Low-element segregation copper-nickel-tin alloy and supergravity preparation method thereof

Abstract

The invention discloses a low-element segregation copper-nickel-tin alloy and a supergravity preparation method thereof. The low-element segregation copper-nickel-tin alloy is mainly prepared by mixing electrolytic copper, a copper-nickel alloy and a copper-tin alloy, and the method comprises the steps that the electrolytic copper, the copper-nickel alloy and the copper-tin alloy are placed in a smelting furnace to be subjected to vacuum smelting, a cast ingot is sequentially subjected to linear cutting, mechanical grinding, ultrasonic cleaning and constant-temperature drying, and a copper-nickel-tin raw material is obtained; processing the copper-nickel-tin raw material into a plurality of block cast ingots, and placing the cast ingots in a crucible; and then through high-vacuum heating and heat preservation treatment, the crucible containing the cast ingot is put into a heat preservation hanging cup of a centrifugal machine to be subjected to high-speed centrifugal rotation treatment, and after the crucible is completely cooled to the room temperature, the cast ingot subjected to supergravity solidification is taken out. According to the method, the high-gravity field is applied on the basis of constant-gravity solidification of the Cu-Ni-Sn alloy, and the strength, the plasticity, the toughness and the electrochemical corrosion resistance of the as-cast copper alloy are remarkably optimized only by adjusting the strength of the high-gravity field.

Description

Technical Field

[0001] The present invention belongs to the technical field of copper alloys, and particularly relates to a low-element segregation copper-nickel-tin alloy and a method for preparing the same by high gravity. Background Art

[0002] Cu-Ni-Sn series copper alloys, as a kind of high-elasticity deformed copper-nickel-based alloys, have been widely used in the fields of electronics industry and mechanical manufacturing due to their excellent comprehensive properties, such as high strength, good toughness, electrical conductivity and wear resistance. For example, Patent CN118006965A designs a Cu-Ni-Sn alloy with ultra-high strength and good high-temperature oxidation resistance, demonstrating its great potential in engineering applications. However, during solidification and subsequent heat treatment processes, such alloys are prone to element segregation, resulting in non-uniform microstructures, thereby affecting the comprehensive properties of the materials. Therefore, reducing element segregation is crucial for improving the overall performance of Cu-Ni-Sn series copper alloys.

[0003] Improving element segregation can not only improve the compositional uniformity of the alloy, but also significantly optimize the mechanical properties. By carefully optimizing the alloy composition and process parameters, the formation of brittle phases and unfavorable phases can be effectively reduced, and the yield strength and ductility of the material can be improved. In addition, a uniform microstructure helps to extend the service life of the alloy under complex usage conditions. Patent CN118147485A proposes adding Ti, Cr and Ce elements to the Cu-Ni-Sn alloy to promote dynamic recrystallization and refine grains, thereby improving the strength and hardness of the alloy.

[0004] At the same time, the electrochemical corrosion resistance is a key index for evaluating the service performance of Cu-Ni-Sn series copper alloys in various application scenarios. Since element segregation may trigger local micro-cell effects, accelerating the corrosion process and thus reducing the material durability. By improving the element distribution, the corrosion rate can be effectively slowed down, and the service life of the alloy can be significantly increased. Patent CN115896537B proposes adding Al, Zn, Nb and Zr elements to the Cu-Ni-Sn alloy subjected to multi-stage thermo-mechanical treatment to enhance the strength and corrosion resistance of the alloy, which is particularly important for fields with high corrosion resistance requirements such as electronic connectors and ocean engineering.

[0005] In summary, there is an urgent need to develop new technologies that can reduce element segregation and improve the mechanical properties and electrochemical corrosion resistance of Cu-Ni-Sn series copper alloys, which has important academic value and broad application prospects, and is expected to promote the wide application of as-cast copper alloys in various engineering fields and provide safer and more reliable material solutions. Summary of the Invention

[0006] In order to improve problems such as severe element segregation, large grain structure, and poor mechanical properties existing in cast Cu-Ni-Sn series copper alloys, the present invention proposes a low-element segregation copper-nickel-tin alloy and a method for preparing the same by high gravity, simultaneously improving the strength, plasticity, and electrochemical corrosion resistance of the Cu-Ni-Sn alloy.

[0007] In order to achieve the above invention objectives, the present invention provides the following technical solutions:

[0008] I. A low-element segregation copper-nickel-tin alloy, characterized in that:

[0009] The low-element segregation copper-nickel-tin alloy is mainly prepared by mixing electrolytic copper, copper-nickel alloy, and copper-tin alloy; in the low-element segregation copper-nickel-tin alloy, the mass percentage content of metallic nickel is 8% - 10%, and the mass percentage content of electrolytic tin is 1.5% - 2.5%.

[0010] In the low-element segregation copper-nickel-tin alloy, the mass percentage content of metallic nickel is 9%, and the mass percentage content of electrolytic tin is 2%.

[0011] II. A preparation method for the low-element segregation copper-nickel-tin alloy, comprising the following steps:

[0012] Step S1: First, put electrolytic copper, copper-nickel alloy, and copper-tin alloy into a melting furnace for vacuum melting and pouring to obtain a poured ingot.

[0013] The melting point of the Sn element is relatively low, only ~231.9 °C. Directly adding metallic Sn will cause serious volatilization and burning loss of the Sn element. Therefore, the present invention selects a Cu-20% Sn master alloy for the preparation of copper-nickel-tin materials.

