Preparation method of low-cost high-performance TC6 titanium alloy large-size forged plate

Abstract

This invention discloses a low-cost, high-performance method for preparing large-size forged plates of TC6 titanium alloy, comprising the following steps: S1, initial forging: TC6 titanium alloy large-size ingots are subjected to 1-3 upsetting and drawing forging passes to obtain a primary intermediate billet; S2, intermediate forging: the primary intermediate billet is subjected to 4-7 forging passes, wherein some passes are heated to 30°C-150°C above the phase transformation point and held at that temperature, while the remaining passes are heated to 20°C-60°C below the phase transformation point and held at that temperature. After all forging passes are completed, the billet is cooled to obtain a secondary intermediate billet; S3, quasi-β forging: the secondary intermediate billet is forged once to obtain an intermediate forged billet; S4, two-phase forging: the intermediate forged billet is forged 1-2 times to obtain a forged plate; S5, overall heat treatment and machining. This invention has a short preparation process, low processing cost, and can simultaneously achieve the collective preparation of multiple forgings, reducing the preparation cycle, improving production efficiency, and is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal processing and relates to a method for preparing large-size forged plates of TC6 titanium alloy with low cost and high performance. Background Technology

[0002] The nominal composition of TC6 titanium alloy is Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si. Forgings made from it possess high strength, good plasticity and toughness, and excellent corrosion resistance. This effectively reduces the overall weight of aircraft, improves their range, and extends their service life, leading to its rapid increase in use in high-performance aerospace key structural components. New and pre-research models extensively utilize this high-strength, high-toughness, lightweight TC6 titanium alloy.

[0003] The traditional production process for TC6 titanium alloy free forgings still follows the methods used in the 1960s and 70s. Titanium material companies produce forging billets and plates, which are then delivered to forging plants. Forging plants produce free forgings, which are then delivered to the main equipment manufacturer (OEM). The OEM then machines these free forgings into the final titanium alloy forgings used in the aerospace industry. This production method suffers from long preparation cycles, complex processes, and significant losses due to repeated testing, and can no longer meet the new requirements of the aerospace field for short processes, low costs, and high performance. Summary of the Invention

[0004] The purpose of this invention is to provide a low-cost, high-performance method for preparing large-size TC6 titanium alloy forgings. The method has a short preparation process, low processing cost, and can simultaneously prepare multiple forgings together, reducing the preparation cycle, improving production efficiency, and is suitable for industrial production.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing large-size forged plates of TC6 titanium alloy with low cost and high performance includes the following steps:

[0007] S1, forging in rough blank:

[0008] Large-sized TC6 titanium alloy ingots are subjected to 1 to 3 upsetting and drawing forging processes. The first upsetting process is a high-temperature homogenization treatment. Each upsetting process involves heating to 60°C to 200°C above the phase transformation point and holding at that temperature before forging. After all upsetting processes are completed, the ingots are cooled to obtain a first-grade intermediate billet.

[0009] S2, intermediate forging:

[0010] The primary intermediate billet is forged in 4 to 7 heats, some of which are heated to 30°C to 150°C above the phase transformation point and held at that temperature, while the remaining heats are heated to 20°C to 60°C below the phase transformation point and held at that temperature. After all heats are completed, the billet is cooled to obtain the secondary intermediate billet.

[0011] S3, Quasi-β Forging:

[0012] The secondary intermediate billet is heated to 10℃~40℃ above the phase transformation point and held at that temperature, then forged in one pass. After forging, it is cooled to obtain the intermediate forging billet.

[0013] S4, Two-phase region forging:

[0014] The intermediate forging billet is forged 1 to 2 times, each time heated to 20°C to 70°C below the phase transformation point and held at that temperature. After all forging is completed, it is cooled to obtain the forged plate.

[0015] S5, overall heat treatment and machining:

[0016] The forged plate is heat-treated and machined to obtain the finished forged plate.

[0017] Preferably, in step S1, the high-temperature homogenization holding time is 45h to 70h.

