Ultrafine grain brass and preparation method thereof

Abstract

The invention belongs to the technical field of metal material processing, and particularly relates to a preparation method of ultra-fine grain brass. The method sequentially comprises the steps of smelting and casting, hot rolling and surface milling, ultrasonic-assisted low-temperature micro-vibration forging treatment, rough rolling, first-time medium-temperature annealing, intense pulsed electric field activation, medium rolling, second-time low-temperature annealing, nano carbide particle composite strengthening, counterfoil rolling, counterfoil annealing, finished product rolling and the like. The grain size of the prepared ultra-fine grain brass material can be stably controlled to be 4.0 microns or below, and the ultra-fine grain brass material has excellent tensile strength, yield strength, ductility and bending performance and is suitable for the fields of high-end connectors, electronic elastic pieces, precise structural parts and the like which have high requirements for obdurability.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, and specifically relates to a method for preparing ultrafine-grained brass. Background Technology

[0002] Copper and copper alloy strips, due to their excellent electrical and thermal conductivity and good corrosion resistance, have been widely used in many industrial fields such as machinery, electronics, automobiles, power, communications, and transportation. In recent years, with the rapid development of science and technology in my country, the application fields of copper and copper alloy strips, as key basic materials, have continued to expand, especially in high-tech fields. This has led to higher market requirements for the performance of copper and copper alloy materials, particularly in terms of the fineness and uniformity of the material's microstructure, resulting in more stringent technical standards.

[0003] In the field of high-end terminal connectors, the fineness and uniformity of the grain structure of copper and copper alloy strips directly determine the stability and service life of the terminal connectors, playing a crucial role in the final product performance. However, taking brass materials as an example, most domestic companies mainly rely on air-cushion furnace annealing processes to control the grain structure. But this process alone is insufficient to achieve truly fine and uniform grains; coarse and uneven grains remain prevalent. This not only makes it difficult for material performance to meet the standards of leading international manufacturers but also further restricts the competitiveness of domestic high-end copper and copper alloy products in the global market. For example, top international connector manufacturers such as TE Connectivity have extremely high requirements for material performance and grain uniformity, while the supply of relevant high-quality copper alloy raw materials in the domestic market is clearly insufficient, necessitating the development of copper and copper alloy materials with finer, more uniform grains and more stable performance.

[0004] Furthermore, insufficient control over grain refinement in traditional processes leads to significant fluctuations in the mechanical properties of processed products, manifesting as unstable tensile strength and insufficient bending performance, which seriously affects the reliability and durability of downstream products. At the same time, traditional annealing processes generally employ high annealing temperatures, resulting in high energy consumption and production costs, thus hindering the industry's economic efficiency and environmental development.

[0005] Therefore, in order to solve the above problems, it is urgent to develop a new copper and copper alloy preparation process to achieve truly fine and uniform grain structure, improve the performance stability of copper materials, reduce production energy consumption and costs, thereby meeting the increasingly stringent technical requirements of the high-end connector field and further enhancing the competitiveness of domestic copper alloy materials in the international market. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing ultrafine-grained brass, in order to solve the problems of coarse and uneven brass grain structure in the prior art, which leads to insufficient tensile strength, unstable bending performance, and inability to meet the stringent performance requirements of high-end terminal connectors, as well as the high energy consumption and high production cost of traditional annealing processes.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing ultrafine-grained brass includes the following steps:

[0009] (1) Smelting and casting: Prepare alloy raw materials according to the following mass percentages: Cu 60.5-81.5%, La 0.01-0.1%, with the balance being Zn; smelt the alloy raw materials at a temperature of 1050-1150℃ to form a uniform melt, and pour the melt into a mold to form a billet;

[0010] (2) Hot rolling to prepare milled billet: The billet is heated to 700-850℃ and then hot rolled. After hot rolling, the surface of the billet is milled to obtain milled billet;

[0011] (3) Ultrasonic-assisted low-temperature micro-vibration forging treatment: heat the milled blank to 150-250℃ and keep it at a constant temperature for 5-10 minutes. Then, the ultrasonic generator and probe are perpendicularly attached to the central area of ​​the milled blank surface and kept in stable contact. Start the ultrasonic equipment to make the milled blank subject to continuous ultrasonic vibration. At the same time, apply a stable forging pressure of 30-300 tons to the blank and maintain the combined action of ultrasonic vibration and forging pressure for 10-30 minutes to obtain the strip blank.

