Corrosion-resistant copper alloy pipe and method of making and using same

Abstract

The application discloses a kind of corrosion-resistant copper alloy pipe, the mass percentage of each component of the copper alloy pipe includes: P: 0.05~0.40%, X: 0.001~0.1%, X is selected at least one of Al, Ni or RE, the balance is Cu and inevitable impurities;The volume fraction of small-angle grain boundary in the organization of the copper alloy pipe is 40~65%, the volume fraction of large-angle grain boundary is 25~50%.The copper alloy pipe has good corrosion resistance and oxidation resistance, while ensuring the beneficial bending, flaring, welding and pressure resistance performance.The application also discloses a preparation method of the copper alloy pipe, and the process flow of the preparation method includes: smelting→casting→milling→rolling→stretching→rewinding→secondary annealing;Among them, the secondary annealing temperature is 350~580 ℃, and the annealing time is 0.5~3.5h.The application also discloses the application of the copper alloy pipe and the copper alloy pipe prepared by the preparation method in preparing the heat conducting pipe of air conditioner heat exchanger, air conditioner indoor and outdoor machine connecting pipe or machine pipe assembly or pipe assembly.

Description

Technical Field

[0001] This invention belongs to the field of copper alloy technology, specifically relating to a corrosion-resistant copper alloy pipe, its preparation method, and its application. Background Technology

[0002] With the large-scale production and widespread application of air conditioning refrigeration units, complaints about refrigeration unit failures due to pitting corrosion are increasing. Pitting corrosion is a form of failure caused by corrosive media, which can penetrate the entire copper pipe wall in severe cases. Because its morphology resembles a complex network of channels resembling an anthill, characterized by severe internal corrosion and a small external opening, this type of corrosion is called "pitting corrosion." Pitting corrosion is extremely harmful and will seriously affect the normal operation of air conditioning and refrigeration systems. Research shows that the main influencing factors for pitting corrosion are the properties of the copper pipe material and corrosive media such as carboxylic acids. For example, traditional TP2 air conditioning refrigeration copper pipes are highly susceptible to pitting corrosion in certain humid environments when exposed to corrosive media such as carboxylic acids, leading to the failure of the air conditioning and refrigeration system. Common corrosive media such as carboxylic acids originate from two sources: firstly, the decomposition products of residual lubricating oil, cleaning agents, and other chemicals from the copper pipe production process; secondly, the use or contact with chemicals during the installation, use, and testing of air conditioning and refrigeration systems may also decompose and produce carboxylic acids, causing pitting corrosion in dephosphorized copper pipes. Therefore, in order to improve the problem of anthill corrosion, in addition to strengthening the control and protection of corrosive media such as carboxylic acids that may be encountered, the corrosion resistance of copper alloy pipe materials can also be optimized.

[0003] Patent application CN105143478A discloses copper pipes suitable for air conditioning and refrigeration equipment, wherein the phosphorus (P) content is 0.05%–1.0% by mass. This document indicates that as the phosphorus content in copper increases, the alloy's resistance to termite corrosion improves. When the P content is increased to above 0.3 wt.%, in an environment with a formic acid concentration of 0.1%, the termite corrosion depth of the copper alloy is still higher than 40 μm after 20 days of corrosion. Although increasing the P content in copper alloys can improve their resistance to termite corrosion to some extent, research shows that as the P content increases, the processing difficulty of the copper pipes also increases significantly.

[0004] Patent application CN114058898A discloses a copper alloy tube for heat exchangers with excellent fracture strength and its manufacturing method. More specifically, it relates to a copper alloy tube with excellent fracture strength and thermal conductivity suitable for use in heat exchangers and its manufacturing method. The copper alloy tube for heat exchangers comprises an oxygen-free copper-tin alloy with an oxygen content of 1–20 ppm. The composition of the oxygen-free copper-tin alloy satisfies the following conditions 1) and 2), with a thermal conductivity of 260–350 W / m·K and an electrical conductivity of IACS ≥ 65%: 1) 0.1 wt% ≤ CSn ≤ 3.0 wt%, 2) CP / CSn ≤ 0.01. In conditions 1) and 2), CP and CSn represent the phosphorus and tin content in the oxygen-free copper-tin alloy, respectively. However, the copper alloy tube disclosed in this patent application only has a corrosion depth of 0.059 mm after 480 hours, which needs further improvement.

[0005] While existing technologies have studied improved resistance to termite corrosion in copper alloy pipes for air conditioning, these technologies typically only address one aspect of the copper alloy pipe's performance. This results in an overall performance that fails to meet the processing and application requirements of copper pipes for air conditioning, making them prone to corrosion cracking and oxidation during processing and use. Therefore, there is a need to provide a copper alloy pipe and its preparation method to improve the installation and use of copper pipes for refrigeration and air conditioning. Summary of the Invention

[0006] This invention provides a corrosion-resistant copper alloy tube with good corrosion resistance and oxidation resistance, while ensuring beneficial bending, flaring, welding and pressure resistance properties.

[0007] This invention provides a corrosion-resistant copper alloy tube, wherein the mass percentage of each component includes: P: 0.05~0.40%, X: 0.001~0.1%, where X is selected from at least one of Al, Ni or RE, and the balance is Cu and unavoidable impurities;

[0008] In the microstructure of the copper alloy tube, the volume fraction of small-angle grain boundaries is 40-65%, and the volume fraction of large-angle grain boundaries is 25-50%.

[0009] It is understood that the small-angle grain boundaries provided by this invention are those with an orientation difference of 0~10° between adjacent grains, and the large-angle grain boundaries are those with an orientation difference of >15° between adjacent grains. This invention can obtain small-angle and large-angle grain boundaries with appropriate contents by controlling the content of element X and controlling the temperature and holding time of the first and second annealing in the preparation process. The copper alloy tubes provided by this invention include plain tubes, internally threaded tubes, and coiled tubes, etc.

[0010] The appropriate amount of phosphorus (P) provided by this invention not only dissolves in the copper matrix, causing lattice distortion and increasing strength, but also inhibits the surface penetration of corrosive media. P promotes the formation of an extremely dense, continuous, and firmly bonded phosphorus-containing cuprous oxide (Cu₂O) protective film on the copper surface / subsurface, significantly improving corrosion resistance. Furthermore, P in molten copper acts as a deoxidizer and improves melt flowability. On one hand, deoxidation reduces the formation of Cu₂O at grain boundaries, indirectly purifying them. On the other hand, improved melt flowability enhances the ingot quality of the alloy, contributing to its performance stability.

[0011] However, excessive phosphorus (P) also poses significant risks. On one hand, excessive P forms a large amount of continuous or coarse network-like brittle Cu3P phase, drastically reducing plasticity, toughness, and ductility, making the alloy brittle and prone to cracking during cold bending, flaring, and other processing. Simultaneously, the scattering effect of P atoms on electrons is intensified, significantly impacting thermal and electrical conductivity. On the other hand, excessive P increases the risk of grain boundary segregation, becoming crack initiation points and rapid propagation channels, and also increasing the susceptibility to stress corrosion cracking, which is detrimental to the alloy's corrosion resistance. When the P content is below 0.05%, the improvement effect of P on copper tubes is not significant; when the P content is above 0.40%, the loss of elongation, plasticity, and thermal conductivity is significant. Therefore, in this invention, the P content is controlled between 0.05% and 0.40%.

