 ≤ 1.8, and the second-phase particles account for more than 60% of all second-phase particles with a diameter greater than 100 nm. By controlling the ratio of the major diameter to the minor diameter of the larger second-phase particles, this invention achieves excellent comprehensive performance. The yield strength of this Cu-Ti alloy strip is ≥800 MPa, and it does not crack under Badway 90° bending with R / t ≤ 2.0. This invention achieves a balance between strength and bending processing performance, while effectively improving impact fatigue performance. It is suitable for manufacturing elastic conductive components under various impact conditions, meeting the application requirements in electronic components such as switches, connectors, and conductive spring sheets.

Description

Technical Field

[0001] This invention belongs to the field of copper alloy technology, specifically relating to a Cu-Ti alloy strip resistant to impact fatigue, its preparation method, and its application. Background Technology

[0002] Cu-based alloys are commonly used in conductive materials due to their excellent electrical and thermal conductivity, strength, and elasticity. Among them, Cu-Be alloys are particularly renowned for their superior strength, hardness, and machinability. However, the production process of Cu-Be alloys is relatively complex, and their resistance to stress relaxation at high temperatures is poor, making them unsuitable for prolonged high-temperature operation. Furthermore, Be is toxic and poses risks to human health and the environment during production and use, thus limiting their application.

[0003] As an ideal alternative to Cu-Be alloys, age-hardening Cu-Ti alloys possess excellent mechanical properties and outstanding stress relaxation resistance among current copper alloys. They are widely used in electronic components such as switches, connectors, and conductive spring sheets. However, their lack of conductivity limits their applicability to most applications where conductivity requirements are not high.

[0004] With the miniaturization and increasing functionality of electronic products, and the growing demand for higher quality products, the reliability of electronic components is receiving increasing attention. Improving the reliability of electronic components has become a hot topic in their manufacturing. Taking conductive springs as an example, high reliability enables springs to withstand impact loads without permanent deformation or breakage, extending the lifespan of electronic products and improving their overall performance. This is especially true in the smartphone industry, where springs, due to their small size, require high strength while also withstanding repeated impacts and actuation cycles.

[0005] To address the above issues, there is an urgent need to develop a Cu-Ti alloy strip with improved impact fatigue performance to meet the material requirements of electronic components. Summary of the Invention

[0006] The first technical problem to be solved by the present invention is to provide a Cu-Ti alloy strip resistant to impact fatigue, its preparation method and application.

[0007] The technical solution adopted by the present invention to solve the first technical problem is as follows: a Cu-Ti alloy strip resistant to impact fatigue, wherein the mass percentage composition of the Cu-Ti alloy strip is Ti: 2.0~6.0wt%, with the balance being Cu and unavoidable impurities; in the microstructure of the cross section of the Cu-Ti alloy strip, the major axis of the second phase particles with a particle size of 100nm or more is denoted as L1 and the minor axis as L2, and the ratio of L1 to L2 satisfies 1.1≤L1 / L2≤1.8, and the second phase particles account for more than 60% of the total number of second phase particles with a particle size of 100nm or more.

[0008] Cu-Ti binary alloys are typical age-hardening alloys. The solid solution content of Ti in the Cu matrix increases with increasing temperature, gradually forming a supersaturated solid solution. As a solute, Ti can significantly improve the strength and hardness of the alloy, but it also causes lattice distortion, leading to increased electron scattering and thus reducing the alloy's conductivity. During the subsequent aging process, Ti precipitates in an ordered or disordered manner, further enhancing the alloy's strength and fatigue performance. To improve fatigue performance without affecting other mechanical properties, this invention selects to add 2.0–6.0 wt% Ti. If the Ti content is below 2.0 wt%, the supersaturation of the matrix is ​​insufficient, and the strength and fatigue performance do not meet the requirements. Conversely, if the Ti content is above 6.0 wt%, it cannot effectively strengthen the alloy's strength and fatigue performance; instead, it significantly reduces the alloy's conductivity and bending workability.