[0012] After this process, the internal grain structure of the milled billet is significantly refined and the microstructure is densified, providing a large number of effective grain refinement nuclei for further grain refinement during subsequent rolling and annealing.

[0013] (4) Rough rolling: The strip from step (3) is rough rolled, and the rough rolling rate is controlled at 70-90%;

[0014] The high processing rate of this step allows the internal structure of the strip to be fully extended and significantly refined, forming a uniform deformed structure, which is conducive to the formation of recrystallization in the subsequent annealing process.

[0015] (5) First bell-type furnace annealing: The rough-rolled strip is placed in a bell-type annealing furnace for medium-temperature annealing. The annealing temperature is controlled between 400-460℃ and held for 4-8 hours.

[0016] This step allows the internal structure of the strip to recrystallize and grow appropriately, thereby softening the strip and ensuring that the material has good deformation capacity when it enters the next processing step.

[0017] (6) Strong pulse electric field assisted grain boundary activation treatment: After the first bell furnace annealing, the strip billet is placed in the strong pulse electric field treatment device and a pulse electric field is applied for 5-15 minutes.

[0018] Pulsed electric field treatment increases grain boundary energy level and grain boundary migration rate, which promotes further refinement of the microstructure and uniform grain distribution in subsequent intermediate rolling.

[0019] (7) Intermediate rolling: The strip after step (6) is rolled again, and the processing rate of the intermediate rolling is controlled at 60-80%;

[0020] This step further improves the compactness of the substrate structure and achieves deeper grain refinement and extension, preparing the microstructure for the next step of low-temperature annealing.

[0021] (8) Second bell-type furnace annealing: The strip after intermediate rolling is annealed at low temperature in a bell-type annealing furnace, with the temperature controlled between 320-400℃ and held for 4-8 hours;

[0022] This step allows the billet structure to recrystallize while strictly controlling excessive grain growth to obtain a finer and more uniform grain structure, and at the same time, the material is appropriately softened.

[0023] (9) Nanocarbide particle composite reinforcement: After the second bell-type furnace annealing, a layer of ethanol or acetone suspension containing TiC or SiC nanoparticles is sprayed onto the surface of the strip and dried.

[0024] This step allows the nano-carbide particles to be embedded in the surface layer of the brass matrix during the under-rolling process, forming stable dispersed reinforcing particles and creating a pinning effect on grain growth, effectively inhibiting grain growth and improving the material's strength, toughness, and bending performance stability.

[0025] (10) Rolling with a bottom layer: Rolling the strip after step (9) with a bottom layer;

[0026] The pre-finishing thickness is calculated and determined according to the finished product requirements, which is the base thickness. The base rolling is carried out according to the base thickness. This step further extends and refines the internal grain structure, providing a uniform grain structure basis for the final product.

[0027] (11) Residual annealing: The strip after residual rolling is subjected to low-temperature annealing again at a temperature of 300-340℃ and held for 4-6 hours;

[0028] During this process, the material structure is fully recrystallized, but grain growth is effectively suppressed, giving the material high ductility and a stable grain structure, laying a good microstructure foundation for the final product rolling.

[0029] (12) Finished product rolling: The strip after the bottom annealing is rolled into finished product to obtain the final ultrafine brass with a grain size of less than 4μm.

[0030] Furthermore, in step (1), the copper raw material is selected from electrolytic copper granules, electrolytic copper ingots or copper plates, with a purity of not less than 99.9%; the zinc raw material is selected from high-purity zinc ingots, electrolytic zinc sheets or zinc granules, with a purity of not less than 99.9%; and lanthanum is introduced in the form of La-Cu master alloy.

[0031] Furthermore, the hot rolling processing rate in step (2) is controlled at 40-70%.

[0032] Furthermore, the frequency of the ultrasound in step (3) is 20-40kHz and the power is 500-3000W.

[0033] Furthermore, the annealing temperature in step (5) is controlled at 420-440℃.

