Deep-sea high-pressure-resistant copper-nickel-tin alloy and low-temperature preparation method thereof

Abstract

The invention discloses a deep-sea high-pressure-resistant copper-nickel-tin alloy and a low-temperature preparation method thereof, and belongs to the technical field of non-ferrous metal alloys, and the alloy comprises the following components in percentage by mass: 68-72% of Cu, 18-22% of Ni, 5-8% of Sn and the balance of at least one element of Fe, Zn and Mg; the average grain size is 50-100 micrometers, the tensile strength is larger than or equal to 850 MPa, the ductility is larger than or equal to 12%, the number of cyclic compression times under the deep sea pressure of 1000 MPa is larger than or equal to 50, and the residual deformation is smaller than or equal to 3%. According to the preparation method, through step-by-step vacuum melting, batch-by-batch addition of microelements and controllable cooling, the problems that in traditional high-temperature melting, element burning loss is serious, and crystal grains are coarse are solved, and synergistic improvement of strength and toughness is achieved.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal alloy technology, and particularly relates to a deep-sea high-pressure resistant copper-nickel-tin alloy and its low-temperature preparation method. Background Technology

[0002] The deep-sea environment places stringent demands on the comprehensive performance of equipment materials: they must simultaneously possess high tensile strength, good elongation, excellent corrosion resistance, and pressure resistance. While traditional marine copper-nickel alloys (such as B30 alloy, 30% Ni) exhibit outstanding corrosion resistance, their excessively high Ni content leads to insufficient plasticity, making them unable to withstand the high pressures of the deep sea. On the other hand, conventional copper-nickel-tin alloys (such as Cu-Ni-Sn systems) are mostly smelted at high temperatures (≥1200℃), resulting in a Sn element burn-off rate >15% and coarse grains (average size >200μm), with an elongation of only 5-7%, which is insufficient to meet the requirements of deep-sea equipment.

[0003] Existing improvement techniques attempt to enhance strength by adding reinforcing elements such as Cr and Mo. However, Cr and Sn easily form a brittle Cr3Sn phase at high temperatures, while Mo competes with Ni for solid solution, leading to compositional segregation and further reducing elongation. Some studies employ rapid solidification (cooling rate > 20℃ / min) to refine grains, but rapid cooling exacerbates Sn microsegregation (segregation degree > 1.5), resulting in localized decreases in corrosion resistance and high equipment costs. Furthermore, traditional processes do not optimize compositional design for the "high pressure-corrosion" coupling effect in deep-sea environments, resulting in residual deformation of alloys generally > 5% under cyclic pressure, leading to insufficient long-term service reliability.

[0004] In summary, existing technologies still face bottlenecks in the composition design and low-temperature preparation process of deep-sea high-pressure resistant copper-nickel-tin alloys: high-temperature melting leads to element loss and grain coarsening, the multi-element synergistic strengthening mechanism is unclear, and performance stability under high-pressure-corrosion coupling environments is insufficient. Therefore, developing a deep-sea high-pressure resistant copper-nickel-tin alloy with precise and controllable composition, simple process, and excellent comprehensive performance, along with its low-temperature preparation method, has significant engineering value. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a deep-sea high-pressure resistant copper-nickel-tin alloy and its low-temperature preparation method, which solves the problems of severe Sn element burn-off, coarse grains and insufficient pressure resistance cycles caused by high-temperature melting in the prior art.

[0006] To address the above problems, the present invention provides the following technical solution: The deep-sea high-pressure resistant copper-nickel-tin alloy, by mass percentage, consists of the following components: The composition is 68-72% Cu, 18-22% Ni, 5-8% Sn, and the balance is composed of at least one element selected from Fe, Zn, and Mg, with the total mass fraction of Fe, Zn, and Mg ≤ 2%.

[0007] Preferably, the above-mentioned deep-sea high-pressure resistant copper-nickel-tin alloy has an average grain size of 50-100 μm and a Vickers hardness of 280-320 HV.

