High-performance titanium alloy surface tension storage tank and low-temperature superplastic forming method

Abstract

The invention discloses a high-performance titanium alloy surface tension storage tank and a low-temperature superplastic forming method, and aims at solving the defects in the prior art based on the new requirement of a carrier aircraft on a high-performance titanium alloy surface tension storage tank shell. Through alloying element regulation and control and special cogging / rolling combined deformation process optimization, preparation of the high-performance and anisotropy-free superplastic formed titanium alloy plate is achieved. On the basis, the overall hot forming time is shortened through low-temperature (less than or equal to 890 DEG C) superplastic forming process evaluation and positive and negative expansion molded surface control; high-temperature charging and high-temperature discharging are combined, continuous high-temperature forming is achieved, and low-temperature and high-efficiency superplastic near-net forming of the large titanium alloy thin-wall component with the meter-scale diameter is achieved. And finally, the tensile strength of the TC4 spherical shell part body is more than or equal to 1010MPa, and is higher than that of the currently common titanium alloy superplastic forming and forging forming spherical shell parts. Therefore, the material-manufacturing process integrated production of the high-performance TC4 titanium alloy surface tension storage tank shell is realized.

Description

Technical Field

[0001] The invention relates to a low-temperature superplastic forming method for a high-performance titanium alloy surface tension tank, belongs to the field of advanced manufacturing technology, and is mainly used for manufacturing structural parts of a carrier aircraft power system. Background Art

[0002] Titanium alloy surface tension tank is a key structural component of the power system of the carrier aircraft. With the improvement of the use environment and performance of the tank, new and higher requirements are put forward for titanium alloy materials and manufacturing technology. The traditional TC4 forging process can no longer meet the requirements of lightweight products. It is urgent to develop titanium alloy materials with higher mechanical properties and corresponding forming process technologies. In addition, in order to increase the use pressure of the tank, in order to meet the structural strength requirements, the structural strength can only be improved by wall thickness compensation, which will undoubtedly increase the weight of the structure and cannot meet the lightweight requirements. Superplastic forming technology is a precision plastic forming process that uses the superplasticity of materials to obtain the required parts. This technology can greatly improve the formability of the material, and has the advantages of high forming accuracy, near-zero rebound, and no residual stress. It is basically not limited by the size of the part, and has become the preferred process for near-net forming of titanium alloy tank products. However, since superplastic forming is an obvious high-temperature thermal deformation process, and the long-term thermal process is bound to cause grain growth, thereby reducing the mechanical properties of the material, and it cannot be strengthened by subsequent heat treatment. At present, the tensile strength of large-size TC4 titanium alloy tank shell after superplastic forming is basically maintained at 900-950MPa, which can no longer meet the use requirements. Summary of the invention

[0003] The technical problem solved by the present application is: to overcome the shortcomings of the prior art, to provide a high-performance titanium alloy surface tension tank and a low-temperature superplastic forming method, to achieve high-performance, non-anisotropic superplastic forming titanium alloy sheet preparation, and on the basis of the titanium alloy sheet, the TC4 spherical shell part body tensile strength ≥1010MPa is obtained by low-temperature (≤920℃) superplastic forming and positive and negative expansion.

[0004] Through the regulation of alloying elements and the optimization of special billet / rolling combined deformation process, high-performance, non-anisotropic superplastic forming titanium alloy sheet materials are prepared; on this basis, through low-temperature (≤920℃) superplastic forming process evaluation and positive and negative bulging surface control, the overall hot forming time is shortened, and low-temperature, high-rate superplastic near-net forming of meter-level large titanium alloy thin-walled components is achieved; finally, the TC4 spherical shell part body tensile strength is stably achieved ≥1010MPa, which is higher than the currently commonly used titanium alloy superplastic forming spherical shell parts. The material-manufacturing process integrated production of high-performance TC4 titanium alloy surface tension tank shell is realized. The project content involved in the patent of this invention can realize the service requirements of carrier aircraft for high-performance titanium alloy tanks.

[0005] Due to the new performance requirements of the new generation of surface tension tanks, spherical shell parts manufactured by traditional processes can no longer meet the requirements. The titanium alloy sheet developed through this patent has excellent mechanical properties and forming properties, and realizes superplastic near-net forming under low temperature and high rate conditions, avoiding coarse grains and performance deterioration after component forming. At the same time, this technology can stably achieve the tensile strength of the TC4 spherical shell part body ≥1010MPa, which is higher than the currently commonly used titanium alloy superplastic formed spherical shell parts. Among them, in the invention points involved, the concept of high-performance superplastic fine-grained titanium alloy sheet refers to a thickness of 8 to 16 mm, and large-size superplastic formed titanium alloy surface tension tank shell generally refers to a tank shell with a diameter of 600 to 1200 mm.

