Micro-alloyed copper-chromium-zirconium alloy, and strip preparation method and application thereof

Abstract

This invention discloses a microalloyed copper-chromium-zirconium alloy. The alloy comprises the following components by mass percentage: Cr: 0.2–1.2%, Zr: 0.05–0.2%, Ni: 0.01–0.05%, Si: 0.001–0.01%, Ti: 0.002–0.006%, Re: 0.001–0.008%, where Re is two or more of Sc, La, Y, and Ce. The microstructure of this microalloyed copper-chromium-zirconium alloy includes a second phase, which comprises a composite nano-precipitate containing Ni, Si, Cr, and Zr. This copper-chromium-zirconium alloy exhibits high strength and electrical conductivity, as well as good bending and high-temperature softening resistance. This invention also discloses a method for preparing the sheet / strip of this microalloyed copper-chromium-zirconium alloy and its application in connectors.

Description

Technical Field

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

[0002] Driven by technological iterations in fields such as new energy vehicles, large-scale energy storage systems, industrial high-frequency inverter equipment, and aerospace power transmission, high-voltage power transmission systems are rapidly evolving towards higher voltage, higher current, miniaturization, and longer lifespan. As a core component enabling reliable interconnection of electrical energy and signals within the system, high-voltage connectors are facing increasingly demanding operating environments—the voltage levels in mainstream applications have generally exceeded 400V, and 800V ultra-high-voltage platforms have become standard in new energy vehicles, fast-charging stations, and other fields. In some industrial and aerospace applications, the withstand voltage can reach over 1500V, with operating currents reaching 250~500A. The reliability of high-voltage connectors directly determines the safety and operational efficiency of the entire high-voltage system, and the material properties of their core load-bearing components, the conductive contacts, are a key bottleneck restricting breakthroughs in the overall performance of connectors.

[0003] To address the challenge of balancing high strength and high conductivity in high-voltage connector contacts, precipitation-strengthened copper alloys have emerged. Among them, copper-chromium-zirconium (Cu-Cr-Zr) alloys are a typical example. By adding chromium and zirconium to a copper matrix and employing a solution-aging heat treatment process, chromium intermetallic compound particles are dispersed and precipitated within the matrix. These uniformly distributed precipitates effectively hinder dislocation movement, thereby significantly improving the alloy's strength, hardness, and heat resistance. Simultaneously, the matrix maintains high purity after precipitation strengthening, allowing the alloy to achieve excellent electrical and thermal conductivity, thus making it an ideal candidate material for high-voltage connector contacts.

[0004] However, in the practical application of existing Cu-Cr-Zr alloys in high-voltage connectors, the following core technical pain points still need to be addressed: (1) The balance between strength and conductivity is still not ideal. Existing technologies usually improve strength by increasing the content of chromium and zirconium or applying a large amount of cold deformation, but this can easily lead to a decrease in the plasticity of the alloy, and cracking is very likely to occur during bending. Conversely, if high conductivity and good plasticity are prioritized, the strength of the alloy often cannot meet the requirements of high-end high-voltage connectors for anti-insertion and anti-vibration. (2) Elements are easily oxidized and have low process stability. Chromium and zirconium are chemically active and are easily oxidized to form inclusions during the smelting process. This not only causes the loss of effective alloy elements, but also introduces defects into the copper matrix, becoming the source of cracks caused by arc impact and insertion stress during the subsequent processing and service of high-voltage connector contacts.

[0005] Patent application CN112030032A discloses a Cu-Cr-Ti-Zr alloy and a method for processing copper strip. The alloy composition is as follows: 0.1wt.%-0.8wt.% Cr, 0.01wt.%-0.20wt.% Ti, 0.001wt.%-0.2wt.% Zr, 0.002wt.%-0.20wt.% Ag, 0.02wt.%-0.07wt.% Si, 0.001wt.%-0.05wt.% P, 0.02wt.%-0.20wt.% Fe, 0.005wt.%-0.10wt.% Mg; one or more elements selected from Ni, Mn, Sn, Ce, Zn, Al, Sr, and Co, with a total content not exceeding 0.15wt.%; the balance being copper and unavoidable impurities. The copper strip processing method described includes the following steps: batching, smelting, casting, sawing, heating, hot rolling, solution treatment, milling, rolling, aging annealing, cleaning, performance testing, finished product shearing, and packaging. The copper alloy material and copper strip of this invention have advantages such as high strength, excellent electrical conductivity, excellent bending performance, and excellent resistance to stress relaxation, and the chemical composition of the material is stable. However, the tensile strength and electrical conductivity of the copper alloy disclosed in this patent application need to be improved.

