Copper alloy with excellent fatigue resistance and preparation method thereof

Abstract

The invention discloses a copper alloy with excellent fatigue resistance and a preparation method thereof.The copper alloy is composed of, by mass, 0.5-2.1 wt% of Ni, 0.1-0.4 wt% of P and the balance copper and unavoidable impurities, the microstructure of the copper alloy contains Ni-P atomic clusters, the average atomic content of Ni in the Ni-P atomic clusters is larger than or equal to 10 at.%, the average atomic content of P in the Ni-P atomic clusters is larger than or equal to 5 at. And the ratio of the average atom content of Ni to the average atom content of P satisfies that Ni / P is greater than or equal to 1 and less than or equal to 3. According to the copper alloy, high-density nano-scale Ni-rich and P-rich atomic clusters serve as a main strengthening structure, meanwhile, the content and proportion of Ni atoms and P atoms in the Ni-P atomic clusters are finely regulated and controlled, high conductivity and high strength are kept, meanwhile, good anti-fatigue performance is achieved, and the copper alloy is non-toxic, free of harmful elements and capable of meeting the environment-friendly requirement. The yield strength Rp0.2 of the strip is larger than or equal to 550 MPa, the fatigue strength is larger than or equal to 1 / 2 Rp0.2, and the thermal stress relaxation rate is smaller than or equal to 20% after the strip is exposed for 1000 h at the temperature of 150 DEG C.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of copper alloy and its application, and particularly relates to a copper alloy with excellent fatigue resistance and a preparation method thereof. BACKGROUND

[0002] The copper-nickel-phosphorus alloy has high strength, good electric conductivity and corrosion resistance, and good bending and processing performance, and is suitable for application scenarios such as mobile phone parts, electric vehicle connectors, current-carrying springs and junction boxes.

[0003] A relay is an electronic control device that can automatically control a switch, and the contact and repulsion of the contact are realized by the attracting force and releasing force generated by the small current coil. With the development of relays towards lightness and high conductivity, a copper alloy with high conductivity and high strength and good fatigue resistance is needed. The copper-nickel-phosphorus alloy gradually begins to be applied to the spring and relay products with high conductivity and high elasticity requirements due to its excellent comprehensive performance. The post-processes involved in such products mainly include stamping, blanking and welding, and therefore the bending, forming and welding performance of the copper-nickel-phosphorus alloy is also required. The mechanical life test is carried out after the assembly of the parts, and the elastic bending of the parts should not be broken under the condition that the stress is greater than 1 / 2 of the yield strength for 100 million times. However, in the application test process, the copper-nickel-phosphorus alloy strip usually has low contact connection reliability, structural loosening or fatigue fracture occurs during service, and problems such as poor signal and current transmission occur, which leads to the risk of product failure. According to the specific application requirements of the relay industry benchmark customers, the parts should not have the phenomenon of not conducting during the experiment, and the electrical parameters should meet the standard requirements after the experiment, so the existing copper-nickel-phosphorus alloy cannot meet the application requirements in the relay industry.

[0004] According to the current market development trend analysis, the copper-nickel-phosphorus alloy has excellent electric conductivity, thermal conductivity and mechanical properties, can meet the demand of large current transmission, and has good cold working forming property, so it is the preferred material for the relay industry in the future. At the same time, the anti-fatigue copper-nickel-phosphorus alloy also has great application potential in different industries. Therefore, it is of great significance and practical value to improve the fatigue strength of the copper-nickel-phosphorus alloy and develop a copper-nickel-phosphorus alloy with high strength, high electric conductivity and excellent fatigue resistance. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a copper alloy with excellent fatigue resistance and a preparation method thereof, which has good fatigue resistance while maintaining high electric conductivity and high strength, and is non-toxic and free of harmful elements, meeting the environmental protection requirements.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a copper alloy with excellent fatigue resistance, the mass percentage composition of the copper alloy is: Ni 0.5-2.1wt%, P 0.1-0.4wt%, and the rest is copper and inevitable impurities. The microstructure of the copper alloy contains Ni-P atomic clusters, the average atomic content of Ni in the Ni-P atomic clusters is ≥10at.%, the average atomic content of P is ≥5at.%, and the ratio of the average atomic content of Ni to the average atomic content of P satisfies: 1≤Ni / P≤3.