[0006] The technical solutions provided by this application are as follows:

[0007] A low temperature superplastic forming method for a high performance titanium alloy surface tension tank, such as Figure 3 As shown, including:

[0008] S1: performing blank forging and slab manufacturing on the TC4 titanium alloy ingot to obtain a forged slab;

[0009] S2: performing multi-stage plate rolling on the forged slab to obtain a rolled slab;

[0010] S3: heat treating the rolled slab to obtain an original slab;

[0011] S4: Perform superplastic property test on the original slab to obtain its average m value at 860-890°C; measure the original slab in this temperature range and 0.0001s -1 ~0.01s -1 m value under strain rate, if the average m value is greater than 0.3, the next step of superplastic forming is carried out;

[0012] S5: Determine the structure of the superplastic forming die, the superplastic forming die includes an upper die and a lower die, the inner surface of the lower die is consistent with the final forming surface of the tank shell blank, and the upper die is provided with an annular groove coaxial with the axis of the final forming surface of the tank shell blank;

[0013] S6: placing the original slab between the upper mold and the lower mold; performing reverse bulging forming to make the original slab fit the surface of the upper mold to obtain a preformed surface;

[0014] S7: Perform positive bulging to make the preformed surface fit with the surface of the lower die to obtain a TC4 titanium alloy tank shell blank.

[0015] In S1, the TC4 titanium alloy ingot is subjected to open forging and slab manufacturing to obtain a forged slab, including: the TC4 titanium alloy ingot is forged three times to obtain a forged slab; the temperature of the first forging is higher than the temperature of the second forging, and the temperature of the third forging is higher than the temperature of the second forging.

[0016] The three-forging process includes: the first forging: the TC4 titanium alloy ingot is forged at the β phase transformation point T β The TC4 titanium alloy ingot is heated with the furnace, and after being taken out of the furnace, it is first upset to a height-to-diameter ratio of ≤2, returned to the furnace for insulation for 1.5±0.5h, and then drawn to a height-to-diameter ratio of 2-2.5, returned to the furnace for insulation for 1.5±0.5h, and then upset to 50-70% of the initial height of the TC4 titanium alloy ingot to obtain a primary forging billet; during the forging process, the temperature is lower than T β When the temperature is +30℃, the TC4 titanium alloy ingot is placed in a 600-700℃ annealing furnace for 6-8h, and finally air-cooled to room temperature;

[0017] Second forging: The first forging billet cooled to room temperature is heated again to T β + (0-50°C) for 5-7h, and then repeatedly upsetting-drawing for 3-5 times at this temperature, upsetting to 50-80% of the height of the first forging billet; if the surface temperature of the billet during the upsetting-drawing process is lower than 900°C, the upsetting-drawing process is continued after the billet is returned to the furnace for heating; if the surface temperature of the billet during the upsetting-drawing process is ≥900°C, the billet is placed in an annealing furnace at 600-700°C for 6-8h; finally, air-cooling to room temperature is performed to obtain a second forging billet;

[0018] The third forging: First, the secondary forging blank is placed on T β + (30~80℃) keep warm for 4~6h, and then go through an upset after taking out of the furnace, the deformation is controlled at 45~60%, if the temperature is not lower than 900℃, continue forging, so that the billet is elongated and the thickness is reduced; after the temperature is lower than 900℃, put it into the furnace and keep warm for 1~1.5h, the holding temperature T β ±30, continue forging at this temperature for 2 to 4 times until the temperature is not less than 900℃, cool to room temperature to obtain a forged slab.

[0019] In S2, the forged slab is subjected to multi-stage plate rolling to obtain a rolled slab, comprising:

[0020] The first fire is to heat the forged slab in T β +(0~50℃), the rolling directions of the previous pass and the next pass are perpendicular, the deformation of each pass is 10~15%, the rolling speed is 2~5m / s, 3~5 passes are rolled, and the total rolling deformation is 40~65%; if the temperature is lower than 900℃ during the rolling process, the furnace is returned to heat up;

[0021] Second heat, rolling temperature T β +(0~50℃), the rolling direction is perpendicular to the final rolling direction of the first heat, the deformation of each pass is 6~12%, the rolling speed is 2~5m / s, 3~5 passes are rolled, the total rolling deformation is 40~65%, and air cooling is performed to room temperature after rolling;

[0022] The third fire, rolling temperature T β -(0~50℃), the pass deformation rate is 10~20%, the rolling speed is 3~4m / s, the final rolling temperature is 850±20℃, and the rolled slab is obtained.

[0023] In S3, the rolled slab is heat treated, including: keeping the rolled slab at 600-700°C for 240±10 min, and air cooling.

[0024] The upper mold is located at the edge of the forming surface of the upper mold, and a rounded corner is formed between the edge of the annular groove and the surface of the upper mold facing the lower mold.