[0018] Preferably, in S1, the cumulative forging ratio per forging pass is controlled between 2.2 and 6.8, and the cumulative deformation is between 40% and 70%. The forging method of the first forging pass is upsetting, drawing, rounding, and inverting octagon. The forging methods of the second and third forging passes are upsetting, drawing, and inverting octagon. Some passes may use reverse upsetting and drawing. The upsetting rate of each pass is 15mm / s to 30mm / s, the drawing rate is 60mm / s to 80mm / s, and the drawing feed is 200mm to 300mm. Each forging pass completes 2 to 3 upsetting and drawing passes, and finally obtains a β structure with a grain size of 10mm to 20mm.

[0019] Preferably, in step S2, 2-4 passes of upsetting and drawing forging are performed first. Each pass involves upsetting, drawing into a square, drawing into a flat square, and drawing into an inverted octagon. A low-to-high forging process is adopted. Specifically, in the first 1-2 passes, the temperature is heated to 20°C-60°C below the phase transformation point, and the holding time is 5-9 hours. In the second 1-2 passes, the temperature is heated to 30°C-150°C above the phase transformation point, and the holding time is 4-8 hours. The upsetting forging ratio is controlled between 1.4 and 4.8 per pass, and the deformation during drawing is controlled between 40% and 6%. The forging rate is 15mm / s to 30mm / s, the drawing rate is 60mm / s to 80mm / s, and the drawing feed is 200mm to 300mm. Then, 2 to 3 forging passes are performed. Each forging pass is forging and flat drawing. The forging ratio per pass is controlled between 1.2 and 2.8. The deformation during drawing is controlled between 25% and 50%. The drawing rate is 60mm / s to 80mm / s, and the drawing feed is 200mm to 300mm.

[0020] Preferably, in step S3, the temperature is heated to 10°C to 40°C above the phase transformation point, and the holding time is 2h to 3.5h. Then, a single-pass drawing forging is performed, with a drawing deformation of 20% to 45%, to obtain a uniform and fine β structure with a grain size of 1mm to 2mm.

[0021] Preferably, in S3, the initial forging temperature of each quasi-β forging is 50°C to 200°C below the phase transformation point, and the final forging temperature is 150°C to 250°C below the phase transformation point.

[0022] Preferably, in step S4, the forging method is direct drawing, with each heating cycle reaching 20°C to 70°C below the phase transformation point, and the holding time is 3 to 6 hours, with the elongation deformation controlled between 5% and 15%.

[0023] Preferably, in S4, the initial forging temperature of each two-phase forging is 100℃~200℃ below the phase transformation point, and the final forging temperature is 150℃~300℃ below the phase transformation point.

[0024] Preferably, in step S5, the forging billet is first heated to 870℃~920℃, held for 1h~2h and then air-cooled, then heated to 550℃~600℃, held for 2h~5h and then air-cooled to obtain a heat-treated forging billet, which is then machined into a finished forging plate in the final delivery state.

[0025] The beneficial effects of this invention are as follows: This invention can produce forged plates with a single weight between 100kg and 3000kg, and the microstructure and properties of different locations on the forged plates meet aerospace standards, consistent with the level of small-sized forged plates. High-temperature homogenization is employed during the initial forging process, fully utilizing the thermal diffusion capacity of atoms under high-temperature conditions, thus improving the composition and microstructure uniformity of the ingot and forged billet. A high-low-high forging process is used during both the initial and intermediate forging processes to achieve refined and consistent microstructure in large-sized forged plates, ensuring that the microstructure and properties at different locations are consistent with those of small-sized forgings. During forging, large deformation, reverse upsetting, flattened drawing, and straight drawing are combined to ensure sufficient refinement of the core microstructure of the billet, improving the deformation uniformity at all locations. The required alloy microstructure is obtained through the shortest deformation process, guaranteeing material quality under low-cost, short-process conditions. In the quasi-β forging process, stepped heating is employed to shorten the holding time above the phase transformation point and ensure thorough heating. The holding temperature above the phase transformation point is carefully selected to avoid excessively high holding temperatures or long holding times that could lead to grain growth, thus achieving uniform and refined alloy grains. During two-phase forging, precise control of heating temperature, deformation amount, and deformation method ultimately controls the microstructure and properties of the forged plate. Large-size TC6 alloy forged plates prepared using this method have a short preparation process, low processing cost, and can simultaneously produce multiple forgings collectively, reducing the preparation cycle and improving production efficiency, making them suitable for industrial production. Attached Figure Description

[0026] Figure 1 The low-magnification microstructure of the bar material is shown in Example 1.

