Pure titanium bipolar plate roll punching forming springback control method based on grain size and texture regulation and control

Abstract

The invention discloses a pure titanium bipolar plate roll punching forming springback control method based on grain size and texture regulation and control, relates to the technical field of hydrogen fuel cells, and solves the technical problems that the springback phenomenon exists in the roll punching forming process of a pure titanium bipolar plate, and the formability and the size stability are difficult to consider at the same time. The springback control method comprises the steps that an industrial pure titanium plate is placed in a vacuum tube furnace to be sequentially subjected to atmosphere control, heating, heat preservation and cooling treatment, a recrystallization structure with the average grain size being 20-35 microns and 0001 base plane preferred orientation is formed under alpha-phase recrystallization, and therefore the springback angle in the rolling direction, the springback angle in the transverse direction and the springback angle in the direction forming a 45-degree included angle with the rolling direction are reduced; and the rebound angle control effect is verified through finite element simulation analysis. According to the method, alpha-phase recrystallization is achieved through atmosphere control, heating, heat preservation and cooling treatment, springback of the pure titanium bipolar plate in the roll punching forming process is effectively reduced, and verification is conducted through a finite element simulation model.

Description

Technical Field

[0001] This invention relates to the field of hydrogen fuel cell technology, and in particular to a method for controlling the springback of pure titanium bipolar plates during roll forming based on grain size and texture control. Background Technology

[0002] A hydrogen fuel cell is a power generation device that directly converts the chemical energy of hydrogen and oxygen into electrical energy. Due to its high efficiency, zero emissions, and rapid refueling, it is considered a key component of the future clean energy system. In a hydrogen fuel cell system, the metal bipolar plate is a crucial core component for achieving high power density and low cost in the stack, serving multiple functions including electrical conductivity, thermal conductivity, separation of reactant gases, and support for the membrane electrode assembly.

[0003] Pure titanium, with its excellent corrosion resistance, good electrical conductivity, and moderate mechanical strength, is an ideal material for metallic bipolar plates. However, the springback behavior of metallic materials is influenced by both their microstructure (such as grain size, texture, and phase composition) and mechanical properties (such as yield strength, elastic modulus, and anisotropy). For pure titanium with a hexagonal close-packed (HCP) structure, its plastic deformation mechanism is highly dependent on crystal orientation, and grain coarsening usually leads to a decrease in yield strength and an increase in elastic recovery. Pure titanium exhibits springback during cold forming (such as roll forming), which seriously affects the geometric accuracy of flow channels and the consistency of battery stack assembly, thus restricting its industrial application. At the same time, conventional heat treatment processes focus on phase transformation or strength control, neglecting the fine control of recrystallization texture and grain uniformity, making it difficult to balance formability and dimensional stability. There is an urgent need for a thermo-mechanical coupling process for ultra-thin pure titanium bipolar plates to achieve synergistic optimization of microstructure and macroscopic forming performance, and to effectively control the springback of pure titanium bipolar plates during roll forming.

[0004] Therefore, in the process of realizing this invention, the inventors discovered at least the following problems in the prior art: Pure titanium bipolar plates exhibit springback during roll forming, making it difficult to balance formability and dimensional stability. This affects the geometric accuracy of the flow channel and the consistency of battery stack assembly, thus hindering industrial application. Summary of the Invention

[0005] The purpose of this invention is to provide a method for controlling the springback during roll forming of pure titanium bipolar plates based on grain size and texture control. This method addresses the technical problem in existing technologies where pure titanium bipolar plates exhibit springback during roll forming, making it difficult to balance formability and dimensional stability, affecting flow channel geometry accuracy and battery stack assembly consistency, and hindering industrial application. The various technical effects of the preferred solutions provided by this invention are detailed below.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control. The method includes the following steps: selecting an industrial pure titanium plate with a thickness of 0.1 mm as the bipolar plate raw material; placing the industrial pure titanium plate in a vacuum tube furnace and sequentially performing atmosphere control, heating, heat preservation, and cooling treatments to form a recrystallized structure with an average grain size of 20 μm to 35 μm and a preferred orientation of the 0001 basal plane under α-phase recrystallization, thereby reducing the springback angle in the rolling direction, the transverse direction, and the direction at a 45° angle to the rolling direction. A pure titanium bipolar plate to be roll-formed was obtained. Based on the flow channel forming parameters of the pure titanium bipolar plate, a finite element simulation model was established to simulate the springback behavior of the pure titanium bipolar plate during roll forming. Through finite element simulation analysis, the influence of different average grain size and texture orientation on the springback angle in the rolling direction, transverse direction and 45° direction was quantitatively evaluated to verify the effect of recrystallization structure with an average grain size of 20μm~35μm and preferred orientation of 0001 basal plane on the springback angle control in the rolling direction, transverse direction and 45° angle with the rolling direction.