[0034] Furthermore, the intensity of the pulsed electric field in step (6) is 10. 3 -10 5 V / m, pulse frequency is 500-2000Hz.

[0035] Furthermore, the annealing temperature in step (8) is controlled at 330-380℃.

[0036] Furthermore, the TiC or SiC nanoparticles in step (9) have a particle size of 10-50 nm, and the amount of suspension sprayed onto the surface of the strip is controlled at 20-40 mL / m. 2 .

[0037] Furthermore, the processing rate of the bottom rolling in step (10) is controlled at 40-60%.

[0038] Furthermore, the finished product rolling rate in step (12) is controlled at 10-40%.

[0039] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0040] This invention provides a method for preparing ultrafine-grained brass with a unique structure, innovative process, and significantly improved performance. Focusing on the goals of grain refinement and microstructure stability control, it achieves a comprehensive upgrade of traditional brass materials in terms of strength, plasticity, microstructure uniformity, and process stability by introducing the synergistic effects of multiple physical fields and multiple strengthening mechanisms. It is especially suitable for applications such as high-end terminal connectors that have extremely high requirements for the comprehensive performance of materials.

[0041] This invention introduces "ultrasonic-assisted low-temperature micro-vibration forging" for the first time in the preparation of brass strip. This step utilizes high-frequency ultrasound (20-40 kHz) coupled with forging pressure at a low temperature of 150-250℃ to couple the forging pressure onto the billet. During deformation, this introduces numerous dynamic dislocation sources and subgrain boundaries, inducing microscale stress disturbances and local vibration strengthening effects, thereby significantly increasing nucleation density, dislocation activity, and the probability of recrystallization nucleus formation. This pretreatment creates an ideal microstructural basis for the subsequent recrystallization process, significantly reducing grain size and improving microstructure uniformity, making it a key factor in controlling the fine grain size of the material.

[0042] Based on this, the present invention further designed a "strong pulsed electric field assisted grain boundary activation treatment", which involves applying a 10-fold strong pulsed electric field to the strip blank after medium-temperature annealing. 3 -10 5 A pulsed electric field of V / m, while maintaining a constant overall sample temperature, modulates the grain boundary potential energy, thereby enhancing grain boundary mobility and energy drive. This makes the material more prone to uniform recrystallization and equiaxed grain growth during subsequent rolling. This non-thermal physical field activation method overcomes the temperature and time limitations of traditional heat treatment for grain control, giving the material's microstructure evolution more freedom of control and effectively overcoming problems such as grain inhomogeneity and localized coarseness.

[0043] Simultaneously, this invention also introduces a "nanocarbide particle composite reinforcement" mechanism. After the second annealing, TiC or SiC nanoparticles are sprayed onto the material surface to form a suspended distribution film, which is mechanically embedded during the under-rolling process, forming a pinned phase dispersed on the surface. This composite reinforcement phase can provide an obstacle to grain boundary migration during the grain growth tendency stage, significantly delaying the grain coarsening process and endowing the material with higher yield strength and crack resistance. In particular, it exhibits excellent anti-crack initiation ability in 180° repeated bending performance, ensuring that the strip maintains stable and reliable plastic deformation behavior during actual processing.

[0044] Furthermore, this invention employs an optimized multi-stage low-temperature bell-type annealing path in the overall process flow, achieving a gradual, balanced, refined, and stable microstructure evolution process. This avoids the abnormal grain growth and performance fluctuations caused by high-temperature annealing, resulting in a fine, uniform, and dense submicron-level grain structure. The final ultrafine-grained brass has a stable grain size controlled below 4.0 μm, a tensile strength exceeding 620 MPa, a yield strength exceeding 560 MPa, and exhibits excellent resilience without cracks in a 180° bending test, which is at an advanced level among similar brass products.

[0045] This invention effectively solves the problems of large and uneven grain size, difficulty in balancing strength and plasticity, poor bending performance and high energy consumption in traditional processes. It has extremely high application value and promotion prospects, and is particularly suitable for upgrading the core materials of high-end copper alloy products such as high-precision electronic connectors, elastic contacts and precision metal stamping parts. Attached Figure Description

[0046] Figure 1 Metallographic image of the ultrafine-grained brass prepared in Example 1.

