Preparation method of TC4ELI ultralow-temperature titanium alloy plate for spaceflight

Abstract

The invention discloses a preparation method of a TC4ELI ultralow-temperature titanium alloy plate for spaceflight, and belongs to the technical field of titanium alloy material preparation. The invention discloses a preparation method of a TC4ELI ultralow-temperature titanium alloy plate for spaceflight. The preparation method comprises the following steps: step 1, selecting a finished cast ingot which is smelted for at least three times and has the diameter specification of phi 720-840 * L; 2, the finished cast ingot is subjected to at least three-heating-number forging treatment, and a finished plate blank is manufactured; 3, the finished plate blank is subjected to at least three-heating-number hot rolling treatment, and a semi-finished plate is manufactured; 4, the semi-finished plate is annealed and polished, and a finished plate is manufactured; step 5, carrying out temperature and flaw detection on the finished plate; according to the ultra-low-temperature TC4ELI titanium alloy plate and the preparation method thereof, by controlling multi-heating-number forging and rolling process parameters, the plate has good tissue and performance, the strength and the toughness are improved, work hardening and residual stress are effectively eliminated through reasonable annealing treatment, the room-temperature plasticity and the ultra-low-temperature toughness of the plate are improved, and the preparation technology of the ultra-low-temperature TC4ELI titanium alloy plate for spaceflight is perfected.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy material preparation, and in particular to a method for preparing a TC4ELI ultra-low temperature titanium alloy plate for aerospace use. Background Art

[0002] With the continuous development of aerospace technology, the performance requirements for materials in ultra-low temperature environments are getting higher and higher. Aerospace liquid fuel engines often use liquid oxygen (boiling point -183℃) liquid hydrogen (boiling point -253℃) or liquid oxygen kerosene as propellant fuel. Therefore, titanium alloy materials for aerospace ultra-low temperature service environments (-183℃, -196℃ and -253℃) are important research directions in the field of titanium alloys at home and abroad. TC4ELI titanium alloy is mostly used in the production of liquid rocket engine fuel tanks due to its good low temperature properties, and has broad application prospects in the aerospace field.

[0003] At present, the research and use of ultra-low temperature titanium alloy materials for aerospace use are mainly concentrated on TA7ELI titanium alloy (Ti-5Al-2.5SnELI), and there is still a lack of in-depth research and preparation methods for ultra-low temperature TC4ELI (Ti-6Al-4VELI) titanium alloy plates for aerospace use. Summary of the invention

[0004] The purpose of the present invention is to solve the problem of imperfect preparation technology of ultra-low temperature TC4ELI titanium alloy sheet in the prior art, and to propose a method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a TC4ELI ultra-low temperature titanium alloy sheet for aerospace use comprises the following steps:

[0007] Step 1: Select finished ingots that have been smelted at least three times and have a diameter specification of φ720~840*L;

[0008] Step 2: The finished ingot is subjected to at least three forging processes to form a finished slab;

[0009] Step 3: hot rolling the finished slab for at least three times to produce a semi-finished plate;

[0010] Step 4: Annealing and polishing the semi-finished plate to produce a finished plate;

[0011] Step 5: Conduct temperature and flaw detection tests on the finished plates.

[0012] Preferably, the deformation temperatures formed by the forging process and the hot rolling process satisfy the form of high-high-low+high-low-low.

[0013] Preferably, the three-stage forging process in step 2 includes:

[0014] First fire: open forging, initial forging temperature is 1050-1150℃, holding time is 6-8 hours, final forging temperature is greater than or equal to 850℃, upsetting forging, forging ratio is greater than 5, air cooling after forging;

[0015] Second fire: forging billet forging, initial forging temperature is 1000-1100℃, holding time is 6-8 hours, final forging temperature is greater than or equal to 800℃, upsetting forging, forging ratio is greater than 5, air cooling after forging;

[0016] The third fire: slab forming forging, the temperature is 920-970℃, the holding time is 5-7 hours, the final forging temperature is greater than or equal to 800℃, the forging ratio is greater than 2, and the slab blank is obtained.

