A copper alloy strip and a method of manufacturing the same

Abstract

The application provides a copper alloy strip and a preparation method thereof. The copper alloy strip comprises the following components in mass percentage: Cr 0.1-0.2%, Ag 0.04-0.06%, Zr 0.02-0.05%, Nb 0.02-0.05%, and the balance of Cu and inevitable impurities. The microstructure of the copper alloy strip comprises a matrix phase and a strengthening phase distributed in the matrix phase. The strengthening phase comprises Cr2Nb and Cr particles. The particle diameter of the strengthening phase is less than or equal to 10 nm, and the particle density per unit area is greater than or equal to 1000 / μm 2 The alloy components of the application add trace amounts of Cr, Zr, Nb and Ag elements, so that Cr2Nb and Cr strengthening phases exist in the alloy microstructure. By controlling the microstructure of the material, the strength, conductivity and high-temperature softening resistance of the material are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of copper alloy technology, and more specifically, to a copper alloy strip and its preparation method. Background Technology

[0002] As the chip carrier of integrated circuits, the leadframe is a key structural component that uses bonding materials to electrically connect the internal circuit leads of the chip with the external leads, forming a circuit. It acts as a bridge connecting to external wires. With my country entering the 5G era, integrated circuits are developing towards ultra-thinness and miniaturization, while requiring increased current and signal transmission. Therefore, higher performance requirements are placed on the chip carrier of integrated circuits—the leadframe.

[0003] Currently, the mobile chip manufacturing industry requires leadframe copper alloys to achieve a conductivity of over 95% IACS, a yield strength of over 550 MPa, and resistance to high-temperature softening, maintaining a hardness of over 85% of the pre-softening hardness after holding at 450℃ for 2 hours. However, current copper alloy series cannot simultaneously meet these performance requirements for conductivity and strength, and achieving the necessary high-temperature softening resistance is also difficult. Therefore, based on application needs, there is an urgent need to develop a new copper alloy strip that maintains high strength while possessing excellent conductivity and high-temperature softening resistance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to provide a copper alloy material with high strength, high conductivity, excellent resistance to high temperature softening, and suitable for the production of lead frames.

[0005] To solve the above-mentioned technical problems, the present invention provides a copper alloy strip comprising the following components by mass percentage: Cr 0.1-0.2%, Ag 0.04-0.06%, Zr 0.02-0.05%, Nb 0.02-0.05%, with the balance being Cu and unavoidable impurities. The microstructure of the copper alloy strip includes a matrix phase and a reinforcing phase distributed in the matrix phase. The reinforcing phase includes Cr₂Nb and Cr particles, the particle diameter of the reinforcing phase being less than or equal to 10 nm, and the particle density per unit area being greater than or equal to 1000 particles / μm. 2 .

[0006] The alloy composition of this invention is scientifically and rationally proportioned, with trace amounts of Cr, Zr, Nb, and Ag elements added. This results in the presence of Cr2Nb and Cr reinforcing phases in the alloy microstructure. These reinforcing phases are distributed at and along grain boundaries, effectively pinning grain boundary movement and improving the material's strength and resistance to high-temperature softening. Furthermore, the diameter of Cr2Nb and Cr is less than 10 nm, and the particle density per unit area is 1000 particles / μm. 2The above fully utilizes the dispersion strengthening effect of the reinforcing phase, significantly improving the material's strength, conductivity, and resistance to high-temperature softening.

[0007] Furthermore, the grain size of the copper alloy strip is less than or equal to 1 μm. According to the Hall-Petch formula σ... s =σ0+Kd -1 / 2 (σ s Let d be the yield strength of the material; σ0 be the average diameter of the grains; σ0 be the yield strength of a single crystal (a constant); and K be the influence coefficient of the grain boundary on the strength (a constant). It can be concluded that within a certain grain size range, the finer the grains, the higher the strength of the material. This invention improves the strength of the material by controlling the grain size to within 1 μm.

[0008] Furthermore, the copper alloy strip has a thickness of 0.1–0.3 mm, a conductivity of ≥95% IACS, a yield strength of ≥550 MPa, and a hardness of ≥85% of its pre-softening hardness after holding at 450°C for 2 hours. The copper alloy strip of this invention possesses high strength, high conductivity, and excellent resistance to high-temperature softening, while simultaneously meeting the thickness specifications required for lead frame materials.

[0009] Furthermore, the ratio of yield strength to tensile strength of the copper alloy strip is above 95%. The copper alloy strip of this invention possesses good bending resistance and ductility, which is beneficial for processing and forming.

[0010] The present invention also provides a method for preparing the above-mentioned copper alloy strip, comprising the following process flow: batching and smelting → semi-continuous casting → hot rolling → milling → rough rolling → edge trimming → primary annealing → finish rolling → stepped aging treatment → finished product rolling → secondary annealing → cleaning; wherein the stepped aging treatment involves first heating to 250-300℃, holding for 2-3 hours, then raising the temperature to 420-460℃, and holding for 5-7 hours.

