Method for achieving grain refinement by asynchronous staggered rolling and controllable DS rolling mill

Abstract

The present invention relates to a method for achieving grain refinement by means of asynchronous staggered rolling and a controllable DS rolling mill thereof. By means of the program-controlled parameters of a dedicated asynchronous staggered rolling mill that is dynamically regulated, all-round rolling, kneading and grain regeneration shaping of high-purity, high-conductivity billets are achieved, including fine forging, shaping, and standardization into strip-shaped or circular plate-shaped finished billets; each rolling is carried out in two steps, and the process parameters of adjacent steps are corrected but not excessively, so as to achieve the minimum driving force and the maximum grain refinement effect. The focus of the improved DS rolling mill structure is on precise online control, immediate parameter correction, and the realization of three-dimensional synchronous deformation of the lattice. It ensures that the distribution of the lattice shaping organization is stable after refinement, and ultimately obtains a chip-level copper sheet with uniform organization on the surface and core and stable grain refinement.

Description

Technical Field

[0001] The present invention belongs to the technical field of copper and copper alloy processing, relates to a method for fine processing of ultra-high purity copper plates and achieving grain refinement, and is related to the improvement and application of a special DS rolling mill system. Background Art

[0002] Ultra-high-purity copper boasts superior electrical and thermal conductivity, strong plasticity and ductility, and high strength, making it widely used in various mechanical and electrical equipment, as well as electronic products. It has become the preferred conductive material in the semiconductor, recording media, and advanced display industries. With the advancement of artificial intelligence (AI) technology and the continuous reduction in the feature size of integrated circuits (ICs), the RC delay of interconnects has become a major issue affecting circuit speed. Therefore, the search for conductive materials with lower resistivity and dielectric materials with lower dielectric constants has become crucial for the development of ultra-large-scale integrated circuits (VLSIs). High-purity copper has clearly become the optimal alternative to existing high-conductivity materials. However, facing the challenges of large-scale production of integrated circuits and the RC delay caused by impedance and capacitance in circuit structure interconnects, sputtering-generated dielectric films are essential to further improve and reduce the negative impact on signal transmission speed. Chemical purity alone is not enough. Electron sputtering technology is essential to enhance the technical performance of ultra-high-purity copper and improve its quality. Upgrading high-conductivity copper to sputtering targets has become an urgent technological upgrade. The key point is that as a means of electron sputtering technology, it must meet the three major technical and economic conditions for upgrading high-purity copper materials to chip-grade materials and comply with large-scale, industrialized production: ① Make the structure of high-purity copper materials more uniform and fine, with an average grain refinement size of 10-20μm and a low proportion of twins, meeting the requirements of the electron sputtering process for fine structure as a Cu target material. ② The processing effect makes the conductor grains finer and the distribution from the upper and lower surfaces to the core uniform and stable. As a plate, the hardness distribution along the thickness direction must be uniform, and the hardness value must be significantly improved, and the upper and lower plate surfaces must be flat and smooth; ③ It must adapt to the needs of large-scale, large-volume, and industrialized production, that is, it must be able to meet and guarantee the technical and economic indicators of further processing of chip-grade copper materials by the end products of the industrial chain. In other words, the development of a process for preparing ultra-high-purity copper-based sputtering targets and improving the utilization rate of sputtering targets has become the key to the development of the large-scale integrated circuit industry. Summary of the Invention

[0003] The present invention aims to provide a method for grain refinement of high-conductivity copper materials using a dedicated controllable asynchronous staggered rolling mill. This method achieves the goal of grain refinement of high-purity copper materials through fine forging, rolling, and kneading, thereby upgrading and modifying high-purity, high-conductivity copper materials to chip-grade copper materials.

[0004] The present invention uses a dedicated DS rolling mill to randomly realize online regulation of shear forces along the rolling direction (RD) and perpendicular to the rolling direction (ND) during the rolling process, thereby greatly reducing the rolling pressure and torque, improving the rolling efficiency, and enhancing the uniformity of the copper material's structure. This makes the grains inside the copper material finer, and ultimately obtains a refined and finished product with an average grain size of 10-20 μm and uniform distribution.

[0005] The technical means adopted in the present invention include:

[0006] Material selection, billet formation, hot forging, DS rolling, and final heat treatment. The key lies in the fact that the above method includes a control method for fine processing of high-purity copper materials and achieving grain refinement. The method includes material selection, billet formation, hot forging, DS rolling, and recrystallization heat treatment. The key lies in the fact that the above method includes the following steps:

[0007] (1) Select 5N (99.999%) - 6N (99.9999%) high-purity copper ingots and use electric furnace refining to cast them into billets;

[0008] (2) The processed blank is cold forged, shaped, and standardized into a strip or round plate-shaped finished blank;

[0009] (3) Determine the geometric dimensions of the finished billet based on the processing capacity of the matching DS rolling mill;

[0010] (4) Each rolling process is carried out in two steps: the speed ratio and offset of the two rollers of the DS rolling mill are dynamically controlled online to achieve synchronous deformation of the grains in three dimensions; between the two rolling steps, the rolling surface of the rolled blank is flipped and the rolling direction is inverted, which is executed by the supporting circuit program with the help of the supporting servo mechanism.