[0047] Figure 2 Metallographic image of the ultrafine-grained brass prepared in Example 2.

[0048] Figure 3 Metallographic image of the ultrafine-grained brass prepared in Comparative Example 1.

[0049] Figure 4 Metallographic image of the ultrafine-grained brass prepared in Comparative Example 2.

[0050] Figure 5 Metallographic image of the ultrafine-grained brass prepared in Comparative Example 3.

[0051] Figure 6 Metallographic image of the ultrafine-grained brass prepared in Comparative Example 4.

[0052] Figure 7 Metallographic image of the ultrafine-grained brass prepared in Comparative Example 5.

[0053] Figure 8 Metallographic image of the ultrafine-grained brass prepared in Comparative Example 6.

[0054] Figure 9 This is a test image of a 180° bent sample from Example 1.

[0055] Figure 10 This is a test image of a 180° bent sample from Example 2.

[0056] Figure 11 This is a test image of the 180° bent sample from Comparative Example 1.

[0057] Figure 12 This is a test image of the 180° bent sample from Comparative Example 2.

[0058] Figure 13 This is a test image of the 180° bent sample from Comparative Example 3.

[0059] Figure 14 This is a test image of the 180° bent sample from Comparative Example 4.

[0060] Figure 15 This is a test image of the 180° bent sample from Comparative Example 5.

[0061] Figure 16 This is a test image of the 180° bent sample from Comparative Example 6. Detailed Implementation

[0062] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] Example 1

[0064] This embodiment provides a method for preparing ultrafine-grained brass, including the following steps:

[0065] (1) Smelting and casting: Prepare alloy raw materials according to the following mass percentages: Cu 64.5%, La 0.1%, balance Zn; wherein, Cu raw material is electrolytic copper granules, La raw material is La-Cu master alloy with La content of 20%, and Zn raw material is high-purity zinc ingot; add the above raw materials into a medium frequency induction furnace, heat to 1100℃ under argon protection, stir the melt evenly for 15 minutes, and after the melt is clear, immediately pour it into a graphite mold to form a billet;

[0066] (2) Hot rolling to prepare milled billet: The billet is heated to 780°C and held for 60 minutes. Multiple hot rolling passes are performed, and the reduction ratio is controlled at about 60%. Then, a CNC milling machine is used to remove the oxide scale of 0.25 mm on the upper and lower surfaces to obtain the milled billet.

[0067] (3) Ultrasonic-assisted low-temperature micro-vibration forging: The milled blank is placed on a constant temperature heating platform and heated to 220°C. It is kept at a constant temperature for 8 minutes. Then, an industrial ultrasonic probe (frequency 20 kHz, power 2000W) is vertically attached to the central area of ​​the milled blank. At the same time, a hydraulic forging press is used to apply 45 tons of pressure, and the ultrasonic vibration and forging resonance are maintained for 15 minutes. This process activates grain boundaries and increases nucleation density.

[0068] (4) Rough rolling: The billet processed in step (3) is cold rolled, and the processing rate is controlled at 80%;

[0069] (5) First bell-type furnace annealing: The cold-rolled strip is wound into a bell-type annealing furnace, the annealing temperature is set to 430℃, and it is held for 6 hours to complete the medium-temperature recrystallization;

[0070] (6) Strong pulsed electric field assisted grain boundary activation treatment: After the first bell-type furnace annealing, the strip billet is taken out, spread out and placed on an insulating platform, and an electric field strength of 1×10 is applied. 4V / m, pulse frequency 1000 Hz, processing time 10 minutes, this step enhances the grain boundary migration driving force and provides a stable foundation for intermediate rolling;

[0071] (7) Intermediate rolling: The strip after step (6) is further cold rolled with a processing rate of 70%;

[0072] (8) Second bell-type furnace annealing: The strip after intermediate rolling is re-wound and placed in a bell-type furnace for annealing at 360°C for 6 hours to further refine and stabilize the microstructure;

[0073] (9) Nanoscale carbide particle composite reinforcement: After the second bell-type furnace annealing, the unfolded strip is immersed in 5% nitric acid solution for 2 minutes to remove the oxide film, rinsed with deionized water, and dried in an 80℃ hot air circulation box for 30 minutes; a TiC nanoparticle suspension (particle size 30 nm, mass concentration 2%, dispersion medium is ethanol) is prepared, and the suspension is uniformly sprayed on both sides of the strip using a spray gun, with the spraying amount controlled at 30 mL / m 2 That is, the total spraying volume is approximately 60 mL / m 2 (Double-sided) After spraying, dry in an environment of 80℃ for 1 hour to allow the particles to adhere firmly to the surface of the blank.