[0006] In view of the shortcomings of existing technologies, there is an urgent need to design copper alloys with high strength and conductivity, as well as good bending and high-temperature softening resistance. Summary of the Invention

[0007] The present invention provides a microalloyed copper-chromium-zirconium alloy, which has high strength and electrical conductivity, as well as good bending resistance and high-temperature softening resistance.

[0008] This invention provides a microalloyed copper-chromium-zirconium alloy, wherein the mass percentages of each component of the microalloyed copper-chromium-zirconium alloy are as follows: Cr: 0.2-1.2%, Zr: 0.05-0.2%, Ni: 0.01-0.05%, Si: 0.001-0.01%, Ti: 0.002-0.006%, Re: 0.001-0.008%, with the balance being Cu, where Re is two or more of Sc, La, Y, and Ce. The microstructure of the microalloyed copper-chromium-zirconium alloy includes a second phase, which comprises a composite nanoprecipitate containing Ni, Si, Cr and Zr.

[0009] This invention, based on a Cu-Cr-Zr alloy, adds trace amounts of Ni and Si to exert a synergistic effect. Under appropriate solution treatment and first-stage aging annealing, these Ni and Si co-precipitate with Cr and Zr to form a composite nano-precipitate phase. Utilizing the aging and solution strengthening effects of this composite nano-precipitate phase, the alloy's yield strength, tensile strength, and softening temperature are significantly improved, while the impact on electrical conductivity is extremely limited. If the Cr content is too high, the low solid solubility easily leads to the formation of coarse primary phases, resulting in decreased strengthening effect, poor plasticity and electrical conductivity, and deteriorated machinability. Excessive Zr easily forms coarse intermetallic compounds, reducing strengthening and thermal stability, impairing electrical conductivity, and increasing casting and forming difficulties.

[0010] This invention adds an appropriate amount of Ti element, which can be enriched on the Cr surface to form a heterogeneous nucleation core, providing sufficient nucleation sites for aging precipitation and minimizing element aggregation. Combined with hot rolling and multi-pass cold rolling to accumulate deformation energy storage, a second phase of appropriate size and relatively uniform distribution can be precipitated during the aging process, thereby obtaining better mechanical properties.

[0011] This invention strictly controls the addition of Ni, Si, and Ti within a trace range, which can avoid the formation of coarse second phases or harmful impurity phases due to excessive introduction, and ensure that the core strengthening mechanism of Cr and Zr is not interfered with.

[0012] This invention provides two or more trace rare earth elements that can further refine the grains, improve the strength of the alloy, and have minimal impact on conductivity, thereby comprehensively optimizing the overall performance of the alloy.

[0013] In summary, the composition design provided by this invention retains the fundamental advantages of Cu-Cr-Zr alloys while effectively compensating for the shortcomings of a single strengthening mechanism through multi-element microalloying, making it particularly suitable for applications with stringent requirements for strength and high-temperature stability. Furthermore, the addition of trace amounts of rare earth elements further refines the grain size, enhances alloy strength, and has minimal impact on conductivity, thereby comprehensively optimizing the alloy's overall performance.

[0014] Preferably, the Si content is 0.003–0.006%, and the Ni content is 0.011–0.042%.

[0015] Preferably, the average size of the second phase is 5~30 nm. This invention controls the Ti element content, causing Ti to accumulate on the Cr surface, forming nucleation heterogeneous points, while avoiding Cr aggregation. Through hot rolling followed by multiple cold rolling cycles, appropriate deformation energy is accumulated, resulting in a uniformly distributed second phase of suitable size. Controlling the size of the second phase in this invention is beneficial for obtaining copper-zirconium alloys with high strength, good bending resistance, and resistance to high-temperature softening.

[0016] More preferably, the average size of the second phase is 5-20 nm.

[0017] Preferably, the second phase further includes a nano-scale Cr phase and a nano-scale Cu5Zr phase. By controlling the content of Cr and Zr and combining a solid solution-precipitation process, this invention can obtain nano-scale Cr and Cu5Zr phases, achieving effective precipitation strengthening without significantly impairing the electrical and thermal conductivity of the copper matrix, precisely meeting the core performance requirements of this type of alloy.

[0018] Preferably, the average grain size of the microalloyed copper-chromium-zirconium alloy is 5~15 μm. This invention controls the average grain size of the copper-chromium-zirconium alloy to a small level by adding multiple types of rare earth elements, thereby ensuring good mechanical properties.