[0009] In the microstructure of the Cu-Ti alloy strip cross-section of this invention, second-phase particles with a diameter greater than 100 nm and a major axis L1 to minor axis L2 ratio of 1.1 to 1.8 account for more than 60% of all second-phase particles with a diameter greater than 100 nm. Since the concentration of plastic slip under impact fatigue is often more severe than under non-impact fatigue, and second-phase precipitates of varying sizes exist on the alloy matrix, if the larger second-phase particles are not controlled, the inhomogeneity of stress and strain within the material will become more pronounced. To improve the impact fatigue performance of Cu-Ti alloy strips, the morphology of the precipitates can be controlled. By controlling the major and minor diameters of the second-phase particles, the precipitates are predominantly elliptical, reducing the proportion of spherical and rod-shaped precipitates. This is because, compared to spherical precipitates, elliptical precipitates have lower coherence with the matrix, require more energy to plastically slide across their interface, are less likely to pass through the same location multiple times, and are less sensitive to impact fatigue. Rod-shaped precipitates, on the other hand, have a negative impact on mechanical properties, especially bending workability, and have very limited strengthening effect on fatigue performance. Therefore, in this invention, the ratio of major diameter L1 to minor diameter L2 of second-phase particles with a particle size of 100 nm or larger is controlled to be 1.1 to 1.8, accounting for more than 60% of all second-phase particles with a particle size of 100 nm or larger. Increasing the proportion of elliptical precipitates can achieve a balance between strength and bending workability, while effectively improving the impact fatigue performance of the alloy.

[0010] In the cross-section of the Cu-Ti alloy strip of the present invention, the area ratio of Gaussian texture with an orientation deviation angle within 15° in the surface layer on the cross-section of the Cu-Ti alloy strip is denoted as G1, and the area ratio of Gaussian texture with an orientation deviation angle within 15° in the central layer on the cross-section of the Cu-Ti alloy strip is denoted as G2. The ratio of G1 to G2 satisfies: 0.8≤G1 / G2≤1.2. The surface layer includes an upper surface layer and a lower surface layer, and the central layer is the portion between the upper surface layer and the lower surface layer. The thickness of the surface layer is 1 / 5 of the thickness of the Cu-Ti alloy strip, and the thickness of the central layer is 4 / 5 of the thickness of the Cu-Ti alloy strip. When materials are subjected to impact during use, the impact direction is often perpendicular to or at an angle to the rolling direction. However, there are also cases where impact loads are applied along the rolling direction. In these cases, there is no uneven stress distribution along the material thickness; the impact stress in the surface layer and the central layer is the same. According to the notch effect theory, the maximum notch stress is not the key factor in the generation of impact fatigue cracks, but rather the average notch stress in that region. This phenomenon is closely related to the microscopic anisotropy of the material. Gaussian texture is closely related to the control of strip anisotropy. When the deviation in the Gaussian texture ratio between the surface layer and the central layer of the strip is small, the microstructure exhibits better uniformity and equiaxedness, with more even distribution in all directions, thus mitigating the microscopic anisotropy of the strip. Therefore, this invention controls the area ratio of Gaussian texture between the surface layer and the central layer of Cu-Ti alloy strips, effectively reducing the notch effect on impact fatigue and improving the overall impact fatigue performance.

[0011] Furthermore, the value range of G1 is 6–18%, and the value range of G2 is 6–18%.

[0012] The Cu-Ti alloy strip of this invention further includes, by weight percentage, at least one element selected from Ni, Sn, Al, Si, Cr, Co, Zr, Fe, Mg, Mn, Zn, B, P, and Nb, in a total amount of 0.01–2.0 wt%. Adding appropriate amounts of these elements, which have a relatively small effect on controlling the morphology of the second phase, to the alloy of this invention allows some of them to exist in the matrix in a solid solution manner, inhibiting the growth of solid solution grains and improving the mechanical properties of the alloy, but correspondingly reducing electrical conductivity. Some elements can form intermetallic compounds with Ti, reducing the solid solution content of Ti and improving conductivity while synergistically strengthening the alloy. Other elements can deoxidize and purify the melt, thereby improving the overall performance of the alloy. This invention controls the content of the above elements to below 2.0 wt%. If the content is too high, it will not produce a significant strengthening effect and will instead reduce the overall performance of the alloy.