[0007] Preferably, the chemical composition of the industrial pure titanium plate is: Fe≤0.035wt%, C≤0.004wt%, N≤0.003wt%, H≤0.003wt%, O≤0.077wt%, with the balance being Ti.

[0008] Preferably, the vacuum tube furnace is an OTF-1200X vacuum tube furnace.

[0009] Preferably, the atmosphere control in the vacuum tube furnace is as follows: by evacuating the vacuum more than three times and circulating high-purity argon gas, an inert gas environment with an oxygen content of <1ppm is established, and argon gas is continuously introduced to protect and maintain a positive pressure of 0.03MPa inside the vacuum tube furnace throughout the heat treatment process.

[0010] Preferably, the heating operation is performed at a rate of 10°C / min to reach the target temperature.

[0011] Preferably, the target temperature is greater than the recrystallization initiation temperature of titanium, and the titanium at the target temperature is only a single-phase α-Ti structure.

[0012] Preferably, the target temperature is 650°C.

[0013] Preferably, the heat preservation operation is to maintain a constant temperature of 650℃±10℃ for 90 minutes to allow for the full recrystallization of titanium.

[0014] Preferably, during the cooling process, if the temperature is >500℃, it is first forced to be cooled to below 500℃ with air at 10℃ / min, and then cooled to room temperature with the furnace.

[0015] Preferably, the pure titanium bipolar plate to be roll-formed is prepared by the following steps: designing the blank layout of the pure titanium bipolar plate, and making the rolling transverse of the blank parallel to the main extension direction of the bipolar plate flow channel; feeding the pure titanium bipolar plate to be roll-formed into a roll forming machine, and performing roll forming based on the bipolar plate flow channel mold to obtain the pure titanium bipolar plate.

[0016] Implementing one of the above-described technical solutions of the present invention has the following advantages or beneficial effects: This application achieves α-phase recrystallization through atmosphere control, heating, heat preservation, and cooling treatment. Under the premise of avoiding α→β phase transformation, a recrystallized structure with an average grain size of 20μm~35μm and a preferred orientation of the 0001 basal plane is formed. This significantly reduces the springback angle in the rolling direction, transverse direction, and direction at a 45° angle to the rolling direction. The effectiveness of the recrystallized structure with an average grain size of 20μm~35μm and a preferred orientation of the 0001 basal plane in controlling the springback angle is verified by finite element simulation model. This effectively reduces the springback of pure titanium bipolar plates during roll forming, taking into account both the formability and dimensional stability of the bipolar plates, ensuring the geometric accuracy of the flow channel and the consistency of battery stack assembly, and facilitating industrial application. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a flowchart of the springback control method for pure titanium bipolar plate roll forming based on grain size and texture control in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the geometry of the bipolar plate flow channel in the finite element simulation model; Figure 3 This is a schematic diagram of the roll forming process in the finite element simulation model; Figure 4 This is the springback diagram of the sheet metal at 550℃ under the roll punching simulation process in the finite element simulation model. Figure 5 This is the springback diagram of the sheet metal at 650℃ under the roll punching simulation process in the finite element simulation model. Figure 6 It is the springback diagram of the sheet metal at 750℃ under the roll punching simulation process in the finite element simulation model; Figure 7 This is a diagram showing the grain distribution and IPF orientation distribution at an annealing temperature of 550℃. Figure 8This is a diagram showing the grain distribution and IPF orientation distribution at an annealing temperature of 650℃; Figure 9 This is a diagram showing the grain distribution and IPF orientation distribution at an annealing temperature of 750℃; Figure 10 It is a histogram of grain distribution at an annealing temperature of 550℃; Figure 11 It is a histogram of grain distribution at annealing temperature of 650℃; Figure 12 It is a histogram of grain distribution at annealing temperature of 750℃; Figure 13 These are images of micro-bent pure titanium sheet samples obtained at three different annealing temperatures. Figure 14 This is a schematic diagram of the micro-bending forming of pure titanium sheet obtained at three annealing temperatures; Figure 15 These are the experimental results of micro-bending of pure titanium sheets obtained at three annealing temperatures; Figure 16 This is a schematic diagram of the micro-bending springback of a thin plate with a typical grain size of 6.9μm; Figure 17 This is a schematic diagram of the micro-bending springback of a thin plate with a typical grain size of 26.8μm; Figure 18 This is a schematic diagram of the micro-bending springback of a thin plate with a typical grain size of 48.7μm; Figure 19 This is a flowchart of the preparation of a pure titanium bipolar plate in Embodiment 2 of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, various exemplary embodiments described below will be referenced to the accompanying drawings, which form part of the exemplary embodiments, illustrating various exemplary embodiments that may be used to implement the present invention. Unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. It should be understood that they are merely examples of processes, methods, and apparatuses consistent with some aspects of the present invention disclosed as detailed in the appended claims, and other embodiments may be used, or structural and functional modifications may be made to the embodiments listed herein without departing from the scope and spirit of the present invention.

