A high-temperature-resistant high-conductivity copper-based alloy containing cobalt and phosphorus and a preparation method thereof

Abstract

The application discloses a high-temperature-resistant and high-conductivity copper-based alloy containing cobalt and phosphorus and a preparation method thereof. The copper alloy comprises the following components in percentage by mass: Co: 0.01-0.15%, P: 0.002-0.02%, Cu: 99.86-99.91%, and O: 5ppm or less. The preparation method comprises the following steps: vacuum melting and casting, homogenization treatment, hot deformation, large-deformation cold processing, and low-temperature and high-temperature staged annealing. According to the application, trace Co and P are precisely introduced into an ultra-high-purity copper matrix, and a specific process is used to synchronously form a recrystallization texture of greater than or equal to 80% and a dispersedly distributed nanometer Co2P precipitated phase in the matrix. The two components synergistically greatly inhibit grain coarsening of the material at high temperatures from the macroscopic and microscopic scales, thereby obtaining excellent high-temperature microstructure stability and mechanical property retention rate without losing the electrical conductivity, and the application is particularly suitable for the fields of power electronics and aerospace under high-temperature working conditions.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal materials technology, specifically to a high-temperature resistant, high-conductivity copper-based alloy containing cobalt and phosphorus and its preparation method. Background Technology

[0002] Oxygen-free copper is a key basic material in fields such as electronics, high-end communications, and aerospace due to its extremely high electrical and thermal conductivity. However, with the increasing extremism of applications, such as electric vehicle power modules (operating temperatures can reach 150-200 °C, with even higher peak temperatures) and rocket engine windings, the shortcomings of traditional oxygen-free copper are becoming increasingly apparent. For example, its strength and hardness decrease significantly at high temperatures. More importantly, under long-term heat exposure, its microstructure undergoes recrystallization and grain coarsening.

[0003] Grain coarsening has two serious consequences: First, mechanical properties deteriorate further, making the material prone to creep or fatigue failure under thermal and mechanical stress. Second, coarse grain boundaries become electron scattering centers and may become the starting point for crack initiation, leading to a decrease in electrical conductivity and mechanical property stability.

[0004] In existing technologies, the high-temperature performance of copper alloys is improved through solid solution strengthening (such as adding Ag) or precipitation strengthening (such as adding Cr and Zr), but these methods severely sacrifice electrical conductivity. Another approach is to perform drastic plastic deformation to refine the grains, but this effect is difficult to maintain at high temperatures; once recrystallization occurs, the performance rapidly declines. Therefore, how to significantly improve the high-temperature microstructure stability of oxygen-free copper without significantly compromising its excellent electrical conductivity has become a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-temperature resistant, high-conductivity copper-based alloy containing cobalt and phosphorus, and its preparation method. This material achieves recrystallization texture and dispersed nanoscale Co2P precipitates within the matrix by precisely adding trace amounts of cobalt (Co) and phosphorus (P) elements to an ultra-high purity copper matrix, followed by a carefully designed large-deformation cold working and graded annealing process. This synergistically suppresses grain coarsening at high temperatures on both macroscopic and microscopic scales, thereby achieving excellent high-temperature stability without significantly sacrificing conductivity.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a high-temperature resistant, high-electrical-conductivity copper-based alloy containing cobalt and phosphorus, which is composed of the following components by mass percentage:

[0008] Co: 0.01-0.15%, P: 0.002-0.02%, Cu: ≥99.99%, O: ≤5ppm, balance being unavoidable impurities;

[0009] Furthermore, the microstructure of the copper-based alloy contains ≥80% recrystallized fibrous texture and diffusely distributed nanoscale Co2P precipitates.

[0010] Preferably, the mass ratio of Co to P is controlled within the range of (5~10):1 to ensure that Co and P can fully form the Co2P precipitate phase.

[0011] Preferably, the size of the nanoscale Co2P precipitate is 2~20 nm, and the average spacing is 50~200 nm.

[0012] Preferably, after the copper-based alloy is held at 500 °C for 100 hours, its average grain size growth rate does not exceed 20%.

[0013] Preferably, the room temperature conductivity of the copper-based alloy is ≥98% IACS.

[0014] Secondly, the present invention provides a method for preparing a high-temperature resistant and highly conductive copper-based alloy containing cobalt and phosphorus, comprising the following steps:

[0015] Step 1, Microalloying and Casting: The purpose of this step is to obtain an ingot with precise composition, high purity, and uniform structure.

