Forming process of high-strength corrosion-resistant copper alloy pipe

Abstract

The application provides a high-strength corrosion-resistant copper alloy pipe forming process and belongs to the technical field of metal material processing. The process comprises the following steps: S1, preparation of multi-element micro-alloyed ingot; S2, gradient preheating and dynamic temperature field regulation, so that the front end temperature of the ingot is 50-150 DEG C lower than the rear end before extrusion and dynamic compensation is performed; S3, composite shear extrusion forming is performed by using an extrusion die with spiral grooves; S4, an in-situ reaction is performed on a boron-containing reinforcing phase precursor to generate zirconium boride and / or carbide ceramic reinforcing particles; S5, ultrasonic-assisted online solid solution treatment; S6, multi-field synergistic treatment is performed by applying an alternating electromagnetic field and then an ultrasonic vibration field on a cooling path. Through gradient preheating, composite shear deformation, in-situ self-reinforcement, ultrasonic-assisted solid solution and electromagnetic-ultrasonic multi-field synergistic regulation, the application effectively refines the grains, homogenizes the structure, eliminates residual stress and improves the mechanical properties and corrosion resistance of the copper alloy pipe.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, specifically to a high-strength corrosion-resistant copper alloy tube forming process. Background Technology

[0002] Copper alloy pipes, due to their excellent mechanical properties, corrosion resistance, and processability, are widely used in high-end equipment fields such as marine engineering and petrochemicals. In particular, large-diameter, high-strength, corrosion-resistant copper alloy pipes, as key structural components of offshore drilling platforms and seawater desalination systems, directly determine the service life of the equipment.

[0003] Currently, large-diameter copper alloy tubing is mainly manufactured using hot extrusion molding, but existing technology still faces the following bottlenecks:

[0004] I. Inherent Defects in the Method of Introducing Ceramic Reinforcing Phase

[0005] Introducing ceramic reinforcing phases into a copper matrix is ​​an effective way to improve material strength. While the external particle method is simple to operate, the poor wettability of ceramic particles with the copper matrix leads to agglomeration, resulting in insufficient interfacial bonding strength and uneven microstructure. The in-situ self-generation method, through a chemical reaction within the matrix, directly generates the reinforcing phase, achieving thermodynamically stable interfacial bonding and a more uniform particle distribution. However, existing in-situ preparation methods generally suffer from complex processes and difficulties in continuous production, especially for the molding of large-diameter pipes, where a mature industrialization solution is still lacking.

[0006] II. It is difficult to achieve uniform microstructure while controlling the extrusion temperature field.

[0007] During hot extrusion, the uneven distribution of deformation heat generated in the deformation zone and the uneven heat dissipation from the die results in a highly non-uniform temperature field. Studies have shown that extrusion temperature directly affects grain size evolution: excessively high temperatures lead to abnormal grain growth, while excessively low temperatures result in insufficient recrystallization. Simultaneously, temperature differences between the inside and outside of the ingot affect metal flow patterns, leading to anisotropy in the microstructure and properties of the tubing. Existing uniform heating methods are insufficient to effectively compensate for deformation heat, and the gradient heating mode (higher at the beginning and lower at the end) does not match the generation pattern of deformation heat, thus having limited effect on improving microstructure uniformity.

[0008] Third, there is a lack of synergistic technologies for online organizational control and residual stress reduction.

[0009] The traditional step-by-step production model of "forming-heat treatment-straightening" suffers from problems such as lengthy processes, low efficiency, and surface oxidation caused by repeated heating. Although ultrasonic vibration technology has been proven to effectively control micro-stress distribution and refine grains, and electromagnetic field treatment can also promote nucleation behavior during solidification and phase transformation, a technical solution that combines the application of both in segments according to temperature ranges to achieve full-process microstructure control has not been reported in existing literature.

[0010] In conclusion, developing a novel molding process that enables integrated control of the entire process, including component design, temperature regulation, composite deformation, and in-situ strengthening, has significant technological value and promising industrial application prospects. Summary of the Invention

[0011] The purpose of this invention is to provide a high-strength corrosion-resistant copper alloy tube forming process. By using gradient preheating, spiral groove composite shearing extrusion, in-situ nano-reinforcement, and multi-field synergistic treatment, the problem of uneven microstructure and poor corrosion resistance of copper alloy tubes is solved.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A high-strength, corrosion-resistant copper alloy tube forming process includes the following steps:

[0014] S1. Preparation of multi-element microalloyed ingot: 0.05-0.5 wt% of rare earth elements and 0.1-1.0 wt% of microalloying elements are added to a copper matrix and then smelted and cast to obtain a multi-element microalloyed copper alloy ingot, wherein the microalloying elements include zirconium and / or hafnium.

[0015] S2. Gradient preheating and dynamic temperature field control: The multi-element micro-alloyed copper alloy ingot is placed in a preheating device with axial gradient heating function to establish a gradient temperature field along the extrusion direction, so that the temperature at the front end of the ingot extrusion is 50-150°C lower than the temperature at the back end of the extrusion. During the extrusion process, the temperature of the deformation zone is monitored in real time by a temperature sensor set in the deformation zone of the die. When the deviation between the temperature of the deformation zone and the preset target temperature exceeds ±30°C, dynamic compensation is performed by adjusting the extrusion speed.

[0016] S3, Composite Shear Extrusion Forming: The ingot, which has been preheated by gradient, is fed into an extrusion die for hot extrusion. The extrusion die includes a compression zone, a shear deformation zone and an expansion zone arranged sequentially along the extrusion direction. The inner wall of the shear deformation zone is provided with a spiral groove, so that the metal generates axial and circumferential composite shear deformation during the extrusion process.

[0017] S4. In-situ self-generated composite reinforcement: During the extrusion forming process, boron-containing reinforcing phase precursor powder is introduced online into the inlet of the shear deformation zone of the extrusion die. The reinforcing phase precursor powder is transported by an inert gas carrier. Utilizing the extrusion temperature and pressure during the extrusion process and the reactivity of zirconium and / or hafnium elements in the ingot, the reinforcing phase precursor reacts with zirconium and / or hafnium elements through solid-phase reaction or substitution reaction to generate zirconium boride and / or zirconium carbide ceramic phase reinforcing particles, which are dispersed in the copper alloy matrix.

[0018] S5. Ultrasonic-assisted online solid solution and grain refinement control: An ultrasonic vibration device is set at the extrusion outlet to apply ultrasonic vibration to the extruded copper alloy tube and perform online solid solution treatment at the same time. The heating method of the online solid solution treatment is induction heating, and the heating temperature is controlled at 850-950℃. The ultrasonic vibration effect is used to promote the homogenization of alloying elements and inhibit grain growth during the solid solution process.

[0019] S6. Multi-field synergistic treatment: On the cooling path of the copper alloy tube from the solution temperature to room temperature, an alternating electromagnetic field is applied first, followed by an ultrasonic vibration field. The alternating electromagnetic field is used to promote the uniform nucleation of precipitates in the initial stage of cooling, and the ultrasonic vibration field is used to eliminate residual stress in the final stage of cooling.

[0020] Preferably, the rare earth element in step S1 includes at least one of cerium, lanthanum, and yttrium, and the microalloying element also includes chromium, and the multi-element dispersed phase is an intermetallic compound formed by rare earth elements and zirconium, hafnium, and chromium.

[0021] Preferably, in step S2, the temperature at the front end of the extrusion is controlled at 650-750°C, and the temperature at the rear end of the extrusion is controlled at 800-900°C.