[0025] In the S6, the original slab is placed between the upper die and the lower die; and reverse bulging is performed, including: the heating rate of the superplastic forming die is 55-75°C / h. When the temperature of the superplastic forming die rises to 650-750°C, the original slab is placed between the upper die and the lower die, and the temperature is continued to rise. When the temperature of the superplastic forming die is 860-890°C, the superplastic forming upper die and the lower die are closed, and the tonnage is maintained at 10-20t; reverse bulging is performed to make the original slab fit with the upper die, the air intake rate is 0.05-0.10MPa / min, the air pressure is increased to 2.0-3.0MPa, and the pressure is released after maintaining the pressure for 15-20min.

[0026] The positive bulging forming includes: after the reverse bulging forming is completed and the air pressure is balanced, and the temperature of the superplastic forming mold is maintained at 860-890°C, positive bulging is performed to make the original slab fit with the lower mold, the air intake speed is ≤0.05MPa / min, and the air pressure is increased to 1.5-2.0MPa; after the hemispherical blank formed by the original slab is completely fitted with the lower mold, the pressure is continued to be maintained for 15-20 minutes, and then the pressure is released to balance the air pressure, and the upper mold is raised at the same time.

[0027] Based on the mass content of each component being 100%, the TC4 titanium alloy ingot includes: Al: 6.55-6.75%, V: 4.20-4.50%, Fe: 0.10-0.30%, O: 0.10-0.20%, C≤0.08; N≤0.05%, H≤0.015, unavoidable impurities≤0.4%; and the balance is Ti.

[0028] A high-performance titanium alloy surface tension tank is prepared according to any of the above-mentioned low-temperature superplastic forming methods for a high-performance titanium alloy surface tension tank.

[0029] The core point of the present invention is to achieve fine control of the microstructure and texture type of the plate by optimizing the preparation process of the raw materials, and obtain the mechanical properties of the commonly used traditional TC4 titanium alloy plate. By optimizing the superplastic forming mold design and the low-temperature superplastic forming process, low-temperature rapid forming of high-performance plates can be achieved. The room temperature mechanical properties of the large-size titanium alloy tank shell blank finally obtained, Rm≥1010MPa, are better than the current superplastic forming and forging forming product performance (900~950MPa), and have a large performance margin. It can be applied to the current and even future development needs of high-performance titanium alloy surface tension tanks in my country, and has a high commercial application value.

[0030] In summary, this application at least includes the following beneficial technical effects:

[0031] (1) Based on the original TC4 alloy composition, the alloying elements are regulated to increase the content of alloying elements such as Al, V, and Fe, and a titanium alloy ingot with high alloying element content and narrow composition range is produced by three vacuum melting. Special billet forging technology is further used to improve the ingot structure. The large deformation in the β single phase region (Tβ+50~150℃) can refine the grains and effectively control the lamellar α phase; the large deformation in the α / β phase region can achieve the fragmentation of the Widmanstätten structure strip α phase and avoid the appearance of strong texture. On this basis, the microstructure and texture type are precisely controlled through multi-fire reversing rolling in the α / β phase region, thereby achieving high strength and non-anisotropy of TC4 titanium alloy plates. Taking the currently formed δ14×1200×1200mm as an example, the longitudinal and transverse tensile strength of the plate is ≥1150MPa, which is significantly improved compared with the commonly used δ14mm plate (GJB2505A-2018) plate.

[0032] (2) Full-scale process performance tests were conducted on high-performance plates. The plate showed stable microstructures in all regions, and the longitudinal and transverse performances were basically consistent, showing good formability. The TC4 titanium alloy thick plate of the present invention was subjected to a high temperature test at 830-890°C / 0.001s -1 It shows obvious high temperature superplasticity. Using the strain rate mutation method, the average m value of TC4 material at 860-890℃ is 0.48, which is better than the m value of traditional TC4 alloy under this condition.

[0033] (3) According to the variable wall thickness and structural characteristics of the titanium alloy tank shell, it belongs to the variable wall thickness and large depth ratio parts. It is necessary to adopt positive and negative bulging to make the edges thin and the middle thick after the pre-forming of the slab, so that the unevenness of the wall thickness during the final bulging can be compensated. This is essentially different from the traditional unidirectional bulging. During unidirectional bulging, the wall thickness varies greatly, the middle is thin, and the edges are thick, which makes it impossible to manufacture parts. In addition, compared with the currently commonly used superplastic bulging process, the forming temperature of less than 890°C in the present invention can achieve low-temperature superplastic forming compared with the currently commonly used 890-910°C forming. High-temperature furnace loading and high-temperature furnace discharge can achieve continuous forming and shorten the heating time of the blank. Overall, the influence of the thermal process on the mechanical properties of the material is reduced, thereby achieving low-temperature and high-efficiency superplastic forming of meter-level large titanium alloy shells.