[0017] Furthermore, the slab blank is milled, with a single-side milling depth of ≥5 mm, and then surface polished, with a surface roughness of Ra ≤3.2 μm, to obtain a finished slab.

[0018] Preferably, the finished slab in step 2 is subjected to ultrasonic flaw detection, and the flaw detection meets the Class A requirement of GB / T5193.

[0019] Preferably, the three-stage hot rolling treatment in step 3 includes:

[0020] First fire: the slab heating temperature is 1050-1100℃, the holding time is 3.5-4.5 hours, the rolling deformation is 50-65%, the rolling speed is 2-3mm / s, the final rolling temperature is greater than or equal to 850℃, residual temperature straightening and leveling, air cooling after rolling, the surface roughness Ra≤3.2μm, and the first fire intermediate slab semi-finished product is obtained;

[0021] Second fire: the heating temperature of the intermediate billet semi-finished product of the first fire is 920-970℃, the holding time is 1.5-2 hours, the rolling deformation is 60-70%, the rolling speed is 1-2mm / s, the final rolling temperature is greater than or equal to 800℃, the residual temperature is straightened and leveled, the surface is air-cooled after rolling, and the surface roughness Ra≤3.2μm is obtained to obtain the intermediate billet semi-finished product of the second fire;

[0022] The third fire: the heating temperature of the semi-finished product of the intermediate billet of the second fire is 920-970℃, the holding time is 0.5-1 hour, the rolling deformation is 60-70%, the rolling speed is 1-2mm / s, the final rolling temperature is greater than or equal to 800℃, the residual temperature is straightened and leveled, and the semi-finished plate is obtained after air cooling;

[0023] Preferably, the annealing treatment in step 4 is as follows: annealing temperature 700-800°C, holding time 1-2 hours, air cooling after being taken out of the furnace, straightening and leveling.

[0024] Preferably, the surface roughness Ra of the polishing treatment in step 4 is ≤1.6 μm.

[0025] Preferably, the temperature parameters for detecting the temperature of the finished plate in step 5 are: 20°C, -196°C and -253°C.

[0026] Preferably, the finished plate in step 5 is subjected to ultrasonic flaw detection, and the flaw detection meets the AA level requirement of GB / T5193.

[0027] Compared with the prior art, the present invention provides a method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use, which has the following beneficial effects:

[0028] 1. The preparation method of TC4ELI ultra-low temperature titanium alloy sheet for aerospace uses finished ingots with qualified chemical composition and 3 VAR smelting to ensure product quality from raw materials and ensure the stability and controllability of subsequent processing parameters;

[0029] 2. The preparation method of TC4ELI ultra-low temperature titanium alloy sheet for aerospace uses controls the process parameters of multi-fire forging and rolling to obtain good structure and performance of the sheet, and improve strength and toughness;

[0030] 3. The preparation method of TC4ELI ultra-low temperature titanium alloy sheet for aerospace use effectively eliminates work hardening and residual stress through reasonable annealing treatment, and improves the room temperature plasticity and low temperature toughness of the sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a finished product picture of the TC4ELI ultra-low temperature titanium alloy plate proposed by the present invention;

[0032] Figure 2 This is a longitudinal microstructure diagram of the TC4ELI ultra-low temperature titanium alloy plate proposed in the present invention;

[0033] Figure 3 This is a test diagram of the bending performance of the TC4ELI ultra-low temperature titanium alloy sheet proposed in the present invention after annealing at room temperature;

[0034] Figure 4 This is the ultrasonic flaw detection waveform diagram of the TC4ELI ultra-low temperature titanium alloy plate proposed in the present invention. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0036] Embodiment 1:

[0037] Reference Figure 1-Figure 4A method for preparing a TC4ELI ultra-low temperature titanium alloy sheet for aerospace use comprises the following steps:

[0038] Step 1: Selection of TC4ELI ingot composition: TC4ELI titanium alloy ingot produced by high-purity sponge titanium and high-quality master alloy is selected, and its main chemical composition (mass fraction) is: Al: 5.5-6.8%, V: 3.5-4.5%, Fe≤0.30%, C≤0.10%, N≤0.05%, H≤0.015%, O≤0.20%, Ti balance, and product quality is guaranteed by selecting raw materials to ensure the stability and controllability of subsequent processing parameters;