[0011] (5) Repeat the above step (4) 3-4 times to obtain the finished copper plate of the final thickness;

[0012] (6) The intermediate product after each rolling needs to be subjected to stress relief annealing treatment;

[0013] (7) The final product after each rolling needs to be recrystallized annealing to ensure that the final structure is fine-grained and the structure distribution is random, and finally a chip-grade copper material with uniform structure on the surface and core and significantly refined grains is obtained.

[0014] The following is a further description, supplement and interpretation of the process and technical means adopted in the method of the present invention:

[0015] The purity of the high-purity copper ingot described in step (1) is preferably 6N.

[0016] In step (3), the finished rolled blank is subjected to post-forging heat treatment at a holding temperature of 390-410° C. for a holding time of not less than 0.5 hours, and is then quenched in water and cooled to room temperature.

[0017] In step (4), the process control range of each rolling of the supporting DS rolling mill is: misalignment amount 0-10mm, misalignment angle 3°-6°, each reduction rate 10%-20%, implemented in two steps, the roller speed ratio is set to v2 / v1=1.1-1.2, and is dynamically controlled by the program; the flipping and rubbing direction of the billet rolling surface are inverted at the configured flipping and transfer station, and are achieved with the help of the flipping and steering mechanism.

[0018] The repeated use of the above technical means not only changes the specific process parameters online, but also promotes the amplitude and shape of the grains to be irregularly kneaded, crushed, broken and expanded to form a refinement effect.

[0019] The annealing temperature in step (7) is 180-200° C., and the holding time is 0.3 hours.

[0020] The rolling surfaces of the two adjacent billets are the same and the rolling directions are consistent; the turning and transfer station at the billet inlet port of the DS rolling mill resets and / or modifies the process parameters in the management and control programs of the DS rolling mill system.

[0021] Although the billet's rolling surface and rolling direction are identical during the two consecutive rolling steps, they actually undergo a two-step process of flipping and reversing. Since the changes in the billet from the previous rolling step can be monitored randomly, experienced operators can flexibly adjust process parameters based on their own experience and, with the help of the experience database, randomly modify and supplement process parameters between the two steps to achieve the best refinement results.

[0022] Each time the rolling surfaces of the billets in two adjacent steps are turned over and rubbed in opposite directions, the process parameters in the management and control programs of the DS rolling mill system are reset and / or modified at the turning and transfer station.

[0023] In step (6), the copper plate after the DS (asynchronous + dislocation) rolling is subjected to a final recrystallization annealing treatment at an annealing temperature of 280-300° C. and a holding time of 1 hour, thereby obtaining a chip-grade copper plate with an average grain size of less than 10 μm.

[0024] The final recrystallization annealing treatment mentioned above is a very important step in this process. This patented method and the empirical database summarized based on the strength of the experience will provide empirical data on the optimal heat treatment temperature, time, and additional conditions under different material properties under various parameter backgrounds, which can successfully achieve the grain refinement effect.

[0025] The following is a further supplementary and improved explanation of the special DS rolling mill used in the method of the present invention:

[0026] The DS rolling mill system dedicated to the control method for fine processing of high-purity copper materials and achieving grain refinement has been comprehensively improved to adapt to the supporting method of the present invention. The supporting experience database module includes the following experience data, process parameter settings and parameter assignments, and experience effect data examples:

[0027] ① Example experience data:

[0028] Standard size of the initial rolled billet: L×K×H, thickness of the rolled billet: 24.5→3.5

[0029] Average structural particle size index: 10 microns, reference design of process steps: three times and six steps;

[0030] Note: A, B: represent the upper and lower surfaces to be pressed, A1, B1: represent the upper and lower surfaces of the initial pressing;

[0031] ② Reference range of dynamic control range of embodiment process

[0032]

[0033] ③Comparison of performance parameters between embodiment and synchronous rolling:

[0034]

[0035] The dynamic online adjustment of process parameters involved in this patented method is key to producing the significant positive effect of grain refinement. Therefore, controlling process parameters is a crucial step. Our research team conducted extensive process parameter testing on a variety of materials and specifications, accumulating and summarizing a vast amount of empirical data to form an empirical database. This empirical database ensures that, for a standardized copper blank, within a limited number of repetitive tasks, each critical parameter value in the dynamic control program can be accurately selected, confirmed, and corrected, laying the foundation for automated equipment management and high-quality production.

[0036] The following describes how the patented method is supported by the important improved features of the dedicated DS rolling mill:

[0037] A special DS rolling mill system for fine processing of high-purity copper materials and a control method for achieving grain refinement is characterized in that the symmetrical frame described in the improvement is an integrated window frame-shaped closed structure composed of an upper crossbeam, a lower base, and left and right vertical columns. A special-shaped middle beam is provided in the window frame structure, and an adjusting compression spring is provided at the concave position of the middle beam. An adjusting oil cylinder is provided in the middle of the upper crossbeam, and a bearing seat for the upper roller shaft head is provided between the upper crossbeam and the compression spring. The bearing seat is limited between two parallel slideways, ensuring that the upper roller shaft head has the freedom of translational adjustment along the vertical direction.

[0038] A special workstation for online blank turning and reversing is set in the blank conveyor device of the servo mechanism of the system. When the blank is turned over and reversed online, the control program completes the supplement or modification of the processing parameters.

[0039] The flipping and transfer station and the feed table are both components of the billet conveyor belt device, and are arranged in parallel at the billet inlet end of the dedicated DS rolling mill. The working surface of the flipping and transfer station is 15-20 cm higher than the working surface of the feed table; the flipping and transfer station panel is equipped with a transfer and flipping device, and the parallel push rod, the lifting intermediate product guide wheel group and the position sensor are combined to form a billet flipping and transfer device.

