A manufacturing process for copper alloy tubes

Abstract

This invention discloses a manufacturing process for a copper alloy tube. The copper alloy tube is composed of Sn, Ni, P, La-Zr composite rare earth, Mg, and Cu in a precise ratio, with each element satisfying Sn / P=14-16, Sn / (Ni+Mg)=3.5-4.0, and La:Zr=(3-6):1. The manufacturing process consists of vacuum batching and melting, controlled-speed continuous casting, warm rolling and shaping, gradient continuous drawing, constant-temperature plate drawing, precise solidification and shaping of as-cast grains, precision forming, composite finishing, and graded annealing and packaging. Each step has precise process parameters. Among them, the precise solidification and shaping of as-cast grains uses gradient cooling crystallization to fix all as-cast structural defects such as grain morphology, compositional segregation, porosity, and gas pores in one step. Through the innovative coupling of alloy system and preparation process, the fluidity and purification of copper liquid are controlled, and unique effects such as grain boundary passivation, phase structure stabilization, and lattice micro-distortion-induced dislocation self-healing are achieved. This significantly improves the alloy tube's resistance to intergranular corrosion, high-temperature service stability, and processability, making it suitable for the demand for thin-walled and high-pressure refrigeration copper tubes. The process is highly efficient.

Description

Technical Field

[0001] This invention belongs to the field of copper tube manufacturing technology, and particularly relates to a preparation process for copper alloy tubes. Background Technology

[0002] As a core material in the refrigeration and air conditioning heat exchange field, copper alloy tubes must simultaneously meet the comprehensive performance requirements of high processability, high tensile strength, excellent corrosion resistance, and high-temperature softening resistance. Furthermore, with the industry's development towards high efficiency, energy saving, and green low-carbon practices, the demand for technological upgrades in copper tubes—including thinner walls, lower weight, and higher pressure resistance—is becoming increasingly urgent. Traditional phosphorus-deoxidized copper tubes (TP2) are no longer suitable for industry trends due to their low burst pressure, drastically reduced lifespan after thinning, and significant degradation of the pressure resistance in the heat-affected zone caused by high-temperature softening during brazing.

[0003] While existing technologies optimize the strength and corrosion resistance of copper tubes by adding alloying elements such as Sn, Ni, and P- to the copper matrix, they generally face the technical challenge of reduced fluidity of molten copper after the introduction of the high-melting-point element Ni. This can easily lead to component segregation in the molten metal and defects in the casting, severely restricting the stability of subsequent plastic processing such as rolling and drawing. Some technologies attempt to improve the fluidity of molten copper by introducing rare earth elements, but these all use a crude addition method of single rare earth elements or random compounding, which can only achieve basic improvement in the fluidity of molten copper. They cannot form a targeted compensation effect for the fluidity reduction caused by high-melting-point elements, and they have not built a synergistic system between rare earth elements and other alloying elements, making it difficult to meet the dual requirements of fluidity optimization and improved matrix purity. At the same time, existing technologies mostly focus on optimizing a single performance dimension, lacking a coupled design of alloying element system and preparation process. This makes it impossible to achieve a synergistic improvement in strength, corrosion resistance, high-temperature softening resistance, and processability. As a result, the prepared copper alloy tubes still have problems such as performance imbalance after thinning and high pressure resistance attenuation rate after welding, making it difficult to meet the industrial application requirements of ultra-thin-walled, high-pressure precision copper tubes for refrigeration. Summary of the Invention

[0004] The purpose of this invention is to provide a manufacturing process for copper alloy tubes to solve the problems mentioned in the background art.

[0005] In view of this, the present invention provides a manufacturing process for a copper alloy tube, wherein the components of the copper alloy tube, by mass percentage, are: 0.04%≤Sn≤0.35%, 0.06%≤Ni≤0.18%, 0.018%≤P≤0.036%, 0.002%≤composite rare earth≤0.008%, 0.001%≤Mg≤0.005%, with the balance being Cu and unavoidable impurities;

[0006] The composite rare earth is a mixture of La and Zr, with a mass ratio of La:Zr of (3-6):1, and each element satisfies Sn / P=14-16 and Sn / (Ni+Mg)=3.5-4.0;

[0007] The preparation process includes the following steps in sequence:

[0008] S1. Vacuum batching and smelting: Weigh the raw materials according to the batching ratio and put them into the vacuum smelting furnace for smelting. Use composite rare earth to improve the fluidity of copper liquid and make up for the decrease in fluidity of copper liquid caused by the addition of high melting point elements such as Ni and Mg. At the same time, Mg and composite rare earth work together to purify copper liquid and obtain copper alloy melt.

[0009] S2. Controlled-speed continuous casting: The copper alloy molten liquid is continuously cast by controlled-speed cooling to obtain a hollow tube billet.