[0019] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," etc., indicate the orientation or positional relationship based on the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the referred element must have a specific orientation, or be constructed and operated in a specific orientation. The terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. The term "multiple" means two or more. The terms "connected" and "linked" should be interpreted broadly, for example, they can be fixed connections, detachable connections, integral connections, mechanical connections, electrical connections, communication connections, direct connections, indirect connections through an intermediate medium, and can be the internal connection of two elements or the interaction relationship between two elements. The term "and / or" includes any and all combinations of one or more of the related listed items. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0020] To illustrate the technical solution described in this invention, specific embodiments are described below, showing only the parts related to the embodiments of this invention.

[0021] Example 1: like Figure 1As shown, this invention provides a method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control, comprising the following steps: S10: Selecting an industrial pure titanium plate with a thickness of 0.1 mm as the raw material for the bipolar plate. Due to its thickness of only 0.1 mm, its specific surface area is extremely large, making it extremely sensitive to temperature and atmosphere, and prone to springback. If the temperature is too high, a few grains will rapidly engulf surrounding grains, resulting in a sharp decline in performance. Therefore, targeted heat treatment is required to control the structural springback. S20: Placing the industrial pure titanium plate in a vacuum tube furnace for sequential atmosphere control, heating, heat preservation, and cooling treatment. The heat preservation and cooling treatment operations are also annealing processes, serving as standard pretreatment steps before roll forming. This facilitates the elimination of internal stress and prevents deformation, enabling the batch production of pure titanium bipolar plates with stable springback and high flow channel precision for roll forming. Under α-phase recrystallization, a recrystallized structure with an average grain size of 20μm~35μm and a preferred orientation of the 0001 basal plane is formed. α-phase recrystallization involves replacing old, deformed grains with new, perfect grains. In the most severely deformed areas (such as grain boundaries), atoms gain energy and rearrange to form new, distortion-free micro-α crystal nuclei. Titanium plates with an average grain size of 20μm~35μm achieve an optimal balance between strength and plasticity, and between elastic recovery and plasticity within this range, thus minimizing springback globally, rather than the opposite of "fineer grains result in less springback" or "coarser grains result in greater springback." In micro-bending tests and roll forming simulations, all three rolling directions (RD, TD, DD) exhibit synergistically optimized low springback characteristics. The preferred orientation of the 0001 basal plane indicates that the vast majority of α grains (hexagonal system) inside the titanium plate are neatly arranged, causing their 0001 crystal planes (i.e., basal planes) to tend to be parallel to the plate surface. This effectively reduces the springback angle in the rolling direction (RD, parallel to the rolling extension of the sheet, i.e., the length direction of the sheet, where grains are typically elongated and arranged), the transverse direction (TD, perpendicular to the rolling direction, parallel to the width of the sheet, and perpendicular to the grain elongation direction), and the direction at a 45° angle to the rolling direction (DD, at a 45° angle to the rolling direction, usually the direction of maximum shear stress and also the direction where some slip systems are most easily activated), thus obtaining the pure titanium bipolar plate to be roll-formed. Based on the flow channel forming parameters of the pure titanium bipolar plate, a finite element simulation model is established to simulate the springback behavior of the pure titanium bipolar plate during roll forming. The specific shape of the pure titanium bipolar plate is as follows: Figure 2 As shown in Table 1, the corresponding parameters are shown in Table 1. The roller punching simulation process in the finite element simulation model is as follows: Figure 3 As shown, finite element simulation analysis was used to quantitatively evaluate the influence of different average grain sizes and texture orientations on the springback angles in the rolling direction, transverse direction, and 45° direction. Figures 4-6As shown in the figure (a), (b), and (c) represent the springback diagrams of the sheet metal in the rolling direction, transverse direction, and direction at a 45° angle to the rolling direction, respectively), the springback results of the roll punching process at 550℃ (corresponding to a typical grain size of 6.9μm and an average grain size of 1-10μm), 650℃ (corresponding to a typical grain size of 26.8μm and an average grain size of 20μm~35μm), and 750℃ (corresponding to a typical grain size of 48.7μm and an average grain size of 10-100+μm with a polydisperse distribution) were simulated and evaluated. This was to verify the effect of recrystallization structure with an average grain size of 20μm~35μm and a preferred orientation of the 0001 basal plane on the rolling direction and transverse direction. The springback angle control effect at a 45° angle to the rolling direction was simulated, and the specific springback angles are shown in Table 2. The data shows that the springback angle is the lowest and the anisotropy is the smallest at 650℃ (average grain size 20μm~35μm): 1.89±0.12° in the rolling direction RD, 1.14±0.10° in the transverse direction TD, and 1.39±0.11° in the direction at a 45° angle to the rolling direction DD. In contrast, the springback angles of the samples at 550℃ and 750℃ are generally higher, especially in the rolling direction RD (average springback angles of 2.01° and 2.07°), indicating that an average grain size of 20μm~35μm is the optimal grain size window. In this embodiment, α-phase recrystallization is achieved through atmosphere control, heating, heat preservation, and cooling treatment. Under the premise of avoiding α→β phase transformation, a recrystallized structure with an average grain size of 20μm~35μm and a preferred orientation of the 0001 basal plane is formed. This significantly reduces the springback angle in the rolling direction, the transverse direction, and the direction at a 45° angle to the rolling direction. The effectiveness of the recrystallized structure with an average grain size of 20μm~35μm and a preferred orientation of the 0001 basal plane in controlling the springback angle is verified by the finite element simulation model. This effectively reduces the springback of pure titanium bipolar plates during the roll forming process, takes into account both the formability and dimensional stability of the bipolar plates, ensures the geometric accuracy of the flow channel and the consistency of battery stack assembly, and facilitates industrial application.