[0039] Step 2: Ingot selection: Select finished ingots that have been melted by vacuum consumable electrode arc for 3 times, have qualified chemical composition, and have specifications of φ720-840×L;

[0040] Step 3: Determine the slab preparation process, and forge the finished ingot for 3 rounds. The process parameters for each round are as follows:

[0041] Step 3.1: The first fire is open forging, the initial forging temperature of the open forging is 1050-1150℃, the holding time is 6-8 hours, the final forging temperature is not less than 850℃, the upsetting forging is performed, the forging ratio is greater than 5, and air cooling is performed after forging;

[0042] Step 3.2: grinding and polishing the surface of the intermediate forging blank after the first fire forging to remove surface cracks, and obtaining the semi-finished product of the first fire forging blank;

[0043] Step 3.3: The second fire is forging the forging blank. The initial forging temperature of the forging blank is 1000-1100℃, the holding time is 6-8 hours, the final forging temperature is not less than 800℃, the forging ratio is greater than 5, and the forging is air-cooled after forging:

[0044] Step 3.4: grinding and polishing the surface of the intermediate forging blank after the second-fire forging blank is forged to remove surface cracks, thereby obtaining a semi-finished product of the second-fire forging blank;

[0045] Step 3.5: The third fire is slab forming forging. The forging temperature of the slab forming is 920-970°C, the holding time is 5-7 hours, the final forging temperature is not less than 800°C, the forging ratio is greater than 2, and the size of the slab blank after forming forging is controlled in the range of 200-220×800-1000×1300-1500mm;

[0046] Step 3.6: Slab machining: the slab blank is machined by a milling machine, with a single-side milling depth of ≥5 mm, to remove the slab oxide layer and contamination layer, and then the surface is polished, and the surface roughness of the slab is Ra≤3.2 μm, to obtain a forged slab that can be used for rolling;

[0047] Step 3.7: Slab flaw detection: ultrasonic flaw detection is performed on the forged slab after machining to ensure that the slab meets the A level of GB / T 5193. This is the intermediate product flaw detection link and is a quality control measure before the production process is transferred. Qualified products are finished slabs;

[0048] Step 4: Plate hot rolling process, the finished slab is hot rolled for 3 times, and the process parameters for each time are as follows:

[0049] Step 4.1: The heating temperature of the slab in the first fire is 1050-1100℃, the holding time is 3.5-4.5 hours, the rolling deformation is 50-65%, the rolling passes are 8-11, the deformation is 6-15%, the rolling speed is 2-3mm / s, the final rolling temperature is not less than 850℃, the residual temperature is straightened and leveled, and air cooling is performed after rolling;

[0050] Step 4.2: grinding and polishing the surface of the intermediate billet after the first rolling to remove surface cracks and oxide scale, with a surface roughness of Ra≤3.2μm, to obtain a semi-finished intermediate billet after the first rolling;

[0051] Step 4.3: The second rolling operation is to heat the semi-finished product of the first intermediate billet to 920-970°C, keep it at this temperature for 1.5-2 hours, the rolling deformation is 60-70%, the rolling passes are 8-11, the deformation is 6-14%, the rolling speed is 1-2mm / s, the final rolling temperature is not less than 800°C, the residual temperature is straightened and leveled, and the product is air-cooled after rolling.

[0052] Step 4.4: cutting the intermediate billet after the second rolling;

[0053] Step 4.5: The surface of the intermediate billet after cutting is ground and polished to remove surface cracks and oxide scale, and the surface roughness Ra≤3.2μm to obtain the semi-finished product of the intermediate billet of the second rolling process.