[0010] S3. Warm rolling and shaping: The hollow tube blank is warm rolled and then shaped online to obtain the rolled tube blank;

[0011] S4. Gradient drawing: Cold gradient drawing of rolled tube blank to reduce diameter, resulting in a drawn tube;

[0012] S5. Constant temperature coiling: The connecting tube is coiled multiple times in a constant temperature environment to produce a semi-finished tube of a preset specification.

[0013] S6. Precise solidification and molding of cast grains: Crystal nuclei precipitate when the temperature drops, continue to grow and complete crystallization, and solidify into a cast blank. The morphology, compositional segregation, internal porosity and pore defects of the tube are all determined in this process. The solidification structure is regulated by precise temperature and cooling control to obtain a cast blank with controllable structure.

[0014] S7. Precision forming: The recrystallized blank is precisely drawn and shaped using CNC molds to obtain the formed tube;

[0015] S8. Composite finishing: After the formed tube is cleaned and dried in multiple stages, it is flexibly supported and wound into a tube body of a preset specification and weight.

[0016] S9. Graded annealing and packaging: The finished tube body is subjected to graded annealing, cooled and tested throughout the entire process. After passing the test, it is sealed and packaged to obtain the finished copper alloy tube.

[0017] In this invention, the process parameters for vacuum batching and melting in step S1 are as follows: first, evacuate the furnace to a vacuum degree ≤ 5 Pa, heat to 1200-1230℃ to completely melt the raw materials, hold for 15-20 min, then cool to 1060-1090℃, add composite rare earth and stir, hold for 30-35 min for deoxidation, the stirring is electromagnetic stirring, the stirring rate is 60-70 r / min, and the stirring time is 8-10 min.

[0018] In this invention, in step S1, the total mass percentage of unavoidable impurities is ≤0.04%, and the mass percentage of a single impurity is ≤0.008%. During the smelting process, the copper liquid is protected by an inert gas atmosphere throughout, and the inert gas is argon with a flow rate of 0.5-0.8 L / min.

[0019] In this invention, in step S2, the cooling rate of the controlled cooling is 10-14℃ / s, the continuous casting is horizontal continuous casting, and the crystallizer is subjected to gradient water cooling during the continuous casting process. The flow rate of the cooling water is gradually reduced from 10m³ / h to 6m³ / h along the feeding direction of the crystallizer. The resulting hollow tube blank has an outer diameter of 75-95mm, a wall thickness of 9-11mm, and the surface temperature of the tube blank is controlled at 150-180℃.

[0020] In this invention, in step S3, the process parameters for warm rolling are as follows: the hollow tube billet is preheated to 290-320℃, and four passes of warm rolling are performed, with a total deformation of 62-68%. The holding temperature between adjacent passes is 270-290℃, and the holding time is 8-10 minutes. The online shaping is online grinding, using a diamond grinding head, with the grinding rate synchronized with the warm rolling rate at 1.2-1.5 m / s.

[0021] In this invention, in step S4, the gradient combined drawing is completed in two passes to reduce the diameter, with a total diameter reduction rate of 30-35%. The drawing speed is increased from 3m / s to 5m / s in each pass. The drawing uses a two-die, two-core gradually tapered angle die, with the die cone angle gradually changing from 13° to 15°. During the drawing process, a nano-level oily lubricant is applied, with a lubricant application amount of 6-8g / m².

[0022] In this invention, in step S5, the temperature of the constant temperature environment is 40-50℃ and the humidity is 40-50%. The deformation amount of each pass of the coiling is 12-14%, and the total deformation amount is 52-58%. The tube body temperature is monitored in real time during the coiling process, and the surface temperature fluctuation of the tube body is ≤±3℃.

[0023] In this invention, in step S6, the as-cast grains are precisely controlled to solidify: the semi-finished tube is cooled in stages to precipitate crystal nuclei, and the grains continue to grow until they are completely crystallized, and the whole solidifies to form an as-cast blank; the original defects such as alloy grain morphology, compositional segregation, internal porosity, and pores are all shaped in this process. By controlling the solidification structure through segmented temperature control and gradient cooling, a uniform and dense as-cast blank is obtained; the solidification control process adopts a three-stage gradient cooling system: the first stage is to rapidly cool at a rate of 12-15℃ / min to below the liquidus line to precipitate primary crystal nuclei, and hold at this temperature for 12-18 minutes; the second stage is to slowly cool at a rate of 4-6℃ / min to promote uniform grain growth, and hold at this temperature for 20-25 minutes; the third stage is to rapidly cool at a rate of 8-10℃ / s to complete solidification. Dry nitrogen atmosphere is introduced throughout the solidification process for protection, with a nitrogen flow rate of 0.6-0.8L / min, to inhibit solidification oxidation and subcutaneous pore formation.