[0012] Preferably, the P content in the copper alloy tube is controlled at 0.1~0.35%.

[0013] Further optimization, to comprehensively consider the corrosion resistance and heat exchange efficiency of the copper alloy tube after installation and application, the P content in the copper alloy tube is controlled at 0.15~0.25%.

[0014] The present invention provides an appropriate amount of element X, which can achieve a good strengthening effect, significantly improve the tensile strength and yield strength of copper tubes, and at the same time improve corrosion resistance.

[0015] This invention provides an appropriate amount of X element, which serves two purposes: firstly, it provides heterogeneous nucleation sites and refines grains; secondly, it has a strong pinning effect on dislocations and grain boundaries. With the annealing process provided by this invention, the nucleation effect prevents abnormal grain growth, thereby stabilizing large-angle grain boundaries with a suitable content. Simultaneously, the pinning effect strongly inhibits the migration of recrystallized grain boundaries, resulting in finer recrystallized grains and stabilizing the substructure formed during recovery, ultimately achieving small-angle grain boundaries with a suitable content.

[0016] When the content of optional element X is less than 0.001%, the effects of improving corrosion resistance, purifying the melt, and refining grains are not significant, and a suitable amount of small-angle grain boundaries cannot be obtained. When its content is higher than 0.1%, excessive X element will have a significant negative impact on the electrical and thermal conductivity of the alloy, which is detrimental to the heat exchange efficiency of the air conditioning pipe. Therefore, this invention controls the content of element X at 0.001~0.1%.

[0017] The Al element provided by this invention, due to its high tendency to ionize, preferentially reacts with corrosive gases and oxygen in solutions to form an extremely thin but very dense and strongly adherent γ-Al₂O₃ protective film. This film can greatly prevent the internal copper from being further oxidized and corroded, thus improving the alloy's corrosion resistance and oxidation resistance. Simultaneously, Al element exhibits excellent resistance to chloride ions and sulfides in cooling water and seawater, with particularly outstanding resistance to erosion corrosion and pitting corrosion.

[0018] The Ni element provided by this invention, dissolved in copper, not only provides solid solution strengthening, simultaneously improving the strength and ductility of copper, but also modifies the surface film, significantly enhancing the copper tube's resistance to pitting corrosion and stress corrosion cracking in media containing chloride ions and ammonia. During corrosion or oxidation, it oxidizes together with copper, forming a Cu₂O-NiO or (Cu,Ni)O composite oxide film on the surface. The Ni-rich oxide film may exhibit resistance to Cl₂O and NiO. - The stronger barrier to penetration inhibited Cl. - Enrichment at the film / metal interface fundamentally raises the threshold for pitting corrosion initiation. Simultaneously, at the crack tip of stress corrosion cracking, the Ni-rich oxide film inhibits the anodic dissolution rate at the crack tip, making it easier for the crack tip to re-passivate and more effectively preventing the continued development of pitting and stress corrosion.

[0019] The RE element provided by this invention has the functions of purification, modification, and grain refinement. On the one hand, the RE element has a strong affinity for trace harmful impurities remaining in molten copper, such as Bi, Pb, and S. These impurities usually segregate at grain boundaries in the form of low-melting-point eutectic, especially at large-angle grain boundaries, which are sensitive channels for corrosion. RE can form high-melting-point, stable intermetallic compounds with them, such as CeBi2, CePb3, and Ce2S3. These newly formed intermetallic compounds are spherical or finely dispersed, transforming the continuously distributed and harmful thin-film impurities at grain boundaries into isolated and harmless spherical particles, greatly improving the corrosion resistance of grain boundaries and effectively inhibiting the spread of corrosion to deeper and wider areas. On the other hand, the newly formed intermetallic compounds can serve as nucleation sites for heterogeneous formation, refining the as-cast microstructure. A finer grain structure implies a greater number of grain boundaries. The addition of reticulum ions (RE) promotes dislocation slip and reorganization, and during and after recrystallization, it promotes polygonization, forming numerous subgrain boundaries, which are small-angle grain boundaries. Therefore, RE can significantly increase the proportion of small-angle grain boundaries, thus dispersing corrosion current and reducing the intensity of localized corrosion. Simultaneously, a finer grain structure also improves the strength and plasticity of the material, providing favorable initial conditions for processing finished pipes and contributing to the improvement of the mechanical and processing properties of the pipes of this invention. Furthermore, RE ions, such as Ce... 3+ / Ce 4+ Ions can be incorporated into the Cu₂O oxide film on the surface of copper. Due to their large ionic radius and high valence state, they can block the Cu in the oxide film. + The presence of cation diffusion channels significantly reduces the growth rate of the oxide film, making it denser and more stable. Simultaneously, when the film is damaged, the presence of RE promotes rapid self-repair, thereby inhibiting the deepening of corrosion pits and enhancing the pitting resistance of the alloy pipe.

[0020] Preferably, the microstructure of the copper alloy tube includes deformable texture and cubic texture, wherein the area ratio of deformable texture is 20-45% and the area ratio of cubic texture is 10-35%.

[0021] The lethality of anthill corrosion lies in its rapid, localized propagation along the depth of the pipe wall. After deformation and heat treatment, copper alloy pipes exhibit different types and proportions of textures, such as deformed textures, cubic textures, and others. Texture determines the crystallographic orientation of the grains, thus affecting the geometric and energy distribution of the grain boundary network, fundamentally controlling the path and efficiency of corrosion propagation. When grain orientation is highly random, as the corrosion tip moves from one grain to the next, it must constantly adjust its dissolution kinetics to adapt to the new crystallographic environment. Each adjustment requires additional energy, continuously consuming the corrosion driving force, significantly slowing down the propagation rate, and increasing the likelihood of the corrosion tip becoming passivated due to changes in local chemical conditions.

[0022] Strong, uniform textures, such as deformable or cubic textures with a single proportion, mean that a large number of grains have specific crystal faces parallel to the pipe wall. If the dissolution rate of corrosion is faster along certain specific crystal faces, these crystal faces become low-resistance downhill channels, which actually promote corrosion propagation. More importantly, highly uniform orientations form a large number of special grain boundaries such as ∑3. These special grain boundaries have low interfacial energy and low activity. Although they can inhibit corrosion and make it difficult for it to propagate, they also pose a risk of forcing corrosion to change direction and find other paths. For example, if some low-energy interfaces are interconnected, they may guide corrosion to the connected, highly active, large-angle random grain boundaries, unexpectedly forming high-speed channels, which in turn accelerates corrosion propagation and is detrimental to corrosion resistance. Therefore, controlling different texture types and proportions can further improve the alloy's resistance to termite corrosion.

[0023] This invention controls the area ratio of deformable and cubic textures to avoid an excessively low proportion of deformable textures, indicating that the microstructure is not fully recrystallized. This minimizes the dominance of cubic or other recrystallized textures, reducing the risk of forming a single texture and achieving suitable material hardness and grain size, resulting in better microstructure uniformity and corrosion inhibition. Furthermore, the microstructure provided by this invention exhibits more complete recrystallization, resulting in better material plasticity. More importantly, it minimizes the high connectivity of strong deformable texture networks. A highly uniform microstructure reduces overall system misalignment, making corrosion easier to predict and adapt to the environment. It also reduces crystallographic turning energy consumption, which could potentially create rapid crystallographic pathways that promote corrosion propagation and negatively impact corrosion resistance.