[0019] More preferably, the average grain size of the microalloyed copper-chromium-zirconium alloy is 5-10 μm.

[0020] Preferably, the microalloyed copper-chromium-zirconium alloy has a hardness of 145-210 HV, a tensile strength of 500-710 MPa, a conductivity of 75-90% IACS, and a softening temperature of 520-580℃.

[0021] Preferably, the microalloyed copper-chromium-zirconium alloy has a hardness of 165-210 HV, a tensile strength of 600-710 MPa, a conductivity of 80-90% IACS, and a softening temperature of 520-580℃.

[0022] On the other hand, the present invention also provides a method for preparing microalloyed copper-chromium-zirconium alloy plates and strips, wherein the microalloyed copper-chromium-zirconium alloy is used to prepare microalloyed copper-chromium-zirconium alloy plates and strips. The process flow of the preparation method includes melting and casting → ingot homogenization heat treatment → hot rolling → first cold rolling → solution treatment → second cold rolling → first-stage aging annealing → third-stage cold rolling → second-stage aging annealing. The components of the microalloyed copper-chromium-zirconium alloy are batched and smelted according to their respective mass percentages. The solution treatment is performed at a temperature of 850~1050℃ for 1-15 minutes.

[0023] Preferably, the solution treatment temperature is 900~1000℃ and the time is 1-15min.

[0024] Because this invention incorporates trace elements, the solution treatment is performed after a single cold rolling process. This allows the strengthening elements to fully dissolve in a thick material with minimal deformation and a relatively uniform microstructure, forming a highly supersaturated solid solution. This ensures the strengthening effect of subsequent aging. Furthermore, since the addition of trace elements such as Ni, Si, and Ti can exacerbate microstructure inhomogeneity during early deformation, this invention performs a solution treatment in advance to eliminate the microstructure inhomogeneity problem left over from deformation. The solution treatment temperature is increased, and the solution treatment time is controlled to prevent the microstructure inhomogeneity problem from being left until aging annealing, which would be impossible to eliminate. This also ensures the full dissolution of each element.

[0025] In the process flow, the first cold rolling, placed after hot rolling, can significantly increase the density of crystal defects and dislocations, providing sufficient nucleation sites for age-aged precipitates. After solution heat treatment, the second cold rolling makes the precipitate distribution more uniform, thereby improving strength and resistance to high-temperature softening. After the first-stage aging heat treatment, the third cold rolling further adjusts the spatial distribution uniformity of the precipitates. Combined with the second-stage aging heat treatment, it is more conducive to the precipitation and distribution of composite nanoprecipitates.

[0026] Preferably, in the casting process, copper-zirconium raw materials are continuously added at a rate of 0.2 to 1 kg per minute.

[0027] The present invention continuously and uninterruptedly adds copper-zirconium master alloy during the casting process. Compared with the intermittent feeding method of the prior art, due to the extremely high reactivity of zirconium, it is very easy to burn off. When not added, the strength decreases due to the loss of zirconium. This makes the strength of the microalloyed copper-chromium-zirconium alloy more stable.

[0028] Based on experiments conducted on the size of a typical heat preservation furnace and the burn-off conditions, this invention, by controlling the feeding rate, ensures the addition of an appropriate amount of Zr, resulting in a smaller difference in Zr content at different locations in the billet, thereby ensuring relatively stable tensile strength at different locations in the billet.

[0029] The microalloyed copper-chromium-zirconium alloy provided by this invention has a tensile strength stability of 500-710 MPa.

[0030] More preferably, in the casting process of the present invention, copper and titanium raw materials are continuously added at a rate of 0.2 to 1 kg per minute.

[0031] Preferably, the melting and casting process is as follows: melting is carried out in a non-vacuum medium-frequency induction furnace, the raw materials are proportioned and then melted in a non-vacuum medium-frequency induction furnace, the melting temperature is 1200~1350℃, and the casting temperature is 1100~1250℃.

[0032] More preferably, an electrolytic copper plate is added to the melting furnace, and after melting, a pure nickel sheet is added. Elements such as Sc, La, Y, or Ce are added to the melt using an intermediate alloy. After melting at 1260~1350℃, the melt is transferred to a holding furnace. Add copper-zirconium master alloy and sponge titanium to the holding furnace. After the composition is qualified, cool down to 1180~1250℃ and then perform casting. During the casting process, use a wire feeder to add copper-zirconium cored wire at a rate of 0.2~1kg per minute.

