High-performance copper alloy pipe and preparation method thereof

Abstract

The invention discloses a high-performance copper alloy pipe and a preparation method thereof. The Sn, Ni and P elements are compositely added into Cu, the content and proportion of all the elements are regulated and controlled, meanwhile, a recrystallization treatment process is combined, a high-proportion sigma 3, sigma 9 and sigma 27 coincidence lattice grain boundary is introduced, and the copper alloy pipe with high strength, high machining forming capacity and excellent pressure resistance, corrosion resistance and high-temperature softening resistance is prepared. Meanwhile, Zr, Co and B (optionally) elements are added on the basis of the alloy components, so that the performance of the copper alloy pipe is further improved. The tensile strength, the processing formability, the pressure resistance, the corrosion resistance and the high-temperature softening resistance of the copper alloy pipe are far better than those of a TP2 copper pipe of the same specification and an existing high-strength copper pipe, the performance requirements of the high-pressure-resistance thin-wall seamless copper pipe are met, and the copper alloy pipe has wide application prospects in the heat exchange field.

Description

Technical Field

[0001] The present application relates to the field of alloys, and in particular to a high-performance copper alloy tube and a preparation method thereof. Background Art

[0002] Copper, with its excellent thermal and electrical conductivity, formability, and corrosion resistance, has become a key material in fields such as electronic communications and advanced thermal management, new energy and power transmission, and high-end equipment manufacturing. Its importance and application scope are continuously expanding with technological advancements. For example, in the heat exchange field, as a core material for refrigeration and air conditioning heat exchangers and piping systems, copper not only requires excellent processing properties such as bending, flaring, tube expansion, and welding, but also requires high strength to meet the increasingly stringent requirements for high-pressure resistance and thin-walled materials.

[0003] Traditional phosphorus-deoxidized copper tubes (TP2) offer excellent bending, flaring, and expansion properties. This is achieved by adding a small amount of phosphorus to the electrolytic copper to remove oxygen and improve its ductility, weldability, and corrosion resistance. However, TP2 copper tubes have a low burst pressure and are no longer able to meet the safety requirements of the growing trend toward lighter, thinner-walled copper tubes.

[0004] To address the low burst pressure of TP2 copper tubes, various high-strength copper tubes have been developed in recent years. However, these currently developed high-strength copper tubes often contain high Sn, Zn, and Ni content. While this can, to some extent, enable the copper tubes to meet burst pressure requirements after wall thickness reduction, they generally suffer from poor formability and insufficient plastic deformation (specifically, poor bending, flaring, and expansion performance).

[0005] Patent CN101469961B discloses a copper alloy containing Sn and P. This material contains 0.1% to 3.0% Sn and 0.005% to 0.1% P, and exhibits a tensile strength exceeding 250 MPa. This material enhances the circumferential tensile strength of the copper alloy, thereby increasing its burst pressure, by limiting the proportion of Gaussian texture and increasing the proportion of low-angle grain boundaries. However, low-angle grain boundaries are essentially accumulations of dislocations. Excessive low-angle grain boundaries can exacerbate the material's brittleness, reduce its formability, and worsen its cold working properties, such as bending, flaring, and tube expansion.

[0006] Patent CN107739880A discloses a high-strength copper alloy containing Ni, Sn, and P. This alloy contains 0.3-0.7% Ni, 0.2-1.0% Sn, and 0.01-0.07% P, and has a tensile strength of 262-290 MPa. It can be processed into seamed copper tubes using a roll-welding process. By controlling the elongation of the copper material to 40-50%, the bending process is guaranteed to prevent wrinkling and cracking. However, under these conditions, the copper tube's formability cannot be effectively guaranteed, and flaring and expansion pose significant risks. Furthermore, its elongation is lower than that of TP2 copper tubes.

[0007] Therefore, in the current research and development and application of high-strength copper alloys, how to achieve a balance between the material's strength and processability has become a technical challenge in the development of copper alloy pipes for heat exchange. Among the many indicators for evaluating the performance of copper alloy pipes, the yield ratio is a key indicator for measuring the balance between material strength and processability. Generally speaking, a low yield ratio indicates that the material has a high tensile strength while also having a low yield strength. This gives the material excellent uniform deformation ability and low resilience, making it easy to process and deform while being able to withstand high destructive stress, thereby resolving the problem of the incompatibility between high strength and excellent processability.

[0008] The yield ratio of TP2 copper tubes is typically between 0.30 and 0.35, while that of high-strength copper tubes is generally between 0.4 and 0.6. This makes high-strength copper tubes significantly inferior to TP2 copper tubes in bending, flaring, and expansion performance. To address the challenge of balancing the strength and formability of high-strength copper alloy materials, it is necessary to develop new high-performance copper tubes with high strength and low yield ratio as the research and development goals to meet the trend of lightweight and compact modern refrigeration equipment.

[0009] It should be noted that copper tubes face two major technical challenges in thin-wall applications: First, reducing the wall thickness significantly reduces the lifespan of the anthill corrosion resistance, and the thinner the wall, the more severe the damage. Furthermore, in bends where residual stress exists, stress corrosion further accelerates the corrosion process. Furthermore, high-temperature softening during brazing is more pronounced, and the burst pressure drop in the heat-affected zone of thin-walled copper tubes can reach 15% to 30%. Furthermore, the thinner the wall, the higher the risk of overburning and the more severe the deterioration in pressure resistance.

[0010] Based on the above problems, it is necessary to develop a high-performance copper alloy tube with high tensile strength, low yield ratio, excellent ant hole corrosion resistance and high temperature softening resistance, so as to solve the problem of poor processing formability of existing high-strength copper tubes, and at the same time meet the requirements of high corrosion resistance and high temperature softening resistance of copper alloy materials in the context of thin-wall development, and promote the development of heat exchange materials towards high efficiency, energy saving, green and low-carbon. Summary of the Invention

[0011] The present invention aims to provide a high-performance copper alloy tube and a method for preparing the same. By designing the copper alloy composition and improving the recrystallization process, the present invention achieves high strength, good formability, and excellent corrosion resistance and high-temperature softening resistance in the copper alloy tube. This overcomes many of the problems associated with existing copper alloy tubes in heat exchange applications.

[0012] The design ideas of the present invention are as follows:

[0013] The copper alloy tube designed in the present invention combines high tensile strength with a low yield ratio to meet the requirements of the heat exchange field for high pressure resistance and excellent processability of copper materials. The present invention mainly reduces the yield ratio of copper materials by increasing the tensile strength of the copper material while maintaining the yield strength basically unchanged. This requires that the copper material meet the following requirements: (1) have a single face-centered cubic (FCC) crystal structure phase without precipitation of hard and brittle phases; (2) have an appropriate grain size; and (3) have a high proportion of low-Σ value re-site grain boundaries.

[0014] Low-Σ value re-site lattice grain boundaries have low energy and coherent properties, and their ability to hinder dislocations in the early stages of deformation is lower than that of random high-angle grain boundaries, which helps limit the increase in yield strength. As plastic deformation proceeds, dislocations gradually accumulate at the interface and hinder the movement of subsequent dislocations through the elastic strain field of the preceding dislocation, thereby strengthening the dislocation storage capacity and causing an increase in flow stress. This is manifested as an increase in the strain hardening rate, giving the copper alloy higher tensile strength and thus achieving a low yield strength ratio.

[0015] The low Σ value has poor mobility of the lattice grain boundary, which can prevent the abnormal grain growth of the copper alloy tube during the welding process, thereby improving its high temperature softening resistance.

[0016] Low Σ value heavy site lattice grain boundaries are purer than random high-angle grain boundaries. Their coherent properties make it difficult for them to accommodate solute atoms, and their intergranular corrosion sensitivity is weak. The increase in the (Σ9+Σ27) / Σ3 ratio can also effectively reduce the connectivity of the random high-angle grain boundary grid, hindering the extension of intergranular corrosion along the grain boundaries, which is beneficial to alleviate the problem of intergranular corrosion promoting anthill corrosion, thereby improving the corrosion life.

[0017] The present invention strengthens the copper alloy by a method of multi-element composite trace addition, and controls the ratio and addition amount of each element to prevent the copper alloy from precipitating hard and brittle phases, so that the copper alloy has a single face-centered cubic crystal structure α phase; at the same time, the stacking fault energy of the alloy system is reduced, so that the copper alloy has the thermodynamic conditions for forming a high proportion of low Σ value heavy site lattice grain boundaries, and on this basis, a high proportion of low Σ value heavy site lattice grain boundaries is introduced in combination with the recrystallization treatment process; the present invention also controls the grain size of the copper alloy by adjusting the annealing process, thereby obtaining a copper alloy tube with high strength, low yield ratio, corrosion resistance and high temperature softening resistance.

[0018] A first aspect of the present invention provides a high-performance copper alloy tube, comprising the following components in percentage by mass: 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, with the remainder being Cu and unavoidable impurities; and f1 = [Sn] + 10 [P], f2 = [Sn] / [Ni], f1 and f2 satisfy: 0.5% ≤ f1 ≤ 1.05%, 1 < f2 ≤ 5, wherein [Sn], [P], and [Ni] are the percentage by mass of Sn, P, and Ni, respectively;

[0019] The copper alloy tube has a single face-centered cubic crystal structure α phase; the average grain size excluding twin boundaries is 10 to 25 μm, and the average grain size including twin boundaries is 5 to 20 μm; the total proportion of Σ3, Σ9 and Σ27 multisite lattice grain boundaries in the copper alloy tube is ≥50%, and the ratio of the proportions of Σ9, Σ27 and Σ3 multisite lattice grain boundaries satisfies: (Σ9+Σ27) / Σ3≥3.5%.

[0020] In the present invention, Sn element can be dissolved in a large amount in the Cu matrix, and a small amount of Sn addition will not precipitate a second phase.

[0021] In the present invention, the Sn element can improve the strength of the copper alloy tube by solid solution strengthening. The solid solution strengthening effect of the alloying element on the copper alloy tube mainly depends on the lattice mismatch coefficient and the shear modulus mismatch coefficient between the solute atoms and the matrix atoms. The larger the two mismatch coefficients, the stronger the solid solution strengthening effect. The atomic radius difference between Sn and Cu is 23.4%, and the shear modulus increase of Sn on the Cu matrix is ​​about 1.35GPa / at.%. This shows that the two mismatch coefficients of Sn and Cu are large, and its solid solution strengthening effect on the Cu matrix is ​​good. Therefore, adding Sn can effectively perform solid solution strengthening.