[0022] Preferably, the spiral angle of the spiral groove in step S3 is 15° to 45°, the groove depth is 0.5 to 3 mm, and the spiral direction of the spiral groove is the same as the extrusion direction.

[0023] Preferably, the compression ratio of the compression zone in step S3 is 5 to 15, and the expansion angle of the expansion zone is 10° to 30°.

[0024] Preferably, the reinforcing phase precursor in step S4 is B4C powder or boron-containing composite powder, and is introduced by argon or nitrogen gas carrier transport, with the blowing amount controlled at 1.3~3.9 kg per ton of copper alloy.

[0025] Preferably, the ultrasonic vibration device in step S5 includes an axial vibration transducer and a radial vibration transducer, the ultrasonic vibration frequency is 15-40kHz, the ultrasonic vibration power is 500-3000W, and the heat preservation time of the online solution treatment is 30-180 seconds.

[0026] Preferably, in step S6, the magnetic field strength of the alternating electromagnetic field is 0.3–0.6 T, the frequency is 10–100 Hz, the electromagnetic field is applied perpendicular to the axis of the copper alloy tube, and the application range is the temperature range from the solution temperature to 500°C; the frequency of the ultrasonic vibration field is 20–40 kHz, and the application range is the temperature range from 300°C to room temperature.

[0027] Preferably, the extrusion die is further provided with a temperature compensation module, which includes a resistance heating element and a temperature sensor embedded in the die wall of the shear deformation zone, for local temperature compensation in the shear deformation zone during the extrusion process.

[0028] Preferably, the ceramic phase reinforcing particles generated by the in-situ reaction in step S4 are nanoscale, and the ceramic phase reinforcing particles are distributed at the grain boundaries and within the grains of the copper alloy.

[0029] Compared with the prior art, the present invention has the following advantages and technical effects:

[0030] I. Achieving Homogeneous Structure and Refined Grain Size. This invention employs axial gradient preheating, ensuring the temperature at the front end of the ingot extrusion is lower than at the rear end. Deformation heat compensation promotes a more uniform temperature in the deformation zone, preventing abnormal grain growth caused by localized overheating. Combined with the spiral groove structure on the inner wall of the shear deformation zone, the metal undergoes both axial and circumferential composite shear deformation during extrusion, increasing equivalent plastic strain, promoting dynamic recrystallization nucleation, and resulting in a uniform and fine grain structure.

[0031] II. Achieving a uniformly dispersed distribution of the nano-reinforcing phase. This invention introduces boron-containing precursor powder online, utilizing the extrusion temperature and pressure, as well as the reactivity of zirconium and hafnium elements in the ingot, to induce a solid-state reaction or substitution reaction between the precursor and the matrix elements, generating in-situ zirconium boride or carbide ceramic reinforcing particles. The reinforcing phase generated in-situ forms a good interfacial bond with the copper matrix, eliminating the problems of poor wettability and agglomeration of externally added particles. The reinforcing particles are distributed at grain boundaries and within grains, achieving a synergistic effect of intragranular strengthening and grain boundary strengthening.

[0032] III. Achieving Homogenization of Alloy Elements and Suppressing Grain Growth. This invention incorporates an ultrasonic vibration device at the extrusion exit, applying ultrasonic vibration to the copper alloy tube while simultaneously performing induction heating for online solution treatment. The ultrasonic vibration effect promotes atomic diffusion, improves solution efficiency, and simultaneously suppresses grain growth, resulting in a uniform and fine solid solution microstructure.

[0033] IV. Achieving Precipitation Phase Control and Residual Stress Elimination. This invention applies an alternating electromagnetic field followed by an ultrasonic vibration field along the cooling path. The electromagnetic field promotes uniform nucleation of the precipitate phase in the initial cooling stage; the ultrasonic vibration field eliminates residual stress in the final cooling stage. Applying the field in stages fully leverages the advantages of each stage and avoids mutual interference.

[0034] V. Synergistic effects of each step form a complete technology chain. Multi-element microalloying provides the necessary elements for in-situ reaction; gradient preheating creates a suitable temperature distribution for extrusion deformation; composite shear deformation refines grains and provides a favorable flow field for powder dispersion; in-situ reaction generates reinforcing phases; ultrasonic-assisted solid solution optimizes the microstructure; and multi-field synergistic treatment regulates precipitated phases and residual stress. These six interconnected steps work together to achieve a synergistic improvement in the strength, plasticity, and corrosion resistance of copper alloy tubes. Attached Figure Description

[0035] Figure 1 Metallographic microscope image of the copper alloy tube prepared in Example 1 of this invention;

[0036] Figure 2 The image shows the secondary electron (SE) morphology of the copper alloy tube prepared in Example 1 of this invention after being immersed in 3.5 wt.% NaCl solution for 7 days.

[0037] Figure 3 The image shows the secondary electron (SE) morphology of the copper alloy tube prepared in Example 1 of this invention after being immersed in a 3.5 wt.% NaCl solution for 15 days.

[0038] Figure 4 The image shows a uniform and dense microstructure obtained by immersing the copper alloy tube prepared in Example 1 of this invention in a 3.5 wt.% NaCl solution for 30 days.

[0039] Figure 5 This is a bar chart comparing the tensile strength of Examples 1-6 and Comparative Examples 1-6 of the present invention;

[0040] Figure 6 This is a bar chart comparing the elongation rates of Examples 1-6 and Comparative Examples 1-6 of the present invention;

[0041] Figure 7 This is a bar chart comparing the corrosion current density of Examples 1-6 and Comparative Examples 1-6 of the present invention. Detailed Implementation

[0042] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0043] In this invention, a high-strength corrosion-resistant copper alloy tube forming process includes the following steps:

[0044] S1. Preparation of multi-element microalloyed ingot: 0.05-0.5 wt% of rare earth elements and 0.1-1.0 wt% of microalloying elements are added to a copper matrix and then smelted and cast to obtain a multi-element microalloyed copper alloy ingot, wherein the microalloying elements include zirconium and / or hafnium.

[0045] S2. Gradient preheating and dynamic temperature field control: The multi-element micro-alloyed copper alloy ingot is placed in a preheating device with axial gradient heating function to establish a gradient temperature field along the extrusion direction, so that the temperature at the front end of the ingot extrusion is 50-150°C lower than the temperature at the back end of the extrusion. During the extrusion process, the temperature of the deformation zone is monitored in real time by a temperature sensor set in the deformation zone of the die. When the deviation between the temperature of the deformation zone and the preset target temperature exceeds ±30°C, dynamic compensation is performed by adjusting the extrusion speed.

[0046] S3, Composite Shear Extrusion Forming: The ingot, which has been preheated by gradient, is fed into an extrusion die for hot extrusion. The extrusion die includes a compression zone, a shear deformation zone and an expansion zone arranged sequentially along the extrusion direction. The inner wall of the shear deformation zone is provided with a spiral groove, so that the metal generates axial and circumferential composite shear deformation during the extrusion process.

[0047] S4. In-situ self-generated composite reinforcement: During the extrusion forming process, boron-containing reinforcing phase precursor powder is introduced online into the inlet of the shear deformation zone of the extrusion die. The reinforcing phase precursor powder is transported by an inert gas carrier. Utilizing the extrusion temperature and pressure during the extrusion process and the reactivity of zirconium and / or hafnium elements in the ingot, the reinforcing phase precursor reacts with zirconium and / or hafnium elements through solid-phase reaction or substitution reaction to generate zirconium boride and / or zirconium carbide ceramic phase reinforcing particles, which are dispersed in the copper alloy matrix.