[0074] (10) Rolling with a minimum allowable thickness: Roll the dried strip to the minimum allowable thickness, with a processing rate of approximately 50%;

[0075] (11) Residual annealing: The strip after residual rolling is annealed in a bell at 330℃ for 6 hours to fully recrystallize, control grain growth, and improve ductility and microstructure stability;

[0076] (12) Finished product rolling: The strip after the bottom annealing is rolled into finished product, and the finished product rolling rate is controlled at 20% to obtain the final ultrafine brass.

[0077] Example 2

[0078] This embodiment provides a method for preparing ultrafine-grained brass, including the following steps:

[0079] (1) Smelting and casting: Prepare alloy raw materials according to the following mass percentages: Cu 61.3%, La 0.05%, balance Zn; wherein, Cu raw material is electrolytic copper granules, La raw material is La-Cu master alloy with La content of 20%, and Zn raw material is high-purity zinc ingot; add the above raw materials into a medium frequency induction furnace, heat to 1100℃ under argon protection, stir the melt evenly for 15 minutes, and after the melt is clear, immediately pour it into a graphite mold to form a billet;

[0080] (2) Hot rolling to prepare milled billet: The cast billet after homogenization and annealing is heated to 750°C, held for 60 minutes, and hot rolled in multiple passes. The reduction ratio is controlled at about 60%. Then, a CNC milling machine is used to remove the oxide scale of 0.25 mm on the upper and lower surfaces to obtain the milled billet.

[0081] (3) Ultrasonic-assisted low-temperature micro-vibration forging treatment: The milled blank is placed on a constant temperature heating platform and heated to 200°C. It is kept at a constant temperature for 10 minutes. Then, an industrial ultrasonic probe (frequency 30 kHz, power 2000W) is vertically attached to the central area of ​​the milled blank. At the same time, a hydraulic forging press is used to apply 50 tons of pressure, and the ultrasonic vibration and forging resonance are maintained for 20 minutes. This process activates grain boundaries and increases nucleation density.

[0082] (4) Rough rolling: The billet processed in step (3) is cold rolled, and the processing rate is controlled at 75%;

[0083] (5) First bell-type furnace annealing: The cold-rolled strip is wound into a bell-type annealing furnace, the annealing temperature is set to 420℃, and the temperature is held for 7 hours to complete the medium-temperature recrystallization;

[0084] (6) Strong pulsed electric field assisted grain boundary activation treatment: After the first bell-type furnace annealing, the strip billet is taken out, spread out and placed on an insulating platform, and an electric field strength of 1×10 is applied. 4 V / m, pulse frequency 1000 Hz, processing time 10 minutes, this step enhances the grain boundary migration driving force and provides a stable foundation for intermediate rolling;

[0085] (7) Intermediate rolling: The strip after step (6) is further cold rolled with a processing rate of 70%;

[0086] (8) Second bell-type furnace annealing: The strip after intermediate rolling is re-wound and placed in a bell-type furnace for annealing at 330°C for 8 hours to further refine and stabilize the microstructure;

[0087] (9) Nanoscale carbide particle composite reinforcement: After the second bell-type furnace annealing, the unfolded strip is immersed in 5% nitric acid solution for 2 minutes to remove the oxide film, rinsed with deionized water, and dried in an 80℃ hot air circulation box for 30 minutes; a SiC nanoparticle suspension (particle size 30 nm, mass concentration 2%, dispersion medium is ethanol) is prepared, and the suspension is uniformly sprayed on both sides of the strip using a spray gun, with the spraying amount controlled at 30 mL / m 2 That is, the total spraying volume is approximately 60 mL / m 2 (Double-sided) After spraying, dry in an environment of 80℃ for 1 hour to allow the particles to adhere firmly to the surface of the blank.

