Large-size high-precision copper alloy pipe batch production method

Abstract

The application discloses a large-size high-precision copper alloy pipe batch production method and belongs to the technical field of non-ferrous metal processing. The method sequentially comprises alloy smelting and semi-continuous casting, ingot homogenization heat treatment and blank pretreatment, hot extrusion forming, multi-pass cold rolling forming, grading heat treatment, full-process online detection and finishing procedures; the application effectively solves the technical problems of great forming difficulty, poor size precision control, uneven organization performance and insufficient batch production stability of the existing large-size copper alloy pipe by optimizing the copper alloy component proportion and full-process process parameters and constructing a full-process online closed-loop control system, and the prepared copper alloy pipe has excellent size precision, mechanical properties and corrosion resistance and can be widely applied to high-end industrial fields such as marine engineering, nuclear power and petroleum chemical industry.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal processing technology, specifically relating to a method for mass production of large-size, high-precision copper alloy tubes. Background Technology

[0002] Large-size, high-precision copper alloy tubes are core materials in high-end equipment fields such as marine engineering, nuclear power equipment, petrochemicals, high-voltage power transmission and distribution, and shipbuilding. These applications place stringent demands on the dimensional accuracy, microstructure uniformity, mechanical property stability, cold and hot forming properties, and consistency in large-scale production of copper alloy tubes. With the rapid transformation and upgrading of my country's high-end equipment manufacturing industry, the market demand for large-size, high-precision copper alloy tubes continues to rise, and the requirements for product performance and production stability are also constantly increasing. However, there are still many bottlenecks in related domestic production technologies, and the long-term reliance on imports for large-size, high-precision copper alloy tubes in high-end fields severely restricts the independent and controllable development of my country's high-end equipment industry chain.

[0003] Currently, extensive research and technological development have been conducted both domestically and internationally regarding the production, processing, composition design, and process control of large-size copper alloy tubes, resulting in a number of related patented technologies and theoretical research achievements. In terms of precision control during processing, authorized patent CN119940040B, "A High-Precision Processing Method and System for Multi-Specification Copper Tubes," developed a dynamic parameter control and real-time closed-loop control technology based on digital twins for the cold drawing process of copper tubes, effectively improving the deformation control precision of the cold drawing process. Authorized patent CN120948483B, "A Comprehensive Detection Device for Copper Tube Surface Defects," developed a multi-dimensional online detection and re-inspection technology for the surface defect detection of finished copper tubes, improving the detection efficiency and accuracy of surface defects. However, these technologies only set up control modules for a single stage of the production process, failing to cover the entire production chain from raw material smelting to finished product finishing. They lack coordinated control of core processes such as casting, extrusion, and heat treatment, making it impossible to achieve real-time correction of dimensional deviations and full-process defect prevention during production, thus hindering the guarantee of product consistency in large-scale production.

[0004] Regarding the forming process of large-diameter pipes, patent CN119566093A, "A Method for Preparing Ultra-Large Diameter Copper-Nickel Alloy Seamless Pipes," employs a process route of casting-forging-skew rolling piercing-hot rolling-cold rolling, achieving the forming and preparation of ultra-large diameter pipes and solving the fundamental forming challenges of large-diameter pipes. However, this type of process does not systematically optimize for problems that easily occur during the forming of large-diameter pipes, such as uneven wall thickness, excessive eccentricity, and forming cracks, making it difficult to simultaneously achieve the dual goals of large-diameter forming and high-precision dimensional control.

[0005] Regarding copper alloy composition and preparation process systems, authorized patent CN118064759B, "Anti-zinc corrosion resistant brass alloy, its preparation method and application," achieves effective control of the microstructure and basic mechanical properties of brass alloys through multi-element alloy composition design and grain boundary optimization processes. Publicly available patent CN119265448A, "A copper alloy tube and its preparation method and application," improves the circumferential and longitudinal performance uniformity of copper tubes through synergistic optimization of multi-pass processing and annealing processes. However, the process routes of such technologies are mostly suitable for the continuous production of small-diameter bars, wires, or conventional-diameter copper tubes. They lack supporting industrial processes for semi-continuous casting, hot extrusion, and multi-pass cold rolling of large-diameter, thick-walled tubes. Furthermore, a comprehensive microstructure and performance control system covering the entire production process has not been established, making it difficult to guarantee the consistency of the microstructure and mechanical properties of large-diameter, thick-walled tubes and failing to meet the large-scale production needs of high-end, high-precision tubes.

[0006] Based on existing technologies and research findings, the current industry still faces several common technical bottlenecks in the production technology of large-size, high-precision copper alloy tubes: First, existing technologies mostly focus on optimizing single processes or single properties, failing to form a comprehensive, systematic technical solution covering alloy composition design, casting, hot working, cold working, heat treatment, and finished product finishing. This makes it difficult to achieve a synergistic improvement in tube dimensional accuracy, microstructure, and production stability. Second, the forming process has not been systematically optimized for the deformation characteristics of large-size, thick-walled copper tubes, making it impossible to solve the problem of dimensional accuracy control during the forming process of large-size tubes. The industry suffers from several pain points, including difficulties in forming and numerous molding defects, making it difficult to simultaneously meet the dual demands of large-scale forming and high-precision control. Thirdly, the production process control lacks a fully online collaborative closed-loop control system, relying heavily on offline detection and post-production adjustments. This makes it impossible to correct parameter deviations in single processes in real time, resulting in large fluctuations in product size and performance and low yield rates in large-scale production. Fourthly, existing technologies struggle to simultaneously meet the comprehensive requirements of large-scale forming, high-precision control, stable mechanical properties, and large-scale mass production, making it difficult to adapt to the self-sufficiency production needs of my country's high-end equipment manufacturing industry for large-scale, high-precision copper alloy tubes.

[0007] Therefore, in response to the core industry bottlenecks of existing large-size, high-precision copper alloy tube production technologies, such as the difficulty in balancing large-size forming and high-precision control, insufficient ability to coordinate and regulate microstructure and properties, and poor stability in large-scale production, developing a set of mass production technologies for large-size, high-precision copper alloy tubes that covers alloy composition design, full-process forming and processing, precise microstructure control, and online closed-loop management has significant engineering application value and industrial promotion significance. It is also of great importance for breaking the dependence on imports of high-end copper alloy tubes and achieving independent control. Summary of the Invention

[0008] This invention addresses industry bottlenecks in existing large-size, high-precision copper alloy tube production technologies, such as the difficulty in balancing large-size forming and high-precision control, insufficient ability to regulate microstructure and properties, low yield in large-scale production, and large batch performance fluctuations. It provides a batch production method that integrates sub-design, forming and processing, microstructure control, and intelligent management. By systematically optimizing the process parameters of all processes, it achieves a synergistic improvement in tube dimensional accuracy, mechanical properties, and production stability.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0010] like Figure 1 As shown, a method for mass production of large-size, high-precision copper alloy tubes includes the following steps:

[0011] S1. Alloy melting and semi-continuous casting: The raw materials are batched according to the designed alloy composition, and then added to a vacuum induction melting furnace. After vacuum melting, online melt purification and composition control, large-size copper alloy ingots are prepared by semi-continuous casting.

[0012] S2. Homogenization heat treatment of ingots and pretreatment of billets: The prepared ingots are subjected to homogenization heat treatment, and after the heat treatment is completed, they are cooled to room temperature in the furnace. Then, the ingots are subjected to pretreatment of turning and boring in sequence to remove the surface and inner hole defect layers and obtain extruded billets.

[0013] S3. Hot extrusion forming: The extrusion blank and the hot extrusion die are preheated in gradient, and a horizontal extruder is used to hot extrude large-size tube blanks. After extrusion, the tube blanks are cooled by online water quenching.

[0014] S4. Multi-pass cold rolling: After surface pretreatment of the extruded tube blank, multi-pass cold rolling is carried out using a Pilger cold rolling mill. After each pass of rolling, intermediate stress-relieving annealing is performed to prepare tube blanks.

[0015] S5. Graded heat treatment: The cold-rolled tube billet is sent into a protective atmosphere heat treatment furnace and subjected to three grades of heat treatment in sequence: low-temperature stress relief annealing, medium-temperature solution treatment, and high-temperature aging treatment.

[0016] S6. Full-process online inspection and finishing: The heat-treated pipes are inspected online, and the inspection data is transmitted to the central control system in real time to realize the closed-loop adjustment of the preceding process. Then, the pipes are straightened, cut off the ends, and polished to obtain large-size high-precision copper alloy pipes.

[0017] Further, in step S1, the alloy composition by mass percentage is: Zn 20.0~28.0%, Ni 3.0~6.0%, Al 1.5~3.5%, Mn 0.5~1.5%, Fe 0.3~1.0%, La-Ce mixed rare earth 0.05~0.2%, with the balance being Cu and unavoidable impurities.

[0018] Furthermore, in step S1, the vacuum degree of vacuum melting is ≤1×10⁻⁶. -2 The melting process is protected by high-purity argon gas, and the melting temperature is 1180~1250℃. After the raw materials are completely melted, they are held at the temperature for 30 minutes. The online melt purification includes online argon gas rotary blowing degassing and online porous ceramic filtration for impurity removal. The composition control uses an online direct-reading spectral composition detection device to detect and adjust the melt composition to the design range in real time. The semi-continuous casting temperature is 1080~1150℃, the casting speed is 80~150mm / min, and the cooling water pressure is 0.2~0.5MPa.

[0019] Furthermore, in step S2, the temperature of the homogenization heat treatment is 780~850℃, and the holding time is 8~16h; the thickness of the car body treatment is 5mm, and the inner diameter of the ingot after boring treatment is 85mm.

[0020] Further, in step S3, the preheating temperature of the extruded billet is 750~810℃, and the holding time is 2~6h; the preheating temperature of the hot extrusion die is 350~450℃, and the holding time is 2h; the extrusion ratio of the hot extrusion is 10:1~25:1, and the extrusion speed is 5~15mm / s; during the extrusion process, the outer diameter and wall thickness of the billet are detected in real time by an online laser diameter gauge and an ultrasonic wall thickness gauge, and the extrusion parameters are adjusted in real time to ensure the dimensional accuracy of the billet.

[0021] Further, in step S4, the total processing rate of the multi-pass cold rolling is 60-80%, with a total of 3-5 passes. The processing rate per pass decreases with each pass, ranging from 16-36%, and the rolling speed is 30-80 times / minute. The intermediate stress-relief annealing temperature is 350-450℃, the holding time is 1-3 hours, and the tube is cooled to room temperature in the furnace after the holding time. During the rolling process, the dimensional parameters of the tube are monitored in real time by online wall thickness detection, online outer diameter detection, and online straightness detection devices, and the rolling parameters are adjusted in real time to correct dimensional deviations.

[0022] Further, in step S5, the specific process of the graded heat treatment is as follows: the first stage is low-temperature stress-relief annealing, with a temperature of 300~400℃ and a holding time of 2~4h, followed by furnace cooling to room temperature; the second stage is medium-temperature solution treatment, with a temperature of 700~780℃ and a holding time of 1~3h, followed by immediate water quenching to room temperature; the third stage is high-temperature aging treatment, with a temperature of 400~500℃ and a holding time of 4~8h, followed by air cooling to room temperature; the furnace temperature fluctuation during the heat treatment process is controlled within ±5℃, and the furnace temperature is precisely controlled through online temperature monitoring during the heat treatment process.