[0014] Step S2: Use the poured ingot to prepare a bulk ingot, and place the bulk ingot in a crucible for heating.

[0015] Step S3: Symmetrically fix a melting hanging cup and a counterweight hanging cup on the horizontal rotor of a centrifuge, connect the horizontal rotor to a slip ring, and equip the centrifuge with a rotational speed sensor for measuring the rotational speed of the centrifuge.

[0016] Step S4: Sequentially place an alumina fiber thermal insulation sleeve and a crucible containing a bulk ingot inside the melting hanging cup, and place dense fireproof quartz wool at the bottom gap position between the alumina fiber thermal insulation sleeve and the melting hanging cup to ensure the stability during rotation. Place metal counterweight blocks inside the counterweight hanging cup and supplement high-density magnesite to ensure the same mass of both hanging cups at both ends to control the dynamic unbalance error of the centrifuge.

[0017] Step S5: Then, place the crucible with a boron nitride double-layer round cover installed as a whole in a muffle furnace for vacuum heating and insulation.

[0018] Step S6: After the heat preservation is completed, take out the crucible after vacuum heating from the muffle furnace, quickly place it in the melting hanging cup of the centrifuge, and then start the centrifuge. By adjusting the rotation speed of the horizontal rotor, make the horizontal rotor drive the crucible to rotate at a high speed.

[0019] Step S7: During the rotation of the horizontal rotor, after the crucible is completely cooled to room temperature, control the horizontal rotor to stop rotating, and take out the completely solidified ingot, which is the Cu-9Ni-2Sn alloy ingot sample prepared by high gravity.

[0020] Step S8: According to the solidified sample (alloy ingot sample) obtained in Step S7, cut it in half along the axial center line, and then conduct metallographic grinding and argon ion polishing treatments in sequence. Cut a sheet sample from the fine grain area in the middle and lower part of the sample, avoiding the coarse dendritic area formed by contacting the inner wall of the crucible at the edge of the sample and the impurity-containing loose area in the upper and middle parts of the ingot. Subsequently, use electron backscatter diffraction and electron probe microanalysis to observe the average grain size and quantitative elemental distribution in the fine grain tissue area respectively.

[0021] On this basis, cut a tensile sample from the fine grain tissue area and grind it with diamond sandpaper to 2000# to remove surface defects. Then, use a universal testing machine to test the yield strength, tensile strength, and elongation of the Cu-9Ni-2Sn alloy prepared under different high gravity conditions. To ensure the reliability of the experimental data, each group of samples is tested at least four times.

[0022] Cut an electrochemical corrosion sample from the fine grain area and grind it with diamond sandpaper to 2000# to remove surface defects. Then, use an electrochemical workstation to test the electrochemical corrosion resistance of the Cu-9Ni-2Sn alloy prepared under different high gravity conditions under simulated seawater conditions (3.5 wt.% NaCl, 20 °C).

[0023] The specific content of the said Step S2 is as follows:

[0024] Step S2.1: First, perform wire cutting, mechanical grinding, ultrasonic cleaning, and constant temperature drying on the cast ingot obtained in Step S1 in sequence to obtain copper-nickel-tin raw materials, which are used to prepare copper-zirconium alloy under high gravity.

[0025] Step S2.2: Then, process the copper-nickel-tin raw materials in Step 2.1 by wire cutting into several ingots with a volume approximately 0.5 cm 3 and place all the ingots inside the crucible.

[0026] Step S2.3: Then, a double-layer boron nitride round cover is installed on the top of the crucible containing the bulk ingot. The double-layer boron nitride round cover is used to prevent heat and the volatilization of Sn element during the process of high-gravity solidification.

[0027] In the step S1, the mass ratio of copper element, nickel element and tin element is 90.5:8:1.5 to 87.5:10:2.5.

[0028] In the step S1, the copper-nickel alloy uses Cu-50%Ni alloy, and the copper-tin alloy uses Cu-20%Sn.

[0029] In the step S5, the vacuum heating conditions of the crucible in the muffle furnace are as follows: the vacuum degree is greater than 10 -3 Pa, the crucible is heated in the muffle furnace to not less than 1150 °C, and the heat preservation time is not less than 50 min.

[0030] In the step S5, the vacuum heating conditions of the crucible in the muffle furnace are as follows: the crucible is heated in the muffle furnace to 1250 °C, and the heat preservation time is 60 min.

[0031] In the step S6, the dynamic unbalance of the centrifuge is less than 2 g·mm.

[0032] In the step S7, by adjusting the rotation speed of the horizontal rotor, the rotation speed range of the crucible is 1000 - 2200 r / min.

[0033] A heat preservation sleeve made of alumina fiber material with low thermal conductivity is filled between the vacuum-heated crucible and the inner wall of the melting hanging cup to reduce the heat loss along the bottom and side wall directions of the crucible. The thermal conductivity of the heat preservation sleeve is lower than 0.2 W / (m·K).

[0034] The size of the crucible containing the raw materials is preferably an inner diameter of 22 mm, a wall thickness of 5 mm, and a height of 110 mm. The size of the double-layer boron nitride round cover is preferably an upper end diameter of 28.5 mm, a lower end diameter of 21.5 mm, and a layer thickness of 5 mm. The rotation time of the horizontal rotor is preferably 10 min.