[0011] This invention employs a step-age aging process with microstructure control, ensuring that the grain size of the material is controlled within 1 μm, thereby improving the material's strength. During the step-age aging process, Cr precipitates, and Zr elements are distributed around the Cr phase, promoting Cr phase nucleation. The low binding energy with vacancies effectively inhibits the bulk diffusion of Cr at medium temperatures, thus improving the alloy's medium-temperature heat resistance. In addition, Nb has a much higher solid solubility in Cr than in copper. During the step-age aging process, Nb exists on the surface and inside the Cr phase, promoting its precipitation and producing the strengthening phase Cr2Nb, which improves the material's strength and resistance to high-temperature softening.

[0012] In a preferred or optional embodiment, the primary annealing employs a single-sheet unfolding air cushion furnace, with an annealing temperature of 860–900°C and an annealing speed of 60–100 m / min. High-temperature rapid air cushion furnace annealing fully dissolves the alloying elements into the matrix, increasing the matrix's solid solubility and enhancing the precipitation ability of subsequent strengthening phases. Combined with a stepped aging process, this promotes the precipitation of strengthening phases Cr₂Nb and Cr, ensuring that the alloy's conductivity reaches above 95% IACS.

[0013] In a preferred or optional embodiment, the secondary annealing is performed using a single-sheet unfolding air cushion furnace at an annealing temperature of 440–470°C and an annealing speed of 100–150 m / min. This invention employs online stress-relief air cushion furnace annealing. Compared to traditional bell-type stress-relief annealing, this annealing process allows for full grain recovery of the alloy's processing texture and complete stress elimination. Simultaneously, the online annealing speed is fast, and the texture does not have time to recrystallize. Therefore, the yield strength to tensile strength ratio of the alloy after stress-relief air cushion furnace annealing can reach over 95%, while the ratio after bell-type stress-relief annealing is below 90%. The higher the yield strength to tensile strength ratio, the better the alloy material's resistance to deformation.

[0014] In a preferred or optional embodiment, the ingot heating temperature for hot rolling is 920–960°C, the holding time is 2–3 hours, the initial hot rolling temperature is 900–940°C, and the final rolling temperature is above 750°C. By employing an innovative low-temperature hot rolling process, the conductivity of the hot-rolled billet is controlled to be 25–35 IACS, thereby ensuring that the finished alloy has high conductivity.

[0015] In a preferred or optional embodiment, the surface roughness Ra of the rolls used for rolling the finished product is 0.01–0.02 μm. Controlling the surface roughness of the rolls results in extremely low surface roughness of the copper alloy strip, which is beneficial for subsequent coating and electroplating operations.

[0016] In a preferred or optional embodiment, the roughing rolling rate is 92-98%, the finishing rolling rate is 40-60%, and the finishing rolling rate is 30-50%. The roughing, finishing, and finishing rolling rates affect the microstructure of the alloy, and controlling the processing rates ensures that the alloy has a high yield strength to tensile strength ratio.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) This invention controls the microstructure of copper alloy by adding Cr, Zr, Nb and Ag elements to the alloy and by using certain heat treatment and processing technology, so that the copper alloy has excellent strength, electrical conductivity and high temperature softening resistance, and is suitable for producing lead frames for mobile phone chips.

[0019] (2) The present invention adopts a high-temperature rapid air cushion furnace annealing and microstructure control step aging process to promote the precipitation of strengthening phases Cr2Nb and Cr, and control the particle size and grain size of the strengthening phase, thereby greatly improving the strength, conductivity and high-temperature softening resistance of the material.

[0020] (3) The present invention uses an online stress-relief gas cushion furnace for annealing. During the annealing process, the processing texture of the alloy grains is fully restored, which improves the resistance to deformation of the alloy material. The prepared copper alloy has low surface roughness, good ductility and bending resistance. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0022] A specific embodiment of the present invention provides a copper alloy strip containing the following elements and mass percentages: Cr 0.1-0.2%, Ag 0.04-0.06%, Zr 0.02-0.05%, Nb 0.02-0.05%, impurities, and the balance being Cu. Its chemical composition is shown in the table below.

[0023] Table 1 Composition of Copper Alloy Strip

[0024] Cr Ag Zr Nb other Cu 0.1-0.2 0.04-0.06 0.02-0.05 0.02-0.05 <0.05 margin

[0025] The copper alloy strip has a grain size of less than or equal to 1 μm. Its microstructure includes a matrix phase and a reinforcing phase distributed within the matrix phase. The reinforcing phase includes Cr2Nb and Cr particles, with a particle diameter of less than or equal to 10 nm and a particle density of greater than or equal to 1000 particles / μm. 2 .

[0026] The copper alloy composition contains trace amounts of Cr, Zr, Nb, and Ag elements. The specific design principle is as follows:

[0027] Cr: During aging treatment, Cr strengthening phases precipitate in the material. These strengthening phases are distributed at and along grain boundaries, which pin grain boundary movement and improve the material's strength and resistance to high-temperature softening.

[0028] Zr: Zr can effectively improve the alloy's resistance to high-temperature softening. At the same time, the element is distributed around the Cr phase, promoting the nucleation of the Cr phase. It has a low binding energy with vacancies and effectively inhibits the bulk diffusion of Cr at medium temperatures, thereby improving the alloy's medium-temperature heat resistance.

[0029] Nb: The solid solubility of Nb in Cr is much greater than that in copper. During aging treatment, Nb exists on the surface and inside the Cr phase, promoting its precipitation and producing the strengthening phase Cr2Nb, which improves the strength and high-temperature softening resistance of the material.