[0023] Furthermore, in step S6, the online quality inspection includes defect detection and dimensional inspection. Defect detection includes online eddy current testing to detect surface defects and online ultrasonic testing to detect internal defects. Dimensional inspection includes real-time detection of the pipe's outer diameter, wall thickness, length, and straightness.

[0024] Further, in step S6, the straightening is performed using a seventeen-roller straightener, and the straightness of the pipe after straightening is ≤1mm / m; the length of the pipe after the head and tail cutting treatment is 10000mm; and the surface roughness Ra of the pipe after the surface polishing treatment is ≤1.6μm.

[0025] Compared with the prior art, the technical advantages of the present invention are as follows:

[0026] 1. The multi-element synergistic alloy composition design achieves a balance of high strength, high corrosion resistance, and excellent formability.

[0027] This invention constructs a Cu-Zn matrix alloy system with multi-element synergistic optimization. Through the multiple synergistic effects of Ni-Al, Mn-Fe, RE, and matrix elements, a leapfrog improvement in performance is achieved. Ni and Al synergistically form a dispersed strengthening phase while simultaneously constructing a dense and stable passivation film, thereby improving both strengthening and corrosion resistance. Mn and Fe synergistically refine as-cast and deformed grains, eliminating the adverse effects of harmful impurities and significantly improving the alloy's cold and hot workability. RE elements synergistically purify grain boundaries and optimize the passivation film structure, further enhancing the alloy's microstructure uniformity and corrosion resistance. This synergistic design system allows the alloy to possess ultra-high strength while retaining excellent cold and hot workability, avoiding the problems of hot working cracking and cold rolling deformation difficulties in large-size ingots, while simultaneously improving corrosion resistance, solving the core defect of existing technologies that sacrifice some performance for others.

[0028] 2. The large-size ingot smelting and casting process has been optimized, achieving precise control over the high purity and microstructure uniformity of the ingots.

[0029] This invention achieves precise quality control of large-size ingots through full-chain process optimization, including vacuum induction melting, online melt treatment, and semi-continuous casting. Vacuum melting avoids gas absorption and element oxidation loss in the melt, ensuring accurate composition. Online treatment employs argon rotary jet degassing and ceramic filtration for impurity removal, combined with real-time adjustment based on online composition detection, efficiently removing gases and inclusions and reducing compositional deviations. In semi-continuous casting, casting temperature, casting speed, and cooling water pressure are synergistically optimized to achieve sequential solidification, refine grains, and eliminate internal defects such as segregation, shrinkage porosity, and gas bubbles. Through this process optimization, the large-size ingots prepared by this invention have a uniform microstructure, fine grains, and no obvious compositional segregation or internal defects. Their purity is significantly superior to conventional technologies, providing high-quality billets for subsequent hot and cold processing. This reduces the risk of defects in subsequent processes from the source, significantly improves the yield of large-size pipes, and enables stable batch production, ensuring raw material consistency.

[0030] 3. The hot extrusion forming process for large-diameter tubes has been optimized, enabling precise control of uniform deformation and microstructure of the tube blank.

[0031] This invention addresses the thermal deformation characteristics of large-size tube blanks by systematically optimizing hot extrusion process parameters and achieving precise control through online monitoring. A gradient preheating process between the extruded billet and the die is employed to avoid excessive temperature drop during contact, ensuring uniform billet temperature during extrusion. The extrusion ratio and speed are synergistically optimized to match the dynamic recrystallization pattern of the tube blank, achieving simultaneous control of uniform deformation and recrystallization. This ensures grain refinement while preventing cracking and uneven deformation. Temperature monitoring and dimensional detection allow for real-time adjustment of extrusion speed and die parameters, promptly correcting temperature and dimensional deviations and preventing cumulative deviations. Through this process optimization, the large-size extruded tube blanks prepared by this invention exhibit uniform microstructure, fine grains, good surface and internal quality, and significantly superior wall thickness uniformity compared to conventional techniques. This lays a solid foundation for subsequent high-precision cold rolling forming, while also significantly improving the yield of the extrusion process, enabling stable mass production of large-size tube blanks.

[0032] 4. Optimization of the multi-pass cold rolling forming process has enabled stable control of the high-precision dimensional and positional dimensions of large-size tubes.

[0033] This invention addresses the unique characteristics of cold rolling deformation in large-diameter, thick-walled copper tubes by systematically optimizing the entire cold rolling process and integrating online monitoring for precise closed-loop dimensional control. Employing a multi-pass Pilger cold rolling mode, it synergistically optimizes the total processing rate and single-pass processing rate, matching the work hardening law to ensure the required deformation for dimensional forming while avoiding excessively rapid work hardening, uneven deformation, and cracking caused by excessively high single-pass processing rates. Intermediate stress-relief annealing is performed after each rolling pass to eliminate residual stress, restore the tube's plasticity, and prevent deformation and cracking caused by the accumulation of residual stress from multiple passes. Simultaneously, online wall thickness, outer diameter, and straightness detection devices monitor dimensional parameters in real time, feeding the data back to the control system for real-time adjustment of rolling parameters, correcting dimensional deviations, and preventing the amplification of cumulative errors. Through this process optimization, this invention achieves high-precision cold rolling forming of large-diameter, thick-walled copper tubes, with the outer diameter, wall thickness, and length tolerances meeting the high-precision requirements of high-end applications.

[0034] 5. A novel graded heat treatment technology enables precise control of the pipe's microstructure and performance matching.

[0035] This invention develops a three-stage heat treatment technology, combined with online precise temperature control, to achieve full-process control of the pipe's microstructure, solving the problem of inconsistent performance in conventional technologies. The first stage, low-temperature stress-relief annealing, eliminates residual stress from cold rolling, preventing deformation and cracking caused by stress release during subsequent solution treatment, ensuring dimensional accuracy, and preserving energy stored from cold deformation to lay the foundation for subsequent processing. The second stage, medium-temperature solution treatment, allows the strengthening phase to fully dissolve, forming a uniform supersaturated solid solution, avoiding coarse grains. The third stage, high-temperature aging treatment, precisely controls aging parameters, ensuring uniform and diffuse precipitation of the strengthening phase, achieving significant age-strengthening, while optimizing grain boundary structure, suppressing the segregation of harmful elements, and improving corrosion resistance. Through the synergistic effect of the three-stage heat treatment, this invention achieves the optimal balance of pipe strength, plasticity, and corrosion resistance. Furthermore, online temperature monitoring and atmosphere control ensure the uniformity and stability of the furnace temperature during the heat treatment process.

[0036] 6. The end-to-end online precision closed-loop control technology enables stable mass production of large-size copper alloy tubes.

[0037] This invention develops an online precision closed-loop control technology covering the entire process, constructing an intelligent system of "central control system + online detection unit for all processes" to achieve closed-loop management of large-size copper alloy tube production. The online detection unit covers all processes including smelting, casting, homogenization, hot extrusion, cold rolling, heat treatment, and finishing, including modules for detecting composition, temperature, dimensions, microstructure, and defects, collecting production data in real time and transmitting it to the central control system. The system analyzes the data in real time using preset process standards and big data models. Once a parameter deviation is detected, it immediately sends adjustment instructions to the corresponding process to correct the process parameters, preventing the cumulative amplification of deviations and achieving closed-loop control throughout the entire process. This technology solves the core bottlenecks of poor batch stability and low yield in conventional technologies, enabling stable large-scale production of large-size, high-precision copper alloy tubes and meeting the application needs of high-end fields. Attached Figure Description

[0038] Figure 1 This is a process flow diagram of the method for mass production of large-size, high-precision copper alloy tubes according to the present invention.

[0039] Figure 2 The image shows the metallographic microstructure of the copper alloy prepared in Example 1.

[0040] Figure 3 The image shows the metallographic microstructure of the copper alloy obtained in Example 1 after etching for 20 seconds.

[0041] Figure 4 The image shows the secondary electron (SE) morphology of the copper alloy prepared in Example 1 after immersion in 3.5 wt.% NaCl solution for 15 days.

[0042] Figure 5 The image shows the microstructure of the copper alloy prepared in Example 1 after immersion in a 3.5 wt.% NaCl solution for 30 days.

[0043] Figure 6 This is a bar chart comparing the tensile strength of pipes in the embodiments and comparative examples of the present invention;

[0044] Figure 7 This is a bar chart comparing the yield strength of pipes in the embodiments and comparative examples of the present invention;

[0045] Figure 8 This is a bar chart comparing the dezincification layer depth of pipes in the embodiments and comparative examples of the present invention;

[0046] Figure 9 This is a bar chart comparing the pipe eccentricity of embodiments and comparative examples of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0048] A method for mass production of large-size, high-precision copper alloy tubes includes the following steps:

[0049] S1. Alloy Melting and Semi-Continuous Casting: Prepare the raw materials according to the designed alloy composition, which is as follows (by mass percentage): Zn 20.0~28.0%, Ni 3.0~6.0%, Al 1.5~3.5%, Mn 0.5~1.5%, Fe 0.3~1.0%, La-Ce mixed rare earth 0.05~0.2%, with the balance being Cu and unavoidable impurities. Add the prepared raw materials to a vacuum induction melting furnace and evacuate to ≤1×10⁻⁶. -2 The mixture is heated to 1180~1250℃ and then filled with high-purity argon as a protective atmosphere. After the raw materials are completely melted, the temperature is maintained for 30 minutes. Subsequently, the melt is degassed by an online argon rotary jet degassing device, and inclusions in the melt are removed by an online porous ceramic filter. At the same time, the melt composition is detected in real time by an online direct-reading spectral composition detection device, and the composition is adjusted to the design range based on the detection results. The processed melt is then transferred to a semi-continuous casting machine, and the casting temperature is controlled at 1080~1150℃, the casting speed at 80~150mm / min, and the cooling water pressure at 0.2~0.5MPa to prepare a large-size copper alloy ingot with an outer diameter of 320mm, an inner diameter of 80mm, and a length of 6000mm.

[0050] S2. Homogenization heat treatment of ingots and pretreatment of billets: The prepared ingots are placed in a bogie-type heat treatment furnace for homogenization heat treatment. The heat treatment temperature is controlled at 780~850℃ and the holding time is 8~16h. After the holding time, the ingots are cooled to room temperature with the furnace. The cooled ingots are then machined to remove the oxide scale and segregation layer on the surface of the ingots. The machined thickness is 5mm. Then, the ingots are bored to remove the defect layer of the inner hole of the ingot. The inner diameter of the bored hole is 85mm, and the pretreated extruded billet is obtained.

[0051] S3. Hot Extrusion Molding: The pretreated extrusion billet is placed in a medium-frequency induction heating furnace for preheating, with the preheating temperature controlled at 750~810℃ and the holding time at 2~6h to ensure uniform temperature inside and outside the ingot; at the same time, the hot extrusion die is placed in a box-type heating furnace for preheating, with the preheating temperature controlled at 350~450℃ and the holding time at 2h; the preheated billet and die are loaded into a horizontal extrusion press for hot extrusion, with the extrusion ratio controlled at 10:1~25:1 and the extrusion speed at 5~15mm / s, to obtain a large-size tube blank with an outer diameter of 90mm, a wall thickness of 10mm, and a length of 25000mm; after extrusion, the tube blank is cooled by online water quenching, and the outer diameter and wall thickness of the tube blank are detected in real time by an online laser diameter gauge and an ultrasonic wall thickness gauge, and the extrusion parameters are adjusted in real time to ensure the dimensional accuracy of the tube blank.