[0054] Step 4.6: The third rolling is to heat the semi-finished product of the second intermediate billet to 920-970°C, keep it at this temperature for 0.5-1 hour, and roll it to a deformation of 60-70%, 8-11 passes, 6-14% pass deformation, 1-2 mm / s rolling speed, a final rolling temperature of not less than 800°C, straighten and level it with residual temperature, and air cool it after rolling to obtain a semi-finished plate with oxide scale;

[0055] Step 5: The annealing process is to anneal the above-mentioned semi-finished plate with oxide scale at a temperature of 700-800°C, keep it at a temperature of 1-2 hours, straighten and level it after it is taken out of the furnace, and cool it in air;

[0056] Step 6: Grind and polish the annealed plate, the surface roughness of the product plate Ra≤1.6μm, and obtain a 2x smooth plate;

[0057] Step 7: The multiple-size plate after grinding is cut into finished plates of specified sizes by cold working method, and the finished plates of TC4ELI ultra-low temperature titanium alloy for aerospace use with specifications of 10×1100×2200mm are obtained;

[0058] Step 8: Performance testing: The finished plate with a specification of 10×1100×2200mm is tested for performance, including room temperature performance at 20°C, -196°C and -253°C;

[0059] Step 9: NDT inspection: Perform ultrasonic NDT inspection on the finished plate with the specification of 10×1100×2200mm to ensure that the finished plate NDT meets the AA level of GB / T5193.

[0060] In the present invention, the TC4ELI aerospace ultra-low temperature titanium alloy sheet obtained by the above preparation technology has a room temperature tensile strength of not less than 895MPa, an elongation of not less than 10%, and an impact toughness of not less than 45J / cm 2 , bending is not less than 70°; in ultra-low temperature environments of -196℃ and -253℃, its tensile strength is not less than 1324MPa, its elongation is not less than 8%, and its impact toughness is not less than 30J / cm 2 It has the advantages of stable process, high quality of finished products and good batch stability. It can meet the use requirements of the aerospace field in ultra-low temperature environments, improve the preparation technology of ultra-low temperature TC4ELI titanium alloy plates for aerospace, and provide reliable material guarantees for the development of the aerospace industry.

[0061] Embodiment 2:

[0062] Based on Example 1, one of the parameter values ​​is selected, and a specific finished product and test results are made. The steps are as follows:

[0063] Step 1: Selection of TC4ELI ingot composition: A TC4ELI titanium alloy ingot produced from high-purity sponge titanium and high-quality master alloy is selected, and its main chemical composition (mass fraction) is: Ti balance, Al: 6.0%, V: 4.0%, Fe: 0.10%, C: 0.08%, N: 0.04%, H: 0.002%, O: 0.10% TC4ELI titanium alloy ingot;

[0064] Step 2: The selected TC4ELI ingot is melted three times in a vacuum consumable arc furnace to prepare an ingot with a specification of φ760×L. The ingot blank is then machined, peeled, inspected, and sawed to produce a finished ingot;

[0065] Step 3: Slab preparation process: The ingot is subjected to multi-fire and multi-pass forging. The process parameters for each fire are as follows:

[0066] Step 3.1: First fire: Open forging: The initial forging temperature of the open forging is 1150℃, the holding time is 7 hours, the final forging temperature is not less than 850℃, the forging ratio is greater than 5, and the forging is air-cooled after forging;

[0067] Step 3.2: grinding and polishing the surface of the intermediate forging blank after the first fire forging to remove surface cracks, and obtaining the semi-finished product of the first fire forging blank;

[0068] Step 3.3: Second fire: Forging billet forging: The initial forging temperature of forging billet forging is 1050℃, the holding time is 6-7 hours, the final forging temperature is not less than 800℃, upsetting forging, the forging ratio is greater than 5, and air cooling is performed after forging;

[0069] Step 3.4: grinding and polishing the surface of the intermediate forging blank after the second-fire forging blank is forged to remove surface cracks, thereby obtaining a semi-finished product of the second-fire forging blank;

[0070] Step 3.5: The third fire: slab forming forging: the forging temperature of the slab forming is 940°C, the holding time is 5 hours, the final forging temperature is not less than 800°C, the forging ratio is greater than 2, the size of the slab blank after forming forging is controlled at 220×890×1420mm, and air cooling is performed after forging;

[0071] Step 3.6: Slab machining: The slab blank is machined by a milling machine, and the single-side milling depth is greater than or equal to 5 mm to remove the slab oxide layer and contamination layer. After surface polishing, the slab surface roughness Ra ≤ 3.2 μm, and a 210×880×1400 mm forged slab for rolling is obtained;

