A chromium bronze alloy strip and its preparation method and connecting terminal

Abstract

This invention discloses a chromium bronze alloy strip and its preparation method, as well as a connecting terminal. The chromium bronze alloy strip has the following weight percentage composition: 0.6–1.0 wt% Cr, 0.15–0.5 wt% Fe, 0.1–0.4 wt% Ti, 0.01–0.12 wt% Si, with the balance being Cu and unavoidable impurities. The microstructure of this chromium bronze alloy strip contains 60–90% small-angle grain boundaries (L) and 10–40% large-angle grain boundaries (H), where small-angle grain boundaries are defined as grain boundaries with an orientation difference ≤15° between adjacent grains, and large-angle grain boundaries are defined as grain boundaries with an orientation difference >15° between adjacent grains. This invention achieves a good balance of strength, conductivity, resistance to thermal stress relaxation, and bending performance by controlling the alloy composition and the percentage of large and small-angle grain boundaries in the microstructure. This chromium bronze alloy strip can be used in applications such as automotive connectors that require high strength, high conductivity, excellent resistance to thermal stress relaxation, and good bending performance.

Description

Technical Field

[0001] This invention belongs to the field of copper alloy technology, specifically relating to a chromium bronze alloy plate and strip, its preparation method, and its application. Background Technology

[0002] In recent years, the rapid development of new energy vehicles in China and the increasing application of automotive electronic products have led to a surge in the number of automotive connectors used, resulting in a sharp increase in demand for high-end copper alloys. Simultaneously, the requirements for automotive safety, environmental protection, comfort, and intelligence are becoming increasingly stringent, demanding materials with high strength, high conductivity, high resistance to thermal stress relaxation, excellent bending processing performance, and good fatigue strength. Traditional beryllium bronze alloys, as a high-performance alloy material, are used in high-performance springs, switches, diaphragms, and spring contacts. However, with the rapid increase in performance requirements across various fields, beryllium bronze has shown some shortcomings. For example, its conductivity cannot meet the needs of high-current, high-voltage switch products. Furthermore, the environmental pollution caused by beryllium significantly limits its application. Therefore, developing a new material to replace beryllium bronze, possessing both good strength and conductivity, has become a new research topic in the field of copper alloy development.

[0003] Currently, high-voltage connector terminals for new energy vehicles, in addition to mechanical and electrical properties, also require high-temperature performance. Specifically, the yield strength must be between 500 and 650 MPa, the conductivity above 60% IACS, and the stress residual rate above 85% after 1000 hours of heat treatment at 150℃. Currently, mass-produced automotive connectors mainly use C70250 and 19010 alloys. C70250 alloy has high strength, but its conductivity is relatively low, only around 40% IACS, making it suitable for environments with high strength requirements but low conductivity requirements. C19010 alloy has a more balanced strength and conductivity, but its high-temperature performance is lacking, making it unsuitable for environments with high high-temperature performance requirements. Therefore, to meet the demands of rapidly developing high-tech industries, there is an urgent need for an environmentally friendly copper alloy sheet / strip product with good strength, conductivity, bending performance, and resistance to thermal stress relaxation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a chromium bronze alloy strip with high strength, high conductivity, excellent resistance to thermal stress relaxation and bending processing performance, and a method for preparing the same, in order to address the shortcomings of the prior art. The chromium bronze alloy strip can be used to prepare connector terminals.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a chromium bronze alloy strip, wherein the weight percentage composition of the chromium bronze alloy strip is: 0.6-1.0 wt% Cr, 0.15-0.5 wt% Fe, 0.1-0.4 wt% Ti, 0.01-0.12 wt% Si, and the balance is Cu and unavoidable impurities; the percentage of small-angle grain boundaries L in the microstructure of the chromium bronze alloy strip is 60-90%, and the percentage of large-angle grain boundaries H is 10-40%, wherein small-angle grain boundaries are grain boundaries with an orientation difference of ≤15° between adjacent grains, and large-angle grain boundaries are grain boundaries with an orientation difference of >15° between adjacent grains.

[0006] According to an exemplary embodiment of the present invention, the ratio of the percentage of small-angle grain boundaries L to the percentage of large-angle grain boundaries H satisfies: L / H≥2.