[0035] During the preparation process, according to the preparation requirements, by regulating the rotation speed of the centrifuge, the centrifugal acceleration required for high-gravity solidification is regulated. For example, when the rotation speed of the horizontal rotor is set to 0 r / min, the high gravity corresponding to the bottom of the crucible is 1G (G = 9.8 m / s 2 ), and a sample solidified under normal gravity (1G) is obtained at this time; when the rotation speed of the horizontal rotor is set to 1193 r / min, the high gravity corresponding to the bottom of the crucible is 250G; when the rotation speed of the horizontal rotor is set to 1687 r / min, the high gravity corresponding to the bottom of the crucible is 500G.

[0036] The present invention utilizes the principle of high-gravity solidification. By adjusting the high-gravity rotation speed, the buoyancy convection in the alloy is continuously enhanced to refine the grain size of the copper-nickel-tin alloy. This method effectively alleviates the segregation phenomenon of Sn element at the grain boundary position and avoids the formation of brittle discontinuous precipitation structure, thereby effectively regulating the microstructure of as-cast copper-nickel-tin alloy without relying on complex thermo-mechanical treatment processes, and realizing the synergistic improvement of the comprehensive mechanical properties and electrochemical corrosion resistance of the alloy. Therefore, the high-throughput preparation of as-cast copper alloy by high-gravity solidification technology has important practical significance and application prospects.

[0037] The present invention proposes a preparation method of copper-nickel-tin alloy that can effectively reduce element segregation. Its chemical composition is: 9% Ni, 2% Sn, and the balance is Cu. In the copper-nickel-tin alloy solidified under conventional gravity conditions, millimeter-sized coarse dendrites usually form, and between these dendrites, the segregation phenomenon of Sn element is severe and the distribution is extremely uneven. However, under high-gravity solidification conditions, with the increase of high-gravity intensity, the grain size of the alloy gradually refines, and the segregation coefficient of Sn element decreases rapidly. This means that the ratio of the Sn element content at the grain boundary and in the grain interior decreases significantly. When the high-gravity intensity reaches 500G, the appropriate Sn element content within the grain boundary reduces the stacking fault energy in the local area and restricts the deformation process in the Sn element-depleted area. This deformation-induced stacking fault structure continuously improves the strain hardening ability of the alloy, achieving the synchronous improvement of strength and toughness.

[0038] In addition, compared with conventional gravity conditions, high-gravity solidification significantly alleviates the segregation behavior of Sn element and the electrochemical potential difference in the local area, reducing the tendency of pitting corrosion and intergranular corrosion. This process helps to form a denser Cu2O passivation film, thus significantly improving the electrochemical corrosion resistance of the alloy. This high-gravity preparation method provides a new technical approach for the preparation of high-performance copper-nickel-tin alloy, promoting the broad prospects of materials in industrial applications.

[0039] Adding a high-gravity field during the conventional gravity solidification process of Cu-9Ni-2Sn alloy melt can significantly refine the microstructure of the alloy, improve the grain uniformity, and effectively alleviate the segregation phenomenon of Sn element. By regulating the distribution characteristics and segregation behavior of Sn element, the stacking fault energy in the area near the grain boundary is reduced, thereby enhancing the strength and toughness of the copper alloy. By reducing the severe segregation structure of Sn element and the electrochemical potential difference in the local area, the tendency of pitting corrosion and intergranular corrosion is reduced, the corrosion resistance of the Cu2O passivation film is enhanced, and the electrochemical corrosion resistance of the alloy is optimized.

[0040] The beneficial effects of the present invention are:

[0041] 1. Based on the normal gravity solidification of Cu-Ni-Sn alloy, the present invention applies a high gravity field. By only adjusting the intensity of the high gravity field, the strength, plasticity-toughness, and electrochemical corrosion resistance of as-cast copper alloy are significantly optimized.

[0042] 2. The present invention provides a high-efficiency short-process high gravity solidification technology. By effectively regulating the grain morphology and the spatial distribution of Sn element, the large dendritic crystals with severe segregation of Sn element are gradually transformed into fine equiaxed crystal structures. This transformation significantly alleviates the segregation problem of Sn element, thus solving the challenges of severe segregation and poor comprehensive performance commonly existing in as-cast copper alloys, and broadening the development space for the high performance of as-cast copper alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is the evolution diagram of the average grain size and Sn element segregation coefficient of Cu-9Ni-2Sn alloy prepared by normal gravity (1G) and high gravity (250G and 500G) in Comparative Example 1;

[0044] Figure 2 It is the engineering stress-engineering strain curve of Cu-9Ni-2Sn alloy prepared by normal gravity (1G) and high gravity (250G and 500G) in Comparative Example 1;

[0045] Figure 3 It is the curve of the open circuit potential of Cu-9Ni-2Sn alloy prepared by normal gravity (1G) and high gravity (500G) in Comparative Example 1 changing with time;

[0046] Figure 4 It is the Tafel polarization curve of Cu-9Ni-2Sn alloy prepared by normal gravity (1G) and high gravity (500G) in Comparative Example 1;

[0047] Figure 5 It is the electrochemical impedance spectroscopy diagram of Cu-9Ni-2Sn alloy prepared by normal gravity (1G) and high gravity (500G) in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0049] Example 1

[0050] A method for preparing a Cu-9Ni-2Sn alloy with low element segregation by high gravity of 250G, the steps are as follows:

[0051] (1) First, put electrolytic copper, Cu-50% Ni master alloy and Cu-20% Sn master alloy into a melting furnace for vacuum melting, casting and homogenization annealing treatment to obtain a cast ingot; among them, the mass percentage contents of copper, nickel and tin elements are 89%, 9% and 2% respectively;