[0040] The transfer and turning device is arranged at the edge of the turning transfer station table and is connected to the feed table with the help of a conveying slope: the transfer and turning device structure includes a turning main shaft and 3-4 driving fins positioned on the turning main shaft, a limiting core shaft and 2-3 limiting rods on the positioning limiting core shaft; the turning main shaft and the limiting core shaft are concentric shafts, the limiting rod passes through a 125-degree arc-shaped groove provided on the wall of the turning main shaft, and limits the core shaft and the limiting rod positioned on the shaft to have a freedom of rotation of 125 degrees, and the limiting core shaft is reset with the help of a reset coil spring provided on the central shaft.

[0041] According to the famous Hall-Petch theory: σ=σ0+kd -1 / 2Reducing grain size d can significantly improve material strength. Our research group conducted an in-depth review and research on effective methods for reducing grain size and improving material strength while collecting literature on large plastic deformation. We also conducted a comprehensive analysis and comparison of techniques such as high-pressure torsion (HPT) and equal-channel angular pressing (ECAP). We recognized that while these methods can effectively reduce grain size and improve copper strength, they are not suitable for large-scale mass production. Existing large-scale production of medium- and high-strength copper sheets still relies on traditional processes, either synchronous rolling, conventional asynchronous rolling, or a simple combination of the two. Synchronous rolling produces copper sheets with uneven microstructure refinement between the surface and core, high rolling forces, and low rolling efficiency. While asynchronous rolling can create a rolling zone, the unequal speeds of the upper and lower rollers can easily induce bending stresses in the sheet. Furthermore, the surface and core microstructures of asynchronously rolled copper sheets are uneven, resulting in significant performance variations. For applications in large-scale integrated circuits, quality improvement and modified applications have become important areas for improvement. The present invention utilizes dynamic DS (asynchronous + offset) rolling, staggering the upper and lower rolls along the rolling direction and employing dynamic control. This bidirectional control offsets the bending deformation of the sheet caused by conventional processes and asynchronous rolling, correcting structural unevenness, controlling grain refinement, and expanding the core, effectively improving the overall quality of high-strength copper sheet. The present invention's preparation process and grain refinement control method focus on the role of dynamic adjustment of the dislocation angle and shear force (DS) in the DS rolling mill and, based on the upgraded specialized equipment structure, utilizes positioning plates to adjust the work rolls, causing them to move horizontally. This ensures dynamic adjustment of the dislocation angle between the upper and lower work rolls. Dynamic dislocation control dynamically adjusts the dislocation angle between the work rolls, roll speed, and front-to-back tension during the rolling process. This enables online control of process parameters during rolling, ultimately establishing a new ultra-high-purity copper sheet fine processing task and grain refinement method supported by an empirical database, ultimately achieving the goal of uniformly refined chip-grade copper.

[0042] In the DS rolling process, the deformation zone can be divided into four different regions: the rear sliding zone (region I), the rolling zone (region II), the front sliding zone (region III), and the reverse bending deformation zone (region IV). The unit pressure of the four control regions can be calculated using the principal stress method to obtain the following formula:

[0043]

[0044]

[0045]

[0046]

[0047] p I , p II , p III , p IV They represent the unit pressures of the rear sliding zone (Zone I), the rolling zone (Zone II), the front sliding zone (Zone III), and the reverse bending deformation zone (Zone IV). Integrating the unit pressures of the four zones yields the total rolling force solution:

[0048]

[0049] Under the condition of the same single-pass reduction, the rolling force measured in the experiment was limited to 145KN for synchronous rolling and 130KN for DS rolling; the DS (asynchronous + staggered) rolling method can effectively reduce the rolling force, which is consistent with the theoretical results.

[0050] Compared to existing technologies, the technical solution of the present invention offers significant improvements and significant benefits: 1. By leveraging the structural upgrades and dynamic control procedures of the DS rolling mill, the present invention enables the provision of shear forces along the RD and ND directions, with random dynamic control. This increases the amplitude and frequency of shear deformation, as well as the online dynamic changes during the rolling process. During online processing, a rolling zone is generated within the high-purity copper billet, promoting the frequency and amplitude of lattice morphology changes, enabling better strain transfer and penetration into the core of the sheet, significantly improving the direction of the rolling force, and enhancing rolling efficiency and refinement. 2. The present invention utilizes random selection of DS parameters for online control, enhancing dynamic control. Compared to conventional synchronous or asynchronous rolling, the horizontal offset of the rolls in the DS rolling process generates a counteracting force, significantly reducing warpage in the intermediate product. This addresses the issues of severe bending, microstructure refinement, and uneven grain size distribution along the thickness of the sheet during fine processing of thicker sheets. Grain refinement simultaneously and significantly improves the uniformity of surface and core refinement, significantly impacting downstream products, particularly those modified using electron sputtering. 3. The present invention's fine processing method for high-purity, high-conductivity copper materials, especially the controlled refinement of regenerated grains, can achieve a finer and more uniform microstructure than that achieved by synchronous rolling and existing asynchronous rolling processes. The resulting microstructure is more uniform, and the grain refinement is more pronounced. A series of standardized success stories have been obtained in a large number of trial productions, and empirical data has been compiled for the process parameters for large-scale production. After annealing, the average grain size of chip-grade high-purity, high-conductivity, and high-strength copper materials stabilizes at 9.9μm, with a twin boundary ratio of 59.75%. Compared to existing technologies using the same rolling procedures and heat treatment process conditions, the present invention can more effectively refine the grain size and reduce the twin boundary ratio. The grain size is refined by 19.5%, and the twin boundary ratio is reduced by 8.8%. 4. The present invention only requires a simple modification of the existing horizontal continuous rolling production line and the design of a supporting automated and intelligent control program to achieve large-scale industrial production and ensure low cost, high production efficiency, and stable product quality. This ensures the safety, reliability, long-term stability, and wide adaptability of cutting-edge products used in ultra-large-scale integrated circuits after electron sputtering processing. It is ideally suited to the rapid development of ultra-large-scale circuits and the demands arising from the further development and application of fine processing and large-scale integrated circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 For the synchronous rolling in Example 2 Figure 1 a and Figure 1 b is the actual sample after rolling in DS rolling method;