[0034] (4) The core point of the present invention is to achieve fine control of the microstructure and texture type of the plate by optimizing the preparation process of the raw materials, and obtain the mechanical properties of the commonly used traditional TC4 titanium alloy plate. By optimizing the superplastic forming mold design and the low-temperature superplastic forming process, low-temperature rapid forming of high-performance plates can be achieved. The room temperature mechanical properties of the large-size titanium alloy tank shell blank finally obtained are Rm≥1010MPa, which is better than the current superplastic forming and forging forming product performance (900~950MPa), and has a large performance margin. It can be applied to the current and even future development needs of high-performance titanium alloy surface tension tanks in my country, and has high commercial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The microstructure of the TC4 titanium alloy superplastic fine-grained plate prepared in the embodiment of the present invention;

[0036] Table 1 is a comparison of the longitudinal and transverse room temperature mechanical properties of the TC4 titanium alloy superplastic fine-grained plate prepared in the embodiment of the present invention;

[0037] Figure 2 Superplastic positive and negative forming die surface designed for the embodiment of the present invention;

[0038] Table 2 shows the mechanical properties of the TC4 titanium alloy surface tension tank shell prepared in the embodiment of the present invention;

[0039] Figure 3 The figure is a specific implementation flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments disclosed in the present invention will be further described in detail below with reference to the accompanying drawings.

[0041] A method for low-temperature superplastic forming of a high-performance titanium alloy surface tension tank, the method comprising the following steps:

[0042] The first step is alloy composition design and smelting. The composition is selected based on TC4 titanium alloy, which has the characteristics of high alloying element content, narrow composition range, and low element extreme difference, including: Al: 6.55-6.75%, V: 4.20-4.50%, Fe: 0.10-0.30%, O: 0.10-0.20%, the balance is Ti, and the C / N / H content meets the requirements of GJB2505A-2018 standard. TC4 titanium alloy ingots with high alloying elements are prepared by three vacuum consumable arc melting, and the melting process parameters are optimized.

[0043] The second step is the special blank forging and slab manufacturing technology. In order to ensure the uniform and fine titanium alloy forging blank and effectively control the thickness of the lamellar α phase, the "high-low-high" forging process is adopted, which is divided into three forging processes. β Keep the temperature at 50-150℃ for 4-6h. The billet is heated with the furnace and immediately transferred to the fast forging machine after it comes out of the furnace. First, it is upset to a height-to-diameter ratio of ≤2, then returned to the furnace for 1.5±0.5h, then stretched to a height-to-diameter ratio of 2-2.5, returned to the furnace for 1.5±0.5h, and then upset to 50-70% of the height. The final forging temperature is T β +30℃, then put it in a 600-700℃ annealing furnace for 6-8h, finally put it in a sand pit to air cool to room temperature, and polish the surface; the blank cooled to room temperature is heated again to T β + (0~50℃) for 5~7h to fully recrystallize, and then repeatedly upsetting-drawing 3~5 times at this temperature. The upsetting-drawing adopts the ordinary upsetting-drawing process combined with the diagonal drawing process. Upsetting to 50~80% of the height, drawing to a height-to-diameter ratio of 1.5~2.3. When the surface temperature of the billet is lower than 900℃ during the upsetting process, it is returned to the furnace for heating for 2±0.5h and then upsetting is continued. The final forging temperature is ≥900℃, and then it is placed in a 600~700℃ annealing furnace for 6~8h, and finally placed in a sand pit for air cooling to room temperature, and the surface is polished; the third forging is to first place the billet at T β + (30~80℃) keep warm for 4~6h, and then go through an upset after leaving the furnace, and the deformation is controlled at 45~60%. If the temperature is not lower than 900℃, continue forging to make the blank elongated and thinner. When the temperature is lower than 900℃, put it into the furnace and keep warm for 1~1.5h. The holding temperature is T β ±30, continue forging 2 to 4 times at this temperature, the final forging temperature is 900℃, after shaping, the slab thickness is 150 to 200mm, cool to room temperature, and grind the surface.

[0044] Special billet forging and slab manufacturing, in the β single phase area, adopts "multiple combined deformation methods" to accumulatively deform with large deformation and control the deformation rate, which can efficiently and evenly refine the grains and effectively control the thickness of the lamellar α phase; in the α / β phase area, adopts "multiple combined deformation methods" to accumulatively deform with large deformation + medium temperature deformation and control the deformation rate, so as to efficiently break the strip α phase and avoid overheating of the core and the appearance of strong texture. A uniform and fine titanium alloy forging billet is obtained.