[0052] S4. Multi-pass cold rolling: The extruded tube blank is headed and pickled to remove surface oxide scale and oil. It is then subjected to multi-pass cold rolling using a Pilger cold rolling mill. The total cold rolling yield is controlled at 60-80%, with 3-5 passes. The yield per pass decreases with each pass, ranging from 16-36%. The rolling speed is controlled at 30-80 times per minute. After each pass, the tube is sent to a box annealing furnace for intermediate stress-relief annealing. The annealing temperature is controlled at 350~450℃, and the holding time is 1~3h. The tube is then cooled to room temperature in the furnace to eliminate residual rolling stress and restore the plasticity of the tube. After the final rolling pass, a tube blank with an outer diameter of 85mm, a wall thickness of 7mm, and a length of 38000mm is obtained. During the rolling process, the dimensional parameters of the tube are monitored in real time by online wall thickness detection, online outer diameter detection, and online straightness detection devices. The rolling parameters are adjusted in real time to correct dimensional deviations and ensure the dimensional accuracy of the tube.

[0053] S5. Graded Heat Treatment: The cold-rolled tube billet is sent to a continuous protective atmosphere heat treatment furnace for graded heat treatment, which is divided into three stages: The first stage is low-temperature stress-relief annealing, with the heat treatment temperature controlled at 300~400℃ and the holding time at 2~4h. After holding, the tube is cooled to room temperature in the furnace. The second stage is medium-temperature solution treatment, with the heat treatment temperature controlled at 700~780℃ and the holding time at 1~3h. After holding, the tube is immediately sent to a water quenching tank for water quenching and cooling to room temperature. The third stage is high-temperature aging treatment, with the heat treatment temperature controlled at 400~500℃ and the holding time at 4~8h. After holding, the tube is air-cooled to room temperature. During the heat treatment process, the furnace temperature is controlled in real time by an online multi-point temperature monitoring device to ensure that the furnace temperature fluctuation is controlled within ±5℃. At the same time, the microstructure changes of the tube are monitored in real time by an online metallographic monitoring device, and the heat treatment parameters are adjusted to ensure the accuracy of microstructure control.

[0054] S6. Full-process online inspection and finishing: The heat-treated pipes are fed into a continuous finishing production line. First, surface and internal defects are detected by online eddy current testing and online ultrasonic testing, respectively, and unqualified products are rejected. Then, online full-size inspection devices are used to detect parameters such as outer diameter, wall thickness, length, and straightness of the pipes in real time. The inspection data is transmitted to the central control system in real time to adjust the process parameters of the previous process in a closed loop. Next, a 17-roll straightener is used to straighten the pipes to ensure that the straightness of the pipes is ≤1mm / m. Then, the ends of the pipes are cut off to remove the deformed sections at both ends, resulting in pipes with a length of 10,000mm. Finally, the surface of the pipes is mirror polished to remove the oxide scale and scratches, resulting in a finished large-size, high-precision copper alloy pipe.

[0055] Technical principle of the invention:

[0056] (I) The role and synergistic effect principle of alloying elements

[0057] 1. The core role of each alloying element

[0058] Zn is the main additive element in the alloy. It dissolves in the Cu matrix to form an α solid solution, resulting in solid solution strengthening, which improves the strength, hardness and machinability of the alloy. At the same time, it optimizes the melt flowability of the alloy and improves casting performance.

[0059] Ni is the core strengthening and corrosion-resistant element. It is miscible with Cu and can produce a significant solid solution strengthening effect. At the same time, it can form a stable NiAl intermetallic compound with Al, which is uniformly dispersed and precipitated during aging, producing a strong dispersion strengthening effect and greatly improving the strength and hardness of the alloy.

[0060] Al is the core strengthening and corrosion-resistant element. It dissolves in the Cu matrix to produce a solid solution strengthening effect, and at the same time, it synergistically forms a NiAl strengthening phase with Ni to achieve dispersion strengthening. In addition, Al can rapidly form a dense and stable Al2O3 passivation film on the alloy surface, isolating the corrosive medium from the substrate and significantly improving the alloy's resistance to media corrosion and high-temperature oxidation.

[0061] Mn is a grain refiner and formability optimizer. When dissolved in the Cu matrix, it provides auxiliary solid solution strengthening. Simultaneously, it can combine with harmful sulfur impurities in the alloy to form MnS, eliminating the hot brittleness caused by sulfur and significantly improving the alloy's hot workability, thus preventing cracking during hot extrusion. Furthermore, Mn can increase the alloy's recrystallization temperature, inhibit grain growth during hot working and heat treatment, and ensure the uniformity and stability of the microstructure.

[0062] Fe is a grain-refining element that can form fine, Fe-rich phases during alloy solidification, acting as heterogeneous nucleation sites to significantly refine the as-cast grains and improve the alloy's strength and toughness. Simultaneously, Fe can inhibit grain coarsening during hot working and heat treatment, ensuring microstructure uniformity and further optimizing the alloy's formability and performance stability.

[0063] RE (La / Ce mixed rare earth) is a microstructure purifying element. It can combine with harmful impurities such as O, S, and H in the alloy to form high-melting-point compounds, thereby purifying the melt and reducing porosity and inclusion defects in the ingot. At the same time, it can be enriched at grain boundaries, inhibiting the segregation of harmful elements at grain boundaries, purifying grain boundaries, refining grains, and improving the strength and plasticity of the alloy.

[0064] Cu is the matrix element of the alloy, providing the alloy with basic electrical conductivity, thermal conductivity, plasticity and corrosion resistance, and is the fundamental carrier of the alloy's properties.

[0065] 2. The principle of synergistic effect of alloying elements

[0066] The synergistic addition of Ni and Al can form a stable NiAl intermetallic compound, which is uniformly dispersed and precipitated during aging. The resulting dispersion strengthening effect is far greater than the sum of the strengthening effects of adding a single element. In terms of corrosion resistance, Ni increases the electrode potential of the alloy matrix and reduces the corrosion driving force, while Al forms a dense passivation film to isolate the corrosive medium. The synergistic effect of the two greatly improves the alloy's resistance to dezincification corrosion.

[0067] The synergistic addition of Mn and Fe maximizes the grain refinement effect. Mn eliminates the hot brittleness of harmful impurities such as S, providing a guarantee for hot working and forming. At the same time, the fine precipitates formed by the combination of Mn and Fe can serve as efficient heterogeneous nucleation cores, significantly refining the grains in both as-cast and deformed states. The refining effect is far superior to that of adding a single element. Furthermore, the refined grains further improve the strength, plasticity, and formability of the alloy.

[0068] The addition of RE element produces multiple synergistic effects with elements such as Ni, Al, Mn, and Fe. RE element purifies the melt and grain boundaries, suppresses grain boundary segregation of alloying elements, and ensures uniform distribution of alloying elements such as Ni and Al in the matrix. This guarantees uniform precipitation of strengthening phases during subsequent aging processes and further improves the stability of the strengthening effect. At the same time, RE element can be doped into the passivation film formed by Ni and Al, optimizing the structure of the passivation film, eliminating defects in the passivation film, and improving the density and adhesion of the passivation film. This achieves multiple synergistic effects of microstructure purification, grain refinement, enhanced strengthening effect, and optimized corrosion resistance.

[0069] (II) Necessity and Technical Effects of Selecting Core Process Parameters

[0070] 1. The necessity of smelting and semi-continuous casting process parameters

[0071] This invention controls the melting temperature at 1180~1250℃, which can ensure that the alloying elements are fully melted and uniformly mixed, avoiding component segregation, and effectively suppress the burning loss of volatile elements such as Zn and Al, and reduce the gas absorption of the melt, thereby obtaining a melt with high purity and accurate composition.

[0072] In semi-continuous casting, the casting temperature (1080~1150℃), casting speed (80~150mm / min), and cooling water pressure (0.2~0.5MPa) are controlled in a coordinated manner. Through precise matching of melt fluidity, solidification rate, and cooling intensity, sequential solidification and uniform cooling of large-size ingots are achieved, refining the as-cast grains and eliminating compositional segregation, internal defects, and residual stress.

[0073] 2. The necessity of homogenizing heat treatment process parameters

[0074] The present invention controls the homogenization heat treatment temperature at 780~850℃ and the holding time at 8~16h, which ensures that the alloying elements have sufficient diffusion driving force to eliminate the segregation of the as-cast composition, homogenize the structure and reduce internal stress, while avoiding grain coarsening and excessive increase in energy consumption.

[0075] 3. The necessity of hot extrusion process parameters

[0076] This invention employs a preheating temperature of 750-810℃ for the extruded billet and a holding time of 2-6 hours, a die preheating temperature of 350-450℃, an extrusion ratio of 10:1-25:1, and an extrusion speed of 5-15 mm / s, with all parameters controlled synergistically. The billet preheating temperature ensures the alloy possesses suitable deformation resistance; the die preheating temperature prevents excessive temperature drop at the contact points; the extrusion ratio provides sufficient deformation to induce dynamic recrystallization; and the extrusion speed ensures stability during the deformation process. The synergistic effect of these four parameters achieves precise control over uniform deformation and dynamic recrystallization in large-diameter tube blanks. The resulting extruded tube blanks exhibit uniform microstructure, fine grains, good surface and internal quality, and excellent wall thickness uniformity, laying a solid foundation for subsequent high-precision cold rolling forming.

[0077] 4. The necessity of cold rolling process parameters

[0078] This invention achieves coordinated control of the total cold rolling processing rate at 60-80%, the single-pass processing rate at 16-36%, and the rolling speed at 30-80 times / minute, coupled with an intermediate stress-relief annealing temperature of 350-450℃ and a holding time of 1-3 hours. Through the matching and optimization of process parameters, the work hardening effect and the plastic recovery of the tube during cold deformation are balanced, enabling high-precision dimensional forming of large-diameter thick-walled tubes. This effectively avoids defects such as rolling cracking, uneven deformation, and dimensional fluctuations, resulting in tubes with an eccentricity of ≤6% and excellent dimensional consistency during mass production.

[0079] 5. The necessity of graded heat treatment process parameters

[0080] The graded heat treatment of this invention is divided into three stages:

[0081] The first stage is low-temperature stress-relief annealing, with the heat treatment temperature controlled at 300~400℃ and the holding time at 2~4h. This fully eliminates residual stress from cold rolling, ensures the dimensional accuracy of the pipe, and at the same time preserves the energy stored from cold deformation to lay the foundation for subsequent heat treatment.

[0082] The second stage involves medium-temperature solution treatment, with the heat treatment temperature controlled at 700~780℃ and the holding time at 1~3h, to allow the strengthening phase to fully dissolve and form a supersaturated solid solution, while avoiding grain coarsening. Water quenching then rapidly suppresses the precipitation of the strengthening phase, ensuring the aging strengthening effect.

[0083] The third stage involves high-temperature aging treatment, with the heat treatment temperature controlled at 400~500℃ and the holding time at 4~8h. This promotes the uniform and dispersed precipitation of the strengthening phase and avoids coarsening of the precipitated phase and continuous precipitation at grain boundaries. Through staged heat treatment, the pipe simultaneously achieves high strength, excellent plasticity, and high corrosion resistance, with a batch production yield of ≥95%.

