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

Abstract

The invention discloses a preparation method of a low-cost and high-performance TC6 titanium alloy large-specification forged plate, which comprises the following steps: S1, cogging and forging: carrying out 1-3 heating number upsetting and drawing forging on a TC6 titanium alloy large-specification cast ingot to obtain a first-stage intermediate blank; s2, intermediate forging is conducted, specifically, 4-7 heating number forging is conducted on the first-stage intermediate blank, part of heating numbers are heated to 30-150 DEG C above the phase transformation point and subjected to heat preservation, the other heating numbers are heated to 20-60 DEG C below the phase transformation point and subjected to heat preservation, cooling is conducted after all heating number forging is completed, and a second-stage intermediate blank is obtained; s3, quasi-beta forging is conducted, specifically, one-heating-number forging is conducted on the second-stage intermediate blank, and an intermediate forging blank is obtained; s4, two-phase region forging is conducted, specifically, forging is conducted on the middle forging stock for 1-2 heating numbers, and a forging plate is obtained; and S5, overall heat treatment and machining are conducted. The method is short in preparation process, low in machining cost, capable of achieving collective preparation of multiple forgings, capable of shortening the preparation period and improving the production efficiency and suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of non-ferrous metal processing and relates to a preparation method of low-cost high-performance TC6 titanium alloy large-size forged plate. BACKGROUND

[0002] TC6 titanium alloy has a nominal composition of Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si, and a forged piece prepared therefrom has high strength, good plasticity and toughness and excellent corrosion resistance, can effectively reduce the total weight of an airplane, improve the endurance of the airplane and prolong the service life of the airplane, and is rapidly increasing in use in high-performance aviation key structural parts. New research and pre-research models all use high-strength and high-toughness lightweight TC6 titanium alloy.

[0003] The production process of a traditional TC6 titanium alloy free forging piece still adopts the production mode in the 1960s-1970s, that is, a titanium material enterprise produces a forging blank and a forged plate, and delivers the same to a forging piece factory; the forging piece factory produces a free forging piece, and delivers the same to a main machine factory; and the main machine factory further machines the same into a final use titanium alloy forging piece. This production mode has problems of long preparation period, complex process flow and large repeated detection loss, and cannot meet the new requirements of short process, low cost and high performance in the field of aviation and aerospace. SUMMARY

[0004] The application aims to provide a preparation method of low-cost high-performance TC6 titanium alloy large-size forged plate, which has a short preparation process, low processing cost, can realize collective preparation of multiple forging pieces, reduces the preparation period, improves the production efficiency and is suitable for industrial production.

[0005] To achieve the above object, the technical scheme adopted by the application is as follows.

[0006] A preparation method of low-cost high-performance TC6 titanium alloy large-size forged plate comprises the following steps.

[0007] S1, blooming forging:

[0008] 1-3 heating and upsetting forging are performed on the TC6 titanium alloy large-size ingot, wherein the first heating is high-temperature homogenization treatment, each heating is heated to 60-200 DEG C above the phase transition point and then kept for a period of time, and then forging is performed; after all the heating and forging are completed, cooling is performed to obtain a first intermediate blank;

[0009] S2, intermediate forging:

[0010] 4-7 heating and forging are performed on the first intermediate blank, wherein part of the heating is heated to 30-150 DEG C above the phase transition point and then kept for a period of time, the remaining heating is heated to 20-60 DEG C below the phase transition point and then kept for a period of time, and then cooling is performed after all the heating and forging are completed to obtain a second intermediate blank;

[0011] S3, quasi-β forging:

[0012] The secondary intermediate blank is heated to 10-40°C above the phase transition point and held for 1 heating pass, and after the forging is completed, the intermediate forged blank is cooled;

[0013] S4, two-phase zone forging:

[0014] The intermediate forged blank is forged for 1-2 heating passes, each heating pass is heated to 20-70°C below the phase transition point and held, and after all the heating passes are completed, the forged plate is cooled;

[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 S1, the high-temperature homogenization holding time is 45-70h.