[0048] S5. Ultrasonic-assisted online solid solution and grain refinement control: An ultrasonic vibration device is set at the extrusion outlet to apply ultrasonic vibration to the extruded copper alloy tube and perform online solid solution treatment at the same time. The heating method of the online solid solution treatment is induction heating, and the heating temperature is controlled at 850-950℃. The ultrasonic vibration effect is used to promote the homogenization of alloying elements and inhibit grain growth during the solid solution process.

[0049] S6. Multi-field synergistic treatment: On the cooling path of the copper alloy tube from the solution temperature to room temperature, an alternating electromagnetic field is applied first, followed by an ultrasonic vibration field. The alternating electromagnetic field is used to promote the uniform nucleation of precipitates in the initial stage of cooling, and the ultrasonic vibration field is used to eliminate residual stress in the final stage of cooling.

[0050] The working mechanism of each step in this invention is as follows:

[0051] S1, Preparation of Multi-element Microalloyed Ingots

[0052] Rare earth elements, along with zirconium and hafnium, form complex intermetallic compounds in a copper matrix, which act as heterogeneous nucleation sites during solidification to refine the as-cast microstructure. Zirconium and hafnium have low diffusion coefficients, and the precipitated nanoscale phases maintain a coherent interface with the copper matrix, improving thermal stability. The rare earth elements simultaneously purify the molten copper, removing impurities and reducing brittle grain boundary phases. The synergistic effect of these three elements results in the complex intermetallic compounds exhibiting superior thermal stability and refining ability compared to single-element compounds.

[0053] S2, Gradient preheating and dynamic temperature field control

[0054] The extrusion front-end temperature is lower than the rear-end temperature. Utilizing the principle that deformation heat accumulates from front to back during extrusion, the actual temperature of the front-end after the accumulated deformation heat is similar to the initial temperature of the rear-end, achieving temperature uniformity in the deformation zone. A temperature sensor monitors the deformation zone in real time; if the deviation exceeds the limit, the extrusion speed is adjusted to change the amount of deformation heat generated, preventing excessively high temperatures from causing grain coarsening or excessively low temperatures from increasing deformation resistance.

[0055] S3, Composite Shear Extrusion Molding

[0056] The spiral grooves subject the metal to both axial compressive stress and circumferential shear stress. Compressive stress promotes densification, while shear stress breaks down coarse grains into subcrystalline structures through grain boundary slip and dislocation movement. Strain energy accumulates in the compression zone, while the shear deformation zone forces the metal to change its flow direction, resulting in intense shearing. The expansion zone restores uniform flow. The grain refinement effect produced by shear deformation is superior to that of simple compression, and requires lower extrusion pressure.

[0057] S4, In-situ Self-generated Composite Reinforcement

[0058] Under high temperature and pressure, B4C undergoes solid-state or substitutional reactions with zirconium and hafnium to form ZrC and ZrB2. The addition of copper alters the reaction pathway, lowers the activation energy, and facilitates rapid nucleation and growth of the reinforcing phase. The in-situ generated ceramic particles form an atomically clean interface with the copper matrix. Particles distributed at grain boundaries pin grain boundary migration, inhibiting grain growth, while particles distributed within the grains hinder dislocation movement, resulting in dispersion strengthening. These two distributions together constitute a composite strengthening mechanism.

[0059] S5, Ultrasonic-assisted online solid solution and grain refinement control

[0060] Ultrasonic vibration produces cavitation and acoustic flow effects. Cavitation creates transient cavities within the metal, which release energy upon collapse, promoting atomic diffusion and phase deformation nuclei. Acoustic flow effects homogenize the temperature and solute fields, promoting uniform diffusion of alloying elements, inhibiting grain growth, and resulting in fine and uniform supersaturated solid solutions.

[0061] S6, Multi-field Collaborative Processing

[0062] An alternating electromagnetic field is applied during the initial cooling stage. The Lorentz force induces forced convection within the metal, promoting uniform solute distribution, increasing nucleation sites, and resulting in fine and dispersed precipitates. An ultrasonic vibration field is applied during the low-temperature stage. The periodic stress causes localized plastic deformation in areas of residual stress concentration, releasing internal stress. The two physical fields are applied segmentally according to temperature ranges, leveraging the optimizing effect of the electromagnetic field on the phase transition process and the stress relaxation effect of the ultrasonic field, respectively.

[0063] To make the present invention more fully disclosed, more specific embodiments are described below.

[0064] I. Detection Methods

[0065] (1) Tensile strength, yield strength, elongation

[0066] The test was conducted according to GB / T 34505-2017 "Tension Test at Room Temperature for Copper and Copper Alloys". An Instron 5985 universal testing machine was used. The specimens were longitudinally curved pipe sections, and the tensile rate was 2 mm / min. The tensile strength Rm (MPa), the specified plastic extension strength Rp0.2 (MPa, i.e., yield strength), and the elongation after fracture A (%) were recorded respectively.

[0067] (2) Hardness

[0068] The test was conducted according to GB / T 231.1-2018 "Metallic materials - Brinell hardness test - Part 1: Test method". A Brinell hardness tester was used, with a load of 3000 kgf, an indenter diameter of 10 mm, and a holding time of 15 s. The results were converted to HRB (Rockwell B scale).

[0069] (3) Corrosion resistance

[0070] The corrosion resistance was evaluated using electrochemical testing methods. The tests were conducted on a PARSTAT 4000 electrochemical workstation using a three-electrode system: the sample served as the working electrode (working area 1 cm²). 2 A saturated calomel electrode was used as the reference electrode, and a platinum sheet was used as the auxiliary electrode. The corrosive medium was a 3.5 wt.% NaCl solution (room temperature, pH = 7.0 ± 0.2). The corrosion current density (μA·cm) was obtained by Tafel extrapolation. -2 ).

[0071] (4) Outer diameter, wall thickness tolerance and eccentricity

[0072] Inspection was conducted according to GB / T 26303.1-2010 "Dimensional Inspection Methods for Copper and Copper Alloy Processed Materials - Part 1: Tubes" and GB / T 16866-2006 "Dimensions and Permissible Deviations of Seamless Copper and Copper Alloy Tubes". A laser diameter gauge was used to measure the outer diameter, and an ultrasonic thickness gauge was used to measure the wall thickness. The eccentricity (%) was calculated. The formula for calculating the eccentricity is: (Maximum wall thickness - Minimum wall thickness) / Average wall thickness × 100%.

[0073] (5) Residual stress

[0074] The circumferential residual stress (MPa) on the outer surface of the pipe was measured by X-ray diffraction (tilt method), and the test standard was in accordance with GB / T 7704-2017 "Determination of Residual Stress by X-ray Diffraction".

[0075] II. Implementation Examples

[0076] Example 1

[0077] A high-strength, corrosion-resistant copper alloy tube forming process includes the following steps:

[0078] S1. Preparation of multi-element microalloyed ingots: Add 0.18wt% cerium, 0.12wt% lanthanum, 0.28wt% zirconium, 0.22wt% hafnium, and 0.20wt% chromium to the copper matrix, melt at 1250℃, refine for 15 minutes, and cast into 300mm diameter round ingots at 1180℃.