[0016] Raw material preparation: High-purity cathode copper with a purity ≥ 99.995% is selected as the base material. Alloying elements Co and P are added in the form of high-purity Cu-Co master alloy (recommended Co content 10%~20%) and Cu-P master alloy (recommended P content 5%~10%). Before use, all raw materials must be surface cleaned (acid pickling and ultrasonic cleaning) and dried to remove oxide scale and oil.

[0017] Charging and Vacuuming: The calculated high-purity copper and Cu-Co master alloy are loaded into the water-cooled copper crucible of the vacuum induction melting furnace. To reduce the volatilization loss of phosphorus at high temperatures, the Cu-P master alloy should be added in subsequent steps.

[0018] Initial melting: Evacuate the furnace cavity to ≤5Pa, then fill it with argon gas of ≥99.999% purity until the furnace pressure is 0.03~0.05MPa; start the induction power supply and slowly heat to 1250~1300 °C, hold for 30 min to melt all the furnace charge and initially homogenize the Co element.

[0019] Secondary feeding and refining: Reduce the furnace temperature to about 1150 °C, add Cu-P master alloy through the feeder, and after it melts, raise the temperature to 1350~1400 °C for refining. Hold the temperature for 15~25 minutes to ensure that Co and P elements are evenly dispersed in the copper liquid.

[0020] Casting: The temperature of the refined melt is stabilized at 1180~1220 °C and poured into a graphite metal mold preheated to 300~400 °C to obtain a dense ingot structure.

[0021] Step 2: Homogenization

[0022] This step aims to eliminate dendritic segregation and residual stress inside the ingot, preparing it for subsequent hot working.

[0023] The ingot is placed in an annealing furnace under a protective atmosphere (such as high-purity nitrogen or argon).

[0024] Heat to the target temperature of 500~600 °C at a rate of ≤5 °C / min.

[0025] The heat preservation time is 1 to 6 hours. The heat preservation time is determined according to the size of the ingot. In principle, it is calculated as 1 hour of heat preservation for every 25mm of cross-sectional diameter (or thickness).

[0026] After the heat preservation is completed, the furnace is cooled or cooled at a slow cooling rate of ≤3 °C / min to below 300 °C, and then removed from the furnace and air-cooled.

[0027] Step 3: Hot Deformation Processing

[0028] This step aims to break down the as-cast structure and achieve thermomechanical forming.

[0029] Preheating: Heat the homogenized ingot to 350~500 °C and hold for 1~2 hours to ensure uniform temperature.

[0030] Hot working: carried out by hot rolling or hot extrusion.

[0031] Hot rolling: Multiple passes are performed on a reversible rolling mill, with the deformation per pass controlled at 15%~25% and the total deformation controlled at 70%~85%. The final rolling temperature should not be lower than 300 °C.

[0032] Hot extrusion: The preheated ingot is placed into the extrusion cylinder and extruded at a temperature of 400~450 °C, with the extrusion ratio controlled at (10:1)~(15:1). After extrusion, water spraying or strong air can be used for rapid cooling to inhibit excessive growth of precipitates.

[0033] Step 4: Cold working with large deformation

[0034] This step is crucial for forming a strong deformation texture and a large number of crystal defects (dislocations), providing the driving force and nucleation sites for the formation of recrystallization texture and nanophase precipitation during subsequent annealing processes.

[0035] Surface treatment: Perform surface treatment on the hot-deformed blank (such as milling, peeling, polishing) to remove oxide layer and surface defects.

[0036] Cold working: carried out by cold rolling or cold drawing.

[0037] Cold rolling: Multiple passes are performed on a multi-roll precision mill, with intermediate low-temperature (≤200 °C) stress-relief annealing between passes (optional, depending on the degree of work hardening). The total cold deformation must be ≥95% (e.g., rolling a 10 mm thick slab to below 0.5 mm).

[0038] Cold drawing: For wire, through multiple drawing passes, combined with die lubrication and intermediate annealing (optional), the total section shrinkage rate is ≥95%.

[0039] Step 5: Graded annealing

[0040] This is the core element in achieving "synergistic enhancement of texture and nano-precipitation". Through precisely controlled two-stage annealing, the formation of recrystallized texture and the stable precipitation of nano-phase are achieved respectively.