[0027] Figure 2 The microstructure of the bar in the heat-treated state is shown in Example 1.

[0028] Figure 3 This is the low-magnification microstructure of the bar material in Example 2.

[0029] Figure 4 The microstructure of the bar in the heat-treated state is shown in Example 2.

[0030] Figure 5 This is a flowchart of the method of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0032] like Figures 1-5 As shown, a method for preparing large-size forged plates of TC6 titanium alloy with low cost and high performance is presented. The forged plates weigh 100kg to 3000kg and have dimensions of 80mm to 250mm (thickness) × 100mm to 1000mm (width) × 300mm to 3000mm (length). The forging preparation cycle is short, the process control is simple, the process stability is high, the production cost is low, the yield is high, and the microstructure and properties meet the requirements of aerospace material standards, making it suitable for industrial production.

[0033] A method for preparing large-size forged plates of TC6 titanium alloy with low cost and high performance, using titanium alloy ingots prepared by Western Superconducting Technologies Co., Ltd. as raw material, and the processing is divided into five parts: billet forging → intermediate forging → quasi-β forging → two-phase region forging → overall heat treatment and machining, specifically including the following steps:

[0034] S1, forging in rough blank:

[0035] Large-sized TC6 titanium alloy ingots are subjected to 1 to 3 upsetting and drawing forging processes (the first process is a high-temperature homogenization treatment). Each process involves heating the ingot to 60°C to 200°C above the phase transformation point and holding it at that temperature before forging. After all processes are completed, the ingots are cooled to obtain a first-grade intermediate billet.

[0036] Large-sized TC6 titanium alloy ingots are subjected to 1-3 passes of upsetting and drawing forging. The first pass is a high-temperature homogenization treatment. The high-temperature homogenization holding time is 45-70 hours, which can eliminate elemental segregation. During the ingot blanking process, the forging deformation breaks down coarse columnar crystals to obtain a uniform and controllable recrystallized structure. The cumulative forging ratio per pass is controlled between 2.2 and 6.8, and the cumulative deformation is between 40% and 70%. The forging method of the first pass is upsetting, drawing, rounding, and octagonalization. The forging methods of the second and third passes are upsetting, drawing, and octagonalization. Some passes may use reverse upsetting and drawing. The upsetting rate of each pass is 15-30 mm / s, the drawing rate is 60-80 mm / s, and the drawing feed is 200-300 mm. Each forging process involves 2 to 3 upsetting and drawing operations, ultimately yielding a β microstructure with a grain size of 10 mm to 20 mm.

[0037] Large deformation upsetting can refine the original coarse cast grains. Reversed upsetting, rounding, and octagonal operations improve the core penetration and deformation uniformity at all locations. The forging process can employ a reheating method to prevent broken grains from growing larger due to excessive heating time.

[0038] After all firing cycles are completed and cooled, a first-stage intermediate billet is obtained.

[0039] S2, intermediate forging:

[0040] The primary intermediate billet is forged in 4 to 7 heats. Some of the heats are heated to 30°C to 150°C above the phase transformation point and held at that temperature, while the remaining heats are heated to 20°C to 60°C below the phase transformation point and held at that temperature. After all the heats are completed, the billet is cooled to obtain the secondary billet.

[0041] For intermediate forging of S2, to obtain alloy billets with a uniform microstructure, the billets after initial forging undergo 2-4 passes of upsetting and drawing forging within two temperature ranges: 20℃-60℃ below the phase transformation point and 30℃-150℃ above the phase transformation point. Each pass involves upsetting, drawing into a square, drawing into a flat square, and drawing into an inverted octagon, employing a low-high forging process. In the first two passes, the temperature is raised to 20℃-60℃ below the phase transformation point, with a holding time of 5-9 hours. In the second pass, the temperature is raised to 30℃-150℃ above the phase transformation point, with a holding time of 4-8 hours. The upsetting ratio per pass is controlled between 1.4 and 4.8. The deformation during drawing is controlled between 40% and 60%, the upsetting rate is 15mm / s-30mm / s, the drawing rate is 60mm / s-80mm / s, and the drawing feed is 200mm-300mm.