[0013] The yield strength of the Cu-Ti alloy strip of this invention is ≥800MPa, and it does not crack when bent at a Badway 90° with R / t ≤2.0, where R is the minimum bending radius of the Cu-Ti alloy strip and t is the thickness of the Cu-Ti alloy strip.

[0014] The second technical problem to be solved by the present invention is to provide a method for preparing Cu-Ti alloy strip resistant to impact fatigue.

[0015] The technical solution adopted by the present invention to solve the second technical problem is: a method for preparing Cu-Ti alloy strip resistant to impact fatigue, the preparation process includes: casting → hot rolling → rough rolling → solution treatment → first-stage aging treatment → intermediate rolling → second-stage aging treatment → finish rolling → low-temperature annealing, wherein the sum of the total processing rate of intermediate rolling and finish rolling is greater than 50% of the total processing rate of rough rolling.

[0016] After solution treatment, Cu-Ti alloy strip requires two aging treatments and two cold rolling processes: primary aging treatment, secondary aging treatment, intermediate rolling, and finish rolling. Because the solute forms a supersaturated solid solution in the matrix after solution treatment, various second phases gradually precipitate within the grains and disperse in the matrix after aging treatment, providing strengthening. Adjusting the cold rolling process after aging treatment helps control the morphology of the second phases. Therefore, considering the thickness variation from ingot to finished strip, this invention controls the sum of the total processing rates of intermediate rolling and finish rolling to be greater than 50% of the total processing rate of rough rolling. Sufficient processing after aging treatment controls the ratio of the major to minor diameter of the second phase particles, increasing the proportion of elliptical precipitates.

[0017] The holding temperature for the first-stage aging treatment is denoted as T1, and the holding temperature for the second-stage aging treatment is denoted as T2. T1 and T2 satisfy the following condition: T1 - T2 ≥ 50℃, where T1 ranges from 300 to 550℃ and T2 ranges from 250 to 500℃. Furthermore, the sum of the holding times for the first-stage and second-stage aging treatments does not exceed 15 hours.

[0018] The first-stage aging treatment uses a relatively high temperature T1 for holding to form a suitable precursor twin structure during the intermediate rolling process. Then, through a second-stage aging treatment with a lower holding temperature T2 and a finishing rolling process, the twin structure smoothly transforms into a Gaussian texture, resulting in the desired texture structure in both the surface and core layers of the strip. Therefore, this invention controls the holding temperature T1 of the first-stage aging treatment to differ from the holding temperature T2 of the second-stage aging treatment by more than 50°C. Simultaneously, considering factors such as recrystallization kinetics and the suppression of excessive grain growth, the range of T1 is controlled between 300 and 550°C, and the range of T2 is controlled between 250 and 500°C.

[0019] In addition, the present invention controls the sum of the holding time of the first-stage aging treatment and the second-stage aging treatment to not exceed 15 hours, so as to prevent the precipitated second phase from agglomerating and coarsening due to long-term aging and holding. This has an adverse effect on the morphology of the second phase of the finished strip and will also lead to the deterioration of the mechanical properties of the strip.

[0020] The third technical problem to be solved by the present invention is to provide an application of impact fatigue resistant Cu-Ti alloy strip in electronic components, specifically, the electronic components include switches, connectors, and conductive spring sheets.

[0021] Compared with existing technologies, the advantages of this invention are as follows: By controlling the ratio of the major to minor diameters of the larger second-phase particles in the microstructure of the Cu-Ti alloy strip, this invention achieves excellent comprehensive performance. The yield strength of this Cu-Ti alloy strip is ≥800MPa, and it does not crack when bent at Badway 90° with R / t ≤2.0. This invention's Cu-Ti alloy strip achieves a balance between strength and bending processing performance, while effectively improving impact fatigue performance. It is suitable for manufacturing elastic conductive components under various impact conditions, meeting the application requirements in electronic components such as switches, connectors, and conductive spring sheets. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the embodiments.

[0023] This invention provides 10 embodiments and 3 comparative examples, and the specific components are shown in Table 1.