[0030] Ag: Adding trace amounts of Ag can increase the recrystallization temperature and creep strength of this alloy, improve the material's resistance to high-temperature softening, and also has an alloy strengthening effect; at the same time, trace amounts of Ag have a negligible effect on the alloy's conductivity, ensuring that the conductivity can still be maintained above 95% IACS after the addition of Ag.

[0031] In a specific implementation, the preparation method of copper alloy strip includes the following process flow: batching and smelting → semi-continuous casting → hot rolling → milling → rough rolling → edge trimming → primary annealing → finish rolling → stepped aging treatment → finished product rolling → secondary annealing → cleaning. The specific steps are as follows:

[0032] S1, Ingredient Batching and Melting

[0033] After removing the tabs from the electrolytic copper, it is added to a smelting furnace and heated to melt. The molten copper in the furnace is then tightly covered with dry charcoal. The temperature is then raised to 1350–1400°C, and pure chromium, niobium, and silver are added according to the composition ratio. After 10–15 minutes, the slag is skimmed off, and the furnace is covered with a covering agent with a thickness of 80–100 mm. The gas diffuser installed at the bottom of the furnace is opened, and high-purity CO gas is introduced. After holding at this temperature for 1–1.5 hours, the temperature of the molten copper is lowered to 1300–1340°C.

[0034] S2, Semi-continuous casting

[0035] Control the temperature of the molten copper at 1300-1340℃, and put the molten copper into the intermediate chute. When the molten copper flows out for 0.5-1 minute, add one 300g bag of copper-zirconium master alloy (containing 20% ​​zirconium). Then add one 300g bag of copper-zirconium master alloy every minute, and add one spoonful of 500g mixed solvent (crystal and sodium carbonate in a 1:1 ratio). Then, turn on the cooling water. When the copper liquid level in the crystallizer reaches about two-thirds of the crystallizer's capacity, start the traction machine and begin casting at 20-30 mm / min. Turn on the vibration at a frequency of 50-70 times / min and an amplitude of 3-6 mm. Throughout the casting process, a mixed solvent (cryolite and sodium carbonate in a 1:1 ratio) is used. When the ingot reaches 0.5-1.0 meters, a steady-speed casting stage is reached, with the casting speed controlled at 40-50 mm / min. The primary cooling water flow rate is 15-20 m³ / h, the inlet temperature is 20-28℃, and the outlet temperature is controlled at 45-55℃. An independent secondary cooling water system is used, with an inlet temperature of 20-28℃ and an inlet flow rate of 6-10 m³ / h. The ingot casting dimensions are 180*630mm*7000mm.

[0036] S3, hot rolled

[0037] The ingot heating temperature is 920℃~960℃, the holding time is 2~3h, the hot rolling start temperature is 900℃~940℃, and the final rolling temperature is above 750℃, ensuring that the electrical conductivity of the hot-rolled billet is controlled within 25~35IACS%. The hot rolling yield is above 90%, and the width after hot rolling expansion is 655±5mm.

[0038] S4, Milling Surface

[0039] The single-sided milling depth is 0.6–0.9 mm.

[0040] S5, rough rolling

[0041] The roughing rate is controlled at 92-98%.

[0042] S6, trimming

[0043] The single-sided shearing is 7-8 mm, and the width after shearing is 640±0.5 mm.

[0044] S7, First Annealing

[0045] Annealing was performed in a single-sheet unfolding air cushion furnace at a temperature of 860–900℃ and a speed of 60–100 m / min. The protective gas was a mixture of nitrogen and hydrogen, with a hydrogen content of 2–4%. The average grain size was controlled to be less than 2 μm after one annealing.

[0046] S8, precision rolling

[0047] The finishing rate is controlled between 40% and 60%.

[0048] S9, Stepped Aging Processing

[0049] Heating to 250–300℃ and holding for 2–3 hours; then raising the temperature to 420–460℃ and holding for 5–7 hours. This ensures that the grain size of the material is controlled within 1 μm, while guaranteeing that the diameter of the precipitated reinforcing phases Cr₂Nb and Cr is within 10 nm, and the number of reinforcing phase particles precipitated per unit area is 1000 / μm. 2 The above fully utilizes the dispersion strengthening effect of the reinforcing phase, significantly improving the material's strength, conductivity, and resistance to high-temperature softening. However, if the size of the precipitated reinforcing phase particles reaches 30 nm or more, its strengthening effect is greatly reduced, making it difficult to provide sufficient reinforcement.

[0050] S10, Finished product rolling

[0051] The rolls used in the finished product rolling process are ground with 400-mesh ceramic grinding wheels. The surface roughness Ra of the rolls is controlled at 0.01 to 0.02 μm, and the processing rate is controlled at 30 to 50%.

[0052] S11, Secondary Annealing

[0053] Online stress-relief annealing was performed using a single-sheet unfolding air cushion furnace at a temperature of 440–470℃ and a speed of 100–150 m / min. The protective gas was a mixture of nitrogen and hydrogen with a hydrogen content of 2–4%.

[0054] S12, Cleaning

[0055] First, degreasing is performed using an aqueous sodium hydroxide solution with a pH range of 7-9 and a solution temperature of 60-70℃. Then, acid washing is performed using a sulfuric acid concentration of 100-130 g / L at a temperature ≤40℃, with Cu in the acid solution. 2+ ≤1.2g / l; clean and dry, oven temperature is 65~70℃.