[0052] Figure 2 RD-ND surface hardness distribution diagram of samples taken at the same position after synchronous rolling and DS rolling in Example 2;

[0053] Figure 3 RD-ND plane grain boundary and twin boundary diagram (a) and orientation misorientation angle distribution diagram (b) of the plate after annealing after synchronous rolling in the embodiment;

[0054] Figure 4 (a) The RD-ND plane grain boundary and twin boundary diagram and (b) the misorientation angle distribution diagram of the DS rolled plate after annealing in Example 2;

[0055] Figure 5 Figure 2 shows the effects of different rolling methods on the deformation of the rolled piece during the rolling process. (a) shows the overall deformation of the rolled piece during synchronous rolling; (b) shows the deformation diagram of the rolling zone during synchronous rolling. (c) shows the overall deformation of the rolled piece during DS rolling; (d) shows the deformation diagram of the rolling zone during DS rolling.

[0056] Figure 6 The equivalent strain distribution cloud diagrams for the synchronous rolling and DS (asynchronous + offset) rolling simulations in Example 2 when the deformation is 60%. (a) Synchronous rolling; (b) DS (asynchronous + offset) rolling; (c) Synchronous rolling cross-section; (d) DS (asynchronous + offset) rolling cross-section.

[0057] Figure 7 The equivalent strain distribution cloud diagrams of Example 2 when the simulated deformation amount of synchronous rolling and DS (asynchronous + staggered) rolling is 70%; (a) is synchronous rolling; (b) is DS (asynchronous + staggered) rolling; (c) is a cross-sectional view of synchronous rolling; (d) is a cross-sectional view of DS (asynchronous + staggered) rolling;

[0058] Figure 8 The equivalent strain distribution cloud diagrams of Example 2 when the simulated deformation of synchronous and asynchronous + staggered rolling is 87.5%; (a) is synchronous rolling; (b) is asynchronous + staggered rolling; (c) is a cross-sectional view of synchronous rolling; (d) is a cross-sectional view of asynchronous + staggered rolling;

[0059] Figure 9 Metallographic images of the ultra-high purity copper ingot of Example 2 after synchronous rolling and subsequent heat treatment at 300°C for 1 hour; (a) shows the edge structure; (b) shows the core structure;

[0060] Figure 10 Metallographic images of the ultra-high purity copper ingot of Example 2 after synchronous + staggered rolling and subsequent heat treatment at 300°C for 1 hour; (a) shows the edge structure; (b) shows the core structure;

[0061] Figure 11 Figure 2 is the microstructure of the sample of Example 2 after final heat treatment (300°C for 1 hour); (a) is the sample after synchronous rolling, and (b) is the sample after DS (asynchronous + offset) rolling;

[0062] Figure 12 The grain size distribution histogram of the sample of Example 2 after final heat treatment (300°C for 1 hour); (a) is the sample after synchronous rolling, and (b) is the sample after DS (asynchronous + staggered) rolling;

[0063] Figure 13 This is a schematic diagram of the layout of the patented method and dedicated DS rolling mill production line;

[0064] Where S represents the working area of ​​DS rolling mill, S1 represents the turning and conveying workbench, S2 represents the feeding table, and S3 represents the conveying slide extending to the bottom of the turning and conveying device;

[0065] Figure 14 Schematic diagram of the turning and conveying workbench structure;

[0066] Figure 15 This is a schematic diagram of the overall structure of the DS rolling mill dedicated to this patented method;

[0067] Figure 16 It is the front view of the symmetrical side frame of the DS rolling mill;

[0068] In the above drawings: S represents the billet conveyor belt device, S1 represents the flipping and transfer station, S2 represents the feeding table, S3 represents the conveying slide, S3-1 represents the rotating guide groove on the conveying slope, S11 represents the transfer and flipping device, S12 represents the linear push rod, S12-1 represents the push rod guide groove, S13 represents the lifting type billet transfer guide wheel group, S14 represents the position sensor, S11-a represents the flipping spindle, S11-b represents the flipping fin, S11-a1 represents the limit core shaft, S11-b1 represents the limit rod, O represents the positioning center axis, h1 and h2 represent the symmetrical side frames, g1 and g2 represent the upper and lower rollers respectively, C represents the integrated window frame-shaped closed structure, L represents the center beam, Z represents the bearing seat, P1 and P2 represent two parallel slides, and Z1 represents the lower roller bearing seat. DETAILED DESCRIPTION

[0069] Example 1:

[0070] The ultra-high purity copper sheet with an initial thickness of 24.5 mm after hot forging is subjected to recrystallization heat treatment, and then DS reciprocating rolling is carried out, accompanied by intermediate annealing heat treatment, until the copper sheet is rolled to 3.5 mm, and then the final heat treatment is carried out. The specific steps are as follows: (1) After hot forging, the ultra-pure copper (99.9999% Cu) is subjected to recrystallization heat treatment. The heat treatment process is: anneal the copper sheet at 390°C for 0.5 hours, then quench and cool it in water to room temperature; (2) The chip-grade ultra-pure copper after heat treatment is subjected to DS rolling, with a misalignment of 0 to 5 mm, a misalignment angle maintained at 2° to 3°, a reduction rate of 10% to 15%, and a roller speed ratio controlled at 1.17. (3) The ultra-high purity copper after rolling is subjected to stress relief annealing heat treatment. The holding temperature is 180°C, the holding time is 0.5 hours, and the sheet is quenched in water to room temperature. (4) The ultra-high purity copper is subjected to reverse room temperature DS rolling using a DS rolling mill. The rolling surfaces (A, B) of the two adjacent billets are the same, and the rubbing directions are consistent; the process parameters in the servo mechanism control program are reset and modified at the dedicated station (S). That is, the rolling direction is opposite to the previous one, and the rolling offset S of the DS rolling mill is dynamically adjusted before rolling so that the offset angle is maintained at 2° to 3°, thereby ensuring that the rolling force direction remains within a certain range. (5) Repeat the above steps 2), 3), and 4) for a total of 3 rolling and intermediate heat treatments to obtain an ultra-high purity copper plate with a thickness of 3.5 mm. (6) The ultra-high purity copper after rolling is subjected to recrystallization annealing heat treatment at an annealing temperature of 300°C and a holding time of 1 hour to obtain a recrystallized structure. The final ultra-high purity copper plate with uniform surface and core structure and significantly refined grains is obtained, and an ultra-high purity copper plate with an average grain size of 11.9±1.0μm is obtained.

[0071] Example 2:

[0072] The ultra-high purity copper sheet with an initial thickness of 24.5 mm after hot forging is subjected to recrystallization heat treatment, and then DS reciprocating rolling is performed, combined with intermediate annealing heat treatment, until the copper sheet is rolled to 3.5 mm, and then final heat treatment is performed. The specific steps are as follows: (1) After hot forging, the ultra-pure copper (99.9999% Cu) is subjected to recrystallization heat treatment. The heat treatment process is: anneal the copper sheet at 390°C for 0.5 hours, then quench and cool it in water to room temperature; (2) The chip-level ultra-pure copper after heat treatment is subjected to DS rolling, with a misalignment of 0 to 5 mm, a misalignment angle maintained at 3° to 6°, a reduction rate of 10% to 15%, and a roller speed ratio controlled at 1.17. (3) The ultra-high purity copper after rolling is subjected to stress relief annealing heat treatment. The holding temperature is 180°C, the holding time is 0.5 hours, and the sheet is quenched in water to room temperature. (4) The ultra-high purity copper is subjected to reverse room temperature DS rolling using a DS rolling mill. The rolling surfaces (A, B) of the two adjacent billets are the same, and the rubbing directions are consistent; the reset and modification of the process parameters in the servo mechanism control program are completed in the special workstation (S). That is, the rolling direction is opposite to the previous one, and the rolling offset s of the DS rolling mill is dynamically adjusted before rolling. The offset angle is kept between 2° and 6°, thereby ensuring that the direction of the rolling force remains within a certain range. (5) Repeat the above steps 2), 3), and 4) for a total of 3 times, each time with two steps of rolling and intermediate heat treatment, to obtain an ultra-high purity copper plate with a thickness of 3.5 mm. (6) The ultra-high purity copper after rolling is subjected to recrystallization annealing heat treatment, with an annealing temperature of 280°C and a holding time of 1 hour to obtain a recrystallized structure. The final ultra-high purity copper plate with uniform surface and core structure and significantly refined grains is obtained, and an ultra-high purity copper plate with an average grain size of 9.9±1.0μm is obtained. In order to demonstrate the improvement of the performance of ultra-high purity copper by the DS rolling method, ultra-high purity copper plates with a thickness of 24.5 mm in the same batch were subjected to synchronous rolling and DS rolling adopted by the present invention under the same rolling conditions. Figure 2 This is the actual sample diagram after rolling by synchronous rolling and DS rolling in Example 2. Figure 3The figure shows the hardness distribution of copper plates produced by synchronous rolling and DS rolling along the RD-ND plane from the top to the bottom surface. As can be seen from the figure, the high-strength, ultrapure copper plates produced using the DS rolling method of the present invention not only have a uniform hardness distribution along the thickness direction, but also have a significant improvement. The advantages of the present invention compared to existing rolling technologies are further illustrated below with reference to the accompanying figures: To address the insufficient deformation of the core of the rolled piece during rolling, a rolling method that increases the total compression ratio or DS rolling can be preferred. The DS rolling method of the present invention creates a linear velocity difference between the upper and lower rollers during rolling, resulting in more intense shear deformation of the rolled piece in the rolling zone, thus reversing the situation in which only positive stress is concentrated on the plate surface during synchronous rolling. This promotes deformation transfer to the central region, resulting in more uniform deformation along the plate thickness. Furthermore, the shear force introduced by the DS rolling method causes more complete grain fragmentation in the core of the rolled piece, facilitating further grain refinement before heat treatment. In the rolling of round targets, since the plate shape is less susceptible to significant deformation, and to achieve more uniform deformation, the plate shape is easily corrected by rotating the target by a certain angle before each rolling pass and employing reverse DS rolling. In the rolling of rectangular pieces, the piece bends more toward the fast roll. Furthermore, increasing the speed ratio results in longer deformation in the rolling zone, more intense shearing of the piece, and greater warping. A speed ratio of 1.25 makes it easier to obtain straight plates, while also maximizing grain fragmentation and improving microstructure uniformity in the ND direction. In DS rolling, the reduction is 10% to 20% and the offset is 1 to 4 mm. Research has shown that as the thickness of the workpiece decreases, the equivalent strain in the workpiece core increases, while the strain on the upper and lower surfaces decreases. When the reduction remains constant, the thicker the workpiece, the less favorable the shear force is on the workpiece core during rolling, and the microstructure uniformity deteriorates. Misalignment is also a significant factor influencing workpiece deformation. A certain amount of offset between the upper and lower rolls can cause longitudinal shear deformation during rolling. Excessive offset increases the length of the inflection zone, leading to increased reduction of the upper and lower rolls on the workpiece. Therefore, the rolling force increases with increasing offset, and increased offset inevitably leads to greater deformation in the workpiece core. By introducing an offset angle α to maintain a constant rolling pattern within each pass, the reduction is appropriately adjusted, decreasing with decreasing workpiece thickness. To prevent the reduction from being too small per pass, the reduction is varied every two to three passes. This minimizes the difference in equivalent strain between the upper and lower surfaces and the workpiece center, improving microstructure uniformity.