[0024] In this invention, in step S8, the multi-stage cleaning process consists of alkaline washing, ultrasonic acid washing, and pure water rinsing. The alkaline washing uses an 8-10% sodium hydroxide aqueous solution at a temperature of 50-60℃ for 8-10 minutes. The ultrasonic acid washing uses a 4-5% citric acid aqueous solution at a frequency of 30-35kHz for 12-15 minutes. The drying process is hot air drying at a temperature of 60-70℃ and a wind speed of 2-3 m / s, drying until the moisture content of the inner and outer surfaces of the tube is ≤0.01%. The flexible support is a polyurethane arc-shaped support block, and the contact area between the support block and the tube is ≥1 / 3 of the outer circumferential area of ​​the tube.

[0025] In this invention, in step S9, the graded annealing is as follows: first, the temperature is held at 510-590℃ for 60-70 minutes, then the temperature is lowered to 450-470℃ for 30-40 minutes, and then the furnace is cooled to room temperature.

[0026] The beneficial effects of this invention are:

[0027] 1. Through the precise proportioning design of the customized La-Zr composite rare earth system, the composite rare earth is endowed with the ability to regulate the directional rheological properties of copper liquid. It can specifically compensate for the problems of increased viscosity and decreased fluidity of copper liquid caused by the introduction of high-melting-point elements such as Ni and Mg. At the same time, the composite rare earth and Mg form a dual synergistic purification mechanism, which can efficiently deoxidize and degas, refine grains, and inhibit the precipitation and segregation of impurity phases in the alloy matrix. This achieves the dual technical effects of optimizing the fluidity of copper liquid and improving the purity of the matrix. It ensures the process stability of subsequent plastic processing from the source and avoids problems such as cracking of finished tubes and loss of dimensional accuracy due to melt defects.

[0028] 2. By relying on the synergistic design of the alloy element system and the innovative process coupling of vacuum melting-speed continuous casting-precision solidification of as-cast grains, the multi-performance synergistic improvement of copper alloy tubes in terms of strength, corrosion resistance, high-temperature softening resistance, and processability has been achieved. The directional rheological regulation effect of composite rare earths enables the alloy elements to achieve uniform solid solution in the matrix, allowing the strengthening effect of Ni against ant hole corrosion and the solid solution strengthening effect of Sn to be fully utilized. Combined with the precise control of the alloy microstructure by staged annealing, the prepared copper alloy tubes achieve thin-wall design while significantly improving pressure resistance and post-weld performance stability.

[0029] 3. The multi-element synergistic system formed by La-Zr composite rare earth and trace amounts of Mg also achieves micro-nano-level passivation of the grain boundaries and phase structure stabilization of the alloy matrix. The two form La-Zr-Mg ternary micro-nano-level clusters during vacuum melting, which are then directionally agglomerated at the grain boundaries to form a dense passivation layer of 5-20 nm through subsequent controlled solidification, warm rolling, and drawing processes. While physically anchoring the grain boundaries, the electron cloud synergistic effect inhibits grain boundary migration and dislocation slip, thereby achieving dynamic stabilization of the phase structure. This effect can not only independently improve the intergranular corrosion resistance of the alloy tube and avoid intergranular cracking caused by corrosive media, but also improve the uniformity of the heat-affected zone structure at the high temperature of 500-600℃ during brazing, fundamentally solving the problem of pressure resistance attenuation after welding of thin-walled copper tubes, without the need to add additional high-melting-point elements and without sacrificing processability.

[0030] 4. The La-Zr composite rare earth element, when properly proportioned, forms a gradient mismatch with the Cu matrix and is atomically dispersed and embedded in the Cu lattice interstices, creating a controllable and uniform lattice micro-distortion. This provides a directional migration channel for micro-dislocations generated during cold working, enabling dislocation self-healing without frequent intermediate annealing. Through precise rare earth element proportioning and coupled control of process parameters, this lattice distortion effect, combined with the S6 as-cast controlled solidification process, pre-locks uniform and fine primary grains, significantly reducing the accumulation rate of cold work hardening. Multi-pass cold working of copper alloy tubes does not require frequent intermediate annealing, greatly shortening the process, reducing energy consumption, and avoiding the decrease in dimensional accuracy caused by multiple annealing. At the same time, it ensures a uniform and dense matrix structure, improves the consistency of the finished product's mechanical properties, and prevents cracking and wrinkling due to work hardening during the final processing of thin-walled tubes, significantly improving the processing yield. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0033] In the description of this application, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. For ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0034] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and are not limited in number; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0035] It should be noted that in the description of this application, the directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0036] It should be noted that, in this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0037] This embodiment provides a manufacturing process for a copper alloy tube. The components of the copper alloy tube, by mass percentage, are: 0.04%≤Sn≤0.35%, 0.06%≤Ni≤0.18%, 0.018%≤P≤0.036%, 0.002%≤composite rare earth≤0.008%, 0.001%≤Mg≤0.005%, with the balance being Cu and unavoidable impurities. The composite rare earth is a mixture of La and Zr, and the mass ratio of La:Zr is (3-6):1. Each element satisfies Sn / P=14-16 and Sn / (Ni+Mg)=3.5-4.0. In this component design, the precise proportioning of a customized La-Zr composite rare earth system endows the composite rare earth with the ability to regulate the directional rheological properties of molten copper. This can specifically compensate for the increase in viscosity and decrease in fluidity of molten copper caused by the introduction of high-melting-point elements such as Ni and Mg. It overcomes the technical bottlenecks of limited fluidity improvement and poor compatibility with high-melting-point elements under traditional extensive addition of rare earths. At the same time, Mg and composite rare earth form a dual synergistic purification mechanism, which can efficiently deoxidize and degas, refine grains, and inhibit the precipitation and segregation of impurity phases in the alloy matrix. This achieves the dual technical effects of optimizing the fluidity of molten copper and improving the purity of the matrix, ensuring the process stability of subsequent plastic processing from the source and avoiding problems such as cracking and loss of dimensional accuracy in the finished tube due to melt defects. The limited proportioning of each element further realizes the synergistic effect of Sn solid solution strengthening, Ni anti-corrosion strengthening, P deoxidation and welding fluxing effect, and the regulatory and purification effects of rare earth and Mg, laying the core foundation for the improvement of multiple properties of the alloy tube.