[0008] This invention relates to a deep-sea high-pressure copper-nickel-tin alloy with a Cu-Ni-Sn matrix. The Cu content is controlled at 68-72%, serving as the alloy matrix to ensure excellent thermal conductivity and processing plasticity, while also providing a carrier for Sn solid solution and precipitation. The Ni content is set at 18-22%, forming a continuous solid solution with Cu, significantly improving the matrix's resistance to seawater corrosion and enhancing its strength through solid solution strengthening. The Sn content is limited to 5-8%, ensuring sufficient solid solution, and precipitating nano-sized Cu3Sn phase through aging treatment, resulting in precipitation strengthening. Simultaneously, the addition of Sn promotes the formation of a dense passivation film, further improving pitting corrosion resistance. The balance consists of at least one of Fe, Zn, and Mg, with a total content ≤2%. Fe refines grains and improves resistance to erosion corrosion, Zn enhances passivation film stability, and Mg improves toughness through deoxidation and grain boundary purification. However, if the total content of these elements exceeds 2%, coarse intermetallic compounds are easily formed, impairing matrix uniformity and pressure resistance stability. This invention improves the overall service performance of the alloy under high pressure in the deep sea by maintaining the alloy's processing performance through the synergistic effect of multiple elements.

[0009] As a general inventive concept, this invention provides a low-temperature preparation method for the deep-sea high-pressure resistant copper-nickel-tin alloy as described above, comprising the following steps: S1. Weigh out at least one of the following raw materials according to the target composition: electrolytic copper with a purity ≥99.95%, electrolytic nickel with a purity ≥99.98%, electrolytic tin with a purity ≥99.99%, and Fe, Zn, and Mg. S2. Electrolytic copper and electrolytic nickel are put into a vacuum induction furnace and melted for 30-40 minutes at a vacuum degree ≤10Pa and a temperature of 1050-1150℃ to form a copper-nickel melt. S3. Add electrolytic tin to the copper-nickel melt and continue melting for 15-20 minutes while maintaining a vacuum of ≤5Pa to completely dissolve the tin; S4. Add at least one of Fe, Zn, and Mg, and keep at 1080-1120℃ for 10-15 min to homogenize the composition; S5. Cool the melt to room temperature at a cooling rate of 5-10℃ / min to obtain the deep-sea high-pressure resistant copper-nickel-tin alloy.

[0010] In the above-described preparation method, preferably, the melting power of the vacuum induction furnace in step S2 is 80-120 kW, and the stirring rate is 200-300 rpm. The power of 80-120 kW is intended to provide sufficient energy to melt Cu and Ni and maintain the melt within a set low-temperature range. Too low a power (<80 kW) may result in uneven melt temperature or the presence of unmelted particles, while too high a power (>120 kW) will exacerbate melt tumbling, increasing the risk of gas entrainment and element volatilization. The stirring rate of 200-300 rpm is intended to eliminate temperature gradients and component segregation through forced convection; too low a rate will result in insufficient mixing, while too high a rate may lead to unstable melt surfaces and oxide inclusions.

[0011] In the above-described preparation method, preferably, the electrolytic tin in step S3 is added in batches, with each addition being 1 / 3 to 1 / 2 of the total amount, and stirring for 5-8 minutes after each addition. This batch-addition of electrolytic tin avoids localized overcooling, clumping, or settling caused by adding a large amount of Sn at once, and reduces the instantaneous vapor pressure of Sn on the melt surface through stepwise dissolution. Stirring for 5-8 minutes after each addition ensures that each batch of Sn is completely dissolved and initially homogenized before adding the next batch, thereby achieving high compositional uniformity.

[0012] In the preferred embodiment of the above preparation method, during the homogenization process in step S4, the vacuum level is controlled at 3-8 Pa, and the stirring rate is 150-250 rpm. The vacuum level of 3-8 Pa in this invention is used to achieve a balance between preventing melt oxidation and avoiding excessive volatilization. This vacuum range is sufficient to remove most oxygen without causing excessive loss of volatile elements such as Mg. The stirring rate of 150-250 rpm is slightly lower than that in the main melting stage, aiming to provide gentle and effective mixing, promoting the dispersion of trace elements without causing violent tumbling of the melt.

[0013] In the above-described preparation method, preferably, the cooling process in step S5 is carried out under an inert gas atmosphere, wherein the inert gas is argon and the pressure is 0.1-0.3 MPa. This invention clearly defines the atmospheric protection conditions during the cooling stage to prevent the high-temperature alloy from oxidizing upon contact with air during cooling, avoiding the formation of oxide scale on the surface or internal grain boundary oxidation, thereby ensuring the surface quality and internal structure purity of the ingot.

[0014] In the above-described preparation method, preferably, the cooling rate in step S5 is 5-10℃ / min. This rate range effectively suppresses abnormal grain coarsening and internal stress concentration caused by rapid cooling (>10℃ / min), promoting the formation of a fine and uniform microstructure; it also avoids the aggravation of component segregation caused by excessively slow cooling (<5℃ / min), maintaining component uniformity.