[0045] The third step is multi-fire plate rolling and heat treatment microstructure control. The idea of ​​multi-fire cooling rolling is adopted, combined with numerical simulation technology, to analyze the strain field during the rolling process and determine the optimal pass deformation and fire deformation. The slab obtained in the second step is cut into square billets of 800 to 1000 mm. First, the first fire is at T β +(0~50℃) for reversing rolling (the rolling directions of the previous pass and the next pass are perpendicular to each other), the temperature during rolling is lower than 900℃ and then the furnace is returned to the furnace for temperature supplementation, the deformation of each pass is 10~15%, the rolling speed is 2~5m / s, 3~5 passes are rolled, and the total rolling deformation is 40~65%; the rolling direction of the second pass is perpendicular to the final rolling direction of the first pass, and the temperature T β +(0~50℃), the deformation of each pass is 6~12%, the rolling speed is 2~5m / s, 3~5 rolling passes, the total rolling deformation is 40~65%, and the slab is air-cooled to room temperature after rolling. The slab is 800~1000mm square billet; the third rolling, the rolling temperature T β -(0~50℃), pass deformation rate is 10~20%, rolling speed is 3~4m / s, final rolling temperature is 850±20℃, final rolling is (14~15)

[0046] ×1200×1200mm high-performance ultrafine-grained titanium alloy plate; the plate is kept at 600-700℃ for 240±10min and air-cooled. Finally, it is straightened and finely calibrated to obtain the original slab. This process is a multi-fire cooling rolling process, which obtains a plate with fine grains and uniform properties. The tensile strength values ​​of the plate in the transverse and longitudinal directions are almost the same, both greater than 1150MPa.

[0047] The fourth step is to explore the processability of low-temperature superplastic forming. The finished plate is subjected to full-size partitioned high-temperature tensile processability test. The TC4 titanium alloy thick plate is subjected to 830~890℃ / 0.001s -1 It shows obvious high-temperature superplasticity, and the grains are fine after superplastic deformation; after increasing the temperature, the grains deteriorate significantly, and forming at high temperatures should be avoided. Using the strain rate mutation method, the average m value of TC4 material at 860-890°C is ≥0.48 (greater than the superplastic m value criterion), which is better than the m value of traditional TC4 alloy under this condition. It also reflects the uniformity of the forming performance of high-performance finished plates.

[0048] The fifth step is to design the superplastic forming die. The superplastic forming die includes an upper die and a lower die. The inner surface of the lower die is consistent with the final forming surface of the tank. The upper die is provided with an annular groove coaxial with the axis of the final forming surface of the tank. The edge of the annular groove and the surface of the upper die facing the lower die are rounded, and the annular groove is located at the edge of the forming surface of the upper die. According to the surface wall and structural characteristics of the titanium alloy tank shell, it belongs to a part with variable wall thickness and large depth ratio. Positive and negative bulging is required to make the slab thin at the edge and thick in the middle after reverse bulging, so that the unevenness of the wall thickness during the final bulging is compensated. Ni7N is selected as the mold material.

[0049] Step 6: Superplastic forming process setting. Heat up the superplastic forming equipment, target temperature 860-890℃, heating rate 55-75℃ / h. When the mold temperature rises to 650-750℃, open the furnace door, move out the shuttle car, and place the original slab 1 on the superplastic mold by hoisting. Move in the shuttle car and close the furnace door. Do not apply pressure during heating to ensure that the distance between the upper mold and the lower mold is 100-150mm. Continue heating.

[0050] Step 7: Superplastic bulging. When the average mold temperature is 870-890℃ and the upper mold temperature is ≥870℃, close the upper and lower superplastic forming molds and maintain a tonnage of 10-20t. Execute the air intake program with an air intake speed of 0.05-0.10MPa / min, raise the air pressure to 2.0-3.0MPa, maintain the pressure for 15-20min, and then release the pressure to obtain the preformed surface 2. Figure 2 shown.

[0051] Step 8: Superplastic positive bulging. After the reverse bulging is completed and the air pressure is balanced, the positive bulging air intake procedure is started, with the air intake speed ≤0.05MPa / min, and the air pressure is raised to 1.5-2.0MPa. After the hemispherical blank is completely attached to the lower mold, the pressure is maintained for 15-20 minutes, and then the pressure is released to balance the air pressure, and the upper mold is raised at the same time to obtain the TC4 titanium alloy tank shell blank 3.

[0052] Step 9: The TC4 titanium alloy tank shell blank is removed from the furnace. When the average temperature of the mold drops to 750°C, the furnace door is opened, the shuttle car is removed, the TC4 titanium alloy tank shell blank is removed from the mold, and placed in a sand pit for cooling.

[0053] The tenth step is to continue production according to the sixth step to achieve efficient manufacturing of TC4 titanium alloy tank shell blanks.