[0056] S13. Finished product slitting and packaging.

[0057] The copper alloy strip prepared according to the embodiments of the present invention has a thickness of 0.1 to 0.3 mm, a conductivity of 95% IACS or higher, a yield strength of 550 MPa or higher, a yield strength to tensile strength ratio of 95% or higher, and a hardness of 85% or higher than the hardness before softening after being kept at 450°C for 2 hours. It is suitable as a material for producing lead frames.

[0058] The technical solution and effects of the present invention will be illustrated below with specific embodiments.

[0059] Example 1

[0060] The copper alloy strip contains the following elements and their mass percentages: Cr 0.19%, Ag 0.045%, Zr 0.045%, Nb 0.029%, with the balance being Cu. Its preparation steps are as follows:

[0061] 1) Batching and Smelting: After removing the tabs from the electrolytic copper, it is added to the smelting furnace and heated to melt. The molten copper in the furnace must be tightly covered with dry charcoal, which must be baked at 200℃ for at least 2 hours. The charcoal covering thickness should be 100-150mm, and no copper liquid should be exposed to the air. Then, the temperature is raised to 1390℃, and pure chromium, niobium, and silver are added according to the composition ratio. After 10-15 minutes, the slag is skimmed off, and a covering agent of cryolite and sodium carbonate in a 1:1 ratio is used for covering, with a covering thickness of 80-100mm. The gas diffuser installed at the bottom of the furnace is opened, and high-purity CO gas is introduced at a pressure of 0.15MPa and a low-pressure gas flow rate of 35L / min. After holding at this temperature for 1.2 hours, the temperature of the molten copper is lowered to 1330℃.

[0062] 2) Semi-continuous casting: Control the temperature of the molten copper at 1330℃, and put the molten copper into an intermediate chute with a width of 0.5m, a length of 0.7m, and a height of 0.5m. When the molten copper flows out for 0.5 to 1 minute, add one bag of 300g copper-zirconium master alloy (containing 20% ​​zirconium). After that, add one bag of 300g copper-zirconium master alloy every minute, and add one spoonful of 500g mixed solvent (crystal and sodium carbonate in a 1:1 ratio). Then turn on the cooling water, and the water pressure should be controlled at about 100-150 kPa. Then rotate the stopper rod. When the copper liquid in the crystallizer reaches about two-thirds of the crystallizer, start the traction machine and start the casting operation at 20-30 mm / min. Turn on the vibration, with a frequency of 50-70 times / min and an amplitude of 3-6 mm. During the entire casting process, the mixed solvent (cryolite and sodium carbonate in a 1:1 ratio) should be added in small amounts and multiple times to prevent the copper liquid from being exposed due to insufficient addition. Also, avoid adding too much mixed solvent at once, which may cause inclusions on the surface of the ingot. Sprinkle it evenly on the surface of the copper liquid so that a thin layer of covering agent covers the liquid surface in the crystallizer. During the steady-speed casting stage (when the ingot is drawn to a length of 0.5–1.0 meters, the casting speed is 48 mm / min. The primary cooling water flow rate of the crystallizer is 19 m³ / h, the inlet temperature is 26℃, and the outlet temperature is controlled at 52℃. An independent secondary cooling water system is used, with an inlet temperature of 27℃ and an inlet flow rate of 9 m³ / h. The ingot dimensions are 180*630mm*7000mm.

[0063] 3) Hot rolling: The ingot heating temperature is 950℃, the holding time is 2.2h, the hot rolling start temperature is 935℃, and the final rolling temperature is 780℃. The hot rolling processing rate is over 90%, the thickness after hot rolling is 17±0.02mm, and the width after hot rolling expansion is 655±5mm.

[0064] 4) Milling: The milling amount on one side is 0.6 to 0.9 mm, and the thickness after milling is 15.5 mm.

[0065] 5) Rough rolling: The rough rolling rate is controlled at 92-98%, and the rolling thickness is 0.75±0.01mm.

[0066] 6) Trimming: The single-sided trimming is 7-8mm, and the width after trimming is 640±0.5mm.

[0067] 7) Single annealing: Annealing is carried out in a single-sheet unfolding air cushion furnace at a temperature of 870℃ and a speed of 90m / min. The protective gas is a mixture of nitrogen and hydrogen (hydrogen content 2-4%).

[0068] 8) Finish rolling: The processing rate is controlled at 40-60%, and the rolling thickness is 0.35±0.005mm.

[0069] 9) Stepped aging treatment: Heat to 290℃ and hold for 2.3 hours. Then raise the temperature to 440℃ and hold for 6 hours.

[0070] 10) Finished product rolling: The processing rate is controlled at 30-50%, and the finished product rolling thickness is 0.2±0.005mm. The rolls used in the finished product rolling process are ground with 400-mesh ceramic grinding wheels, and the surface roughness Ra of the rolls is controlled at 0.018μm.

[0071] 11) Secondary annealing: Online stress-relief annealing is carried out using a single-sheet unfolding air cushion furnace. The annealing temperature is 460℃, the annealing speed is 115m / min, and the protective gas is a mixture of nitrogen and hydrogen (hydrogen content 2-4%).

[0072] 12) Cleaning: Clean with degreasing agent, sulfuric acid and water in sequence, and then dry.