[0084] 6. The necessity of end-to-end online closed-loop control

[0085] The full-process online closed-loop control of this invention covers all production processes from raw materials to finished products. It can correct deviations in a timely manner when they occur, avoiding the accumulation and amplification of deviations. At the same time, it can achieve continuous optimization of production processes through full-process data traceability, reducing the risk of defects from the root and solving the industry bottleneck of large-size copper alloy tubes being unable to be produced in stable batches.

[0086] The present invention will be further illustrated below through specific embodiments and comparative examples.

[0087] Example 1

[0088] A method for mass production of large-size, high-precision copper alloy tubes includes the following steps:

[0089] S1. Alloy Melting and Semi-Continuous Casting: Prepare the raw materials according to the designed alloy composition, which is as follows (by mass percentage): Zn 22.0%, Ni 4.0%, Al 2.0%, Mn 1.0%, Fe 0.5%, La-Ce mixed rare earth 0.1%, with the balance being Cu and unavoidable impurities. Add the prepared raw materials to a vacuum induction melting furnace and evacuate to ≤1×10⁻⁶. -2The mixture was heated to 1200℃ and then filled with high-purity argon as a protective atmosphere. After the raw materials were completely melted, the temperature was maintained for 30 minutes. Subsequently, the melt was degassed by an online argon rotary jet degassing device, and inclusions in the melt were removed by an online porous ceramic filter. At the same time, the melt composition was detected in real time by an online direct-reading spectral composition detection device, and the composition was adjusted to the design range based on the detection results. The processed melt was then transferred to a semi-continuous casting machine, and the casting temperature was controlled at 1100℃, the casting speed at 100 mm / min, and the cooling water pressure at 0.3 MPa to prepare a large-size copper alloy ingot with an outer diameter of 320 mm, an inner diameter of 80 mm, and a length of 6000 mm.

[0090] S2. Homogenization heat treatment of ingots and pretreatment of billets: The prepared ingots are placed in a bogie-type heat treatment furnace for homogenization heat treatment. The heat treatment temperature is controlled at 800℃ and the holding time is 12h. After the holding time is completed, the ingots are cooled to room temperature with the furnace. The cooled ingots are then machined to remove the oxide scale and segregation layer on the surface of the ingots. The machined thickness is 5mm. Subsequently, the ingots are bored to remove the defect layer in the inner hole of the ingot. The inner diameter after boring is 85mm, and the pretreated extruded billet is obtained.

[0091] S3. Hot Extrusion Molding: The pretreated extrusion billet is placed in a medium-frequency induction heating furnace for preheating, with the preheating temperature controlled at 780℃ and the holding time at 4h to ensure uniform temperature inside and outside the ingot; at the same time, the hot extrusion die is placed in a box-type heating furnace for preheating, with the preheating temperature controlled at 400℃ and the holding time at 2h; the preheated billet and die are loaded into a horizontal extrusion press for hot extrusion, with the extrusion ratio controlled at 15:1 and the extrusion speed at 10mm / s, to obtain a large-size tube blank with an outer diameter of 90mm, a wall thickness of 10mm, and a length of 25000mm; after extrusion, the tube blank is cooled by online water quenching.

[0092] S4. Multi-pass cold rolling: The extruded tube blank is headed and pickled to remove surface oxide scale and oil. Then, it is cold rolled in multiple passes using a Pilger cold rolling mill. The total cold rolling rate is controlled at 70%, with a total of 4 passes. The single pass rates are 33%, 29%, 23%, and 18% respectively, and the rolling speed is controlled at 50 times / minute. After each pass, the tube is sent to a box annealing furnace for intermediate stress-relief annealing. The annealing temperature is controlled at 400℃, the holding time is 2 hours, and the tube is cooled to room temperature in the furnace to eliminate residual rolling stress and restore the tube's plasticity. After the last pass, a tube blank with an outer diameter of 85mm, a wall thickness of 7mm, and a length of 38000mm is obtained.

[0093] S5. Graded Heat Treatment: The cold-rolled tube billets are fed into a continuous protective atmosphere heat treatment furnace for graded heat treatment, which is divided into three stages: The first stage is low-temperature stress-relief annealing, with the heat treatment temperature controlled at 350℃ and the holding time at 3h. After holding, the tubes are cooled to room temperature in the furnace. The second stage is medium-temperature solution treatment, with the heat treatment temperature controlled at 750℃ and the holding time at 2h. After holding, the tubes are immediately sent to a water quenching tank for water quenching and cooling to room temperature. The third stage is high-temperature aging treatment, with the heat treatment temperature controlled at 450℃ and the holding time at 6h. After holding, the tubes are air-cooled to room temperature. During the heat treatment process, the furnace temperature is controlled in real time by an online multi-point temperature monitoring device to ensure that the furnace temperature fluctuation is controlled within ±5℃.

[0094] S6. Full-process online inspection and finishing: The heat-treated pipes are fed into a continuous finishing production line. First, surface and internal defects are detected by online eddy current testing and online ultrasonic testing, respectively, and unqualified products are rejected. Then, online full-size inspection devices are used to detect parameters such as outer diameter, wall thickness, length, and straightness of the pipes in real time. The inspection data is transmitted to the central control system in real time to adjust the process parameters of the previous process in a closed loop. Next, a 17-roll straightener is used to straighten the pipes to ensure that the straightness of the pipes is ≤1mm / m. Then, the ends of the pipes are cut off to remove the deformed sections at both ends, resulting in pipes with a length of 10,000mm. Finally, the surface of the pipes is mirror polished to remove the oxide scale and scratches, resulting in a finished large-size, high-precision copper alloy pipe.

[0095] The microstructure and corrosion resistance of the finished copper alloy tubing obtained in Example 1 were characterized and tested. Figure 2 The image shows the metallographic microstructure of the copper alloy prepared in Example 1. The matrix is ​​dense and uniform, without macroscopic defects such as casting shrinkage, porosity, and cracks. There are no obvious dendritic segregation or compositional segregation zones, and only a very small number of diffusely distributed micro-second phase particles exist. Figure 3 The image shows the metallographic microstructure of the copper alloy obtained in Example 1 after etching for 20 seconds. The alloy has a uniform equiaxed crystal structure with concentrated grain size distribution. There are no mixed crystals or abnormally large grains. The grain boundaries are clear and complete. A large number of fine precipitates are dispersed in the grains and at the grain boundaries. There are no continuous network grain boundary precipitation or structural deterioration. Figure 4 The image shows the secondary electron (SE) morphology of the copper alloy prepared in Example 1 after immersion in 3.5 wt.% NaCl solution for 15 days. The alloy surface forms a complete and dense passivation film with no obvious pitting, corrosion cracks and film peeling. Only a very small number of micropores exist, and there are no signs of local corrosion initiation. Figure 5The image shows the microstructure of the copper alloy prepared in Example 1 after immersion in a 3.5 wt.% NaCl solution for 30 days. The passivation film on the alloy surface remains intact and dense, with no obvious pitting corrosion, grain boundary corrosion, or large-area peeling of the film. Only the uniform growth of the product particles is observed, and there is no accelerated spread of localized corrosion.

[0096] Example 2

[0097] A method for mass production of large-size, high-precision copper alloy tubes includes the following steps:

[0098] S1. Alloy Melting and Semi-Continuous Casting: Prepare the raw materials according to the designed alloy composition, which is as follows (by mass percentage): Zn 20.0%, Ni 3.0%, Al 1.5%, Mn 0.5%, Fe 0.3%, La-Ce mixed rare earth 0.05%, with the balance being Cu and unavoidable impurities. Add the prepared raw materials to a vacuum induction melting furnace and evacuate to a vacuum level ≤1×10⁻⁶. -2 The mixture was heated to 1180℃ and then filled with high-purity argon as a protective atmosphere. After the raw materials were completely melted, the temperature was maintained for 30 minutes. Subsequently, the melt was degassed using an online argon rotary jet degassing device, and inclusions in the melt were removed using an online porous ceramic filter. At the same time, the melt composition was detected in real time using an online direct-reading spectral composition detection device, and the composition was adjusted to the design range based on the detection results. The processed melt was then transferred to a semi-continuous casting machine, and the casting temperature was controlled at 1080℃, the casting speed at 80 mm / min, and the cooling water pressure at 0.2 MPa to produce a large-size copper alloy ingot with an outer diameter of 320 mm, an inner diameter of 80 mm, and a length of 6000 mm.

[0099] S2. Homogenization heat treatment of ingots and pretreatment of billets: The prepared ingots are placed in a bogie-type heat treatment furnace for homogenization heat treatment. The heat treatment temperature is controlled at 780℃ and the holding time is 8h. After the holding time is completed, the ingots are cooled to room temperature with the furnace. The cooled ingots are then machined to remove the oxide scale and segregation layer on the surface of the ingots. The machined thickness is 5mm. Subsequently, the ingots are bored to remove the defect layer in the inner hole of the ingot. The inner diameter after boring is 85mm, and the pretreated extruded billet is obtained.

[0100] S3. Hot Extrusion Molding: The pretreated extrusion billet is placed in a medium-frequency induction heating furnace for preheating, with the preheating temperature controlled at 750℃ and the holding time at 2h to ensure uniform temperature inside and outside the ingot; at the same time, the hot extrusion die is placed in a box-type heating furnace for preheating, with the preheating temperature controlled at 350℃ and the holding time at 2h; the preheated billet and die are loaded into a horizontal extrusion press for hot extrusion, with the extrusion ratio controlled at 10:1 and the extrusion speed at 5mm / s, to obtain a large-size tube blank with an outer diameter of 90mm, a wall thickness of 10mm, and a length of 25000mm; after extrusion, the tube blank is cooled by online water quenching.

[0101] S4. Multi-pass cold rolling: The extruded tube blank is headed and pickled to remove surface oxide scale and oil. Then, it is cold rolled in multiple passes using a Pilger cold rolling mill. The total cold rolling rate is controlled at 60%, with a total of 4 passes. The single pass rates are 24%, 22%, 19%, and 16% respectively, and the rolling speed is controlled at 30 times / minute. After each pass, the tube is sent to a box annealing furnace for intermediate stress-relief annealing. The annealing temperature is controlled at 350℃, the holding time is 1 hour, and the tube is cooled to room temperature in the furnace to eliminate residual rolling stress and restore the tube's plasticity. After the last pass, a tube blank with an outer diameter of 85mm, a wall thickness of 7mm, and a length of 38000mm is obtained.

[0102] S5. Graded Heat Treatment: The cold-rolled tube billet is sent to a continuous protective atmosphere heat treatment furnace for graded heat treatment, which is divided into three stages: The first stage is low-temperature stress-relief annealing, with the heat treatment temperature controlled at 300℃ and the holding time at 2h. After the holding time, the tube is cooled to room temperature in the furnace. The second stage is medium-temperature solution treatment, with the heat treatment temperature controlled at 700℃ and the holding time at 1h. After the holding time, the tube is immediately sent to a water quenching tank for water quenching and cooling to room temperature. The third stage is high-temperature aging treatment, with the heat treatment temperature controlled at 400℃ and the holding time at 4h. After the holding time, the tube is air-cooled to room temperature. During the heat treatment process, the furnace temperature is controlled in real time by an online multi-point temperature monitoring device to ensure that the furnace temperature fluctuation is controlled within ±5℃.