[0007] According to an exemplary embodiment of the present invention, the plate texture type in the microstructure of the chromium bronze alloy strip is mainly S texture {123} <634> and R texture {124} <211> The area proportion of S texture (a) is 20-40%, and the area proportion of R texture (b) is 15-35%.

[0008] According to an exemplary embodiment of the present invention, the area ratio a of the S texture and the area ratio b of the R texture satisfy 0.5 ≤ b / a ≤ 1.2.

[0009] According to an exemplary embodiment of the present invention, the chromium bronze alloy strip further includes at least one element selected from Ni, Zr, Sn, Zn, Ag and Ce in a total weight percentage of less than 0.5 wt%.

[0010] According to an exemplary embodiment of the present invention, the chromium bronze alloy strip has a yield strength of 500-650 MPa, a conductivity of ≥60% IACS, a stress retention rate of over 85% after being kept at 150°C for 1000 hours, and a bending radius r in the bad direction to the plate thickness t when bent at 90°, with the ratio r / t ≤ 1.

[0011] According to the preparation method of chromium bronze alloy strip of the present invention, the preparation process is as follows: semi-casting → hot rolling → milling → first cold rolling → solution treatment → second cold rolling → aging treatment. The second cold rolling and subsequent aging treatment constitute a cycle step, and the cycle step is repeated several times. The solution treatment first passes through a preheating zone at a temperature of 800-850°C and holds for 0.5-5 minutes, then passes through a high temperature zone at a temperature of 1020-1050°C and holds for 0.1-2 minutes, and then cools to room temperature at a cooling rate of 100°C / s or higher.

[0012] According to an exemplary embodiment of the present invention, the aging temperature of the aging treatment is 400-550°C, the heating rate is 20°C / min or higher, and after holding at the temperature for 6-10 hours, it is cooled to room temperature at a cooling rate of 1-10°C / min.

[0013] According to an exemplary embodiment of the present invention, the chromium bronze alloy sheet can be made into a connecting terminal.

[0014] Compared with existing technologies, the advantages of this invention are as follows: By controlling the composition of the chromium bronze alloy strip and the percentage of small-angle and large-angle grain boundaries in the microstructure, this invention achieves a good match between strength, conductivity, resistance to thermal stress relaxation, and bending performance. Its yield strength is 500–650 MPa, conductivity is ≥60% IACS, and the stress retention rate after holding at 150℃ for 1000 hours reaches over 85%. When bent at 90°, the ratio of the bending radius r in the worst direction to the plate thickness t is r / t≤1. This chromium bronze alloy strip can be applied to applications such as automotive connectors that require high strength, high conductivity, excellent resistance to thermal stress relaxation, and good bending performance. Attached Figure Description

[0015] Figure 1 This is a percentage diagram showing the number of small-angle and large-angle grain boundaries in the chromium bronze alloy strip sample of Example 1. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to the accompanying drawings, embodiments, and comparative examples.

[0017] According to embodiments of the present invention, the main element Cr in the chromium bronze alloy strip has low solid solubility in the copper matrix. During the solid solution process, various Cr-containing phases are formed and precipitated during subsequent aging, playing a synergistic role in strengthening the alloy. When the Cr content is low, the strengthening effect of Cr is insufficient, leading to a decrease in strength; conversely, when the Cr content is too high, due to the low solid solubility of Cr in the copper matrix, even if excessive Cr is added, the strengthening effect is very limited, and it will also significantly reduce the conductivity of the alloy. On the other hand, it is also easy to coarsen the Cr-containing phases, causing local stress concentration and leading to a deterioration in high-temperature performance. To obtain better overall performance, the Cr content in the chromium bronze alloy strip of the present invention is controlled at 0.6-1.0 wt%.

[0018] The addition of Fe can inhibit grain growth in chromium bronze alloys during solid solution treatment, thus providing grain refinement and strengthening. It can also form intermetallic compounds with other alloying elements to improve the alloy's mechanical properties. If the Fe content is too low, the strengthening effect is not significant; if the Fe content is too high, it increases the tendency to form large-sized intermetallic compounds, thereby reducing the alloy's bending workability. Furthermore, because Fe has high solid solubility at room temperature, excessive Fe can cause increased crystal lattice distortion, leading to a decrease in conductivity. Therefore, the Fe content in the chromium bronze alloy strip of this invention is controlled at 0.15–0.5 wt%.