[0024] In this invention, RE refers to rare earth elements, specifically gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), and europium (Eu).

[0025] Preferably, the RE is at least one of La, Ce, and Y.

[0026] Preferably, X includes RE, and the mass ratio of P to RE satisfies: 50 ≤ P / RE ≤ 100.

[0027] This invention achieves a superior synergistic effect between P and RE by controlling the mass ratio of P to RE. The appropriate amount of RE provided by this invention refines the Cu3P phase, which helps to mitigate the coarse and harmful effects of the Cu3P phase under high P content conditions, resulting in suitable plasticity. Simultaneously, it ensures that the P content remains at a high level to obtain appropriate strength. Furthermore, the appropriate amount of RE provided by this invention, by purifying grain boundaries and removing elements such as O and S, can also reduce the tendency of P to agglomerate at grain boundaries, further enhancing grain boundary bonding and improving resistance to intergranular corrosion.

[0028] Furthermore, this invention provides a limited range for the ratio of P to RE, which can minimize the formation of coarse and brittle rare earth compounds, such as CeCu5 and Ce-PO complex phases, thereby reducing new crack sources and corrosion initiation points and minimizing the impact on strength, conductivity, and plasticity. At the same time, it can also minimize the formation of coarsened Cu3P phase and brittle impurity phases, such as Cu2O and Cu2S, thereby reducing their impact on processing plasticity. It can also ensure that RE atoms are sufficient to cover Cu3P phase interfaces and grain boundary impurities, thereby improving corrosion resistance.

[0029] Preferably, the corrosion-resistant copper alloy tube further includes Ag with a mass percentage content of 0.002~0.05%.

[0030] Due to its extremely high solid solubility in copper, Ag provides a moderate degree of solid solution strengthening. This invention provides an appropriate amount of Ag that can improve the strength and hardness of the alloy. An appropriate amount of Ag has minimal impact on electrical / thermal conductivity, which is beneficial for air conditioning heat exchange efficiency. More importantly, an appropriate amount of Ag has a strong effect on pulling grain boundaries and dislocations, significantly increasing the recrystallization temperature and creep resistance of the copper alloy. This allows the copper tube to maintain a fine-grained structure and strength even at the high temperatures of brazing, resisting high-temperature softening and ensuring that the copper tube does not undergo microscopic plastic deformation or grain boundary slippage during manufacturing processes such as brazing and long-term service under vibration and stress. This not only ensures the dimensional stability and long-term service reliability of the copper tube but also minimizes the rupture of the protective oxide film and the formation of new defects, thus ensuring stable long-term corrosion resistance. Furthermore, Ag itself also possesses certain antibacterial and corrosion-resistant properties.

[0031] More preferably, the mass ratio of P to Ag satisfies: 5 ≤ P / Ag ≤ 40.

[0032] In this invention, the addition of phosphorus (P) and ag exhibits a synergistic effect. Ag can, to some extent, compensate for the deficiencies of P. On one hand, Ag has the same solid solution strengthening and corrosion resistance as P. On the other hand, Ag strongly pulls grain boundaries and dislocations, significantly improving the recrystallization temperature and creep resistance of copper alloys. Meanwhile, Ag's impact on the electrical and thermal conductivity of copper alloys is much weaker than that of P, but the cost of adding Ag is high. To obtain excellent overall performance, this invention regulates the mass ratio of P to Ag. Appropriate amounts of P and Ag can effectively segregate and stabilize most Cu3P phase boundaries and grain boundaries, strongly pinning dislocations and grain boundary migration, achieving peak resistance to high-temperature softening and recrystallization temperature. It can also improve the corrosion resistance of the alloy to a certain extent, resulting in a significant synergistic effect and contributing to a balanced and excellent overall performance in terms of strength, electrical conductivity, and processing properties.

[0033] By controlling the mass ratio of P to Ag, it is possible to minimize the formation of independent, soft, Ag-rich phases (or Ag particles) in the matrix, which could lead to the generation of new crack sources. It is also possible to reduce the enhancing effect of Ag on electron scattering and avoid its impact on the electrical and thermal conductivity of the alloy.

[0034] Preferably, the oxygen content in the corrosion-resistant copper alloy tube is controlled to be ≤5ppm.

[0035] Preferably, other unavoidable impurities besides the aforementioned elements, such as Fe, S, Se, Te, Sb, Bi, As, and Pb, have a content of ≤5 ppm for each element and a total content of ≤30 ppm for all impurities.

[0036] In copper alloys containing impurities, corrosion is essentially an electrochemical process. Due to the standard electrode potential difference between copper and impurity elements, countless tiny galvanic cells automatically form when the alloy encounters a corrosive medium, accelerating the corrosion and dissolution of the copper alloy. Therefore, minimizing the content of harmful impurities such as Fe, S, O, and Bi, eliminating the cathodes or anodes of localized corrosion cells, and reducing the number of micro-cells formed due to the potential difference between impurities and copper are beneficial for improving the corrosion resistance of copper alloys.

[0037] O, existing in the form of Cu₂O, serves as a highly efficient cathode phase, significantly accelerating the dissolution reaction of the surrounding copper anode and posing a risk of corrosion and cracking. Furthermore, when operating in a reducing atmosphere containing H₂, H₂ penetrates and reacts with Cu₂O to generate high-pressure water vapor, such as H₂ + Cu₂O → 2Cu + H₂O↑, leading to internal microcracks and causing brittle fracture of the material under low stress. Therefore, this invention controls the oxygen content, ensuring that the O content is ≤5 ppm.

[0038] Other impurity elements, such as Fe, S, Se, Te, Sb, Bi, As, and Pb, act as anodes and cathodes in copper alloys, forming tiny "galvanic cells" that accelerate copper dissolution and negatively impact the alloy's corrosion resistance. Furthermore, elements like Bi and S tend to segregate at grain boundaries, forming corrosion pits or severely weakening grain boundaries, making intergranular corrosion more likely.

[0039] More preferably, in order to further obtain good corrosion resistance, the content of individual impurity elements such as Fe, S, Se, Te, Sb, Bi, As and Pb in the unavoidable impurities is ≤3ppm, and the total content of impurities is ≤25ppm.

[0040] Preferably, to further obtain a better ratio of large and small grain boundaries, the corrosion-resistant copper alloy tube further includes 0.005~0.05% Ag by mass percentage, X includes RE, and the mass ratio of P to RE satisfies: 60≤P / RE≤85.

[0041] The mass ratio of P to Ag satisfies: 10 ≤ P / Ag ≤ 30.

[0042] By controlling the addition of P, RE, and Ag elements within the above-mentioned ranges and combining them with appropriate preparation method process parameters, this invention can achieve the maximum synergistic effect, further obtain the optimal ratio of large / small angle grain boundaries, and thus greatly improve the corrosion resistance of the alloy.

[0043] The addition of P, RE, and Ag elements is controlled within the above-mentioned range. Ag can increase the recrystallization initiation temperature, which is beneficial for sufficient softening of the material during annealing and further obtaining a sufficient amount of large-angle grain boundaries. The pinning of P and RE ensures that dislocations form a high-density, stable small-angle grain boundary network during recrystallization, ensuring an appropriate proportion of small-angle grain boundaries. At the same time, the small number of pinned recrystallized grain boundaries form dispersed, fine large-angle grain boundaries. In addition, the synergy of P, RE, and Ag can broaden and stabilize the parameter range of the annealing process, which is beneficial to the stability and reproducibility of product performance.