[0015] The preparation method of this invention focuses on low-temperature melting and precise process control. By limiting the melting temperature to 1050-1150℃ (significantly lower than the ≥1200℃ of traditional processes), the high-temperature volatilization of Sn is suppressed. Sn is added in batches (1 / 3-1 / 2 of the total amount each time) combined with vacuum gradient control (10Pa→3Pa) to solve the problems of high Sn density and easy segregation, achieving high homogeneity of the multi-component composition. Finally, a controllable cooling rate of 5-10℃ / min refines the average grain size to 50-100μm, avoiding the formation of internal stress and microcracks. Through synergistic optimization of process parameters, this method significantly improves the strength, toughness, corrosion resistance, and pressure stability of the alloy while ensuring precise control of the composition.

[0016] Compared with the prior art, the advantages of the present invention are as follows: 1. This invention, through the synergistic ratio of Cu 68-72%, Ni 18-22%, and Sn 5-8%, ensures excellent corrosion resistance (corrosion rate ≤0.03mm / a) while strengthening with nano-scale Cu3Sn precipitates, resulting in a tensile strength ≥850MPa and an elongation ≥12%, thus resolving the contradiction between strength and toughness in deep-sea materials. 2. This invention reduces the melting temperature to 1050-1150℃ and combines batch addition of Sn with vacuum gradient control (10Pa→3Pa) to control the Sn burn-off rate to <5% and reduce the composition segregation to ≤1.2, fundamentally avoiding the formation of brittle phases and macroscopic segregation, and ensuring the uniformity of the microstructure. 3. This invention employs a controllable cooling rate of 5-10℃ / min and is carried out under inert gas protection, which refines the average grain size to 50-100μm, while avoiding microcracks caused by thermal stress, ensuring that the residual deformation of the alloy under 1000MPa high-pressure cycling is ≤3% and the number of pressure cycles is ≥50. 4. The preparation method in this invention has a short process flow, simple operation, low process cost, and is suitable for large-scale application. Detailed Implementation

[0017] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0018] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0019] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0020] Example 1 The deep-sea high-pressure resistant copper-nickel-tin alloy of the present invention is composed of the following components by mass percentage: Cu 70%, Ni 20%, Sn 7%, Fe 1%, Zn 1%.

[0021] The preparation method of the deep-sea high-pressure resistant copper-nickel-tin alloy in this embodiment includes the following steps: S1. Weigh the raw materials according to the target composition, including 700g of electrolytic copper with a purity ≥99.95%, 200g of electrolytic nickel with a purity ≥99.98%, 70g of electrolytic tin with a purity ≥99.99%, 10g of electrolytic iron with a purity ≥99.99%, and 10g of electrolytic zinc with a purity ≥99.99%. S2. Melting the copper-nickel matrix: The weighed electrolytic copper and electrolytic nickel are put into the crucible of a ZG-0.5 type vacuum induction furnace, the furnace door is closed and the vacuum system is started to evacuate the vacuum degree inside the furnace to 8Pa; then the induction heating is turned on, the power is set to 100kW and the stirring speed is 250rpm, the furnace temperature is raised to 1100℃ and held at this temperature for 35min to obtain a copper-nickel melt with uniform composition; S3. Add tin in batches. Add 70g of electrolytic tin to the copper-nickel melt in three batches, with each batch containing approximately 23.3g. After each batch is added, maintain the vacuum level in the furnace at ≤4Pa and continue melting at a stirring speed of 250rpm for 6 minutes until the tin in that batch is completely dissolved and the melt is clear. Then add the next batch, and continue until all the tin has been added and dissolved. S4. Micro-addition and homogenization: Add 10g of electrolytic iron and 10g of electrolytic zinc to the melt, maintain the melt temperature at 1100℃, adjust the vacuum to 5Pa and the stirring speed to 200rpm, and keep it at this temperature for 12min to ensure that the added micro-elements are fully diffused and homogenized in the melt. S5. Controllable cooling and forming: Turn off the heating power, introduce high-purity argon into the furnace and maintain a protective gas pressure of 0.2MPa; pour the melt into a cast iron mold preheated to 200℃, control the cooling rate to 8℃ / min to cool to room temperature, and obtain the deep-sea high-pressure copper-nickel-tin alloy ingot after demolding.