[0033] Preferably, the homogenization heat treatment of the ingot is performed at a temperature of 850–1020 °C for 3–6 h. This invention, by controlling the temperature and time of the homogenization heat treatment of the ingot, can eliminate casting segregation, dissolve coarse second phases, and release internal stress, significantly improving the plasticity of subsequent processing. Low temperatures result in insufficient diffusion rates, making it difficult to fully eliminate segregation and coarse phases. High temperatures easily lead to overheating, abnormal grain coarsening, or even localized melting, which deteriorates plasticity and properties. Short treatment times result in insufficient diffusion and poor homogenization; long treatment times lead to excessive grain coarsening, decreased plasticity, and increased energy consumption and production cycle.

[0034] Preferably, the total processing rate of the hot rolling is 80% or more, and the total processing rate of the single cold rolling is 80-90%. More preferably, the total processing rate of the hot rolling is 85%-90%.

[0035] This invention controls the processing rate of hot rolling and one-time cold rolling to enable the billet to recrystallize from the as-cast structure, forming a more uniform recrystallized structure.

[0036] Preferably, the temperature of the first-stage aging annealing is 300-500℃, and the holding time is 5-15h.

[0037] More preferably, the first-stage aging annealing is performed using a bell-type annealing furnace, in which a mixture of hydrogen and nitrogen gas is used to prevent oxidation of the strip and sheet.

[0038] This invention promotes the nucleation of fine, dispersed strengthening phases and avoids coarse precipitates by controlling the temperature and holding time of the first-stage aging annealing, thus laying a good microstructure foundation for the second-stage aging. At the same time, it can also soften the billet after the second cold rolling, improve its plasticity, facilitate subsequent rolling, and effectively prevent cracking during the rolling process.

[0039] Preferably, the total processing rate of the secondary cold rolling is 40-90%, and the total processing rate of the tertiary cold rolling is 15-70%. By controlling the total processing rate of the secondary and tertiary cold rolling, the present invention can obtain the required strip size, refine the grains, and provide sufficient energy for the precipitation of the second phase during the secondary aging process.

[0040] Preferably, the temperature of the secondary aging annealing is 400-600℃, and the holding time is 4-10h.

[0041] This invention forces the precipitated phase to nucleate and grow synchronously throughout the matrix by controlling the temperature and holding time of the second-stage aging process, resulting in a denser and more uniform structure. At the same time, after the second-stage high-temperature stabilization treatment, the precipitated phase reaches a thermodynamically stable state, which can effectively inhibit over-aging softening under long-term use or high-temperature environment, resulting in higher product life and reliability.

[0042] More preferably, the secondary aging process employs a bell-type annealing furnace, in which a mixture of hydrogen and nitrogen gas is used to prevent strip oxidation.

[0043] On the other hand, the present invention also provides the application of the aforementioned microalloyed copper-chromium-zirconium alloy in connectors.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention, by adding trace amounts of Ni and Si elements, can co-precipitate with Cr and Zr to form a composite nano-precipitate phase. Compared with the prior art which only contains Cr phase and Cu5Zr phase, this composite nano-precipitate phase can significantly improve the yield strength, tensile strength and softening temperature of the alloy through solid solution strengthening and precipitation strengthening, while having a very limited effect on electrical conductivity. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to the embodiments.

[0046] This invention provides 5 embodiments and 13 comparative examples, and the specific components are shown in Table 1.

[0047] Examples 1-2: This invention provides a method for preparing microalloyed copper-chromium-zirconium strip, comprising: (1) Melting and casting: Melting is carried out in a non-vacuum medium-frequency induction furnace. Electrolytic copper plates are added to the melting furnace, and pure nickel sheets are added after melting. Elements such as Sc, La, Y, or Ce are added to the melt using intermediate alloys. The temperature is raised to 1290℃ to melt, and the temperature is held for 30 minutes to take samples for composition testing. After the composition is qualified, it is transferred to a holding furnace. Copper-zirconium intermediate alloy and sponge titanium are added to the holding furnace. After the composition is qualified, the temperature is lowered to 1240℃ and then cast. During the casting process, copper-zirconium cored wire is added at a rate of 0.8 kg per minute using a wire feeder.

[0048] (2) Homogenization heat treatment of ingots: The ingots are placed in a walking beam furnace at 890°C for 6 hours.

[0049] (3) Hot rolling: The total processing volume is 88%, and water cooling is used.

[0050] (4) One-time cold rolling: The total processing volume is 90%.

[0051] (5) Solution treatment: The temperature of solution heat treatment is 950℃ and the time is 12min. Then, the product is taken out of the furnace and quickly cooled to room temperature.