[0052] (2) Wire-cut, mechanically grind the cast ingot obtained in step S1, ultrasonically clean it with ethanol in an ultrasonic cleaner, and then dry it at a constant temperature in a blast drying oven to obtain the copper-nickel-tin raw material for preparing copper-nickel-tin alloy by high gravity. Then, wire-cut the copper-nickel-tin raw material into several block ingots with an approximate volume of 0.5 cm 3 and place all the block ingots inside a crucible with an inner diameter of 22 mm;

[0053] (3) Then, install a boron nitride double-layer round cover with an upper end diameter of 28.5 mm, a lower end diameter of 21.5 mm and a layer thickness of 5 mm on the top of the crucible to prevent heat dissipation during the high gravity solidification process and the volatilization of low melting point Sn element;

[0054] (4) Symmetrically fix a counterweight hanging cup and a melting hanging cup on the horizontal rotor of the centrifuge, connect the horizontal rotor with a slip ring, and equip the centrifuge with a rotational speed sensor;

[0055] (5) Then, place a heat preservation material sleeve in the gap between the crucible containing the block ingots and the melting hanging cup to reduce the heat loss along the bottom and side walls of the crucible; and place dense fireproof quartz wool at the bottom gap position between the heat preservation material sleeve and the melting hanging cup to ensure the stability during rotation;

[0056] (6) In the stationary state of the hanging cup, add metal counterweight blocks to the counterweight hanging cup and supplement high-density magnesia. By adjusting the counterweight hanging cup to have the same mass and centroid as the melting hanging cup, the dynamic rotational balance of the horizontal rotor is ensured, and it is ensured that the dynamic unbalance of the centrifuge is less than 2 g·mm;

[0057] (7) Subsequently, place the crucible containing the ingots as a whole in a muffle furnace for vacuum heating. The crucible is heated to 1250 °C with the furnace, the vacuum degree is pumped to 10 -3 Pa, and keep it warm for 60 min;

[0058] (8) After the heat preservation stage is over, quickly transfer the crucible containing the alloy ingots to the melting hanging cup on the centrifuge turntable, and immediately start the centrifuge device;

[0059] (9) Under the conditions of high-gravity solidification, the rotational speed of the centrifuge turntable equipped with a high-speed electric slip ring is set to 1,193 r / min, and the corresponding high-gravity field strength at the bottom of the crucible is 250 G. After the alloy melt in the crucible is completely cooled to room temperature, the high-gravity (250 G) prepared alloy ingot is taken out, which is the high-gravity prepared copper-nickel-tin alloy sample;

[0060] (10) Cut the alloy ingot sample flat along the diameter direction. Cut the sample from the bottom position of the ingot, and successively carry out mechanical grinding and argon ion polishing treatments, and conduct electron backscatter diffraction analysis to observe the fine-grained tissue area of the sample;

[0061] (11) Select the fine-grained tissue area to carry out electron probe wave spectrum analysis, respectively count the Sn element content in the grain boundary and intragranular regions, randomly select at least 10 positions of the same type, and calculate the average value of the element content;

[0062] (12) Select the fine-grained area to cut tensile specimens, and use a universal testing machine and a video extensometer to measure the yield strength, tensile strength and elongation of the high-gravity prepared copper-nickel-tin alloy sample. Samples under the same conditions are repeatedly measured 4 times, and the average value is calculated.

[0063] Example 2

[0064] A method for preparing a 500 G high-gravity Cu-9Ni-2Sn alloy with low element segregation, the steps are as follows:

[0065] (1) First, put electrolytic copper, Cu-50% Ni master alloy and Cu-20% Sn master alloy into a melting furnace for vacuum melting, casting and homogenization annealing treatment to obtain a cast ingot; the mass percentage contents of copper, nickel and tin elements are 89%, 9% and 2% respectively;

[0066] (2) The cast ingot obtained in step S1 is successively subjected to wire cutting, mechanical grinding, ultrasonic cleaning with ethanol in an ultrasonic cleaning machine, and then thermostatic drying in a blast drying oven to obtain the copper-nickel-tin raw material of the high-gravity prepared copper-nickel-tin alloy. Then the copper-nickel-tin raw material is wire cut into several block ingots with an approximate volume of 0.5 cm 3 and all the block ingots are placed inside a crucible with an inner diameter of 22 mm;

[0067] (3) Then install a boron nitride double-layer round cover with an upper end diameter of 28.5 mm, a lower end diameter of 21.5 mm and a layer thickness of 5 mm on the top of the crucible to prevent heat dissipation and volatilization of low-melting-point Sn elements during the high-gravity solidification process;

[0068] (4) Symmetrically fix a counterweight hanging cup and a melting hanging cup on the horizontal rotor of the centrifuge, connect the horizontal rotor with the slip ring, and equip the centrifuge with a rotational speed sensor;

[0069] (5) First, place a thermal insulation material sleeve in the gap between the crucible containing the bulk ingot and the melting ladle to reduce heat loss along the bottom and side walls of the crucible; and place dense fireproof quartz wool at the bottom gap position between the sleeve and the melting ladle to ensure the stability during rotation;

[0070] (6) When the ladle is in a stationary state, add metal counterweight blocks to the counterweight ladle and supplement high-density magnesia. By adjusting the counterweight ladle to have the same mass and centroid as the melting ladle, the dynamic rotational balance of the horizontal rotor is ensured, and it is ensured that the dynamic unbalance of the centrifuge is less than 2 g·mm;