[0019] The solid solubility of Ti in a copper matrix at room temperature is approximately 0.4 wt%. The trace amount of Ti added primarily serves as solid solution strengthening. On the other hand, it can form a second phase with elements such as Cr and Fe, improving the tensile strength and electrical conductivity of the alloy. Considering the overall performance of the alloy, the Ti content in the chromium bronze alloy strip of this invention is controlled at 0.1–0.4 wt%.

[0020] Si (silicon) plays a role in solid solution strengthening and work hardening. During aging, it can form a second phase with elements such as Cr and Ti, which can balance the excess Cr and Ti dissolved in the copper matrix. However, when the Si content is too high, it will cause a sharp decrease in conductivity. Therefore, the Si content in the chromium bronze alloy strip of this invention is controlled at 0.01–0.12 wt%.

[0021] According to embodiments of the present invention, the percentage L of small-angle grain boundaries in the microstructure of the chromium bronze alloy strip is 60-90%, and the percentage H of large-angle grain boundaries is 10-40%. Small-angle grain boundaries are defined as grain boundaries with an orientation difference of ≤15° between adjacent grains, and large-angle grain boundaries are defined as grain boundaries with an orientation difference of >15° between adjacent grains. The chromium bronze alloy strip of the present invention is a polycrystalline material. Small-angle grain boundaries are composed of a series of dislocations. A high degree of dislocation pile-up leads to lattice distortion, causing an elastic stress field and increasing crystal energy. This increases the material's strength. However, at a certain temperature, the crystal energy generated by the elastic stress field caused by lattice distortion decreases, resulting in poor resistance to thermal stress relaxation and adversely affecting the thermal stress relaxation rate. Furthermore, an excessive percentage of small-angle grain boundaries can lead to easy crack propagation, causing material cracking and poor bending processing performance. Excessive small-angle grain boundaries also increase the energy within the crystal. This energy is easily released and unstable when held at a certain temperature for a long time, resulting in poor resistance to thermal stress relaxation and a low thermal stress relaxation rate. When the percentage of small-angle grain boundaries is low and the percentage of large-angle grain boundaries is high, the strength and hardness of the material decrease, and springback cannot be guaranteed. In order to obtain higher strength and better bending processing performance, this invention controls the percentage of small-angle grain boundaries L in the microstructure to be 60-90% and the percentage of large-angle grain boundaries H to be 10-40%, thereby achieving excellent comprehensive performance of chromium bronze alloy strips.

[0022] Preferably, according to an embodiment of the present invention, the ratio of the percentage of small-angle grain boundaries L to the percentage of large-angle grain boundaries H in the chromium bronze alloy strip satisfies: L / H ≥ 2. During cold working plastic deformation, dislocations form within the chromium bronze alloy strip under an applied load. Compared to large-angle grain boundaries, dislocations require a greater driving force to pass through small-angle grain boundaries, which is more conducive to increasing dislocation density during plastic deformation. Ultimately, dislocations entangle at the small-angle grain boundaries and form dislocation cells. This high-dislocation-density entangled dislocation cell structure inhibits recrystallization and grain boundary migration during heat treatment of the strip, thereby improving the strip's resistance to thermal stress relaxation. Simultaneously, the increased dislocation density further enhances the work hardening effect of the strip.

[0023] Preferably, according to an embodiment of the present invention, the plate texture type in the microstructure of the chromium bronze alloy strip is mainly S-texture {123} <634> and R texture {124} <211> The area proportion of S texture (a) is 20-40%, and the area proportion of R texture (b) is 15-35%.