[0044] The further preferred ratio of small and large angle grain boundaries obtained by the present invention is that the volume fraction L1 of the small angle grain boundary is 45~60% and the volume fraction L2 of the large angle grain boundary is 30~45%, and the ratio of L1 to L2 satisfies: 1.0≤L1 / L2≤1.8.

[0045] This invention further controls the volume fraction and ratio of large-angle and small-angle grain boundaries, enabling them to exert a better synergistic effect. This achieves a continuous network of small-angle grain boundaries, which inhibits corrosion propagation, while large-angle grain boundaries are effectively divided by the small-angle network. This minimizes corrosion propagation channels formed by the connectivity of the large-angle grain boundary network, avoids the formation of localized rapid and deep propagation, and enhances the resistance to anthill corrosion.

[0046] Meanwhile, by controlling the volume fraction of small-angle grain boundaries, the risk of pitting corrosion is reduced. This is because if corrosion occurs in a narrow area surrounded by dense small-angle grain boundaries, it is extremely difficult for it to expand in any direction. Corrosion products may accumulate rapidly in this highly enclosed space, leading to a vicious cycle of local acidification and chloride ion concentration. This, in turn, accelerates the deep dissolution of the tiny area and may induce a more hidden and concentrated superpitting corrosion.

[0047] This invention provides a superior ratio between large-angle and small-angle grain boundaries, ensuring that large-angle grain boundaries are not highly segmented but rather isolated into island-like distributions. This allows for the full utilization of the regulatory role of large-angle grain boundaries, providing deformation coordination, stress relaxation, and crack inhibition capabilities. During processing deformation, large-angle grain boundaries can act as active regions for dislocation rearrangement and annihilation, promoting local dynamic recovery and softening the material. This makes the material less prone to microcrack initiation due to local stress exceeding the strength limit under large deformation, thereby improving uniform plastic deformation capacity and processing performance. Therefore, while further enhancing corrosion resistance, it also maintains good alloy pipe bending processing performance and avoids cracking.

[0048] Therefore, by further controlling the content and proportion of grain boundaries of different sizes, this invention provides the necessary crystallographic randomness and processing plasticity, while preventing them from forming effective fast channels and becoming dominant corrosion propagation channels. This results in excellent corrosion resistance and good processing and forming properties.

[0049] More preferably, the area ratio of the deformed texture of the copper alloy tube is 30-40%, and the area ratio of the cubic texture is 20-30%.

[0050] More preferably, the deformable texture includes <111> ||X and <100> ||X texture, the <111> The area ratio of the X texture is 15-40%, the aforementioned <100> The area ratio of the X texture is 1-25%.

[0051] <111> ||X and <100> The X-texture refers to two basic crystal orientations that are rotationally symmetric about the axis, resulting from axial machining deformation in copper alloy tubing. <111> ||X represents a large number of grains in the material. <111> The crystallographic direction is parallel or nearly parallel to the axial direction (X direction) of the tube. <100> ||X represents a large number of grains in the material. <100> The crystallographic direction is parallel or nearly parallel to the axial direction (X-direction) of the tube. In the deformation texture... <111> It is the hardest direction in face-centered cubic metals, giving the material its basic high-temperature creep resistance and softening resistance. Meanwhile... <111> Oriented grains and {100} <001> The strict mirror symmetry between cubic grains is the most reliable combination for forming highly corrosion-resistant coherent ∑3 twin boundaries.

[0052] This invention controls <111> The area ratio of the X texture ensures sufficient tissue density within the organization. <111> Texture indicates high deformation energy storage or structural stability, which is beneficial for corrosion inhibition and can also limit corrosion. <111> The texture is so strong and interconnected that it may form a quasi-single-crystal channel network that is crystallographically anisotropic. Although the {111} plane is itself resistant to corrosion, corrosion finds its way along specific crystal orientations (such as...). <110> ) Paths that are easily expanded within the {111} plane. Furthermore, excessively strong <111> Texture inhibits the formation of randomly recrystallized grains, thereby weakening the corrosion resistance of other textures. This makes corrosion more adaptable to and predictable in the environment, and the ability to resist deep penetration decreases rather than increases.

[0053] The deformable texture provided by this invention contains an appropriate amount of <100> Oriented grains, with their relatively high {100} facet activity, can be used in highly corrosion-resistant applications. <111> By introducing controllable, dispersed local active sites into the substrate, the overall corrosion resistance is comprehensively enhanced. <100> Oriented grains can promote recrystallization nucleation, facilitating the generation of randomly or cubically oriented grains during subsequent critical annealing, enhancing crystallographic diversity, and thus inhibiting corrosion. In materials with crystallographic diversity, the driving force of the corrosion reaction can be consumed to the greatest extent, leading to rapid passivation and stagnation of corrosion tips. Simultaneously, it can disrupt the continuity of the corrosion propagation path, causing the path to be continuously deflected, branched, and scattered, transforming deep, narrow pores into wide, shallow, dish-shaped pits, thus inhibiting the formation of anthill corrosion.

[0054] The deformable texture provided by this invention contains an appropriate amount of <100> Oriented grains can also control excessive {100} planes parallel to the surface, directly exposed to the corrosive medium, significantly increasing the risk of overall corrosion initiation and increasing pitting corrosion. <100> The risk of faster inward propagation of oriented grains due to their initiation on grains can be minimized. <100> Orientation competes with cubic texture, thus affecting the quality and distribution of ∑3 twins. When ∑3 twins are in a low-quality state of incoherence or contamination, their interfacial energy increases, chemical activity rises, and they become vulnerable to even slight corrosion attacks. Simultaneously, the distribution of ∑3 twins in an over-connected state concentrates corrosion in the more active ordinary grain boundary regions. These regions become easy sites for corrosion to propagate and extend, forming efficient propagation channels. This is equivalent to the ∑3 network unintentionally guiding and concentrating the corrosion flow, leading to more severe and rapid localized corrosion.

[0055] More preferably, the copper alloy tube <111> The area proportion of the X texture is 20-30%. <100> The area ratio of the X texture is 10-20%.

[0056] Preferably, the average grain diameter of the copper alloy tube is ≤10μm, and the standard deviation of the average grain diameter is ≤1.0μm.

[0057] From the perspective of improving corrosion resistance, controlling grain size can effectively prevent corrosion from progressing deeper along grain boundaries. Fine-grained structures can disperse corrosion current, extend corrosion paths, and promote the formation of stable oxide films. First, in the initial stage of pitting corrosion, fine-grained structures divide the macro-anodic region into numerous micro-anodes, effectively dispersing and reducing local corrosion current density, making pit nucleation and stable growth more difficult. Second, even if corrosion occurs at a single point, it must continuously traverse or follow the labyrinthine grain boundary network to penetrate deeper into the material, significantly extending the corrosion path and slowing the corrosion rate. Finally, fine grains mean more grain boundaries leading to the surface, providing channels for the rapid diffusion of reactive elements such as refractive elements (REs), contributing to the formation of a more uniform and stable protective oxide film on the surface. However, it is important to note that the grain size should be as uniform as possible to avoid abnormally large grains becoming a bottleneck for corrosion. For example, grains of varying sizes are prone to corrosion due to stress concentration. Therefore, small and uniform grains mean a longer total grain boundary length per unit area, which is more conducive to preventing corrosion from progressing deeper along grain boundaries.