[0071] (7) Subsequently, place the crucible containing the ingot as a whole in a muffle furnace for vacuum heating. The crucible is heated with the furnace to 1250 °C, the vacuum degree is pumped to 10 -3 Pa, and keep it warm for 60 min;

[0072] (8) After the insulation stage ends, quickly transfer the crucible containing the alloy ingot to the melting ladle on the centrifuge turntable and immediately start the centrifuge device;

[0073] (9) Under the conditions of supergravity solidification, the rotational speed of the centrifuge turntable equipped with a high-speed electric slip ring is set to 1687 r / min, and the corresponding supergravity field strength at the bottom of the crucible is 500G. After the alloy melt in the crucible is completely cooled to room temperature, take out the alloy ingot prepared under supergravity (500G), which is the supergravity-prepared copper-nickel-tin alloy sample;

[0074] (10) Cut the alloy ingot sample flat along the diameter direction. Cut a sample from the bottom position of the ingot, and conduct mechanical grinding and argon ion polishing treatments in sequence, and carry out electron backscatter diffraction analysis to observe the fine-grained tissue area of the sample;

[0075] (11) Select the fine-grained tissue area to carry out electron probe wave spectrum analysis, and respectively count the Sn element content in the grain boundary and intragranular regions. Randomly select at least 10 positions of the same type and calculate the average value of the element content;

[0076] (12) Select the fine-grained area to cut tensile specimens, and use a universal testing machine and a video extensometer to measure the yield strength, tensile strength and elongation of the supergravity-prepared copper-nickel-tin alloy sample. Repeat the measurement of samples under the same conditions 4 times and calculate the average value;

[0077] (13) Select the fine-grained area to cut electrochemical corrosion specimens. All electrochemical tests are carried out by a standard three-electrode system, which is powered by a Princeton 3000A-DX electrochemical workstation. With a size of 10×10 mm 2A platinum sheet electrode is used as the counter electrode; a saturated calomel electrode (SCE) is used as the reference electrode; the defect-free initial-state sample is loaded on the platinum sheet electrode clip, exposing 10×10 mm 2 as the working electrode;

[0078] (14) Assemble the three electrodes in the C001 sealed electrolytic cell, and use a dropper to add 3.5 wt.% NaCl electrolyte with the composition of simulated seawater to the electrolytic cell until the liquid level of the electrolyte is tangent to the lower surface of the platinum sheet electrode clip, ensuring that the test sample is completely immersed in the electrolyte;

[0079] (15) Place the installed electrolytic cell on a constant-temperature stage to ensure that the temperature of the electrolyte is 20 °C throughout the test process;

[0080] (16) First, to obtain a stable passive film structure, place the electrochemically corroded sample in the sealed electrolytic cell and soak it for 72 hours, then conduct an open-circuit potential test. Start reading the open-circuit potential from when the working electrode is placed in the electrolyte. After the test potential stabilizes, read the open-circuit potential value;

[0081] (17) Subsequently, at the open-circuit potential, in the frequency range of 10 -2 ~10 5 Hz, use a 10 mV AC signal as the amplitude to collect the electrochemical impedance spectrum, and read the measurement results with Versa.Studio v2.66.2 software;

[0082] (18) At the open-circuit potential, set the initial potential of the Tafel polarization curve test to -0.25 V vs OC, the termination potential to 0.25 V vs OC, and the scanning speed to 0.1666 mV / s;

[0083] (19) Conduct a repeatability test on the above tests, read and calculate the average values of the open-circuit potential, electrochemical impedance, corrosion current, and corrosion potential to ensure the reliability of the data.

[0084] Comparative Example 1

[0085] The method for preparing a Cu-9Ni-2Sn alloy with obvious element segregation by normal gravity is as follows:

[0086] (1) First, put electrolytic copper, Cu-50% Ni master alloy, and Cu-20% Sn master alloy into a melting furnace for vacuum melting, casting, and homogenization annealing treatment to obtain a cast ingot; the mass percentage contents of copper, nickel, and tin elements are 89%, 9%, and 2% respectively;

[0087] (2) The cast ingot obtained in step S1 is successively subjected to wire cutting, mechanical grinding, ultrasonic cleaning with ethanol in an ultrasonic cleaner, and then dried at a constant temperature in a blast drying oven to obtain the copper-nickel-tin raw material for the preparation of the copper-nickel-tin alloy by high gravity. Then, the copper-nickel-tin raw material is processed by wire cutting into several block ingots with a volume approximately 0.5 cm 3 , and all the block ingots are placed inside a crucible with an inner diameter of 22 mm;

[0088] (3) Then, a boron nitride double-layer round cover with an upper end diameter of 28.5 mm, a lower end diameter of 21.5 mm, and a layer thickness of 5 mm is installed on the top of the crucible to prevent heat dissipation during the high-gravity solidification process and the volatilization of low-melting-point Sn elements;

[0089] (4) First, a heat-insulating material sleeve is placed in the gap between the crucible containing the metal raw material and the melting hanging cup to reduce heat loss along the bottom and side walls of the crucible. Subsequently, the crucible containing the ingots is placed entirely in a muffle furnace for vacuum heating. The crucible is heated to 1250 °C with the furnace, and the vacuum degree is pumped to 10 -3 Pa, and held for 60 min;

[0090] (5) After the holding stage is completed, the crucible containing the alloy ingots is quickly transferred to the hanging cup on the centrifuge turntable and left to stand until the melt is completely cooled to room temperature. The alloy ingots prepared under normal gravity (1G) are taken out, which are the copper-nickel-tin alloy samples prepared under normal gravity;