[0072] Step 3.7: Slab flaw detection: Perform ultrasonic flaw detection on the slab after machining to ensure that the slab meets the A level of GB / T5193. This is the intermediate product flaw detection link and is a quality control measure before the production process is transferred. Qualified products are finished slabs;

[0073] Step 4: Plate hot rolling process: The finished slab is hot rolled for 3 times, and the process parameters for each time are as follows:

[0074] Step 4.1: First fire: the slab heating temperature is 1080℃, the holding time is 4 hours, the total rolling deformation of this fire is 59%, the plate specification after one fire rolling is 86×880×3410mm, the rolling passes are 8, the deformation of each pass is 6.2%, 6.6%, 10.9%, 12.2%, 13.9%, 12.9%, 12.0%, 9.5%, the rolling speed is 2-3mm / s, the final rolling temperature is not less than 850℃, and air cooling is performed after rolling;

[0075] Step 4.2: grinding and polishing the surface of the intermediate billet after the first rolling to remove the surface oxide scale, with the surface roughness Ra≤3.2μm, to obtain the semi-finished intermediate billet after the first rolling;

[0076] Step 4.3: Second fire: The heating temperature of the intermediate billet semi-finished product of the first fire is 930℃, the holding time is 1.5 hours, the total deformation of this fire is 65%, the plate specification after the second fire is 30×880×9770mm, the rolling passes are 10, and the deformation of each pass is 5.8%, 7.4%, 10.7%, 13.4%, 13.8%, 12.0%, 11.4%, 10.3%, 8.6%, 6.3%, the rolling speed is 1-2mm / s, the final rolling temperature is not less than 800℃, residual temperature straightening and leveling, and air cooling after rolling;

[0077] Step 4.4: Cut the intermediate billet after the second rolling process to a size of 30×880×2300mm;

[0078] Step 4.5: grinding and polishing the surface of the intermediate billet after cutting to remove the surface oxide scale, with the surface roughness Ra≤3.2μm, to obtain the semi-finished intermediate billet of the second rolling process;

[0079] Step 4.6: the third fire: the heating temperature of the intermediate billet semi-finished product of the second fire is 930℃, the holding time is 0.6 hours, the total deformation of this fire rolling is 65%, the third fire is reverse rolling, the plate specification after rolling is 10.5×2300×2510mm, the rolling passes are 10 passes, the deformation of each pass is 5.3%, 7.0%, 11.4%, 13.7%, 13.9%, 12.1%, 11.8%, 11.1%, 7.5%, 5.4%, the rolling speed is 1-2mm / s, the final rolling temperature is not less than 800℃, the residual temperature is straightened and leveled, and the semi-finished plate with oxide scale is obtained after air cooling;

[0080] Step 5: Sheet annealing process: The annealing temperature of the semi-finished sheet with oxide scale is 750℃, the holding time is 1 hour, the sheet is straightened and leveled after being taken out of the furnace, and the cooling method is air cooling;

[0081] Step 6: Plate surface grinding and polishing: Grind and polish the annealed plate, with a single-side grinding and polishing depth of 0.25mm. The surface roughness of the finished plate is Ra≤1.6μm, and a 2x smooth plate is obtained;

[0082] Step 7: The multiple-size plate after grinding is cut into finished plates of specified sizes by cold working method, and the finished plates of TC4ELI ultra-low temperature titanium alloy for aerospace use with specifications of 10×1100×2200mm are obtained;

[0083] Step 8: Plate performance testing: The finished plate with a specification of 10×1100×2200mm is subjected to performance testing, including room temperature performance testing at 20°C and ultra-low temperature performance testing at -196°C and -253°C;

[0084] The following table shows the room temperature (20°C) mechanical properties of TC4ELI ultra-low temperature titanium alloy sheet after annealing and the ultra-low temperature mechanical properties data of -196°C and -253°C:

[0085]

[0086] Step 9: Plate flaw detection: Perform ultrasonic flaw detection on the finished plate to ensure that the finished plate flaw detection meets the AA level of GB / T5193.