[0042] Each forging process involves upsetting, square drawing, flattening, and inverting octagonal shapes to ensure uniform deformation of all parts of the billet.

[0043] The billet that has undergone the above forging is heated at 20℃ to 60℃ below the phase transformation point and held for 4h to 8h. Then, it is forged 2 to 3 times. Each forging is upsetting and flat drawing. The forging ratio per forging is controlled between 1.2 and 2.8. The deformation during drawing is controlled between 25% and 50%. The drawing rate is 60mm / s to 80mm / s and the drawing feed is 200mm to 300mm.

[0044] After forging, air cooling is used to obtain secondary billets.

[0045] S3, Quasi-β Forging:

[0046] The intermediate billet is heated to 10°C to 40°C above the phase transformation point and held at that temperature. It is then forged in one pass and cooled after forging to obtain the intermediate forging billet.

[0047] For the S3 quasi-β forging, the secondary intermediate billet that has completed intermediate forging is heated in a stepped manner to 10℃~40℃ above the phase transformation point, and held for 2h to 3.5h before undergoing a single-pass drawing forging. The straight drawing deformation is 20%~45%, resulting in a uniform and fine β structure with a grain size of 1mm~2mm. The initial forging temperature of each quasi-β forging pass is 50℃~200℃ below the phase transformation point, and the final forging temperature is 150℃~250℃ below the phase transformation point.

[0048] By adopting stepped heating, the holding time of the alloy above the phase transformation point can be shortened and the alloy can be fully heated. By rationally selecting the holding temperature above the phase transformation point, grain growth caused by excessively high holding temperature or long holding time can be avoided, thus achieving uniform and refined alloy grains.

[0049] S4, Two-phase region forging:

[0050] The intermediate forging billet is forged 1 to 2 times, each time heated to 20°C to 70°C below the phase transformation point and held at that temperature. After all forging is completed, it is cooled to obtain the forged plate.

[0051] S4 two-phase zone forging involves taking the intermediate forging billet after quasi-β forging and performing 1-2 forging passes using a direct drawing method. Each pass is heated to 20°C-70°C below the phase transformation point, with a holding time of 3-6 hours. Reheating in the furnace is permitted as needed, and the elongation deformation is controlled between 5% and 15%. This direct drawing forging method, combined with a smaller forging ratio and appropriate reheating in the furnace, not only ensures uniform metal flow and deformation in all directions during forging but also simplifies process control. The initial forging temperature for each two-phase zone forging pass is 100°C-200°C below the phase transformation point, and the final forging temperature is 150°C-300°C below the phase transformation point.

[0052] S5, overall heat treatment and machining:

[0053] The forged plate is heat-treated and machined to obtain the finished forged plate.

[0054] The overall heat treatment and machining of S5 involves first heating the forging billet to 870℃~920℃, holding it at that temperature for 1h~2h, and then air cooling it. Then, it is heated to 550℃~600℃, held at that temperature for 2h~5h, and then air cooled to obtain the heat-treated forging billet. Finally, it is machined into the finished forging plate in the final delivery state.

[0055] The present invention will be further described in detail below with reference to specific embodiments. Specific Implementation Example 1:

[0057] 1. Forging of blanks:

[0058] TC6 titanium alloy ingots with the required chemical composition and a phase transformation point of 980℃ were selected. The initial forging was completed in two stages. A stepped heating process was used to raise the temperature to 1170℃, followed by a 55-hour holding period for high-temperature homogenization. After removal from the furnace, upsetting and drawing forging were performed, with a cumulative deformation of approximately 65% ​​and an upsetting-drawing ratio controlled at 6.2. Subsequently, after holding at 1080℃ for approximately 1 hour, upsetting and drawing forging were performed again, with a single-pass deformation of approximately 30% and a cumulative deformation of approximately 60%, maintaining an upsetting-drawing ratio of 3.4. After forging, the ingots were air-cooled. During upsetting, slow, multi-hammer upsetting was used at a rate of 15 mm / s. The first drawing in each stage was radial, and the second was axial. The feed rate for axial drawing was 300 mm, and the drawing rate was 60 mm / s.

