A method for microstructure control in microchannel forming of titanium alloy foil

Abstract

This invention discloses a method for controlling the microstructure of titanium alloy foil in microchannel forming, comprising: pre-annealing a titanium alloy sheet; cold rolling a first pass to form a first intermediate material, with a cumulative total deformation of 50%–66% in the first pass; performing a first annealing on the first intermediate material; cold rolling a second pass after annealing to form a second intermediate material, with a cumulative total deformation of 46%–60% in the second pass; performing a second annealing on the second intermediate material; cold rolling a third pass after annealing to form a foil of the target thickness, with a cumulative total deformation of ≤50% in the third pass; and performing a third annealing on the foil to produce a titanium alloy foil. This invention improves the formability of the titanium alloy foil by designing the deformation distribution of each pass, the intermediate annealing process, and the finished product annealing process during foil rolling, thereby controlling the formation of a microstructure conducive to formability and generating more basal surface textures to meet the processing requirements of microchannels.

Description

Technical Field

[0001] This invention relates to the field of hydrogen fuel cell technology, and in particular to a method for microstructure control in the microfluidic formation of titanium alloy foil. Background Technology

[0002] Hydrogen fuel cells have advantages such as zero pollution and high efficiency, and are an important direction for the development of next-generation clean energy.

[0003] Bipolar plates are key components determining the lifespan and cost of fuel cells, and must meet comprehensive performance requirements such as corrosion resistance, conductivity, long lifespan, ultra-thin and high strength, and ease of processing. Using titanium alloys, which have better corrosion resistance and lower density, as the substrate for bipolar plates can significantly extend battery life and reduce stack weight, demonstrating significant application value. However, compared to stainless steel, titanium alloys have relatively poor formability, making it difficult to meet the processing requirements for microchannels in bipolar plates. This can easily lead to cracking along the grooves during stamping, resulting in poor application reliability. To address the poor formability of titanium alloys, it is necessary to optimize the processing technology to improve material formability. Since titanium alloys belong to the hexagonal crystal system, microstructure is easily generated during deformation processing, leading to anisotropic elongation properties. Inadequate texture control will further reduce the material's formability.

[0004] Therefore, there is a need to improve the existing methods for controlling the microstructure of titanium alloy foil. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a method for controlling the microstructure of titanium alloy foil microchannel forming. This invention controls the formation of microstructure that is conducive to formability by designing the distribution of deformation in each rolling stroke, intermediate annealing process and finished product annealing process during foil rolling, generating more base surface texture to improve the formability of titanium alloy foil and meet the processing requirements of microchannels.

[0006] To achieve the above objectives, this invention provides a method for controlling the microstructure of titanium alloy foil microchannels, comprising the following steps:

[0007] S1. Pre-annealing treatment of titanium alloy sheet;

[0008] S2. The titanium alloy sheet is rolled in the first rolling pass using cold rolling to form the first intermediate material, with a cumulative total deformation of 50% to 66% in the first rolling pass;

[0009] S3. Perform the first annealing treatment on the first intermediate material;

[0010] S4. After annealing, the first intermediate material is cold-rolled in a second rolling process to form the second intermediate material. The cumulative total deformation of the second rolling process is 46%~60%.

[0011] S5. Perform a second annealing treatment on the second intermediate material;

[0012] S6. After annealing, the second intermediate material is cold-rolled in a third rolling process to form foil of the target thickness. The total cumulative deformation in the third rolling process is ≤50%.

[0013] S7. Perform a third annealing treatment on the foil to produce titanium alloy foil;

[0014] In each of the annealing processes from S1 to S7, the annealing temperature decreases progressively, while the number of rolling passes increases progressively.

[0015] In some embodiments, the annealing temperature of the pre-annealing treatment is 650~750℃, the holding time is 30~60min, and the titanium alloy plate is cooled to below 100℃ in the furnace after pre-annealing before being taken out of the furnace.

[0016] In some embodiments, the first rolling pass includes 8 to 10 rolling passes, with a deformation of 5% to 15% per pass, and the thickness of the first intermediate material is 0.5 mm to 0.75 mm.

[0017] In some embodiments, the annealing temperature during the first annealing treatment is 600℃~700℃, the holding time is 20~40min, and the first intermediate material is cooled to below 100℃ in the furnace after annealing before being taken out of the furnace.

[0018] In some embodiments, the second rolling pass includes 12 to 16 rolling passes, with a single pass deformation of no more than 8%, and the thickness of the second intermediate material is 0.2 mm to 0.4 mm.