[0054] Example:

[0055] The first step is alloy composition design and smelting. TC4 titanium alloy was selected for composition design. Under the premise of meeting GJB2505A-2018, Al%: 6.6%, V%: 4.3%, Fe%: 0.25%, O%: 0.18%, C: 0.02%; N: 0.004%, H: 0.001%, unavoidable impurities ≤ 0.25%; the balance is Ti. High-alloy ingots were prepared by three vacuum consumable arc melting.

[0056] The second step is special blank forging and slab manufacturing. In order to ensure uniform and fine titanium alloy forging billets, the ingot is kept at 1100℃ for 4.5h, and then quickly forged after being taken out of the furnace, upset to an aspect ratio of 1.9, returned to the furnace for 1.5h, and then stretched to 2.2. After being returned to the furnace for 1.5h, the ingot is upset to 60% of the original height, then kept at 700℃ for 6h, air-cooled in the sand pit after being taken out of the furnace, and surface cracks are polished. The temperature is raised to 1000℃ again, and after being kept for 5.5h, it is upset and stretched 4 times, upset to 70% of the height, and then kept at 700℃ for 6h, air-cooled in the sand pit after being taken out of the furnace, and surface cracks are polished. Finally, the billet is placed in a high-temperature furnace at 1050℃ for 4h, with a deformation of 52%, and forged 4 times in the range of 960℃ to 1050℃, and the final slab thickness is 180mm. Preheat the tooling before forging to ensure that the tooling temperature is 200℃~240℃.

[0057] The third step is multi-fire plate rolling and heat treatment microstructure control. The slab obtained in the second step is cut into square billets of 800-1000 mm. First, the first fire is reversed at 1000 ° C (the rolling directions of the previous and next passes are perpendicular). After the temperature is lower than 900 ° C during the rolling process, it is returned to the furnace for temperature replenishment. The deformation of each pass is 10-15%, the rolling speed is 3.1-3.5 m / s, and the rolling is 4 passes. The total rolling deformation is 55%; the rolling direction of the second fire is perpendicular to the final rolling direction of the first fire, the deformation of each pass is 6-12%, the rolling speed is 3.1-3.5 m / s, and the rolling is 5 passes. The total rolling deformation is 60%, and the slab is air-cooled to room temperature after rolling. The slab is cut into square billets of 800-1000mm. The third rolling process is consistent with the second rolling process. The last rolling temperature is 960℃, the pass deformation rate is 15-18%, the rolling speed is 2.5-3.1m / s, the final rolling temperature is 850℃, and the final rolling is 14±0.2mm thick titanium plate, which is cut and shaped into 1200×1200mm high-performance ultrafine-grained titanium alloy plate. The plate is kept at 600-700℃ for 240±10min and air-cooled. Finally, it is straightened and fine-tuned. The tensile strength values ​​of the plate in the transverse and longitudinal directions are almost the same, both greater than 1150MPa.

[0058] The fourth step is to explore the superplastic forming process of high-strength fine-grained titanium alloy plates. TC4 titanium alloy thick plates are 830-920℃ / 0.01s-1 ~0.0001s -1 High temperature stretching of 9 areas in the longitudinal and transverse directions, 830~890℃ / 0.01s -1 The TC4 alloy has obvious superplasticity under the condition. The average m value of TC4 material at 860-890℃ is ≥0.48 by using the strain rate mutation method, which is better than the m value of traditional TC4 alloy under this condition.

[0059] The fifth step is to design the superplastic forming die. The hemispherical part has thin-wall variable-thickness characteristics, with a depth / diameter ≥ 0.5 and a diameter of 1000 mm. The die is designed using positive and negative bulging technology, and Ni7N is selected as the die material.

[0060] Step 6: Superplastic forming process settings. Heat up the superplastic forming equipment, target temperature 880℃, heating rate 775℃ / h. When the mold temperature rises to 700℃, open the furnace door, move out the shuttle car, and place the slab on the superplastic mold by hoisting. Move in the shuttle car and close the furnace door. Do not apply pressure during heating to ensure that the distance between the upper mold and the lower mold is 120mm. Continue to heat up.

[0061] Step 7: Superplastic bulging. When the average mold temperature is 870-880℃ and the upper mold temperature is ≥870℃, close the upper and lower molds of superplastic forming and keep the tonnage at 16t. Execute the air intake program with an air intake speed of 0.08MPa / min, raise the air pressure to 2.5MPa, maintain the pressure for 20min, and then release the pressure. Figure 2 shown.

[0062] Step 8: Superplastic positive bulging. After the reverse bulging is completed and the air pressure is balanced, the positive bulging air intake procedure is started, with an air intake speed of 0.05MPa / min, and the air pressure is raised to 2.0MPa. After the hemispherical blank is completely attached to the lower mold, the pressure is maintained for 20 minutes, and then the pressure is released to balance the air pressure, and the upper platform is raised at the same time.

[0063] Step 9: The hemispherical blank is taken out of the furnace. When the average temperature of the mold drops to 750°C, open the furnace door, remove the shuttle car, remove the hemispherical blank from the mold, and place it in a sand pit to cool.