[0007] 0.5 to 2.1 wt% of Ni is added to the copper alloy of the present invention. When Ni and P are added simultaneously, Ni-P atomic clusters can be formed, which helps to improve the electrical conductivity and mechanical properties of the copper alloy. When the Ni content is less than 0.5 wt%, it cannot form Ni-P atomic clusters of sufficient quantity and density with the P element. Although the copper alloy has a high electrical conductivity, its fatigue resistance does not meet the use requirements, which limits its application in the market. When the Ni content is greater than 2.1 wt%, due to the limited content of the added P element, the Ni element cannot be completely consumed, and a part of Ni still remains in the copper matrix, affecting the electrical conductivity of the copper alloy. If too much P element is added, a large amount of brittle compounds will be formed, resulting in deterioration of the fatigue resistance of the copper alloy. Therefore, the Ni content in the copper alloy of the present invention is 0.5 to 2.1 wt%.

[0008] The copper alloy of the present invention adds 0.1 to 0.4 wt% of P. The added P element can form Ni-P atomic clusters with Ni element, thereby improving the electrical conductivity and mechanical properties of the copper alloy. However, when the P content is less than 0.1 wt%, too few Ni-P atomic clusters are formed, and the strengthening effect is not obvious, which affects the performance of the copper alloy. In the copper alloy of the present invention, the P content is controlled below 0.4 wt%. If it exceeds 0.4 wt%, it will lead to the precipitation of too many coarse NiP precipitated phases, whose orientation is incoherent with the matrix, which is detrimental to the fatigue resistance of the copper alloy. Only by adding an appropriate amount of P element can part of the P element be allowed to exist in the copper matrix in a free state through the control process, thereby playing the role of deoxidation and degassing, reducing oxide inclusions in the alloy, avoiding the initiation of crack sources, and effectively improving the fatigue resistance of the copper alloy. Therefore, the P content in the copper alloy of the present invention is 0.1 to 0.4 wt%.

[0009] The microstructure of the copper alloy of the present invention contains high-density nanometer-scale Ni-rich and P-rich atomic clusters, namely Ni-P atomic clusters, accompanied by a small amount of incoherent NiP precipitated phase. The shape of the Ni-P atomic clusters is irregular and coherent with the copper matrix. The Ni and P atomic pairs in the crystal structure occupy random positions, and the chemical composition between the Ni-P atomic clusters and the copper matrix transitions smoothly without a sudden change in composition interface. As the main strengthening structure of the copper alloy of the present invention, the Ni-P atomic clusters are nanometer-scale in size and are dispersed in the copper matrix, playing a role in pinning dislocations and strengthening the copper matrix. Since the Ni-P atomic clusters are completely coherent with the copper matrix and do not have a sudden change in crystal orientation interface, they have a strong elastic-plastic deformation ability and can suppress crack initiation during fatigue. At the same time, even if a small amount of impurities in the copper alloy act as crack sources, the Ni-P atomic clusters can also coordinate plastic deformation to resist crack propagation during fatigue. At high temperatures, Ni-P atomic clusters can decompose into free Ni and P atoms, improving the high temperature resistance and thermal stress relaxation resistance of copper alloys.

[0010] In the Ni-P atomic cluster, the average atomic content of Ni is ≥10at.%, the average atomic content of P is ≥5at.%, and the ratio of the average atomic content of Ni to the average atomic content of P satisfies: 1≤Ni / P≤3. If the content of Ni and P elements in the Ni-P atomic cluster is too low, the purification effect on the copper matrix is ​​not obvious, which will cause a decrease in conductivity. According to the extranuclear electron configuration of Ni and P atoms, when the ratio of the average atomic content of Ni to the average atomic content of P, Ni / P, is within the range of 1≤Ni / P≤3, the Ni-P atomic pairs have strong chemical bonds, which can form an ordered structure, reduce the scattering effect on electrons, and improve the conductivity of the copper alloy. At the same time, the structure has thermodynamic stability and can also play a strengthening role.