[0019] In some embodiments, the annealing temperature during the second annealing treatment is 550~650℃, the holding time is 10~20min, and the furnace is cooled to below 50℃ before the furnace is removed.

[0020] In some implementations, the third rolling pass includes 15 to 20 rolling passes, with a single pass deformation of no more than 5%, and the target thickness of the foil is 0.1 mm to 0.2 mm.

[0021] In some embodiments, the annealing temperature during the third annealing is 500°C to 600°C, and the annealing time is 40 to 60 minutes.

[0022] In some embodiments, the thickness of the titanium alloy sheet is 1.0~1.5mm.

[0023] In some implementations, vacuum annealing is used for each annealing process.

[0024] The present invention has at least the following beneficial technical effects:

[0025] This invention optimizes and adjusts the rolling and heat treatment processes, controls the microstructure of the material, and forms a high-strength base surface texture that is beneficial to formability, thereby improving the formability of titanium alloy foil. Specifically:

[0026] (1) Pre-annealing can soften the cold-rolled titanium alloy sheet, reduce its strength, improve its plasticity, and ensure the deformation of the subsequent foil rolling process. On the other hand, by setting a reasonable annealing temperature, the grains can be completely recrystallized, and a higher volume fraction of basal texture can be obtained in advance. The higher the volume fraction of this texture, the smaller the anisotropy of the material and the better its formability.

[0027] (2) Multiple rolling processes and control of cold rolling deformation in each process are adopted. On the one hand, in order to further refine the grain size, sufficient deformation needs to be accumulated in each rolling process. On the other hand, in order to retain the basal texture that is conducive to formability and avoid the formation of too much pyramidal texture, which will be inherited by the final product and affect the formability.

[0028] (3) Multiple annealing treatments are adopted. Based on the crystallization characteristics, a reasonable annealing temperature range is set to ensure complete recrystallization while avoiding grain growth and retaining the obtained basal texture for the next rolling process. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0030] Figure 1 A schematic diagram of an embodiment of the microtexture control method for microchannel forming of titanium alloy foil provided by the present invention;

[0031] Figure 2 Pole diagram of titanium alloy foil before implementation of the optimized solution provided by the present invention;

[0032] Figure 3 Pole diagram of EBSD microtexture determination of titanium alloy foil in Example 1;

[0033] Figure 4 Pole diagram of EBSD microtexture determination of titanium alloy foil in Example 2;

[0034] Figure 5 Pole diagram of EBSD microtexture determination of titanium alloy foil in Example 3;

[0035] Figure 6This is a schematic diagram of an embodiment of microchannel forming of titanium alloy foil provided by the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0037] The terms "comprising" and "having," and any variations thereof, used in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion; the terms "first," "second," etc., used in the specification, claims, and accompanying drawings are used to distinguish different objects, not to describe a particular order. "A plurality of" means two or more, unless otherwise explicitly specified.

[0038] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0039] This invention addresses the problem of poor formability of titanium alloy foil products, which cannot meet the forming requirements of microchannels in hydrogen fuel cell electrode plates. By optimizing and adjusting the rolling and heat treatment processes, and controlling the microstructure of the material, a high-strength base surface texture beneficial to formability is formed, thereby improving the formability of the titanium alloy foil. Figure 1 As shown, the method of the present invention includes the following steps:

[0040] S1. Pre-annealing treatment of titanium alloy sheet;

[0041] S2. The titanium alloy sheet is rolled in the first rolling pass using cold rolling to form the first intermediate material, with a cumulative total deformation of 50% to 66% in the first rolling pass;

[0042] S3. Perform the first annealing treatment on the first intermediate material;

[0043] S4. After annealing, the first intermediate material is cold-rolled in a second rolling process to form the second intermediate material. The cumulative total deformation of the second rolling process is 46%~60%.

[0044] S5. Perform a second annealing treatment on the second intermediate material;

[0045] S6. After annealing, the second intermediate material is cold-rolled in a third rolling process to form foil of the target thickness. The total cumulative deformation in the third rolling process is ≤50%.

[0046] S7. Perform a third annealing treatment on the foil to produce titanium alloy foil;

[0047] In each of the annealing processes from S1 to S7, the annealing temperature decreases progressively, while the number of rolling passes increases progressively.