[0087] In the present invention, by controlling the multi-fire forging and rolling process parameters, the plate obtains good structure and performance, improves the strength and toughness, and reasonable annealing treatment effectively eliminates the work hardening and residual stress, improves the room temperature plasticity and low temperature toughness of the plate, so that the TC4ELI aerospace ultra-low temperature titanium alloy plate has excellent comprehensive performance, can meet the complex working conditions requirements in the aerospace field under ultra-low temperature environment, and provides a reliable material guarantee for the development of the aerospace industry.

[0088] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use, characterized in that: The steps include: Step 1: Select finished ingots that have been smelted at least three times and have a diameter specification of φ720~840*L; Step 2: The finished ingot is subjected to at least three forging processes to form a finished slab; Step 3: hot rolling the finished slab for at least three times to produce a semi-finished plate; Step 4: Annealing and polishing the semi-finished plate to produce a finished plate; Step 5: Conduct temperature and flaw detection tests on the finished plates.

2. The method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use according to claim 1, characterized in that: The deformation temperatures formed by forging and hot rolling satisfy the form of high-high-low + high-low-low.

3. The method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use according to claim 1, characterized in that: The three-fire forging process in step 2 includes: First fire: open forging, initial forging temperature is 1050-1150℃, holding time is 6-8 hours, final forging temperature is greater than or equal to 850℃, upsetting forging, forging ratio is greater than 5, air cooling after forging; Second fire: forging billet forging, initial forging temperature is 1000-1100℃, holding time is 6-8 hours, final forging temperature is greater than or equal to 800℃, upsetting forging, forging ratio is greater than 5, air cooling after forging; The third fire: slab forming forging, the temperature is 920-970℃, the holding time is 5-7 hours, the final forging temperature is greater than or equal to 800℃, the forging ratio is greater than 2, and the slab blank is obtained.

4. The method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use according to claim 3, characterized in that: The slab blank is milled, with a single-side milling depth of ≥5 mm, and then the surface is polished, with the surface roughness of the slab Ra ≤3.2 μm, to obtain a finished slab.

5. The method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use according to claim 1 or 4, characterized in that: The finished slab in step 2 is subjected to ultrasonic flaw detection, and the flaw detection meets the A-level requirements of GB / T5193.

6. The method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use according to claim 1, characterized in that: The three-stage hot rolling process in step 3 includes: First fire: the slab heating temperature is 1050-1100℃, the holding time is 3.5-4.5 hours, the rolling deformation is 50-65%, the rolling speed is 2-3mm / s, the final rolling temperature is greater than or equal to 850℃, residual temperature straightening and leveling, air cooling after rolling, the surface roughness Ra≤3.2μm, and the first fire intermediate slab semi-finished product is obtained; Second fire: the heating temperature of the intermediate billet semi-finished product of the first fire is 920-970℃, the holding time is 1.5-2 hours, the rolling deformation is 60-70%, the rolling speed is 1-2mm / s, the final rolling temperature is greater than or equal to 800℃, the residual temperature is straightened and leveled, the surface is air-cooled after rolling, and the surface roughness Ra≤3.2μm is obtained to obtain the intermediate billet semi-finished product of the second fire; The third fire: the heating temperature of the semi-finished product of the intermediate billet of the second fire is 920-970℃, the holding time is 0.5-1 hour, the rolling deformation is 60-70%, the rolling speed is 1-2mm / s, the final rolling temperature is greater than or equal to 800℃, the residual temperature is straightened and leveled, and the semi-finished plate is air-cooled after rolling to obtain the semi-finished plate.

7. The method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use according to claim 1, characterized in that: The annealing treatment in step 4 is as follows: annealing temperature 700-800°C, holding time 1-2 hours, air cooling after being taken out of the furnace, straightening and leveling.

8. The method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use according to claim 1, characterized in that: The surface roughness Ra of the polished surface in step 4 is ≤1.6 μm.

9. The method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use according to claim 1, characterized in that: The temperature parameters for the finished plate temperature detection in step 5 are: 20°C, -196°C and -253°C.

10. The method for preparing TC4ELI ultra-low temperature titanium alloy sheet for aerospace use according to claim 1, characterized in that: The finished plate in step 5 is subjected to ultrasonic flaw detection, and the flaw detection meets the AA grade requirement of GB / T5193.

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