[0073] 13) Finished products are slitting and packaging.

[0074] Example 2

[0075] The copper alloy strip contains the following elements and their mass percentages: Cr 0.17%, Ag 0.052%, Zr 0.037%, Nb 0.036%, with the balance being Cu. Its preparation steps are as follows:

[0076] 1) Batching and Smelting: After removing the tabs from the electrolytic copper, it is added to the smelting furnace and heated to melt. The molten copper in the furnace must be tightly covered with dry charcoal, which must be baked at 200℃ for at least 2 hours. The charcoal covering thickness should be 100-150mm, and no molten copper should be exposed to the air. Then, the temperature is raised to 1390℃, and pure chromium, niobium, and silver are added according to the composition ratio. After 10-15 minutes, the slag is skimmed off, and a covering agent of cryolite and sodium carbonate in a 1:1 ratio is used for covering, with a covering thickness of 80-100mm. The gas diffuser installed at the bottom of the furnace is opened, and high-purity CO gas is introduced at a pressure of 0.2MPa and a low-pressure gas flow rate of 28L / min. After holding at this temperature for 1.4 hours, the temperature of the molten copper is lowered to 1320℃.

[0077] 2) Semi-continuous casting: Control the temperature of the molten copper at 1320℃, and place the molten copper into an intermediate chute measuring 0.5m wide * 0.7m long * 0.5m high. Add one 300g bag of copper-zirconium master alloy (containing 20% ​​zirconium) 0.5–1 minute after the molten copper flows out. Then add one 300g bag of copper-zirconium master alloy every minute, along with one spoonful of 500g mixed solvent (cryolite and sodium carbonate in a 1:1 ratio). Turn on the cooling water, maintaining the water pressure at approximately 100–150 kPa. Rotate the stopper rod until the molten copper in the crystallizer reaches about two-thirds full. Start the traction machine at a speed of 20–30 mm / min to begin casting. Turn on the vibration at a frequency of 50–70 times / min and an amplitude of 3–6 mm. Cover the entire casting process with the mixed solvent (cryolite and sodium carbonate in a 1:1 ratio). During the steady-speed casting stage, the casting speed is controlled at 43 mm / min. The primary cooling water flow rate of the crystallizer is 17 m³ / h, the inlet water temperature is 24℃, and the outlet water temperature is controlled at 50℃. An independent secondary cooling water system is used, with the secondary cooling water inlet temperature at 24℃ and the inlet flow rate at 8 m³ / h. The ingot dimensions are 180*630mm*7000mm.

[0078] 3) Hot rolling: The ingot heating temperature is 930℃, the holding time is 2.8h, the hot rolling start temperature is 920℃, and the final rolling temperature is 765℃. The hot rolling processing rate is over 90%, the thickness after hot rolling is 16.5±0.02mm, and the width after hot rolling expansion is 655±5mm.

[0079] 4) Milling: The milling amount on one side is 0.6 to 0.9 mm, and the thickness after milling is 15 mm.

[0080] 5) Rough rolling: The rough rolling rate is controlled at 92-98%, and the rolling thickness is 0.7±0.01mm.

[0081] 6) Trimming: The single-sided trimming is 7-8mm, and the width after trimming is 640±0.5mm.

[0082] 7) Single annealing: Annealing is carried out in a single-sheet unfolding air cushion furnace at a temperature of 870℃ and a speed of 90m / min. The protective gas is a mixture of nitrogen and hydrogen (hydrogen content 2-4%).

[0083] 8) Finish rolling: The processing rate is controlled at 40-60%, and the rolling thickness is 0.37±0.005mm.

[0084] 9) Stepped aging treatment: Heat to 280℃ and hold for 2.5 hours. Then raise the temperature to 450℃ and hold for 5 hours.

[0085] 10) Finished product rolling: The processing rate is controlled at 30-50%, and the finished product rolling thickness is 0.2±0.005mm. The rolls used in the finished product rolling process are ground with 400-mesh ceramic grinding wheels, and the surface roughness Ra of the rolls is controlled at 0.012μm.

[0086] 11) Secondary annealing: Online stress-relief annealing is carried out using a single-sheet unfolding air cushion furnace. The annealing temperature is 450℃, the annealing speed is 110m / min, and the protective gas is a mixture of nitrogen and hydrogen (hydrogen content 2-4%).

[0087] 12) Cleaning: Clean with degreasing agent, sulfuric acid and water in sequence, and then dry.

[0088] 13) Finished products are slitting and packaging.

[0089] Example 3

[0090] The copper alloy strip contains the following elements and their mass percentages: Cr 0.13%, Ag 0.058%, Zr 0.024%, Nb 0.046%, with the balance being Cu. Its preparation steps are as follows:

[0091] 1) Batching and Smelting: After removing the tabs from the electrolytic copper, it is added to the smelting furnace and heated to melt. The molten copper in the furnace must be tightly covered with dry charcoal, which must be baked at 200℃ for at least 2 hours. The charcoal covering thickness should be 100-150mm, and no copper liquid should be exposed to the air. Then, the temperature is raised to 1390℃, and pure chromium, niobium, and silver are added according to the composition ratio. After 10-15 minutes, the slag is skimmed off, and a covering agent of cryolite and sodium carbonate in a 1:1 ratio is used for covering, with a covering thickness of 80-100mm. The gas diffuser installed at the bottom of the furnace is opened, and high-purity CO gas is introduced at a pressure of 0.15MPa and a low-pressure gas flow rate of 35L / min. After holding at this temperature for 1.3 hours, the temperature of the molten copper is lowered to 1310℃.