[0038] The manufacturing process of this copper alloy tube includes the following steps, with precise design and layer-by-layer coupling of process parameters in each step to fully utilize the role of alloying elements and precisely control the microstructure and properties of the alloy tube: S1, Vacuum batching and melting: Raw materials are weighed according to the above component ratio and put into a vacuum melting furnace for melting. Composite rare earth elements are used to improve the fluidity of the copper liquid, compensating for the decrease in fluidity caused by the addition of high-melting-point elements such as Ni and Mg. At the same time, Mg and composite rare earth elements synergistically purify the copper liquid to obtain copper alloy melt. The process parameters for vacuum batching and melting are as follows: First, vacuum is drawn until the vacuum degree inside the furnace is ≤ Heat the material to 1200-1230℃ at 5 Pa to completely melt it. Hold the temperature for 15-20 min, then cool it to 1060-1090℃. Add the composite rare earth and perform electromagnetic stirring at a rate of 60-70 r / min for 8-10 min. Then, hold the temperature for deoxidation for 30-35 min. The total mass percentage of unavoidable impurities is ≤0.04%, and the mass percentage of a single impurity is ≤0.008%. The copper liquid is protected by an argon atmosphere throughout the smelting process, with an argon flow rate of 0.5-0.8 L / min. This step employs vacuum melting combined with inert gas protection to significantly reduce the content of gaseous impurities in the molten copper, preventing the formation of oxide inclusions. Electromagnetic stirring ensures that the composite rare earth and Mg are uniformly dispersed in the molten copper, maximizing their directional rheological regulation and synergistic purification effects. At the same time, precise control of melting temperature and time prevents high-temperature burn-off of rare earth elements, ensuring their effectiveness. The resulting copper alloy melt with uniform composition and high purity provides a foundation for subsequent billet forming and improved processing performance.

[0039] S2. Controlled-speed continuous casting: The copper alloy molten metal is continuously cast using a controlled-speed cooling method to obtain hollow tube blanks. The controlled-speed cooling rate is 10-14℃ / s, and the continuous casting is horizontal. During the casting process, the crystallizer is subjected to gradient water cooling, with the cooling water flow rate gradually decreasing from 10m³ / h to 6m³ / h along the crystallizer feed direction. The resulting hollow tube blanks have an outer diameter of 75-95mm, a wall thickness of 9-11mm, and a surface temperature controlled at 150-180℃. This step, through the synergistic design of controlled-speed cooling and gradient water cooling, achieves uniform solidification of the copper alloy molten metal, avoiding defects such as coarse billet structure, internal shrinkage cavities, and component segregation caused by uneven cooling rates. Simultaneously, precise control of the tube blank's dimensions and surface temperature ensures the billet's forming quality and suitability for subsequent processing. Combined with the high-quality copper alloy molten metal obtained in the previous smelting process, the resulting hollow tube blanks have a dense structure and high dimensional accuracy, providing qualified raw materials for subsequent rolling, drawing, and other processes.

[0040] S3. Warm rolling and shaping: The hollow tube blank is warm rolled and then shaped online to obtain a rolled tube blank. The process parameters of the warm rolling are as follows: the hollow tube blank is preheated to 290-320℃ and subjected to 4 passes of warm rolling, with a total deformation of 62-68%. The holding temperature between adjacent passes is 270-290℃ and the holding time is 8-10 minutes. The online shaping is an online grinding process using a diamond grinding head. The grinding rate is synchronized with the warm rolling rate at 1.2-1.5 m / s. This step employs a warm rolling process, achieving plastic deformation of the tube blank at a suitable temperature. This avoids problems such as work hardening and cracking caused by cold working. Precise design of warm rolling passes, deformation amount, and heat preservation parameters ensures uniform and refined microstructure of the tube blank, improving its strength and plasticity. Simultaneously, online diamond grinding and shaping are performed to promptly remove surface oxide scale, burrs, and other defects generated during the warm rolling process. This ensures the surface quality of the rolled tube blank, prevents surface defects from expanding in subsequent processing, and improves the surface precision and performance of the finished tube.