[0048] Furthermore, in S1, titanium alloy sheets with a thickness of 1.0~1.5mm are pre-annealed at a temperature of 650~750℃ for 30~60 minutes using vacuum annealing. After pre-annealing, the titanium alloy sheets are cooled in the furnace to below 100℃ before being removed from the furnace. The pre-annealing process softens the cold-rolled titanium alloy sheet, reducing its strength and increasing its plasticity, thus ensuring deformation during subsequent foil rolling. Furthermore, by setting a reasonable annealing temperature, complete recrystallization of the grains can be achieved, resulting in a higher volume fraction of basal texture. A higher volume fraction of this texture indicates lower material anisotropy and better formability.

[0049] Furthermore, in S2, the first rolling pass includes 8 to 10 rolling passes, with a deformation of 5% to 15% per pass, and the thickness of the first intermediate material is 0.5 mm to 0.75 mm.

[0050] Furthermore, in S3, the annealing temperature during the first annealing treatment is 600℃~700℃, the holding time is 20~40min, and the first intermediate material is cooled to below 100℃ in the furnace after annealing before being taken out of the furnace.

[0051] Furthermore, in S4, the second rolling pass includes 12 to 16 rolling passes, with a single pass deformation of no more than 8%, and the thickness of the second intermediate material is 0.2 mm to 0.4 mm.

[0052] Furthermore, in S5, the annealing temperature during the second annealing treatment is 550~650℃, the holding time is 10~20min, vacuum annealing is used, and the material is cooled in the furnace to below 50℃ before being removed from the furnace. For the annealing treatments in S3 and S5, the titanium alloy cold-rolled sheet is softened on the one hand to reduce strength and increase plasticity, ensuring deformation in subsequent foil rolling processes; on the other hand, annealing within a reasonable temperature range ensures complete recrystallization while preventing grain growth and preserving the obtained basal texture for the next rolling pass. The first intermediate annealing temperature is higher than the second intermediate annealing temperature because after cold rolling deformation, the deformation energy inside the grains accumulates, lowering the recrystallization temperature.

[0053] Furthermore, in S6, the third rolling pass includes 15-20 rolling passes, with a single-pass deformation of no more than 5%, and the target foil thickness is 0.1mm-0.2mm. Regarding the control of cold rolling deformation in S2, S4, and S6, on the one hand, to further refine the grain size, sufficient deformation accumulation is required in each rolling pass; on the other hand, to retain the basal texture beneficial to formability and avoid the formation of excessive pyramidal textures that are inherited by the final product and affect formability. Since when the cumulative deformation of titanium alloy materials is ≤30%, deformation is mainly twinning; within the deformation range of 30-70%, twinning and slip are the main deformation mechanisms; and when the deformation is ≥70%, dislocation slip becomes the only deformation mechanism. The formation of pyramidal textures is a result of slip, and the formation of pyramidal textures will produce anisotropic effects, which are detrimental to material forming. Therefore, the cumulative deformation of a single rolling pass in this invention is controlled to be below 70%.

[0054] Furthermore, in S7, the annealing temperature for the third annealing is 500℃~600℃, and the annealing time is 40~60min, using vacuum annealing. This third annealing step, with a temperature set lower than the first and second intermediate annealing temperatures, is also because the material's recrystallization temperature is lower; a lower annealing temperature setting will retain more of the basal texture that is beneficial to formability.

[0055] The present invention will be further explained below with reference to specific embodiments.

[0056] Example 1

[0057] ① A 1.5mm thick, 300mm wide titanium alloy cold-rolled plate for hydrogen fuel cell electrode plates is vacuum pre-annealed at a temperature of 750℃ for 40 minutes and then cooled to 50℃ in the furnace before being removed from the furnace.

[0058] ② The cold-rolled sheet obtained in step ① is subjected to the first rolling process. The rolling method is cold rolling, and the sheet thickness is rolled from 1.5mm to 0.6mm. The total number of rolling passes is 10, the deformation per pass is 8%~12%, and the cumulative total deformation is 50%.

[0059] ③ The cold-rolled sheet obtained in step ② is subjected to the first intermediate annealing at a temperature of 650℃ and a holding time of 30 minutes. The annealing method is vacuum annealing. After cooling to 50℃ in the furnace, it is taken out of the furnace.

[0060] ④ The cold-rolled sheet obtained in step ③ is subjected to a second cold rolling process to reduce the sheet thickness from 0.5 mm to 0.2 mm. The number of rolling passes is controlled to be 14, with a single pass deformation amount of ≤8% and a cumulative total deformation amount of 60%.