[0024] Copper alloy sheets and strips are generally reprocessed into parts through stamping. This invention, using chromium bronze alloy sheets and strips as automotive connector parts, requires good bending performance. Copper alloy sheets and strips are polycrystalline; under external force, the grains within the crystals aggregate and align along certain directions. These arrangements resemble the structure and texture of natural fibers or fabrics, hence the term texture. Texture directly affects material properties. Texture types in the microstructure of copper alloys are classified into deformation texture and recrystallization texture. Deformation textures include Goss texture, Brass texture, and S texture, while common recrystallization textures are Cube texture and R texture. The amount of recrystallization texture is positively correlated with the bending performance of the material, especially when the proportion of R texture increases. This increases the energy required to activate the slip system, making slippage more difficult, resulting in better bending performance and greater stability at high temperatures. Deformation texture, on the other hand, has a greater impact on the mechanical properties of the material. A high proportion of deformation texture indicates a large number of slip bands within the crystals, creating a slip-prone state that easily leads to a decrease in bending performance and resistance to thermal stress relaxation. Therefore, in order to simultaneously satisfy the properties of the material such as strength, bending workability, and thermal stability, the area ratio a of S texture in the microstructure of the chromium bronze alloy strip of this invention is controlled to be 20-40%, and the area ratio b of R texture is controlled to be 15-35%.

[0025] More preferably, the area ratio 'a' of the S-texture and the area ratio 'b' of the R-texture satisfy 0.5 ≤ b / a ≤ 1.2. When b / a < 0.5, the number of recrystallized R-type textures is relatively small. At this time, there are a large number of slip bands inside the crystal, which are in a state of easy slip, resulting in poor bending workability and resistance to thermal stress relaxation of the material. When b / a > 1.2, there are more recrystallized textures and fewer deformable textures. At this time, more energy is required to activate the slip system, making slip difficult. The bending workability and resistance to thermal stress relaxation of the material are better, but the reduction of deformable textures significantly reduces the strength of the material. Therefore, in order to make the material have excellent bending workability and high strength, the present invention controls the area ratio of S-texture and R-texture to satisfy: 0.5 ≤ b / a ≤ 1.2.

[0026] Preferably, according to embodiments of the present invention, the chromium bronze alloy strip further includes at least one element selected from Ni, Zr, Sn, Zn, Ag, and Ce, with a total content of less than 0.5 wt%. These elements have a relatively small effect on hindering the formation of small-angle grain boundaries and can be present in a certain amount. Zr, Sn, Zn, and Ag can be dissolved in the copper matrix, achieving solid solution strengthening and improving the alloy's strength and fatigue resistance. Ni can form a second phase with elements such as Ti and Si during aging, achieving precipitation strengthening and reducing the impact of excess Ti on conductivity. Rare earth element Ce has high chemical activity, effectively removing impurities, purifying the copper matrix, and reducing the adverse effects of impurity elements on the material's fatigue resistance and conductivity.

[0027] According to an embodiment of the present invention, the yield strength of the chromium bronze alloy strip is 500-650 MPa, the conductivity is ≥60% IACS, the stress retention rate after holding at 150°C for 1000 h reaches more than 85%, and when bent at 90°, the ratio of the bending radius r in the bad direction to the plate thickness t is r / t≤1.

[0028] According to an embodiment of the present invention, chromium bronze alloy strips can be prepared as strips with a thickness of 0.05 to 3 mm.

[0029] According to an embodiment of the present invention, the preparation method of chromium bronze alloy strip is as follows: semi-casting → hot rolling → milling → first cold rolling → solution treatment → second cold rolling → aging treatment. The second cold rolling and subsequent aging treatment constitute one cycle step, and this cycle step is repeated several times. The solution treatment first passes through a preheating zone at a temperature of 800-850°C for 0.5-5 minutes, then passes through a high-temperature zone at 1020-1050°C for 0.1-2 minutes, and then cools to room temperature at a cooling rate of 100°C / s or higher.

[0030] According to an embodiment of the present invention, the specific preparation process of chromium bronze alloy plate and strip is as follows:

[0031] 1) Semi-melting casting: Take each raw material according to the ratio and melt it at 1200-1300℃. After the raw materials are completely melted, argon gas is introduced for protection to prevent the added Ti element from being oxidized and burned off during the melting and casting process, and to ensure the Ti element content.

[0032] 2) Hot rolling: The hot rolling temperature of the ingot is controlled at 850-900℃. To achieve the purpose of homogenization, hot rolling can also be carried out after holding for 2-4 hours. In order to minimize the precipitation of second phase particles during hot rolling, the final rolling temperature of the hot rolling process should be controlled at a high temperature, specifically above 650℃, and the hot rolling processing rate should be above 85%.

