A method for producing a Cu-Ni-Co-Si alloy strip

Abstract

This invention relates to the field of copper alloy processing technology, and more particularly to a method for preparing Cu-Ni-Co-Si alloy strip. The invention includes the following steps: Step 1, casting; Step 2, hot rolling followed by milling; Step 3, first cold rolling; Step 4, annealing; Step 5, cold rolling before solution treatment; Step 6, first solution treatment; Step 7, cold rolling before solution treatment; Step 8, second solution treatment; Step 9, aging treatment; Step 10, fine rolling and low-temperature annealing of the aged strip; Step 11, tension bending and straightening. Through a series of process designs, this invention can refine grain size, reduce large-size second-phase particles, and improve bending performance of the product without affecting its original properties, thus meeting the market application requirements of Cu-Ni-Co-Si alloys.

Description

Technical Field

[0001] This invention relates to the field of copper alloy processing technology, specifically a method for preparing Cu-Ni-Co-Si alloy strip. Background Technology

[0002] Cu-Ni-Co-Si alloys, with their core advantages such as high strength and conductivity, resistance to stress relaxation, and good processability, have become key materials in the fields of electronic information and high-end manufacturing. Their core applications include integrated circuit leadframes, precision electronic connectors and terminals, special electromagnetic components, and heat dissipation parts. Among these, integrated circuit leadframes are the dominant application. With tensile strength ≥700MPa, conductivity ≥40%IACS, and bending R / t ≤0.5 in both good and bad directions, they meet the high-density packaging requirements of copper alloy processing with lead pitch <0.1mm. They can withstand the high temperature of 260℃ reflow soldering in copper alloy processing and have replaced traditional alloys in high-end applications such as smartphone processors and automotive ECU processing.

[0003] Currently, most existing technologies for preparing Cu-Ni-Co-Si alloys rely on increasing the aging power to ensure the tensile strength of the product and on multi-stage aging to improve its conductivity.

[0004] However, these preparation methods often cannot simultaneously achieve grain refinement, elimination of coarse second-phase particles, and improvement of bending performance. Coarse second-phase particles and uneven grain structure become stress concentration points, deteriorating the bending performance and fatigue life of the material, making it difficult to meet the stringent requirements of high-end applications for comprehensive material performance.

[0005] Based on this, a method for preparing Cu-Ni-Co-Si alloy strips is proposed, providing a solution to this problem. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing Cu-Ni-Co-Si alloy strips to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing Cu-Ni-Co-Si alloy strip, comprising the following steps: Step 1, casting: Prepare alloy ingots according to the alloy composition ratio; Step 2, hot rolling: After holding at 950-1000℃ for 2 hours, the alloy ingot is hot rolled, followed by milling. Step 3, First cold rolling: The milled strip is cold rolled, with a total processing rate of 60-90%; Step 4: Annealing: Anneal the cold-rolled strip. Step 5, Cold rolling before solution treatment: Cold roll the annealed strip with a total processing rate of ≥50% and a single-pass processing rate of 15-30%; Step 6, First Solution Treatment: The cold-rolled strip before the first solution treatment is subjected to solution treatment; Step 7, Cold rolling before secondary solution treatment: Cold rolling is performed on the strip after the primary solution treatment, with a total processing rate of ≥50%; Step 8, Secondary Solution Treatment: The cold-rolled strip before secondary solution treatment is subjected to solution treatment; Step 9, Aging Treatment: The strip after the secondary solution treatment is subjected to aging treatment; Step 10, Finish rolling and low-temperature annealing: The aged strip is finished rolled and annealed at a low temperature.

[0008] Furthermore, the alloy composition described in step one, by weight percentage, is as follows: Ni: 0.3-1.0%; Co: 1.3-2.0%; Si: 0.3-0.8%; Sn: 0.03-0.08%; Zn: 0.05-0.10%; Cr: 0.01-0.05%; the balance being Cu and unavoidable non-metallic impurities.

[0009] Furthermore, the melting and casting temperature in step one is 1180-1250℃, and the casting speed is 70-100mm / min.

[0010] Furthermore, in step two, the hot rolling power is 78-95%, and the final rolling temperature is 800-900℃.