[0041] Phase 1: Low-temperature annealing (recrystallization and pre-precipitation)

[0042] Objective: To induce incomplete recrystallization in materials subjected to large deformations at lower temperatures, forming a recrystallization texture (typically a copper-type texture, such as {112}). <111> Meanwhile, supersaturated Co and P atoms begin to segregate at high dislocation densities and grain boundaries, forming nanoscale Co2P phase nuclei.

[0043] Process: Under a protective atmosphere (high-purity nitrogen or argon), the material is heated to 400~500 °C at a rate of ≤10 °C / min.

[0044] Heat preservation: Hold for 10-60 minutes. Shorter holding time is beneficial for the formation of fine recrystallized grains and texture; longer time results in more complete recrystallization, but the texture strength may be weakened. The recrystallization completion rate should be controlled at 80%-95% during this stage.

[0045] Second stage: High-temperature stabilization annealing (texture stabilization and precipitation phase formation)

[0046] Objective: To ensure complete recrystallization at higher temperatures and further stabilize and strengthen the recrystallized texture. Simultaneously, to promote the full precipitation and appropriate coarsening of the nano-Co2P phase to the optimal pinning size (2–20 nm) to achieve the best dispersion distribution.

[0047] Process: Immediately following the first stage, the furnace temperature is increased to 550~650 °C at a rate of ≤5 °C / min.

[0048] Insulation: Insulate at this temperature for 1-3 hours. This temperature and time are sufficient to allow the Co2P phase to fully precipitate and reach a thermodynamically stable state, while ensuring complete recrystallization and recovery of the matrix and the elimination of internal stress.

[0049] Cooling: After the holding period, cool with the furnace or at a slow cooling rate of ≤3 °C / min to room temperature. Slow cooling helps to avoid introducing new thermal stress and maintain the stability of the microstructure.

[0050] Through the above five precisely controlled steps, the high-temperature resistant copper-based alloy obtained has both recrystallization texture and dispersed nano-Co2P precipitates, thus achieving a balance between excellent high-temperature performance and high conductivity.

[0051] Preferably, in step one, the melting is carried out by vacuum induction melting. After the vacuum degree is reduced to below 5 Pa, argon gas is introduced for protection. The melting temperature is 1300~1400 °C, the holding time is 15~30 min, and the casting temperature is 1150~1250 °C.

[0052] Preferably, in step two, the homogenization treatment is carried out at a temperature of 500-600 °C for 1-6 hours.

[0053] Preferably, in step three, the temperature of hot rolling or hot extrusion is 350~500 °C.

[0054] Preferably, in step four, the cold working is cold rolling or cold drawing.

[0055] Preferably, in step five, the holding time for the low-temperature annealing is 10-60 min, which aims to induce recrystallization and form a fibrous texture, while allowing the nano-Co2P phase to initially precipitate; the holding time for the high-temperature stabilization annealing is 1-3 h, which aims to allow the recrystallized texture to fully develop and stabilize, ultimately achieving a structural proportion of ≥80%, while allowing the Co2P phase to fully precipitate and coarsen to the optimal size.

[0056] Compared with the prior art, the outstanding advantages and beneficial effects of the present invention are as follows:

[0057] 1. This invention suppresses grain boundary migration at both the macroscopic and microscopic scales through the synergistic effect of "texture strengthening" and "nanoprecipitation strengthening." Recrystallization texture provides a macroscopically anisotropic grain boundary distribution, significantly increasing the energy barrier to grain coarsening; while the nano-Co2P phase acts as an efficient pinning point, mechanically hindering grain boundary migration at the microscopic level. The synergistic effect of these two mechanisms is significantly superior to either mechanism alone.

[0058] 2. This synergistic strengthening mechanism enables the material to greatly suppress recrystallization and grain coarsening processes during long-term service at high temperatures (≥500 °C), thereby maintaining excellent mechanical properties.

[0059] 3. Since Co and P elements mainly exist as nano-Co2P precipitates with minimal conductivity loss, rather than being dissolved in the copper matrix, this invention achieves high strength and high thermal stability while essentially preserving the intrinsic high conductivity of the copper-based alloy, with a conductivity exceeding 98% IACS.