[0073]

[0074] h o =h-Δh (7)

[0075] Where: ΔS is the amount of dislocation, R1 is the radius of the upper roller, R2 is the radius of the lower roller, h is the thickness before rolling, and Δh is the pass reduction. At the same time, stress relief heat treatment and stress relief heat treatment before each DS rolling can reduce the internal deformation force of the rolled piece. At the same time, the heat treatment process has a good effect on eliminating residual stress, which can weaken or even eliminate the residual stress generated during the rolling process. The higher the initial hardness of the material before rolling, the greater the hardness index and dislocation movement resistance of the material, resulting in a slower stress release rate. In order to eliminate some coarse grains in the structure, the layered structure of the last rolling state can be restored and recrystallized, and the banding generated in the structure after rolling can be improved. Figure (7) shows the grain boundary map and twin boundary distribution map of the sample after synchronous rolling, and Figure (8) shows the grain boundary and twin boundary distribution map of the sample after DS rolling. It can be seen from the figure that the twin boundary of the sample after DS rolling is significantly reduced.

[0076] Table 1 Comparison of rolling performance parameters in Example 2:

[0077]

[0078] DS rolling, whether it is the same speed but different roll diameters or the same diameter but different roll speeds, essentially means that the linear speeds of the upper and lower rolls are different, such as Figure 6 As shown in the figure, this speed difference will cause severe shear deformation of the workpiece in the ND direction. In DS rolling, the grid in the core of the workpiece tilts toward the fast roller along the rolling direction, and the distortion is obvious. This shows that under the action of this shear stress, the grains in the core structure of the workpiece can be more fully broken compared to the synchronous rolling method. The change from the single plane compressive stress of synchronous rolling to the compressive stress of DS rolling, while introducing strong shear strain, changes the single stress-strain mode of the workpiece during the rolling process. This is the main reason for effectively promoting core deformation and microstructure refinement. Figure 7-9 - shows the range of equivalent strain variation of rolled pieces in different rolling schemes. It can be seen from the figure that at the three deformation amounts of 60%, 70% and 87.5%, the cumulative deformation in the thickness direction of the plate after DS rolling deformation is greater than that of ordinary rolling. The higher strain indicates that asynchronous staggered rolling has a better effect on grain refinement of ultra-high purity copper plate structure. Figure 10-12 It can be seen that the DS rolling method makes the copper plate grain refinement better than the synchronous rolling method.

[0079] As rolling continues, the front end of the workpiece passes through the rolling zone and enters a relatively stable rolling process. It can be seen that during asynchronous rolling, due to the unequal strain on the upper and lower surfaces, the workpiece surface begins to bend, with the deformation being most pronounced when the rolling deformation reaches 40% to 70%. When the workpiece becomes thinner, flatness compensation correction through reverse offset rolling can effectively meet the flatness requirements of the workpiece.

[0080] Figure 12 a is the EBSD map of the microstructure after heat treatment and the grain size distribution histogram. The average grain size after heat treatment by synchronous rolling is 12.3±2.3μm. Figure 12 b is the EBSD image and grain size distribution histogram of the microstructure after heat treatment of DS rolling. The grain size obtained by DS rolling is 9.9±1.0μm. As can be seen from the figure, the synchronous rolling method has a large proportion of grain sizes in the range of 0-22μm. DS rolling has a significant reduction in grains larger than 15μm, and the grain size is concentrated in the range of 4-6μm, indicating that the DS rolling method is more conducive to grain refinement.