[0011] Preferably, in the microstructure of the copper alloy of the present invention, more than 90% of the Ni-P atomic clusters have an equivalent circle diameter distributed between 0.5 and 10 nm, and a surface density of 1×10 12 ~1×10 14 Pieces / mm 2; The surface density of Ni-P atomic clusters with an equivalent circular diameter distribution between 0.5 and 1 nm is denoted as a, the surface density of Ni-P atomic clusters with an equivalent circular diameter distribution between 1 and 5 nm is denoted as b, and the surface density of Ni-P atomic clusters with an equivalent circular diameter distribution between 5 and 10 nm is denoted as c, then the ratio of a, b, and c satisfies: a≥2b≥10c. In the copper alloy of the present invention, the size and surface density of Ni-P atomic clusters have an important influence on the electrical conductivity, strength and fatigue life of the material. The higher the proportion of fine Ni-P atomic clusters, the more obvious the improvement in the fatigue resistance of the material. By controlling the size and distribution of Ni-P atomic clusters, that is, the numerical ratio of a, b, and c, the electrical conductivity, strength and fatigue life of the copper alloy can be improved. In the copper alloy of the present invention, it is key to ensure that fine and dispersed Ni-P atomic clusters are formed first and to inhibit the precipitation and growth of NiP precipitated phase. If the number of fine Ni-P atomic clusters is insufficient, the electrical conductivity and strength of the copper alloy will be reduced; if the number of Ni-P atomic clusters is excessive, they are likely to further evolve into NiP precipitation phase particles, which will reduce the fatigue strength of the copper alloy. More preferably, a=2×10 12 ~8×10 13 Pieces / mm 2 , b = 1 × 10 12 ~3×10 13 Pieces / mm 2 , c≤1×10 11 Pieces / mm 2 .

[0012] Preferably, the ratio of the major axis of the Ni-P atomic cluster to the equivalent circular diameter is in the range of 1 to 1.5, where the major axis is the length of the longest line segment formed by connecting two arbitrary points on the outer edge of the Ni-P atomic cluster. Although the shape of the Ni-P atomic cluster is irregular, its major axis ratio can also intuitively indicate the contact transition between the atomic cluster and the substrate. Under the condition of the same area, Ni-P atomic clusters with a smaller major axis ratio have better resistance to fatigue cracking.

[0013] Preferably, the surface density of the incoherent NiP precipitate phase is less than 5×10 9 Pieces / mm 2, and the sum of the mass percentages of Ni atoms and P atoms in the free state in the copper alloy is not less than 0.01wt%. The above-mentioned incoherent NiP precipitate phase is in the form of a compound with a regular shape, a fixed atomic ratio and a crystal structure, a clear interface with the matrix, and a sudden change in chemical composition. To further improve the conductivity of the copper alloy, the precipitation of a small amount of smaller NiP precipitate phase particles (average 10-30nm) is allowed, but the process must be strictly controlled. Otherwise, the number of NiP precipitate phase particles will be too large and the size will be abnormally coarsened. The incoherent interface between the NiP precipitate phase and the copper matrix will act as a crack source, seriously affecting the fatigue resistance of the copper alloy. Free Ni atoms and P atoms exist in the copper matrix lattice in the form of replacement atoms. Since the atomic radius of the two is significantly different from that of copper atoms, they can cause lattice distortion and play a role in solid solution strengthening. If the sum of the mass percentages of free Ni atoms and P atoms is less than 0.01wt%, the effect on improving the strength and fatigue resistance of the copper alloy is limited. On the contrary, if the content of free Ni atoms and P atoms is too high, the electrical conductivity of the copper alloy will be greatly damaged.