[0060] 4. The preparation method provided by this invention has a clear process flow and well-defined process parameters. By controlling the amount of cold deformation and the graded annealing process, the strength of the texture and the size and distribution of the nano-precipitates can be precisely controlled. It has good reproducibility and is suitable for industrial production. Attached Figure Description

[0061] Figure 1 The image shows a TEM image of the microstructure of the high-temperature resistant copper-based alloy prepared in Example 1 of this invention after graded annealing. The image shows a diffusely distributed nanoscale Co2P precipitate phase.

[0062] Figure 2 Metallographic images showing the grain size comparison between samples of Comparative Example 1 (Fig. a) and Example 1 of the present invention (Fig. b) after heat exposure at 500 °C for 100 h. Detailed Implementation

[0063] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. Example 1

[0064] A method for preparing a high-temperature resistant, high-conductivity copper-based alloy containing cobalt and phosphorus, the process comprising the following sequential steps:

[0065] (1) Microalloying and casting: High-purity cathode copper (6.440 kg) and Cu-10%Co master alloy (52 g) were placed in a water-cooled copper crucible. Before use, all raw materials were polished (surface roughness Ra of 1.6 μm) and cleaned (acid pickling and ultrasonic cleaning) and dried to remove oxide scale and oil.

[0066] (2) Secondary charging: The calculated Cu-10%P master alloy (7.8 g) is charged into the feeder of the vacuum induction melting furnace.

[0067] (3) Initial melting: Evacuate the furnace cavity to ≤5Pa, and then fill it with high-purity argon gas (purity ≥99.999%) to a slightly positive pressure (approximately 0.03~0.05MPa). Start the induction power supply and slowly heat it to 1300 °C. Hold the temperature for 30 min to melt all the furnace charge and initially homogenize the Co element.

[0068] (4) Secondary feeding and refining: Reduce the furnace temperature to about 1150 °C and feed the Cu-P master alloy through the feeder. After it melts, raise the temperature to 1350 °C for refining and hold for 20 min to ensure that the Co and P elements are evenly dispersed in the copper liquid.

[0069] (5) Casting: The temperature of the refined melt is stabilized at 1200 °C and poured into a graphite metal mold preheated to 300 °C to obtain a dense ingot with dimensions of 200mm*100mm*25mm.

[0070] (6) Homogenization treatment: Place the ingot in an annealing furnace under a protective atmosphere (such as high-purity nitrogen or argon). Heat to the target temperature of 550 °C at a rate of ≤5 °C / min. Hold for 1 h. After holding, cool with the furnace or at a slow cooling rate of ≤3 °C / min to below 300 °C, and then remove from the furnace and air cool.

[0071] (7) Hot deformation processing: The homogenized ingot is heated to 400 °C and held for 1 hour. It is then rolled in multiple passes on a reversible rolling mill to produce a thin slab with a thickness of 6 mm. The final rolling temperature should not be lower than 300 °C.

[0072] (8) Large deformation cold working: The hot-deformed billet undergoes surface treatment (such as milling, peeling, and polishing) to achieve a surface roughness of Ra=1.6 μm, thereby removing the oxide layer and surface defects. Multiple passes are performed on a multi-roll precision mill, with intermediate low-temperature (≤200 °C) stress-relief annealing between passes. The final product is a copper-based alloy plate with a thickness of 0.3 mm.

[0073] (9) Staged annealing: Under a protective atmosphere (high-purity nitrogen or argon), the material is heated to 400 °C at a rate of ≤10 °C / min and held for 30 min. Immediately following the first stage, the furnace temperature is increased to 600 °C at a rate of ≤5 °C / min. The temperature is held for 2 hours. After holding, the material is cooled in the furnace or at a slow cooling rate of ≤3 °C / min to room temperature, finally obtaining a high-temperature resistant copper-based alloy plate. Figure 1 The image shows a TEM image of the microstructure of the high-temperature resistant copper-based alloy prepared in Example 1 of this invention after graded annealing. The image shows a diffusely distributed nanoscale Co2P precipitate phase. Example 2

[0074] A method for preparing a high-temperature resistant and highly conductive copper-based alloy containing cobalt and phosphorus is similar to that in Example 1, except that the weights of the raw materials in steps 1 and 2 are adjusted. The high-purity cathode copper (6.410 kg), Cu-10%Co master alloy (78 g), and Cu-10%P master alloy (11.7 g) are adjusted. The step (9) is also adjusted: first annealed at 480 °C for 15 min, and then annealed at 620 °C for 1.5 h.