[0059] 2. Intermediate forging:

[0060] The intermediate forging process is completed in six passes. First, four passes of upsetting and drawing are performed using a low-high forging process. The first pass is heated to 950℃ and held for 8.5 hours before upsetting and drawing; the second pass is heated to 1040℃ and held for 6.5 hours before upsetting and drawing; the third pass is heated to 950℃ and held for 8 hours before upsetting and drawing; and the fourth pass is heated to 1040℃ and held for 5.5 hours before upsetting and drawing. The upsetting ratio for each pass is controlled at 1.6, and the deformation during drawing is controlled at 40%. Slow-speed hammer upsetting is used at a rate of 25 mm / s during upsetting. Octagonal and flat-square drawing methods are used for drawing, with a feed rate of 250 mm and a drawing rate of 75 mm / s, ensuring uniform deformation of the billet. Each pass is followed by air cooling.

[0061] The billet that has undergone the above forging is heated to 940℃ and held for 5 hours, and then subjected to two forging cycles. The forging ratio is controlled at 1.8, and the deformation during drawing is controlled at 35%. The forging methods are upsetting and flat square drawing. The drawing feed is 250mm, and the drawing rate is 75mm / s. After forging, the billet is air-cooled.

[0062] 3. Quasi-β forging:

[0063] The forging of the billet is completed in one heat. It is heated to 1020℃ in a stepped manner and held for 3 hours. Then it is forged to a thickness of 180mm by straight drawing with a straight drawing deformation of 30%. A uniform and fine β structure with a grain size of 1.5mm is obtained. The initial forging temperature of the quasi-β forging is 850℃ and the final forging temperature is 750℃.

[0064] 4. Two-phase region forging:

[0065] The forging of the billet is completed in one heat, with a heating temperature of 950℃ and a holding time of 3 hours. It is then forged to a thickness of 170mm by straight drawing, with a straight drawing deformation of 9%. The initial forging temperature during two-phase forging is 800℃, and the final forging temperature is 700℃.

[0066] 5. Overall heat treatment:

[0067] The forging billet is heated to 900℃ and held for 2 hours, then air-cooled, and then held at 600℃ for 5 hours and air-cooled again to obtain the heat-treated forging billet. It is then machined into the final delivered finished forging plate with a size of 160mm×720mm×2000mm.

[0068] The low-magnification microstructure of the 160mm×720mm×2000mm TC6 titanium alloy forged plate prepared in Example 1 of the Invention is detailed below. Figure 1 The microstructure of the 160mm×720mm×2000mm TC6 titanium alloy forged plate prepared in Example 1 of the Invention is detailed in [the following text is missing]. Figure 2 The room temperature properties of the slab after solution treatment and aging are shown in Table 1, indicating a good balance between strength and toughness.

[0069] Table 1. Room temperature properties of TC6 titanium alloy 160mm×720mm×2000mm forged plate in double annealed state.

[0070]

[0071] The TC6 titanium alloy 160mm×720mm×2000mm forged plate prepared in Example 1 has a room temperature tensile strength Rm≥980MPa in the L, LT, and ST directions, a yield strength Rp0.2≥900MPa, an elongation A≥12%, a reduction of area Z≥25%, and a fracture toughness K. IC ≥80MPa·m 1 / 2 .

[0072] Ultrasonic testing was performed on the TC6 titanium alloy 160mm×720mm×2000mm forged plate prepared in Example 1. The results were uniform and consistent, all meeting the requirement of Φ1.2-9dB or higher. Specific Implementation Example 2:

[0074] 1. Forging of blanks:

[0075] TC6 titanium alloy ingots with the required chemical composition and a phase transformation point of 980℃ were selected. The initial forging was completed in three passes. A stepped heating process was used to raise the temperature to 1170℃, holding for 55 hours for high-temperature homogenization. After exiting the furnace, upsetting and drawing forging were performed, with a cumulative deformation of approximately 55% and an upsetting-drawing ratio controlled at 6.8. The ingots were then returned to the furnace and held at 1080℃ for approximately 1 hour before upsetting and drawing forging again. After forging, the ingots were air-cooled, then heated to 1050℃ and held for 4 hours. The single-pass deformation in these passes was approximately 45%, with a cumulative deformation of approximately 65% ​​and an upsetting-drawing ratio controlled at 5.2. After forging, the ingots were air-cooled. During upsetting, slow, multi-hammer upsetting was used at a rate of 25 mm / s. The first drawing in each pass was radial, and the second drawing was axial. The feed rate for axial drawing was 200 mm, and the drawing rate was 80 mm / s.