[0022] Testing revealed that the deep-sea high-pressure resistant copper-nickel-tin alloy prepared in this embodiment had an average grain size of 75 μm, a tensile strength of 880 MPa, an elongation of 13%, a corrosion rate of 0.015 mm / a in 3.5% NaCl solution, and under simulated deep-sea pressure of 1000 MPa, underwent 55 cycles of compression with a residual deformation of 2.5%. Its Sn burn-off rate was only 4.5%, and its compositional segregation was 1.15, indicating that through low-temperature melting, batch addition of Sn, and controlled cooling processes, synergistic optimization of compositional uniformity and fine-grained structure was achieved, and its overall performance fully meets the stringent requirements of deep-sea high pressure.

[0023] Example 2 The deep-sea high-pressure resistant copper-nickel-tin alloy of the present invention is composed of the following components by mass percentage: Cu 70%, Ni 20%, Sn 5%, Fe 1%, Zn 1%.

[0024] The preparation method of the deep-sea high-pressure resistant copper-nickel-tin alloy in this embodiment includes the following steps: S1. Weigh the raw materials according to the target composition, including 700g of electrolytic copper with a purity ≥99.95%, 200g of electrolytic nickel with a purity ≥99.98%, 50g of electrolytic tin with a purity ≥99.99%, 10g of electrolytic iron with a purity ≥99.99%, and 10g of electrolytic zinc with a purity ≥99.99%. S2. Melting the copper-nickel matrix: The weighed electrolytic copper and electrolytic nickel are put into the crucible of a ZG-0.5 type vacuum induction furnace, the furnace door is closed and the vacuum system is started to evacuate the vacuum degree inside the furnace to 8Pa; then the induction heating is turned on, the power is set to 100kW and the stirring speed is 250rpm, the furnace temperature is raised to 1100℃ and held at this temperature for 35min to obtain a copper-nickel melt with uniform composition; S3. Add tin in batches. Add 50g of electrolytic tin to the copper-nickel melt in three batches, with each batch containing approximately 16.7g. After each batch is added, maintain the vacuum level in the furnace at ≤4Pa and continue melting at a stirring rate of 250rpm for 6 minutes until the tin in that batch is completely dissolved and the melt is clear. Then add the next batch, and continue until all the tin has been added and dissolved. S4. Micro-addition and homogenization: Add 10g of electrolytic iron and 10g of electrolytic zinc to the melt, maintain the melt temperature at 1100℃, adjust the vacuum to 5Pa and the stirring speed to 200rpm, and keep it at this temperature for 12min to ensure that the added micro-elements are fully diffused and homogenized in the melt. S5. Controllable cooling and forming: Turn off the heating power, introduce high-purity argon into the furnace and maintain a protective gas pressure of 0.2MPa; pour the melt into a cast iron mold preheated to 200℃, control the cooling rate to 8℃ / min to cool to room temperature, and obtain the deep-sea high-pressure copper-nickel-tin alloy ingot after demolding.

[0025] Testing revealed that the deep-sea high-pressure resistant copper-nickel-tin alloy prepared in this embodiment had an average grain size of 80 μm, a tensile strength of 860 MPa, an elongation of 12.5%, a corrosion rate of 0.020 mm / a in 3.5% NaCl solution, and underwent 50 cycles at 1000 MPa pressure with a residual deformation of 2.8%. Although the Sn content was lower than in Example 1, the Sn burn-off rate (4.3%) was still controlled through a batch-addition process, and the compositional segregation degree was 1.12, verifying the effectiveness of the Sn content range of 5-8%. Although the strength and corrosion resistance were slightly reduced, the overall performance was still superior to that of the traditional process, meeting the requirements of deep-sea equipment for a balance between corrosion resistance and strength.

[0026] Example 3 The deep-sea high-pressure resistant copper-nickel-tin alloy of the present invention is composed of the following components by mass percentage: Cu 70%, Ni 20%, Sn 7%, Fe 1.0%, Mg 0.5%.