[0079] S2. Gradient Preheating and Dynamic Temperature Field Control: The ingot is placed in an axial gradient heating preheating device to establish a gradient temperature field along the extrusion direction. The temperature at the front end of the extrusion is 700℃, and the temperature at the rear end is 800℃, with a temperature difference of 100℃. The preheating rate is 8℃ / min, and the holding time is 90 minutes. During the extrusion process, the temperature of the deformation zone is monitored in real time by a temperature sensor in the die deformation zone. The target temperature of the deformation zone is set at 760℃. When the deviation exceeds ±30℃, the extrusion speed is adjusted: if it is too high, the speed is increased by 8mm / s per 10℃; if it is too low, the speed is decreased by 6mm / s per 10℃.

[0080] S3. Composite Shear Extrusion Forming: The preheated ingot is fed into an extrusion die for hot extrusion. The extrusion die includes a compression zone, a shear deformation zone, and an expansion zone. The compression ratio is 10. The inner wall of the shear deformation zone has spiral grooves with a spiral angle of 30° and a groove depth of 1.8mm. The spiral direction is the same as the extrusion direction. The expansion zone has an expansion angle of 20°. The extrusion speed is 32mm / s, and the extrusion temperature is approximately 760℃.

[0081] S4. In-situ self-generated composite reinforcement: During the extrusion forming process, B4C powder is introduced online at the entrance of the shear deformation zone and transported by argon gas at a flow rate of 8 L / min and a blowing amount of 2.6 kg / t copper alloy. Utilizing the extrusion temperature and pressure, as well as the reactivity of zirconium and hafnium, B4C reacts with zirconium and hafnium through a solid-state reaction to generate ZrC and ZrB2 ceramic reinforcing particles, which are dispersed in the copper alloy matrix.

[0082] S5. Ultrasonic-assisted online solution treatment and fine grain control: An ultrasonic vibration device is installed at the extrusion outlet, including axial and radial transducers. The ultrasonic vibration frequency is 28kHz axially and 32kHz radially, with a power of 1800W. Simultaneously, induction heating is performed for online solution treatment at a solution temperature of 900℃ and a holding time of 96 seconds.

[0083] S6. Multi-field Coordinated Treatment: Along the cooling path of the copper alloy tube from its solution temperature to room temperature, an alternating electromagnetic field is applied first, followed by an ultrasonic vibration field. The alternating electromagnetic field has a magnetic field strength of 0.45T and a frequency of 55Hz, applied perpendicular to the tube axis, and the application range extends from 900℃ to 500℃. The ultrasonic vibration field has a frequency of 32kHz and a power density of 98W / cm². 2 The temperature range is cooled from 300°C to room temperature.

[0084] Microstructure and corrosion-resistant morphology observation

[0085] The metallographic structure of the copper alloy tube prepared in Example 1 of this invention is as follows: Figure 1 As shown in the metallographic micrographs, the copper alloy tube matrix prepared by this process has a uniform and fine equiaxed crystal structure, without coarse columnar crystals, unrecrystallized deformation structure, or obvious compositional segregation. The grain size distribution is uniform, which corroborates the core effect of the present invention in achieving grain refinement through the synergistic effect of the technical means.

[0086] The surface microstructure of the copper alloy tube prepared in Example 1 of this invention after immersion in 3.5 wt.% NaCl solution for different durations is shown below. Figures 2-4 As shown: After soaking for 7 days ( Figure 2 The alloy tube surface is smooth and dense, with no obvious pitting, corrosion grooves, or grain boundary corrosion, and the passivation film is intact and continuous; after soaking for 15 days ( Figure 3 The surface still maintains a complete passivation film structure, with only very slight uniform corrosion marks, and no localized corrosion expansion, preferential grain boundary corrosion, or pitting initiation; after immersion for 30 days ( Figure 4The surface maintains a uniform and dense microstructure, with no corrosion layer peeling, deep grain boundary corrosion, or pitting corrosion. The SEM morphology results demonstrate, from the perspective of long-term service micro-corrosion behavior, that the copper alloy tube prepared by this process possesses excellent resistance to both uniform and localized corrosion, meeting the long-term service requirements of harsh corrosive environments such as marine engineering and petrochemicals.

[0087] Key process single-factor experiment and result analysis

[0088] 1. The effect of B4C injection volume

[0089] With other parameters fixed the same as in Example 1, only the amount of B4C powder sprayed in S4 was changed to investigate the effect on tensile strength and elongation.

[0090]

[0091] Conclusion and analysis (based on Table 1):

[0092] (1) Below 2.6 kg / t: When the blowing amount is insufficient, the absolute amount of B4C powder at the entrance of the shear deformation zone is small, the probability of contact reaction with zirconium and hafnium elements is reduced, and the volume fraction of in-situ generated ZrC and ZrB2 ceramic reinforcing particles is low. The low volume fraction of reinforcing particles means that the average spacing of particles in the copper matrix is ​​too large, the probability of dislocations encountering particles during sliding is small, and the stress increment that needs to bypass the particles is very small, so the tensile strength is only 492 MPa. At the same time, due to the lack of a sufficient number of ceramic particles pinning at the grain boundaries, the tendency of grain growth increases. Although the elongation is high, this is the result at the cost of strength, not a real improvement in the plasticity of the material itself.

[0093] (2) Above 2.6 kg / t: When the injection volume is too high, B4C powder accumulates locally at the entrance of the deformation zone, resulting in an excessively high volume fraction of ceramic particles generated by in-situ reaction. Excessive reinforcing particles preferentially nucleate and aggregate at grain boundaries, forming continuous particle chains or clusters. These aggregated particles disrupt the integrity of the grain boundary structure, leading to a decrease in grain boundary bonding force, and cracks are more likely to initiate and propagate along the grain boundaries during deformation. At the same time, due to the excessively high particle volume fraction, the matrix is ​​fragmented by the particles, hindering the continuity of metal flow, and the plastic deformation capacity during tension decreases sharply, with the elongation dropping from 11.8% to 7.6%. The tensile strength also decreases to 522 MPa due to stress concentration and interfacial debonding caused by particle agglomeration.

[0094] (3) Conclusion: 2.6 kg / t is the critical point for B4C powder to be fully dispersed and to react completely with zirconium and hafnium. At this injection rate, the particle volume fraction is about 5.1%, and the particles are distributed in an isolated and dispersed state at the grain boundaries and within the grains. This provides significant Orowan reinforcement without destroying the grain boundary bonding. The tensile strength reaches 563 MPa, and the elongation is maintained at 11.8%, achieving the best match between strength and plasticity. This is the optimal injection rate in this invention.

[0095] 2. The Influence of Helical Groove Helix Angle

[0096] With other parameters fixed the same as in Example 1, only the helix angle of the spiral groove in S3 was changed to investigate the effect on tensile strength and recrystallization effect.

[0097]

[0098] Conclusion and analysis (based on Table 2):

[0099] (1) Below 30°: When the helix angle is too small, the circumferential component force generated by the helical groove on the inner wall of the shear deformation zone is small. During the extrusion process, the metal mainly bears axial compression, and the amount of circumferential shear deformation is insufficient. The low cumulative shear strain leads to insufficient driving force for dynamic recrystallization. A large number of deformed structures fail to transform into fine equiaxed crystals, but remain as elongated deformed grains and subgrain structures. The grains in the non-recrystallized area are coarse and the dislocation density is uneven, resulting in low strength. At the same time, the presence of deformed structures makes it easier for corrosive media to penetrate along the grain boundaries, thus reducing corrosion resistance.