[0022] Table 1. Flow channel forming parameters of pure titanium bipolar plates Table 2. Average springback angle of pure titanium bipolar plates under different grain sizes and orientations. As an optional implementation, the chemical composition of the industrial pure titanium plate is: Fe≤0.035wt%, C≤0.004wt%, N≤0.003wt%, H≤0.003wt%, O≤0.077wt%, with the balance being Ti. That is, the industrial pure titanium plate in this embodiment is a high-purity titanium plate to meet the performance requirements of pure titanium bipolar plates.

[0023] As an optional implementation, the vacuum tube furnace is the OTF-1200X vacuum tube furnace. This model of vacuum tube furnace adopts a double-layer air-cooled structure, with the furnace body surface temperature below 60°C, ensuring operational safety. The inner wall of the furnace chamber is coated with a high-temperature alumina coating, which can improve heating efficiency and extend service life. It is equipped with a 30-segment programmable PID controller, supporting over-temperature and thermocouple failure alarm functions. Both ends of the furnace tube are equipped with stainless steel sealing flanges, and optional accessories such as hinged flanges and digital vacuum gauges can be added to achieve vacuum or atmosphere protection.

[0024] As an optional implementation, the atmosphere control in the vacuum tube furnace involves: vacuuming and circulating high-purity argon gas at least three times, with the number of cycles potentially increased as needed, to establish an inert gas environment with an oxygen content of <1 ppm (parts per million), representing an extremely high-purity inert protective environment. Argon gas is continuously introduced throughout the heat treatment process to maintain a positive pressure of 0.03 MPa inside the vacuum tube furnace. This slight positive pressure of 0.03 MPa prevents outside air from being drawn into the vacuum tube furnace due to negative pressure. Atmosphere control is used to isolate oxygen, preventing oxidation, decarburization, or other undesirable chemical reactions in the material during high-temperature treatment, thereby ensuring the purity and performance of the material. Argon is chemically extremely stable, denser than air, and provides excellent protection; it is also one of the most commonly used protective gases. The continuous argon gas protection throughout the heat treatment process can ensure that there is no oxygen residue as much as possible. Titanium has extremely strong chemical activity at high temperatures (>600℃) and easily absorbs gases. Oxygen absorption will cause the formation of a hard and brittle "α shell" on the surface, making the material brittle. The continuous argon gas protection ensures the material quality of the pure titanium bipolar plate to be formed by roll forming.