[0024] The process flow of this embodiment is as follows: melting and casting → hot rolling → rough rolling → solution treatment → first-stage aging treatment → intermediate rolling → second-stage aging treatment → finish rolling → low-temperature annealing; melting is carried out in a vacuum melting furnace, and then rectangular billets with a thickness of 30-50mm are formed by semi-continuous casting. After holding at 950℃ for 3h, the billets are hot rolled, followed by rough rolling with a 90% machining rate. After solution treatment at 600℃ for 10min, the billets are cooled to room temperature and then processed according to the conditions shown in Table 2. Finally, a low-temperature annealing at 350℃ for 0.1h is applied to obtain a strip sample with a thickness of 0.15mm.

[0025] The difference between Comparative Examples 1 and 2 and the Examples is that their compositions are not within the range of Cu-Ti alloy compositions of the present invention.

[0026] The composition of Comparative Example 3 is the same as that of Example 1, the difference being the process used, where the sum of the total processing rates of intermediate rolling and finishing rolling is less than 50% of the total processing rate of rough rolling.

[0027] The yield strength, bending processing performance, impact fatigue performance, and microstructure of the alloy strips of Examples 1-10 and Comparative Examples 1-3 of this invention were evaluated according to the methods specified in the relevant national and industry standards. The test and measurement methods for each evaluation item are as follows, and the evaluation results are shown in Table 3.

[0028] Yield strength: The room temperature tensile test was conducted on an electronic universal mechanical performance testing machine in accordance with GB / T 228.1-2010 Metallic materials, tensile testing - Part 1: Room temperature test method.

[0029] Bending performance: A long strip sample with a width of 10 mm was taken along the direction perpendicular to the rolling direction (i.e., the Bayway direction). The strip sample was then bent using a 90° V-shaped punch with different radii at the tip. The outer surface of the bent area was then observed using a stereomicroscope. The bending performance was represented by the minimum bending radius R / Cu-Ti alloy strip thickness t that did not produce surface cracks.

[0030] Impact fatigue performance: A 10mm wide strip sample was used as the specimen. One side of the specimen was fixed, and alternating stress loads along the length direction were repeatedly applied to the other side for tensile testing. The load magnitude was the load that caused 0.5% strain in the specimen. Impact load was simulated at a loading rate of 0.1% / s. The test was conducted for 10 days. 5 After the test, the surface appearance, deformation, and crack initiation of the samples were observed to evaluate the impact fatigue performance of the strip. Samples with good surface quality and no obvious deformation were marked with ◎, indicating good impact fatigue performance; samples with slight deformation but no crack initiation were marked with ○, indicating qualified impact fatigue performance; samples with obvious cracks on the surface or fractured midway were marked with ×, indicating poor impact fatigue performance.

[0031] Second phase: Cut the alloy strip into test samples along the rolling direction, grind, polish, pickle and etch, and observe the strip cross section using a scanning electron microscope or a transmission electron microscope. Randomly select 10 viewing areas, and take the average of the major and minor diameters of each second phase particle as the particle size. Measure the major diameter L1 and minor diameter L2 of the second phase with a particle size greater than 100 nm in the viewing area, and calculate the proportion of second phase particles in the total number of particles with L1 / L2 in the range of 1.1 to 1.8.

[0032] Microtexture: The EBSD method was used to test the cross-section of the strip within a measurement area of ​​500 μm × 500 μm. The angle between the sample surface and the incident electron beam was 70 degrees. The accelerating voltage was 20 kV, the accelerating current was 1 nA, and the test step size was 0.4 μm. Existing analysis software was used to analyze the texture type and area proportion of the surface and central layers, determining the Gaussian texture area proportions G1 and G2 and their ratio. The Gaussian texture area proportion refers to {110} <001> The ratio of the area within 15° of the orientation deviation angle to the total measured area; the cross-section is divided into the upper surface layer, the lower surface layer, and the part between the upper and lower surface layers of the strip, wherein the total thickness of the upper and lower surface layers is 1 / 5 of the strip thickness.