[0011] Furthermore, the annealing temperature in step four is 420-520℃, and the annealing time is 6-12h.

[0012] Furthermore, the temperature of the first solution treatment in step six is ​​900-1020℃, and the annealing rate is 27-40 m / min; the temperature of the second solution treatment in step eight is 850-980℃, and the annealing rate is 30-45 m / min.

[0013] Furthermore, the aging treatment in step nine is carried out at a temperature of 420-520℃ for 6-12 hours.

[0014] Furthermore, the aging treatment in step nine is carried out at a temperature of 450-480℃ for 7-11 hours.

[0015] Furthermore, in step ten, the finishing rate of the finishing rolling is 15-30%, the temperature of the low-temperature annealing is 250-400℃, and the annealing rate is 37-48m / min.

[0016] Furthermore, it also includes the following steps: Step 11, Bending and Straightening: Unwinding tension is 20-45 N / mm 2 The winding tension is 35-60 N / mm. 2 The entry extension rate is 0.1-0.4%.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention significantly increases the dislocation density and stored energy within the alloy matrix by introducing a large-deformation cold rolling step between two solution treatments. This high-defect structure provides a strong driving force for the subsequent secondary solution treatment, promoting the decomposition and resolution of coarse second-phase particles that may remain after the first solution treatment. During the resolution process, a large number of dispersed fine second-phase particles precipitate at the defect sites. These fine second-phase particles effectively pin grain boundaries and strongly inhibit grain growth in subsequent aging treatments and the final product, resulting in a fine recrystallized grain structure. Ultimately, the product achieves a synergistic effect of grain refinement and dispersion strengthening, significantly refining the grains and reducing coarse second-phase particles while maintaining or even improving strength and conductivity. This results in excellent bending performance and superior overall performance, well meeting the requirements of applications such as high-end lead frames. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the second-phase particle image of the alloy strip obtained in Example 1 of the present invention under a scanning electron microscope; Figure 2 This is a schematic diagram of the grain size of the alloy strip obtained in Example 1 of the present invention under a metallographic microscope. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1:

[0020] Please refer to the following: Figure 1 and Figure 2 This invention provides a method for preparing Cu-Ni-Co-Si alloy strip, comprising the following steps: Melting and casting: Weigh the raw materials according to the following composition and weight percentage: Ni 0.8%, Co 1.6%, Si 0.6%, Sn 0.05%, Zn 0.08%, Cr 0.03%, with the balance being Cu and unavoidable impurities; add materials according to their melting points and ease of burning to complete the alloy melting and casting. During the melting process, pay attention to adding an appropriate amount of covering agent to prevent volatilization. After the alloy composition is uniform, add trace amounts of Zn, Sn, and Cr. After holding at the temperature for 10 minutes, casting can begin at a casting temperature of 1250℃ and a casting speed of 75mm / min. Hot rolling: The ingot is heated by a walking beam furnace. The initial rolling temperature is 950℃ and the final rolling temperature is 850℃. The total power is 80%. After hot rolling, the ingot is immediately water-cooled and then milled until the surface is free of defects and oxide scale, so as to prevent the residue on the surface of the ingot from affecting the subsequent cold rolling. Cold rolling: The milled copper alloy strip is cold rolled with a total power of 75%, which is completed in 7 passes. The power of each pass is 10-20%, which is beneficial to the generation of second phase particles in the subsequent annealing process. Annealing: The cold-rolled strip is coiled and sent to a bell furnace for annealing at a temperature of 450℃. This annealing not only serves as recrystallization but also as an aging treatment. The strip is held at this temperature for 6 hours to completely eliminate the work hardening caused by the previous cold rolling process and to prevent the formation of coarse second-phase particles that could affect subsequent processing. After the intermediate aging treatment, the strip is sent to a brush cleaning line for cleaning. Cold rolling before solution treatment: The copper strip that has been cleaned in the previous process is cold rolled. The total cold rolling power is 60%, and the rolling is carried out in 4 passes. The power of each pass is 15-30%. The main purpose of this cold rolling is to increase the dislocation density inside the strip and break up large grains through the large power, thereby enhancing the recrystallization effect of the subsequent solution treatment. In other embodiments, the power can be increased as appropriate according to the specific product. One-time solution treatment: The cold-rolled strip is fed into the continuous annealing line for online annealing. The online annealing temperature is 980℃ and the annealing rate is 40m / min. The high-temperature solution treatment can dissolve most of the second phase particles, and the fine second phase particles generated during the intermediate aging process can inhibit grain growth during the solution treatment stage. Cold rolling before secondary solution treatment: The strip after solution treatment is cold rolled again with a total power of 70% in 5 passes, with a power of 15-30% in each pass, thereby breaking the grains and increasing the stored energy of the matrix, promoting the resolution and decomposition of large-sized second-phase particles and the stabilization of fine grains in the secondary solution treatment. Secondary solution treatment: The cold-rolled strip is fed into the continuous annealing line for annealing. The annealing temperature is 950℃ and the annealing rate is 45m / min. During the secondary solution treatment, the coarse second phase decomposes and the re-dissolution process generates a large number of fine second phase particles. The fine second phase particles can inhibit grain growth and can further increase the supersaturated solid solubility during the re-dissolution process. Aging treatment: The strip after the second solution treatment is sent into a bell jar for aging treatment. The aging treatment temperature is 450℃ and the holding time is 10h. This aging treatment mainly causes the solute atoms such as Ni, Co and Si in the matrix to precipitate in the form of second phase particles and be evenly distributed, taking into account the hardness and conductivity of the strip. Finish rolling and low-temperature annealing: After aging, a cold rolling with a per-pass power increase of 25% is performed. This processing rate can ensure that the hardness of the material is improved without affecting bending. Then, low-temperature annealing is performed at 300℃ with an annealing speed of 40m / min to eliminate residual stress in the strip and reduce the number of dislocations on the slip surface, thereby improving stress relaxation performance. Bending and straightening, unwinding tension 35 N / mm 2 Winding tension 40 N / mm 2 The inlet extends by 0.2%, which effectively corrects the shape, relieves stress, and eliminates metal memory.