[0091] (6) Cut the alloy ingot sample flat along the diameter direction. Cut a sample from the bottom position of the ingot and conduct electron backscatter diffraction analysis to observe the fine-grained tissue area of the sample;

[0092] (7) Select the fine-grained tissue area to carry out electron probe microanalysis, and respectively count the Sn element content in the grain boundary and intragranular regions. At least randomly select 10 positions of the same type and calculate the average value of the element content;

[0093] (8) Select the fine-grained tissue area to cut tensile specimens, and use a universal testing machine and a video extensometer to measure the yield strength, tensile strength, and elongation of the copper-nickel-tin alloy samples prepared by high gravity. Samples under the same conditions are measured 4 times repeatedly, and the average value is calculated;

[0094] (9) Select the fine-grained tissue area to cut electrochemical corrosion specimens. All electrochemical tests are carried out by a standard three-electrode system, which is powered by a Princeton 3000A-DX electrochemical workstation. A platinum sheet electrode of 10×10 mm 2 is used as the counter electrode; a saturated calomel electrode (SCE) is used as the reference electrode; the defect-free initial-state sample is loaded on the platinum sheet electrode clamp, and 10×10 mm 2 is exposed as the working electrode;

[0095] (10) Assemble the three electrodes in the C001 sealed electrolytic cell, and use a dropper to add 3.5 wt.% NaCl electrolyte with the composition of simulated seawater into the electrolytic cell until the liquid level of the electrolyte is tangent to the lower surface of the platinum electrode clamp, ensuring that the test sample is completely immersed in the electrolyte;

[0096] (11) Place the installed electrolytic cell on the constant temperature stage, ensuring that the temperature of the electrolyte is 20 °C throughout the test process;

[0097] (12) First, to obtain a stable passivation film structure, place the electrochemically corroded sample in the sealed electrolytic cell and soak it for 72 hours, then conduct an open circuit potential test. Start reading the open circuit potential from when the working electrode is placed in the electrolyte. After the test potential stabilizes, read the open circuit potential value;

[0098] (13) Subsequently, at the open circuit potential, in the frequency range of 10 -2 ~10 5 Hz, use a 10 mV alternating current signal as the amplitude to collect the electrochemical impedance spectrum, and read the measurement results with Versa.Studio v2.66.2 software;

[0099] (14) At the open circuit potential, set the initial potential of the dynamic polarization curve test to -0.3 V vs OC, the termination potential to 2 V vs OC, and the scanning speed to 0.5 mV / s;

[0100] (15) Conduct a repeatability test on the above tests, read and calculate the average values of the open circuit potential, electrochemical impedance, corrosion current, and corrosion potential to ensure the reliability of the data.

[0101] Samples were respectively cut from the fine grain structure region at the bottom of the longitudinal section of the low element segregation copper-nickel-tin alloy prepared by high gravity in Examples 1-2 and the coarse dendrite region at the longitudinal bottom of the copper-nickel-tin alloy with obvious element segregation prepared by normal gravity in Comparative Example 1. The normal gravity samples are all coarse dendrite structures. Electron backscatter diffraction analysis and electron probe wave spectrum analysis were carried out. The evolution trends of the average grain size and the segregation degree of Sn element are as Figure 1 shown by the solid line and the dashed line; Tensile specimens were cut from the coarse dendrite region of the normal gravity sample and the fine grain structure region of the high gravity sample, and tensile tests were carried out at room temperature. The tensile strain rate was 10 -3 / s, and a video extensometer was used to calculate the strain in real time. The results of the engineering stress-strain curve are as Figure 2 shown.

[0102] Electrochemical corrosion test samples were respectively cut from the fine-grained tissue region in the middle and lower part of the longitudinal section of the low-element segregation copper-nickel-tin alloy ingot prepared by high gravity of 500G in Example 2 and the coarse dendritic region at the same position of the copper-nickel-tin alloy ingot with relatively serious element segregation prepared by normal gravity in Comparative Example 1. The normal gravity samples were both coarse-grained tissues. The obtained electrochemical corrosion analysis results are as Figures 3-5 shown.

[0103] Figure 1 Fig. shows the evolution trends of the grain size and Sn element segregation coefficient of the Cu-9Ni-2Sn alloy prepared under normal gravity conditions (1G) and high gravity conditions (250G and 500G). The Sn element segregation coefficient is defined as the ratio of the average content of Sn element at the grain boundary to the average content of Sn element in the grain of the same grain, and is used to characterize the degree of Sn element segregation. The larger the segregation coefficient, the more serious the element segregation, and thus the greater the impact on the comprehensive performance of the alloy. From Figure 1 Fig., it can be seen that under normal gravity (1G) conditions, the microstructure of the alloy is mainly composed of coarse dendritic tissues with an average grain size of 441.2 μm. At this time, the Sn element is mainly concentrated at the boundaries of the dendrite trunks and secondary dendrite arms, and the Sn element segregation coefficient is about 4.69. When the high gravity increases to 250G, the average grain size of the Cu-9Ni-2Sn alloy sample significantly decreases to 144.6 μm. At the same time, the Sn element segregation coefficient decreases to about 1.11, indicating that the distribution of Sn elements in the grain and at the grain boundary is more uniform. As the high gravity further increases to 500G, the average grain size continues to shrink to 109.1 μm, and some Sn elements in the grain begin to diffuse to the grain boundary region, and the Sn element segregation coefficient slightly rises to 1.53.