[0022] In the present invention, the Sn element can effectively reduce the stacking fault energy of the copper alloy system, thereby forming a large number of stacking faults during the recrystallization process. These stacking faults serve as nucleation points for annealing twins and expand into complete annealing twins through atomic rearrangement. During the migration process, the annealing twin boundaries will also encounter random high-angle grain boundaries, and react to generate a large number of low-Σ value re-site lattice grain boundaries (Σ3, Σ9, Σ27 re-site lattice grain boundaries, where Σ27 is further divided into Σ27a and Σ27b), thereby consuming the random high-angle grain boundaries and increasing the proportion of low-Σ value re-site lattice grain boundaries.

[0023] It should be pointed out that when the amount of Sn added is too small, the reduction of the stacking fault energy of the alloy and the improvement of the solid solution strengthening effect are not obvious; however, excessive addition will lead to the formation of hard and brittle δ phase (Cu 41 Sn 11) precipitation, microsegregation of Sn, and grain boundary segregation lead to a decrease in intergranular bonding and deterioration of the alloy's hot workability. Therefore, the present invention controls the Sn content to 0.05% ≤ Sn ≤ 0.6%. This introduces a high proportion of low-Σ value re-site lattice grain boundaries and improves the alloy's solid solution strengthening ability, while also avoiding the precipitation of hard and brittle δ phase, the decrease in intergranular bonding, and the deterioration of hot workability.

[0024] Therefore, the present invention adds Sn elements to solid solution strengthen the copper alloy and reduces the stacking fault energy of the alloy system to introduce a high proportion of low Σ value heavy site lattice grain boundaries, so that the copper alloy tube has both high strength and low yield ratio characteristics, thereby achieving a high degree of synergy between high strength and excellent processing formability, and to a certain extent improving corrosion resistance and high temperature softening resistance.

[0025] In the present invention, the addition of nickel improves the copper matrix's resistance to formicary cavitation corrosion. Ni ions fill defects in the cuprous oxide film on the copper alloy surface, making the surface oxide layer more stable and dense, thereby reducing the copper alloy's formicary cavitation corrosion rate. Furthermore, as the nickel content increases, the copper alloy's formicary cavitation corrosion resistance improves.

[0026] In the present invention, Ni and Cu are isomorphous and have infinite solid solution characteristics, and no brittle second phase that deteriorates ductility is precipitated.

[0027] In the present invention, Ni also has a certain solid solution strengthening effect, but the difference in atomic radius between Ni and Cu is only 3.2%, and the increase in the shear modulus of the Cu matrix is ​​only 0.19 GPa / at.%. Both mismatch coefficients are much lower than those of Sn, and the solid solution strengthening effect is limited. Therefore, Ni is only used as a supplement to Sn to strengthen copper alloys.

[0028] It should be noted that the addition of Ni slightly increases the stacking fault energy of the alloy system, which is not conducive to the introduction of low-Σ value re-site grain boundaries, that is, it is not conducive to reducing the yield ratio of the copper alloy. Therefore, its addition level should not be too high, and the Sn:Ni ratio should be controlled to ensure a high proportion of low-Σ value re-site grain boundaries.

[0029] Therefore, in order to significantly improve the copper alloy's resistance to anthill corrosion and maintain the alloy's yield ratio, ductility, and processing properties such as bending, flaring, and tube expansion, the present invention controls the Ni content to 0.08%≤Ni<0.3%.

[0030] The present invention improves the copper alloy's resistance to formicary corrosion by adding Ni, and achieves a high degree of synergy between mechanical properties and corrosion resistance through the combined addition of Sn and Ni. Ni compensates for the problem that Sn cannot significantly improve the formicary corrosion resistance of thin-walled copper alloy tubes, while Sn compensates for the negative problem of Ni increasing the stacking fault energy of the alloy system.

[0031] In the present invention, the trace addition of P not only deoxidizes the copper solution but also further reduces the stacking fault energy of the alloy system. P is more effective than Sn in reducing the stacking fault energy, which can, to a certain extent, compensate for the limited reduction in stacking fault energy caused by the limited Sn content. Furthermore, P can also improve the fluidity of the copper solution, compensating for the reduced fluidity of the copper solution caused by Sn.

[0032] It should be noted that the maximum solid solubility of P is low. Excessive addition will form Cu3P phase, which segregates at grain boundaries and deteriorates the ductility of the copper alloy. Therefore, the present invention limits the amount of P added to 0.015%≤P≤0.045%.

[0033] The present invention weightedly controls the total addition of Sn and P elements and the ratio of Sn and Ni elements to achieve an f1 value ≥ 0.5% and an f2 value > 1, thereby imparting a low stacking fault energy to the alloy. Simultaneously, in conjunction with the subsequent recrystallization process, the fraction of low-Σ heavy-site grain boundaries is ≥ 50%, thereby achieving high strength and a low yield ratio. Furthermore, the ratio (Σ9 + Σ27) / Σ3 is controlled to be ≥ 3.5%, providing a certain improvement in corrosion resistance. Furthermore, the present invention controls f1 ≤ 1.05 and f2 ≤ 5 to prevent excessive Sn additions and total element additions from exceeding certain limits. This would significantly degrade the matrix's deformability due to the reduced pinning spacing, hindering the maintenance of a low yield ratio. Controlling the upper limits of f1 and f2 also facilitates the copper alloy of the present invention to possess a single face-centered cubic α-phase crystal structure.

[0034] The copper alloy tube features a single face-centered cubic α phase, which prevents microcrack initiation caused by deformation disharmony between the matrix and the secondary phase. Furthermore, the face-centered cubic phase possesses a rich slip system, resulting in strong plastic deformation and a low stress concentration. This facilitates plastic deformation and maintains low yield strength, providing the microstructural foundation for achieving a low yield-to-strength ratio.

[0035] According to the Hall-Petch relationship, grain refinement can increase the interface area, increase the resistance to dislocation movement, and improve the yield strength and tensile strength to a certain extent. The present invention controls the average grain size excluding twin boundaries to 10 to 25 μm to maintain the yield strength from increasing excessively. Twin boundaries divide the original grains, further reducing the grain size, but they have low energy and coherent characteristics, which have a small increase in yield strength, but can avoid strain concentration and greatly improve the strain hardening ability. However, the average grain size of the twin boundaries should not be too low, otherwise it will also cause an increase in yield strength. Therefore, the present invention controls the average grain size of the twin boundaries to 5 to 20 μm to maintain a lower yield strength, while providing a certain strain hardening ability to promote an increase in tensile strength.

[0036] The present invention controls the proportion of Σ3, Σ9, and Σ27 heavy site lattice grain boundaries to more than 50% to achieve high strength and low yield ratio, improve the processing deformation ability of the alloy, and at the same time controls the ratio of (Σ9+Σ27) / Σ3 to ≥3.5% to improve the corrosion resistance of the alloy.

[0037] By controlling the composition, proportion, and microstructural parameters of the elements within the above ranges, the present invention can achieve a yield strength of 60 to 90 MPa, a tensile strength of ≥260 MPa, a yield strength ratio of 0.23 to 0.30, and an elongation of ≥50%. Compared with a TP2 copper tube of the same specification, the bursting pressure is increased by ≥7%, the wall thickness can be reduced by ≥10% while maintaining the bursting pressure unchanged, and the bursting pressure decay rate after welding is ≤10%. After 21 days of alternating hot and cold corrosion in a 0.4% formic acid aqueous solution, the maximum corrosion depth of a single tube is ≤170 μm, and the maximum corrosion depth at the bend is ≤190 μm. The single tube's resistance to anthill corrosion is improved by more than 15% compared to a TP2 copper tube of the same specification, and the corrosion resistance decay rate at the bend is ≤15%.

[0038] A second aspect of the present invention provides a high-performance copper alloy tube, comprising the following components in percentage by mass: 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, with the remainder being Cu and unavoidable impurities; and f1 = [Sn] + 10 [P], f2 = [Sn] / [Ni], f1 and f2 satisfy: 0.5% ≤ f1 ≤ 1.05%, 1 < f2 ≤ 5, wherein [Sn], [P], and [Ni] are the percentage by mass of Sn, P, and Ni, respectively;

[0039] The copper alloy tube has a single face-centered cubic crystal structure α phase; the average grain size excluding twin boundaries is 10 to 25 μm, and the average grain size including twin boundaries is 5 to 20 μm; the total proportion of Σ3, Σ9 and Σ27 multisite lattice grain boundaries in the copper alloy tube is ≥68%, and the ratio of the proportions of Σ9, Σ27 and Σ3 multisite lattice grain boundaries satisfies: (Σ9+Σ27) / Σ3 ≥10%.

[0040] While maintaining the chemical composition and content unchanged, the present invention adjusts the single recrystallization process to a repeated recrystallization process, thereby further increasing the total proportion of Σ3, Σ9 and Σ27 heavy site lattice grain boundaries and the (Σ9+Σ27) / Σ3 value in the copper alloy, which can further improve the strength, corrosion resistance and high-temperature softening resistance of the material and reduce the yield strength ratio.

[0041] By controlling the composition, proportions, and microstructural parameters of the elements within the above ranges, the copper alloy prepared by the present invention has a yield strength of 65 to 90 MPa, a tensile strength of ≥285 MPa, a yield strength ratio of 0.21 to 0.28, and an elongation at break of ≥50%. Compared with a TP2 copper tube of the same specification, the bursting pressure is increased by ≥20%, the wall thickness can be reduced by ≥18% while maintaining the bursting pressure unchanged, and the bursting pressure decay rate after welding is ≤5%. After 21 days of alternating hot and cold corrosion in a 0.4% formic acid aqueous solution, the maximum corrosion depth of a single tube is ≤155 μm, and the maximum corrosion depth at the bend is ≤165 μm. The single tube's resistance to anthill corrosion is increased by more than 20% compared to a TP2 copper tube of the same specification, and the corrosion resistance decay rate at the bend is ≤10%.

[0042] For the high performance copper alloy tubes according to the first and second aspects of the present invention, preferably, in the copper alloy tube, f1 and f2 satisfy the following: 0.65%≤f1≤1.05%, 3.4≤f2≤5.

[0043] The present invention can further improve the tensile strength, reduce the stacking fault energy of the alloy system, and achieve an increase in the proportion of low-Σ value heavy site lattice grain boundaries and the (Σ9+Σ27) / Σ3 value by further improving the f1 and f2 values ​​and increasing the content of solid solution elements, while maintaining a low yield ratio, thereby reducing the bursting pressure decay rate and the corrosion resistance decay rate at the bend to a certain extent.