[0033] 3) Milling: After hot rolling, the oxide scale on the surface is relatively thick. In order to ensure the surface quality of the strip in the later stage, the top and bottom surfaces of the hot-rolled plate are milled by 0.5 to 1.0 mm, and the left and right surfaces are milled by 1.0 to 2.0 mm.

[0034] 4) Single-stage cold rolling: The total rolling rate is controlled above 80%, which not only yields a deformed microstructure but also facilitates the subsequent solution treatment process. A cold working rate of over 80% provides sufficient strain energy for the chromium bronze alloy strip of this invention, thereby promoting the integration of second-phase particles into the copper matrix during solution quenching. This allows for the precipitation of fine, dispersed particles during subsequent deformation heat treatment. These precipitated phase particles act as pinning agents against grain boundaries and dislocation cells, significantly improving the alloy's strength.

[0035] 5) Solution Treatment: During the solution treatment process, coarse precipitates in the original casting structure and precipitates formed during hot rolling and cooling are fully dissolved back into the matrix. In the solution treatment process, before entering the high-temperature zone, the material is preheated at 800–850°C for 0.5–5 minutes. The subsequent high-temperature zone holding time must ensure the material temperature reaches above 1020°C but not exceeding 1050°C to ensure that solute atoms are dissolved as completely as possible into the copper matrix. Simultaneously, the high-temperature zone holding time is controlled at 0.1–2 minutes to prevent overheating. The purpose of the preheating zone holding time is to ensure that the material quickly reaches the set solution temperature when entering the high-temperature zone, extending the overall holding time of the solution treatment and ensuring the transformation of the material's internal structure. When the temperature in the high-temperature zone is below 1020℃, the driving force for atomic diffusion is insufficient, resulting in an unsatisfactory solid solution effect. This fails to guarantee the solubility of solute atoms in the copper matrix and prevents the conversion of small-angle grain boundaries into a suitable percentage during subsequent deformation heat treatment, affecting the material's mechanical properties and high-temperature stability. Conversely, when the temperature in the high-temperature zone exceeds 1050℃, abnormal grain growth is likely, along with grain boundary melting, leading to overheating and scrapping of the billet. After holding in the high-temperature zone, the cooling rate must be greater than 100℃ / s to rapidly cool to room temperature, ensuring a supersaturated solid solution and reducing the precipitation of strengthening phases during cooling. This facilitates the precipitation of fine, dispersed phases during subsequent deformation heat treatment. These fine, dispersed phases pinning the grain boundaries makes grain boundary movement more difficult, thus making the transformation from small-angle to large-angle grain boundaries more challenging. This significantly improves the material's strength, conductivity, and stability.

[0036] 6) Secondary cold rolling: The purpose of secondary cold rolling is to provide more energy and channels for the precipitation of precipitates, and to cause orientation rotation of the microstructure after solid solution treatment during the secondary cold rolling process, thereby regulating the transformation of recrystallization texture to Copper texture and S texture. Simultaneously, a large number of dislocations are generated during the cold rolling process, forming many substructures, the boundaries of which are small-angle grain boundaries. In the preparation process of the chromium bronze alloy strip of this invention, the rolling rate of the secondary cold rolling is controlled between 20% and 70%. When the rolling rate is below 20%, it cannot provide sufficient deformation energy for subsequent aging, resulting in insufficient precipitation of precipitates, a small percentage of recrystallization texture in the microstructure transforming into S-texture and Copper texture, and the absence of many dislocations, which prevents the formation of sufficient small-angle grain boundaries, leading to poor material properties. When the rolling rate is above 70%, the recrystallization texture in the microstructure will transform into brass texture instead of Copper texture and S-texture. At the same time, the large deformation rate generates a large number of dislocations, forming more small-angle grain boundaries, which in turn reduces the bending workability of the alloy. Therefore, the rolling rate of the second cold rolling is controlled between 20% and 70%.