[0025] As an optional implementation, the heating operation is to raise the temperature to the target temperature at a rate of 10°C / min. This 10°C / min rate is the maximum rated heating rate of the OTF-1200X tube furnace, thus achieving rapid heating. The target temperature must be higher than the recrystallization initiation temperature of titanium, which is 550°C. Therefore, the target temperature needs to be greater than 550°C. Furthermore, at the target temperature, titanium exhibits only a single-phase α-Ti structure. The single-phase α-Ti structure is the most fundamental and critical target in the heat treatment of titanium alloys, eliminating internal processing stress, phase transformation products, or metastable phases, achieving the most thermodynamically stable close-packed hexagonal structure. In the β-phase region (>882°C), a martensitic α' phase may be obtained, which is slightly different from the single-phase α-Ti structure in crystallography and has high hardness and poor plasticity, making it difficult to use as a pure titanium bipolar plate. Therefore, the target temperature also needs to be lower than 882°C. In this embodiment, the target temperature is 650°C. This temperature is between 550°C and 882°C, which can achieve recrystallization of titanium metal while avoiding the formation of martensite α' phase.

[0026] As an optional implementation, the holding operation involves maintaining a constant temperature of 650℃±10℃ for 90 minutes to allow for the full recrystallization of titanium. Recrystallization is a nucleation and growth process, achieved through precise control of temperature, holding time, and heating / cooling rates. Atomic diffusion and grain boundary migration require time; therefore, the holding operation is crucial for recrystallization. This operation is achieved by setting the temperature and time of the isothermal phase in the tube furnace. To ensure full recrystallization (i.e., obtaining a fully recrystallized equiaxed crystal structure and eliminating work hardening), the holding temperature of 650℃±10℃ is appropriately higher than the recrystallization initiation temperature of titanium (550℃) to ensure sufficient recrystallization. This process has a clear window, is easily implemented in industrial vacuum annealing furnaces or continuous annealing lines, exhibits good repeatability and consistency, and facilitates large-scale production of low-resilience titanium plates.

[0027] As an optional implementation, during the cooling process, if the temperature is >500℃, it is first forced to cool to below 500℃ at a rate of 10℃ / min. This temperature is lower than the recrystallization initiation temperature, thus preventing further recrystallization. Then, it is cooled to room temperature in the furnace, preventing drastic phase transformation and ultimately obtaining pure titanium bipolar plates to be rolled and formed. Above 500℃ is the critical region for "recrystallization kinetics." Above 500℃, titanium has strong atomic diffusion capabilities, and both grain nucleation and growth are active. Forced air cooling (rapid cooling) can interrupt the grain growth process, quickly "freezing" the grain size within the target range (20~35μm), preventing abnormal grain coarsening caused by prolonged exposure to high temperatures. Below 500℃ is the secondary zone of "phase transformation and stress". When the temperature drops below 500℃, the recrystallization process of titanium basically stops (insufficient power), the grain size tends to be stable and is no longer affected by the cooling rate. At this time, furnace cooling can avoid the introduction of excessive thermal stress in the ultra-thin plate (0.1mm) due to excessively rapid cooling (such as water cooling or rapid air cooling), which would cause the plate to deform or warp. While ensuring the flatness of the plate, the process goal of obtaining a flat and stress-free plate is achieved.

[0028] To verify the technical effectiveness of this embodiment, the following physical tests were also conducted.

[0029] Since the recrystallization temperature of pure titanium is higher than 500℃, the minimum annealing temperature was set at 550℃ to ensure complete recrystallization. Simultaneously, the phase transition temperature of titanium's two allotropes is 882℃, so the maximum annealing temperature was set at 750℃ to prevent phase transformation during annealing. A temperature gradient of 100℃ was established, namely 550℃, 650℃, and 750℃, with each temperature held for 90 minutes. Three heat treatment experiments were conducted. Samples were placed in large magnetic boats, with different samples placed on separate boats to avoid confusion. Then, they were placed in a tube furnace, and the flanges at both ends were tightened. The furnace tube was first evacuated more than three times using a pump, and argon gas was introduced for protection to ensure as little oxygen residue as possible. Argon gas was continuously introduced throughout the heat treatment process, maintaining the pressure inside the furnace tube at 0.03 MPa above atmospheric pressure.