[0014] The copper alloy of the present invention preferably includes no more than 2 wt% by weight of at least one of the following elements: B, Mg, Al, Si, Ca, Cr, Mn, Fe, Co, Zn, Zr, Nb, Mo, Ag, In, Sn, Sb, Te, and RE. The addition of these elements to the copper alloy of the present invention can improve the copper alloy's strength and fatigue resistance. However, the addition of these elements should not be too high, as this will not only reduce the copper alloy's electrical conductivity but also adversely affect its processing and fatigue resistance.

[0015] Yield strength Rp of the copper alloy strip of the present invention 0.2 ≥550MPa, fatigue strength ≥1 / 2Rp 0.2 , and the thermal stress relaxation rate after exposure at 150℃ for 1000h is ≤20%.

[0016] The copper alloy preparation method of the present invention primarily includes the following process flow: batching → melting and casting → hot rolling → rough rolling → solution pretreatment → online solution quenching → intermediate rolling → bell annealing → finishing rolling → final annealing. Sawing, milling, cleaning, and straightening processes can be performed before and after these main steps as needed.

[0017] The hot rolling process starts at a temperature of 900-950°C, with a holding time of 2-6 hours. The total hot rolling processing rate is greater than 90%, and the final rolling temperature is 750-800°C. After rolling to the target thickness, cooling water is used to achieve residual heat quenching. A shorter holding time prevents overheating of the ingot, while a higher final rolling temperature reduces the precipitation of solute atoms, providing a material basis for the formation of atomic clusters.

[0018] After milling, the hot-rolled strip is subjected to rough rolling to adjust the thickness. The total processing rate of rough rolling is greater than 90%. A higher rough rolling processing rate helps to further break up the residual primary phase and create a large number of nucleation points, which is beneficial to the recrystallization of the deformed structure and the dissolution of the precipitated phase in the subsequent online solution quenching process.

[0019] After rough rolling, solution pretreatment is performed at a temperature of 850-900°C for 10-30 minutes, followed by cooling to room temperature. This step, placed between rough rolling and in-line solution quenching, improves the uniformity of the recrystallized structure through relatively high pretreatment temperatures and duration, providing more suitable preconditions for the subsequent formation of atomic clusters.

[0020] Then, online solution quenching is performed with a solution temperature of 750-950°C, a material belt running speed of 3-30 m / min, water as the cooling medium, and a cooling rate exceeding 150°C / s. A higher solution temperature and a lower material belt running speed can ensure that the precipitated phase is completely dissolved back into the copper matrix, forming a supersaturated solid solution. The solution temperature and material belt running speed of online solution quenching are denoted as Ts and vs, respectively, where Ts is in °C and vs is in m / min. Ts and vs satisfy the following relationship:

[0021]

[0022] After online solution quenching, intermediate rolling is performed, with a total processing rate of 50-80%. A higher processing rate in intermediate rolling can introduce high-density dislocations into the recrystallized grains, providing distortion energy for the formation of atomic clusters. Keeping the total processing rate within 80% can reserve deformation for the subsequent finishing rolling process.

[0023] After intermediate rolling, bell annealing is performed at a temperature of 350-450°C. The bell annealing temperature and holding time are respectively denoted as T1 and t1, and T1 and t1 satisfy the relationship: t1 = 600-(0.6-0.9) × T1, where T1 is in °C and t1 is in min.

[0024] After the bell annealing, the steel is subjected to finish rolling, and the total processing rate of the finish rolling is 10-60%. Preferably, the total processing rate from the intermediate rolling to the finish rolling does not exceed 96%.

[0025] After finishing rolling, the finished product is annealed at a temperature of 325-425° C. The temperature and holding time of the finished product annealing are respectively recorded as T2 and t2, and T2 and t2 satisfy the relationship: t2=600-(0.6-0.9)×T2, where T2 is in degrees Celsius and t2 is in minutes.

[0026] By adjusting the relationship between the solution temperature and the material strip running speed during online solution quenching, the NiP precipitate phase and other impurities can be fully dissolved into atomic form and incorporated into the copper matrix, reducing the potential risk of crack initiation and thus improving the fatigue resistance of the copper alloy. At the same time, by controlling the relationship between the temperature and holding time during the hood annealing and finished annealing processes, high-density Ni-P atomic clusters can be formed while preventing the precipitation of coarse NiP precipitate phase particles, thereby strengthening the copper matrix, improving the electrical conductivity of the copper alloy, and ensuring its fatigue life.