[0027] The preparation method of the deep-sea high-pressure resistant copper-nickel-tin alloy in this embodiment includes the following steps: S1. Weigh the raw materials according to the target composition, including 700g of electrolytic copper with a purity ≥99.95%, 200g of electrolytic nickel with a purity ≥99.98%, 70g of electrolytic tin with a purity ≥99.99%, 10g of electrolytic iron with a purity ≥99.99%, and 5g of metallic magnesium with a purity ≥99.95%. S2. Melting the copper-nickel matrix: The weighed electrolytic copper and electrolytic nickel are put into the crucible of a ZG-0.5 type vacuum induction furnace, the furnace door is closed and the vacuum system is started to evacuate the vacuum degree inside the furnace to 8Pa; then the induction heating is turned on, the power is set to 100kW and the stirring speed is 250rpm, the furnace temperature is raised to 1100℃ and held at this temperature for 35min to obtain a copper-nickel melt with uniform composition; S3. Add tin in batches. Add 70g of electrolytic tin to the copper-nickel melt in three batches, with each batch containing approximately 23.3g. After each batch is added, maintain the vacuum level in the furnace at ≤4Pa and continue melting at a stirring rate of 250rpm for 6 minutes until the tin in that batch is completely dissolved and the melt is clear. Then add the next batch, and continue until all the tin has been added and dissolved. S4. Micro-addition and homogenization: Add 10g of electrolytic iron and 5g of metallic magnesium to the melt, maintain the melt temperature at 1100℃, adjust the vacuum to 5Pa and the stirring speed to 200rpm, and keep it at this temperature for 12min to allow the added micro-elements to be fully diffused and homogenized in the melt. S5. Controllable cooling and forming: Turn off the heating power, introduce high-purity argon into the furnace and maintain a protective gas pressure of 0.2MPa; pour the melt into a cast iron mold preheated to 200℃, control the cooling rate to 8℃ / min to cool to room temperature, and obtain the deep-sea high-pressure copper-nickel-tin alloy ingot after demolding.

[0028] Testing revealed that the deep-sea high-pressure resistant copper-nickel-tin alloy prepared in this embodiment had an average grain size of only 65 μm, a tensile strength of 895 MPa, an elongation of 13.5%, a corrosion rate of 0.012 mm / a in 3.5% NaCl solution, 58 cycles at 1000 MPa pressure, and a residual deformation of 2.3%. Its Sn burn-off rate was 4.5%, and its compositional segregation degree was 1.14. These results indicate that the composite addition of Fe and Mg in this invention further promoted grain refinement and passivation film stability, achieving a synergistic improvement in corrosion resistance, toughness, and pressure resistance, thus verifying the effectiveness of trace element microalloying.

[0029] Example 4 The deep-sea high-pressure resistant copper-nickel-tin alloy of the present invention is composed of the following components by mass percentage: Cu 70%, Ni 20%, Sn 7%, Fe 1%, Zn 1%.

[0030] The preparation method of the deep-sea high-pressure resistant copper-nickel-tin alloy in this embodiment includes the following steps: S1. Weigh the raw materials according to the target composition, including 700g of electrolytic copper with a purity ≥99.95%, 200g of electrolytic nickel with a purity ≥99.98%, 70g of electrolytic tin with a purity ≥99.99%, 10g of electrolytic iron with a purity ≥99.99%, and 10g of electrolytic zinc with a purity ≥99.99%. S2. Melting the copper-nickel matrix: The weighed electrolytic copper and electrolytic nickel are put into the crucible of a ZG-0.5 type vacuum induction furnace, the furnace door is closed and the vacuum system is started to evacuate the vacuum degree inside the furnace to 8Pa; then the induction heating is turned on, the power is set to 100kW and the stirring speed is 250rpm, the furnace temperature is raised to 1100℃ and held at this temperature for 35min to obtain a copper-nickel melt with uniform composition; S3. Add tin in batches. Add 70g of electrolytic tin to the copper-nickel melt in three batches, with each batch containing approximately 23.3g. After each batch is added, maintain the vacuum level in the furnace at ≤4Pa and continue melting at a stirring speed of 250rpm for 6 minutes until the tin in that batch is completely dissolved and the melt is clear. Then add the next batch, and continue until all the tin has been added and dissolved. S4. Micro-addition and homogenization: Add 10g of electrolytic iron and 10g of electrolytic zinc to the melt, maintain the melt temperature at 1100℃, adjust the vacuum to 5Pa and the stirring speed to 200rpm, and keep it at this temperature for 12min to ensure that the added micro-elements are fully diffused and homogenized in the melt. S5. Controllable cooling and forming: Turn off the heating power, introduce high-purity argon into the furnace and maintain a protective gas pressure of 0.2MPa; pour the melt into a cast iron mold preheated to 200℃, control the cooling rate to 5℃ / min to cool to room temperature, and obtain the deep-sea high-pressure copper-nickel-tin alloy ingot after demolding.