[0076] 2. Intermediate forging:

[0077] The intermediate forging process is completed in five stages. First, three stages of upsetting and drawing are performed using a low-high forging process. The first stage involves heating to 920℃ and holding for 6.5 hours before upsetting and drawing; the second stage involves heating to 920℃ and holding for 6 hours before upsetting and drawing; the third stage involves heating to 1050℃ and holding for 5 hours before upsetting and drawing. The upsetting-to-roughing ratio is controlled at 3.8, and the deformation during drawing is controlled at 55%. Slow-speed hammer upsetting is used at a rate of 15mm / s during roughing. Eight-sided and flat-sided drawing methods are used for drawing, with a feed rate of 200mm and a drawing rate of 60mm / s, ensuring uniform deformation of all parts of the billet. Each stage of forging is followed by air cooling.

[0078] The billet that has undergone the above forging is heated to 920℃ and held for 4 hours, and then subjected to two forging cycles. The forging ratio is controlled at 2.2, and the deformation during drawing is controlled at 40%. The forging methods are upsetting and flat square drawing. The drawing feed is 200mm and the drawing rate is 60mm / s. After forging, the billet is air-cooled.

[0079] 3. Quasi-β forging:

[0080] The forging of the billet is completed in one heat. It is heated to 990℃ in a stepped manner and held for 3.5 hours. Then it is forged to a thickness of 285mm. The direct drawing deformation is 42%, and a uniform and fine β structure with a grain size of 1.1mm is obtained. The initial forging temperature during quasi-β forging is 800℃ and the final forging temperature is 700℃.

[0081] 4. Two-phase region forging:

[0082] The forging of the billet is completed in two forging cycles. First, it is heated to 940℃ and held for 4 hours. Then, it is forged straight to a thickness of 265mm with a straight forging deformation of 7%. After holding at 940℃ for about 60 minutes, it is forged straight to a thickness of 260mm with a straight forging deformation of 4%. The initial forging temperature in the two-phase zone is 780℃, and the final forging temperature is 680℃.

[0083] 5. Overall heat treatment:

[0084] The forging billet is heated to 870℃ and held for 2 hours, then air-cooled, and then held at 550℃ for 4 hours and air-cooled again to obtain the heat-treated forging billet. It is then machined into the final delivered finished forging plate with a size of 250mm×600mm×1000mm.

[0085] The low-magnification microstructure of the TC6 titanium alloy 250mm×600mm×1000mm forged plate prepared in Example 2 of the Invention is detailed in [reference needed]. Figure 3 The microstructure of the TC6 titanium alloy 250mm×600mm×1000mm forged plate prepared in Example 1 of the invention is detailed in [the following text is missing]. Figure 4 The room temperature properties of the slab after solution treatment and aging are shown in Table 2, indicating a good balance between strength and toughness.

[0086] Table 2. Room temperature properties of TC6 titanium alloy 250mm×600mm×1000mm forged plates in double annealed state.

[0087]

[0088] The TC6 titanium alloy 250mm×600mm×1000mm forged plate prepared in Example 2 has a room temperature tensile strength Rm≥980MPa in the L, LT, and ST directions, a yield strength Rp0.2≥900MPa, an elongation A≥12%, a reduction of area Z≥25%, and a fracture toughness K. IC ≥80MPa·m 1 / 2 .

[0089] Ultrasonic testing was performed on the TC6 titanium alloy 250mm×600mm×1000mm forged plate prepared in Example 2. The results were uniform and consistent, all meeting the requirement of Φ1.2-6dB or higher.