[0044] Taking a single recrystallization process as an example, the present invention controls the f1 and f2 values ​​within the above range, and the resulting copper alloy still has a single face-centered cubic crystal structure α phase, with an average grain size of 10 to 25 μm excluding twin boundaries and an average grain size of 5 to 20 μm including twin boundaries, which can provide a microstructural basis for achieving a low yield ratio. At the same time, by further increasing the f1 and f2 values, the present invention can increase the proportion of low Σ value heavy site lattice grain boundaries to ≥60%, and the (Σ9+Σ27) / Σ3 ratio to ≥3.8%, so that the yield strength of the prepared copper alloy is between 65 and 90 MPa, the tensile strength is ≥270 MPa, the yield ratio is between 0.23 and 0.30, and the elongation after fracture is ≥50%. Compared with copper pipes of the same specification, the bursting pressure is increased by ≥13%, the wall thickness can be thinned by ≥14% while maintaining the bursting pressure without reducing, and the bursting pressure decay rate after welding is ≤7%. After 21 days of alternating hot and cold corrosion in a 0.4% formic acid aqueous solution atmosphere, the maximum corrosion depth of a single tube is ≤165μm, and the maximum corrosion depth at the elbow is ≤180μm. Compared with TP2 copper tubes of the same specifications, the anthill corrosion resistance of a single tube is improved by more than 17%, and the corrosion resistance attenuation rate at the elbow is ≤12%.

[0045] A third aspect of the present invention provides a high-performance copper alloy tube, comprising the following components in percentage by mass: 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, 0.001% ≤ Zr < 0.03%, 0.001% ≤ Co < 0.01%, 0 ≤ B < 0.01%, with the remainder being Cu and unavoidable impurities; and f1 = [Sn] + 10 [P] + 10 [Zr], f2 = [Sn] / [Ni], f1 and f2 satisfy: 0.65% ≤ f1 < 1.15%, 1 < f2 ≤ 5, wherein [Sn], [P], [Zr], and [Ni] are the percentage by mass of Sn, P, Zr, and Ni, respectively;

[0046] The copper alloy tube has a single face-centered cubic crystal structure α phase; the average grain size excluding twin boundaries is 10 to 25 μm, and the average grain size including twin boundaries is 5 to 20 μm; the total proportion of Σ3, Σ9 and Σ27 multisite lattice grain boundaries in the copper alloy tube is ≥60%, and the ratio of Σ9, Σ27 and Σ3 multisite lattice grain boundaries satisfies: (Σ9+Σ27) / Σ3 ≥4.0%.

[0047] Based on the Sn, Ni, and P composite-reinforced copper alloy, the present invention further reduces the stacking fault energy of the alloy system by adding Zr, significantly increasing the proportion of low-Σ value heavy-site grain boundaries, further improving strength and reducing yield ratio. The addition of Co specifically improves the copper alloy's high-temperature softening resistance, significantly reducing the burst pressure decay rate of the copper tube after welding. Furthermore, the optional addition of B improves the quality of the ingot and reduces the oxygen content, further enhancing the corrosion resistance of the finished copper tube.

[0048] Specifically, the present invention further reduces the stacking fault energy of the copper alloy system by adding a trace amount of Zr, thereby activating a higher proportion of stacking faults and forming a higher proportion of low-Σ value re-site grain boundaries, further optimizing the performance of the copper alloy. Zr is much more effective in reducing the stacking fault energy than Sn and P. Zr can work together with Sn and P to reduce the stacking fault energy to a lower level, and can also replace Sn to a certain extent, reducing the Sn usage and improving the alloy's economic efficiency.

[0049] It should be noted that the solid solubility of Zr in the Cu matrix is ​​very limited. According to the Cu-Zr binary phase diagram, the maximum solid solubility of Zr in Cu at room temperature is less than 0.11%. In actual use, the Zr content must be reduced to below 0.03% to ensure that a brittle Zr-containing second phase is not precipitated. Therefore, to ensure that the Zr element can significantly reduce the stacking fault energy while preventing the precipitation of a brittle Zr-containing second phase, the present invention strictly controls the Zr addition to 0.001% ≤ Zr < 0.03%.

[0050] In the present invention, the Co element, with its high melting point, significantly increases the recrystallization temperature of the copper alloy. It also pins random high-angle grain boundaries, effectively limiting the rapid migration of random high-angle grain boundaries during welding, inhibiting abnormal grain growth, and improving the high-temperature softening resistance of the copper alloy. However, the solid solubility of the Co element in the Cu matrix is ​​also extremely low. Therefore, in order to achieve the effect of improving high-temperature softening resistance while maintaining a single face-centered cubic crystal structure, the present invention controls the Co element addition to 0.001% ≤ Co < 0.01%.

[0051] In the present invention, element B has the dual functions of deoxidizing the copper melt and refining the dendritic structure of the ingot. Element B reacts with cuprous oxide and free oxygen in the copper melt to form boron trioxide, which forms a slag that floats upward, achieving the deoxidizing effect. However, the maximum solid solubility of element B in the Cu matrix at room temperature is only 0.01%. Therefore, to achieve both deoxidation and grain refinement while maintaining a single face-centered cubic crystal structure, the present invention controls the addition of element B to less than 0.01%.

[0052] In the present invention, by weightedly controlling the total addition of Sn, P, and Zr elements, the ratio of Sn and Ni elements, and the individual additions of Co and B elements, f1 is set to ≥0.65% and f2 is set to >1. The strong stacking fault energy-reducing effect of Zr is utilized to further reduce the stacking fault energy or reduce the Sn addition. In conjunction with the subsequent recrystallization process, the proportion of low-Σ value heavy-site lattice heavy-site grain boundaries is increased to ≥60%, thereby improving strength while maintaining a low yield ratio. The ratio of (Σ9+Σ27) / Σ3 is increased to ≥4.0%, which helps improve corrosion resistance. Furthermore, by controlling the individual additions of each element and maintaining f1 values ​​of <1.15% and f2 ≤5, the copper alloy can maintain a single α phase.

[0053] By adjusting the composition and proportion of elements and controlling the microstructural parameters within the above ranges, the copper alloy prepared by the present invention has a yield strength between 65 and 90 MPa, a tensile strength of ≥275 MPa, a yield strength ratio of 0.22 to 0.29, and an elongation of ≥50%. Compared with a TP2 copper tube of the same specification, the bursting pressure is increased by ≥18%, the wall thickness can be reduced by ≥15% while maintaining the bursting pressure unchanged, and the bursting pressure decay rate after welding is ≤6%. After 21 days of alternating hot and cold corrosion in a 0.4% formic acid aqueous solution, the maximum corrosion depth of a single tube is ≤165 μm, and the maximum corrosion depth at the bend is ≤180 μm. The single tube's resistance to formic acid corrosion is improved by more than 18% compared to a TP2 copper tube of the same specification, and the corrosion resistance decay rate at the bend is ≤11%.

[0054] Preferably, in the copper alloy of the present invention, in terms of mass percentage, 0.001%≤B<0.01%.

[0055] By controlling the boron content within the aforementioned range, the present invention reduces the oxygen content in the copper alloy to below 15 ppm while refining the dendritic structure of the ingot, thereby improving its resistance to formicary pitting corrosion. After adding boron, after 21 days of alternating hot and cold corrosion in a 0.4% formic acid aqueous solution, the maximum corrosion depth of a single tube was ≤155 μm, and the maximum corrosion depth at the bend was ≤170 μm. This represents a 21% improvement in formicary pitting resistance compared to a TP2 copper tube of the same specification, with a corrosion resistance degradation rate of ≤10% at the bend.

[0056] A fourth aspect of the present invention provides a high-performance copper alloy tube, comprising the following components in percentage by mass: 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, 0.001% ≤ Zr < 0.03%, 0.001% ≤ Co < 0.01%, 0 ≤ B < 0.01%, the remainder being Cu and unavoidable impurities; and f1 = [Sn] + 10 [P] + 10 [Zr], f2 = [Sn] / [Ni], f1 and f2 satisfy: 0.65% ≤ f1 < 1.15%, 1 < f2 ≤ 5, wherein [Sn], [P], [Zr], and [Ni] are the percentage by mass of Sn, P, Zr, and Ni, respectively;

[0057] The copper alloy tube has a single face-centered cubic crystal structure α phase; the average grain size excluding twin boundaries is 10 to 25 μm, and the average grain size including twin boundaries is 5 to 20 μm; the total proportion of Σ3, Σ9 and Σ27 multisite lattice grain boundaries in the copper alloy tube is ≥72%, and the ratio of Σ9, Σ27 to Σ3 multisite lattice grain boundaries satisfies: (Σ9+Σ27) / Σ3 ≥12%.

[0058] Based on the above-mentioned combined addition of alloying elements, the present invention combines repeated recrystallization processes to further increase the total proportion of Σ3, Σ9 and Σ27 grain boundaries in the alloy, (Σ9+Σ27) / Σ3≥12%, which can maintain a sufficiently low yield ratio while improving strength, and effectively reduce the post-weld pipe burst pressure decay rate and the corrosion resistance decay rate at the bend.

[0059] By controlling the composition, proportions, and microstructural parameters of the elements within the aforementioned ranges, the present invention achieves a copper alloy tube having a yield strength of 65 to 90 MPa, a tensile strength of ≥295 MPa, a yield strength ratio of 0.20 to 0.27, and an elongation of ≥50%. Compared to a TP2 copper tube of the same specification, the bursting pressure is increased by ≥25%, the wall thickness can be reduced by ≥20% while maintaining the bursting pressure unchanged, and the bursting pressure decay rate after welding is ≤2%. After 21 days of alternating hot and cold corrosion in a 0.4% formic acid aqueous solution, the maximum corrosion depth of a single tube is ≤150 μm, and the maximum corrosion depth at the bend is ≤160 μm. The single tube's resistance to formic acid pitting is improved by more than 23% compared to a TP2 copper tube of the same specification, with a corrosion resistance decay rate of ≤7% at the bend.

[0060] Preferably, based on the above-mentioned repeated recrystallization process, by controlling the B element content to 0.001% ≤ B < 0.01%, the oxygen content of the copper alloy can be reduced to below 15 ppm, so that after 21 days of alternating hot and cold corrosion in an atmosphere of 0.4% concentration of formic acid aqueous solution, the maximum corrosion depth of a single tube is ≤ 145 μm, the maximum corrosion depth at the bend is ≤ 155 μm, the single tube's anthill corrosion resistance is improved by more than 25% compared with the TP2 copper tube of the same specification, and the corrosion resistance attenuation rate at the bend is ≤ 5%.

[0061] A fifth aspect of the present invention provides a method for preparing the above-mentioned high-performance copper alloy tube, which can be used to prepare copper alloy seamless tubes. The method can be implemented using existing production lines and has strong adaptability to existing equipment.