[0064] The tenth step is to continue production according to the sixth step to achieve efficient manufacturing of the titanium alloy hemisphere blank.

[0065] The microstructure of the TC4 titanium alloy superplastic fine-grained plate prepared in this example is as follows: Figure 1As shown. The tensile strength, elongation and tensile strength of the plate in the RD and TD directions are almost the same, and the tensile strength value is between 1160 and 1170 MPa, showing good isotropic characteristics of mechanical properties. At present, the tensile strength of the plate with a thickness of 10 to 100 mm in GJB2505A-2018 is 895 to 1100 MPa, and the yield strength is ≥ 825 MPa; the tensile strength of the plate with a thickness of 14 mm that meets the GJB2505A-2018 standard is generally between 1030 and 1070 MPa.

[0066] Table 1 Finished plate properties

[0067]

[0068] Table 2 Comparison of properties of TC4 titanium alloy tank shell blanks

[0069]

[0070] Comparative Example:

[0071] The only difference from the embodiment is that during the reverse bulging and forward bulging, the temperature of the mold is 920°C, and the other parameters remain the same. The obtained hemispherical properties are shown in the following table:

[0072] Table 2 Comparison of properties of TC4 titanium alloy tank shell blanks

[0073]

[0074] In summary, by optimizing the preparation process of raw materials, the performance of the sheet is improved, and mechanical properties that are better than the commonly used TC4 titanium alloy sheet are obtained. By optimizing the low-temperature superplastic forming process, low-temperature rapid forming of high-performance sheets can be achieved. The room temperature mechanical properties of the large-size titanium alloy tank shell blank finally obtained are Rm≥1010MPa, which is better than the current superplastic forming and forging forming product performance (900~950MPa), and has a large performance margin. It can be applied to the current and even future development needs of high-performance titanium alloy surface tension tanks in my country, and has high commercial application value.

[0075] The contents not described in detail in this application specification belong to the common knowledge of those skilled in the art.

[0076] The present application is described in detail above in conjunction with specific implementation methods and exemplary examples, but these descriptions cannot be understood as limiting the present application. Those skilled in the art understand that, without departing from the spirit and scope of the present application, a variety of equivalent replacements, modifications or improvements can be made to the technical solution of the present application and its implementation methods, all of which fall within the scope of the present application. The scope of protection of the present application shall be subject to the attached claims.

Claims

1. A low-temperature superplastic forming method for a high-performance titanium alloy surface tension tank, characterized in that: include: S1: performing blank forging and slab manufacturing on the TC4 titanium alloy ingot to obtain a forged slab; S2: performing multi-stage plate rolling on the forged slab to obtain a rolled slab; S3: heat treating the rolled slab to obtain an original slab; S4: Perform superplastic property test on the original slab to obtain its average m value at 860-890°C; measure the original slab in this temperature range and 0.0001s -1 ~0.01s -1 m value under strain rate, if the average m value is greater than 0.3, the next step of superplastic forming is carried out; S5: Determine the structure of the superplastic forming die, the superplastic forming die includes an upper die and a lower die, the inner surface of the lower die is consistent with the final forming surface of the tank shell blank, and the upper die is provided with an annular groove coaxial with the axis of the final forming surface of the tank shell blank; S6: placing the original slab between the upper mold and the lower mold; performing reverse bulging forming to make the original slab fit the surface of the upper mold to obtain a preformed surface; S7: Perform positive bulging to make the preformed surface fit with the surface of the lower die to obtain a TC4 titanium alloy tank shell blank.

2. The low-temperature superplastic forming method of a high-performance titanium alloy surface tension tank according to claim 1, characterized in that: In S1, the TC4 titanium alloy ingot is subjected to blanking forging and slab manufacturing to obtain a forged slab, comprising: The TC4 titanium alloy ingot is forged three times to obtain a forged slab; The temperature of the first forging is higher than that of the second forging, and the temperature of the third forging is higher than that of the second forging.