[0030] To determine the grain size of pure titanium sheets heat-treated at different temperatures, electron backscatter diffraction (EBSD) tests were performed on the samples after different heat treatments using an Oxford C-nano+SH apparatus. Polishing of the samples was required before testing; however, due to the thinness of the pure titanium sheets, mechanical polishing was difficult, so electrolytic polishing was employed. The electrolytic polishing parameters for pure titanium were as follows: electrolyte composition (acetic acid: perchloric acid = 90:10), polishing voltage (50V), polishing conditions (room temperature), cathode (304 stainless steel), and polishing time (45s).

[0031] Figures 7-9 The electron backscattering diffraction patterns along the thickness direction of the original material are shown at different heat treatment temperatures. The inverse pole figure (IPF) represents the inverse pole figure. The figures reveal that the original material after annealing exhibits a predominantly hexagonal close-packed (HCP) structure. The grains are mostly equiaxed, and no twins were observed. The predominantly red microscopic images show a significant 0001 basal plane preferred orientation characteristic. Microstructural analysis indicates that high-angle grain boundaries (HAGBs, orientation difference > 10°) dominate (marked by black lines in the figures), while low-angle grain boundaries (LAGBs, orientation difference 2°–10°) exist only in a discrete form (marked by yellow lines). Combined with the annealing process parameters, it can be seen that the material formed a complete recrystallized structure after heat treatment. The grain size distribution of this structure exhibits significant polydispersity; specific grain size distribution data are shown below. Figures 10-12The bar chart shows that the average grain size of the samples increases significantly with increasing annealing temperature. An average grain size of 6.9 μm was obtained at 550℃, concentrated in the 1-10 μm range; an average grain size of 26.8 μm was obtained at 650℃, with a more uniform distribution; and an average grain size of 48.7 μm was obtained at 750℃, exhibiting a polydisperse distribution of 10-100+ μm, consistent with the Ostwald ripening mechanism. High-angle grain boundaries (HAGBs) are dominant, confirming complete recrystallization.

[0032] To verify the springback data, a micro-bending test was also conducted in this embodiment. The micro-bending test was performed on a UTM5105X microcomputer-controlled electronic universal testing machine. The force sensor of the testing machine has a range of 100KN, an accuracy of 0.5 grade, a displacement resolution of 0.04μm, and a speed accuracy of 0.1 grade. A micro-bending mold that can be adjusted to any forming angle and a mold base for connecting to the electronic universal testing machine were designed and manufactured. The mold is positioned with the mold base by locating pins and fastened with bolts. Based on the sample length and bending angle, the distance between the two supporting molds was designed to be 20mm.

[0033] The micro-bending sample was a pure titanium sheet with dimensions of length L = 50 mm, width W = 15 mm, and thickness 0.1 mm. The length direction was parallel to the rolling direction. Figure 13 As shown. Using the previously obtained heat treatment parameters of 550℃, 650℃, and 750℃, samples with three grain sizes were prepared for each forming angle. Since the forming angles are 30°, 60°, and 90°, respectively, as... Figure 14 As shown, based on the corresponding mathematical relationships and actual measurements, when forming at 30°, the punch descent distance is 12.026 mm; when forming at 60°, the punch descent distance is 8.52 mm; and when forming at 90°, the punch descent distance is 5.921 mm. The micro-bending experiment results are as follows... Figure 15 As shown. Photos of the moment of complete forming and the moment of complete unloading were selected from the experimental records. The bending angle of the specimen was measured using image processing software. Based on the measured angle data, the springback angle of the specimen was calculated. The relevant process and results are as follows. Figures 16-18 As shown in the figure, when the typical grain size increases from 28.6 μm to 48.7 μm, the average springback angle of samples in each orientation decreases by 27-35%. Furthermore, samples in the transverse direction are more prone to initiating the slip system due to the 0001 basal plane being parallel to the bending direction, resulting in a generally lower springback angle compared to other orientations. The springback angles for different typical grain sizes and orientations are shown in Table 3.

[0034] Table 3 Springback Angle under Different Grain Sizes and Orientations The embodiment is merely a specific example and does not indicate that this is the only way to implement the present invention.