[0052] (6) Secondary cold rolling: The total processing volume is 63%.

[0053] (7) First-level aging annealing: 400℃ for 10h, with hydrogen and nitrogen mixed gas used for protection inside the furnace, and the furnace exit temperature <50℃.

[0054] (8) Three-stage cold rolling: processing amount is 40%. (9) Secondary aging annealing: 460℃ for 5 hours, with hydrogen and nitrogen mixed gas used for protection inside the furnace, and the furnace exit temperature <50℃.

[0055] Example 3: (1) Melting and casting: Melting was carried out in a non-vacuum medium-frequency induction furnace. Electrolytic copper plates were added to the melting furnace, and pure nickel sheets were added after melting. Elements such as Sc, La, Y, or Ce were added to the melt using intermediate alloys. The temperature was raised to 1280℃ to melt, and the composition was tested after holding for 30 minutes. After the composition was qualified, the melt was transferred to a holding furnace. Copper-zirconium intermediate alloy and sponge titanium were added to the holding furnace. After the composition was tested and qualified, the temperature was lowered to 1200℃ and then cast. During the casting process, copper-zirconium cored wire was added at a rate of 0.4 kg per minute using a wire feeder.

[0056] (2) Homogenization heat treatment of ingots: The ingots are placed in a walking beam furnace at 920°C for 4 hours.

[0057] (3) Hot rolling: The total processing volume is 83%, and water cooling is used.

[0058] (4) One-time cold rolling: The total processing volume is 87%.

[0059] (5) Solution treatment: The temperature of solution heat treatment is 960℃ and the time is 6min. Then, the product is taken out of the furnace and quickly cooled to room temperature.

[0060] (6) Secondary cold rolling: The total processing volume is 75%.

[0061] (7) First-level aging annealing: 440℃ for 10h, with hydrogen and nitrogen mixed gas used for protection inside the furnace, and the furnace exit temperature <50℃.

[0062] (8) Three-stage cold rolling: The total processing volume is 35%. (9) Secondary aging annealing: 480℃ for 6 hours, with hydrogen and nitrogen mixed gas used for protection inside the furnace, and the furnace exit temperature <50℃. Example

[0063] (1) Melting and casting: Melting is carried out in a non-vacuum medium-frequency induction furnace. Electrolytic copper plates are added to the melting furnace, and pure nickel sheets are added after melting. Elements such as Sc, La, Y, or Ce are added to the melt using intermediate alloys. The temperature is raised to 1280℃ to melt, and the temperature is held for 30 minutes to take samples for composition testing. After the composition is qualified, it is transferred to a holding furnace. Copper-zirconium intermediate alloy and sponge titanium are added to the holding furnace. After the composition is qualified, the temperature is lowered to 1210℃ and then cast. During the casting process, copper-zirconium cored wire is added at a rate of 0.6 kg per minute using a wire feeder.

[0064] (2) Homogenization heat treatment of ingots: The ingots are placed in a walking beam furnace at 880°C for 6 hours.

[0065] (3) Hot rolling: The total processing volume is 91%, water cooling.

[0066] (4) One-time cold rolling: The total processing volume is 86%.

[0067] (5) Solution treatment: The temperature of solution heat treatment is 900℃ and the time is 15min. Then, the product is taken out of the furnace and quickly cooled to room temperature.

[0068] (6) Secondary cold rolling: The total processing volume is 60%.

[0069] (7) First-level aging annealing: 400℃ for 10h, with hydrogen and nitrogen mixed gas used for protection inside the furnace, and the furnace exit temperature <50℃.

[0070] (8) Three-stage cold rolling: The total processing volume is 45%.

[0071] (9) Secondary aging annealing: 460℃ for 5 hours, with hydrogen and nitrogen mixed gas used for protection inside the furnace, and the furnace exit temperature <50℃.

[0072] Example 5: (1) Melting and casting: Melting was carried out in a non-vacuum medium-frequency induction furnace. Electrolytic copper plates were added to the melting furnace, and pure nickel sheets were added after melting. Elements such as Sc, La, Y, or Ce were added to the melt using intermediate alloys. The temperature was raised to 1300℃ to melt, and the composition was tested after holding for 30 minutes. After the composition was qualified, the melt was transferred to a holding furnace. Copper-zirconium intermediate alloy and sponge titanium were added to the holding furnace. After the composition was tested and qualified, the temperature was lowered to 1250℃ and then cast. During the casting process, copper-zirconium cored wire was added at a rate of 0.9 kg per minute using a wire feeder.