[0081] Example 3:

[0082] The ultra-high purity copper sheet with an initial thickness of 24.5mm after hot forging is subjected to recrystallization heat treatment, followed by DS reciprocating rolling and intermediate annealing heat treatment until the copper sheet is rolled to 3.5mm, and then subjected to final heat treatment. The specific steps are as follows:

[0083] (1) Ultrapure copper (99.9999% Cu) was subjected to recrystallization heat treatment after hot forging. The heat treatment process was as follows: the copper plate was annealed at 390°C for 0.5 hours and then quenched in water and cooled to room temperature;

[0084] (2) The chip-grade ultrapure copper after heat treatment was subjected to DS rolling, with a misalignment of 0 to 5 mm, a misalignment angle maintained at 3° to 6°, a reduction rate of 10% to 15%, and a roller speed ratio controlled at 1.17.

[0085] (3) The rolled ultra-high purity copper is subjected to stress relief annealing heat treatment at a holding temperature of 180°C for 0.5 hours, and then quenched in water and cooled to room temperature.

[0086] (4) Using a DS rolling mill to perform reverse room temperature DS rolling on ultra-high purity copper. The rolling surfaces (A, B) of the billets in two adjacent passes are the same, and the rolling directions are consistent; the process parameters in the servo mechanism control program are reset and modified at the dedicated station (S). That is, the rolling direction is opposite to that of the previous pass, and the rolling offset S of the DS rolling mill is dynamically adjusted before rolling so that the offset angle is maintained at 2° to 6°, thereby ensuring that the rolling force direction remains within a certain range.

[0087] (5) Repeat the above steps 2), 3), and 4) three times of rolling and intermediate heat treatment to obtain an ultra-high purity copper plate with a thickness of 3.5 mm.

[0088] (6) The rolled ultra-high purity copper was subjected to recrystallization annealing heat treatment at 310°C for 1 hour to obtain a recrystallized structure. The resulting ultra-high purity copper sheet had a uniform surface and core structure and significantly refined grains, with an average grain size of 10.5±1.0 μm.

[0089] Example 4:

[0090] An ultra-high purity copper ingot with a size of φ170×200 (mm) was used, and the specific steps were roughly the same as those in Example 1. The differences from Example 1 were:

[0091] (1) In step (1), the post-forging heat treatment process is: annealing at 410°C for 1 hour, then quenching in water and cooling to room temperature;

[0092] (2) In step (2), the offset of the upper and lower rollers is 0 to 5 mm, the offset angle is maintained at 6° to 9°, the upper and lower roller speed ratio is 1.25, and the reduction rate is 10% to 15%.

[0093] (3) In step (3), the rolled ultra-high purity copper ingot is subjected to an intermediate stress relief annealing heat treatment process of annealing at 200° C. for 0.3 hours and then quenching in water to cool to room temperature.

[0094] (4) In step (4), the rolling offset S of the DS rolling mill is dynamically adjusted before rolling so that the offset angle is maintained at 4° to 7°.

[0095] (5) In step (5), before the ultra-high purity copper ingot is rolled to a thickness of 60 mm, the reduction in each pass is 10% to 12%; the reduction in each pass is 12% to 14% until the thickness reaches 30 mm; and the reduction in each pass is 14% to 15% until the thickness reaches 25 mm.

[0096] (6) In step (6), the rolled ultra-high purity copper plate is subjected to recrystallization annealing heat treatment at an annealing temperature of 280° C. for 1 hour to obtain an ultra-high purity copper plate with an average grain size of 13±1.7 μm.

[0097] Example 5:

[0098] An ultra-high purity copper ingot with a size of φ170×200 (mm) was used, and the specific steps were roughly the same as those in Example 1. The differences from Example 1 were:

[0099] (1) In step (1), the post-forging heat treatment process is: annealing at 410°C for 1 hour, then quenching in water and cooling to room temperature;

[0100] (2) In step (2), the offset of the upper and lower rollers is 0 to 5 mm, the offset angle is maintained at 6° to 9°, the upper and lower roller speed ratio is 1.25, and the reduction rate is 10% to 15%.

[0101] (3) In step (3), the rolled ultra-high purity copper ingot is subjected to an intermediate stress relief annealing heat treatment process of annealing at 200° C. for 0.3 hours and then quenching in water to cool to room temperature.

[0102] (4) In step (4), the rolling offset S of the DS rolling mill is dynamically adjusted before rolling so that the offset angle is maintained at 4° to 7°.

[0103] (5) In step (5), before the ultra-high purity copper ingot is rolled to a thickness of 60 mm, the reduction in each pass is 10% to 12%; the reduction in each pass is 12% to 14% until the thickness reaches 30 mm; and the reduction in each pass is 14% to 15% until the thickness reaches 25 mm.

[0104] (6) In step (6), the rolled ultra-high purity copper plate is subjected to recrystallization annealing heat treatment at an annealing temperature of 310° C. for 1 hour to obtain an ultra-high purity copper plate with an average grain size of 15±2.3 μm.