[0037] 7) Aging Treatment: Aging treatment brings the alloy to an over-aged state, significantly improving its conductivity while allowing the strengthening phase to fully precipitate. Aging treatment is a key process for achieving primary aging precipitation strengthening. High temperatures promote complete recrystallization and the precipitation of the second phase, while low-temperature aging is detrimental to both recrystallization and the precipitation of the second phase. Therefore, in the preparation of the chromium bronze alloy sheet and strip of this invention, the aging temperature is controlled at 400–550°C, the heating rate is above 20°C / min, and after holding at this temperature for 6–10 hours, it is cooled to room temperature at a rate of 1–10°C / min. During the primary aging process, the higher temperature facilitates the full precipitation of the second phase, achieving the over-aging effect. After aging, the brass and cubic textures in the microstructure transform into copper and R textures. The numerous dislocations that were originally entangled within the dislocation cells during aging have loosened, and the dislocations have become more straight and regular. Due to the limited movement distance of the dislocations and nanoparticles, several groups of regularly arranged dislocations react to form a dislocation network. At this point, a large number of dislocations at the subgrain boundaries remain entangled due to the pinning of nanoprecipitates, and the dislocation cell structure is still evident. However, the dislocation density inside the dislocation cells is reduced, resulting in a decrease in the large number of small-angle grain boundaries generated during cold rolling. Through the interaction between the precipitates and the small and large-angle grain boundaries, the alloy achieves a better match between strength and bending workability.

[0038] Please refer to Table 1 for the specific alloy compositions of 15 embodiments and 2 comparative examples provided according to the present invention.

[0039] Taking strip as an example, the preparation process according to various embodiments of the present invention is as follows: semi-casting → hot rolling → milling → first cold rolling → solution treatment → second cold rolling → aging treatment, finally obtaining a strip sample with a thickness of 0.25 mm, specifically including the following steps:

[0040] 1) Semi-casting: Prepare raw materials and batch them according to the alloy chemical composition in Table 1. After all the raw materials have melted, argon gas is introduced for protection. The casting temperature is 1250℃.

[0041] 2) Hot rolling: Hold at 880℃ for 3 hours and then hot roll, with a final rolling temperature of 700℃ or higher, and a hot rolling processing rate of 85% or higher.

[0042] 3) Milling: Mill the top and bottom surfaces of the hot-rolled plate by 0.5 to 1.0 mm, and the left and right surfaces by 1.0 to 2.0 mm;

[0043] 4) First cold rolling: The strip after milling is cold rolled, with a processing rate of over 80%;

[0044] 5) Solution treatment: The strip after the first cold rolling is subjected to solution treatment. The relevant parameters of solution treatment are shown in Table 3.

[0045] 6) Second cold rolling: The strip after solution treatment is subjected to a second cold rolling process, with a processing rate of 20-70%;

[0046] 7) Aging treatment: The strip after the second cold rolling process is subjected to aging treatment. The relevant parameters of aging treatment are shown in Table 3 to obtain the finished chromium bronze alloy strip.

[0047] The difference between Comparative Examples 1 and 2 and Example 1 is that the solution treatment did not distinguish between the preheating zone and the high-temperature zone, but instead directly used a lower or higher temperature for heat treatment.

[0048] The microstructure, yield strength, electrical conductivity, stress retention rate, and bending performance of the alloy strips of Examples 1-15 and Comparative Examples 1-2 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 2.

[0049] 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.

[0050] Conductivity: The conductivity of the samples was tested according to GB / T 32791-2016 "Eddy Current Test Method for Conductivity of Copper and Copper Alloys".

[0051] Stress retention rate: The high-temperature stress relaxation test was conducted in accordance with GB / T 10120-2013 "Metallic Materials Tensile Stress Relaxation Test Method". A bending moment ring specimen was used for testing. A Vickers hardness indenter was used to make an indentation to mark the displacement of the specimen. The test was carried out at 150℃ for 1000 hours of exposure, and the stress retention rate was calculated.

[0052] Bending performance: A long strip sample with a width of 10 mm was taken along the rolling direction (i.e. the bad direction). Then, a V-shaped punch with a 90° angle and different radii at the tip was used to bend the long strip sample. The outer surface of the bending point was then observed with a stereomicroscope. The bending performance was expressed as the minimum bending radius R without surface cracking / plate thickness T.

[0053] Small-angle grain boundaries and large-angle grain boundaries: Based on the crystal orientation determined by the EBSD method, small-angle grain boundaries are defined as grain boundaries with an orientation difference of ≤15° between adjacent grains, and large-angle grain boundaries are grain boundaries with an orientation difference of >15° between adjacent grains. The corresponding percentages of small-angle and large-angle grain boundaries are the proportions of their number relative to the total number of crystal grain boundaries.