[0073] (2) Homogenization heat treatment of ingots: The ingots are placed in a walking beam furnace at 890°C for 6 hours.

[0074] (3) Hot rolling: The total processing volume is 88%, and water cooling is used.

[0075] (4) One-time cold rolling: The total processing volume is 90%.

[0076] (5) Solution treatment: The solution heat treatment temperature is 930℃ and the time is 10min, and then the product is taken out of the furnace and quickly cooled to room temperature.

[0077] (6) Secondary cold rolling: The total processing volume is 50%.

[0078] (7) First-level aging annealing: 400℃ for 10h, with hydrogen and nitrogen mixed gas used for protection inside the furnace, and the furnace exit temperature <50℃.

[0079] (8) Three-stage cold rolling: processing amount is 55% (9) Secondary aging annealing: 420℃ for 5 hours, with hydrogen and nitrogen mixed gas used for protection inside the furnace, and the furnace exit temperature <50℃.

[0080] Comparative Examples 1-13: The processes of Comparative Examples 1-11 are the same as those of Examples 1-2 of the present invention, but the element content is different.

[0081] The process for Comparative Example 12 is as follows: (1) Melting and casting: Melting is carried out in a non-vacuum medium-frequency induction furnace. Electrolytic copper plates are added to the melting furnace, and pure nickel sheets are added after melting. Elements such as Sc, La, Y, or Ce are added to the melt using intermediate alloys. The temperature is raised to 1290℃ to melt, and the temperature is held for 30 minutes to take samples for composition testing. After the composition is qualified, it is transferred to a holding furnace. Copper-zirconium intermediate alloy and sponge titanium are added to the holding furnace. After the composition is qualified, the temperature is lowered to 1240℃ and then cast. During the casting process, copper-zirconium cored wire is added at a rate of 0.8 kg per minute using a wire feeder.

[0082] (2) Homogenization heat treatment of ingots: The ingots are placed in a walking beam furnace at 890°C for 6 hours.

[0083] (3) Hot rolling: The total processing volume is 88%, and water cooling is used.

[0084] (4) One-time cold rolling: The total processing volume is 90%.

[0085] (5) Solution treatment: The temperature of solution heat treatment is 920℃ and the time is 15min. Then, the product is taken out of the furnace and quickly cooled to room temperature.

[0086] (6) Secondary cold rolling: The total processing volume is 63%.

[0087] (7) Intermediate material annealing: 470℃ for 7 hours, with hydrogen and nitrogen mixed gas used for protection inside the furnace, and the furnace exit temperature <50℃.

[0088] (8) Three-stage cold rolling: processing amount is 40%. (9) Aging annealing: Hold at 420℃ for 8 hours, with a mixture of hydrogen and nitrogen gas for protection inside the furnace, and the furnace exit temperature <50℃.

[0089] The process for Comparative Example 13 is as follows: (1) Melting and casting: Melting is carried out in a non-vacuum medium-frequency induction furnace. Electrolytic copper plates are added to the melting furnace, and pure nickel sheets are added after melting. Elements such as Sc, La, Y, or Ce are added to the melt using intermediate alloys. The temperature is raised to 1290℃ to melt, and the temperature is held for 30 minutes to take samples for composition testing. After the composition is qualified, it is transferred to a holding furnace. Copper-zirconium intermediate alloy and sponge titanium are added to the holding furnace. After the composition is qualified, the temperature is lowered to 1240℃ and then cast. During the casting process, copper-zirconium cored wire is added at a rate of 0.8 kg per minute using a wire feeder.

[0090] (2) Homogenization heat treatment of ingots: The ingots are placed in a walking beam furnace at 890°C for 6 hours.

[0091] (3) Hot rolling: The total processing volume is 88%, and water cooling is used.

[0092] (4) One-time cold rolling: The total processing volume is 90%.

[0093] (5) Intermediate material annealing: 450℃ for 8 hours, with hydrogen and nitrogen mixed gas used for protection inside the furnace, and the furnace exit temperature <50℃.

[0094] (6) Secondary cold rolling: The total processing volume is 63%.

[0095] (7) Solution treatment: The temperature of solution heat treatment is 950℃ and the time is 10min. Then, the product is taken out of the furnace and quickly cooled to room temperature.

[0096] (8) Three-stage cold rolling: processing amount is 40%. (9) Aging annealing: Hold at 480℃ for 6 hours, with a mixture of hydrogen and nitrogen gas for protection inside the furnace, and the furnace exit temperature <50℃.