[0062] Specifically, the method for preparing a high-performance copper alloy tube of the present invention comprises the following steps: batch smelting → continuous casting → rolling → continuous drawing → recrystallization treatment; wherein,

[0063] Ingredient smelting: smelting the raw materials that meet the proportion;

[0064] Continuous casting: Continuously casting the molten metal into billets;

[0065] Rolling: rolling the billet to obtain a rolled tube;

[0066] Joint drawing: reducing the diameter of the rolled tube;

[0067] Recrystallization treatment: By controlling the deformation amount and annealing parameters, products with target performance are obtained.

[0068] Based on the design of alloying components and contents, this invention increases the proportion of low-Σ re-site grain boundaries by improving the recrystallization process. Recrystallization processes can be divided into single recrystallization processes and repeated recrystallization processes. Both recrystallization processes essentially increase the proportion of low-Σ re-site grain boundaries through strain-induced grain boundary migration.

[0069] Preferably, the recrystallization treatment is a single recrystallization process, and the single recrystallization is "disk pulling→finished product annealing", the total deformation of the disk pulling is not less than 80%, the finished product annealing temperature is 500-750°C, and the annealing time is 30-150min.

[0070] In the present invention, single recrystallization has a large deformation amount and a high annealing temperature. During the annealing process, due to the low stacking fault energy of the alloy system, a large number of strain-induced annealing twins are formed. The formed annealing twin boundaries (Σ3) will also encounter random high-angle grain boundaries during migration, reacting to form a large number of low-Σ value re-site lattice grain boundaries (Σ3, Σ9, Σ27a and Σ27b), thereby increasing the proportion of low-Σ value re-site lattice grain boundaries. Among them, Σ9 and Σ27 re-site lattice grain boundaries will occupy the random high-angle grain boundary positions, interrupting the random high-angle grain boundary network.

[0071] The present invention controls the total deformation of a single recrystallization to be no less than 80% to accumulate sufficient strain energy, introduces high-density dislocations and destroys the original grain boundary structure. Based on the high strain energy structure, large-scale recrystallization and grain boundary migration are driven by annealing treatment at 500-750°C for 30-150 minutes, thereby forming a low-Σ value re-site lattice grain boundary with a proportion fraction of no less than 50%.

[0072] Preferably, the recrystallization treatment is a repeated recrystallization process, wherein the repeated recrystallization is a multiple cycle of "disc pulling → annealing" after 1 to 3 passes of disc pulling, and the total deformation of the 1 to 3 disc pulling passes before the cycle is ≤72%; in the multiple "disc pulling → annealing" cycles, the number of cycles of "disc pulling → annealing" is 3 to 6 times, the disc pulling deformation in a single cycle is 25 to 35%, the annealing temperature is 500 to 600°C, and the annealing time is 10 to 70 minutes.

[0073] In the present invention, the repeated recrystallization process has the characteristics of small deformation in a single pass and a relatively low annealing temperature. During annealing at a relatively low temperature, selective recrystallization is preferentially induced at high defects, resulting in strain-induced annealing twins. The annealing twin boundaries also migrate and react with random high-angle grain boundaries to form low-Σ value re-site lattice grain boundaries without introducing a strong crystallization orientation, while controlling the grains from growing excessively. When the recrystallized structure is deformed again, the low-energy low-Σ value re-site lattice grain boundaries are not easily destroyed, while the random high-angle grain boundaries can be continuously activated and migrated through deformation and annealing to form new annealing twins and low-Σ value re-site lattice grain boundaries. The low-Σ value re-site lattice grain boundaries are superimposed and accumulated, thereby increasing the proportion of low-Σ value re-site lattice grain boundaries.

[0074] The present invention controls the deformation of a single pass in the cycle to be within the range of 25% to 35% to achieve controllable strain energy introduction, preferentially destroying high-energy random high-angle grain boundaries and avoiding destroying existing low-energy interfaces. Then, by controlling the annealing temperature and annealing time of the cycle, the strain energy is gradually released, and the high-strain energy structure is selectively driven to preferentially recrystallize and form low-energy interfaces. Through cyclic processing, a higher proportion of low-Σ value re-site lattice grain boundaries can be accumulated, and the control of low-Σ value re-site lattice grain boundaries is more precise.

[0075] After 3 to 6 cycles, the repeated recrystallization process of the present invention significantly increases the number of low-Σ re-site grain boundaries compared to conventional processes and single annealing processes. The proportion of low-Σ re-site grain boundaries exceeds 65%, and the proportions of Σ9, Σ27a, and Σ27b also increase significantly, with (Σ9 + Σ27) / Σ3 greater than 10.3%, effectively reducing the connectivity of the random high-angle grain boundary network. However, after more than 6 cycles, the proportion of low-Σ re-site grain boundaries no longer increases significantly due to saturation.

[0076] Preferably, in the batching and smelting process, the raw materials that meet the proportions are first dried and then smelted at 1170-1350°C. Among them, Ni, Co, B, Zr, P, and Sn elements are added in the form of commercially available copper-nickel master alloy, copper-cobalt master alloy, copper-boron master alloy, copper-zirconium master alloy, phosphorus-copper master alloy, and copper-tin master alloy, respectively. After the raw materials are completely melted, they are kept warm for 45-90 minutes to allow the trace elements to fully diffuse and homogenize. Adding trace elements in the form of a master alloy can promote melting, diffusion, and reduce burnout. Subsequently, under nitrogen protection, the copper liquid is transferred to a casting furnace with a holding temperature of 1180-1190°C for 8-12 minutes, and then continuously cast into a tube billet.

[0077] Preferably, the continuous casting process is horizontal continuous casting, with a pulling speed of 330-380 mm / min, a primary cooling water flow rate of 30-35 L / min, and a secondary cooling water flow rate of 65-75 L / min. The outer diameter of the horizontal continuous casting tube can be designed according to actual needs, for example, 88-98 mm, preferably 92 mm.

[0078] Preferably, during the rolling process, the rolling speed is 1.2 to 2.2 m / min, and a rolled tube blank is obtained after the rolling process. The size of the rolled tube blank can be designed according to actual needs, for example, the outer diameter of the rolled tube blank is 50 to 55 mm, and the wall thickness is 2.3 to 2.7 mm.

[0079] The combined drawing process preferably provides semi-finished products that meet dimensional requirements for subsequent processing steps. The combined drawing speed is controlled at 70-92 m / min, resulting in precision tube blanks with significantly reduced outer diameters. For example, combined drawing can reduce the outer diameter of a rolled tube blank with an outer diameter of 50-55 mm and a wall thickness of 2.3-2.7 mm to 30-35 mm, and the wall thickness to 1.4-1.7 mm.

[0080] After the joint drawing process, the obtained precision tube blank is subjected to a single recrystallization process or a repeated recrystallization process to prepare a high-performance copper alloy tube with a high proportion of low Σ value heavy site grain boundaries. The prepared tube is not restricted by specifications and dimensions, and includes but is not limited to plain tubes and internally threaded tubes.

[0081] In a single recrystallization process, the number of coiling passes and specific process parameters can be flexibly adjusted based on actual production needs to ensure that the final product meets the target specifications and dimensional requirements. However, the total coiling deformation must be ≥80% to store sufficient strain energy, effectively promoting the formation of a uniformly recrystallized structure in the finished product during annealing and significantly increasing the proportion of low-Σ value heavy-site grain boundaries. For example, a rolled tube with an outer diameter of 30-35mm and a wall thickness of 1.4-1.7mm undergoes 6-9 coiling passes to produce a smooth tube with an outer diameter of 5-12mm and a wall thickness of 0.40-0.65mm. The total deformation is 81.5%-96.7%, with a coiling speed of 450-700m / min.

[0082] In the repeated recrystallization process, the total deformation of the 1-3 coiling passes before the cycle is ≤72%. The specific deformation distribution between passes and the specific process parameters can be flexibly adjusted according to actual production needs. In the "coil pulling → annealing" cyclic process, the number of coiling passes and specific process parameters within a single cycle can also be flexibly adjusted according to actual production needs. However, the total coiling deformation within a single cycle must be 25% to 35%, and the annealing temperature within a single cycle must be 500-600°C, the annealing time must be 10-70 minutes, and the number of cycles must be 3-6 to accumulate a high proportion of low-Σ value re-site grain boundaries and improve the (Σ9+Σ27) / Σ3 ratio. For example, a rolled tube with an outer diameter of 30 to 35 mm and a wall thickness of 1.4 to 1.7 mm undergoes 1 to 2 coiling processes to produce an intermediate tube with an outer diameter of 20 to 26 mm and a wall thickness of 0.85 to 1.2 mm. This intermediate tube is then subjected to a "coil-drawing-annealing" cycle to produce a smooth tube with an outer diameter of 5 to 12 mm and a wall thickness of 0.40 to 0.65 mm, wherein the coiling speed is 450 to 700 m / min.

[0083] When producing internally threaded tubes using a single recrystallization process, after the coiling step, an online annealing process is required to soften the tube blank. Preferred online annealing parameters are: a speed of 300-450 m / min and a current of 3600-5000 A. The resulting tube blank is then subjected to internal thread spinning, preferably at a spinning speed of 480-650 rpm, more preferably 550-600 rpm. This is followed by a final annealing process to produce the internally threaded tube. Preferred final annealing temperatures are 510-650°C and annealing time is 30-120 minutes.

[0084] When producing internally threaded tubes using a repeated recrystallization process, the final "spinning"-annealing cycle is replaced with an "internal thread forming → internal thread tube annealing" process. The spinning speed for internal thread forming is preferably 480-650 rpm, more preferably 550-600 rpm. The annealing temperature for the internally threaded tube is preferably 500-580°C, and the annealing time is 10-70 minutes.

[0085] It should be noted that the copper alloy composition provided by the present invention is not only suitable for pipe production, but can also be used in the preparation of various copper alloy products such as wire, rod, plate, strip, etc. Its production process can adopt existing mature processing technologies such as extrusion, rolling, drawing, forging, etc., or it can optimize and adjust process parameters or develop new processing methods according to specific product performance requirements and application scenarios to meet the diverse needs of different industries for copper alloy materials. The high-performance copper alloy tube is not only suitable for the field of heat exchange, but also can play an important role in the fields of marine engineering, energy and chemical industry, etc., especially in scenes with complex environments and high requirements for material performance.

[0086] Compared with the prior art, the present invention has at least the following technical effects:

[0087] (1) The present invention adds Sn, Ni, and P elements to Cu, regulates the content and ratio of each element, and combines it with a subsequent recrystallization treatment process, so that the copper alloy has a high proportion of low Σ value heavy site grain boundaries while strengthening the strength, effectively reducing the yield strength ratio, maintaining high processing forming ability, showing excellent application process performance such as bending, flaring, and tube expansion, and having more excellent pressure resistance, corrosion resistance, and high temperature softening resistance.