[0061] ⑤ The cold-rolled sheet obtained in step ④ is subjected to a second intermediate annealing at a temperature of 600℃ and a holding time of 20 minutes. The annealing method is vacuum annealing. After cooling to 30℃ in the furnace, the sheet is removed from the furnace.

[0062] ⑥ Perform a third cold rolling pass on the cold-rolled sheet obtained in step ⑤ to roll the sheet thickness from 0.25mm to the target thickness of 0.15mm. The rolling passes are controlled to be 18 passes, with a single pass deformation amount of ≤5% and a cumulative total deformation amount of 40%.

[0063] ⑦ The titanium alloy foil obtained in step ⑥ is subjected to vacuum annealing to further control the texture type. The annealing temperature is 550℃ and the annealing time is 40min.

[0064] ⑧ The EBSD microstructure of the finished annealed titanium alloy foil was measured, and the results are as follows: Figure 3 From the pole figure in the (0001) direction, it can be seen that compared to the product pole figure before process optimization (e.g., Figure 2 The texture type has changed from pyramidal texture to basal texture, and the texture type has been effectively controlled, which will be beneficial to the formation of the electrode microchannel.

[0065] Example 2

[0066] ① A 1.0mm thick, 300mm wide titanium alloy cold-rolled plate for hydrogen fuel cell electrode plates is vacuum pre-annealed at a temperature of 720℃ for 30 minutes and then cooled to 50℃ in the furnace before being removed from the furnace.

[0067] ② The cold-rolled sheet obtained in step ① is subjected to the first rolling pass. The rolling method is cold rolling, and the sheet thickness is rolled from 1.0 mm to 0.5 mm. The total number of rolling passes is 8, the deformation per pass is 6%~10%, and the cumulative total deformation is 50%.

[0068] ③ The cold-rolled sheet obtained in step ② is subjected to the first intermediate annealing at a temperature of 620℃ and a holding time of 20min. The annealing method is vacuum annealing. After cooling to 50℃ in the furnace, it is taken out of the furnace.

[0069] ④ Perform a second cold rolling pass on the cold-rolled sheet obtained in step ③ to reduce the sheet thickness from 0.5 mm to 0.20 mm. Control the number of rolling passes to 12, with a single-pass deformation amount ≤6% and a cumulative total deformation amount of 60%.

[0070] ⑤ The cold-rolled sheet obtained in step ④ is subjected to a second intermediate annealing at a temperature of 580℃ and a holding time of 20 minutes. The annealing method is vacuum annealing. After cooling to 30℃ in the furnace, the sheet is removed from the furnace.

[0071] ⑥ Perform a third cold rolling pass on the cold-rolled sheet obtained in step ⑤ to reduce the sheet thickness from 0.20 mm to the target thickness of 0.10 mm. The rolling passes are controlled to be 18 passes, with a single pass deformation amount of ≤4% and a cumulative total deformation amount of 50%.

[0072] ⑦ The titanium alloy foil obtained in step ⑥ is subjected to vacuum annealing to further control the texture type. The annealing temperature is 550℃ and the annealing time is 40min.

[0073] ⑧ The EBSD microstructure of the finished annealed titanium alloy foil was measured, and the results are as follows: Figure 4 As can be seen from the pole figure in the (0001) direction, the texture type is still basal texture, but compared with Example 1, the intensity of basal texture is reduced from 8.42 to 7.79, indicating that the total percentage of basal texture type grains in Example 2 is smaller than that in Example 1.

[0074] Example 3

[0075] ① A 1.0mm thick, 300mm wide titanium alloy cold-rolled plate for hydrogen fuel cell electrode plates is vacuum pre-annealed at a temperature of 720℃ for 30 minutes and then cooled to 50℃ in the furnace before being removed from the furnace.

[0076] ② The cold-rolled sheet obtained in step ① is subjected to the first rolling pass. The rolling method is cold rolling, and the sheet thickness is rolled from 1.0 mm to 0.4 mm. The total number of rolling passes is 8, the deformation per pass is 6%~10%, and the cumulative total deformation is 60%.

[0077] ③ The cold-rolled sheet obtained in step ② is subjected to the first intermediate annealing at a temperature of 600℃ and a holding time of 20min. The annealing method is vacuum annealing. After cooling to 50℃ in the furnace, it is taken out of the furnace.