Claims

1. A method for preparing large-size forged plates of TC6 titanium alloy with low cost and high performance, characterized in that, Includes the following steps: S1, forging in rough blank: Large-sized TC6 titanium alloy ingots are subjected to 1 to 3 upsetting and drawing forging processes. The first upsetting process is a high-temperature homogenization treatment. Each upsetting process involves heating to 60°C to 200°C above the phase transformation point and holding at that temperature before forging. After all upsetting processes are completed, the ingots are cooled to obtain a first-grade intermediate billet. In S1, the cumulative forging ratio per forging pass is controlled between 2.2 and 6.8, and the cumulative deformation is between 40% and 70%. The forging method of the first forging pass is upsetting, drawing, rounding, and inverted octagon. The forging methods of the second and third forging passes are upsetting, drawing, and inverted octagon. Some passes may use reverse upsetting and drawing. The upsetting rate of each pass is 15mm / s to 30mm / s, the drawing rate is 60mm / s to 80mm / s, and the drawing feed is 200mm to 300mm. Each forging pass completes 2 to 3 upsetting and drawing passes, and finally obtains a β structure with a grain size of 10mm to 20mm. S2, intermediate forging: The primary intermediate billet is forged 4 to 7 times, with some of the forgings heated to 30°C to 150°C above the phase transformation point and held at that temperature, and the remaining forgings heated to 20°C to 60°C below the phase transformation point and held at that temperature. After all forgings are completed, the billet is cooled to obtain the secondary intermediate billet. In step S2, 2-4 passes of upsetting and drawing forging are performed. Each pass involves upsetting, drawing a square, drawing a flat square, and drawing an inverted octagon, employing a low-to-high forging process. In the first two passes, the temperature is raised to 20°C-60°C below the phase transformation point, with a holding time of 5-9 hours. In the next two passes, the temperature is raised to 30°C-150°C above the phase transformation point, with a holding time of 4-8 hours. The upsetting forging ratio is controlled between 1.4 and 4.8 per pass, and the deformation during drawing is controlled between 40% and 60%. The upsetting rate is 15mm / s~30mm / s, the drawing rate is 60mm / s~80mm / s, the drawing feed is 200mm~300mm, and then 2~3 forgings are performed. Each forging method is upsetting and flat square drawing. The forging ratio per forging is controlled between 1.2 and 2.

8. The deformation during drawing is controlled between 25% and 50%. The drawing rate is 60mm / s~80mm / s, and the drawing feed is 200mm~300mm. S3, Quasi-β Forging: The intermediate billet is heated to 10°C~40°C above the phase transformation point and held at that temperature, then forged in one pass. After forging, it is cooled to obtain the intermediate forging billet. In S3, the temperature is heated in a stepped manner to 10°C to 40°C above the phase transformation point, and the holding time is 2h to 3.5h. Then, a single-pass drawing forging is performed, with a drawing deformation of 20% to 45%, to obtain a uniform and fine β structure with a grain size of 1mm to 2mm. In S3, the initial forging temperature of each quasi-β forging is 50℃~200℃ below the phase transformation point, and the final forging temperature is 150℃~250℃ below the phase transformation point. S4, Two-phase region forging: The intermediate forging billet is forged 1 to 2 times, each time heated to 20°C to 70°C below the phase transformation point and held at that temperature. After all forging is completed, it is cooled to obtain the forged plate. S5, overall heat treatment and machining: The forged plate is heat-treated and machined to obtain the finished forged plate.

2. The method for preparing large-size forged plates of low-cost, high-performance TC6 titanium alloy according to claim 1, characterized in that, In S1, the high-temperature homogenization holding time is 45h~70h.

3. The method for preparing large-size forged plates of low-cost, high-performance TC6 titanium alloy according to claim 1, characterized in that, In S4, the forging method is direct drawing, and each heating is carried out to 20°C to 70°C below the phase transformation point, with a holding time of 3 to 6 hours, and the elongation deformation is controlled between 5% and 15%.

4. The method for preparing large-size forged plates of low-cost, high-performance TC6 titanium alloy according to claim 1, characterized in that, In S4, the initial forging temperature of each two-phase forging process is 100℃~200℃ below the phase transformation point, and the final forging temperature is 150℃~300℃ below the phase transformation point.

5. The method for preparing large-size forged plates of low-cost, high-performance TC6 titanium alloy according to claim 1, characterized in that, In step S5, the forging billet is first heated to 870℃~920℃, held for 1h~2h and then air-cooled, then heated to 550℃~600℃, held for 2h~5h and then air-cooled to obtain the heat-treated forging billet, which is then machined into the finished forging plate in the final delivery state.

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