[0018] Preferably, in S1, the cumulative forging ratio of each heating pass during forging is controlled to be between 2.2 and 6.8, the cumulative deformation amount is between 40% and 70%, the first heating pass is upsetting, elongation, rounding, and inverted octagon, the second and third heating passes are upsetting, elongation, and inverted octagon, and some heating passes can use reversing upsetting and elongation, wherein the upsetting rate of each heating pass is 15-30mm / s, the elongation rate is 60-80mm / s, the elongation feed amount is 200-300mm, 2-3 upsetting and elongation are completed for each heating pass, and finally a β structure with a grain size of 10-20mm is obtained.

[0019] Preferably, in S2, 2-4 heating passes of upsetting and elongation are first performed, the heating pass is upsetting, square elongation, flat square elongation, and inverted octagon, and a low-high forging process is used, wherein 1-2 heating passes are heated to 20-60°C below the phase transition point, the holding time is 5-9h, 1-2 heating passes are heated to 30-150°C above the phase transition point, the holding time is 4-8h, the upsetting ratio of each heating pass is controlled to be between 1.4 and 4.8, the deformation amount during elongation is controlled to be between 40% and 60%, the upsetting rate is 15-30mm / s, the elongation rate is 60-80mm / s, and the elongation feed amount is 200-300mm, and then 2-3 heating passes are performed, the heating pass is upsetting and flat square elongation, the forging ratio of each heating pass is controlled to be between 1.2 and 2.8, the deformation amount during elongation is controlled to be between 25% and 50%, the elongation rate is 60-80mm / s, and the elongation feed amount is 200-300mm.

[0020] Preferably, in the S3, the step heating is adopted to reach 10 DEG C to 40 DEG C above the phase transition point, the holding time is 2h to 3.5h, then 1 fire lengthening forging is carried out, the direct deformation is 20% to 45%, and the grain size of the obtained beta organization is 1mm to 2mm.

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

[0022] Preferably, in the S4, the forging mode is direct drawing, each fire is heated to 20 DEG C to 70 DEG C below the phase transition point, the holding time is 3h to 6h, and the lengthening deformation is controlled to be between 5% and 15%.

[0023] Preferably, in the S4, the initial forging temperature of each fire two-phase zone forging is 100 DEG C to 200 DEG C below the phase transition point, and the final forging temperature is 150 DEG C to 300 DEG C below the phase transition point.

[0024] Preferably, in the S5, the forging blank is first heated to 870 DEG C to 920 DEG C, and then air-cooled after holding for 1h to 2h, and then heated to 550 DEG C to 600 DEG C, and then air-cooled after holding for 2h to 5h, to obtain a heat-treated forging blank, which is then machined into a final delivery state of a finished forging plate.

[0025] The present application has the advantages that: the present application can prepare a forging plate with a single weight of 100kg to 3000kg, and the organization and performance of different positions of the forging plate meet the aviation standard requirements, and are consistent with small size forging plate. High temperature homogenization is adopted in the breakdown forging, the heat diffusion capacity of atoms under high temperature conditions is fully utilized, and the composition and organization uniformity of the ingot and the forging blank are improved. High-low-high forging process is adopted in the breakdown forging and intermediate forging, so as to realize the refinement and consistency of the organization of the large size forging plate, and ensure that the organization performance of different positions is consistent with the small size forging. The deformation modes such as large deformation, reversing upsetting, flat square lengthening, and direct drawing are combined in the forging, so as to ensure that the core organization of the blank is fully refined, the deformation uniformity of each position of the blank is improved, the required alloy organization is obtained through the shortest deformation process, and the material quality under the low cost and short process is ensured. In the quasi-beta forging process, step heating is adopted, the holding time of the alloy above the phase transition point is shortened, and the alloy is fully heat penetrated, the holding temperature above the phase transition point is reasonably selected, the grain growth caused by the excessively high holding temperature or excessively long holding time is avoided, and the alloy grain is uniformly refined. In the two-phase zone forging, the heating temperature, deformation amount, and deformation mode are accurately controlled, and finally the organization and performance of the forging plate are controlled. The TC6 alloy large size forging plate prepared by the processing method has the advantages of short preparation process, low processing cost, and can realize the collective preparation of multiple forgings, reduces the preparation period, improves the production efficiency, and is suitable for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Macrostructure of the Example 1 bar.

[0027] Figure 2 Microstructure of the Example 1 bar in the heat-treated state.

[0028] Figure 3 Macrostructure of the Example 2 bar.

[0029] Figure 4 Microstructure of the Example 2 bar in the heat-treated state.