[0021] Following the above steps, the prepared alloy strip has a thickness of 0.5-0.125 mm, a hardness of 220-250 HV, a conductivity of 60-66% IACS, a grain size of 0.008-0.01 mm, a tensile strength of 700-880 MPa, a yield strength of 650-720 MPa, and a second-phase particle size (500-900 nm) ≤ 1.5 × 10⁻⁶. 3 pcs / mm 2 .

[0022] This invention employs a core strengthening system combined with precise micro-level control logic. The core strengthening system involves three alloying elements: Ni, Co, and Si. Ni serves as the core component of the precipitated phase and the solid solution strengthening carrier. Ni and Si elements can form an orthogonal structure. Compared to the single Ni2Si phase, this phase is more stable. Ni has a high solid solubility in the Cu matrix, and solid solution strengthening can be achieved through solute atom lattice distortion. Simultaneously, it enhances the Cu matrix's ability to dissolve Co and Si, reducing the formation of coarse second phases in the as-cast state. Co partially replaces Ni in the Ni2Si lattice to form the (Ni,Co)2Si phase, refining the precipitate size and improving the phase interface bonding strength. It can also synergistically work with the fine second phase to exert grain boundary pinning, suppressing abnormal grain growth at high temperatures. Si is the core component of the (Ni,Co)2Si phase, and its content directly determines the volume fraction and distribution density of the strengthening phase. A Si content of 0.3-0.8% can avoid the formation of coarse Ni3Si or Co3Si phases, ensuring a uniform and dispersed distribution of precipitates after aging.

[0023] Trace alloying element Sn can hinder dislocation movement and grain boundary migration. During solid solution treatment, it works synergistically with the (Ni,Co)2Si phase to exert a dispersion strengthening effect, increasing peak hardness by 10-15%. Secondly, Zn atomic radius is close to Cu atomic radius, so the lattice distortion caused by solid solution has a smaller impact and can promote the precipitation of phases during aging, improving conductivity. Cr preferentially enriches at grain boundaries, reducing grain boundary segregation and weakening, lowering the risk of intergranular cracking, and improving bending and other machinability. A dense Cr2O3 passivation film is formed on the surface, blocking the intrusion of corrosive media. In environments such as salt spray and NaCl, it can significantly reduce the corrosion rate and pitting tendency, extend the life of components such as connectors, and promote the uniform dispersion precipitation of nanoscale (Ni,Co)2Si strengthening phase, improving the synergistic level of strength and conductivity. Cr3Si and other phases are stable at high temperatures, effectively pinning dislocations and grain boundaries, improving resistance to softening and stress relaxation.