[0100] (2) Above 30°: When the helix angle is too large, the circumferential shear force generated by the helical groove is too large, and the metal is subjected to excessive torsional stress in the shear deformation zone. This additional circumferential tensile stress component exceeds the high-temperature strength of the copper alloy in local areas, resulting in microcracks inside the deformation zone. The microcracks become fracture sources in the subsequent tensile process, causing a decrease in tensile strength. At the same time, the excessive shear strain causes a sharp increase in deformation heat, and the local temperature rise promotes the abnormal growth of recrystallized grains. Although the recrystallization volume fraction is still high, the grain size is uneven.

[0101] (3) Conclusion: 30° is the balance point between axial compression and circumferential shear deformation. At this angle, the cumulative shear strain is sufficient to drive complete dynamic recrystallization without the generation of additional microcracks. The grains are fine and uniform, and the tensile strength reaches 563 MPa, which is the optimal helix angle in this invention.

[0102] 3. The effect of extrusion front end temperature

[0103] With other parameters fixed the same as in Example 1, only the extrusion front temperature in S2 was changed to investigate the effect on tensile strength and grain size.

[0104]

[0105] Conclusion and analysis (based on Table 3):

[0106] (1) Below 700℃: When the extrusion front temperature is too low, the initial temperature of the metal at the front of the ingot after entering the deformation zone is too low. Even with the added deformation heat, the actual temperature of the deformation zone is still lower than the dynamic recrystallization temperature window of the copper alloy. At low temperatures, the metal has high deformation resistance, poor fluidity, and uneven deformation. Some areas fail to undergo dynamic recrystallization, forming coarse, non-recrystallized grains. At the same time, the low temperature reduces the solid-phase reaction rate between B4C and zirconium and hafnium elements, resulting in insufficient ZrC and ZrB2 formation. The volume fraction of the ceramic reinforcing phase is lower than the design value, weakening the strengthening effect and reducing the tensile strength to only 478 MPa.

[0107] (2) Above 700℃: When the extrusion front temperature is too high, the local temperature of the deformation zone exceeds the overheating temperature of the copper alloy after the superposition of deformation heat. Under the overheated state, the grain boundaries begin to soften or even melt locally, the grains coarsen rapidly, and the precipitates at the grain boundaries undergo re-dissolution or coarsening. The coarse grains reduce the grain boundary area per unit volume, reduce the resistance to dislocation slip, and decrease the yield strength; in addition, the coarse grain structure weakens the barrier effect on the corrosive medium, and the corrosion resistance decreases. The tensile strength drops to 509 MPa.

[0108] (3) Conclusion: 700℃ is the critical value at which the deformation zone is exactly within the full recrystallization temperature range after the initial front-end temperature and deformation heat are superimposed, without overheating. At this temperature, the deformation zone temperature is uniform, dynamic recrystallization is sufficient, the grains are fine, and the in-situ reaction rate is sufficient, with the tensile strength reaching 563MPa, which is the optimal extrusion front-end temperature in this invention.

[0109] 4. Effect of solution treatment temperature

[0110] With other parameters fixed the same as in Example 1, only the heating temperature of the online solution treatment in S5 was changed to investigate the effect on tensile strength and grain size.

[0111]

[0112] Conclusion and analysis (based on Table 4):

[0113] (1) Below 900℃: When the solution temperature is too low, the diffusion rate of alloying elements in the copper matrix is ​​insufficient, and atoms such as Zr and Cr cannot fully dissolve into the matrix within a fixed holding time, leaving a large number of undissolved coarse second-phase particles. These undissolved particles cannot be transformed into fine, dispersed precipitates during subsequent cooling, resulting in the loss of precipitation strengthening effect. At the same time, the undissolved particles themselves are large in size and cannot effectively hinder dislocation movement, instead becoming stress concentration points and crack initiation sources, resulting in a tensile strength of only 496 MPa. Although the grain size is not significantly coarsened, the strength is low due to insufficient precipitation.

[0114] (2) Above 900℃: When the solution temperature is too high, the atomic diffusion rate is too fast, and the grain boundary migration rate increases exponentially. Under the same holding time, the grain growth rate is much higher than at lower temperatures, and the grain size increases sharply from 7.6 μm at 900℃ to 12.2 μm at 1000℃. According to the Hall-Petch relationship, grain coarsening leads to a decrease in yield strength of about 30-40 MPa. In addition, excessively high solution temperatures may cause excessive re-dissolution of precipitates at some grain boundaries, resulting in a decrease in nucleation density during subsequent cooling and a weakening of precipitation strengthening. The tensile strength drops to 528 MPa.

[0115] (3) Conclusion: 900℃ is the optimal balance temperature for the alloying elements to be fully dissolved and the grain growth to be suppressed under the condition of a fixed holding time of 96 seconds. At this temperature, elements such as Zr and Cr are completely dissolved into the matrix, and the grain size is maintained at a fine grain level of 7.6μm. The precipitation strengthening and fine grain strengthening work together to achieve a tensile strength of 563MPa, which is the optimal solution temperature in this invention.

[0116] 5. Influence of electromagnetic field strength

[0117] With other parameters fixed the same as in Example 1, only the magnetic field strength of the alternating electromagnetic field in S6 was changed to investigate the effect on tensile strength and precipitate distribution.

[0118]

[0119] Conclusion and analysis (based on Table 5):

[0120] (1) Below 0.45T: When the magnetic field strength is too low, the eddy current intensity induced by the alternating electromagnetic field inside the copper alloy tube is weak, and the melt flow velocity driven by the Lorentz force is low, which is insufficient to effectively break dendrites or homogenize the solute field. During the cooling process, the precipitated phase tends to preferentially nucleate and grow at the grain boundaries, forming local aggregations, while the precipitated phase inside the grains is sparse, and the average spacing between the precipitated phases is large. This uneven distribution leads to insufficient strengthening effect, with low strength in some areas and high brittleness in others, and the overall tensile strength is only 508MPa.

[0121] (2) Above 0.45T: When the magnetic field strength is too high, the excessive electromagnetic stirring causes the melt to flow too violently, resulting in excessive segregation of solute atoms in local areas, which in turn promotes the coarsening of the precipitated phase. The coarsened precipitated phase has a poorer coherence relationship with the matrix, and the critical shear stress required for dislocations to bypass them is reduced. At the same time, the excessively strong electromagnetic field may generate additional thermal stress inside the tube, affecting the uniformity of the microstructure. The tensile strength drops to 532MPa.

[0122] (3) Conclusion: 0.45T is the optimal strength for electromagnetic stirring to homogenize the solute field without causing coarsening of the precipitated phase. At this strength, the precipitated phase is evenly distributed, avoiding both local aggregation and excessive coarsening. The precipitation strengthening effect reaches its peak, and the tensile strength is 563MPa, which is the optimal electromagnetic field strength in this invention.

[0123] Example 2

[0124] A high-strength, corrosion-resistant copper alloy tube forming process includes the following steps:

[0125] S1. Preparation of multi-element microalloyed ingots: Add 0.06wt% cerium, 0.04wt% lanthanum, 0.15wt% zirconium, 0.12wt% hafnium, and 0.10wt% chromium to the copper matrix, melt at 1250℃, refine for 15 minutes, and cast into 300mm diameter round ingots at 1180℃.