[0027] Furthermore, the preparation method of the present invention controls T1 ≥ T2. Using a higher hood annealing temperature T1 facilitates the formation of high-density Ni-P atomic clusters, while also regulating the size and distribution of the Ni-P atomic clusters, thereby achieving dispersion strengthening. Using a lower final annealing temperature T2 further promotes the formation of Ni-P atomic clusters, while preventing the abnormal growth of Ni-P atomic clusters formed during hood annealing, and preventing the abnormally grown Ni-P atomic clusters from evolving into NiP precipitated phases.

[0028] Furthermore, the preparation method of the present invention controls Ts ≥ T1 + T2. A higher Ts allows the NiP precipitate phase and other impurities to be fully dissolved, while a lower T1 + T2 ensures that the material is in an under-aged state, that is, the Ni and P atoms are not completely precipitated, while ensuring that the sum of the free Ni and P solute atoms in the copper matrix is ​​above 0.01 wt%.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. Based on the copper-nickel-phosphorus alloy system, the copper alloy with excellent fatigue resistance of the present invention uses high-density nanoscale Ni-rich and P-rich atomic clusters, namely Ni-P atomic clusters, as the main strengthening structure, and the content and ratio of Ni and P atoms in the Ni-P atomic clusters are finely controlled. The Ni-P atomic clusters are completely coherent with the copper matrix, without crystal orientation mutations, and have a smooth transition in chemical composition. They are dispersed in the copper matrix, playing the role of pinning dislocations to strengthen the copper matrix, inhibiting crack initiation and propagation during fatigue, and significantly improving fatigue resistance while strengthening the copper matrix.

[0031] 2. The preparation method of the present invention ensures that the microstructure of the copper alloy contains Ni-P atomic clusters by precisely controlling processes such as online solution quenching, so that the copper alloy has good fatigue resistance while maintaining high conductivity and high strength. In addition, the copper alloy is non-toxic and free of harmful elements, meeting environmental protection requirements.

[0032] 3. The strip made of the copper alloy of the present invention is 1 / 2Rp 0.2The number of bending cycles without breaking under stress is greater than 10 million, and the thermal stress relaxation rate after exposure to 150°C for 1000 hours is ≤20%. The strip made of the copper alloy of the present invention maintains high strength (yield strength Rp 0.2 ≥550MPa), high electrical conductivity (≥60% IACS) and excellent fatigue resistance (fatigue strength ≥1 / 2Rp 0.2 ), and resistance to thermal stress relaxation, meeting the market demand for high-strength, high-conductivity and fatigue-resistant materials, and can be used in relays, electronic connectors, connectors, dynamic reeds and other products. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is clearly and completely described below through specific embodiments.

[0034] Twenty-six examples and six comparative examples were selected, with their specific compositions shown in Table 1. All were processed into finished strips with a thickness of 0.2 mm using the preparation method of the present invention. Key process parameters are shown in Table 2. The preparation process for the copper alloy strips of this embodiment is as follows: batching → melting and casting → sawing → hot rolling → milling → rough rolling → online solution quenching → intermediate rolling → bell annealing → cleaning → finishing rolling → finished product annealing → cleaning → tension leveling, specifically comprising the following steps:

[0035] 1) Batching and Casting: Prepare the raw materials and batch the materials according to the alloy chemical composition shown in Table 1. Use an induction furnace for smelting. Casting is performed after the composition meets the requirements and after sufficient degassing and slag removal. The melting temperature is 1250-1350°C and the casting temperature is 1160-1200°C.

[0036] 2) Hot rolling: hot rolling the steel into pieces after keeping the temperature at 900-950°C for 2-6 hours, with the total processing rate greater than 90% and the final rolling temperature at 750-800°C.

[0037] 3) Rough rolling: The hot-rolled strip is milled and then subjected to rough rolling, with the total rough rolling processing rate being 70-95%.