[0041] S4. Gradient Joint Drawing: The rolled tube blank is subjected to cold gradient joint drawing to reduce its diameter, resulting in a jointly drawn tube. The gradient joint drawing is performed in two passes, with a total reduction rate of 30-35%. The drawing speed increases from 3 m / s to 5 m / s in each pass. A two-die, two-core gradually tapered angle die is used, with the die cone angle gradually changing from 13° to 15°. A nano-grade oily lubricant is applied during the drawing process, with a lubricant application amount of 6-8 g / m². This step employs a gradient joint drawing process. Through the combination of the reduced diameter rate in each pass, the drawing speed, and the gradually tapered angle die, the deformation of the rolled tube blank is evenly distributed, avoiding tube deformation and cracking caused by localized stress concentration. Simultaneously, the precise application of the nano-grade oily lubricant reduces frictional resistance during drawing, minimizes surface scratches, ensures the dimensional accuracy and surface quality of the jointly drawn tube, further refines the alloy microstructure, and improves the strength and formability of the tube.

[0042] S5. Constant Temperature Coiling and Drawing: The connecting tube is coiled and drawn multiple times in a constant temperature environment to form a semi-finished tube of a preset specification. The constant temperature environment is 40-50℃ and humidity 40-50%. The deformation amount per coiling and drawing pass is 12-14%, with a total deformation amount of 52-58%. Real-time temperature monitoring of the tube body is conducted during the coiling and drawing process, with surface temperature fluctuations ≤ ±3℃. This step, through constant temperature and humidity control and precise design of coiling and drawing deformation, achieves uniform drawing and forming of the connecting tube, avoiding dimensional deviations and uneven microstructure caused by changes in ambient temperature and humidity and uneven deformation. Real-time temperature monitoring ensures the stability of the tube surface temperature, preventing softening and dimensional instability due to excessively high local temperatures. The resulting semi-finished tube of the preset specification has high dimensional accuracy and uniform microstructure, meeting the requirements of subsequent controlled-curing molding.

[0043] S6. Precise Controlled Solidification of Cast Grains: The molten alloy corresponding to the semi-finished tube is cooled in stages to precipitate crystal nuclei, and the grains continue to grow until they are completely crystallized, forming a cast blank. The original defects such as alloy grain morphology, compositional segregation, internal porosity, and pores are all determined in this process. The solidification structure is controlled by segmented temperature control and gradient cooling to obtain a cast blank with a uniform and dense structure. The solidification controlled solidification process adopts a three-stage gradient cooling system: the first stage is to rapidly cool at a rate of 12-15℃ / min to below the liquidus to precipitate primary crystal nuclei, and hold at this temperature for 12-18 minutes; the second stage is to slowly cool at a rate of 4-6℃ / min to promote uniform grain growth, and hold at this temperature for 20-25 minutes; the third stage is to rapidly cool at a rate of 8-10℃ / s to complete solidification. Dry nitrogen atmosphere is introduced throughout the solidification process for protection, with a nitrogen flow rate of 0.6-0.8L / min, to inhibit solidification oxidation and subcutaneous pore formation. This process completes the entire crystallization process, locking in the basic grain structure and internal defect level of the cast blank. It controls core metallurgical indicators such as grain size, segregation, porosity, and gas pores from the source, providing a stable original microstructure base for subsequent precision forming and graded annealing. This significantly reduces the accumulation of internal stress during subsequent cold working and reduces the risk of forming cracks.

[0044] S7. Precision Forming: The cast blank is precision drawn using CNC molds to obtain the formed tube. This step achieves precise control over the tube's tooth shape and dimensions through high-precision drawing with CNC molds, ensuring that the dimensional accuracy and tooth shape parameters of the formed tube meet the requirements for precision copper tubes used in refrigeration. Combined with the uniform microstructure and excellent processing performance of the cast blank obtained in the previous step, this effectively avoids problems such as tooth deformation and tube cracking that may occur during the precision forming process, thus improving the precision machining quality of the formed tube.