[0104] The average grain size, the content of Sn element at the grain boundary, the content of Sn element in the grain, and the Sn element segregation coefficient of the normal gravity Cu-9Ni-2Sn alloy prepared in Comparative Example 1 and the high gravity Cu-9Ni-2Sn alloys obtained in Examples 1-2 were compared, and the results are shown in Table 1.

[0105] Table 1 Average grain size and Sn element segregation coefficient of Cu-9Ni-2Sn alloy prepared by high gravity solidification

[0106]

[0107] Figure 2 Fig. shows the engineering stress-engineering strain curves of the Cu-9Ni-2Sn alloy prepared by normal gravity (1G) and high gravity (250G and 500G) in Comparative Example 1.

[0108] By Figure 2It can be seen that compared with the normal gravity condition, when the intensity of the supergravity field reaches 250G, the mechanical properties of the Cu-9Ni-2Sn alloy are significantly improved. Among them, the yield strength increases from 115.8 MPa to 131.2 MPa, the tensile strength increases from 224.9 MPa to 266.7 MPa, and the elongation increases from 47.4% to 54.2%. After further increasing the supergravity field intensity to 500G, the alloy shows more obvious strain hardening ability, and the mechanical properties are further enhanced. The yield strength, tensile strength and elongation reach 144.8 MPa, 296.4 MPa and 57.0% respectively, realizing the coordinated improvement of strength and toughness.

[0109] The yield strength, tensile strength and elongation of the normal gravity Cu-9Ni-2Sn alloy prepared in Comparative Example 1 and the supergravity Cu-9Ni-2Sn alloys obtained in Example 1 and Example 2 were compared at room temperature, and the results are shown in Table 2.

[0110] Table 2 Yield strength, tensile strength and elongation of Cu-9Ni-2Sn alloy prepared by supergravity solidification

[0111]

[0112]

[0113] As can be seen from Table 2, the strength of the Cu-9Ni-2Sn supergravity solidification samples obtained in Examples 1-4 is steadily improved. When the intensity of the applied supergravity field is greater, the yield strength, tensile strength and elongation of the alloy all show a trend of first increasing and then decreasing. When the supergravity field intensity is 500G, the peak yield strength, tensile strength and elongation of the Cu-9Ni-2Sn alloy are increased by 25.0%, 31.8% and 20.3% respectively compared with the normal gravity solidification condition, realizing the coordinated optimization of strength and toughness.

[0114] Figure 3 It is the curve of the open circuit potential of the Cu-9Ni-2Sn alloy prepared by the normal gravity (1G) in Comparative Example 1 and the supergravity (500G) in Experimental Example 2 versus time. From Figure 4 it can be seen that after the sample of normal gravity (1G) in Comparative Example 1 enters the electrolyte, the potential moves in the positive direction, indicating that a protective passivation film is formed on the surface of the working electrode. As the test time increases, the open circuit potential continues to increase. At the final stage of the test, the open circuit voltage stabilizes at -0.109V and remains at this value until the end of the test. The initial potential of the sample of supergravity (500G) in Experimental Example 2 is almost the same as that in Comparative Example 1. After that, its open circuit potential shows a continuous increasing trend. When the sample is soaked for 3600 seconds, the open circuit voltage of the supergravity (500G) sample is read as -0.098V, with a 10% increase compared with Comparative Example 1.

[0115] Figure 4 For Comparative Example 1 under normal gravity (1G) and Experimental Example 2 under supergravity (500G), the potentiodynamic polarization curves of the Cu-9Ni-2Sn alloy were obtained. Both the cathodic and anodic branches in the Tafel region of the potentiodynamic polarization curves were used to determine the corrosion current (I corr ) and corrosion potential (E corr ) of the alloy material in Comparative Example 1 under normal gravity (1G). Generally, the higher the corrosion potential E corr and the lower the corrosion current I corr , the better the corrosion resistance of the material. As Figure 4 shown, the corrosion potential of the sample in Comparative Example 1 under normal gravity (1G) was -42.466 mV and the corrosion current was 34.512 pA. While for the Cu-9Ni-2Sn alloy sample prepared in Experimental Example 2 under supergravity (500G), the corrosion potential was -17.358 mV and the corrosion current was 19.785 pA, indicating that the electrochemical corrosion resistance of the alloy sample was significantly improved by treatment in the supergravity field.

[0116] Figure 5 For Comparative Example 1 under normal gravity (1G) and Experimental Example 2 under supergravity (500G), the electrochemical impedance spectroscopy (EIS) diagrams of the Cu-9Ni-2Sn alloy were obtained. By applying small-amplitude sinusoidal wave interference signals with different frequencies to the system, the equivalent circuit during the electrochemical corrosion process was deduced, aiming to obtain information on the electrode interface structure and kinetics. For the Cu-9Ni-2Sn alloy prepared in Comparative Example 1 under normal gravity (1G) and Experimental Example 2 under supergravity (500G), capacitive reactance arc curves with different radii were observed in the Nyquist diagrams of the two groups of samples. The larger the radius of the capacitive reactance arc, the higher the impedance value of its passive film. Compared with the sample under normal gravity (1G), the radius of the capacitive reactance arc of the sample under supergravity (500G) increased significantly, indicating that the passive film formed on the surface of the sample under supergravity (500G) had better corrosion resistance.