[0126] S2. Gradient preheating and dynamic temperature field control: Extrusion front end temperature 700℃, extrusion rear end temperature 800℃, temperature difference 100℃. Preheating rate 8℃ / min, holding time 90 minutes. Target temperature in the deformation zone 760℃; adjust extrusion speed if deviation exceeds ±30℃.

[0127] S3, Composite Shear Extrusion Molding: Compression ratio 10, helix angle 30°, groove depth 1.8mm, expansion angle 20°, extrusion speed 28mm / s, extrusion temperature 758℃.

[0128] S4. In-situ self-generated composite strengthening: B4C powder is transported by argon gas carrier, with a blowing rate of 2.6 kg / t copper alloy.

[0129] S5. Ultrasonic-assisted online solid solution and grain refinement control: ultrasonic frequency axial 28kHz, radial 32kHz, power 1600W, solid solution temperature 900℃, holding time 118 seconds.

[0130] S6. Multi-field coordinated processing: Alternating electromagnetic field magnetic field strength 0.45T, frequency 55Hz, applied range from 900℃ to 500℃; ultrasonic vibration field frequency 32kHz, power density 98W / cm². 2 The temperature range is cooled from 300°C to room temperature.

[0131] Example 3

[0132] A high-strength, corrosion-resistant copper alloy tube forming process includes the following steps:

[0133] S1. Preparation of multi-element microalloyed ingots: Add 0.22wt% cerium, 0.14wt% lanthanum, 0.42wt% zirconium, 0.32wt% hafnium, and 0.32wt% chromium to the copper matrix, melt at 1250℃, refine for 15 minutes, and cast into 300mm diameter round ingots at 1180℃.

[0134] S2. Gradient preheating and dynamic temperature field control: Extrusion front end temperature 700℃, extrusion rear end temperature 800℃, temperature difference 100℃. Preheating rate 8℃ / min, holding time 90 minutes. Target temperature in the deformation zone 760℃; adjust extrusion speed if deviation exceeds ±30℃.

[0135] S3, Composite Shear Extrusion Molding: Compression ratio 10, helix angle 30°, groove depth 1.8mm, expansion angle 20°, extrusion speed 26mm / s, extrusion temperature 756℃.

[0136] S4. In-situ self-generated composite strengthening: B4C powder is transported by argon gas carrier, with a blowing rate of 2.6 kg / t copper alloy.

[0137] S5. Ultrasonic-assisted online solution treatment and grain refinement control: ultrasonic frequency axial 28kHz, radial 32kHz, power 1800W, solution temperature 920℃, holding time 82 seconds.

[0138] S6. Multi-field coordinated processing: Alternating electromagnetic field magnetic field strength 0.45T, frequency 55Hz, applied range from 920℃ to 510℃; ultrasonic vibration field frequency 32kHz, power density 98W / cm². 2 The temperature range is cooled from 300°C to room temperature.

[0139] Example 4

[0140] A high-strength, corrosion-resistant copper alloy tube forming process includes the following steps:

[0141] S1. Preparation of multi-element microalloyed ingots: Same as in Example 1.

[0142] S2. Gradient preheating and dynamic temperature field control: Extrusion front end temperature 650℃, extrusion rear end temperature 800℃, temperature difference 150℃. Preheating rate 8℃ / min, holding time 90 minutes. Target temperature in the deformation zone 740℃; adjust extrusion speed if deviation exceeds ±30℃.

[0143] S3, Composite Shear Extrusion Molding: Compression ratio 10, helix angle 30°, groove depth 1.8mm, expansion angle 20°, axial length of shear deformation zone increased to 1.5 times the outlet diameter of compression zone, extrusion speed 22mm / s, extrusion temperature 730℃.

[0144] S4. In-situ self-generated composite reinforcement: Same as in Example 1.

[0145] S5. Ultrasonic-assisted online solid solution and grain refinement control: Same as in Example 1.

[0146] S6. Multi-field collaborative processing: Same as in Example 1.

[0147] Example 5

[0148] A high-strength, corrosion-resistant copper alloy tube forming process includes the following steps:

[0149] S1. Preparation of multi-element microalloyed ingots: Same as in Example 1.

[0150] S2, Gradient preheating and dynamic temperature field control: Same as in Example 1.

[0151] S3, Composite shear extrusion molding: Same as in Example 1.

[0152] S4. In-situ self-generated composite reinforcement: Same as in Example 1.

[0153] S5. Ultrasonic-assisted online solid solution and grain refinement control: ultrasonic frequency axial 25kHz, radial 35kHz, power 2600W, solid solution temperature 900℃, holding time 72 seconds.

[0154] S6. Multi-field coordinated processing: Alternating electromagnetic field magnetic field strength 0.45T, frequency 55Hz, applied range cooled from 900℃ to 500℃ at a cooling rate of 32℃ / s; ultrasonic vibration field frequency 32kHz, power density 98W / cm². 2 The temperature range is cooled from 300°C to room temperature.

[0155] Example 6

[0156] A high-strength, corrosion-resistant copper alloy tube forming process includes the following steps:

[0157] S1. Preparation of multi-element microalloyed ingots: Same as in Example 1.

[0158] S2, Gradient preheating and dynamic temperature field control: Same as in Example 1.

[0159] S3, Composite shear extrusion molding: Same as in Example 1.

[0160] S4. In-situ self-generated composite reinforcement: Same as in Example 1.

[0161] S5. Ultrasonic-assisted online solid solution and grain refinement control: Same as in Example 1.

[0162] S6. Multi-field coordinated processing: Alternating electromagnetic field magnetic field strength 0.60T, frequency 80Hz, applied range cooled from 900℃ to 520℃, cooling rate 28℃ / s; ultrasonic vibration field frequency 32kHz, power density 98W / cm². 2 The temperature range is cooled from 300°C to room temperature.

[0163] III. Comparative Example

[0164] Comparative Example 1

[0165] This comparative example is basically the same as Example 1, except that gradient preheating is not used in S2, and uniform heating is used: the ingot is heated to 760°C as a whole, and there is no dynamic temperature compensation during extrusion. The remaining steps are the same as in Example 1.

[0166] Comparative Example 2

[0167] This comparative example is basically the same as Example 1, except that dynamic temperature compensation is not performed during the extrusion process in S2: the gradient preheating parameters are the same as in Example 1, but the extrusion speed is not adjusted when the temperature deviation in the deformation zone exceeds ±30℃. The remaining steps are the same as in Example 1.

[0168] Comparative Example 3

[0169] This comparative example is basically the same as Example 1, except that the inner wall of the shear deformation zone of the extrusion die in S3 is a smooth surface and does not have spiral grooves. The remaining steps are the same as in Example 1.

[0170] Comparative Example 4

[0171] This comparative example is basically the same as Example 1, except that B4C reinforcing phase precursor powder is not introduced in S4. The remaining steps are the same as in Example 1.

[0172] Comparative Example 5

[0173] This comparative example is basically the same as Example 1, except that ultrasonic vibration is not applied in S5, and only online induction heating solution treatment is performed (temperature 900°C, holding time 96 seconds). The remaining steps are the same as in Example 1.

[0174] Comparative Example 6

[0175] This comparative example is basically the same as Example 1, except that no alternating electromagnetic field and ultrasonic vibration field are applied in S6, and the sample is allowed to cool naturally to room temperature. The remaining steps are the same as in Example 1.

[0176] IV. Summary of Experimental Results:

[0177] (a) Test Results

[0178] The detection results of Examples 1-6 and Comparative Examples 1-6 are shown in Table 6.