[0030] Figure 5 Flow chart of the method of the application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the application clearer, the technical scheme of the application will be described clearly and completely below in combination with the drawings of the application.

[0032] As shown in Figures 1-5 A low-cost, high-performance TC6 titanium alloy large-size forged plate preparation method, the single weight of the forged plate is 100kg-3000kg, the size is 80mm-250mm (thick) x 100mm-1000mm (wide) x 300mm-3000mm (long). The forging blank preparation cycle is short, the process control difficulty is low, the process stabilization degree is high, the production cost is low, the finished product rate is high, the microstructure and performance meet the requirements of the aviation material standard, and it is suitable for industrial production.

[0033] A low-cost, high-performance TC6 titanium alloy large-size forged plate preparation method, the raw material is a titanium alloy ingot prepared by the Western Superconducting Company, the machining process is divided into five parts: blooming forging, intermediate forging, quasi-beta forging, two-phase zone forging, overall heat treatment and machining, and specifically includes the following steps:

[0034] S1, blooming forging:

[0035] The TC6 titanium alloy large-size ingot is subjected to 1-3 times of upsetting and drawing forging (the first time is high-temperature homogenization treatment), each time is heated to 60-200℃ above the phase transition point and then heat treated, and then subjected to forging; after all the times of forging are completed, cooling is performed to obtain a primary intermediate blank.

[0036] The TC6 titanium alloy large-size ingot is forged by 1-3 passes, wherein the first pass is high-temperature homogenization treatment. The high-temperature homogenization holding time is 45-70 h, which can eliminate element segregation and break coarse columnar crystals during the ingot breakdown process to obtain a uniform and controllable recrystallized structure. The cumulative forging ratio of each pass is controlled to be 2.2-6.8, and the cumulative deformation is 40%-70%. The first pass is upset, elongated, rounded and inverted octagonal, the second and third passes are upset, elongated and inverted octagonal, and the upset rate of each pass is 15-30 mm / s, the elongated rate is 60-80 mm / s, and the elongated feed is 200-300 mm. Two to three upsets are performed in each pass, and a β structure with a grain size of 10-20 mm is finally obtained.

[0037] The large deformation upset can refine the original coarse as-cast grains, the reversing upset, rounding and inverted octagonal operations improve the forging penetration of the core and the deformation uniformity of each position. The forging process can use the forging method of back-furnace temperature compensation to prevent the broken grains from growing due to excessive heating time.

[0038] After all the passes are completed, the first-stage intermediate billet is obtained.

[0039] S2, intermediate forging:

[0040] The first-stage intermediate billet is forged by 4-7 passes, wherein some passes are heated to 30-150 °C above the phase transition point and held, and the rest of the passes are heated to 20-60 °C below the phase transition point and held. After all the passes are completed, the second-stage billet is obtained.

[0041] S2, intermediate forging, to obtain an alloy billet with uniform structure, the billet after the breakdown forging is forged by 2-4 passes at 20-60 °C below the phase transition point and 30-150 °C above the phase transition point. The forging method of each pass is upset, square drawing, flat square drawing and inverted octagonal, and the low-high forging process is adopted. The first 1-2 passes are heated to 20-60 °C below the phase transition point, and the holding time is 5-9 h. The first 1-2 passes are heated to 30-150 °C above the phase transition point, and the holding time is 4-8 h. The upset ratio of each pass is controlled to be 1.4-4.8, the deformation during elongation is controlled to be 40%-60%, the upset rate is 15-30 mm / s, the elongation rate is 60-80 mm / s, and the elongation feed is 200-300 mm.

[0042] The forging method of each pass is upset, square drawing, flat square drawing and inverted octagonal to ensure the deformation uniformity of each part of the billet.

[0043] The billet after the above forging is heated below 20-60°C of the phase transition point, and after holding for 4-8 hours, 2-3 times of forging are performed, the forging mode of each time is upsetting and flat elongation, the forging ratio of each time is controlled to be 1.2-2.8, the deformation amount during elongation is controlled to be 25%-50%, the elongation speed is 60-80 mm / s, and the elongation feed amount is 200-300 mm.

[0044] After the forging, the secondary billet is obtained through air cooling.

[0045] S3, quasi-beta forging:

[0046] The secondary intermediate billet is heated to 10-40°C above the phase transition point and held, 1 time of forging is performed, and the intermediate forged billet is obtained after the forging is completed and cooling.