[0054] Texture proportion: The EBSD method was used to analyze the texture type and area proportion of the strip. The area proportion of each orientation refers to the ratio of the area within 15° of the deviation angle of each orientation to the measured area. The ratio of the area proportion 'a' of the S texture and the area proportion 'b' of the R texture was calculated.

[0055] According to the evaluation results shown in Table 2, the microstructures of Examples 1-15 of the present invention are within the scope of the present invention, achieving a good match between strength, conductivity, and etching performance. The yield strength is in the range of 500-650 MPa, the conductivity is ≥60% IACS, the stress retention rate after holding at 150℃ for 1000 h is above 85%, and the ratio of the bending radius r in the bad direction to the plate thickness t is r / t≤1 when bending at 90°. In the samples of Comparative Examples 1-2, although the strength and conductivity meet the requirements, the stress relaxation resistance and bending processing performance are significantly affected because the percentage of large-angle and small-angle grain boundaries is not controlled.

[0056] Table 1. Components of the Examples and Comparative Examples

[0057]

[0058] Table 2. Microstructure and properties of the embodiments and comparative examples

[0059]

[0060] Table 3 Key process parameter control for examples and comparative examples

[0061]

Claims

1. A chromium bronze alloy sheet strip characterized by: The chromium bronze alloy strip has the following weight percentage composition: 0.6–1.0 wt% Cr, 0.15–0.5 wt% Fe, 0.1–0.4 wt% Ti, and 0.01–0.12 wt% Si, with the balance being Cu and unavoidable impurities. The microstructure of the chromium bronze alloy strip contains 60–90% small-angle grain boundaries (L) and 10–40% large-angle grain boundaries (H). Small-angle grain boundaries are defined as grain boundaries with an orientation difference ≤ 15° between adjacent grains, and large-angle grain boundaries are defined as grain boundaries with an orientation difference > 15° between adjacent grains. The ratio of the percentage of small-angle grain boundaries (L) to the percentage of large-angle grain boundaries (H) satisfies: L / H ≥ 2.

2. The chromium bronze alloy sheet strip defined in claim 1 wherein: The microstructure of this chromium bronze alloy strip exhibits plate texture types including S-texture {123}. <634> and R texture {124} <211> The area proportion of S texture (a) is 20-40%, and the area proportion of R texture (b) is 15-35%.

3. The chromium bronze alloy sheet strip defined in claim 2 wherein: The area ratio 'a' of the S texture and the area ratio 'b' of the R texture satisfy 0.5 ≤ b / a ≤ 1.

2.

4. The chrome bronze alloy sheet strip of claim 1 wherein: The chromium bronze alloy strip also includes at least one element selected from Ni, Zr, Sn, Zn, Ag and Ce in a total weight percentage of less than 0.5 wt%.

5. The chrome bronze alloy sheet strip of claim 1 wherein: The chromium bronze alloy strip has a yield strength of 500-650 MPa, a conductivity of ≥60% IACS, and a stress retention rate of over 85% after being kept at 150℃ for 1000 hours. When bent at 90°, the ratio of the bending radius r in the bad direction to the plate thickness t is r / t≤1.

6. A method of producing a chromium bronze alloy sheet or strip as claimed in any one of claims 1 to 5, characterised in that: The preparation process is as follows: semi-molten casting → hot rolling → milling → first cold rolling → solution treatment → second cold rolling → aging treatment. The second cold rolling and subsequent aging treatment constitute one cycle step, and this cycle step is repeated several times. The solution treatment first passes through a preheating zone at a temperature of 800-850℃ and holds for 0.5-5 minutes, then passes through a high-temperature zone at 1020-1050℃ and holds for 0.1-2 minutes, and then cools to room temperature at a cooling rate of 100℃ / s or higher.

7. The method of making a sheet or strip of chromium bronze alloy according to claim 6, characterized in that: The aging treatment is carried out at an aging temperature of 400-550℃, with a heating rate of 20℃ / min or higher. After holding at the temperature for 6-10 hours, the temperature is cooled to room temperature at a cooling rate of 1-10℃ / min.

8. A connecting terminal made using a chromium bronze alloy plate or strip as described in any one of claims 1 to 5.

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