[0058] In addition, the finer grain size of the copper alloy microstructure, suppressing deviations in grain diameter, is beneficial to the processing performance of copper alloy tubes, such as bending, expanding, and flaring. During these processes, not only does the average grain diameter significantly affect bending workability, but deviations in grain diameter also have a substantial impact. Fine and uniform grains can better coordinate deformation and reduce stress concentration. Furthermore, a higher number of grain boundaries also improves the corrosion resistance of the copper alloy. To obtain a copper alloy with balanced high strength and excellent workability, it is necessary to reduce coarse grains in the copper alloy microstructure and make each grain as fine as possible.

[0059] More preferably, the average grain diameter of the copper alloy tube is ≤8μm, and the standard deviation of the average grain diameter is ≤0.95μm.

[0060] Preferably, the copper alloy tube has a tensile strength of 230-330 MPa, a yield strength of 70-90 MPa, and an elongation of 15-55%.

[0061] Preferably, the copper alloy tube has the following bending performance: it can be bent 180° around a 3D mandrel without cracking, and its flaring performance can be achieved with a flaring rate of 25% without cracking.

[0062] Preferably, the copper alloy tube has good pressure resistance, with a burst pressure ≥35MPa.

[0063] Preferably, the maximum corrosion depth of the copper alloy tube is ≤40μm after 30 days of exposure to a 5% NaCl neutral salt spray environment, and ≤60μm after 42 days of exposure.

[0064] Preferably, the maximum corrosion depth of the copper alloy tube after 30 days of alternating hot and cold corrosion in a 2% formic acid aqueous solution is ≤90μm.

[0065] Preferably, the maximum corrosion depth of the copper alloy tube after 42 days of alternating hot and cold corrosion in a 2% formic acid aqueous solution is ≤120μm.

[0066] On the other hand, the present invention also provides a method for preparing the corrosion-resistant copper alloy tube, the process flow of which includes: melting → casting → milling → rolling → stretching → rewinding → secondary annealing;

[0067] The components of the corrosion-resistant copper alloy tube are batched and smelted according to their mass percentages.

[0068] The secondary annealing temperature is 350~580℃, and the annealing time is 0.5~3.5h.

[0069] The purpose of secondary annealing is twofold: to obtain soft-state properties and to achieve the ultimate microstructure resistant to pitting corrosion. Annealing below 350℃ results in incomplete stress relief, and residual stress may lead to localized electrochemical potential differences, forming stress corrosion-sensitive zones. Annealing above 580℃ increases the driving force for grain growth, resulting in a fully recrystallized state, leading to grain coarsening and excessive large-angle grain boundaries, which in turn creates long-range continuous corrosion channels. Matching the annealing time with the annealing temperature ensures complete stress release from previous deformation passes. Annealing times below 0.5 hours result in incomplete stress relief, causing uneven microstructure and potential localized corrosion; annealing times above 3.5 hours enter the grain growth-dominated stage, causing excessive grain growth and adversely affecting corrosion resistance. Using the above process, optical tubes with superior corrosion resistance can be produced.

[0070] Preferably, the total processing rate of the stretching is 65-99%. Based on the alloy composition, this invention employs high-processing-rate deformation to introduce high-density dislocations and deformation bands, promoting dynamic recrystallization. Simultaneously, combined with the subsequent annealing process, the microstructure of the alloy is controlled, the grain size is refined, and the proportion of large and small angle grain boundaries and special textures is optimized, thereby obtaining a copper alloy with excellent corrosion resistance.

[0071] Preferably, after stretching, an annealing and internal thread forming are performed sequentially, followed by rewinding;

[0072] The primary annealing temperature is 400~580℃, and the annealing rate is 200~550m / min.

[0073] The annealing process provided by this invention is an online annealing process. By controlling the online annealing temperature and speed, this invention can trigger complete recrystallization, eliminate work hardening, and avoid excessive grain growth. The aim is to obtain an equiaxed, fully recrystallized soft microstructure, forming a fine-grained strengthening effect, reducing stress concentration caused by uneven grain distribution, and preventing stress corrosion cracking. Simultaneously, it achieves a better cubic texture and grain boundary ratio, providing a foundation for the subsequent formation of large and small grain boundaries and texture types and ratios in the finished internally threaded pipe fittings.

[0074] More preferably, after the first annealing, the average grain size of the copper alloy tube is 20~40μm.

[0075] This invention controls the temperature and speed of the first annealing process to ensure that the average grain size of the copper alloy tube is within a suitable range and the total grain boundary area is appropriate. This allows for the accumulation of suitable grain boundary energy during subsequent large deformation, resulting in a suitable recrystallization nucleation rate during the second annealing. Consequently, a stable subgrain structure can be formed, which is beneficial for obtaining the final small-angle grain boundary ratio. Furthermore, controlling the average grain size after the first annealing process ensures more uniform deformation during subsequent large deformation, avoiding excessive stress accumulation at grain boundaries. After the second annealing, uniform high-density subgrains can be formed within the grains, which is beneficial for obtaining suitable small-angle grain boundaries. At the same time, it can also suppress excessive grain boundary migration ability, preventing excessive engulfment of surrounding small grains and disruption of the uniformity of the microstructure.

[0076] Preferably, after the first annealing, the volume fraction of small-angle grain boundaries in the copper alloy tube is <10%, and the volume fraction of large-angle grain boundaries is >70%.

[0077] This invention controls small-angle grain boundaries within a small range after the first annealing, thereby controlling the non-recrystallized deformation region or substructure. These small-angle grain boundaries and deformation zones will become the source of uneven deformation in subsequent large deformations. By controlling them within a small range, this invention makes the energy storage distribution more uniform, so that a suitable proportion and more uniformly distributed small-angle grain boundaries can be generated during the second annealing, thereby obtaining better uniformity and reliability of corrosion resistance.

[0078] Preferably, after the first annealing, the area ratio of the deformed texture of the copper alloy tube is 1-30%, and the area ratio of the cubic texture is 10-40%.

[0079] When the area ratio of deformed texture is greater than 30% and the area ratio of cubic texture is less than 10%, the residual deformed texture indicates that recrystallization has not occurred, and its interior still retains a deformed structure with a high dislocation density. In subsequent large deformations, the deformation mechanism of the residual deformed texture differs from that of the surrounding recrystallized region, potentially leading to localized shear bands or microcracks. During secondary annealing, these dislocation and deformed texture regions may form coarse recrystallized grains or chaotic structures, becoming preferential pathways for corrosion propagation and weak points in performance, thus negatively impacting the alloy's corrosion resistance. When the area ratio of deformed texture is less than 1% and the area ratio of cubic texture is greater than 40%, the excessively strong cubic texture indicates significant orientation-selective growth during recrystallization. In subsequent large deformations, although these strongly cubic oriented grains will be pulled towards the fibrous texture, they are prone to uneven deformation. During secondary annealing, these regions may preferentially revert to cubic texture, resulting in a final product with a cubic texture ratio exceeding 35%, disrupting texture balance and making it difficult to achieve optimal corrosion resistance. Therefore, after one annealing, the area ratio of deformed texture in the copper alloy tube is 1-30%, and the area ratio of cubic texture is 10-40%.