[0075] Comparative Example 1

[0076] Traditional oxygen-free copper (TU1) was used, with the raw material weight adjusted in step 1 to high-purity cathode copper (6.5 kg). The preparation process was the same as in Example 1.

[0077] Comparative Example 2

[0078] Rare earth-strengthened oxygen-free copper was prepared by adjusting the weight of the raw materials in step 1: high-purity cathode copper (6.175 kg) and Cu-10%La master alloy (0.325 kg). The preparation process was the same as in Example 1.

[0079] Performance testing

[0080] The materials obtained in Examples 1, 2, 1, and 2 were subjected to performance tests, and the results are shown in the table below:

[0081]

[0082] Results analysis:

[0083] Based on the table above Figure 2 As can be seen, the copper-based alloys prepared in Examples 1 and 2 of this invention, while maintaining extremely high conductivity (≥98% IACS), exhibit higher room-temperature strength and exceptionally good high-temperature performance retention. After heat exposure at 500 °C for 100 hours, their strength retention is significantly higher than that of Comparative Example 1, which uses traditional oxygen-free copper, and also superior to Comparative Example 2, which is strengthened with rare earth elements. In terms of grain size, the material of this invention demonstrates significantly better resistance to grain coarsening than the two comparative examples, fully proving the remarkable effect of the synergistic strengthening mechanism of "texture + nano-Co2P precipitation" in improving the high-temperature microstructural stability of copper-based alloys.

Claims

1. A high-temperature resistant, high-conductivity copper-based alloy containing cobalt and phosphorus, characterized in that, The alloy is composed of the following components by mass percentage: Co: 0.01 ~ 0.15%, P: 0.002 ~ 0.02%, Cu: 99.86 ~ 99.91%, O: ≤5ppm, with the balance being unavoidable impurities; the mass ratio of Co to P is (5 ~ 10): 1; and the microstructure of the copper-based alloy contains ≥80% recrystallized fibrous texture and diffusely distributed nanoscale Co2P precipitates, the size of which is 2 ~ 20 nm and the average spacing is 50 ~ 200 nm.

2. The high-temperature resistant and high-conductivity copper-based alloy containing cobalt and phosphorus according to claim 1, characterized in that, After the copper-based alloy is held at 500 °C for 100 hours, its average grain size growth rate does not exceed 20%.

3. The high-temperature resistant and high-conductivity copper-based alloy containing cobalt and phosphorus according to claim 1, characterized in that, The copper-based alloy has a room temperature conductivity ≥98% IACS.

4. A method for preparing a high-temperature resistant, high-conductivity copper-based alloy containing cobalt and phosphorus as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Step 1, Microalloying and Casting: Under vacuum or protective atmosphere, high-purity copper, Cu-Co master alloy and Cu-P master alloy are melted and cast into ingots. Step 2, Homogenization treatment: The ingot is subjected to homogenization heat treatment; Step 3, Hot Deformation Processing: The homogenized ingot is hot rolled or hot extruded. Step 4, large deformation cold working: cold working is performed on the material after hot deformation, and the total deformation is ≥95%; Step 5, graded annealing: The cold-worked material is subjected to graded annealing. First, it is annealed at a low temperature of 400~500 °C, and then it is annealed at a high temperature of 550~650 °C for stabilization.

5. The method for preparing the high-temperature resistant and highly conductive copper-based alloy containing cobalt and phosphorus according to claim 4, characterized in that, In step one, the melting is carried out using vacuum induction melting. After the vacuum degree is reduced to below 5 Pa, argon gas is introduced for protection. The melting temperature is 1300~1400 °C, and the casting temperature is 1150~1250 °C.

6. The method for preparing the high-temperature resistant and highly conductive copper-based alloy containing cobalt and phosphorus according to claim 4, characterized in that, In step two, the homogenization process is carried out at a temperature of 500-600 °C for 1-6 hours.

7. The method for preparing the high-temperature resistant and highly conductive copper-based alloy containing cobalt and phosphorus according to claim 4, characterized in that, In step five, the holding time for low-temperature annealing is 10-60 minutes, and the holding time for high-temperature stabilization annealing is 1-3 hours.

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