[0088] (10) Rolling with a minimum allowable thickness: Roll the dried strip to the minimum allowable thickness, with a processing rate of approximately 50%;

[0089] (11) Residual annealing: The strip after residual rolling is annealed in a bell at 310℃ for 5 hours to fully recrystallize, control grain growth, and improve ductility and microstructure stability;

[0090] (12) Finished product rolling: The strip after the bottom annealing is rolled into finished product, and the finished product rolling rate is controlled at 20% to obtain the final ultrafine brass.

[0091] Comparative Example 1

[0092] This comparative example provides a method for preparing ultrafine-grained brass, which differs from Example 1 in that the ultrasonic-assisted low-temperature micro-vibration forging process in step (3) is not performed.

[0093] Comparative Example 2

[0094] This comparative example provides a method for preparing ultrafine-grained brass, which differs from Example 1 in that the temperature of the first bell-type furnace annealing in step (5) is 500°C.

[0095] Comparative Example 3

[0096] This comparative example provides a method for preparing ultrafine-grained brass, which differs from Example 1 in that the strong pulsed electric field assisted grain boundary activation treatment step (6) is not performed.

[0097] Comparative Example 4

[0098] This comparative example provides a method for preparing ultrafine-grained brass, which differs from Example 1 in that the temperature of the second bell-type furnace annealing in step (8) is 450°C.

[0099] Comparative Example 5

[0100] This comparative example provides a method for preparing ultrafine crystalline brass, which differs from Example 1 in that the nano-carbide particle composite reinforcement step (9) is not performed.

[0101] Comparative Example 6

[0102] This comparative example provides a method for preparing ultrafine crystalline brass, which differs from Example 1 in that the temperature of the bottom annealing in step (11) is 270°C.

[0103] Performance testing

[0104] The performance of the ultrafine-grained brasses prepared in Examples 1-2 and Comparative Examples 1-6 was tested. The average grain size was measured using a metallographic microscope. The tensile strength and yield strength were tested according to GB / T34505-2017, and the 180° bending test was tested according to GB / T232-2010. The metallographic images of Examples 1-2 and Comparative Examples 1-6 are shown below. Figure 1-8 As shown, the bending test is as follows Figure 9-16As shown.

[0105] The test results are shown in Table 1:

[0106] Table 1

[0107]

[0108] The above results demonstrate that the ultrafine-grained brass prepared in Examples 1-2 of this invention possesses significant performance advantages, meeting the requirements for high strength, high ductility, and high reliability in high-end connectors and other fields. Comparative Example 1, without ultrasonic-assisted low-temperature micro-vibration forging, exhibited a grain size increase to 15.2 μm and a tensile strength decrease to 598 MPa. A slight edge crack appeared in the bending test (an extremely fine crack with a width <0.05 mm appeared in the edge region of the outer bend). This indicates that ultrasonic micro-vibration forging effectively promotes grain refinement and increases nucleation density, playing a crucial role in improving mechanical properties. In Comparative Example 2, the first bell-type annealing temperature was increased to 500℃, resulting in a significant increase in grain size and a further decrease in tensile strength to 562 MPa. The 180° bending test showed edge cracks (a clearly visible crack with a width <0.1 mm appeared in the edge region of the outer bend). This indicates that improper control of the medium-temperature annealing temperature can lead to abnormal grain growth and reduced overall mechanical properties. Comparative Example 3, without strong pulsed electric field-assisted grain boundary activation treatment, showed further grain coarsening, with tensile strength decreasing to 559 MPa and yield strength to 539 MPa. A noticeable crack appeared during a 180° bend (a visible crack with a penetrating tendency at the outer bend). This indicates that electric field activation treatment helps regulate grain boundary migration and refine recrystallized grains. In Comparative Example 4, the second bell-type annealing temperature was increased to 450℃, resulting in a decrease in tensile strength to 604 MPa. Edge cracking occurred during the bending test (obvious openings or localized peeling appeared at the edge of the outer bend), indicating that excessively high temperatures at this stage easily lead to grain coarsening, reducing plasticity and crack resistance. Comparative Example 5, without composite reinforcement with nano-carbide particles, had a tensile strength of 580 MPa. The bending result showed obvious cracks, indicating a lack of pinning effect from nanoparticles, uncontrolled grain growth, poor microstructure uniformity, and decreased plasticity. In Comparative Example 6, the annealing temperature was reduced to 270℃, and the bending performance showed slight cracks (shallow cracks with a width of <0.05 mm appeared in the edge area of ​​the outer bending part). This indicates that the annealing temperature was too low, the recrystallization of the structure was insufficient, the residual stress of deformation was not completely released, resulting in insufficient plasticity.