[0024] Second-phase particles hinder grain growth and the performance of the finished product in the following ways: 1. Fine second phase: Refines grains and inhibits growth. Fine second-phase particles can serve as heterogeneous nucleation sites for recrystallization, accelerating recrystallization. At the same time, fine second-phase particles exert a pinning effect to inhibit grain growth. 2. Accelerated solute diffusion and homogenization: Due to the small size of the second-phase particles, the lattice mismatch between the particle size and the copper matrix is ​​small. Solute atoms can diffuse rapidly into the matrix along the phase boundary, accelerating the dissolution and homogenization of the residual phase. 3. During the solid solution process, the dissolution of second-phase particles leaves a large number of vacancies and dislocation defects at the phase interface. These defects become preferential nucleation sites for the (Ni,Co)2Si phase in the aging stage. The nanoscale particles remaining after solid solution can limit the growth of the aging precipitated phase. Example 2:

[0025] The difference from Example 1 is: Hot rolling: heating temperature is 980℃, initial rolling temperature is 980℃, final rolling temperature is 700℃, and the total processing rate is 80%. Intermediate aging annealing: annealing temperature is 450℃, and holding time is 5h; Secondary solution treatment: annealing temperature is 920℃, annealing rate is 45m / min; Example 3:

[0026] The difference from Example 1 is: Melting and casting: casting temperature 1250℃, casting speed 70mm / min.

[0027] Hot rolling: heating temperature is 950℃, initial rolling temperature is 920℃, final rolling temperature is 780℃, and the total processing rate is 82%. Cold rolling before solution treatment: total processing rate 40%.

[0028] Comparative Example 1: The difference from Example 1 is the absence of secondary cold rolling and secondary solution treatment.

[0029] Comparative Example 2: The difference from Example 1 is the absence of secondary cold rolling.

[0030] Comparative Example 3: The difference from Example 1 is that the secondary solution annealing temperature is 1000℃ and the annealing rate is 45m / min.

[0031] Table 1. Performance and microstructure of Examples 1-3 and Comparative Examples 1-3 Results analysis: As can be seen from Table 1: The finished products obtained in Examples 1-2 have small average grain size, few coarse second phase particles, and also have high strength, high conductivity and excellent bending performance.

[0032] The finished product performance of Example 3 was slightly inferior to that of Examples 1 and 2, indicating that large deformation cold rolling before two solution treatments is the key to obtaining the best results.

[0033] The finished products of Comparative Example 1 and Comparative Example 2 showed significant grain coarsening and a large number of coarse second-phase particles, which led to a sharp deterioration in bending performance and poor overall performance in terms of strength and conductivity.

[0034] Compared with the finished product of Example 3, the grains grew, the number of second-phase particles increased, and the bending performance decreased, indicating that the solution temperature needs to be precisely controlled.

[0035] In summary, this invention discloses a method for preparing Cu-Ni-Co-Si alloy strip. Compared with the prior art, the advantages of this invention are that by adjusting the solution treatment process, coarse second-phase particles are further dissolved back, and fine second-phase particles generated by amplitude-modulated decomposition during the solution treatment process are used to refine the grains and optimize the alloy microstructure. The supersaturation inside the alloy is further increased during the solution treatment stage, resulting in an increased number of second-phase particles precipitated and a smaller number of large-sized particles during the subsequent aging process. This ensures that the grains in the solution treatment stage remain fine-grained during the subsequent aging process. Since the aging process is close to peak aging, the hardness and tensile strength of the finished product are increased by 5% compared to the original, the conductivity is slightly improved, and the alloy strip exhibits good bending performance due to the reduction of large-sized second-phase particles.