[0103] S6. Full-process online inspection and finishing: The heat-treated pipes are fed into a continuous finishing production line. First, surface and internal defects are detected by online eddy current testing and online ultrasonic testing, respectively, and unqualified products are rejected. Then, online full-size inspection devices are used to detect parameters such as outer diameter, wall thickness, length, and straightness of the pipes in real time. The inspection data is transmitted to the central control system in real time to adjust the process parameters of the previous process in a closed loop. Next, a 17-roll straightener is used to straighten the pipes to ensure that the straightness of the pipes is ≤1mm / m. Then, the ends of the pipes are cut off to remove the deformed sections at both ends, resulting in pipes with a length of 10,000mm. Finally, the surface of the pipes is mirror polished to remove the oxide scale and scratches, resulting in a finished large-size, high-precision copper alloy pipe.

[0104] Example 3

[0105] A method for mass production of large-size, high-precision copper alloy tubes includes the following steps:

[0106] S1. Alloy Melting and Semi-Continuous Casting: Prepare the raw materials according to the designed alloy composition, which is as follows (by mass percentage): Zn 28.0%, Ni 6.0%, Al 3.5%, Mn 1.5%, Fe 1.0%, La-Ce mixed rare earth 0.2%, with the balance being Cu and unavoidable impurities. Add the prepared raw materials to a vacuum induction melting furnace and evacuate to ≤1×10⁻⁶. -2 Pa, then high-purity argon gas is introduced as a protective atmosphere, and the temperature is raised to 1250℃ for melting. After the raw materials are completely melted, the temperature is held for 30 minutes. Subsequently, the melt is degassed by an online argon rotary jet degassing device, and inclusions in the melt are removed by an online porous ceramic filter. At the same time, the melt composition is detected in real time by an online direct-reading spectral composition detection device, and the composition is adjusted to the design range based on the detection results. The processed melt is transferred to a semi-continuous casting machine, and the casting temperature is controlled at 1150℃, the casting speed at 150mm / min, and the cooling water pressure at 0.5MPa to prepare a large-size copper alloy ingot with an outer diameter of 320mm, an inner diameter of 80mm, and a length of 6000mm.

[0107] S2. Homogenization heat treatment of ingots and pretreatment of billets: The prepared ingots are placed in a bogie-type heat treatment furnace for homogenization heat treatment. The heat treatment temperature is controlled at 850℃ and the holding time is 16h. After the holding time is completed, the ingots are cooled to room temperature with the furnace. The cooled ingots are then machined to remove the oxide scale and segregation layer on the surface of the ingots. The machined thickness is 5mm. Subsequently, the ingots are bored to remove the defect layer in the inner hole of the ingot. The inner diameter after boring is 85mm, and the pretreated extruded billet is obtained.

[0108] S3. Hot Extrusion Molding: The pretreated extrusion billet is placed in a medium-frequency induction heating furnace for preheating, with the preheating temperature controlled at 810℃ and the holding time at 6h to ensure uniform temperature inside and outside the ingot; at the same time, the hot extrusion die is placed in a box-type heating furnace for preheating, with the preheating temperature controlled at 450℃ and the holding time at 2h; the preheated billet and die are loaded into a horizontal extrusion press for hot extrusion, with the extrusion ratio controlled at 25:1 and the extrusion speed at 15mm / s, to obtain a large-size tube blank with an outer diameter of 90mm, a wall thickness of 10mm, and a length of 25000mm; after extrusion, the tube blank is cooled by online water quenching.

[0109] S4. Multi-pass cold rolling: The extruded tube blank is headed and pickled to remove surface oxide scale and oil. Then, it is cold rolled in multiple passes using a Pilger cold rolling mill. The total cold rolling rate is controlled at 80%, with a total of 4 passes. The single pass rates are 35%, 34%, 32%, and 30% respectively, and the rolling speed is controlled at 80 times / minute. After each pass, the tube is sent to a box annealing furnace for intermediate stress-relief annealing. The annealing temperature is controlled at 450℃, the holding time is 3 hours, and the tube is cooled to room temperature in the furnace to eliminate residual rolling stress and restore the tube's plasticity. After the last pass, a tube blank with an outer diameter of 85mm, a wall thickness of 7mm, and a length of 38000mm is obtained.

[0110] S5. Graded Heat Treatment: The cold-rolled tube billet is sent to a continuous protective atmosphere heat treatment furnace for graded heat treatment, which is divided into three stages: The first stage is low-temperature stress-relief annealing, with the heat treatment temperature controlled at 400℃ and the holding time at 4h. After the holding time, the tube is cooled to room temperature in the furnace. The second stage is medium-temperature solution treatment, with the heat treatment temperature controlled at 780℃ and the holding time at 3h. After the holding time, the tube is immediately sent to a water quenching tank for water quenching and cooling to room temperature. The third stage is high-temperature aging treatment, with the heat treatment temperature controlled at 500℃ and the holding time at 8h. After the holding time, the tube is air-cooled to room temperature. During the heat treatment process, the furnace temperature is controlled in real time by an online multi-point temperature monitoring device to ensure that the furnace temperature fluctuation is controlled within ±5℃.

[0111] S6. Full-process online inspection and finishing: The heat-treated pipes are fed into a continuous finishing production line. First, surface and internal defects are detected by online eddy current testing and online ultrasonic testing, respectively, and unqualified products are rejected. Then, online full-size inspection devices are used to detect parameters such as outer diameter, wall thickness, length, and straightness of the pipes in real time. The inspection data is transmitted to the central control system in real time to adjust the process parameters of the previous process in a closed loop. Next, a 17-roll straightener is used to straighten the pipes to ensure that the straightness of the pipes is ≤1mm / m. Then, the ends of the pipes are cut off to remove the deformed sections at both ends, resulting in pipes with a length of 10,000mm. Finally, the surface of the pipes is mirror polished to remove the oxide scale and scratches, resulting in a finished large-size, high-precision copper alloy pipe.

[0112] Example 4

[0113] A method for mass production of large-size, high-precision copper alloy tubes includes the following steps:

[0114] S1. Alloy Melting and Semi-Continuous Casting: Prepare the raw materials according to the designed alloy composition, which is as follows (by mass percentage): Zn 25.0%, Ni 5.0%, Al 2.5%, Mn 1.2%, Fe 0.8%, La-Ce mixed rare earth 0.15%, with the balance being Cu and unavoidable impurities. Add the prepared raw materials to a vacuum induction melting furnace and evacuate to ≤1×10⁻⁶. -2 The mixture was heated to 1220℃ and then filled with high-purity argon as a protective atmosphere. After the raw materials were completely melted, the temperature was maintained for 30 minutes. Subsequently, the melt was degassed by an online argon rotary jet degassing device, and inclusions in the melt were removed by an online porous ceramic filter. At the same time, the melt composition was detected in real time by an online direct-reading spectral composition detection device, and the composition was adjusted to the design range based on the detection results. The processed melt was then transferred to a semi-continuous casting machine, and the casting temperature was controlled at 1120℃, the casting speed at 120 mm / min, and the cooling water pressure at 0.4 MPa to prepare a large-size copper alloy ingot with an outer diameter of 320 mm, an inner diameter of 80 mm, and a length of 6000 mm.

[0115] S2. Homogenization heat treatment of ingots and pretreatment of billets: The prepared ingots are placed in a bogie-type heat treatment furnace for homogenization heat treatment. The heat treatment temperature is controlled at 820℃ and the holding time is 14h. After the holding time is completed, the ingots are cooled to room temperature with the furnace. The cooled ingots are then machined to remove the oxide scale and segregation layer on the surface of the ingots. The machined thickness is 5mm. Subsequently, the ingots are bored to remove the defect layer in the inner hole of the ingot. The inner diameter after boring is 85mm, and the pretreated extruded billet is obtained.

[0116] S3. Hot Extrusion Molding: The pretreated extrusion billet is placed in a medium-frequency induction heating furnace for preheating, with the preheating temperature controlled at 800℃ and the holding time at 5h to ensure uniform temperature inside and outside the ingot; at the same time, the hot extrusion die is placed in a box-type heating furnace for preheating, with the preheating temperature controlled at 420℃ and the holding time at 2h; the preheated billet and die are loaded into a horizontal extrusion press for hot extrusion, with the extrusion ratio controlled at 20:1 and the extrusion speed at 12mm / s, to obtain a large-size tube blank with an outer diameter of 90mm, a wall thickness of 10mm, and a length of 25000mm; after extrusion, the tube blank is cooled by online water quenching.

[0117] S4. Multi-pass cold rolling: The extruded tube blank is headed and pickled to remove surface oxide scale and oil. Then, it is cold rolled in multiple passes using a Pilger cold rolling mill. The total cold rolling rate is controlled at 75%, with a total of 4 passes. The single pass rates are 36%, 31%, 26%, and 23% respectively, and the rolling speed is controlled at 60 times / minute. After each pass, the tube is sent to a box annealing furnace for intermediate stress-relief annealing. The annealing temperature is controlled at 420℃, the holding time is 2.5h, and the tube is cooled to room temperature in the furnace to eliminate residual rolling stress and restore the tube's plasticity. After the last pass, a tube blank with an outer diameter of 85mm, a wall thickness of 7mm, and a length of 38000mm is obtained.

[0118] S5. Graded Heat Treatment: The cold-rolled tube billets are fed into a continuous protective atmosphere heat treatment furnace for graded heat treatment, which is divided into three stages: The first stage is low-temperature stress-relief annealing, with the heat treatment temperature controlled at 380℃ and the holding time at 3.5h. After the holding time, the tubes are cooled to room temperature in the furnace. The second stage is medium-temperature solution treatment, with the heat treatment temperature controlled at 760℃ and the holding time at 2.5h. After the holding time, the tubes are immediately sent to a water quenching tank for water quenching and cooling to room temperature. The third stage is high-temperature aging treatment, with the heat treatment temperature controlled at 470℃ and the holding time at 7h. After the holding time, the tubes are air-cooled to room temperature. During the heat treatment process, the furnace temperature is controlled in real time by an online multi-point temperature monitoring device to ensure that the furnace temperature fluctuation is controlled within ±5℃.

[0119] S6. Full-process online inspection and finishing: The heat-treated pipes are fed into a continuous finishing production line. First, surface and internal defects are detected by online eddy current testing and online ultrasonic testing, respectively, and unqualified products are rejected. Then, online full-size inspection devices are used to detect parameters such as outer diameter, wall thickness, length, and straightness of the pipes in real time. The inspection data is transmitted to the central control system in real time to adjust the process parameters of the previous process in a closed loop. Next, a 17-roll straightener is used to straighten the pipes to ensure that the straightness of the pipes is ≤1mm / m. Then, the ends of the pipes are cut off to remove the deformed sections at both ends, resulting in pipes with a length of 10,000mm. Finally, the surface of the pipes is mirror polished to remove the oxide scale and scratches, resulting in a finished large-size, high-precision copper alloy pipe.