Claims

1. A control method for fine processing of high-purity copper plates and achieving grain refinement, the method comprising material selection, forming Billet, hot forging, matching DS rolling and recrystallization heat treatment, characterized by The above method comprises the following steps: (1) selecting 5N-6N high purity copper ingots, refining and casting into billets in an electric furnace; (2) Cold forging and shaping the processed billet into a standard bar or round plate-shaped finished billet; (3) Determine the geometric dimensions of the finished billet based on the processing capacity of the matching DS rolling mill; (4) Each rolling process is carried out in two steps: the finishing billet is rolled by the speed ratio and offset of the DS rolling mill, and the grains are dynamically controlled online to achieve synchronous deformation of the grains in the three-dimensional direction; the rolling surface of the rolled billet is flipped and the rubbing direction is inverted between the two rolling steps, which is realized in the configured flip transfer station (S1), and the system uses the matching circuit program to issue instructions and is executed with the help of the matching servo mechanism; the process control range of each rolling process of the matching DS rolling mill is: offset 0-10mm, offset angle 3°-6°, and reduction rate 10%-20% each time, which is realized in two steps, and the speed ratio of the roller is set v 2 / v 1=1.1-1.2, dynamically controlled by the program; (5) Repeat the above step (4) 3-4 times to obtain the final thickness of the finished copper plate; (6) The intermediate product after each rolling needs to be subjected to stress relief annealing treatment; (7) The final product after rolling needs to be recrystallized and annealed to ensure that the final structure is fine-grained and the structure distribution is random, and finally a chip-grade copper plate with uniform structure on the surface and core and significantly refined grains is obtained.

2. The control method for fine processing of high-purity copper plate and achieving grain refinement according to claim 1, characterized in that: The purity of the high-purity copper ingot described in step (1) is selected to be 6N.

3. The control method for fine processing of high-purity copper sheet and achieving grain refinement according to claim 1, characterized in that: In step (3), the finished rolled blank is subjected to post-forging heat treatment at a holding temperature of 390-410°C for a holding time of not less than 0.5 hours, and is then quenched in water and cooled to room temperature.

4. The control method for fine processing of high-purity copper sheet and achieving grain refinement according to claim 1, characterized in that: In step (7), the annealing temperature of the recrystallization annealing treatment is 280-300°C, and the holding time is 1 hour, so that a chip-grade copper plate with an average grain size of less than 10 μm can be obtained.

5. A dedicated DS rolling mill system for fine processing of high-purity copper plates and achieving grain refinement according to the control method of claim 1, wherein the system structure includes upper and lower rollers (g1, g2) limited by symmetrical frames (h1, h2), and a differential drive mechanism and an offset angle control mechanism connected thereto. The DS rolling mill system is also provided with a control circuit and a servo mechanism, characterized in that: The control circuit and servo mechanism above constitute a comprehensive, dynamic control system. The functional structural units of the system include: The control circuit includes: (a) an experience database module for process parameters associated with an online dynamic control program for the DS rolling mill, and (b) a correction module for process parameters of the control program before each and every rolling start; The servo mechanism includes: (a) a differential transmission system with two output ends, which are respectively connected to the upper and lower roll shafts to realize differential rotation and continuous fine adjustment of the differential speed ratio during rolling; (b) a hydraulic stack and its supporting linear drive cylinder group, which are fixedly connected to the bearing seats at both ends of the lower roll to form a translational drive mechanism for horizontally displaced rolls; (c) a billet conveyor belt device (S) connected between the inlet and outlet ports of the DS rolling mill, and an online billet turning and transfer station (S1) set at the feed port of the rolling mill.

6. The dedicated DS rolling mill system according to claim 5, characterized in that The side panels of the symmetrical frame are composed of an upper crossbeam, a lower base, and left and right vertical columns to form an integrated window frame-shaped closed structure (C). A special-shaped middle beam (L) is provided in the window frame-shaped closed structure (C). An adjusting compression spring is provided at a recessed position of the middle beam (L). An adjusting oil cylinder is provided in the middle of the upper crossbeam, and a bearing seat (Z) for the upper roller shaft head is provided between the adjusting oil cylinder and the adjusting compression spring. The bearing seat (Z) is limited between two parallel slideways (P1, P2), ensuring that the upper roller shaft head can be adjusted in a vertical translation, thereby forming a random regulation of the rolling pressure.

7. The dedicated DS rolling mill system according to claim 5, characterized in that The system is equipped with a billet conveyor belt device (S), which uses a semicircular conveyor belt structure to automatically rotate the conveyed billet 180 degrees at the billet outlet.

8. According to the dedicated DS rolling mill system described in claim 5, the turning and transfer station (S1) and the feed table (S2) are both components of the billet conveyor belt device (S), and are arranged in parallel at the feed port of the dedicated DS rolling mill. The working surface of the turning and transfer station (S1) is 15-20 cm higher than the working surface of the feed table (S2); a transfer and turning device (S11) is provided on the panel of the turning and transfer station (S1), and a parallel push rod (S12), a lifting intermediate product guide wheel group (S13) and a position sensor (S14) are combined to form the billet transfer and turning device (S11).

9. The dedicated DS rolling mill system according to claim 8, characterized in that The transfer and turning device (S11) is arranged at the edge of the turning transfer station (S1) and is connected to the feeding station (S2) by means of a conveying slope (S3); the transfer and turning device (S11) structure includes a turning spindle (S11-a) and 3-4 driving fins (S11-b) positioned on the turning spindle (S11-a), a limiting core shaft (S11-a1) and 2-3 limiting core shafts (S11-a1) positioned on the limiting core shaft (S11-a1). Rod (S11-b1); the flip main shaft (S11-a) and the limit core shaft (S11-a1) are concentric axes, and the limit rod (S11-b1) passes through a 125-degree arc-shaped through groove provided on the flip main shaft wall. The 125-degree arc-shaped through groove limits the limit core shaft (S11-a1) and the limit rod (S11-b1) to have a 125-degree degree of freedom of rotation. The limit core shaft (S11-a1) is reset with the help of a reset coil spring provided on the central shaft (O).

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