[0036] Through a series of processes including casting, hot rolling, milling, cold rolling, annealing, cold rolling before primary solution treatment, primary solution treatment, cold rolling before secondary solution treatment, secondary solution treatment, aging treatment, and annealing, the average grain size is controlled, coarse second-phase particles are reduced, and strength and conductivity are improved. The high-performance Cu-Ni-Co-Si alloy strip of this invention has a thickness of 0.5-0.125 mm, with a conductivity of 60-66% IACS; hardness of 220-250 HV; grain size of 0.008-0.01 mm; tensile strength of 700-800 MPa; yield strength of 650-720 MPa; and second-phase grain size (500-900 nm) ≤ 1.5 × 10⁻⁶. 3 pcs / mm 2 Grain size is stably controlled within It has high strength and good electrical conductivity and bending properties, which can meet the requirements of high-end lead frame materials.

[0037] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing Cu-Ni-Co-Si alloy strip, characterized in that, Includes the following steps: Step 1, casting: Prepare alloy ingots according to the alloy composition ratio; Step 2, hot rolling: After holding at 950-1000℃ for 2 hours, the alloy ingot is hot rolled, followed by milling. Step 3, First cold rolling: The milled strip is cold rolled, with a total processing rate of 60-90%; Step 4: Annealing: Anneal the cold-rolled strip. Step 5, Cold rolling before solution treatment: Cold roll the annealed strip with a total processing rate of ≥50% and a single-pass processing rate of 15-30%; Step 6, First Solution Treatment: The cold-rolled strip before the first solution treatment is subjected to solution treatment; Step 7, Cold rolling before secondary solution treatment: Cold rolling is performed on the strip after the primary solution treatment, with a total processing rate of ≥50%; Step 8, Secondary Solution Treatment: The cold-rolled strip before secondary solution treatment is subjected to solution treatment; Step 9, Aging Treatment: The strip after the secondary solution treatment is subjected to aging treatment; Step 10, Finish rolling and low-temperature annealing: The aged strip is finished rolled and annealed at a low temperature.

2. The method for preparing Cu-Ni-Co-Si alloy strip according to claim 1, characterized in that, The alloy composition described in step one, by weight percentage, is as follows: Ni: 0.3-1.0%; Co: 1.3-2.0%; Si: 0.3-0.8%; Sn: 0.03-0.08%; Zn: 0.05-0.10%; Cr: 0.01-0.05%; the balance being Cu and unavoidable non-metallic impurities.

3. A method for preparing Cu-Ni-Co-Si alloy strip according to any one of claims 1 or 2, characterized in that, The melting and casting temperature in step one is 1180-1250℃, and the casting speed is 70-100mm / min.

4. The method for preparing Cu-Ni-Co-Si alloy strip according to claim 1, characterized in that, The hot rolling power in step two is 78-95%, and the final rolling temperature is 800-900℃.

5. The method for preparing Cu-Ni-Co-Si alloy strip according to claim 1, characterized in that, The annealing temperature in step four is 420-520℃, and the annealing time is 6-12 hours.

6. The method for preparing Cu-Ni-Co-Si alloy strip according to claim 1, characterized in that, The temperature of the first solution treatment in step six is ​​900-1020℃, and the annealing rate is 27-40 m / min; the temperature of the second solution treatment in step eight is 850-980℃, and the annealing rate is 30-45 m / min.

7. The method for preparing Cu-Ni-Co-Si alloy strip according to claim 1, characterized in that, The aging treatment in step nine is carried out at a temperature of 420-520℃ for 6-12 hours.

8. The method for preparing Cu-Ni-Co-Si alloy strip according to claim 7, characterized in that, The aging treatment in step nine is carried out at a temperature of 450-480℃ for 7-11 hours.

9. The method for preparing Cu-Ni-Co-Si alloy strip according to claim 1, characterized in that, The finishing rate of the finishing rolling in step ten is 15-30%, the temperature of the low-temperature annealing is 250-400℃, and the annealing rate is 37-48m / min.

10. The method for preparing Cu-Ni-Co-Si alloy strip according to claim 1, characterized in that, It also includes the following steps: Step 11, Bending and Straightening: Unwinding tension is 20-45 N / mm 2 The winding tension is 35-60 N / mm. 2 The entry extension rate is 0.1-0.4%.

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