[0031] Testing revealed that the deep-sea high-pressure resistant copper-nickel-tin alloy prepared in this embodiment had an average grain size of 95 μm, a tensile strength of 865 MPa, an elongation of 14.2%, a corrosion rate of 0.018 mm / a in 3.5% NaCl solution, and a residual deformation of 2.8% after 52 cycles of compression at 1000 MPa. Its Sn burn-off rate was 4.5%, and its compositional segregation degree was 1.18, indicating that even at the lower limit of the process cooling rate, it can still maintain a fine-grained structure and excellent comprehensive performance, verifying the stability of the 5-10℃ / min controllable cooling process.

[0032] Comparative Example 1 The copper-nickel-tin alloy, by mass percentage, consists of the following components: Cu 70%, Ni 20%, Sn 4%, Fe 1%, Zn 1%.

[0033] The preparation method of the copper-nickel-tin alloy in this comparative example includes the following steps: S1. Weigh the raw materials according to the target composition, including 700g of electrolytic copper with a purity ≥99.95%, 200g of electrolytic nickel with a purity ≥99.98%, 40g of electrolytic tin with a purity ≥99.99%, 10g of electrolytic iron with a purity ≥99.99%, and 10g of electrolytic zinc with a purity ≥99.99%. S2. Melting the copper-nickel matrix: The weighed electrolytic copper and electrolytic nickel are put into the crucible of a ZG-0.5 type vacuum induction furnace, the furnace door is closed and the vacuum system is started to evacuate the vacuum degree inside the furnace to 8Pa; then the induction heating is turned on, the power is set to 100kW and the stirring speed is 250rpm, the furnace temperature is raised to 1100℃ and held at this temperature for 35min to obtain a copper-nickel melt with uniform composition; S3. Add tin in batches. Add 40g of electrolytic tin to the copper-nickel melt in three batches, with each batch containing approximately 13.3g. After each batch is added, maintain the vacuum level in the furnace at ≤4Pa and continue melting at a stirring speed of 250rpm for 6 minutes until the tin in that batch is completely dissolved and the melt is clear. Then add the next batch, and continue until all the tin has been added and dissolved. S4. Micro-addition and homogenization: Add 10g of electrolytic iron and 10g of electrolytic zinc to the melt, maintain the melt temperature at 1100℃, adjust the vacuum to 5Pa and the stirring speed to 200rpm, and keep it at this temperature for 12min to ensure that the added micro-elements are fully diffused and homogenized in the melt. S5. Controllable cooling and forming: Turn off the heating power, introduce high-purity argon into the furnace and maintain a protective gas pressure of 0.2MPa; pour the melt into a cast iron mold preheated to 200℃, control the cooling rate to 8℃ / min to cool to room temperature, and obtain the copper-nickel-tin alloy ingot after demolding.

[0034] Testing revealed that the copper-nickel-tin alloy prepared in this comparative example had an average grain size of 120 μm, a tensile strength of only 800 MPa, an elongation of 10%, a corrosion rate of 0.045 mm / a in 3.5% NaCl solution, a pressure cycle life of only 45 cycles at 1000 MPa, and a residual deformation of 3.5%. Despite employing low-temperature melting and a batch-addition Sn process, resulting in a Sn burn-off rate of 3.8%, the insufficient Sn content disrupted the strengthening synergistic effect of the Cu-Ni-Sn system, leading to a comprehensive deterioration in corrosion resistance, toughness, and pressure stability. This validates the necessity of a Sn content of 5-8%. Comparative Example 2 The copper-nickel-tin alloy, by mass percentage, consists of the following components: Cu 70%, Ni 20%, Sn 7%, Fe 1%, Zn 1%.

[0035] The preparation method of the copper-nickel-tin alloy in this comparative example includes the following steps: S1. Weigh the raw materials according to the target composition, including 700g of electrolytic copper with a purity ≥99.95%, 200g of electrolytic nickel with a purity ≥99.98%, 70g of electrolytic tin with a purity ≥99.99%, 10g of electrolytic iron with a purity ≥99.99%, and 10g of electrolytic zinc with a purity ≥99.99%. S2. Melting the copper-nickel matrix: The weighed electrolytic copper and electrolytic nickel are put into the crucible of a ZG-0.5 type vacuum induction furnace, the furnace door is closed and the vacuum system is started to evacuate the vacuum degree inside the furnace to 8Pa; then the induction heating is turned on, the power is set to 100kW and the stirring speed is 250rpm, the furnace temperature is raised to 1100℃ and held at this temperature for 35min to obtain a copper-nickel melt with uniform composition; S3. Add tin in batches. Add 70g of electrolytic tin to the copper-nickel melt in three batches, with each batch containing approximately 23.3g. After each batch is added, maintain the vacuum level in the furnace at ≤4Pa and continue melting at a stirring speed of 250rpm for 6 minutes until the tin in that batch is completely dissolved and the melt is clear. Then add the next batch, and continue until all the tin has been added and dissolved. S4. Micro-addition and homogenization: Add 10g of electrolytic iron and 10g of electrolytic zinc to the melt, maintain the melt temperature at 1100℃, adjust the vacuum to 5Pa and the stirring speed to 200rpm, and keep it at this temperature for 12min to ensure that the added micro-elements are fully diffused and homogenized in the melt. S5. Rapid cooling and forming: Turn off the heating power, introduce high-purity argon into the furnace and maintain a protective gas pressure of 0.2MPa; pour the melt into a cast iron mold preheated to 200℃, control the cooling rate to 15℃ / min to cool to room temperature, and obtain the copper-nickel-tin alloy ingot after demolding.