[0080] Preferably, the total machining rate of the internal thread forming and rewinding process is 20-50%.

[0081] This invention controls the total processing rate of the internal thread forming and rewinding processes, and introduces a large and uniform cold deformation energy storage before the second annealing. The sufficiently large cold processing rate achieves extremely high dislocation density and uniform energy storage, providing sufficient and uniform driving force for high-density nucleation and full recovery during the second annealing, thereby obtaining ideal large and small angle grain boundaries, texture and corrosion resistance.

[0082] This invention achieves a suitable proportion of large and small angle grain boundaries and a texture proportion by controlling the total processing rate of the first annealing, internal thread forming, and rewinding processes, thereby obtaining an internally threaded copper alloy tube with high corrosion resistance.

[0083] Preferably, the rolling process adopts planetary rolling, and the total processing rate of the rolling process is 70-95%.

[0084] The planetary rolling process provided by this invention employs a high deformation rate to thoroughly and uniformly transform the casting microstructure. The enormous deformation energy is entirely converted into heat and dislocation energy, providing an undeniable driving force for comprehensive and uniform dynamic recrystallization. This triggers dynamic recrystallization, regulates the recrystallization texture ratio, significantly refines the grain size, increases grain boundaries, and results in a uniform, equiaxed, and fine-grained microstructure.

[0085] More preferably, the average grain size of the rolled copper alloy tube is 30~50μm.

[0086] This invention controls the average grain size of the rolled copper alloy tube, meaning that work hardening is within a controllable range and dynamic recrystallization is more sufficient. As a result, there are fewer deformable structures such as banded structures, mixed grains, and high dislocation density, which are extremely difficult to eliminate in subsequent cold drawing and annealing and affect the longitudinal and transverse properties of the tube, significantly reduce the corrosion resistance of local areas, and become the preferred sites for anthole corrosion. Furthermore, the total area of ​​the grain boundaries under the average grain size is appropriate, which facilitates dislocation movement during subsequent cold deformation and avoids severe blockage. After the finished product is annealed, it is easy to form uniform and fine subgrains, making it less likely to form local weak points.

[0087] Preferably, the smelting process involves a smelting temperature of 1150~1200℃.

[0088] Preferably, the casting process is as follows: casting temperature is 1150-1180℃, traction speed is 280-420mm / min, cooling water inlet flow rate is 25-50L / min, and the inlet and outlet water temperature difference is controlled at 15-20℃.

[0089] Preferably, the milling speed is 1.8 to 2.5 m / s.

[0090] To further optimize the process and obtain better volume fraction and ratio of large and small angle grain boundaries, as well as better texture ratio, the total processing rate of the rolling process is 70-95%.

[0091] The total processing rate of the stretching is 80-99%;

[0092] The primary annealing temperature is 450~580℃, and the annealing rate is 300~450m / min;

[0093] The total processing rate of the internal thread forming and rewinding process is 20-50%;

[0094] The secondary annealing temperature is 380~500℃, and the annealing time is 1.0~2.5h.

[0095] By controlling the process parameters of the above-mentioned key processes within a certain range, and by adding X and Ag elements, this invention can further obtain ideal grain size and optimal ratio of large / small angle grain boundaries and texture, thereby greatly improving the corrosion resistance of the alloy.

[0096] This invention further improves the processing efficiency of the rolling process to provide a combined driving force of high heat and strong deformation, which can more thoroughly break down and recrystallize the as-cast structure, and dislocations can be rapidly rearranged and annihilated to form new, undistorted, fine equiaxed grains, thus providing a good microstructure basis.

[0097] The present invention further controls the pass rate of the stretching process to introduce moderate and uniform deformation energy storage, which provides power for further obtaining a fully recrystallized structure; by further controlling the temperature and speed of the first annealing, more small-angle grain boundaries and dislocation structures are eliminated to achieve full recrystallization, while eliminating strong deformation texture memory and forming a weak texture dominated by randomness, which prepares for the introduction of a new, uniform strong deformation texture in subsequent large deformation.

[0098] This invention further controls the total processing rate of the internal thread forming and rewinding processes before final annealing by introducing a large and uniform cold deformation energy storage. Through extremely high dislocation density and uniform energy storage, it provides sufficient and uniform driving force for high-density nucleation and random recrystallization, full recovery and subgrain formation during secondary annealing, which is a prerequisite for forming the final ideal structure.

[0099] This invention eliminates processing stress through further controlled secondary annealing, avoiding localized corrosion susceptibility caused by stress concentration. It also prevents excessive grain growth, achieving an ideal microstructure with optimal grain size and proportions of large / small angle grain boundaries and texture. Combined with the synergistic effect of appropriate amounts of X and Ag additives, where RE ensures the cleanliness of both large and small angle grain boundaries, the inertia advantage of small-angle grain boundaries and the geometric resistance advantage of large-angle grain boundaries are fully utilized without being weakened or reversed by impurity segregation due to their chemical reactivity. Furthermore, Ag helps stabilize this non-equilibrium microstructure where subgrains and recrystallized grains coexist, maintaining the optimal ratio during long-term service and thus improving the overall corrosion resistance of the copper alloy tube.

[0100] On the other hand, the present invention also provides the application of the corrosion-resistant copper alloy tube or the corrosion-resistant copper alloy tube prepared according to the preparation method of the corrosion-resistant copper alloy tube in the preparation of heat-conducting tubes of air conditioner heat exchangers, connecting pipes of air conditioner indoor and outdoor units, internal pipes or pipe assemblies.

[0101] The copper alloy pipe of the present invention has good tensile strength, elongation and corrosion resistance, and also has excellent processing characteristics such as bending, flaring, welding and pressure resistance, making it particularly suitable for manufacturing indoor and outdoor connection piping for air conditioning.

[0102] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0103] This invention relates to a copper alloy tube made of polycrystalline material. By controlling the content of small-angle grain boundaries, this invention fully utilizes the functions of small-angle grain boundaries in reducing corrosion sensitivity, altering corrosion propagation patterns, and inhibiting impurity segregation, thus significantly improving corrosion resistance. Firstly, small-angle grain boundaries have a low degree of atomic misalignment and a denser structure. Their low energy makes them less prone to adsorbing impurity atoms, resulting in significantly stronger resistance to corrosive media compared to chaotic large-angle grain boundaries. Secondly, when the corrosion front encounters a small-angle grain boundary network, its propagation direction frequently changes, or is even blocked. Corrosion cannot find a continuous, penetrating channel through large-angle grain boundaries to rapidly penetrate inwards, thus being forced to transform into a more uniform and slower corrosion form, thereby inhibiting corrosion propagation to a certain extent. Finally, because harmful impurities, such as sulfur, tend to segregate at the high-energy large-angle grain boundaries, increasing the proportion of small-angle grain boundaries is equivalent to reducing the "breeding ground" for impurities, purifying the main corrosion channels at the source. If the volume fraction of small-angle grain boundaries is too high, it will affect plastic processing. Small-angle grain boundaries are composed of a series of dislocations. A high degree of dislocation pile-up can improve the strength of the material. However, if the volume fraction of small-angle grain boundaries is too high, cracks will easily propagate, making the material prone to cracking during bending deformation.