[0047] The quasi-beta forging of S3 is performed on the secondary intermediate billet after the intermediate forging, the billet is heated to 10-40°C above the phase transition point in a step manner, and after holding for 2-3.5 hours, 1 time of elongation forging is performed, the direct elongation deformation amount is 20%-45%, and the beta structure with a grain size of 1-2 mm is obtained. The initial forging temperature of each time of quasi-beta forging is 50-200°C below the phase transition point, and the final forging temperature is 150-250°C below the phase transition point.

[0048] The step heating can shorten the holding time of the alloy above the phase transition point and fully heat the alloy, the holding temperature above the phase transition point is reasonably selected, the grain growth caused by the excessively high holding temperature or excessively long holding time is avoided, and the uniform grain refinement of the alloy is realized.

[0049] S4, two-phase zone forging:

[0050] The intermediate forged billet is forged for 1-2 times, each time is heated to 20-70°C below the phase transition point and held, and the forged plate is obtained after the forging of all times is completed and cooling.

[0051] The two-phase zone forging of S4 is performed on the intermediate forged billet after the quasi-beta forging, 1-2 times of forging are performed, the forging mode is direct elongation, each time is heated to 20-70°C below the phase transition point, the holding time is 3-6 hours, the billet can be appropriately reheated, the elongation deformation amount is controlled to be 5%-15%, the forging mode of direct elongation, the smaller forging ratio, and the appropriate reheating can not only ensure the uniform flow and deformation of the metal in all directions during the forging, but also realize the convenience of the forging process control. The initial forging temperature of each time of two-phase zone forging is 100-200°C below the phase transition point, and the final forging temperature is 150-300°C below the phase transition 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 whole heat treatment and machining of S5 is as follows: the forging blank is heated to 870-920℃, and then air-cooled after 1-2h of holding; then heated to 550-600℃, and then air-cooled after 2-5h of holding, to obtain the heat-treated forging blank, which is then machined into the finished forged plate in the final delivery state.

[0055] The application is further described in detail below with reference to specific examples. Example 1

[0057] 1. Upsetting and forging:

[0058] A TC6 titanium alloy ingot with required chemical composition is selected, and the phase transition point of the ingot is 980℃. Upsetting and forging is completed in 2 heating times. The ingot is heated to 1170℃ in steps, and then homogenized for 55h. After the furnace is discharged, upsetting and drawing are performed, and the cumulative deformation is about 65%, and the upsetting and drawing ratio is controlled to be 6.2. Then, upsetting and drawing are performed after the ingot is heated to 1080℃ and held for about 1h, and the single-pass deformation is about 30%, the cumulative deformation is about 60%, and the upsetting and drawing ratio is controlled to be 3.4. After the forging is completed, the ingot is air-cooled. The upsetting is slow and divided, and the upsetting rate is 15mm / s. The first drawing is radial, and the second drawing is axial, and the axial feeding amount is 300mm, and the drawing rate is 60mm / s.

[0059] 2. Intermediate forging:

[0060] The intermediate forging is completed in 6 heating times. Upsetting and drawing are first performed in 4 heating times. The forging process is low-high, the heating temperature of the first heating time is 950℃, and then upsetting and drawing are performed after holding for 8.5h; the heating temperature of the second heating time is 1040℃, and then upsetting and drawing are performed after holding for 6.5h; the heating temperature of the third heating time is 950℃, and then upsetting and drawing are performed after holding for 8h; the heating temperature of the fourth heating time is 1040℃, and then upsetting and drawing are performed after holding for 5.5h. The upsetting ratio of the above heating times is controlled to be 1.6, and the deformation during drawing is controlled to be 40%. The upsetting is slow and divided, and the upsetting rate is 25mm / s. The drawing is eight-square drawing and flat-square drawing, the feeding amount is 250mm, the drawing rate is 75mm / s, and the deformation of each part of the blank is ensured to be uniform. The blank is air-cooled after each heating time.

[0061] The blank after the above forging is heated to 940℃, and then held for 5h, and then the blank is forged in 2 heating times, the forging ratio is controlled to be 1.8, the deformation during drawing is controlled to be 35%, the forging mode is upsetting and flat-square drawing, the drawing feeding amount is 250mm, the drawing rate is 75mm / s, and the blank is air-cooled after forging.