[0097] Compared with Examples 1-5, Comparative Examples 1-11 have different elemental composition contents, as detailed in Table 1.

[0098] Performance Analysis: Conductivity Test Method: According to GB / T 351 "Methods for Measuring Resistivity of Metallic Materials". The material of this invention achieves a conductivity of 85% IACS while maintaining high strength.

[0099] Mechanical property testing methods: The tensile strength test method shall be in accordance with GB / T 228.1 "Metallic materials, tensile testing - Part 1: Test method at room temperature", and the hardness test method shall be in accordance with CB / T 4340.1 "Metallic materials, Vickers hardness test - Part 1: Test method". The material of this invention, with high electrical conductivity, can achieve a tensile strength of up to 610 MPa and a hardness above 170 HV.

[0100] High-temperature softening resistance test method: Performed according to GB / T 33370 "Determination of softening temperature of copper and copper alloys". The initial test temperature is 380℃, and the holding time is 1 hour. The material of this invention can still retain 80% of its original hardness at 600℃.

[0101] Second phase testing method: When testing the size of the precipitated phase, observe the microstructure of the sample under scanning electron microscope and transmission electron microscope, calculate the average particle size of the alloy precipitated phase based on the observation results, and calculate its number density.

[0102] The chemical composition of the materials used in the experiment is shown in Table 1. The test methods for grain size, tensile strength, hardness, conductivity, and high-temperature softening resistance were performed according to YS / T347 "Determination of Average Grain Size of Copper and Copper Alloys", GB / T 228.1 "Tensive Testing of Metallic Materials - Part 1: Room Temperature Test Method", CB / T 4340.1 "Vickers Hardness Test of Metallic Materials - Part 1: Test Method", GB / T 351 "Method for Measurement of Resistivity of Metallic Materials", and GB / T 33370 "Determination of Softening Temperature of Copper and Copper Alloys", respectively. The 90° bending forming performance was tested according to YS / T 1773 "Bending Test Method for Copper and Copper Alloy Strips and Foils". Table 2 shows the measured results as follows:

[0103] Table 2 Performance Test Results

[0104] Comparative Example 1, without the addition of Sc, La, Y, or Ce, had an average grain size of 24 μm. Comparative Examples 2-5, with the addition of one of Sc, La, Y, or Ce, had an average grain size of 18-22 μm. Due to the lack of addition or insufficient variety of rare earth elements, the grain refinement effect was poor. In Examples 1-5 of this invention, with the addition of two or more of Sc, La, Y, or Ce, the average grain size of the material was 5-10 μm. Therefore, the embodiments of this invention can further refine the grain size by providing two or more trace amounts of rare earth elements.

[0105] Comparative Example 6 did not add Ni and Si elements, thus it was unable to precipitate together with Cr and Zr to form a composite nano-precipitate phase. The tensile strength of the material prepared in Comparative Example 6 was 578 MPa, the hardness was 159 HV, and the softening temperature was 540 ℃. Due to the lack of composite nano-precipitate phase, the tensile strength, hardness, and softening temperature of the material were all relatively low.

[0106] Comparative Examples 7 and 8, which only added Ni or Si respectively, did not co-precipitate with Cr and Zr to form composite nano-precipitates. Their tensile strengths were 593 MPa and 586 MPa, and their hardnesses were 167 HV and 163 HV, respectively. The tensile strength and hardness of the materials were relatively low.

[0107] In Comparative Example 9, the excessive Ni and Si content led to the formation of coarse second phases or harmful impurity phases. While the material strength was significantly improved, the conductivity was significantly reduced to only 78.18% IACS.

[0108] In Comparative Example 10, the Ni and Si contents were too low, resulting in fewer composite nano-precipitates. Although the conductivity was high, the tensile strength was only 581 MPa, which is low.

[0109] Comparative Example 11, without the addition of Ti, had poor uniformity in the distribution of the second phase, and lower tensile strength and hardness compared to Examples 1 and 2.

[0110] The copper alloys provided in Examples 1-5 of this invention exhibit superior overall performance in terms of tensile strength, hardness, conductivity, and softening temperature. In particular, the copper alloy provided in Example 2 achieves a conductivity of 85% IACS at a tensile strength of 610 MPa and a softening temperature of 560 °C. Furthermore, it exhibits no cracking in either the good or bad way when bent at 90° with R / T=0. Therefore, the materials described in this invention possess high tensile strength and hardness while also exhibiting excellent bending performance, minimal conductivity attenuation, and a significantly improved high-temperature softening temperature.