[0179]

[0180] (II) Data Comparison and Analysis

[0181] 1. Tensile strength performance analysis

[0182] like Figure 5 As shown in Table 6, the tensile strength of all embodiments of the present invention is higher than that of the comparative examples. The tensile strength range of Examples 1-6 is 522-563 MPa, with Example 1 having the highest tensile strength at 563 MPa. The highest tensile strength of Comparative Examples 1-6 is 509 MPa. The tensile strength of Example 1 is 20.56% higher than that of Comparative Example 1, 16.32% higher than that of Comparative Example 2, 18.28% higher than that of Comparative Example 3, 24.83% higher than that of Comparative Example 4, 13.05% higher than that of Comparative Example 5, and 10.61% higher than that of Comparative Example 6.

[0183] From a theoretical perspective, the improved tensile strength of this invention stems from the following combined effects: gradient preheating lowers the extrusion front-end temperature compared to the rear-end, achieving temperature homogenization in the deformation zone through deformation heat compensation, preventing grain coarsening caused by localized overheating, and refining the grain size to 7.6 μm, contributing to fine-grain strengthening. The spiral grooves on the inner wall of the shear deformation zone induce axial and circumferential composite shear deformation in the metal during extrusion, increasing cumulative shear strain and promoting dynamic recrystallization nucleation, achieving a recrystallization volume fraction of 89%. The ZrC and ZrB2 nano-ceramic particles generated by the in-situ reaction are dispersed within the grain boundaries and grains, hindering dislocation movement through the Orowan bypass mechanism. Ultrasonic-assisted online solid solution utilizes the ultrasonic vibration effect to promote atomic diffusion, improving solid solution efficiency while inhibiting grain growth. The alternating electromagnetic field promotes uniform nucleation of precipitates in the initial cooling stage, refining the precipitate size. Comparative Example 1, due to the lack of gradient preheating, resulted in grain coarsening to 26.4 μm and a tensile strength of only 467 MPa; Comparative Example 4, due to the lack of in-situ self-generated reinforcement and the absence of second-phase reinforcement, had a tensile strength of only 451 MPa; Comparative Example 5, due to the lack of ultrasonic-assisted solid solution, resulted in grain size increasing to 12.8 μm and a tensile strength of only 498 MPa.

[0184] 2. Yield Strength Performance Analysis

[0185] The yield strength range of Examples 1-6 is 462–494 MPa, with Example 1 exhibiting the highest yield strength at 494 MPa. The highest yield strength among Comparative Examples 1-6 is 452 MPa. The yield strength of Example 1 is 19.90% higher than that of Comparative Example 1, 15.42% higher than that of Comparative Example 2, 18.18% higher than that of Comparative Example 3, 24.75% higher than that of Comparative Example 4, 12.02% higher than that of Comparative Example 5, and 9.29% higher than that of Comparative Example 6.

[0186] From a theoretical perspective, yield strength reflects the resistance of a material to begin plastic deformation. The increased yield strength in this invention is mainly attributed to: the increased critical shear stress required for dislocation pile-up due to fine-grained microstructure; the strong resistance of nano-ceramic particles to dislocation movement; and the increased resistance to dislocation movement due to lattice distortion caused by solid solution atoms. Comparative Example 4, without in-situ self-reinforcing, had a yield strength of only 396 MPa, a 19.8% decrease compared to Example 1. Comparative Example 1, without gradient preheating, had coarse grains and a yield strength of only 412 MPa. Comparative Example 6, without multi-field synergistic treatment, had an uneven precipitate distribution and a yield strength of 452 MPa.

[0187] 3. Hardness Performance Analysis

[0188] The hardness range of Examples 1-6 was 87.6–94.7 HRB, with Example 1 exhibiting the highest hardness at 94.7 HRB. The highest hardness among Comparative Examples 1-6 was 86.7 HRB. The hardness of Example 1 was 20.79% higher than Comparative Example 1, 16.63% higher than Comparative Example 2, 18.97% higher than Comparative Example 3, 27.46% higher than Comparative Example 4, 12.07% higher than Comparative Example 5, and 9.23% higher than Comparative Example 6.

[0189] From a theoretical perspective, the increase in hardness mainly stems from: nano-sized ZrC and ZrB2 ceramic particles, acting as high-hardness hard points, being dispersed throughout the matrix, directly improving macroscopic hardness; the fine-grained structure increasing grain boundary area and deformation resistance; and solid solution strengthening increasing lattice distortion and dislocation movement resistance. Comparative Example 4, without B4C powder and ceramic reinforcing particles, had a hardness of only 74.3 HRB, a 21.5% decrease compared to Example 1. Comparative Example 1, due to grain coarsening and the lack of gradient preheating, had a hardness of only 78.4 HRB.

[0190] 4. Elongation Performance Analysis

[0191] like Figure 6 As shown in Table 6, the elongation range of Examples 1-6 is 10.7% to 12.6%, with Example 2 having the highest elongation at 12.6%, followed by Example 1 at 11.8%. The elongation of Comparative Examples 1-6 ranges from a minimum of 9.2% to a maximum of 13.4%. The elongation of Example 1 is 28.26% higher than that of Comparative Example 1, 20.41% higher than that of Comparative Example 2, 24.21% higher than that of Comparative Example 3, 11.32% higher than that of Comparative Example 5, and 5.36% higher than that of Comparative Example 6.

[0192] From a theoretical perspective, elongation reflects a material's ability to undergo plastic deformation. In this invention, the elongation of Example 1 is higher than that of Comparative Examples 1-3 and 5-6, but lower than that of Comparative Example 4. This is because Comparative Example 4 did not add B4C powder and lacked ceramic reinforcing particles, resulting in the best matrix continuity and highest plasticity, but at the cost of a significant decrease in strength. The core advantage of this invention lies in the balance between strength and plasticity: while increasing the tensile strength to 563 MPa, it still maintains an elongation of 11.8%, meeting engineering application requirements. Maintaining the elongation is due to: a fine-grained structure that homogenizes deformation and avoids localized stress concentration; nano-ceramic particles distributed in a dispersed and isolated state, without forming continuous grain boundary chains, thus not disrupting grain boundary bonding; and ultrasonic-assisted solid solution that homogenizes the structure and reduces stress concentration points. Comparative Examples 1-3, due to inhomogeneous structures, the presence of non-recrystallized regions, or microcracks, all had elongations below 10%.

[0193] 5. Corrosion Resistance Analysis

[0194] like Figure 7 As shown in Table 6, the corrosion current density range for Examples 1-6 is 0.113–0.126 μA·cm. -2 In Example 1, the lowest corrosion current density was 0.113 μA·cm. -2 This indicates that it has the best corrosion resistance. The lowest corrosion current density was 0.128 μA·cm in Comparative Examples 1-6. -2 In Example 1, the corrosion current density was reduced by 20.98% compared to Comparative Example 1, 17.52% compared to Comparative Example 2, 19.29% compared to Comparative Example 3, 24.67% compared to Comparative Example 4, 14.39% compared to Comparative Example 5, and 11.72% compared to Comparative Example 6.