[0088] (2) The present invention adds Zr, Co, and B (optionally) elements to Cu, Sn, Ni, and P elements. By controlling the content and ratio of each element and combining it with a subsequent improved recrystallization treatment process, the strength, plastic deformation ability, pressure resistance, corrosion resistance, and high-temperature softening resistance of the alloy are further improved compared to copper alloys prepared from Cu, Sn, Ni, and P elements.

[0089] (3) The recrystallization treatment process of the present invention includes single recrystallization and repeated recrystallization, which can be implemented using existing production lines and has strong adaptability to existing equipment. The present invention can obtain a copper alloy with excellent performance by combining the designed alloy composition with a single recrystallization process. Combined with the repeated recrystallization process, the proportion of low Σ value heavy site lattice grain boundaries and the ratio of (Σ9+Σ27) / Σ3 will be significantly improved, and the strength, plastic deformation ability, pressure resistance, corrosion resistance and high temperature softening resistance of the alloy are further improved compared to the copper alloy prepared by the single recrystallization process. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Figure 1 It is the process route diagram of the present invention.

[0091] Figure 2 These are the X-ray diffraction (XRD) spectra of Example 2, Example 5, Example 12, Example 15 and Comparative Example 1 of the present invention.

[0092] Figure 3 The inverse pole figures (IPF figures) and grain boundary distribution figures of the sample of Example 2 of the present invention, the sample of Example 5 after 3 cycles of repeated recrystallization, the sample of Example 5 after 4 cycles of repeated recrystallization and the sample of Comparative Example 1 are obtained by electron backscatter diffraction (EBSD) testing, wherein (a) is the IPF figure of Comparative Example 1; (b) is the grain boundary distribution figure of Comparative Example 1; (c) is the IPF figure of Example 2; (d) is the grain boundary distribution figure of Example 2; (e) is the IPF figure of Example 5 after 3 cycles of repeated recrystallization; (f) is the grain boundary distribution figure of Example 5 after 3 cycles of repeated recrystallization; (g) is the IPF figure of Example 5 after 4 cycles of repeated recrystallization; (h) is the grain boundary distribution figure of Example 5 after 4 cycles of repeated recrystallization.

[0093] Figure 4 These are the engineering stress-strain curves of Example 2, Example 5, Example 12, Example 15 and Comparative Example 1 of the present invention.

[0094] Figure 5 These are typical corrosion morphologies of the cross-sections of the samples after ant hole corrosion in Example 2 and Comparative Example 1 of the present invention, and the corrosion depth is provided, wherein (a) is a cross-sectional morphology of the sample of Comparative Example 1 after the ant hole corrosion test; (b) is a cross-sectional morphology of the elbow sample of Comparative Example 1 after the ant hole corrosion test; (c) is a cross-sectional morphology of the sample of Example 2 after the ant hole corrosion test; and (d) is a cross-sectional morphology of the elbow sample of Example 2 after the ant hole corrosion test.

[0095] Figure 6These are pictures of the rupture of the samples of Example 2 and Comparative Example 1 of the present invention after the hydraulic pressure blasting test, and pictures of the rupture of the welded pipe sample after the hydraulic pressure blasting test, wherein (a) is a picture of the rupture of the sample of Comparative Example 1 after the hydraulic pressure blasting test; (b) is a picture of the rupture of the welded pipe sample of Comparative Example 1 after the hydraulic pressure blasting test; (c) is a picture of the rupture of the sample of Example 2 after the hydraulic pressure blasting test; and (d) is a picture of the rupture of the welded pipe sample of Example 2 after the hydraulic pressure blasting test.

[0096] Figure 7 These are the Kernel average orientation difference maps (KAM maps) of Example 2 of the present invention and Comparative Example 1 after 5% tensile deformation, wherein (a) is the KAM map of Comparative Example 1 after 5% tensile deformation; (b) is the KAM map of Example 2 after 5% tensile deformation. DETAILED DESCRIPTION

[0097] The following will be combined with the drawings and specific implementation methods of the embodiments of this application to more clearly and completely describe the technical solutions and advantages of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0098] If no specific conditions are specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All raw materials and reagents used were commercially available conventional products.

[0099] The performance parameters involved in the embodiments of the present invention are measured using the following methods.

[0100] The average grain size of the metallographic structure is tested in accordance with GB / T 6394-2017 Metal Grain Size Determination Method.

[0101] Room temperature mechanical properties such as yield strength, ultimate tensile strength, and elongation were tested on an electronic universal mechanical properties testing machine in accordance with GB / T 228.1-2010 Tensile tests on metallic materials Part 1: Room temperature test methods. An extensometer was used with a gauge length of 50 mm, a tensile speed of 5 mm / min, and three parallel specimens.

[0102] The burst pressure of copper alloy pipes is determined by performing a pressure test according to GB / T 241-2007 Metal Pipe Hydraulic Test Methods. The copper pipes are then subjected to the same pressure test after welding to obtain the post-weld burst pressure. The post-weld burst pressure decay rate is defined as:

[0103] Attenuation rate of burst pressure after welding pipe = (bursting pressure - burst pressure after welding pipe) / burst pressure * 100%.

[0104] The bending test for process performance is conducted in accordance with GB / T 244-2008, Metal Tube Bending Test Method. With a bending core diameter of 1.5 times the outer diameter of the copper tube, the inner and outer surfaces of the tube are smooth, without wrinkles or cracks, after a 180° bend. The flaring test is conducted in accordance with GB / T 17791-1999, Seamless Copper Tubes for Air Conditioning and Refrigeration. The flaring is conducted with a 60° taper angle and a 40% flaring ratio, or when the distance between the two walls after flattening is equal to the wall thickness. The absence of visible cracks and fissures on the specimen indicates excellent process performance.

[0105] For the anthill corrosion test, 13 parallel specimens of each copper alloy were taken, each with a length of 10 cm. The copper tube specimens were first pretreated by ultrasonic cleaning with anhydrous ethanol, acetone, and deionized water for 3 minutes each to remove oil stains on the surface of the copper tube. The copper tube specimens were then sealed at both ends, with only the outer surface of the copper tube exposed to the formic acid atmosphere. The pretreated copper tubes were hung in a sealed box filled with a 0.4% formic acid aqueous solution, with the solution volume to specimen area ratio of not less than 5 cm. 3 / cm 2 , heated in a water bath to 40°C for 48 hours, then placed at room temperature for 48 hours, and repeated this cycle for 21 days. After the corrosion test, seven equally spaced cross sections of each specimen were selected for corrosion depth testing. The seven data points with the largest corrosion depths for each specimen were recorded, and the average value was taken as the maximum corrosion depth of the specimen. The average value of the maximum corrosion depths of the 13 parallel specimens was then calculated as the maximum corrosion depth of a single tube for the copper alloy under the above test conditions.

[0106] The elbow corrosion test prepares elbow specimens according to the elbow test conditions. Each specimen is 15 cm long, and the center of the elbow is located at the axial center of the specimen. The specimens are pretreated and sealed according to the above-mentioned anthill corrosion test steps. The outer part of the elbow of the specimen is hung downward in a sealed box filled with formic acid aqueous solution for corrosion. After the corrosion test, each specimen is sampled at 5 mm intervals on both sides starting from the center of the elbow, and 3 sections are taken on each side, including a total of 7 sections including the center section of the elbow, for corrosion depth testing. The remaining test and data processing requirements are consistent with the anthill corrosion test, and the maximum corrosion depth at the elbow is obtained.

[0107] The corrosion resistance attenuation rate at the bend is defined as:

[0108] Corrosion resistance attenuation rate at the bend = (maximum corrosion depth at the bend - maximum corrosion depth of a single pipe) / maximum corrosion depth of a single pipe * 100%.

[0109] The XRD pattern test was conducted using a Rigaku Smartlab X-ray diffractometer with a continuous scanning speed of 1° / min, a 2θ range of 35° to 100°, and a copper target.

[0110] EBSD testing was performed using a Carl Zeiss Sigma 300 field emission scanning electron microscope equipped with an Oxford Symmetry S2 EBSD probe, with a scanning step size of 0.5 μm. Data analysis was performed using AZtec Crystal 2.1 software. The type of the re-site grain boundary was determined according to the Brandon standard, where the 60° / <111> The grain boundaries with misorientation, angle deviation ≤ 8.7°, and axis deviation ≤ 8.2° are defined as Σ3 multi-site grain boundaries. <110> The grain boundaries with misorientation, angle deviation ≤ 5.0°, and axis deviation ≤ 2.7° are defined as Σ9 multi-site grain boundaries. <110> and 35.4° / <210> Grain boundaries with misorientation, angle deviation ≤ 2.9°, and axis deviation ≤ 0.9° are defined as Σ27a double-site lattice grain boundaries and Σ27b double-site grain boundaries.

[0111] Examples 1 to 4

[0112] Examples 1 to 4 provide a light pipe made of a copper alloy containing Sn, Ni, and P and a preparation method thereof using a single recrystallization process. The specific preparation method of Example 1 includes the following steps:

[0113] S1. Ingredient smelting

[0114] According to the designed copper alloy chemical composition, raw materials including electrolytic copper (purity ≥ 99.98%), copper-nickel master alloy (Cu-42% Ni), phosphorus copper master alloy (Cu-14% P) and copper-tin master alloy (Cu-50% Sn) are prepared and dried for use. Feeding the raw materials in the form of master alloys is beneficial to lowering the melting temperature of high-melting-point elements, accelerating dissolution, and reducing element burnout and oxidation.

[0115] After melting the electrolytic copper plate, the temperature of the copper liquid is adjusted to 1200℃. Copper-nickel master alloy, phosphorus-copper master alloy and copper-tin master alloy are added in proportion. The copper liquid is stirred with a graphite rod and covered with charcoal to prevent oxidation and reduce burning. The temperature is kept for 60 minutes to allow the elements to fully diffuse, promote the homogenization of the copper liquid elements, and provide time for the floating and escape of gas and non-metallic inclusions, thereby promoting deoxidation and degassing. The copper liquid is transferred to the casting furnace for casting preparation. Nitrogen protection is used during the transfer process to physically isolate the air and reduce the risk of oxidation and impurity absorption during the transfer process. The surface of the copper liquid in the casting furnace is covered with graphite flakes to prevent oxidation of the copper liquid. The copper liquid in the casting furnace is kept warm at a temperature of 1185℃ for 10 minutes.