[0104] Since large-angle grain boundaries are grain boundaries between grains, an appropriate amount of large-angle grain boundaries can make crack propagation more difficult, thereby reducing the tendency of the material to bend and deform and crack. Therefore, this invention seeks a balance between corrosion resistance and processing performance by controlling the content of small-angle and large-angle grain boundaries. Attached Figure Description

[0105] Figure 1 The image shows the metallographic structure of the copper alloy tube prepared in Example 1 of this invention after salt spray corrosion (5% NaCl, 30 days).

[0106] Figure 2 The image shows the metallographic structure of the copper alloy tube prepared in Example 7 of this invention after salt spray corrosion (5% NaCl, 30 days).

[0107] Figure 3 The image shows the metallographic structure of the copper alloy tube prepared in Comparative Example 1 after salt spray corrosion (5% NaCl, 30 days).

[0108] Figure 4 The image shows the metallographic structure of the copper alloy tube prepared in Example 1 after ant hole corrosion (2% formic acid, 30 days).

[0109] Figure 5 Metallographic image of the copper alloy tube prepared in Example 7 after ant hole corrosion (2% formic acid, 30 days).

[0110] Figure 6 The image shows the metallographic structure of the copper alloy tube prepared in Comparative Example 1 after anthole corrosion (2% formic acid, 30 days).

[0111] Figure 7 This is a grain size distribution diagram of the copper alloy tube prepared in Example 1.

[0112] Figure 8 This is a grain size distribution diagram of the copper alloy tube prepared in Comparative Example 1.

[0113] Figure 9 The figure shows the EBSD characterization results (grain boundary type and volume fraction) of the copper alloy tube prepared in Example 1.

[0114] Figure 10 The figure shows the EBSD (grain boundary type and volume fraction) characterization results of the copper alloy tube prepared in Comparative Example 1.

[0115] Figure 11 The figure shows the EBSD (texture and area fraction) characterization results of the copper alloy tube prepared in Example 1.

[0116] Figure 12 The figure shows the EBSD (texture and area fraction) characterization results of the copper alloy tube prepared in Comparative Example 1. Detailed Implementation

[0117] The present invention will be further described in detail below with reference to the embodiments.

[0118] The specific composition of the alloys in the embodiments and comparative examples of this invention is shown in Table 1.

[0119] The manufacturing process is as follows: melting → horizontal continuous casting → milling → rolling → stretching → primary annealing → internal thread forming → rewinding → secondary annealing. The specific manufacturing method is as follows:

[0120] 1) Ingredients: The ingredients are prepared according to the composition in Table 1, using electrolytic pure copper plates and pure Al. Other elements are added in the form of intermediate alloys.

[0121] 2) Smelting: The smelting temperature is 1150~1200℃, and the charcoal covering thickness is 180~220mm;

[0122] 3) Horizontal continuous casting: casting temperature is 1150~1180℃, traction speed is 280~420mm / min, cooling water inlet flow rate is 25~50L / min, inlet and outlet water temperature difference is controlled at 15~20℃, specification φ92*25mm;

[0123] 4) Milling: Milling speed is 1.8~2.5m / s, specification φ91*24mm;

[0124] 5) Rolling: Planetary rolling is adopted, with a total rolling processing rate of 70-95%, a feeding speed of 1.8-2.5m / s, a discharge speed of 20-30m / s, and a rolling specification of φ50*3mm;

[0125] 5) Stretching: A two-stage stretching and disc stretching method is adopted, with a total stretching processing rate of 65% to 99% and a stretching specification of φ7.5*0.3mm;

[0126] 6) Single annealing: Annealing temperature is 400~580℃, annealing speed is 200~550m / min;

[0127] 7) Internal thread forming: forming rate 25-50%, forming speed 35-65m / min, specification φ5*0.32mm;

[0128] 8) Rewinding: The rewinding rate is 150-450 m / min. After rewinding, a second annealing is performed. The specification is φ5*0.32mm.

[0129] 9) Secondary annealing: The secondary annealing temperature is 350~580℃, and the annealing time is 0.5~3.5h;

[0130] 10) Packaging: Pack according to requirements.

[0131] The key process parameters for the control of the embodiments and comparative examples of this invention are shown in Table 2.

[0132] The prepared alloys of the examples and comparative examples were tested at room temperature for grain size, grain boundary area ratio, tensile mechanical properties, bending, flaring, anthole (formic acid) corrosion and salt spray corrosion, etc. The specific data are shown in Table 3.

[0133] The average grain size of the metallographic structure was tested according to GB / T 6394-2017 Method for Determination of Grain Size of Metals.

[0134] EBSD analysis was used to analyze the grain boundary type and volume fraction, texture type and area fraction of the pipe material in the example.

[0135] The room temperature tensile test was conducted in accordance with GB / T 228.1-2010 Metallic materials, tensile testing - Part 1: Room temperature test method, on an electronic universal mechanical performance testing machine at a tensile speed of 5 mm / min.

[0136] The bending test was conducted according to GB / T 244-2008 Metal pipes - Bending test method. With the mandrel diameter being 1.5 times the outer diameter of the copper pipe, the inner and outer surfaces were smooth after bending 180°, without wrinkles or cracks.

[0137] The flaring test was conducted according to GB / T 17791-1999 "Seamless Copper Tubes for Air Conditioning and Refrigeration". When the flaring ratio (60° taper) of the copper alloy tube is 40% or the distance between the two walls after flattening is equal to the wall thickness, the absence of visible cracks and fissures in the copper alloy tube sample indicates excellent processing performance of the copper alloy tube.

[0138] The burst pressure was tested according to the "GB / T 241-2007 Hydraulic Test Method for Metal Pipes";

[0139] (Neutral) Salt spray corrosion tests were conducted according to GB / T 10125-1997 "Artificial Atmosphere Corrosion Tests—Salt Spray Tests". 50mm length test tubes were cut from the pipe, degreased, dried, and then placed in a salt spray test chamber containing 5% NaCl (50g / L). Different types of test tubes were removed and observed every three days, with a maximum duration of 42 days. After sampling, the corrosion depth and perforation of the test tube cross-section were observed. If the maximum corrosion depth of the sample was greater than the wall thickness of the test tube, it was considered perforated; if the maximum corrosion depth was less than the wall thickness, the maximum corrosion depth within that cross-section was recorded. Results were statistically analyzed: the average maximum corrosion depth of the test tubes was the sum of the maximum corrosion depths of all tested test tubes divided by the total number of test test tubes; the perforation rate was the number of perforated samples divided by the total number of test test tubes.

[0140] The test method for resistance to pitting corrosion was conducted with a formic acid concentration of 2%, alternating between ambient temperatures of 50℃ / 12h and 20℃ / 12h. Fifteen parallel straight tube samples were taken for each type of test, and the corrosion time was 30 days. After pitting corrosion, the depth of pitting corrosion was observed by metallography. The test results were recorded, and the distribution of the recorded data and the number of outliers were statistically analyzed. Based on the results of the Nell method, the number of maximum and minimum values ​​to be removed was determined. The average value of the remaining samples was taken as the corrosion depth for that type of sample.

[0141] The microstructure and properties of the alloys in the embodiments and comparative examples of this invention are shown in Table 3. The mechanical properties and processing and application properties of the alloys in the embodiments and comparative examples are shown in Table 4.