[0038] 4) Solution pretreatment: The pretreatment temperature is 850-900℃, the pretreatment time is 10-30min, and then cooled to room temperature.

[0039] 5) Online solution quenching: The rough-rolled strip is subjected to online solution quenching treatment. The solution temperature and strip running speed are shown in Table 2. The cooling medium is water, and the cooling speed exceeds 150°C / s. The online solution quenching temperature is recorded as Ts, and the strip running speed is recorded as vs. The unit of Ts is °C, and the unit of vs is m / min. Then Ts and vs satisfy the relationship:

[0040] 6) intermediate rolling: the strip after solution quenching is subjected to intermediate rolling processing, and the total processing rate of the intermediate rolling is 50-80%.

[0041] 7) batch annealing: the strip after intermediate rolling processing is subjected to batch annealing treatment, and the parameters of the batch annealing are shown in Table 2, wherein the temperature T1 of the batch annealing and the holding time t1 satisfy the relationship: t1 = 600-(0.6-0.9) x T1, wherein the unit of T1 is degree Celsius, and the unit of t1 is minute.

[0042] 8) finish rolling: the strip after batch treatment is cleaned and then subjected to finish rolling processing, and the total processing rate of the finish rolling is 10-60%.

[0043] 9) product annealing: the strip after finish rolling processing is subjected to product annealing treatment, and the parameters of the product annealing are shown in Table 2, wherein the product annealing temperature T2 and the holding time t2 satisfy the relationship: t2 = 600-(0.6-0.9) x T2, wherein the unit of T2 is degree Celsius, and the unit of t2 is minute.

[0044] The alloy component design and preparation method of the examples are strictly performed according to the above technical scheme, and the components or processing technology in the comparative examples are different from the present application as follows:

[0045] The difference between Comparative Example 1 and Example 1 is that the content of Ni element in the alloy component is lower than the lower limit, and the content of P element is relatively high.

[0046] The difference between Comparative Example 2 and Example 7 is that the running speed of the strip in the online solution quenching process is higher, which is 40 m / min.

[0047] The difference between Comparative Example 3 and Example 10 is that the temperature used in the online solution quenching is higher, which is 960℃.

[0048] The difference between Comparative Example 4 and Example 14 is that the temperature used in the online solution quenching is lower, which is 740℃.

[0049] The difference between Comparative Example 5 and Example 23 is that the running speed of the strip in the online solution quenching process is lower, which is 2.5 m / min.

[0050] The difference between Comparative Example 6 and Example 17 is that the contents of Ni and P elements both exceed the range of the present application.

[0051] The electrical conductivity, yield strength, fatigue resistance and microstructure of the alloy strip of Examples 1-26 and Comparative Examples 1-6 of the present application are evaluated according to the methods specified in the relevant national standards and industry standards, specifically:

[0052] The conductivity is tested in accordance with GB / T 32791-2016 Eddy Current Test Method for Electrical Conductivity of Copper and Copper Alloys. The sample thickness is 0.2 mm, and three samples are stacked for measurement. The test frequency is 480 kHz, and the results are expressed in % IACS.

[0053] The yield strength is tested on an electronic universal mechanical properties testing machine in accordance with "GB / T 228.1-2021 Metallic Materials Tensile Tests Part 1: Room Temperature Test Method" at a tensile speed of 5 mm / min.

[0054] Fatigue strength is defined as the maximum bending stress a material can withstand without breaking under 10 million cycles of loading. Fatigue strength is tested on a fatigue testing machine using the JCBA-T308-2018 Repeated Plane Bending Fatigue Test Standard at a frequency of 50 Hz and an amplitude of 2 mm. The bending stress is determined based on the material's yield strength and is generally between 0.4 and 0.6 Rp0.2.

[0055] The thermal stress relaxation performance was tested using the ASTM E328-2013 Standard Test Methods for StressRelaxation Tests for Materials and Structures. The test conditions were: exposure temperature of 150°C and test time of 1000 h.