[0111] Comparative Example 12, using the process of "single cold rolling → solution treatment → second cold rolling → intermediate material annealing → third cold rolling → aging annealing", yielded a material with a tensile strength of 586 MPa and a conductivity of 84.03% IACS. Comparative Example 13, using the process of "single cold rolling → intermediate material annealing → second cold rolling → solution treatment → third cold rolling → aging annealing", yielded a material with a tensile strength of 593 MPa and a conductivity of 83.27% IACS. Examples 1-5 employ a "single cold rolling → solution treatment + secondary aging" process. Under the condition of identical alloying elements and appropriate content, the embodiments of the present invention, after a first-stage aging heat treatment, further adjust the spatial uniformity of the precipitated phase distribution through a third cold rolling. The secondary aging process facilitates the precipitation and distribution of composite nano-precipitates. The materials prepared in Examples 1 and 2 of the present invention achieve tensile strengths of 618 MPa and 610 MPa, respectively, and electrical conductivity of 85.28% IACS and 85.85% IACS, respectively, with finer grains. Therefore, under the same alloy composition, the finished product prepared by the process described in this invention exhibits superior overall performance.

[0112] Meanwhile, Zr content was measured at 0.5m intervals along the length of the ingots from Examples 1 and 2, and the results are shown in Table 3. This invention effectively compensates for Zr loss during the smelting process by continuously adding intermediate alloy via a wire feeder, ensuring uniform and stable Zr content and providing a solid foundation and reliable guarantee for the consistency and stability of the finished product's performance.

[0113] Table 3 Zr content at different sampling locations

Claims

1. A microalloyed copper-chromium-zirconium alloy, characterized in that, The microalloyed copper-chromium-zirconium alloy comprises the following components by mass percentage: Cr: 0.2–1.2%, Zr: 0.05–0.2%, Ni: 0.01–0.05%, Si: 0.001–0.01%, Ti: 0.002–0.006%, Re: 0.001–0.008%, with the balance being Cu, and Re being two or more of Sc, La, Y, and Ce. The microstructure of the microalloyed copper-chromium-zirconium alloy includes a second phase, which comprises a composite nanoprecipitate containing Ni, Si, Cr and Zr.

2. The microalloyed copper-chromium-zirconium alloy according to claim 1, characterized in that, The average size of the second phase is 5-30 nm.

3. The microalloyed copper-chromium-zirconium alloy according to claim 1, characterized in that, The second phase also includes nanoscale Cr phase and nanoscale Cu5Zr phase.

4. The microalloyed copper-chromium-zirconium alloy according to claim 1, characterized in that, The average grain size of the microalloyed copper-chromium-zirconium alloy is 5-15 μm.

5. The microalloyed copper-chromium-zirconium alloy according to claim 1, characterized in that, The microalloyed copper-chromium-zirconium alloy has a hardness of 145-210 HV, a tensile strength of 500-710 MPa, a conductivity of 75-90% IACS, and a softening temperature of 520-580℃.

6. A method for preparing microalloyed copper-chromium-zirconium alloy plates and strips, characterized in that, Microalloyed copper-chromium-zirconium alloy plates and strips are prepared using the microalloyed copper-chromium-zirconium alloy according to any one of claims 1-5. The process flow of the preparation method includes melting and casting → ingot homogenization heat treatment → hot rolling → first cold rolling → solution treatment → second cold rolling → first-stage aging annealing → third-stage cold rolling → second-stage aging annealing. The components of the microalloyed copper-chromium-zirconium alloy according to any one of claims 1-5 are batched and smelted according to their respective mass percentages. The solution treatment is performed at a temperature of 850-1050℃ for a time of 1-15 minutes.

7. The method for preparing microalloyed copper-chromium-zirconium alloy plates and strips according to claim 6, characterized in that, In the casting process, a wire feeder is used to continuously add copper-zirconium raw materials at a rate of 0.2~1kg per minute.

8. The method for preparing microalloyed copper-chromium-zirconium alloy plates and strips according to claim 7, characterized in that, The total processing rate of the hot rolling is over 80%, and the total processing rate of the single cold rolling is 80-90%.

9. The method for preparing microalloyed copper-chromium-zirconium alloy plates and strips according to claim 7, characterized in that, The total processing rate of the secondary cold rolling is 40-90%, and the total processing rate of the tertiary cold rolling is 15-70%.

10. The application of a microalloyed copper-chromium-zirconium alloy according to any one of claims 1-5 in a connector.

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