[0195] From a theoretical perspective, the improved corrosion resistance stems from: the fine-grained structure increases grain boundary density, making the penetration path of the corrosive medium along the grain boundaries more tortuous; nanoscale ceramic particles distributed at the grain boundaries block the continuous penetration channels of the corrosive medium; gradient preheating and composite shear deformation eliminate component segregation and coarse second phases in the casting structure, reducing the formation of localized corrosion cells. Comparative Example 4, without in-situ self-reinforcement and without ceramic particle pinning at the grain boundaries, allows the corrosive medium to penetrate rapidly along the grain boundaries, with a maximum corrosion current density reaching 0.150 μA·cm. -2 Comparative Example 1, due to its coarse grains and uneven microstructure, exhibited unobstructed corrosion channels, resulting in a corrosion current density of 0.143 μA·cm. -2 .

[0196] 6. Residual stress analysis

[0197] The residual stress range of Examples 1-6 is -42 to -33 MPa, all under compressive stress, with the residual stress of Example 1 being -38 MPa. In Comparative Examples 1-6, Comparative Examples 1-3 and 6 are under tensile stress, while Comparative Examples 4-5 are under compressive stress. The residual stress in Example 1 decreased by 138.78% compared to Comparative Example 1 (stress state changed from tensile to compressive), decreased by 150.00% compared to Comparative Example 2, decreased by 145.24% compared to Comparative Example 3, and decreased by 130.16% compared to Comparative Example 6.

[0198] From a theoretical perspective, the control of residual stress stems from: gradient preheating ensuring uniform temperature in the deformation zone, reducing thermal stress caused by temperature gradients; composite shear extrusion ensuring uniform deformation, reducing residual stress caused by uneven plastic deformation; alternating electromagnetic field promoting uniform nucleation of precipitates, reducing micro-stress caused by uneven precipitate distribution; and ultrasonic vibration field relaxing and eliminating residual stress through high-frequency micro-impact during the final cooling stage. Comparative Example 6, without multi-field synergistic treatment, exhibits significant residual tensile stress due to natural cooling. Comparative Examples 1-3 all generate residual tensile stress due to uneven temperature fields or uneven deformation. Example 1 achieves the maximum compressive stress state at the highest strength, demonstrating the outstanding advantages of multi-field synergistic treatment.

[0199] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A forming process for high-strength, corrosion-resistant copper alloy tubes, characterized in that, Includes the following steps: S1. Preparation of multi-element microalloyed ingot: 0.05-0.5 wt% of rare earth elements and 0.1-1.0 wt% of microalloying elements are added to a copper matrix and then smelted and cast to obtain a multi-element microalloyed copper alloy ingot, wherein the microalloying elements include zirconium and / or hafnium. S2. Gradient preheating and dynamic temperature field control: The multi-element micro-alloyed copper alloy ingot is placed in a preheating device with axial gradient heating function to establish a gradient temperature field along the extrusion direction, so that the temperature at the front end of the ingot extrusion is 50-150°C lower than the temperature at the back end of the extrusion. During the extrusion process, the temperature of the deformation zone is monitored in real time by a temperature sensor set in the deformation zone of the die. When the deviation between the temperature of the deformation zone and the preset target temperature exceeds ±30°C, dynamic compensation is performed by adjusting the extrusion speed. S3, Composite Shear Extrusion Forming: The ingot, which has been preheated by gradient, is fed into an extrusion die for hot extrusion. The extrusion die includes a compression zone, a shear deformation zone and an expansion zone arranged sequentially along the extrusion direction. The inner wall of the shear deformation zone is provided with a spiral groove, so that the metal generates axial and circumferential composite shear deformation during the extrusion process. S4. In-situ self-generated composite reinforcement: During the extrusion forming process, boron-containing reinforcing phase precursor powder is introduced online into the inlet of the shear deformation zone of the extrusion die. The reinforcing phase precursor powder is transported by an inert gas carrier. Utilizing the extrusion temperature and pressure during the extrusion process and the reactivity of zirconium and / or hafnium elements in the ingot, the reinforcing phase precursor reacts with zirconium and / or hafnium elements through solid-phase reaction or substitution reaction to generate zirconium boride and / or zirconium carbide ceramic phase reinforcing particles, which are dispersed in the copper alloy matrix. S5. Ultrasonic-assisted online solid solution and grain refinement control: An ultrasonic vibration device is set at the extrusion outlet to apply ultrasonic vibration to the extruded copper alloy tube and perform online solid solution treatment at the same time. The heating method of the online solid solution treatment is induction heating, and the heating temperature is controlled at 850-950℃. The ultrasonic vibration effect is used to promote the homogenization of alloying elements and inhibit grain growth during the solid solution process. S6. Multi-field synergistic treatment: On the cooling path of the copper alloy tube from the solution temperature to room temperature, an alternating electromagnetic field is applied first, followed by an ultrasonic vibration field. The alternating electromagnetic field is used to promote the uniform nucleation of precipitates in the initial stage of cooling, and the ultrasonic vibration field is used to eliminate residual stress in the final stage of cooling.

2. The high-strength corrosion-resistant copper alloy tube forming process according to claim 1, characterized in that, The rare earth element mentioned in step S1 includes at least one of cerium, lanthanum, and yttrium, and the microalloying element also includes chromium.

3. The high-strength corrosion-resistant copper alloy tube forming process according to claim 1, characterized in that, In step S2, the temperature at the front end of the extrusion is controlled at 650-750℃, and the temperature at the rear end of the extrusion is controlled at 800-900℃.

4. The high-strength corrosion-resistant copper alloy tube forming process according to claim 1, characterized in that, The spiral angle of the spiral groove in step S3 is 15° to 45°, the groove depth is 0.5 to 3 mm, and the spiral direction of the spiral groove is the same as the extrusion direction.

5. The high-strength corrosion-resistant copper alloy tube forming process according to claim 1, characterized in that, In step S3, the compression ratio of the compression zone is 5 to 15, and the expansion angle of the expansion zone is 10° to 30°.

6. The high-strength corrosion-resistant copper alloy tube forming process according to claim 1, characterized in that, The reinforcing phase precursor mentioned in step S4 is B4C powder or boron-containing composite powder, which is introduced by argon or nitrogen gas carrier transport, and the blowing amount is controlled to be 1.3 to 3.9 kg per ton of copper alloy.

7. The high-strength corrosion-resistant copper alloy tube forming process according to claim 1, characterized in that, The ultrasonic vibration device in step S5 includes an axial vibration transducer and a radial vibration transducer. The ultrasonic vibration frequency is 15-40kHz, the ultrasonic vibration power is 500-3000W, and the heat preservation time of the online solution treatment is 30-180 seconds.

8. The high-strength corrosion-resistant copper alloy tube forming process according to claim 1, characterized in that, In step S6, the magnetic field strength of the alternating electromagnetic field is 0.3–0.6 T, the frequency is 10–100 Hz, the direction of the electromagnetic field is perpendicular to the axis of the copper alloy tube, and the application range is the temperature range from the solution temperature to 500°C. The frequency of the ultrasonic vibration field is 20–40 kHz, and the application range is the temperature range from 300°C to room temperature.

9. The high-strength corrosion-resistant copper alloy tube forming process according to claim 1, characterized in that, The extrusion die is also equipped with a temperature compensation module, which includes a resistance heating element and a temperature sensor embedded in the die wall of the shear deformation zone, and is used to perform local temperature compensation in the shear deformation zone during the extrusion process.

10. The high-strength corrosion-resistant copper alloy tube forming process according to claim 1, characterized in that, The ceramic phase reinforcing particles generated by the in-situ reaction in step S4 are nanoscale and are distributed at the grain boundaries and within the grains of the copper alloy.

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