[0036] Testing revealed that the copper-nickel-tin alloy prepared in this comparative example had an average grain size of 120 μm, a tensile strength of 850 MPa, an elongation of only 9%, a corrosion rate of 0.028 mm / a in 3.5% NaCl solution, and underwent 48 cycles at 1000 MPa pressure with a residual deformation of 3.2%. Its Sn burn-off rate was 4.5%, and its compositional segregation was 1.25. However, due to the excessively rapid cooling rate, the grains were not sufficiently refined, internal stress increased, and plasticity and compressive strength significantly decreased, highlighting the criticality of a controllable cooling process of 5-10℃ / min.

[0037] Comparative Example 3 The copper-nickel-tin alloy, by mass percentage, consists of the following components: Cu 70%, Ni 20%, Sn 7%, Fe 1%, Zn 1%.

[0038] The preparation method of the copper-nickel-tin alloy in this comparative example includes the following steps: S1. Weigh the raw materials according to the target composition, including 700g of electrolytic copper with a purity ≥99.95%, 200g of electrolytic nickel with a purity ≥99.98%, 70g of electrolytic tin with a purity ≥99.99%, 10g of electrolytic iron with a purity ≥99.99%, and 10g of electrolytic zinc with a purity ≥99.99%. S2. High-temperature melting of copper-nickel matrix: The weighed electrolytic copper and electrolytic nickel are put into the crucible of ZG-0.5 vacuum induction furnace, the furnace door is closed and the vacuum system is started to evacuate the vacuum degree in the furnace to 8Pa; then the induction heating is turned on, the power is set to 150kW and the stirring speed is 300rpm, the furnace temperature is raised to 1250℃ and held at this temperature for 20min to obtain copper-nickel melt; S3. Add tin element at once: Add 70g of electrolytic tin to the copper-nickel melt at once, maintain the vacuum degree in the furnace ≤5Pa, and continue to melt for 3min at a stirring speed of 300rpm; S4. Adding trace amounts and holding for a short time: Add 10g of electrolytic iron and 10g of electrolytic zinc to the melt, maintain the melt temperature at 1250℃, adjust the vacuum to 8Pa and the stirring speed to 100rpm, and hold for 5min. S5. Rapid cooling and forming: Turn off the heating power, introduce high-purity argon into the furnace and maintain a protective gas pressure of 0.1MPa; pour the melt into a cast iron mold preheated to 200℃, control the cooling rate to 20℃ / min to cool to room temperature, and obtain the alloy ingot after demolding.

[0039] Testing revealed that the copper-nickel-tin alloy prepared in this comparative example had an average grain size of 220 μm, a tensile strength of only 720 MPa, an elongation of 8%, a corrosion rate in 3.5% NaCl solution >0.05 mm / a, a pressure cycle of only 35 times at 1000 MPa, and a residual deformation of 6%. Its Sn burn-off rate was as high as 18%, and its compositional segregation degree was 1.80. This exposed the comprehensive performance defects caused by high-temperature volatilization, compositional segregation, and grain coarsening in traditional processes, forming a stark contrast with the low-temperature process of this invention, highlighting the key technological value of "low-temperature melting + batch Sn addition + controlled-rate cooling".