[0092] 2) Semi-continuous casting: Control the temperature of the molten copper at 1310℃, and place the molten copper into an intermediate chute measuring 0.5m wide * 0.7m long * 0.5m high. After the molten copper has flowed out for 0.5–1 minute, add one 300g bag of copper-zirconium master alloy (containing 20% ​​zirconium). Then add one 300g bag of copper-zirconium master alloy every minute, along with one spoonful of 500g mixed solvent (cryolite and sodium carbonate in a 1:1 ratio). Next, turn on the cooling water, maintaining the water pressure at approximately 100–150 kPa. Rotate the stopper rod until the molten copper in the crystallizer reaches about two-thirds full. Start the traction machine at a speed of 20–30 mm / min to begin casting. Turn on the vibration at a frequency of 50–70 times / min and an amplitude of 3–6 mm. During the steady-speed casting stage, the casting speed is controlled at 47 mm / min. The primary cooling water flow rate of the crystallizer is 19 m³ / h, the inlet water temperature is 22℃, and the outlet water temperature is controlled at 48℃. An independent secondary cooling water system is used, with a secondary cooling water inlet temperature of 24℃ and an inlet water flow rate of 8 m³ / h. The ingot dimensions are 180*630mm*7000mm.

[0093] 3) Hot rolling: The ingot heating temperature is 940℃, the holding time is 2.5h, the hot rolling start temperature is 925℃, and the final rolling temperature is 770℃. The hot rolling processing rate is over 90%, the thickness after hot rolling is 15.5±0.02mm, and the width after hot rolling expansion is 655±5mm.

[0094] 4) Milling: The milling amount on one side is 0.6 to 0.9 mm, and the thickness after milling is 14 mm.

[0095] 5) Rough rolling: The rough rolling rate is controlled at 92-98%, and the rolling thickness is 0.65±0.01mm.

[0096] 6) Trimming: The single-sided trimming is 7-8mm, and the width after trimming is 640±0.5mm.

[0097] 7) Single annealing: Annealing is carried out in a single-sheet unfolding air cushion furnace at an annealing temperature of 890℃ and an annealing speed of 95m / min. The protective gas is a mixture of nitrogen and hydrogen (hydrogen content 2-4%).

[0098] 8) Finish rolling: The processing rate is controlled at 40-60%, and the rolling thickness is 0.27±0.005mm.

[0099] 9) Stepped aging treatment: Heat to 260℃ and hold for 2.6 hours. Then raise the temperature to 430℃ and hold for 7 hours.

[0100] 10) Finished product rolling: The processing rate is controlled at 30-50%, and the finished product rolling thickness is 0.15±0.005mm. The rolls used in the finished product rolling process are ground with 400-mesh ceramic grinding wheels, and the surface roughness Ra of the rolls is controlled at 0.014μm.

[0101] 11) Secondary annealing: Online stress-relief annealing is carried out using a single-sheet unfolding air cushion furnace. The annealing temperature is 440℃, the annealing speed is 130m / min, and the protective gas is a mixture of nitrogen and hydrogen (hydrogen content 2-4%).

[0102] 12) Cleaning: Clean with degreasing agent, sulfuric acid and water in sequence, and then dry.

[0103] 13) Finished products are slitting and packaging.

[0104] Example 4

[0105] The copper alloy strip contains the following elements and their mass percentages: Cr 0.15%, Ag 0.05%, Zr 0.035%, Nb 0.035%, with the balance being Cu. Its preparation steps are as follows:

[0106] 1) Batching and Smelting: After removing the tabs from the electrolytic copper, it is added to the smelting furnace and heated to melt. The molten copper in the furnace must be tightly covered with dry charcoal, which must be baked at 200℃ for at least 2 hours. The charcoal covering thickness should be 100-150mm, and no copper liquid should be exposed to the air. Then, the temperature is raised to 1390℃, and pure chromium, niobium, and silver are added according to the composition ratio. After 10-15 minutes, the slag is skimmed off, and a covering agent of cryolite and sodium carbonate in a 1:1 ratio is used for covering, with a covering thickness of 80-100mm. The gas diffuser installed at the bottom of the furnace is opened, and high-purity CO gas is introduced at a pressure of 0.25MPa and a low-pressure gas flow rate of 26L / min. After holding at this temperature for 1.1 hours, the temperature of the molten copper is lowered to 1335℃.

[0107] 2) Semi-continuous casting: Control the temperature of the molten copper to 1335°C and place it into an intermediate chute (0.5m wide x 0.7m long x 0.5m high). Add one 300g bag of copper-zirconium master alloy (containing 20% ​​zirconium) 0.5-1 minute after the molten copper flows out. Then add one 300g bag of copper-zirconium master alloy every minute, along with one spoonful of 500g mixed solvent (cryolite and sodium carbonate in a 1:1 ratio). Turn on the cooling water, maintaining a pressure of approximately 100-150 kPa. Rotate the stopper rod until the molten copper in the crystallizer reaches about two-thirds full. Start the traction machine at a speed of 20-30 mm / min to begin casting. Turn on the vibration at a frequency of 50-70 times / min and an amplitude of 3-6 mm. Cover the casting process with the mixed solvent (cryolite and sodium carbonate in a 1:1 ratio). During the steady-speed casting stage, control the casting speed at 46 m / min and the primary cooling water flow rate in the crystallizer at 19 m³ / min. 3 The system operates at a flow rate of 7 m³ / h, with an inlet water temperature of 22℃ and an outlet water temperature controlled at 47℃. It employs an independent secondary cooling water system with an inlet water temperature of 22℃ and an inlet flow rate of 7 m³ / h. 3 / h. The ingot dimensions are 180*630mm*7000mm.