[0078] ④ Perform a second cold rolling pass on the cold-rolled sheet obtained in step ③ to reduce the sheet thickness from 0.4 mm to 0.18 mm. Control the number of rolling passes to 12, with a single-pass deformation amount ≤6% and a cumulative total deformation amount of 55%.

[0079] ⑤ The cold-rolled sheet obtained in step ④ is subjected to a second intermediate annealing at a temperature of 580℃ and a holding time of 20 minutes. The annealing method is vacuum annealing. After cooling to 30℃ in the furnace, the sheet is removed from the furnace.

[0080] ⑥ Perform a third cold rolling pass on the cold-rolled sheet obtained in step ⑤ to reduce the sheet thickness from 0.18 mm to the target thickness of 0.10 mm. The number of rolling passes is controlled to be 15, with a single pass deformation amount of ≤4% and a cumulative total deformation amount of 44.4%.

[0081] ⑦ The titanium alloy foil obtained in step ⑥ is subjected to vacuum annealing to further control the texture type. The annealing temperature is 530℃ and the annealing time is 40min.

[0082] ⑧ The EBSD microstructure of the finished annealed titanium alloy foil was measured, and the results are as follows: Figure 5 As can be seen from the pole figure in the (0001) direction, the texture type is still basal texture, and the strength of the basal texture is increased to 9.32, indicating that the texture control effect is better than that of Examples 1 and 2. The titanium alloy foil obtained in this example was subjected to pole plate microchannel forming tests, such as... Figure 6 As shown, the microchannel edge height is 0.7mm and the edge width is 1.0mm. No defects such as cracking have occurred, which meets the microchannel forming requirements of hydrogen fuel cell plates.

[0083] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0084] It should be understood that, as used herein, unless the context clearly supports an exception. It should also be understood that, as used herein, "and / or" means any and all possible combinations of one or more of the associated listed items.

[0085] The embodiment numbers disclosed in the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0086] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for microstructure control of microchannel forming of a titanium alloy foil, characterized by, The application relates to a titanium alloy foil manufacturing method. S1, pre-annealing a titanium alloy plate, wherein the pre-annealing temperature is 650-750 DEG C, the holding time is 30-60 min, and the titanium alloy plate is cooled to below 100 DEG C after pre-annealing and then discharged from the furnace; S2, first rolling of the titanium alloy plate by a cold rolling method to form a first intermediate material, wherein the cumulative total deformation of the first rolling is 50-66%; S3, first annealing of the first intermediate material, wherein the annealing temperature is 600-700 DEG C, the holding time is 20-40 min, and the first intermediate material is cooled to below 100 DEG C after annealing and then discharged from the furnace; S4, second rolling of the first intermediate material by a cold rolling method after annealing to form a second intermediate material, wherein the cumulative total deformation of the second rolling is 46-60%; S5, second annealing of the second intermediate material, wherein the annealing temperature is 550-650 DEG C, the holding time is 10-20 min, and the second intermediate material is cooled to below 50 DEG C after annealing and then discharged from the furnace; S6, third rolling of the second intermediate material by a cold rolling method after annealing to form a foil with a target thickness, wherein the cumulative total deformation of the third rolling is less than 50%; S7, third annealing of the foil to form a titanium alloy foil. In S1-S7, the annealing temperature is gradually reduced, and the rolling pass is gradually increased.

2. The method of claim 1, wherein the titanium alloy foil microchannel forming microtexture control method is characterized by, The first rolling includes 8-10 rolling passes, the single-pass deformation is 5-15%, and the thickness of the first intermediate material is 0.5-0.75 mm.

3. The method of claim 1, wherein the titanium alloy foil microchannel forming microtexture control method is characterized by The second rolling includes 12-16 rolling passes, the single-pass deformation is not more than 8%, and the thickness of the second intermediate material is 0.2-0.4 mm.

4. The method of claim 1, wherein the titanium alloy foil microchannel forming microtexture control method is characterized by, The third rolling includes 15-20 rolling passes, the single-pass deformation is not more than 5%, and the target thickness of the foil is 0.1-0.2 mm.

5. The method of claim 1, wherein the titanium alloy foil microchannel forming microtexture control method is characterized by: The annealing temperature of the third annealing is 500-600 DEG C, and the annealing time is 40-60 min.

6. The method of claim 1, wherein the titanium alloy foil microchannel forming microtexture control method is characterized by: Each annealing is vacuum annealing.

7. The method of claim 1, wherein the titanium alloy foil microchannel forming microtexture control method is characterized by, The thickness of the titanium alloy plate is 1.0-1.5 mm.

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