[0056] Microstructure characterization and quantitative analysis:

[0057] Since the Ni-P atomic clusters are extremely small, at the nanometer level, a transmission electron microscope (FEITalos F200X) was used for observation. More than ten STEM and HRTEM images were taken perpendicular to the strip plane, with a magnification of 2 million times and a field size of 10,000 nm. 2 The elemental composition and atomic ratio of Ni-P atomic clusters were determined with the help of energy spectrum distribution technology, and the crystal structure and unit cell parameters of Ni-P atomic clusters were calibrated with the help of crystallographic orientation analysis technology, so as to distinguish Ni-P atomic clusters from NiP precipitated phases.

[0058] The test and calculation method for the average content and ratio of Ni and P in Ni-P atomic clusters is as follows: switch to the energy spectrum point measurement mode, select the approximate center area of ​​the Ni-P atomic cluster, wait for 5 seconds for signal acquisition, and obtain the atomic percentage of the element content, where the ratio of the atomic percentage of Ni element to the atomic percentage of P element is the Ni / P atomic ratio Ni / P; shoot three fields of view, select 10 Ni-P atomic clusters in each field of view for element content test, and the average Ni and P content of the Ni-P atomic cluster is the average value of the element content of 3*10 Ni-P atomic clusters.

[0059] Calculation of the equivalent circular diameter and surface density of Ni-P atomic clusters: The image processing software ImageJ was used to calculate the equivalent circular diameter and number of Ni-P atomic clusters. The surface density was calculated by dividing the number of Ni-P atomic clusters in the photograph by the area represented by the photograph. The equivalent circular diameter of the Ni-P atomic cluster was calculated by converting the area of ​​the atomic cluster into a circle of equal area. The equivalent diameter of this circle was recorded as the equivalent circular diameter of the Ni-P atomic cluster. The final equivalent circular diameter and surface density of the Ni-P atomic clusters were averaged from the statistical results of ten photographs. The mass percentage of free Ni and P elements in the copper matrix was measured by using the energy spectrum point measurement mode in STEM imaging mode. During measurement, care was taken to avoid grain boundaries, Ni-P atomic clusters, and NiP phases (Ni-P atomic clusters have obvious element enrichment, and NiP precipitates are regular granular). Clean grain areas in the copper matrix were selected for composition analysis. More than 10 points were measured in each field of view, and a total of 10 fields were counted. The final sum of the mass percentages of Ni and P elements is the average of all the point measurement results in ten fields of view.

[0060] Major axis ratio: The length of the longest line segment connecting two arbitrary points on the outer edge of the Ni-P atomic cluster is defined as the major axis. According to the same point selection rule as mentioned above, the ratio of the major axis of the Ni-P atomic cluster to the equivalent circle diameter is calculated and the average value is taken.

[0061] Table 3 shows the test results of various properties and microstructures of the Examples and Comparative Examples. As can be seen from Table 3, the copper alloy of the present invention exhibits excellent fatigue resistance while maintaining high strength and conductivity. The number of unbroken bending cycles under a stress of 1 / 2Rp0.2 exceeds 10 million. The alloy also exhibits excellent resistance to thermal stress relaxation, effectively meeting the fatigue resistance requirements of copper alloys in various applications.

[0062] By comparing comparative examples 1 to 6, it can be seen that since the Ni and P contents are outside the scope of the present invention, the mechanical properties, stress relaxation resistance and fatigue performance of the strip deteriorate; and if the strip running speed is too fast or the solution quenching temperature is too low during online solution quenching, it will lead to insufficient solid solution, and a large amount of coarse primary phase will remain in the matrix, which will deteriorate the fatigue performance; on the contrary, if the running speed is too slow or the solution quenching temperature is too high, it will lead to abnormal grain growth and reduced strength and fatigue performance.