[0142] The copper alloy tubes provided in Examples 1-7 have relatively uniform microstructures and a high proportion of textured area, exhibiting suitable mechanical properties, bending properties, and pressure resistance, as well as high corrosion resistance. Among them, Example 7, by optimizing the composition (P / RE, P / Ag ratio) and process (processing rate, annealing regime), obtained a more uniform and dense microstructure and a more suitable ratio of large and small angle grain boundaries, significantly improving the salt spray corrosion resistance.

[0143] like Figure 1 and Figure 2As shown, the copper alloy tubes obtained in Examples 1 and 7 of this invention have good resistance to salt spray corrosion, and the copper alloy tube obtained in Example 7 has even more outstanding resistance to salt spray corrosion. Figure 3 As shown, Comparative Example 1 suffered from structural deterioration due to component imbalance, resulting in a severe decrease in salt spray corrosion resistance.

[0144] like Figure 4 , Figure 5 and Figure 6 As shown, both Embodiment 1 and Embodiment 7 of the present invention have good resistance to anthole corrosion. The optimized microstructure of Embodiment 7 can effectively block the spread of corrosive media along grain boundaries or defects, resulting in better resistance to anthole corrosion. In contrast, the microstructure in Comparative Embodiment 1 is uneven, leading to increased anthole corrosion sensitivity. This further verifies the advantages of the technical solution of this application in complex corrosive environments.

[0145] like Figure 7 and Figure 8 As shown, the grain size distribution of Example 1 is relatively reasonable, but Comparative Example 1 has abnormal recrystallization due to compositional imbalance, and the grain size distribution is extremely uneven. This structural inhomogeneity is an important reason for its poor corrosion resistance.

[0146] like Figure 9 , Figure 10 , Figure 11 and Figure 12 As shown, although the microstructure of Example 1 has a certain distribution ratio of texture and grain boundary types, Comparative Example 1 has a single texture and an unbalanced proportion of grain boundaries due to composition issues, which seriously weakens the overall performance of the material.

[0147] In summary, Examples 1 and 7 exhibit relatively uniform microstructures with a high proportion of texture area, resulting in suitable mechanical, flexural, and pressure resistance properties, as well as good corrosion resistance. Due to the crystalline phase, Example 7, in particular, achieved optimal corrosion resistance through composition optimization (P / RE and P / Ag within specific ranges) and process control (processing rate and annealing parameters within preferred ranges), resulting in uniform grain size, coordinated texture composition, and a reasonable ratio and distribution of small / large angle grain boundaries. In contrast, Comparative Example 1 suffered from microstructure deterioration (extremely wide grain size distribution, monotonous texture, and unbalanced grain boundary ratio) due to compositional imbalance (excessive X element), leading to a significant decrease in corrosion resistance.

[0148] Table 1 Alloy composition of embodiments and comparative examples of the present invention

[0149]

[0150] Table 2 Key process parameter control of embodiments and comparative examples of the present invention

[0151]

[0152] Table 3 Microstructure properties of copper alloy tubes in the embodiments and comparative examples of the present invention

[0153]

[0154] Table 4. Performance of copper alloy tubes in embodiments and comparative examples of the present invention.

[0155]

Claims

1. A corrosion-resistant copper alloy pipe, characterized in that, The mass percentage of each component includes: P: 0.05~0.40%, X: 0.001~0.1%, where X is selected from at least one of Al, Ni or RE, and the balance is Cu and unavoidable impurities; In the microstructure of the copper alloy tube, the volume fraction of small-angle grain boundaries is 40-65%, and the volume fraction of large-angle grain boundaries is 25-50%. The microstructure of the copper alloy tube also includes deformable texture and cubic texture, wherein the area of ​​deformable texture accounts for 20-45% and the area of ​​cubic texture accounts for 10-35%. The average grain diameter of the copper alloy tube is ≤10μm, and the standard deviation of the average grain diameter is ≤1.0μm.

2. The corrosion-resistant copper alloy pipe according to claim 1, characterized in that, X includes RE, and the mass ratio of P to RE satisfies: 50 ≤ P / RE ≤ 100.

3. The corrosion-resistant copper alloy pipe according to claim 1, characterized in that, The corrosion-resistant copper alloy pipe also includes Ag with a mass percentage content of 0.002~0.05%.

4. The corrosion-resistant copper alloy pipe according to claim 3, characterized in that, The mass ratio of P to Ag satisfies: 5 ≤ P / Ag ≤ 40.

5. The corrosion-resistant copper alloy pipe according to claim 1, characterized in that, The corrosion-resistant copper alloy pipe further includes Ag with a mass percentage content of 0.002~0.05%, X includes RE, and the mass ratio of P to RE satisfies: 60≤P / RE≤85; The mass ratio of P to Ag satisfies: 10 ≤ P / Ag ≤ 30; The volume fraction L1 of the small-angle grain boundary is 45~60%, and the volume fraction L2 of the large-angle grain boundary is 30~45%. The ratio of L1 to L2 satisfies: 1.0≤L1 / L2≤1.

8.

6. The corrosion-resistant copper alloy pipe according to claim 5, characterized in that, The microstructure of the copper alloy tube also includes deformable texture and cubic texture, with the deformable texture accounting for 30-40% of the area and the cubic texture accounting for 20-30% of the area.

7. The corrosion-resistant copper alloy pipe according to claim 6, characterized in that, The deformable texture includes <111> ||X and <100> ||X texture, the <111> The area ratio of the X texture is 15-40%, the aforementioned <100> The area ratio of the X texture is 1-25%; <111> ||X represents the grain size in the material. <111> The crystallographic direction is parallel or nearly parallel to the X-axis direction of the tube; <100> ||X represents the grain size in the material. <100> The crystallographic direction is parallel or nearly parallel to the X-direction of the tube.

8. The corrosion-resistant copper alloy pipe according to claim 1, characterized in that, The RE is at least one of La, Ce, and Y.

9. A method for preparing a corrosion-resistant copper alloy tube according to any one of claims 1-8, characterized in that, The process flow of the preparation method includes: melting → casting → milling → rolling → stretching → rewinding → secondary annealing; The components of the corrosion-resistant copper alloy tube according to any one of claims 1-8 are batched and smelted according to their respective mass percentages. The secondary annealing temperature is 350~580℃, and the annealing time is 0.5~3.5h.

10. The method for preparing the corrosion-resistant copper alloy tube according to claim 9, characterized in that, The total processing rate of the stretching is 65-99%.

11. The method for preparing the corrosion-resistant copper alloy tube according to claim 9, characterized in that, After stretching, annealing and internal thread forming are performed in sequence, followed by rewinding; The primary annealing temperature is 400~580℃, and the annealing rate is 200~550m / min.

12. The method for preparing the corrosion-resistant copper alloy tube according to claim 11, characterized in that, The total processing rate of the rolling process is 70-95%; The total processing rate of the stretching is 80-99%; The primary annealing temperature is 450~580℃; The total processing rate of the internal thread forming and rewinding process is 20-50%; The secondary annealing temperature is 380~500℃, and the annealing time is 1.0~2.5h.

13. The application of the corrosion-resistant copper alloy tube according to any one of claims 1-8, or the corrosion-resistant copper alloy tube prepared by the method according to any one of claims 9-12, in the preparation of heat-conducting pipes for air conditioner heat exchangers, connecting pipes between indoor and outdoor units of air conditioners, or internal pipes or pipe assemblies.

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