[0033] According to the evaluation results shown in Table 3, the microstructure of Examples 1-10 of the present invention is within the scope of the present invention, achieving a yield strength of Cu-Ti alloy strip ≥800MPa, a minimum bending radius R of Badway 90° bend to strip thickness t ratio R / t ≤2.0, good impact fatigue performance, and excellent comprehensive performance. In Comparative Examples 1-2, the bending processing performance and impact fatigue performance were significantly affected due to excessively low or high Ti content; in Comparative Example 3, the sum of the total processing rates of intermediate rolling and finishing rolling was less than 50% of the total processing rate of rough rolling, the microstructure was not within the scope of the present invention, and the impact fatigue performance was poor.

[0034] Table 1. Components of the Examples and Comparative Examples

[0035]

[0036] Table 2 Key process parameter control for examples and comparative examples

[0037]

[0038] Table 3 Microstructure and properties of the Examples and Comparative Examples

[0039]

Claims

1. A Cu-Ti alloy strip resistant to impact fatigue, characterized in that, The mass percentage composition of the Cu-Ti alloy strip is Ti: 2.0~6.0wt%, with the balance being Cu and unavoidable impurities. In the microstructure of the cross-section of the Cu-Ti alloy strip, the major axis of the second phase particles with a particle size of 100nm or more is denoted as L1 and the minor axis as L2. The ratio of L1 to L2 satisfies 1.1≤L1 / L2≤1.

8. The second phase particles account for more than 60% of the total number of second phase particles with a particle size of 100nm or more.

2. The impact-fatigue-resistant Cu-Ti alloy strip according to claim 1, characterized in that, On the cross-section of the Cu-Ti alloy strip, the area ratio of Gaussian texture with an orientation deviation angle within 15° in the surface layer is denoted as G1, and the area ratio of Gaussian texture with an orientation deviation angle within 15° in the central layer is denoted as G2. The ratio of G1 to G2 satisfies: 0.8 ≤ G1 / G2 ≤ 1.

2. The surface layer includes an upper surface layer and a lower surface layer, and the central layer is the portion between the upper surface layer and the lower surface layer. The thickness of the surface layer is 1 / 5 of the thickness of the Cu-Ti alloy strip, and the thickness of the central layer is 4 / 5 of the thickness of the Cu-Ti alloy strip.

3. The impact-fatigue-resistant Cu-Ti alloy strip according to claim 2, characterized in that, The value range of G1 is 6 to 18%, and the value range of G2 is 6 to 18%.

4. The impact-fatigue-resistant Cu-Ti alloy strip according to claim 1, characterized in that, The Cu-Ti alloy strip also includes at least one element selected from Ni, Sn, Al, Si, Cr, Co, Zr, Fe, Mg, Mn, Zn, B, P and Nb in a total amount of 0.01 to 2.0 wt%.

5. The impact fatigue-resistant Cu-Ti alloy strip according to any one of claims 1-4, characterized in that, The yield strength of the Cu-Ti alloy strip is ≥800MPa, and it does not crack when bent at 90° in Badway with R / t ≤2.0, where R is the minimum bending radius of the Cu-Ti alloy strip and t is the thickness of the Cu-Ti alloy strip.

6. The method for preparing the impact fatigue-resistant Cu-Ti alloy strip according to any one of claims 1-5, characterized in that, The preparation process includes: casting → hot rolling → rough rolling → solution treatment → primary aging treatment → intermediate rolling → secondary aging treatment → finish rolling → low temperature annealing. The total processing rate of intermediate rolling and finish rolling is greater than 50% of the total processing rate of rough rolling.

7. The method for preparing the impact fatigue-resistant Cu-Ti alloy strip according to claim 6, characterized in that, The heat preservation temperature of the first-stage aging treatment is denoted as T1, and the heat preservation temperature of the second-stage aging treatment is denoted as T2. T1 and T2 satisfy the following condition: T1-T2≥50℃, the value range of T1 is 300~550℃, and the value range of T2 is 250~500℃.

8. The method for preparing the impact fatigue-resistant Cu-Ti alloy strip according to claim 7, characterized in that, The sum of the holding times for the first-level aging treatment and the second-level aging treatment shall not exceed 15 hours.

9. The application of the impact fatigue resistant Cu-Ti alloy strip according to any one of claims 1-5 in electronic components.

10. The application according to claim 9, characterized in that, The electronic components include switches, connectors, and conductive spring sheets.

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