[0108] 3) Hot rolling: The ingot heating temperature is 955℃, the holding time is 2.6h, the hot rolling start temperature is 935℃, and the final rolling temperature is 790℃. The hot rolling processing rate is over 90%, the thickness after hot rolling is 13±0.02mm, and the width after hot rolling expansion is 655±5mm.

[0109] 4) Milling: The milling amount on one side is 0.6 to 0.9 mm, and the thickness after milling is 11.5 mm.

[0110] 5) Rough rolling: The rough rolling rate is controlled at 92-98%, and the rolling thickness is 0.65±0.01mm.

[0111] 6) Trimming: The single-sided trimming is 7-8mm, and the width after trimming is 640±0.5mm.

[0112] 7) Single annealing: Annealing is carried out in a single-sheet unfolding air cushion furnace at an annealing temperature of 890℃ and an annealing speed of 95m / min. The protective gas is a mixture of nitrogen and hydrogen (hydrogen content 2-4%).

[0113] 8) Finish rolling: The processing rate is controlled at 40-60%, and the rolling thickness is 0.27±0.005mm.

[0114] 9) Stepped aging treatment: Heat to 260℃ and hold for 2.6 hours. Then raise the temperature to 430℃ and hold for 7 hours.

[0115] 10) Finished product rolling: The processing rate is controlled at 30-50%, and the finished product rolling thickness is 0.15±0.005mm. The rolls used in the finished product rolling process are ground with 400-mesh ceramic grinding wheels, and the surface roughness Ra of the rolls is controlled at 0.014μm.

[0116] 11) Secondary annealing: Online stress-relief annealing is carried out using a single-sheet unfolding air cushion furnace. The annealing temperature is 440℃, the annealing speed is 130m / min, and the protective gas is a mixture of nitrogen and hydrogen (hydrogen content 2-4%).

[0117] 12) Cleaning: Clean with degreasing agent, sulfuric acid and water in sequence, and then dry.

[0118] 13) Finished products are slitting and packaging.

[0119] Comparative Example 1

[0120] The copper alloy strip contains the following elements and mass percentages: Cr 0.20%, Ag 0.052%, and the balance Cu. Zr and Nb are not added to the alloy. The preparation steps are the same as in Example 4.

[0121] Comparative Example 2

[0122] The copper alloy strip contains the following elements and their mass percentages: Cr 0.15%, Ag 0.05%, Zr 0.035%, Nb 0.035%, with the balance being Cu. The preparation steps differ from those in Example 4 in that step 9) does not employ a microstructure-controlled step-aging treatment, but instead uses a single aging treatment at 455℃ for 6.5 hours.

[0123] Comparative Example 3

[0124] The copper alloy strip contains the following elements and their mass percentages: Cr 0.15%, Ag 0.05%, Zr 0.035%, Nb 0.035%, with the balance being Cu. The preparation steps differ from those in Example 4 in that, in step 7), the annealing temperature is 700°C during the first annealing.

[0125] Comparative Example 4

[0126] The copper alloy strip contains the following elements and their mass percentages: Cr 0.15%, Ag 0.05%, Zr 0.035%, Nb 0.035%, with the balance being Cu. The preparation steps differ from those in Example 4 in that step 11) the secondary annealing uses traditional bell-type annealing at a temperature of 260℃ for 3 hours.

[0127] The specific compositions of the copper alloy strips of Examples 1-4 and Comparative Examples 1-4 are shown in Table 2 below, and the key process parameters are shown in Table 3 below.

[0128] Table 2 Chemical composition (wt%) of various embodiments and comparative examples of the present invention

[0129] serial number Ag Cr Zr Nb Cu Example 1 0.045 0.19 0.045 0.029 margin Example 2 0.052 0.17 0.037 0.036 margin Example 3 0.058 0.13 0.024 0.046 margin Example 4 0.05 0.15 0.035 0.035 margin Comparative Example 1 0.052 0.20 — — margin Comparative Example 2 0.05 0.15 0.035 0.035 margin Comparative Example 3 0.05 0.15 0.035 0.035 margin Comparative Example 4 0.05 0.15 0.035 0.035 margin

[0130] Table 3 Key process parameters control for each embodiment and comparative example of the present invention

[0131]

[0132]

[0133] The mechanical properties, electrical conductivity, and microstructure of the copper alloy strips prepared in Examples 1-4 and Comparative Examples 1-4 were tested, and the results are recorded in Table 4. The test methods are as follows:

[0134] Mechanical property testing: The room temperature tensile test was conducted on an electronic universal mechanical property testing machine in accordance with GB / T 228.1-2010 Metallic materials, tensile testing - Part 1: Room temperature test method. A 20 mm wide specimen with a head was used, and the tensile speed was 5 mm / min.