[0109] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing ultra-fine grain brass, comprising the following steps: (1) melting and casting a copper alloy raw material to form a cast blank; (2) hot-rolling and milling the cast blank to obtain a milled blank; (3) heating the milled blank, applying ultrasonic vibration thereto, and simultaneously applying a stable forging pressure to obtain a strip blank; (4) rough-rolling the strip blank; (5) annealing the rough-rolled strip blank in a bell-type annealing furnace at a temperature of 400-460℃ for 4-8 hours; (6) after the annealing, applying a pulse electric field to the strip blank for 5-15 minutes; (7) re-rolling the strip blank after the treatment in step (6); (8) annealing the rolled strip blank in a bell-type annealing furnace at a temperature of 320-400℃ for 4-8 hours; (9) after the annealing, spraying a layer of ethanol or acetone suspension containing TiC or SiC nanoparticles on the surface of the strip blank and drying; (10) bottom-remaining rolling the dried strip blank; (11) bottom-remaining annealing the bottom-remaining rolled strip blank at a temperature of 300-340℃ for 4-6 hours; (12) finish-rolling the bottom-remaining annealed strip blank to obtain the final ultra-fine grain brass.

2. The production method according to claim 1, characterized by, In step (1), the mass percentage of the copper alloy raw material is as follows: Cu 60.5-81.5%, La 0.01-0.1%, and the balance being Zn; the copper raw material is selected from electrolytic copper particles, electrolytic copper ingots or copper plates, and has a purity of not less than 99.9%; the zinc raw material is selected from high-purity zinc ingots, electrolytic zinc sheets or zinc particles, and has a purity of not less than 99.9%; the lanthanum is introduced in the form of La-Cu intermediate alloy; and the melting temperature is controlled at 1050-1150℃.

3. The preparation method according to claim 1, characterized in that, In step (2), the processing rate of the hot-rolling is controlled at 40-70%.

4. The preparation method according to claim 1, characterized in that, In step (3), the milled blank is heated to 150-250℃ and kept at a constant temperature for 5-10 minutes, then the ultrasonic generator and the probe are vertically attached to the central region of the surface of the milled blank and kept in stable contact, the ultrasonic device is started, the milled blank is subjected to continuous ultrasonic vibration, and a stable forging pressure of 30-300 tons is applied to the blank, the ultrasonic vibration and the forging pressure are combined for 10-30 minutes to obtain the strip blank; the frequency of the ultrasonic vibration is 20-40 kHz, and the power is 500-3000 W.

5. The preparation method according to claim 1, characterized in that, In step (4), the processing rate of the rough-rolling is controlled at 70-90%, and in step (5), the annealing temperature is controlled at 420-440℃.

6. The method of claim 1, wherein, The intensity of the pulse electric field in step (6) is 10 3 -10 5 V / m, and the pulse frequency is 500-2000 Hz.

7. The preparation method according to claim 1, characterized in that, In step (7), the processing rate of the rolling is controlled at 60-80%, and in step (8), the annealing temperature is controlled at 330-380℃.

8. The method of claim 1, wherein, The particle size of the TiC or SiC nanoparticles in step (9) is 10-50 nm, and the spraying amount of the suspension on the surface of the strip is controlled at 20-40 mL / m 2 .

9. The method of claim 1, wherein, In step (10), the processing rate of the bottom-remaining rolling is controlled at 40-60%.

10. The method of claim 1, wherein, In step (12), the processing rate of the finish-rolling is controlled at 10-40%.

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