[0040] In summary, the embodiments of the present invention have verified the advantages of low-temperature melting, batch-wise Sn addition, and controlled cooling processes through comparative examples: Examples 1-2 (Sn content 7%, 5%) and Examples 3-4 (Fe / Mg composite addition, lower limit of cooling rate 5℃ / min) all adopted low-temperature melting at 1050-1150℃, added Sn in batches (1 / 3-1 / 2 of the total amount per batch) and combined with controlled cooling at 5-10℃ / min. The results showed that the Sn burn-off rate was only 4.3-4.5% (comparative example 3 traditional high-temperature melting). The results showed that the material exhibited the following properties: a high temperature melting rate (18%), a compositional segregation ≤1.18 (comparative Example 3: 1.80), an average grain size refined to 50-100 μm (comparative Example 3: 220 μm), tensile strength ≥860 MPa (comparative Example 3: 720 MPa), elongation ≥12.5% ​​(comparative Example 3: 8%), a 3.5% NaCl corrosion rate ≤0.020 mm / a (comparative Example 3: >0.05 mm / a), and 1000 MPa pressure resistance cycles ≥50 times (comparative Example 3: only 35 times). Comparative Example 2 (cooling rate 15℃ / min, exceeding the upper limit) resulted in coarse grains (120 μm) and an elongation of only 9% due to excessively rapid cooling, further demonstrating the necessity of controlled cooling rate. These data indicate that this invention, through synergistic optimization of process parameters, systematically solves the problems of severe burn-off, coarse grains, and insufficient corrosion resistance and pressure resistance in traditional high-temperature Sn smelting, exhibiting superior comprehensive performance compared to traditional materials in deep-sea high-pressure environments.

Claims

1. A deep-sea high-pressure resistant copper-nickel-tin alloy, characterized in that: It consists of the following components by weight percentage: The alloy comprises 68-72% Cu, 18-22% Ni, 5-8% Sn, and the balance being at least one element selected from Fe, Zn, and Mg; the total mass fraction of Fe, Zn, and Mg is ≤2%; the average grain size of the alloy is 50-100 μm, and the Vickers hardness is 280-320 HV.

2. A low-temperature preparation method for deep-sea high-pressure resistant copper-nickel-tin alloy, characterized in that: Includes the following steps, S1. Weigh out at least one of the following raw materials according to the target composition: electrolytic copper with a purity ≥99.95%, electrolytic nickel with a purity ≥99.98%, electrolytic tin with a purity ≥99.99%, and Fe, Zn, and Mg. S2. Electrolytic copper and electrolytic nickel are put into a vacuum induction furnace and melted for 30-40 minutes at a vacuum degree ≤10Pa and a temperature of 1050-1150℃ to form a copper-nickel melt. S3. Add electrolytic tin to the copper-nickel melt and continue melting for 15-20 minutes while maintaining a vacuum of ≤5Pa to completely dissolve the tin; S4. Add at least one of Fe, Zn, and Mg, and keep at 1080-1120℃ for 10-15 min to homogenize the composition; S5. Cool the melt to room temperature to obtain the deep-sea high-pressure resistant copper-nickel-tin alloy.

3. The low-temperature preparation method of the deep-sea high-pressure resistant copper-nickel-tin alloy as described in claim 2, characterized in that: In step S2, the melting power of the vacuum induction furnace is 80-120kW, and the stirring speed is 200-300rpm.

4. The low-temperature preparation method of the deep-sea high-pressure resistant copper-nickel-tin alloy as described in claim 2, characterized in that: In step S3, the electrolytic tin is added in batches, with each batch containing 1 / 3 to 1 / 2 of the total amount, and stirred for 5-8 minutes after each addition.

5. The low-temperature preparation method of the deep-sea high-pressure resistant copper-nickel-tin alloy as described in claim 2, characterized in that: During the homogenization process in step S4, the vacuum degree is controlled at 3-8 Pa, and the stirring rate is 150-250 rpm.

6. The low-temperature preparation method of the deep-sea high-pressure resistant copper-nickel-tin alloy as described in claim 2, characterized in that: The cooling process in step S5 is carried out under the protection of an inert gas, which is argon, at a pressure of 0.1-0.3 MPa.

7. The low-temperature preparation method of the deep-sea high-pressure resistant copper-nickel-tin alloy as described in claim 2, characterized in that: The cooling rate in step S5 is 5-10℃ / min.

8. The deep-sea high-pressure resistant copper-nickel-tin alloy as described in claim 1, characterized in that: The corrosion rate of the alloy in 3.5% NaCl solution is 0.01-0.03 mm / a.

9. The deep-sea high-pressure resistant copper-nickel-tin alloy as described in claim 1, characterized in that: The conductivity of the alloy is 45-55 MS / m.

10. The deep-sea high-pressure resistant copper-nickel-tin alloy as described in claim 1, characterized in that: The alloy has a yield strength ≥750MPa, a tensile strength ≥850MPa, and an elongation ≥12%.