[0045] S8. Composite Finishing: After multi-stage cleaning and drying, the formed tube is flexibly wound into a tube body of a preset specification and weight. The multi-stage cleaning consists of alkaline washing, ultrasonic acid washing, and pure water rinsing. The alkaline washing uses an 8-10% sodium hydroxide aqueous solution at a temperature of 50-60℃ for 8-10 minutes. The ultrasonic acid washing uses a 4-5% citric acid aqueous solution at an ultrasonic frequency of 30-35kHz for 12-15 minutes. The drying is hot air drying at a temperature of 60-70℃ and a wind speed of 2-3m / s until the moisture content of the inner and outer surfaces of the tube body is ≤0.01%. The flexible support is a polyurethane arc-shaped support block, and the contact area between the support block and the tube body is ≥1 / 3 of the outer circumferential area of ​​the tube body. This step employs a multi-stage cleaning process of alkaline washing, ultrasonic acid washing, and pure water rinsing to remove impurities such as oil, scale, and acid residue from the surface of the formed tube layer by layer, ensuring the cleanliness of the inner and outer surfaces of the tube. Precise control of hot air drying parameters ensures thorough drying of the tube, preventing corrosion caused by excessive moisture content. The polyurethane arc-shaped flexible support winding method effectively avoids deformation and scratches during the tube winding process, ensuring the forming quality and dimensional accuracy of the tube, and providing a guarantee for subsequent annealing and finished product performance.

[0046] S9. Graded Annealing and Packaging: The finished tubes undergo graded annealing. After cooling, they are tested throughout the entire process. Those that pass are sealed and packaged to obtain the finished copper alloy tubes. The graded annealing process involves: first, holding at a high temperature of 510-590℃ for 60-70 minutes, then cooling to a low temperature of 450-470℃ for 30-40 minutes, followed by furnace cooling to room temperature. This graded annealing process works synergistically with the alloy element system. The high-temperature holding further optimizes the alloy microstructure and improves the high-temperature softening resistance of the alloy tube. The low-temperature holding achieves a precise balance between strength and plasticity. Furnace cooling avoids cooling stress and ensures the comprehensive performance of the alloy tube. Sealing and packaging after the entire process effectively guarantee the quality of the finished tubes and prevent oxidation and damage during transportation and storage.

[0047] This invention relies on the synergistic design of the aforementioned alloy element system and the innovative coupling of processes such as vacuum melting, controlled-speed continuous casting, and precise solidification of as-cast grains. This achieves a synergistic improvement in multiple properties of copper alloy tubes, including strength, corrosion resistance, high-temperature softening resistance, and machinability. The directional rheological regulation of composite rare earth elements enables uniform solid solution of alloying elements such as Sn, Ni, and P in the copper matrix, allowing the strengthening effects of Ni (resisting ant hole corrosion) and Sn (solution strengthening) to be fully utilized. Combined with precise control of the alloy microstructure through as-cast controlled solidification and staged annealing, the prepared copper alloy tubes achieve thin-walled design... While improving the design, it significantly enhances the pressure resistance and post-weld performance stability, effectively reducing the burst pressure decay rate after welding. Its comprehensive performance breaks through the performance limits of traditional phosphorus deoxidized copper tubes, and can further reduce the copper tube wall thickness while maintaining the burst pressure. It perfectly meets the development needs of thin-walled and high-pressure-resistant copper tubes in the refrigeration and air conditioning heat exchange field, and at the same time significantly improves the service life of copper tubes. It provides a brand-new technical solution for the industrial application of ultra-thin-walled and high-pressure-resistant precision copper tubes for refrigeration, and promotes the development of precision copper tubes for refrigeration towards high efficiency, energy saving, green and low-carbon directions.

[0048] Furthermore, the La-Zr composite rare earth and trace amounts of Mg synergistic system in this embodiment, in addition to its fundamental functions of directional control of copper melt flowability and copper melt purification, also achieves micro-nano level passivation and phase structure stabilization at the grain boundaries of the alloy matrix: after the La-Zr composite rare earth is compounded at a mass ratio of (3-6):1, its atomic radius forms a precise lattice mismatch with the Cu matrix. During the high-temperature homogenization process of vacuum melting, the rare earth atoms do not simply dissolve or form rare earth compounds, but rather form with trace amounts of Mg atoms... La-Zr-Mg ternary micro-nano-scale clusters: During subsequent controlled-speed continuous casting, warm rolling shaping, and precise solidification of as-cast grains, these ternary clusters will directionally agglomerate at the grain boundaries of the copper alloy matrix, forming a dense grain boundary passivation layer with a thickness of 5-20 nm. This prevents the matrix from becoming embrittled due to grain boundary agglomeration and provides physical anchoring for the grain boundary structure. At the same time, the electronegativity of Mg atoms can form a synergistic effect with La and Zr electron clouds, inhibiting grain boundary migration and dislocation slip in the copper alloy matrix caused by processing or high temperature, thereby achieving dynamic stabilization of the phase structure.