[0062] 3. Quasi-β forging:

[0063] The forging blank is forged in one fire, heated in steps to 1020℃, kept warm for 3 hours, and then straight-draw forged to a thickness of 180mm. The straight-draw deformation is 30%, and a uniform and fine β structure with a grain size of 1.5mm is obtained. The initial forging temperature during quasi-β forging is 850℃ and the final forging temperature is 750℃.

[0064] 4. Two-phase zone forging:

[0065] The forging blank is completed in one forging process, with a heating temperature of 950℃ and a holding time of 3h. It is then straight-draw forged to a thickness of 170mm with a straight-draw deformation of 9%. During two-phase zone forging, the initial forging temperature is 800℃ and the final forging temperature is 700℃.

[0066] 5. Overall heat treatment:

[0067] The forging blank is heated to 900℃ and kept at this temperature for 2 hours. After air cooling, it is kept at 600℃ and air cooled for 5 hours to obtain the heat-treated forging blank. It is then machined into the finished forging plate in the final delivery state. The finished product specifications are 160mm×720mm×2000mm.

[0068] The macrostructure of the 160 mm × 720 mm × 2000 mm forged plate of TC6 titanium alloy prepared in Example 1 is shown in FIG. Figure 1 The microstructure of the TC6 titanium alloy 160mm×720mm×2000mm forging plate prepared in Example 1 is shown in Figure 2 The room temperature properties of the slab after overall solution aging are shown in Table 1, with a good match between strength and toughness.

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

[0070]

[0071] The room temperature tensile strength Rm of the TC6 titanium alloy 160mm×720mm×2000mm forging plate prepared in Example 1 is 980MPa or higher in L, LT and ST directions, the yield strength Rp0.2 is 900MPa or higher, the elongation A is 12% or higher, the section shrinkage Z is 25% or higher, and the fracture toughness K is 0. IC ≥80MPa·m 1 / 2 .

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

[0074] 1. Open forging:

[0075] The TC6 titanium alloy ingot with qualified chemical composition was selected, and the phase transition point of the ingot was 980 °C. The open-die forging was completed in 3 heating times. The temperature was increased to 1170 °C in steps, and then the high-temperature homogenization treatment was performed for 55 h. After the furnace was discharged, the upsetting and drawing forging was performed, and the cumulative deformation was about 55%. The upsetting and drawing forging ratio was controlled to be 6.8. After the furnace was heated to 1080 °C and kept for about 1 h, the upsetting and drawing forging was performed. After the forging was completed, the blank was air-cooled, and then the blank was heated to 1050 °C and kept for 4 h. The single-pass deformation of the above heating times was about 45%, the cumulative deformation was about 65%, and the upsetting and drawing forging ratio was controlled to be 5.2. After the forging was completed, the blank was air-cooled. The upsetting was performed at a slow speed, and the upsetting rate was 25 mm / s. The first drawing was performed in the radial direction, and the second drawing was performed in the axial direction. When the axial drawing was performed, the feeding amount was 200 mm, and the drawing rate was 80 mm / s.

[0076] 2. Intermediate forging:

[0077] The intermediate forging was completed in 5 heating times. The upsetting and drawing forging was first performed in 3 heating times. The low-high forging process was adopted. The heating temperature of the first heating time was 920 °C, and the upsetting and drawing were performed after the blank was kept for 6.5 h. The heating temperature of the second heating time was 920 °C, and the upsetting and drawing were performed after the blank was kept for 6 h. The heating temperature of the third heating time was 1050 °C, and the upsetting and drawing were performed after the blank was kept for 5 h. The upsetting forging ratio of the above heating times was controlled to be 3.8, and the deformation amount during drawing was controlled to be 55%. The upsetting was performed at a slow speed, and the upsetting rate was 15 mm / s. The drawing was performed in the eight-square, flat-square and axial directions, the feeding amount was 200 mm, and the drawing rate was 60 mm / s. The deformation of each part of the blank was ensured to be uniform. After each heating time, the blank was air-cooled.

[0078] After the blank was heated to 920 °C and kept for 4 h, the blank was forged in 2 heating times. The forging ratio was controlled to be 2.2, the deformation amount during drawing was controlled to be 40%, the forging mode was upsetting and flat-square drawing, the drawing feeding amount was 200 mm, and the drawing rate was 60 mm / s. After the forging was completed, the blank was air-cooled.