[0120] Example 5

[0121] A method for mass production of large-size, high-precision copper alloy tubes includes the following steps:

[0122] S1. Alloy Melting and Semi-Continuous Casting: Prepare the raw materials according to the designed alloy composition, which is as follows (by mass percentage): Zn 22.0%, Ni 4.0%, Al 2.0%, Mn 1.0%, Fe 0.5%, La-Ce mixed rare earth 0.1%, with the balance being Cu and unavoidable impurities. Add the prepared raw materials to a vacuum induction melting furnace and evacuate to ≤1×10⁻⁶. -2 The mixture was heated to 1200℃ and then filled with high-purity argon as a protective atmosphere. After the raw materials were completely melted, the temperature was maintained for 30 minutes. Subsequently, the melt was degassed by an online argon rotary jet degassing device, and inclusions in the melt were removed by an online porous ceramic filter. At the same time, the melt composition was detected in real time by an online direct-reading spectral composition detection device, and the composition was adjusted to the design range based on the detection results. The processed melt was then transferred to a semi-continuous casting machine, and the casting temperature was controlled at 1100℃, the casting speed at 100 mm / min, and the cooling water pressure at 0.3 MPa to prepare a large-size copper alloy ingot with an outer diameter of 320 mm, an inner diameter of 80 mm, and a length of 6000 mm.

[0123] S2. Homogenization heat treatment of ingots and pretreatment of billets: The prepared ingots are placed in a bogie-type heat treatment furnace for homogenization heat treatment. The heat treatment temperature is controlled at 800℃ and the holding time is 12h. After the holding time is completed, the ingots are cooled to room temperature with the furnace. The cooled ingots are then machined to remove the oxide scale and segregation layer on the surface of the ingots. The machined thickness is 5mm. Subsequently, the ingots are bored to remove the defect layer in the inner hole of the ingot. The inner diameter after boring is 85mm, and the pretreated extruded billet is obtained.

[0124] S3. Hot Extrusion Molding: The pretreated extrusion billet is placed in a medium-frequency induction heating furnace for preheating, with the preheating temperature controlled at 780℃ and the holding time at 4h to ensure uniform temperature inside and outside the ingot; at the same time, the hot extrusion die is placed in a box-type heating furnace for preheating, with the preheating temperature controlled at 400℃ and the holding time at 2h; the preheated billet and die are loaded into a horizontal extrusion press for hot extrusion, with the extrusion ratio controlled at 18:1 and the extrusion speed at 8mm / s, to obtain a large-size tube blank with an outer diameter of 90mm, a wall thickness of 10mm, and a length of 25000mm; after extrusion, the tube blank is cooled by online water quenching.

[0125] S4. Multi-pass cold rolling: The extruded tube blank is headed and pickled to remove surface oxide scale and oil. Then, it is cold rolled in multiple passes using a Pilger cold rolling mill. The total cold rolling rate is controlled at 65%, with three rolling passes. The single-pass rates are 34%, 30%, and 25% respectively, and the rolling speed is controlled at 40 times / minute. After each rolling pass, the tube is sent to a box annealing furnace for intermediate stress-relief annealing. The annealing temperature is controlled at 400℃, the holding time is 2 hours, and the tube is cooled to room temperature in the furnace to eliminate residual rolling stress and restore the tube's plasticity. After the last rolling pass, a tube blank with an outer diameter of 85mm, a wall thickness of 7mm, and a length of 38000mm is obtained.

[0126] S5. Graded Heat Treatment: The cold-rolled tube billets are fed into a continuous protective atmosphere heat treatment furnace for graded heat treatment, which is divided into three stages: The first stage is low-temperature stress-relief annealing, with the heat treatment temperature controlled at 350℃ and the holding time at 3h. After holding, the tubes are cooled to room temperature in the furnace. The second stage is medium-temperature solution treatment, with the heat treatment temperature controlled at 730℃ and the holding time at 2h. After holding, the tubes are immediately sent to a water quenching tank for water quenching and cooling to room temperature. The third stage is high-temperature aging treatment, with the heat treatment temperature controlled at 430℃ and the holding time at 6h. After holding, the tubes are air-cooled to room temperature. During the heat treatment process, the furnace temperature is controlled in real time by an online multi-point temperature monitoring device to ensure that the furnace temperature fluctuation is controlled within ±5℃.

[0127] S6. Full-process online inspection and finishing: The heat-treated pipes are fed into a continuous finishing production line. First, surface and internal defects are detected by online eddy current testing and online ultrasonic testing, respectively, and unqualified products are rejected. Then, online full-size inspection devices are used to detect parameters such as outer diameter, wall thickness, length, and straightness of the pipes in real time. The inspection data is transmitted to the central control system in real time to adjust the process parameters of the previous process in a closed loop. Next, a 17-roll straightener is used to straighten the pipes to ensure that the straightness of the pipes is ≤1mm / m. Then, the ends of the pipes are cut off to remove the deformed sections at both ends, resulting in pipes with a length of 10,000mm. Finally, the surface of the pipes is mirror polished to remove the oxide scale and scratches, resulting in a finished large-size, high-precision copper alloy pipe.

[0128] Example 6

[0129] A method for mass production of large-size, high-precision copper alloy tubes includes the following steps:

[0130] S1. Alloy Melting and Semi-Continuous Casting: Prepare the raw materials according to the designed alloy composition, which is as follows (by mass percentage): Zn 22.0%, Ni 4.0%, Al 2.0%, Mn 1.0%, Fe 0.5%, La-Ce mixed rare earth 0.1%, with the balance being Cu and unavoidable impurities. Add the prepared raw materials to a vacuum induction melting furnace and evacuate to ≤1×10⁻⁶. -2 The mixture was heated to 1200℃ and then filled with high-purity argon as a protective atmosphere. After the raw materials were completely melted, the temperature was maintained for 30 minutes. Subsequently, the melt was degassed by an online argon rotary jet degassing device, and inclusions in the melt were removed by an online porous ceramic filter. At the same time, the melt composition was detected in real time by an online direct-reading spectral composition detection device, and the composition was adjusted to the design range based on the detection results. The processed melt was then transferred to a semi-continuous casting machine, and the casting temperature was controlled at 1100℃, the casting speed at 100 mm / min, and the cooling water pressure at 0.3 MPa to prepare a large-size copper alloy ingot with an outer diameter of 320 mm, an inner diameter of 80 mm, and a length of 6000 mm.

[0131] S2. Homogenization heat treatment of ingots and pretreatment of billets: The prepared ingots are placed in a bogie-type heat treatment furnace for homogenization heat treatment. The heat treatment temperature is controlled at 800℃ and the holding time is 12h. After the holding time is completed, the ingots are cooled to room temperature with the furnace. The cooled ingots are then machined to remove the oxide scale and segregation layer on the surface of the ingots. The machined thickness is 5mm. Subsequently, the ingots are bored to remove the defect layer in the inner hole of the ingot. The inner diameter after boring is 85mm, and the pretreated extruded billet is obtained.

[0132] S3. Hot Extrusion Molding: The pretreated extrusion billet is placed in a medium-frequency induction heating furnace for preheating, with the preheating temperature controlled at 780℃ and the holding time at 4h to ensure uniform temperature inside and outside the ingot; at the same time, the hot extrusion die is placed in a box-type heating furnace for preheating, with the preheating temperature controlled at 400℃ and the holding time at 2h; the preheated billet and die are loaded into a horizontal extrusion press for hot extrusion, with the extrusion ratio controlled at 15:1 and the extrusion speed at 10mm / s, to obtain a large-size tube blank with an outer diameter of 90mm, a wall thickness of 10mm, and a length of 25000mm; after extrusion, the tube blank is cooled by online water quenching.

[0133] S4. Multi-pass cold rolling: The extruded tube blank is headed and pickled to remove surface oxide scale and oil. Then, it is cold rolled in multiple passes using a Pilger cold rolling mill. The total cold rolling rate is controlled at 72%, with a total of 5 passes. The single pass rates are 27%, 25%, 23%, 21%, and 18% respectively, and the rolling speed is controlled at 55 times / minute. After each pass, the tube is sent to a box annealing furnace for intermediate stress-relief annealing. The annealing temperature is controlled at 400℃, the holding time is 2 hours, and the tube is cooled to room temperature in the furnace to eliminate residual rolling stress and restore the tube's plasticity. After the last pass, a tube blank with an outer diameter of 85mm, a wall thickness of 7mm, and a length of 38000mm is obtained.

[0134] S5. Graded Heat Treatment: The cold-rolled tube billets are fed into a continuous protective atmosphere heat treatment furnace for graded heat treatment, which is divided into three stages: The first stage is low-temperature stress-relief annealing, with the heat treatment temperature controlled at 320℃ and the holding time at 3.5h. After the holding time, the tubes are cooled to room temperature in the furnace. The second stage is medium-temperature solution treatment, with the heat treatment temperature controlled at 740℃ and the holding time at 1.5h. After the holding time, the tubes are immediately sent to a water quenching tank for water quenching and cooling to room temperature. The third stage is high-temperature aging treatment, with the heat treatment temperature controlled at 440℃ and the holding time at 5h. After the holding time, the tubes are air-cooled to room temperature. During the heat treatment process, the furnace temperature is controlled in real time by an online multi-point temperature monitoring device to ensure that the furnace temperature fluctuation is controlled within ±5℃.

[0135] S6. Full-process online inspection and finishing: The heat-treated pipes are fed into a continuous finishing production line. First, surface and internal defects are detected by online eddy current testing and online ultrasonic testing, respectively, and unqualified products are rejected. Then, online full-size inspection devices are used to detect parameters such as outer diameter, wall thickness, length, and straightness of the pipes in real time. The inspection data is transmitted to the central control system in real time to adjust the process parameters of the previous process in a closed loop. Next, a 17-roll straightener is used to straighten the pipes to ensure that the straightness of the pipes is ≤1mm / m. Then, the ends of the pipes are cut off to remove the deformed sections at both ends, resulting in pipes with a length of 10,000mm. Finally, the surface of the pipes is mirror polished to remove the oxide scale and scratches, resulting in a finished large-size, high-precision copper alloy pipe.

[0136] Comparative Example 1 (Prior Art CN119566093A)

[0137] A method for preparing an ultra-large diameter seamless copper-nickel alloy tube includes the following steps:

[0138] S1. Casting: Casting a solid ingot with a diameter of 445mm, with a single solid ingot weighing 610kg;

[0139] S2. Heating: The solid ingots that have been cast are heated to 920°C using a high-temperature box-type resistance furnace and held at that temperature for 60 minutes after heating.

[0140] S3. Forging: The heated solid ingot is forged using a high-speed forging press to forge a 445mm diameter solid ingot into a 650mm diameter round billet;

[0141] S4. Skew rolling: Skew rolling is performed on a round billet with a diameter of 650mm after forging. The diameter of the hole after skew rolling is 560mm, and the skew rolling temperature is 880℃.

[0142] S5. Hot rolling: The billet tube after skew rolling and piercing is hot rolled at a temperature of 750℃, and the diameter of the hot-rolled billet tube is 560mm.

[0143] S6. Cold rolling: The hot-rolled tube blank is cold-rolled at room temperature, and the diameter after cold rolling is 508mm;

[0144] S7. Heat treatment: Anneal the cold-rolled tube blank at 750℃ for 60 minutes.

[0145] S8. Stretching: The annealed tube blank is stretched using a stretching machine with a capacity of 300 tons or more, and the wall thickness of the tube blank is adjusted to 4mm.

[0146] Comparative Example 2 (Prior Art CN118064759B)

[0147] A method for preparing dezincification-resistant and corrosion-resistant brass alloys includes the following steps:

[0148] S1: By mass percentage, the alloy composition is Cu 66.0%, Al 0.5%, Fe 0.21%, P 0.08%, In 0.01%, Zr 0.02%, B 0.005%, Ce 0.01%, with the balance being Zn and unavoidable impurities. The raw materials include electrolytic copper, CuFe master alloy, CuP master alloy, CuIn master alloy, CuZr master alloy, CuB master alloy, CuCe master alloy, pure Al (purity ≥99.5%), and pure Zn (purity ≥99.0%).