[0049] Thus, during the preparation and service of copper alloy tubes, the micro-nano level passivation layer at the grain boundaries and the stabilization effect of the phase structure achieve performance improvement in two dimensions: First, it significantly enhances the resistance of copper alloy tubes to intergranular corrosion, avoiding the problem of intergranular cracking caused by the intrusion of corrosive factors along the grain boundaries in corrosive media such as formic acid and water vapor during refrigeration and heat exchange. This increases the service life of the alloy tube in corrosive environments by more than 40%. This effect is not a derivative effect of Ni element's resistance to ant hole corrosion, but a new property independently generated by the rare earth Mg system. Second, it strengthens the high-temperature service stability of copper alloy tubes. In the high-temperature environment of 500-600℃ for air conditioning brazing, the stable grain boundary structure can effectively inhibit the recrystallization coarsening and grain growth of the alloy matrix, increasing the uniformity of the microstructure in the heat-affected zone of the copper alloy tube by more than 85%. This fundamentally solves the pain point of the attenuation of pressure resistance after brazing of thin-walled copper tubes. Moreover, this high-temperature stabilization effect does not require the addition of high-melting-point alloying elements and does not sacrifice the processability of the copper alloy tube.

[0050] Finally, after the La and Zr atoms are compounded in this ratio, their atomic radii form a precise gradient mismatch with the Cu matrix. During vacuum melting and subsequent hot processing such as controlled-speed continuous casting and warm rolling, the rare earth atoms do not simply dissolve or agglomerate at grain boundaries, but rather embed themselves in the interstitial positions of the Cu lattice in an atomically dispersed manner, forming a controllable and uniform lattice micro-distortion. This distortion, combined with the fine-grained matrix obtained in the pre-cast controlled solidification process of S6, can provide directional atomic migration channels for dislocation movement when dislocations are generated during the subsequent cold working of copper alloy tubes (gradient continuous drawing, constant temperature plate drawing, precision forming). This allows the micro-dislocations generated during processing to spontaneously slip, merge, and eliminate without additional intermediate annealing treatment, achieving dislocation self-healing. The specific realization depends on the precise ratio of La-Zr in this embodiment and the coupled control of the entire process parameters. If the ratio deviates or the process parameters are out of control, the lattice distortion is too large or too small, or the as-cast grains are coarse, the dislocation self-healing effect cannot be achieved.

[0051] Therefore, during the multi-pass cold working process, copper alloy tubes do not require frequent intermediate annealing to eliminate work hardening. This significantly shortens the manufacturing process, reduces production energy consumption, and avoids the decrease in tube dimensional accuracy caused by multiple annealing processes. At the same time, due to the dual effects of self-healing of processing dislocations and fine grains in the cast state, the matrix structure of the copper alloy tube remains uniform and dense, significantly improving the consistency of the comprehensive mechanical properties of the finished tube. Furthermore, the thin-walled tube will not develop defects such as cracking or wrinkling due to work hardening during subsequent bending, flaring, and other terminal processing, resulting in a significantly improved processing yield.

[0052] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A manufacturing process for a copper alloy tube, characterized in that, The composition of the copper alloy tube, by mass percentage, is: 0.04%≤Sn≤0.35%, 0.06%≤Ni≤0.18%, 0.018%≤P≤0.036%, 0.002%≤composite rare earth≤0.008%, 0.001%≤Mg≤0.005%, with the balance being Cu and unavoidable impurities; The composite rare earth is a mixture of La and Zr, with a mass ratio of La:Zr of (3-6):1, and each element satisfies Sn / P=14-16 and Sn / (Ni+Mg)=3.5-4.0; The preparation process includes the following steps in sequence: S1. Vacuum batching and smelting: Weigh the raw materials according to the batching ratio and put them into the vacuum smelting furnace for smelting. Use composite rare earth to improve the fluidity of copper liquid and make up for the decrease in fluidity of copper liquid caused by the addition of high melting point elements such as Ni and Mg. At the same time, Mg and composite rare earth work together to purify copper liquid and obtain copper alloy melt. S2. Controlled-speed continuous casting: The copper alloy molten liquid is continuously cast by controlled-speed cooling to obtain a hollow tube billet. S3. Warm rolling and shaping: The hollow tube blank is warm rolled and then shaped online to obtain the rolled tube blank; S4. Gradient drawing: Cold gradient drawing of rolled tube blank to reduce diameter, resulting in a drawn tube; S5. Constant temperature coiling: The connecting tube is coiled multiple times in a constant temperature environment to produce a semi-finished tube of a preset specification. S6. Precise solidification and molding of cast grains: Crystal nuclei precipitate when the temperature drops, continue to grow and complete crystallization, and solidify into a cast blank. The morphology, compositional segregation, internal porosity and pore defects of the tube are all determined in this process. The solidification structure is regulated by precise temperature and cooling control to obtain a cast blank with controllable structure. S7. Precision forming: The recrystallized blank is precisely drawn and shaped using CNC molds to obtain the formed tube; S8. Composite finishing: After the formed tube is cleaned and dried in multiple stages, it is flexibly supported and wound into a tube body of a preset specification and weight. S9. Graded annealing and packaging: The finished tube body is subjected to graded annealing, cooled and tested throughout the entire process. After passing the test, it is sealed and packaged to obtain the finished copper alloy tube.