[0135] Conductivity test: According to GB / T 3048.2-2007 Electrical properties test method for wires and cables Part 2: Resistivity test for metallic materials, expressed as %IACS.

[0136] Metallographic grain size test: The grain size in the photographs acquired using a 500x metallographic microscope was tested according to the intercept method in GB / T 6394-2007, "Method for Determination of Average Grain Size of Metals". The sample width was 10 mm and the length was 10 mm.

[0137] Roughness inspection: The surface roughness Ra is inspected using the JIS2001 roughness test standard.

[0138] Table 4. Tissue structure and performance of various embodiments and comparative examples of the present invention.

[0139]

[0140] The copper alloy strips prepared in Examples 1-4 have a conductivity of 96-97.5% IACS, a yield strength of 569-580 MPa, a yield strength to tensile strength ratio of over 97%, and a hardness of over 90% of the pre-softening hardness after holding at 450℃ for 2 hours. They exhibit good bending resistance, high strength, excellent high-temperature softening resistance, and good conductivity.

[0141] Comparing Example 4 with Comparative Example 1, it is evident that the addition of Zr and Nb elements promotes the precipitation of strengthening phases, significantly improving the material's strength, bending resistance, electrical conductivity, and high-temperature softening resistance. Comparing Example 4 with Comparative Example 2, it is evident that the microstructure-controlled step-aging treatment, compared to single aging treatment, can reduce the grain size of the material, decrease the size of the strengthening phase particles, and increase the unit particle density, thereby significantly improving the material's strength, bending resistance, electrical conductivity, and high-temperature softening resistance. Comparing Example 4 with Comparative Example 3, it is evident that the temperature of the first annealing affects the microstructure of the material; high-temperature annealing is beneficial for improving the material's mechanical properties, electrical conductivity, and high-temperature softening resistance. Comparing Example 4 with Comparative Example 4, it is evident that online stress-relief gas cushion furnace annealing, compared to traditional bell-type stress-relief annealing, is beneficial for improving the alloy's yield strength to tensile strength ratio, resulting in better resistance to deformation.

[0142] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A copper alloy strip, characterized in that, The copper alloy strip comprises the following components by mass percentage: Cr 0.1–0.2%, Ag 0.04–0.06%, Zr 0.02–0.05%, Nb 0.02–0.05%, with the balance being Cu and unavoidable impurities. The microstructure of the copper alloy strip includes a matrix phase and a reinforcing phase distributed within the matrix phase. The reinforcing phase comprises Cr₂Nb and Cr particles, with a particle diameter less than or equal to 10 nm and a particle density greater than or equal to 1000 particles / μm. 2 ; The preparation method of the copper alloy strip includes the following process flow: batching and smelting → semi-continuous casting → hot rolling → milling → rough rolling → edge trimming → primary annealing → finish rolling → stepped aging treatment → finished product rolling → secondary annealing → cleaning; the stepped aging treatment involves first heating to 250-300℃, holding for 2-3 hours, then raising the temperature to 420-460℃ and holding for 5-7 hours; the annealing temperature of the primary annealing is 860-900℃, and the annealing temperature of the secondary annealing is 440-470℃.

2. The copper alloy strip according to claim 1, characterized in that, The grain size of the copper alloy strip is less than or equal to 1 μm.

3. The copper alloy strip according to claim 2, characterized in that, The copper alloy strip has a thickness of 0.1 to 0.3 mm, a conductivity of 95% IACS or higher, a yield strength of 550 MPa or higher, and a hardness of 85% or higher than the pre-softening hardness after being kept at 450°C for 2 hours.

4. The copper alloy strip according to claim 3, characterized in that, The ratio of the yield strength to the tensile strength of the copper alloy strip is 95% or higher.

5. A method for preparing copper alloy strip as described in any one of claims 1-4, characterized in that, The process includes the following steps: batching and smelting → semi-continuous casting → hot rolling → milling → rough rolling → trimming → primary annealing → finish rolling → stepped aging treatment → finished product rolling → secondary annealing → cleaning; the stepped aging treatment involves first heating to 250-300℃ and holding for 2-3 hours, then raising the temperature to 420-460℃ and holding for 5-7 hours; the primary annealing temperature is 860-900℃, and the secondary annealing temperature is 440-470℃.

6. The method for preparing copper alloy strip according to claim 5, characterized in that, The primary annealing is performed using a single-sheet unfolding air cushion furnace, with an annealing speed of 60–100 m / min.

7. The method for preparing copper alloy strip according to claim 5, characterized in that, The secondary annealing is performed in a single-sheet unfolding air cushion furnace at a speed of 100–150 m / min.

8. The method for preparing copper alloy strip according to claim 5, characterized in that, The hot-rolled ingot heating temperature is 920-960℃, the holding time is 2-3 hours, the hot rolling start temperature is 900-940℃, and the final rolling temperature is above 750℃.

9. The method for preparing copper alloy strip according to claim 5, characterized in that, The surface roughness Ra of the rolls used in the finished product rolling process is 0.01 to 0.02 μm.

10. The method for preparing copper alloy strip according to claim 5, characterized in that, The roughing rate is 92-98%, the finishing rate is 40-60%, and the finished product rolling rate is 30-50%.

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