[0149] S2: Electrolytic copper is smelted and subjected to a first heat preservation at a temperature of 1150℃. Pure Zn, pure Al and CuFe intermediate alloy are added sequentially under the first heat preservation condition to obtain a brass intermediate mixture resistant to dezincification corrosion.

[0150] S3: The intermediate mixture of dezincification corrosion resistant brass alloy is subjected to a second heat preservation at a temperature of 1055℃. Then, CuB intermediate alloy, CuP intermediate alloy, CuIn intermediate alloy, CuZr intermediate alloy and CuCe intermediate alloy are added, and a third heat preservation is performed at a temperature of 950℃. Finally, the mixture is continuously cast upwards to obtain the dezincification corrosion resistant brass billet.

[0151] S4: The dezincification-resistant and corrosion-resistant brass billet is extruded on a continuous extrusion press at a preheating temperature of 380℃, a continuous extrusion temperature of 490℃, and a continuous extrusion speed of 53mm / s to obtain a continuously extruded billet; the continuously extruded billet is drawn with a drawing deformation of 62%, and then subjected to full recrystallization annealing at a temperature of 640℃ for 1 hour to obtain the initial billet;

[0152] S5: The initial billet is subjected to 15% medium deformation, then annealed at 700℃ for 40s, and then subjected to 15% medium deformation again, and then annealed at 700℃ for 40s again to obtain the finished brass wire.

[0153] Comparative Example 3 (without multi-pass gradient cold rolling and intermediate annealing)

[0154] The difference from Example 1 is that the cold rolling process adopts a single-pass cold rolling, with a total processing rate of 70%, and no intermediate stress-relieving annealing is performed. The remaining process steps are completely consistent with Example 1.

[0155] Comparative Example 4 (without adding Ni or Al elements)

[0156] The difference from Example 1 is that Ni and Al elements were not added to the alloy composition, while the remaining components are the same as in Example 1, and the production process steps are completely the same as in Example 1.

[0157] Comparative Example 5 (without graded heat treatment)

[0158] The difference from Example 1 is that the heat treatment uses conventional recrystallization annealing at a temperature of 600°C for 4 hours, followed by air cooling to room temperature. No graded heat treatment is performed. The remaining process steps are completely consistent with Example 1.

[0159] Comparative Example 6 (without using full-process online closed-loop control)

[0160] The difference from Example 1 is that all processes are conducted offline and adjusted afterward, without full-process online precise closed-loop control. The remaining process steps are completely consistent with Example 1.

[0161] Single-factor experiments on key process parameters

[0162] To systematically investigate the influence of various process parameters on pipe performance, this study designed seven groups of single-factor experiments, focusing on individual variables such as Ni content, homogenization heat treatment temperature, hot extrusion temperature, hot extrusion ratio, total cold rolling processing rate, solution treatment temperature, and aging treatment temperature, in order to clarify the effects of each factor on mechanical properties, corrosion resistance, and dimensional accuracy.

[0163] 1. The effect of Ni content on pipe performance

[0164] The alloy composition, except for Ni, was the same as in Example 1. Only the mass percentage of Ni was changed, with six levels set: 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, and 7.0%. All other process steps were exactly the same as in Example 1. Pipes were prepared and their mechanical and corrosion resistance properties were tested. The test results are shown in Table 1.

[0165]

[0166] Results Analysis: Increasing the Ni content from 2.0% to 4.0% continuously improved the tensile strength and yield strength of the alloy, significantly reduced the dezincification layer depth, and greatly improved corrosion resistance. Increasing the Ni content from 4.0% to 6.0% resulted in a slight increase in strength, but a decrease in elongation and some loss of plasticity. When the Ni content exceeded 6.0%, excess Ni formed coarse intermetallic compounds, leading to significant deterioration in strength, plasticity, and corrosion resistance. Considering the overall balance of strength, plasticity, and corrosion resistance, the optimal Ni content was determined to be 4.0 wt%.

[0167] 2. The effect of homogenization heat treatment temperature on pipe properties

[0168] With the Ni content fixed at 4.0 wt%, the remaining alloy composition was the same as in Example 1. All process steps were the same as in Example 1 except for the homogenization heat treatment temperature. Only the homogenization heat treatment temperature was changed, and five levels were set: 745℃, 780℃, 815℃, 850℃, and 885℃. Pipes were prepared and their mechanical properties were tested. The test results are shown in Table 2.

[0169]

[0170] Results Analysis: As the homogenization temperature increased from 745℃ to 815℃, as-cast compositional segregation gradually disappeared, the alloy microstructure homogeneity improved, and mechanical properties continued to increase. When the temperature increased from 815℃ to 850℃, the mechanical properties remained at a high level, but showed a slight decrease. When the temperature exceeded 850℃, the ingot grains became severely coarsened, leading to a significant deterioration in mechanical properties. Considering all performance factors, the optimal homogenization heat treatment temperature was determined to be 815℃.

[0171] 3. The effect of hot extrusion temperature on pipe properties

[0172] With a fixed Ni content of 4.0 wt% and a homogenization heat treatment temperature of 815℃, the remaining alloy composition and process steps were the same as in Example 1, except for the preheating temperature of the extruded billet. Only the preheating temperature of the extruded billet was changed, and six levels were set: 730℃, 750℃, 770℃, 790℃, 810℃, and 830℃. Tubes were prepared and their mechanical properties and dimensional accuracy were tested. The test results are shown in Table 3.

[0173]

[0174] Results Analysis: As the extrusion temperature increased from 730℃ to 770℃, the alloy's deformation resistance decreased, dynamic recrystallization became more complete, microstructure uniformity improved, and mechanical properties and dimensional accuracy continued to optimize. When the temperature increased from 770℃ to 810℃, mechanical properties and accuracy remained at a high level, but showed a slight decrease. When the temperature exceeded 810℃, grain coarsening became severe, and surface oxidation and die sticking of the billet intensified, leading to a significant deterioration in mechanical properties and dimensional accuracy. Considering both performance and dimensional accuracy, the optimal hot extrusion temperature was determined to be 770℃.

[0175] 4. Effect of hot extrusion ratio on pipe properties

[0176] With a fixed Ni content of 4.0 wt%, a homogenization heat treatment temperature of 815℃, and a hot extrusion temperature of 770℃, the remaining alloy composition and process steps were the same as in Example 1, except for the extrusion ratio. Only the hot extrusion ratio was changed, with 6 levels set: 5:1, 10:1, 15:1, 20:1, 25:1, and 30:1. Tubes were prepared and their mechanical properties and microstructure uniformity were tested. The test results are shown in Table 4.

[0177]

[0178] Results Analysis: As the extrusion ratio increased from 5:1 to 15:1, the deformation gradually increased, dynamic recrystallization became more complete, grain size became more uniform, and mechanical properties continued to improve. When the extrusion ratio increased from 15:1 to 25:1, the mechanical properties remained at a high level, but showed a slight decrease. When the extrusion ratio exceeded 25:1, the deformation resistance increased dramatically, deformation unevenness intensified, and the risk of pipe cracking increased, leading to a significant deterioration in mechanical properties. Considering both performance and microstructure uniformity, the optimal value for the hot extrusion ratio was determined to be 15:1.

[0179] 5. The impact of total cold rolling processing rate on pipe properties

[0180] With a fixed Ni content of 4.0 wt%, a homogenization heat treatment temperature of 815℃, a hot extrusion temperature of 770℃, and a hot extrusion ratio of 15:1, the remaining alloy composition and process steps were consistent with Example 1, except for the total cold rolling processing rate. Only the total cold rolling processing rate was changed, and five levels of 50%, 60%, 70%, 80%, and 90% were set. Tubes were prepared and their dimensional accuracy and mechanical properties were tested. The test results are shown in Table 5.

[0181]

[0182] Results Analysis: As the total processing rate increases from 50% to 70%, the cold deformation gradually increases, dimensional accuracy continues to improve, and the energy stored in cold deformation increases, leading to a more significant strengthening effect from subsequent heat treatment and a continuous increase in mechanical properties. When the total processing rate increases from 70% to 80%, the strength still shows a slight increase, but the dimensional accuracy decreases slightly. When the total processing rate exceeds 80%, work hardening becomes severe, the plasticity of the tube decreases significantly, and the risk of rolling cracks increases dramatically, resulting in a significant deterioration in both dimensional accuracy and mechanical properties. Considering dimensional accuracy, performance, and yield, the optimal value for the total cold rolling processing rate is determined to be 70%.

[0183] 6. The effect of solution treatment temperature on pipe properties

[0184] With a fixed Ni content of 4.0 wt%, a homogenization heat treatment temperature of 815℃, a hot extrusion temperature of 770℃, a hot extrusion ratio of 15:1, and a total cold rolling processing rate of 70%, the remaining alloy composition and process steps were consistent with Example 1, except for the solution treatment temperature. Only the solution treatment temperature was changed, and five levels were set: 660℃, 700℃, 740℃, 780℃, and 820℃. Pipes were prepared and their mechanical properties and corrosion resistance were tested. The test results are shown in Table 6.

[0185]

[0186] Results Analysis: As the solution temperature increased from 660℃ to 740℃, the strengthening phase gradually and fully dissolved, the homogeneity of the supersaturated solid solution improved, and the subsequent aging strengthening effect became more significant, with continuous optimization of mechanical properties and corrosion resistance. When the temperature increased from 740℃ to 780℃, the performance and corrosion resistance remained at a high level, but showed a slight decrease. When the temperature exceeded 780℃, the grains coarsened severely, and even overheating and burning occurred, the grain boundary structure was destroyed, leading to a significant deterioration in mechanical properties and corrosion resistance. Considering strength, plasticity, and corrosion resistance, the optimal solution treatment temperature was determined to be 740℃.

[0187] 7. The effect of aging treatment temperature on pipe properties

[0188] With a fixed Ni content of 4.0 wt%, homogenization heat treatment temperature of 815℃, hot extrusion temperature of 770℃, hot extrusion ratio of 15:1, total cold rolling rate of 70%, and solution treatment temperature of 740℃, the remaining alloy composition and process steps were consistent with those in Example 1, except for the aging treatment temperature. Only the aging treatment temperature was changed, and five levels were set: 350℃, 400℃, 450℃, 500℃, and 550℃. Pipes were prepared and their mechanical properties and corrosion resistance were tested. The test results are shown in Table 7.

[0189]

[0190] Results Analysis: As the aging temperature increased from 350℃ to 450℃, the strengthening phase precipitated more fully and dispersed more uniformly, resulting in a continuous improvement in the aging strengthening effect. Simultaneously, the grain boundary structure was optimized, leading to a sustained improvement in mechanical properties and corrosion resistance. When the temperature increased from 450℃ to 500℃, the strengthening phase began to coarsen, causing a slight decrease in performance and corrosion resistance. When the temperature exceeded 500℃, the strengthening phase became severely coarsened, and the precipitated phase at the grain boundaries was continuously distributed, leading to a significant deterioration in mechanical properties and corrosion resistance. Considering both strength, plasticity, and corrosion resistance, the optimal aging temperature was determined to be 450℃.