[0035] Example 2: like Figure 19 As shown, the pure titanium bipolar plate to be roll-formed obtained in Example 1 is prepared by the following steps: S100: The blank layout design of the pure titanium bipolar plate is carried out, and the rolling transverse of the blank is parallel to the main extension direction of the bipolar plate flow channel; S200: Example 1 shows that the springback stability in the TD direction is high. Rolling the blank transversely parallel to the main extension direction of the bipolar plate flow channel can further utilize the anisotropy of the material and minimize the forming error of the final product. The pure titanium bipolar plate to be roll-formed is fed into a roll forming machine, and roll forming is performed based on the bipolar plate flow channel mold to obtain the pure titanium bipolar plate. Using the pure titanium bipolar plate preparation method of this embodiment, the forming accuracy of the pure titanium bipolar plate flow channel is significantly improved, which can reduce the dependence on complex mold compensation design, reduce the cost of mold trial and repair, and shorten the product development cycle. At the same time, the stable low springback characteristics are conducive to improving the consistency and yield of mass production, and have good economic benefits and industrialization prospects.

[0036] The above description is merely a preferred embodiment of the present invention. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control, characterized in that, Includes the following steps: Industrial pure titanium plates with a thickness of 0.1 mm were selected as the raw material for the bipolar plates; Industrial pure titanium plates are placed in a vacuum tube furnace and subjected to atmosphere control, heating, heat preservation, and cooling treatment in sequence. Under α-phase recrystallization, a recrystallized structure with an average grain size of 20μm~35μm and preferred orientation of the 0001 basal plane is formed to reduce the springback angle in the rolling direction, the transverse direction, and the direction at a 45° angle with the rolling direction, so as to obtain pure titanium bipolar plates to be roll-formed. Based on the flow channel forming parameters of pure titanium bipolar plates, a finite element simulation model was established to simulate the springback behavior of pure titanium bipolar plates during roll forming. Through finite element simulation analysis, the influence of different average grain sizes and texture orientations on the springback angles in the rolling direction, transverse direction, and 45° direction was quantitatively evaluated. This was to verify the effect of recrystallization structure with an average grain size of 20μm~35μm and a preferred orientation of the 0001 basal plane on the control of the springback angles in the rolling direction, transverse direction, and direction at a 45° angle to the rolling direction.

2. The method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control according to claim 1, characterized in that, The chemical composition of the industrial pure titanium plate is: Fe≤0.035wt%, C≤0.004wt%, N≤0.003wt%, H≤0.003wt%, O≤0.077wt%, with the balance being Ti.

3. The method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control according to claim 1, characterized in that, The vacuum tube furnace is an OTF-1200X vacuum tube furnace.

4. The method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control according to claim 1, characterized in that, The atmosphere control in the vacuum tube furnace is as follows: by evacuating the vacuum more than three times and circulating high-purity argon gas, an inert gas environment with an oxygen content of <1ppm is established, and argon gas is continuously introduced to protect and maintain a positive pressure of 0.03MPa inside the vacuum tube furnace throughout the heat treatment process.

5. The method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control according to claim 1, characterized in that, The heating operation is to raise the temperature to the target temperature at a rate of 10°C / min.

6. The method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control according to claim 5, characterized in that, The target temperature is greater than the recrystallization initiation temperature of metallic titanium, and the metallic titanium at the target temperature is only a single-phase α-Ti structure.

7. The method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control according to claim 6, characterized in that, The target temperature is 650°C.

8. The method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control according to claim 1, characterized in that, The heat preservation operation is as follows: maintain a constant temperature of 650℃±10℃ for 90 minutes to allow for the full recrystallization of metallic titanium.

9. The method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control according to claim 1, characterized in that, During cooling, if the temperature is >500℃, first force air cooling at 10℃ / min to below 500℃, and then cool it to room temperature with the furnace.

10. The method for controlling springback during roll forming of pure titanium bipolar plates based on grain size and texture control according to claim 1, characterized in that, The pure titanium bipolar plate to be formed by roll forming is prepared by the following steps: Design the billet layout for pure titanium bipolar plates, and make the rolling transverse of the billet parallel to the main extension direction of the bipolar plate flow channel; The pure titanium bipolar plate to be formed by roll forming is fed into a roll forming machine, and roll forming is performed based on the bipolar plate flow channel mold to obtain the pure titanium bipolar plate.

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