3. The low temperature superplastic forming method of a high performance titanium alloy surface tension tank according to claim 2, characterized in that: The three-step forging process includes: First forging: TC4 titanium alloy ingot is cast at the β phase transformation point T β The TC4 titanium alloy ingot is heated with the furnace, and after being taken out of the furnace, it is first upset to a height-to-diameter ratio of ≤2, returned to the furnace for insulation for 1.5±0.5h, and then drawn to a height-to-diameter ratio of 2-2.5, returned to the furnace for insulation for 1.5±0.5h, and then upset to 50-70% of the initial height of the TC4 titanium alloy ingot to obtain a primary forging billet; during the forging process, the temperature is lower than T β When the temperature is +30℃, the TC4 titanium alloy ingot is placed in a 600-700℃ annealing furnace for 6-8h, and finally air-cooled to room temperature; Second forging: The first forging billet cooled to room temperature is heated again to T β + (0-50°C) for 5-7h, and then repeatedly upsetting-drawing for 3-5 times at this temperature, upsetting to 50-80% of the height of the first forging billet; if the surface temperature of the billet during the upsetting-drawing process is lower than 900°C, the upsetting-drawing process is continued after the billet is returned to the furnace for heating; if the surface temperature of the billet during the upsetting-drawing process is ≥900°C, the billet is placed in an annealing furnace at 600-700°C for 6-8h; finally, air-cooling to room temperature is performed to obtain a second forging billet; The third forging: First, the secondary forging blank is placed on T β + (30~80℃) keep warm for 4~6h, and then go through an upset after taking out of the furnace, the deformation is controlled at 45~60%, if the temperature is not lower than 900℃, continue forging, so that the billet is elongated and the thickness is reduced; after the temperature is lower than 900℃, put it into the furnace and keep warm for 1~1.5h, the holding temperature T β ±30, continue forging at this temperature for 2 to 4 times until the temperature is not less than 900℃, cool to room temperature to obtain a forged slab.

4. The low temperature superplastic forming method of a high performance titanium alloy surface tension tank according to claim 1, characterized in that: In S2, the forged slab is subjected to multi-stage plate rolling to obtain a rolled slab, comprising: The first fire is to heat the forged slab in T β +(0~50℃), the rolling directions of the previous pass and the next pass are perpendicular, the deformation of each pass is 10~15%, the rolling speed is 2~5m / s, 3~5 passes are rolled, and the total rolling deformation is 40~65%; if the temperature is lower than 900℃ during the rolling process, the furnace is returned to heat up; Second heat, rolling temperature T β +(0~50℃), the rolling direction is perpendicular to the final rolling direction of the first heat, the deformation of each pass is 6~12%, the rolling speed is 2~5m / s, 3~5 passes are rolled, the total rolling deformation is 40~65%, and air cooling is performed to room temperature after rolling; The third fire, rolling temperature T β -(0~50℃), the pass deformation rate is 10~20%, the rolling speed is 3~4m / s, the final rolling temperature is 850±20℃, and the rolled slab is obtained.

5. The low temperature superplastic forming method of a high performance titanium alloy surface tension tank according to claim 1, characterized in that: In S3, the rolled slab is heat treated, including: The rolled slab is kept at 600-700°C for 240±10 min and air-cooled.

6. The low temperature superplastic forming method of a high performance titanium alloy surface tension tank according to claim 1, characterized in that: The upper mold is located at the edge of the forming surface of the upper mold, and a rounded corner is formed between the edge of the annular groove and the surface of the upper mold facing the lower mold.

7. The low temperature superplastic forming method of a high performance titanium alloy surface tension tank according to claim 1, characterized in that: In S6, the original slab is placed between the upper mold and the lower mold; The reverse bulging forming is carried out, including: the heating rate of the superplastic forming mold is 55-75℃ / h, when the temperature of the superplastic forming mold rises to 650-750℃, the original slab is placed between the upper mold and the lower mold, and the temperature is continued to rise. When the temperature of the superplastic forming mold is 860-890℃, the superplastic forming upper mold and the lower mold are closed, and the tonnage is maintained at 10-20t; reverse bulging air intake is performed to make the original slab fit with the upper mold, the air intake rate is 0.05-0.10MPa / min, the air pressure is increased to 2.0-3.0MPa, the pressure is maintained for 15-20min, and then the pressure is released.

8. The low temperature superplastic forming method of a high performance titanium alloy surface tension tank according to claim 7, characterized in that: The positive bulging forming includes: after the reverse bulging forming is completed and the air pressure is balanced, and the temperature of the superplastic forming mold is maintained at 860-890°C, positive bulging is performed to make the original slab fit with the lower mold, the air intake speed is ≤0.05MPa / min, and the air pressure is increased to 1.5-2.0MPa; after the hemispherical blank formed by the original slab is completely fitted with the lower mold, the pressure is continued to be maintained for 15-20 minutes, and then the pressure is released to balance the air pressure, and the upper mold is raised at the same time.

9. The low temperature superplastic forming method of a high performance titanium alloy surface tension tank according to claim 1, characterized in that: Based on the mass content of each component being 100%, the TC4 titanium alloy ingot includes: Al: 6.55-6.75%, V: 4.20-4.50%, Fe: 0.10-0.30%, O: 0.10-0.20%, C≤0.08; N≤0.05%, H≤0.015, unavoidable impurities≤0.4%; and the balance is Ti.

10. A high performance titanium alloy surface tension tank, characterized in that: A high performance titanium alloy surface tension tank is prepared by a low temperature superplastic forming method according to any one of claims 1 to 9.

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