[0117] Based on the normal gravity solidification of Cu-9Ni-2Sn alloy, different intensities of supergravity fields are applied in this invention, effectively refining the average grain size and improving the segregation behavior of Sn element at grain boundaries. This is because under supergravity conditions, the dendritic structure is continuously broken during solidification, and the generated dendrite fragments can serve as new nucleation sites, thus promoting grain refinement. As the grain size decreases, the grain boundary number density of Cu-9Ni-2Sn alloy increases significantly. Since the total amount of Sn element remains unchanged, compared with the normal gravity condition, the segregation coefficient of Sn decreases significantly. When the supergravity intensity is 500G, the appropriate content of Sn element at grain boundaries helps to reduce the stacking fault energy in local areas, which increases the probability of forming stacking fault structures and twin structures during plastic deformation, thus enhancing the strain hardening ability of Cu-9Ni-2Sn alloy. However, if the supergravity intensity is too high, strong melt convection may lead to excessive enrichment of Sn element at grain boundaries, forming brittle discontinuous precipitation regions. This phenomenon will cause serious stress concentration during plastic deformation, ultimately leading to premature fracture and failure of the alloy. Therefore, regulating an appropriate supergravity intensity is crucial for optimizing the properties of Cu-9Ni-2Sn alloy.

[0118] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A low-element segregation copper-nickel-tin alloy, characterized in that: The low-element segregation copper-nickel-tin alloy is mainly prepared by mixing electrolytic copper, copper-nickel alloy and copper-tin alloy; in the low-element segregation copper-nickel-tin alloy, the mass percentage content of metallic nickel is 8% - 10%, and the mass percentage content of electrolytic tin is 1.5% - 2.5%.

2. The low-element segregation copper-nickel-tin alloy according to claim 1, characterized in that: In the low-element segregation copper-nickel-tin alloy, the mass percentage content of metallic nickel is 9%, and the mass percentage content of electrolytic tin is 2%.

3. A method for preparing a low-element segregation copper-nickel-tin alloy as described in any one of claims 1-2, characterized in that, It includes the following steps: Step S1: First, put electrolytic copper, copper-nickel alloy and copper-tin alloy into a melting furnace for vacuum melting and pouring to obtain a poured ingot; Step S2: Use the poured ingot to prepare a bulk ingot, and place the bulk ingot in a crucible for heating; Step S3: Symmetrically fix a melting hanging cup and a counterweight hanging cup on the horizontal rotor of a centrifuge, and connect the horizontal rotor to a slip ring; Step S4: Sequentially install an alumina fiber heat preservation sleeve and a crucible containing a bulk ingot inside the melting hanging cup; Step S5: Then, place the entire crucible in a muffle furnace for vacuum heating and insulation; Step S6: After the insulation is completed, take out the crucible after vacuum heating from the muffle furnace and place it in the melting hanging cup of the centrifuge. Immediately start the centrifuge, and by adjusting the rotation speed of the horizontal rotor, make the horizontal rotor drive the crucible to rotate; Step S7: During the rotation of the horizontal rotor, after the crucible is completely cooled to room temperature, take out the completely solidified bulk ingot, which is the sample of the Cu-9Ni-2Sn alloy ingot prepared by high gravity.

4. The preparation method of a low-element segregation copper-nickel-tin alloy according to claim 3, characterized in that: The specific content of the said Step S2 is: Step S2.1: First, perform wire cutting, mechanical grinding, ultrasonic cleaning and constant temperature drying on the poured ingot obtained in Step S1 to obtain copper-nickel-tin raw materials, which are used to prepare copper-zirconium alloy under high gravity; Step S2.2: Then, wire-cut the copper-nickel-tin raw materials in Step 2.1 into several bulk ingots, and place all the bulk ingots inside the crucible; Step S2.3: Then, install a boron nitride double-layer round cover on the top of the crucible containing the bulk ingot, and the boron nitride double-layer round cover is used to prevent the volatilization of heat and Sn element during the high gravity solidification process.

5. The preparation method of a low-element segregation copper-nickel-tin alloy according to claim 3, characterized in that: In the said Step S1, the mass ratio of copper element, nickel element and tin element is 90.5:8:1.5 - 87.5:10:2.

5.

6. The preparation method of a low-element segregation copper-nickel-tin alloy according to claim 3, characterized in that: In the said Step S1, the copper-nickel alloy uses a Cu-50%Ni alloy, and the copper-tin alloy uses a Cu-20%Sn.

7. A method for preparing a low-element segregation copper-nickel-tin alloy according to claim 3, characterized in that: In the step S5, the vacuum heating conditions of the crucible in the muffle furnace are as follows: the vacuum degree is greater than 10 -3 Pa, the crucible is heated in the muffle furnace to not less than 1150 °C, and the heat preservation time is not less than 50 min.

8. The preparation method of a low-element segregation copper-nickel-tin alloy according to claim 3, characterized in that: In the said Step S5, the vacuum heating conditions of the crucible in the muffle furnace are as follows: the crucible is heated to 1250°C with the muffle furnace and kept warm for 60 minutes.

9. The preparation method of a low-element segregation copper-nickel-tin alloy according to claim 3, characterized in that: The dynamic unbalance amount of the centrifuge in the said Step S6 is less than 2 g·mm.

10. The preparation method of a low-element segregation copper-nickel-tin alloy according to claim 3, characterized in that: In the said Step S7, by adjusting the rotation speed of the horizontal rotor, the rotation speed range of the crucible is 1000 - 2200 r / min.

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