[0063] Table 1 Chemical composition of the embodiments of the present invention

[0064]

[0065] Table 2 Key process control parameters of the embodiment of the present invention

[0066]

[0067] Table 3 Performance test results of the embodiments of the present invention and comparative examples

[0068]

[0069] Table 4 Microstructure characterization results of the embodiments of the present invention and the comparative examples

[0070]

Claims

1. A copper alloy with excellent fatigue resistance, characterized in that: The copper alloy comprises 0.5-2.1 wt% Ni, 0.1-0.4 wt% P, and the remainder copper and unavoidable impurities. The microstructure of the copper alloy contains Ni-P atomic clusters, wherein the average atomic content of Ni in the Ni-P atomic clusters is ≥10 at.%, the average atomic content of P is ≥5 at.%, and the ratio of the average atomic content of Ni to the average atomic content of P satisfies the following conditions: 1≤Ni / P≤3.

2. The copper alloy having excellent fatigue resistance according to claim 1, characterized in that: More than 90% of the Ni-P atomic clusters have an equivalent circular diameter ranging from 0.5 to 10 nm, with a surface density of 1×10 12 ~1×10 14 Pieces / mm 2 ; The surface density of Ni-P atomic clusters with equivalent circular diameters distributed between 0.5 and 1 nm is denoted as a, the surface density of Ni-P atomic clusters with equivalent circular diameters distributed between 1 and 5 nm is denoted as b, and the surface density of Ni-P atomic clusters with equivalent circular diameters distributed between 5 and 10 nm is denoted as c, then the ratio relationship of a, b, and c satisfies: a≥2b≥10c.

3. The copper alloy having excellent fatigue resistance according to claim 2, characterized in that: a=2×10 12 ~8×10 13 Pieces / mm 2 , b = 1 × 10 12 ~3×10 13 Pieces / mm 2 , c≤1×10 11 Pieces / mm 2 .

4. The copper alloy with excellent fatigue resistance according to claim 1, characterized in that: The ratio of the major axis of the Ni-P atomic cluster to the equivalent circle diameter is in the range of 1 to 1.5, wherein the major axis is the length of the longest line segment in the line segment connecting any two points on the outer edge of the Ni-P atomic cluster.

5. The copper alloy having excellent fatigue resistance according to claim 1, characterized in that: The surface density of the incoherent NiP precipitate phase is less than 5×10 9 Pieces / mm 2 , and the sum of the mass percentages of Ni atoms and P atoms existing in the copper alloy in a free state is not less than 0.01wt%.

6. The copper alloy having excellent fatigue resistance according to claim 1, characterized in that: The copper alloy also includes, in its mass percentage composition, at least one element selected from the group consisting of B, Mg, Al, Si, Ca, Cr, Mn, Fe, Co, Zn, Zr, Nb, Mo, Ag, In, Sn, Sb, Te, and RE elements, with a total amount not exceeding 2 wt%.

7. The copper alloy having excellent fatigue resistance according to any one of claims 1 to 6, characterized in that: The yield strength Rp of the copper alloy strip 0.2 ≥550MPa, fatigue strength ≥1 / 2Rp 0.2 , and the thermal stress relaxation rate after exposure at 150℃ for 1000h is ≤20%.

8. The method for preparing the copper alloy having excellent fatigue resistance according to any one of claims 1 to 7, characterized in that: The process mainly includes the following steps: batching → melting and casting → hot rolling → rough rolling → solution pretreatment → online solution quenching → intermediate rolling → bell annealing → finishing rolling → finished product annealing. The solution temperature and the material strip running speed of the online solution quenching are respectively denoted as Ts and vs, where the unit of Ts is °C and the unit of vs is m / min. Ts = 750-950 °C. Ts and vs satisfy the following relationship:

9. The method for preparing the copper alloy with excellent fatigue resistance according to claim 8, characterized in that: The temperature and holding time of the bell annealing are respectively recorded as T1 and t1, and the temperature and holding time of the finished product annealing are respectively recorded as T2 and t2, wherein the units of T1 and T2 are both °C, and the units of t1 and t2 are both min, T1 = 350-450 °C, T2 = 325-425 °C, and T1 and t1, T2 and t2 respectively satisfy the following relationship: t1=600-(0.6~0.9)×T1 t2=600-(0.6~0.9)×T2 10. The method for preparing a copper alloy with excellent fatigue resistance according to claim 9, characterized in that: T1≥T2, Ts≥T1+T2.

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