[0191] Performance testing and data analysis

[0192] (I) Testing methods and standards

[0193] The finished pipes from Examples 1-6 and Comparative Examples 1-6 were subjected to performance testing. All tests were conducted in accordance with current national standards, as detailed below:

[0194] 1. Mechanical property testing: The tensile strength, yield strength, and elongation of the pipe were tested using a universal testing machine in accordance with GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test at room temperature".

[0195] 2. Hardness testing: The Rockwell hardness (HRB) of the pipe was tested using a Rockwell hardness tester in accordance with GB / T 230.1-2018 "Metallic materials - Rockwell hardness test - Part 1: Test method".

[0196] 3. Dimensional accuracy inspection: GB / T 16866-2006 "Dimensions and permissible deviations of seamless copper and copper alloy tubes" is adopted. Laser diameter gauge, ultrasonic wall thickness gauge and steel tape measure are used to test the outer diameter, wall thickness and length tolerance of the tubes. The wall thickness difference (eccentricity) of the tubes is measured by the circumferential scanning method of ultrasonic thickness gauge.

[0197] 4. Corrosion resistance test: The dezincification corrosion test was carried out in accordance with GB / T 10119-2008 "Determination of dezincification corrosion resistance of brass", and the depth of the dezincification layer of the pipe was measured using a metallographic microscope;

[0198] 5. Grain size inspection: The average grain size of the pipe was measured using a metallographic microscope in accordance with GB / T 6394-2017 "Method for determination of average grain size of metals".

[0199] 6. Finished Product Rate Statistics: Calculate the percentage of qualified products out of 100 pipes in the same batch. Qualified products must simultaneously meet the design requirements for dimensional accuracy, mechanical properties, and corrosion resistance.

[0200] (II) Test Results

[0201] The comprehensive test results of the pipe performance of Examples 1-6 and Comparative Examples 1-6 are shown in Tables 8 and 9, respectively.

[0202]

[0203]

[0204] To more intuitively display the test results, plots were drawn separately. Figure 6 Bar chart comparing the tensile strength of pipes in the examples and comparative examples. Figure 7 Bar chart comparing the yield strength of pipes in the examples and comparative examples. Figure 8 Bar chart comparing the dezincification depth of pipes in the examples and comparative examples. Figure 9 Bar chart comparing the eccentricity of pipes in the examples and comparative examples.

[0205] (III) Data Analysis and Theoretical Verification

[0206] The outer diameter and wall thickness tolerances of the pipes prepared in Examples 1-6 were all controlled within 0.25 mm, and the eccentricity was ≤6%, achieving the design specifications for high-precision pipes. In terms of mechanical properties, the tensile strength of all pipes in all examples was ≥520 MPa, yield strength ≥450 MPa, hardness ≥88 HRB, and elongation ≥11%, achieving a good balance between strength and plasticity while ensuring high strength. Regarding corrosion resistance, the depth of the dezincified layer was stably controlled between 530 and 730 μm, the average grain size was ≤23 μm, the microstructure was uniform and fine, and the corrosion resistance was excellent.

[0207] Comparative Example 1 uses the traditional process of copper-nickel cupronickel forging + skew rolling piercing. Although it can form large-size pipes, the dimensional accuracy is poor, with the outer diameter and wall thickness tolerances both exceeding 0.7 mm and the eccentricity exceeding 12%. Simultaneously, the tensile strength is only 396.4 MPa, and the dezincification layer depth exceeds 1000 μm, with both strength and corrosion resistance far below standard. Comparative Example 2 uses a continuous extrusion + drawing process suitable for small-size bars. When preparing large-size pipes, the dimensional control capability is severely insufficient, and the alloy system lacks Ni and Mn strengthening elements, resulting in a tensile strength of only 431.7 MPa, which cannot meet the high-strength requirements. Comparative Example 3 uses single-pass cold rolling without intermediate annealing, leading to a large accumulation of residual rolling stress. This not only significantly deteriorates the dimensional accuracy but also reduces the elongation to 8.6%, resulting in severe loss of plasticity. Comparative Example 4, lacking Ni and Al core elements, struggled to form a dispersed strengthening phase to improve mechanical properties and a continuous, dense passivation film, resulting in a tensile strength of only 412.6 MPa and a dezincification layer depth as high as 1351.4 μm, leading to comprehensive performance degradation. Comparative Example 5, without staged heat treatment, failed to uniformly disperse the strengthening phase, resulting in unoptimized grain boundary structure, a tensile strength of only 431.8 MPa, and a significant decrease in corrosion resistance. Comparative Example 6, while similar in composition and basic process to the examples, lacked full-process online closed-loop control, leading to significant dimensional and performance fluctuations during mass production, resulting in a yield of only 78.4%.

[0208] The batch production yield of Examples 1-6 of this invention is ≥95%, and the stability of large-scale production is excellent, far exceeding the yield level of 70-82% of the comparative examples. This fully demonstrates the comprehensive technical advantages of this invention through multi-alloy synergistic design, precise hot working and forming, graded heat treatment control and full-process online closed-loop control. It also verifies the rationality and advancement of this technical solution in the preparation of large-size, high-precision, high-strength corrosion-resistant copper alloy pipes.

[0209] The above content should not be construed as limiting the specific implementation of this invention to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of this invention, and all such deductions or substitutions should be considered as falling within the patent protection scope defined by the submitted claims.

Claims

1. A method for mass production of large-size, high-precision copper alloy tubes, characterized in that, Includes the following steps: S1. Alloy melting and semi-continuous casting: The raw materials are batched according to the designed alloy composition, and then added to a vacuum induction melting furnace. After vacuum melting, online melt purification and composition control, large-size copper alloy ingots are prepared by semi-continuous casting. S2. Homogenization heat treatment of ingots and pretreatment of billets: The prepared ingots are subjected to homogenization heat treatment, and after the heat treatment is completed, they are cooled to room temperature in the furnace. Then, the ingots are subjected to pretreatment of turning and boring in sequence to remove the surface and inner hole defect layers and obtain extruded billets. S3. Hot extrusion forming: The extrusion blank and the hot extrusion die are preheated in gradient, and a horizontal extruder is used to hot extrude large-size tube blanks. After extrusion, the tube blanks are cooled by online water quenching. S4. Multi-pass cold rolling: After surface pretreatment of the extruded tube blank, multi-pass cold rolling is carried out using a Pilger cold rolling mill. After each pass of rolling, intermediate stress-relieving annealing is performed to prepare tube blanks. S5. Graded heat treatment: The cold-rolled tube billet is sent into a protective atmosphere heat treatment furnace and subjected to three grades of heat treatment in sequence: low-temperature stress relief annealing, medium-temperature solution treatment, and high-temperature aging treatment. S6. Full-process online inspection and finishing: The heat-treated pipes are inspected online, and the inspection data is transmitted to the central control system in real time to realize the closed-loop adjustment of the preceding process. Then, the pipes are straightened, cut off the ends, and polished to obtain large-size high-precision copper alloy pipes.

2. The method for mass production of large-size, high-precision copper alloy tubes according to claim 1, characterized in that, In step S1, the alloy composition by mass percentage is: Zn 20.0~28.0%, Ni 3.0~6.0%, Al 1.5~3.5%, Mn 0.5~1.5%, Fe 0.3~1.0%, La-Ce mixed rare earth 0.05~0.2%, with the balance being Cu and unavoidable impurities.

3. The method for mass production of large-size, high-precision copper alloy tubes according to claim 1 or 2, characterized in that, In step S1, the vacuum degree of vacuum melting is ≤1×10 -2 The melting process is protected by high-purity argon gas, and the melting temperature is 1180~1250℃. After the raw materials are completely melted, they are held at the temperature for 30 minutes. The online melt purification includes online argon gas rotary blowing degassing and online porous ceramic filtration for impurity removal. The composition control uses an online direct-reading spectral composition detection device to detect and adjust the melt composition to the design range in real time. The semi-continuous casting temperature is 1080~1150℃, the casting speed is 80~150mm / min, and the cooling water pressure is 0.2~0.5MPa.

4. The method for mass production of large-size, high-precision copper alloy tubes according to claim 1, characterized in that, In step S2, the temperature of the homogenization heat treatment is 780~850℃, and the holding time is 8~16h; the thickness of the car body treatment is 5mm, and the inner diameter of the ingot after boring treatment is 85mm.

5. The method for mass production of large-size, high-precision copper alloy tubes according to claim 1, characterized in that, In step S3, the preheating temperature of the extruded billet is 750~810℃, and the holding time is 2~6h; the preheating temperature of the hot extrusion die is 350~450℃, and the holding time is 2h; the extrusion ratio of the hot extrusion is 10:1~25:1, and the extrusion speed is 5~15mm / s; during the extrusion process, the outer diameter and wall thickness of the billet are detected in real time by an online laser diameter gauge and an ultrasonic wall thickness gauge, and the extrusion parameters are adjusted in real time to ensure the dimensional accuracy of the billet.

6. The method for mass production of large-size, high-precision copper alloy tubes according to claim 1, characterized in that, In step S4, the total processing rate of the multi-pass cold rolling is 60-80%, with 3-5 passes. The processing rate per pass decreases with each pass, ranging from 16-36%, and the rolling speed is 30-80 times / minute. The intermediate stress-relief annealing temperature is 350-450℃, the holding time is 1-3 hours, and the tube is cooled to room temperature in the furnace after the holding time. During the rolling process, the dimensional parameters of the tube are monitored in real time by online wall thickness detection, online outer diameter detection, and online straightness detection devices, and the rolling parameters are adjusted in real time to correct dimensional deviations.

7. The method for mass production of large-size, high-precision copper alloy tubes according to claim 1, characterized in that, In step S5, the specific process of the graded heat treatment is as follows: the first stage is low-temperature stress-relief annealing, with a temperature of 300~400℃ and a holding time of 2~4h, followed by furnace cooling to room temperature; the second stage is medium-temperature solution treatment, with a temperature of 700~780℃ and a holding time of 1~3h, followed by immediate water quenching to room temperature; the third stage is high-temperature aging treatment, with a temperature of 400~500℃ and a holding time of 4~8h, followed by air cooling to room temperature; the furnace temperature fluctuation during the heat treatment process is controlled within ±5℃, and the furnace temperature is precisely controlled through online temperature monitoring during the heat treatment process.

8. The method for mass production of large-size, high-precision copper alloy tubes according to claim 1, characterized in that, In step S6, the online quality inspection includes defect detection and dimensional inspection. Defect detection includes online eddy current testing to detect surface defects and online ultrasonic testing to detect internal defects. Dimensional inspection includes real-time detection of the pipe's outer diameter, wall thickness, length, and straightness.

9. The method for mass production of large-size, high-precision copper alloy tubes according to claim 1, characterized in that, In step S6, the straightening is performed using a seventeen-roller straightener, and the straightness of the pipe after straightening is ≤1mm / m; the length of the pipe after the head and tail cutting treatment is 10000mm; and the surface roughness Ra of the pipe after the surface polishing treatment is ≤1.6μm.

10. The method for mass production of large-size, high-precision copper alloy tubes according to claim 1, characterized in that, The finished large-size high-precision copper alloy tubes meet the following requirements: tensile strength ≥520MPa, yield strength ≥450MPa, hardness ≥88HRB, elongation ≥11%, and dezincification layer depth 530~730μm.

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