[0116] S2.Continuous Casting

[0117] The casting furnace continuously casts the molten copper into tube billets horizontally at a pulling speed of 350 mm / min, with a primary cooling water flow rate of 35 L / min and a secondary cooling water flow rate of 69 L / min. The tube billets have an outer diameter of 92 mm, an inner diameter of 38.5 mm, and a cut length of 8 m. The tube billets are then milled to a depth of 1 mm to remove surface oxide scale and prevent surface defects from penetrating the material during subsequent rolling.

[0118] S3. Rolling

[0119] The continuous casting tube billet is reduced in diameter by three-roll planetary rolling. During the rolling process, the tube billet generates heat through friction and assists deformation. The rolling speed is 1.4m / min, the outer diameter is reduced to 51mm, and the wall thickness is reduced to 2.4mm.

[0120] S4. Lianla

[0121] The rolled intermediate tube was subjected to joint drawing and diameter reduction at a speed of 72 m / min. The outer diameter of the tube was reduced to 31 mm and the wall thickness was reduced to 1.4 mm.

[0122] S5. Single recrystallization process

[0123] The intermediate tube was subjected to seven winding passes, with the first winding pass at a speed of 450 m / min, the second to sixth winding passes at a speed of 660 m / min, and the seventh winding pass at a speed of 620 m / min. This resulted in a smooth tube with an outer diameter of 9.52 mm and a wall thickness of 0.55 mm, with a total deformation of 88.1%. The tube was then subjected to a final annealing process in a vacuum atmosphere at a temperature of 580°C for 90 minutes, yielding the copper alloy tube of Example 1. The specific chemical composition of the tube is shown in Table 1.

[0124] The preparation method of Example 2 is the same as that of Example 1, except that, in step S1, the chemical composition and raw material ratio of the copper alloy are different. The specific chemical composition is shown in Table 1.

[0125] The difference between Example 3 and Example 1 is that:

[0126] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 1.

[0127] In step S5, the annealing temperature is 600° C. and the annealing time is 90 min. The purpose of changing the annealing temperature is to make the degree of complete recrystallization of each embodiment consistent after the chemical composition changes, that is, the average grain size excluding twin boundaries is similar.

[0128] Example 4

[0129] The difference between this embodiment and embodiment 1 is that:

[0130] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 1.

[0131] In step S5, the annealing temperature is 600° C. and the annealing time is 90 minutes.

[0132] Examples 5-6

[0133] Examples 5 and 6 provide a light pipe made of a copper alloy containing Sn, Ni, and P and a method for preparing the light pipe using a repeated recrystallization process.

[0134] The difference between Example 5 and Example 1 is that,

[0135] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 1.

[0136] The step S5 is a repeated recrystallization process, and the specific process is as follows:

[0137] The intermediate tube billet undergoes two coiling passes, with the first pass at a coiling speed of 450 m / min and the second at a coiling speed of 660 m / min. The outer diameter is reduced to 21 mm, the wall thickness to 0.98 mm, and the total coiling deformation is 52.7%. A "coil-and-anneal" cycle is then implemented. In the first cycle, the coiling deformation is 30.3%, the coiling speed is 600 m / min, the annealing temperature is 530°C, and the annealing time is 20 minutes. In the second cycle, the coiling deformation is 29.4%, the coiling speed is 600 m / min, the annealing temperature is 530°C, and the annealing time is 20 minutes. In the third cycle, the coiling deformation is 29.2%, the coiling speed is 600 m / min, the annealing temperature is 530°C, and the annealing time is 20 minutes. In the fourth cycle, the coiling deformation was 27.9%, the coiling speed was 600 m / min, the annealing temperature was 530° C., and the annealing time was 20 min. The copper alloy tube of Example 5 was obtained, and its specific chemical composition is shown in Table 1.

[0138] The difference between Example 6 and Example 5 is that:

[0139] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 1.

[0140] In the step S5, the annealing temperature is 540°C.

[0141] Examples 7 to 10

[0142] Examples 7 to 10 provide a copper alloy light tube containing Sn, Ni, P, Zr, and Co and a preparation method thereof using a single recrystallization process route.

[0143] The difference between Examples 7 and 9 and Example 1 is that:

[0144] In step S1, the chemical composition and raw material ratio of the copper alloy vary. In addition to adding the copper-nickel master alloy, phosphorus-copper master alloy, and copper-tin master alloy according to the designed ratio, a copper-cobalt master alloy (Cu-10% Co) and a copper-zirconium master alloy (Cu-10% Zr) are also required. The specific chemical composition is shown in Table 1.

[0145] The difference between Examples 8 and 10 and Example 7 is that:

[0146] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 1.

[0147] In the step S5, the annealing temperature is 620°C.

[0148] Example 11

[0149] This embodiment provides a copper alloy light tube containing Sn, Ni, P, Zr, Co, and B and a preparation method thereof using a single recrystallization process route.

[0150] The difference between this embodiment and embodiment 7 is that:

[0151] In step S1, the chemical composition and raw material ratio of the copper alloy vary. In addition to adding copper-nickel master alloy, copper-cobalt master alloy, copper-zirconium master alloy, phosphorus-copper master alloy, and copper-tin master alloy according to the designed ratio, a copper-boron master alloy (Cu-5%B) is also required. The specific chemical composition is shown in Table 1.

[0152] Examples 12 to 15

[0153] Examples 12 to 15 provide a copper alloy light tube containing Sn, Ni, P, Zr, Co and optionally B, and a preparation method thereof using a repeated recrystallization process.

[0154] The chemical composition of Example 12 is the same as that of Example 7 (the same batch of ingots), and the difference is that step S5 is a repeated recrystallization process.

[0155] The repeated recrystallization process used in Example 12 is the same as that in Example 5.

[0156] The difference between Example 13 and Example 12 is that,

[0157] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 1.

[0158] In the repeated recrystallization process of step S5, the annealing temperature of the "disk pulling-annealing" cycle process is 540° C. and the annealing time is 20 minutes to allow the alloy to be completely recrystallized.

[0159] The difference between Examples 14 and 15 and Example 13 is that in step S1, the chemical composition and raw material ratio of the copper alloy are different. The specific chemical composition is shown in Table 1.

[0160] Example 16

[0161] This embodiment provides a copper alloy internally threaded tube containing Sn, Ni, P, Zr, Co, and B and a preparation method thereof using a repeated recrystallization process route.

[0162] This embodiment has the same chemical composition as that of embodiment 15 (same batch of castings), except that:

[0163] In step S5, the fourth cycle is replaced by the "internal thread forming→internal thread tube annealing" process, and the tube blank after the third cycle is spun at a spinning speed of 550 r / m to form an internal threaded tube of 7 mm*0.23 mm+0.1 mm (outer diameter*bottom wall thickness+tooth height), and then annealed at an annealing temperature of 570°C for 30 min.

[0164] Comparative Example 1

[0165] This comparative example provides an existing copper tube sample of Zhejiang Hailiang Co., Ltd., which is made of TP2 light tube with a specification of 9.52mm*0.55mm (outer diameter*wall thickness). Its specific composition is shown in Table 2.

[0166] Comparative Example 2

[0167] This comparative example provides an existing copper tube sample of Zhejiang Hailiang Co., Ltd., which is made of TP2 internal threaded tube with a specification of 7mm*0.23mm+0.1mm. Its specific composition is shown in Table 2.

[0168] Comparative Example 3

[0169] This comparative example provides a Cu-Sn-Ni-P copper alloy material with high Sn content and high f2 value and the specific steps for preparing the same using a single recrystallization process route.

[0170] The difference between this comparative example and Example 1 is that

[0171] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 2.

[0172] In step S5, the annealing temperature is 620° C. and the annealing time is 90 minutes.

[0173] Comparative Example 4

[0174] This comparative example provides a Cu-Sn-Ni-P copper alloy light tube with low f1 and f2 values ​​and specific steps for preparing the tube using a single recrystallization process.

[0175] The difference between this comparative example and Example 1 is that

[0176] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 2.

[0177] In step S5, the annealing temperature is 620° C. and the annealing time is 90 minutes.

[0178] Comparative Example 5

[0179] This comparative example provides a Cu-Sn-Ni-P copper alloy light tube with high Ni content and low f2 value and specific steps for preparing the same using a single recrystallization process.

[0180] The difference between this comparative example and Example 1 is that

[0181] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 2. The melting temperature is increased to 1250°C.

[0182] In step S5, the pulling speed of the second to sixth passes is 600 m / min, the pulling speed of the seventh pass is 550 m / min, the finished product annealing temperature is 650° C., and the annealing time is 90 min.

[0183] Comparative Example 6

[0184] This comparative example provides a Cu-Sn-Ni-P copper alloy light tube with high Sn content and high f1 and f2 values ​​and specific steps for preparing the tube using a single recrystallization process.

[0185] The difference between this comparative example and Example 1 is that

[0186] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 2. The melting temperature is increased to 1250°C.

[0187] In step S5, the pulling speed of the second to sixth passes is 600 m / min, the pulling speed of the seventh pass is 550 m / min, the finished product annealing temperature is 650° C., and the annealing time is 90 min.

[0188] Comparative Example 7

[0189] This comparative example provides a Cu-Sn-Ni-P-Zr-Co copper alloy light tube with high Co and Zr content and specific steps for preparing the tube using a single recrystallization process.

[0190] The difference between this comparative example and Example 7 is that

[0191] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 2.

[0192] In step S5, the pulling speed of the second to sixth passes is 600 m / min, the pulling speed of the seventh pass is 550 m / min, the finished product annealing temperature is 650° C., and the annealing time is 90 min.

[0193] Comparative Example 8

[0194] This comparative example provides a Cu-Sn-Ni-P-Zr-Co-B copper alloy light tube with high Zr, Co, and B contents and specific steps for preparing the tube using a single recrystallization process.

[0195] The difference between this comparative example and Example 11 is that

[0196] In step S1, the chemical composition and raw material ratio of the copper alloy are different, and the specific chemical composition is shown in Table 2. The melting temperature is increased to 1250°C.

[0197] In step S5, the pulling speed of the second to sixth passes is 600 m / min, the pulling speed of the seventh pass is 550 m / min, the finished product annealing temperature is 650° C., and the annealing time is 90 min.

[0198] The chemical composition and f1 and f2 values ​​of the copper alloys of the embodiments of the present invention and the comparative examples are shown in Tables 1 and 2. The low Σ value heavy site lattice grain boundary ratio and the average grain size of the copper alloys of the embodiments of the present invention and the comparative examples are shown in Table 3. A detailed table of the low Σ value heavy site lattice grain boundary ratio of the copper alloys of the embodiments of the present invention and the comparative examples and the effect of the number of cycles of the repeated recrystallization process on the heavy site lattice grain boundary ratio are shown in Table 4. The mechanical properties, bursting pressure and processing and forming properties of the copper alloys of the embodiments of the present invention and the comparative examples are shown in Table 5. The anthill corrosion resistance of the copper alloys of the embodiments of the present invention and the comparative examples is shown in Table 6.