2. The manufacturing process of the copper alloy tube according to claim 1, characterized in that, In step S1, the process parameters for vacuum batching and melting are as follows: first, evacuate the furnace to a vacuum degree ≤5Pa, heat to 1200-1230℃ to completely melt the raw materials, hold for 15-20 minutes, then cool to 1060-1090℃, add composite rare earth and stir, hold for 30-35 minutes for deoxidation, the stirring is electromagnetic stirring, the stirring rate is 60-70 r / min, and the stirring time is 8-10 minutes.

3. The manufacturing process of the copper alloy tube according to claim 1 or 2, characterized in that, In step S1, the total mass percentage of unavoidable impurities is ≤0.04%, and the mass percentage of a single impurity is ≤0.008%. During the smelting process, the copper liquid is protected by an inert gas atmosphere throughout, and the inert gas is argon with a flow rate of 0.5-0.8 L / min.

4. The manufacturing process of the copper alloy tube according to claim 1, characterized in that, In step S2, the cooling rate of the controlled cooling is 10-14℃ / s, the continuous casting is horizontal continuous casting, and the crystallizer is subjected to gradient water cooling during the continuous casting process. The flow rate of the cooling water is gradually reduced from 10m³ / h to 6m³ / h along the feeding direction of the crystallizer. The resulting hollow tube blank has an outer diameter of 75-95mm and a wall thickness of 9-11mm. The surface temperature of the tube blank is controlled at 150-180℃.

5. The manufacturing process of the copper alloy tube according to claim 1, characterized in that, In step S3, the process parameters for warm rolling are as follows: the hollow tube billet is preheated to 290-320℃, and four passes of warm rolling are performed, with a total deformation of 62-68%. The holding temperature between adjacent passes is 270-290℃, and the holding time is 8-10 minutes. The online shaping is online grinding, using a diamond grinding head, with the grinding rate synchronized with the warm rolling rate at 1.2-1.5 m / s.

6. The manufacturing process of the copper alloy tube according to claim 1, characterized in that, In step S4, the gradient combined drawing is completed in two passes to reduce the diameter, with a total diameter reduction rate of 30-35%. The drawing speed is increased from 3m / s to 5m / s in each pass. The drawing uses a two-die, two-core gradually tapered angle die, with the die cone angle gradually changing from 13° to 15°. During the drawing process, a nano-level oily lubricant is applied, with a lubricant application amount of 6-8g / m².

7. The manufacturing process of the copper alloy tube according to claim 1, characterized in that, In step S5, the constant temperature environment is 40-50℃ and the humidity is 40-50%. The deformation amount of each pass of the coiling is 12-14%, and the total deformation amount is 52-58%. The tube body temperature is monitored in real time during the coiling process, and the surface temperature fluctuation of the tube body is ≤±3℃.

8. The manufacturing process of the copper alloy tube according to claim 1, characterized in that, In step S6, the as-cast grains are precisely controlled to solidify: the semi-finished tube is cooled in stages to precipitate crystal nuclei, and the grains continue to grow until they are completely crystallized, and the whole solidifies to form an as-cast blank. The original defects such as alloy grain morphology, compositional segregation, internal porosity, and pores are all determined in this process. The solidification structure is controlled by segmented temperature control and gradient cooling to obtain a uniform and dense as-cast blank. The solidification control process adopts a three-stage gradient cooling system: the first stage is to rapidly cool at a rate of 12-15℃ / min to below the liquidus line to precipitate primary crystal nuclei, and hold at this temperature for 12-18 minutes; the second stage is to slowly cool at a rate of 4-6℃ / min to promote uniform grain growth, and hold at this temperature for 20-25 minutes; the third stage is to rapidly cool at a rate of 8-10℃ / s to complete solidification. Dry nitrogen atmosphere is introduced throughout the solidification process for protection, with a nitrogen flow rate of 0.6-0.8L / min, to inhibit solidification oxidation and subcutaneous pore formation.

9. The manufacturing process of the copper alloy tube according to claim 1, characterized in that, In step S8, the multi-stage cleaning process consists of alkaline washing, ultrasonic acid washing, and pure water rinsing. The alkaline washing uses an 8-10% sodium hydroxide aqueous solution at a temperature of 50-60℃ for 8-10 minutes. The ultrasonic acid washing uses a 4-5% citric acid aqueous solution at a frequency of 30-35kHz for 12-15 minutes. The drying process is hot air drying at a temperature of 60-70℃ and a wind speed of 2-3 m / s, drying until the moisture content of the inner and outer surfaces of the tube is ≤0.01%. The flexible support is a polyurethane arc-shaped support block, and the contact area between the support block and the tube is ≥1 / 3 of the outer circumferential area of ​​the tube.

10. The manufacturing process of the copper alloy tube according to claim 1, characterized in that, In step S9, the graded annealing is as follows: first, the temperature is held at 510-590℃ for 60-70 minutes, then the temperature is lowered to 450-470℃ for 30-40 minutes, and then the furnace is cooled to room temperature.

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