[0199] Examples 1 to 3 and Comparative Example 1 show that when the Ni and P contents remain essentially unchanged, with the increase of Sn content, the f1 and f2 values ​​increase accordingly, and the proportions of Σ3, Σ9 and Σ27 lattice boundaries increase to 57.36%, 61.12% and 62.97%, respectively (see Table 3 and Table 4). Figure 3 (a) Figure 3 (b) Figure 3 (c) Figure 3(d)), and the XRD test results show that it has a single α phase (see Figure 2 ). At the same time, it can be seen from Examples 1-3 that the yield strength and tensile strength of the copper alloy increase synchronously with the increase of Sn content (see Table 5), which proves that the Sn element has a significant solid solution strengthening effect and can simultaneously improve the yield strength and tensile strength. Compared with Comparative Example 1, the tensile strengths of Examples 1, 2, and 3 increased by 12.1%, 17.7%, and 21.1%, respectively, but the yield strength of Example 1 did not exceed that of Comparative Example 1, indicating that the high Σ3, Σ9, and Σ27 heavy site lattice grain boundaries are conducive to providing a high proportion of low-energy, coherent low Σ value heavy site lattice grain boundaries. The ability of this part of the grain boundary to restrict dislocation movement in the early stage of plastic deformation is lower than that of random high-angle grain boundaries. Therefore, the low yield strength can be maintained to a certain extent by reducing the obstruction of the interface to dislocation movement in the early stage of deformation, so that the yield strength ratio is reduced to within 0.30.

[0200] According to Table 5, the bursting pressure of copper alloy tubes of the same specification increases with the increase of Sn content. The bursting pressures of Examples 1, 2, and 3 are respectively increased by 7.3%, 14.2%, and 20.7% compared with Comparative Example 1. The post-blasting pressure decay rates of the welded pipes of Examples 1, 2, and 3 are all lower than 10.0%. This is because the introduction of high-proportion, low-Σ value heavy-site lattice grain boundaries inhibits grain boundary migration and abnormal grain growth at high temperatures to a certain extent, thereby reducing the post-blasting pressure decay rate of the welded pipes. The fracture locations and morphologies of the samples after the hydraulic blasting test of Example 2 and the welded pipe after the hydraulic blasting test are shown in FIG. Figure 6 .

[0201] According to Table 6, under the same formic acid atmosphere corrosion conditions, the maximum corrosion depths of Examples 1, 2, and 3 gradually decrease compared to Comparative Example 1, and their corrosion resistance is improved by 15.8%, 17.9%, and 21.5%, respectively. Compared with Comparative Example 1, Examples 1 to 3 have a certain Ni content, which helps to improve corrosion resistance. Although the Ni content of Examples 1 to 3 is similar, Example 3 has a higher total amount of Σ3, Σ9, and Σ27. These low-Σ value heavy site lattice grain boundaries have better coherence, lower energy, and very little impurity element segregation. They are channels that are difficult to expand corrosion and do not have the effect of promoting the corrosion process of random high-angle grain boundaries. As (Σ9+Σ27) / Σ3 increases (see Table 4 for data of Examples 1 to 3 and Comparative Example 1), the original random high-angle grain boundary grid is broken, and the original intergranular corrosion channel is interrupted, thereby slowing down the anthill corrosion process to a certain extent.

[0202] The corrosion resistance of Examples 1, 2, and 3 after bending is also improved compared to Comparative Example 1, and the corrosion resistance attenuation rate at the bend is less than 17.0%, indicating that the high total amount of Σ3, Σ9, and Σ27 also has a certain resistance to the conditions of stress corrosion and intergranular corrosion promoting anthill corrosion. Figure 7It can be seen that compared with Comparative Example 1, Example 2 has a more uniform strain distribution after 5% tensile deformation and a lower average KAM value, that is, its strain concentration is much lower than that of TP2 copper, indicating that a finer grain size (twin boundaries) and a high proportion of low Σ value heavy site lattice grain boundaries are conducive to promoting uniform strain distribution, thereby reducing stress and intergranular corrosion.

[0203] Example 4 increases the Ni content compared to Example 2, resulting in a slightly lower f2 value, reducing the total amount of Σ3, Σ9, and Σ27 to 57.42%. However, due to the higher Ni content, it exhibits improved formicary corrosion resistance, an 8.8% improvement over Example 2. However, due to the slightly lower total amount of Σ3, Σ9, and Σ27, the corrosion resistance degradation rate at the bend is slightly higher than that of Example 2.

[0204] Examples 2 and 3 demonstrate that by controlling the f1 and f2 values ​​within the preferred ranges of 0.65% ≤ f1 ≤ 1.05% and 3.4 ≤ f2 ≤ 5, the tensile strength of the copper alloy can be further increased to 275 MPa or above while maintaining a low yield ratio. This allows the copper alloy to meet the requirements of tube bending, expansion, and flaring processes while further improving its pressure resistance, corrosion resistance, and thermal softening resistance. Compared to Comparative Example 1, Example 1's burst pressure and single-tube corrosion resistance increased by only 7.3% and 15.8%, respectively, while Example 3 achieved increases of 20.7% and 21.5%, respectively. This demonstrates that the copper alloy tubes prepared after this optimization significantly improve both pressure resistance and corrosion resistance. Furthermore, Example 3 exhibits reduced burst pressure decay and corrosion resistance decay compared to Example 1.

[0205] Comparative Example 3 shows that when the Sn atom concentration reaches the limit of dilute solid solution solute atoms, the distance between solute atoms will become smaller, which will dramatically increase the solute atoms' ability to hinder dislocation movement. As a result, the beneficial effect of reducing the yield ratio brought by the low Σ value heavy site lattice grain boundaries in Comparative Example 3 is almost offset by the hardening effect brought by the solute atoms, which is manifested as a good bending test but a failed flaring test.

[0206] Comparative Example 4 shows that when the values ​​of f1 and f2 are too low, the total amount of Σ3, Σ9 and Σ27 cannot reach more than 50%, and it is difficult to maintain good processing formability. Therefore, although the strength of Comparative Example 4 is improved and the bending test is qualified, the expansion performance is poor.

[0207] Comparative Example 5 shows that even if the copper alloy with a high Ni content has a suitable f1 value, its elongation after fracture will be significantly deteriorated, the yield strength ratio is as high as 0.40, the expansion performance is extremely poor, and the bending performance cannot meet the requirements.

[0208] Comparative Example 6 shows that the high Sn content can bring about a strong hardening effect. This hardening effect makes Comparative Example 6 have a yield ratio as high as 0.39 and extremely poor expansion performance, and the bending performance also fails to meet the requirements.

[0209] Comparison of Examples 5 and 6 with Examples 2 and 3 demonstrates that, when using a repeated recrystallization process to prepare copper alloys with similar chemical compositions, the total amount of Σ3, Σ9, and Σ27 can be effectively accumulated through cyclic processing, increasing from approximately 60% to 72-75% (see Table 3), while slightly reducing the average grain size (including twin boundaries). For Examples 2 and 5, the (Σ9 + Σ27) / Σ3 ratio increased from 4.3% to 12.5% ​​(see Table 4), demonstrating that Example 5 exhibits significant improvements in tensile strength and pressure resistance, while reducing the yield ratio, while maintaining a yield strength similar to that of Example 2. The post-blasting pressure decay rate of the welded pipe in Example 5 is only 3.2%, and the corrosion resistance decay rate at the bend is only 6.2%, demonstrating that a high proportion of Σ3, Σ9, and Σ27 heavy-site lattice grain boundaries and a high (Σ9 + Σ27) / Σ3 ratio are beneficial for improving the copper alloy's resistance to high-temperature softening and mitigating corrosion caused by grain boundaries and stress.

[0210] Comparisons of Examples 7 and 9 with Example 2, and of Examples 8 and 10 with Example 3, show that the trace addition of Zr, in addition to the composite addition of Sn, Ni, and P, further improves the alloy's f1 value, increases the proportion of Σ3, Σ9, and Σ27 heavy-site grain boundaries, further enhances tensile strength and burst pressure, and maintains a low yield ratio of approximately 0.22 to 0.29. The trace addition of Co can generally reduce the attenuation rate after welding to less than 6%. Comparison of Example 10 with Example 8 shows that further increasing the Zr and Co content further enhances the alloy's pressure resistance, corrosion resistance, and high-temperature softening resistance. Particularly notably, the addition of Co and Zr significantly reduces the alloy's burst pressure attenuation rate.

[0211] Comparative Example 7 shows that when the Sn and Ni contents are appropriate, excessive Zr and Co additions will reduce the elongation after fracture and increase the yield strength ratio due to the introduction of hard and brittle second phases, while deteriorating the bending and flaring performance.

[0212] Comparison of Example 11 with Example 7 demonstrates that trace addition of element B effectively reduces the alloy's oxygen content to below 15 ppm, significantly refining the size of the cast dendrite structure. Compared to Example 7, Example 11's formicary corrosion resistance improves from 18.7% to 23.5% relative to that of the TP2 alloy.

[0213] Comparative Example 8 shows that the addition amounts of Zr, Co, and B elements cannot be too high, otherwise the hard-brittle phase inclusions formed will greatly increase the yield strength and yield strength ratio and reduce the ductility, thereby reducing the processing formability and seriously deteriorating the bending and flaring performance.

[0214] Examples 12 to 15 show that by comprehensively adjusting the contents of Sn, Ni, P, Zr, Co, and B, and making the f1 and f2 values ​​both at relatively optimal levels, and adopting a repeated recrystallization process, the comprehensive properties of the copper alloy tube can be effectively improved. Compared with Comparative Example 1, the tensile strength of Example 12 is increased by about 27.6% (see Figure 4 ), and the copper alloy tube has a yield strength ratio of no more than 0.25 and excellent processing and forming properties. Its bursting pressure is increased by more than 30%, but the bursting pressure decay rate after welding is less than 2%. Under the same test conditions, the maximum corrosion depth of the single tube is less than 150μm, and the maximum corrosion depth at the bend is less than 160μm. XRD patterns show that reasonable control of the content of Zr, Co, and B can ensure that the copper alloy forms a single α phase solid solution without precipitation of hard and brittle second phases (see Figure 2 ). The Sn and Ni contents of Example 12 are basically the same as those of Example 2, but the Zr, Co, and B contents are significantly higher. The addition of Zr helps to offset the hardening effect brought by the Ni, Co, and B elements, and enables the copper alloy to have a high total amount of Σ3, Σ9, and Σ27, so that it maintains a low yield ratio of 0.25. Co is beneficial to improving the high-temperature softening resistance of the copper alloy. Due to the effect of Co, the bursting pressure decay rate of Example 12 is only 1.8%. B mainly improves the quality of the ingot and reduces the oxygen content, ensuring the successful preparation of low-oxygen copper alloy materials without casting defects using existing equipment.

[0215] Example 16 shows that the high-performance copper alloy tube of the present invention and the combined recrystallization treatment process can be applied to the preparation of internally threaded tubes, and its various performance indicators can achieve the expected results.

[0216] Table 4 and Figure 3 It shows that the number of recrystallization cycles in the repeated recrystallization process has a significant impact on the proportion of Σ3, Σ9, and Σ27 multi-site lattice grain boundaries. By analyzing the grain boundary distribution diagrams of the samples of Examples 5, 13, and 15 after 3 cycles of repeated recrystallization and 4 cycles of repeated recrystallization, it can be seen that increasing the number of recrystallization cycles can not only increase the proportion of Σ3 multi-site lattice grain boundaries, but also significantly increase the proportion of Σ9, Σ27a, and Σ27b multi-site lattice grain boundaries, thereby increasing the (Σ9+Σ27) / Σ3 ratio and reducing the connectivity of the random high-angle grain boundary network. However, it is obvious that when the number of cycles is too small, such as less than 3 recrystallization cycles, the comprehensive performance and cost balance brought by the repeated recrystallization process will not be as good as the single recrystallization process. Similarly, after the number of cycles reaches 6, the proportion of low-Σ value heavy site lattice grain boundaries tends to be saturated, and even if the recrystallization cycle is repeated, it is difficult to increase the total amount of Σ3, Σ9 and Σ27. Therefore, after the number of cycles exceeds 6, the comprehensive performance and cost balance brought by the repeated recrystallization process is not as good as the repeated recrystallization process with a cycle number between 3 and 6.

[0217] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0218] Table 1 Chemical composition of Examples 1 to 16

[0219]

[0220] Table 2 Chemical composition of comparative examples 1 to 8

[0221]

[0222]

[0223] Table 3 Low Σ value heavy site grain boundary ratio and average grain size of copper alloys in Examples and Comparative Examples

[0224]

[0225] Table 4 Detailed table of the proportion of low Σ value lattice grain boundaries of copper alloys in the embodiment and comparative example and the effect of the number of cycles of repeated recrystallization process on the proportion of lattice grain boundaries

[0226]

[0227] Table 5 Mechanical properties, blasting pressure and processing properties of copper alloys in Examples and Comparative Examples

[0228]

[0229]

[0230] Note: “○” represents qualified; “×” represents unqualified; “-” represents that there is no data for the item or the test has not failed.

[0231] Table 6 Ant pit corrosion resistance of copper alloys in Examples and Comparative Examples

[0232]

Claims

1. A high performance copper alloy tube, characterized in that: Composed of the following components in percentage by mass: 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, with the balance being Cu and unavoidable impurities; and f1 = [Sn] + 10 [P], f2 = [Sn] / [Ni], f1 and f2 satisfy: 0.5% ≤ f1 ≤ 1.05%, 1 < f2 ≤ 5, wherein [Sn], [P] and [Ni] are the percentage by mass of Sn, P and Ni, respectively; The copper alloy tube has a single face-centered cubic crystal structure α phase; the average grain size excluding twin boundaries is 10 to 25 μm, and the average grain size including twin boundaries is 5 to 20 μm; the total proportion of Σ3, Σ9 and Σ27 multisite lattice grain boundaries in the copper alloy tube is ≥50%, and the ratio of the proportions of Σ9, Σ27 and Σ3 multisite lattice grain boundaries satisfies: (Σ9+Σ27) / Σ3≥3.5%.

2. The high performance copper alloy tube according to claim 1, characterized in that: The copper alloy tube has a tensile strength of ≥260 MPa, a yield strength ratio of 0.23 to 0.30, a bursting pressure attenuation rate of ≤10%, and after 21 days of alternating hot and cold corrosion in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of a single tube is ≤170 μm, and the maximum corrosion depth at the bend is ≤190 μm.

3. A high performance copper alloy tube, characterized in that: Composed of the following components in percentage by mass: 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, with the balance being Cu and unavoidable impurities; and f1 = [Sn] + 10 [P], f2 = [Sn] / [Ni], f1 and f2 satisfy: 0.5% ≤ f1 ≤ 1.05%, 1 < f2 ≤ 5, wherein [Sn], [P] and [Ni] are the percentage by mass of Sn, P and Ni, respectively; The copper alloy tube has a single face-centered cubic crystal structure α phase; the average grain size excluding twin boundaries is 10 to 25 μm, and the average grain size including twin boundaries is 5 to 20 μm; the total proportion of Σ3, Σ9 and Σ27 multisite lattice grain boundaries in the copper alloy tube is ≥68%, and the ratio of the proportions of Σ9, Σ27 and Σ3 multisite lattice grain boundaries satisfies: (Σ9+Σ27) / Σ3 ≥10%.

4. The high performance copper alloy tube according to claim 3, characterized in that: The copper alloy tube has a tensile strength of ≥285MPa, a yield strength ratio of 0.21-0.28, and a blast attenuation rate of ≤5%. After 21 days of alternating hot and cold corrosion in a 0.4% formic acid aqueous solution atmosphere, the maximum corrosion depth of a single tube is ≤155μm, and the maximum corrosion depth at the bend is ≤165μm.

5. A high performance copper alloy tube, characterized in that: Composed of the following components in percentage by mass: 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, 0.001% ≤ Zr < 0.03%, 0.001% ≤ Co < 0.01%, 0 ≤ B < 0.01%, the balance being Cu and unavoidable impurities; and f1 = [Sn] + 10 [P] + 10 [Zr], f2 = [Sn] / [Ni], f1 and f2 satisfy: 0.65% ≤ f1 < 1.15%, 1 < f2 ≤ 5, wherein [Sn], [P], [Zr], and [Ni] are the percentage by mass of Sn, P, Zr, and Ni, respectively; The copper alloy tube has a single face-centered cubic crystal structure α phase; the average grain size excluding twin boundaries is 10 to 25 μm, and the average grain size including twin boundaries is 5 to 20 μm; the total proportion of Σ3, Σ9 and Σ27 multisite lattice grain boundaries in the copper alloy tube is ≥60%, and the ratio of Σ9, Σ27 and Σ3 multisite lattice grain boundaries satisfies: (Σ9+Σ27) / Σ3 ≥4.0%.

6. The high performance copper alloy tube according to claim 5, characterized in that: The copper alloy tube has a tensile strength of ≥275 MPa, a yield strength ratio of 0.22 to 0.29, and a blasting attenuation rate of ≤6%. After 21 days of alternating hot and cold corrosion in a 0.4% formic acid aqueous solution atmosphere, the maximum corrosion depth of a single tube is ≤165 μm, and the maximum corrosion depth at the bend is ≤180 μm.

7. The high performance copper alloy tube according to claim 5 or 6, characterized in that: 0.001％≤B＜0.01％。 8. The high performance copper alloy tube according to claim 7, characterized in that: After the copper alloy tube is subjected to hot and cold alternating corrosion for 21 days in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of a single tube is ≤155 μm, and the maximum corrosion depth at the bend is ≤170 μm.

9. A high performance copper alloy tube, characterized in that: Composed of the following components in percentage by mass: 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, 0.001% ≤ Zr < 0.03%, 0.001% ≤ Co < 0.01%, 0 ≤ B < 0.01%, the balance being Cu and unavoidable impurities; and f1 = [Sn] + 10 [P] + 10 [Zr], f2 = [Sn] / [Ni], f1 and f2 satisfy: 0.65% ≤ f1 < 1.15%, 1 < f2 ≤ 5, wherein [Sn], [P], [Zr], and [Ni] are the percentage by mass of Sn, P, Zr, and Ni, respectively; The copper alloy tube has a single face-centered cubic crystal structure α phase; the average grain size excluding twin boundaries is 10 to 25 μm, and the average grain size including twin boundaries is 5 to 20 μm; the total proportion of Σ3, Σ9 and Σ27 multisite lattice grain boundaries in the copper alloy tube is ≥72%, and the ratio of Σ9, Σ27 to Σ3 multisite lattice grain boundaries satisfies: (Σ9+Σ27) / Σ3 ≥12%.

10. The high performance copper alloy tube according to claim 9, characterized in that: The copper alloy tube has a tensile strength of ≥295 MPa, a yield strength ratio of 0.20 to 0.27, and a blasting attenuation rate of ≤2%. After 21 days of alternating hot and cold corrosion in a 0.4% formic acid aqueous solution atmosphere, the maximum corrosion depth of a single tube is ≤150 μm, and the maximum corrosion depth at the bend is ≤160 μm.

11. The high performance copper alloy tube according to claim 9 or 10, characterized in that: 0.001％≤B＜0.01％。 12. The high performance copper alloy tube according to claim 11, characterized in that: After the copper alloy tube is subjected to hot and cold alternating corrosion for 21 days in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of a single tube is ≤145 μm, and the maximum corrosion depth at the bend is ≤155 μm.

13. The method for preparing a high performance copper alloy tube according to any one of claims 1 to 12, characterized in that: The following steps are involved: Ingredient smelting: smelting the raw materials that meet the proportion; Continuous casting: Continuously casting the molten metal into billets; Rolling: rolling the billet to obtain a rolled tube; Joint drawing: reducing the diameter of the rolled tube; Recrystallization treatment: By controlling the deformation amount and annealing parameters, products with target performance are obtained.

14. The method for preparing a high performance copper alloy tube according to claim 13, wherein: The recrystallization treatment is a single recrystallization, and the single recrystallization is "disk pulling→finished product annealing". The total deformation of the disk pulling is not less than 80%, the finished product annealing temperature is 500-750° C., and the annealing time is 30-150 minutes.

15. The method for preparing a high performance copper alloy tube according to claim 13, wherein: The recrystallization treatment is repeated recrystallization, wherein the repeated recrystallization is performed after 1 to 3 passes of coil drawing and then multiple cycles of "coil drawing → annealing", wherein the total deformation of the first 1 to 3 coil drawing passes of the cycle is ≤72%; in the multiple cycles of "coil drawing → annealing", the number of cycles of "coil drawing → annealing" is 3 to 6, the coil drawing deformation in a single cycle is 25 to 35%, the annealing temperature is 500 to 600°C, and the annealing time is 10 to 70 minutes.

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