[0079] 3. Quasi-β forging:

[0080] The forging of the blank was completed in 1 heating time. The temperature was increased to 990 °C in steps, and then the blank was kept for 3.5 h. The straight drawing forging was performed until the thickness of the blank was 285 mm, and the straight drawing deformation amount was 42%. The grain size of the obtained β structure was 1.1 mm, which was uniform and fine. The initial forging temperature during the quasi-β forging was 800 °C, and the final forging temperature was 700 °C.

[0081] 4. Two-phase region forging:

[0082] The forging blank is forged twice, first heated to 940℃, holding time is 4h, straightening forging to 265mm thick, straightening deformation is 7%, then heated to 940℃ for about 60min, straightening forging, straightening to 260mm thick, straightening deformation is 4%, the initial forging temperature is 780℃, the final forging temperature is 680℃ during intercritical forging.

[0083] 5. Integral heat treatment:

[0084] The forging blank is heated to 870℃ for 2h, air cooling, then heated to 550℃ for 4h, air cooling, to obtain the heat treated forging blank, then machined to the final delivery state of the finished forging plate, the finished product specification is 250mmx600mmx1000mm.

[0085] The macrostructure of the TC6 titanium alloy 250mmx600mmx1000mm forging plate prepared in Example 2 is shown in Figure 3 ; the microstructure of the TC6 titanium alloy 250mmx600mmx1000mm forging plate prepared in Example 1 is shown in Figure 4 . The room temperature performance of the plate blank after integral solution and aging is shown in Table 2, and the strength and toughness match well.

[0086] Table 2 Room temperature performance of TC6 titanium alloy 250mmx600mmx1000mm forging plate after double annealing

[0087]

[0088] The room temperature tensile strength Rm of the TC6 titanium alloy 250mmx600mmx1000mm forging plate prepared in Example 2 is ≥980MPa, the yield strength Rp0.2 is ≥900MPa, the elongation A is ≥12%, the reduction of area Z is ≥25%, and the fracture toughness K IC ≥80MPa·m 1 / 2 .

[0089] The TC6 titanium alloy 250mmx600mmx1000mm forging plate prepared in Example 2 is subjected to ultrasonic flaw detection, and the results are uniform and consistent, all reaching the requirement of Φ1.2-6dB or more.

Claims

1. A method for preparing a low-cost, high-performance TC6 titanium alloy large-size forging plate, characterized in that: The following steps are involved: S1, billet forging: The large-size TC6 titanium alloy ingot is subjected to 1 to 3 fire upsetting forgings, wherein the first fire is a high-temperature homogenization treatment, and each fire is heated to 60℃ to 200℃ above the phase transformation point and kept warm before forging; after all the fires are completed, the ingot is cooled to obtain a first-level intermediate billet; S2, intermediate forging: The first-level intermediate billet is forged 4 to 7 times, wherein some of the forging times are heated to 30°C to 150°C above the phase transformation point and kept warm, and the remaining forging times are heated to 20°C to 60°C below the phase transformation point and kept warm. After all the forging times are completed, the billet is cooled to obtain the second-level intermediate billet; S3, Quasi-Beta Forging: The secondary intermediate billet is heated to 10°C to 40°C above the phase transformation point and kept warm, and then subjected to one-time forging. After forging, the billet is cooled to obtain an intermediate forging billet. S4, two-phase zone forging: The intermediate forging blank is forged 1 to 2 times, and each time it is heated to 20 to 70 degrees Celsius below the phase transformation point and kept warm. After all the forging times are completed, it is cooled to obtain a forged plate; S5, overall heat treatment and machining: The forged plate is heat treated and machined to obtain a finished forged plate.

2. The method for preparing a low-cost, high-performance TC6 titanium alloy large-size forging plate according to claim 1, characterized in that: In S1, the high-temperature homogenization and heat preservation time is 45 hours to 70 hours.

3. The method for preparing a low-cost, high-performance TC6 titanium alloy large-size forging plate according to claim 1, characterized in that: In the above-mentioned S1, during forging, the cumulative forging ratio of each fire is controlled between 2.2 and 6.8, the cumulative deformation is between 40% and 70%, the forging method of the first fire is upsetting, drawing, rounding and squaring, and the forging method of the second and third fires is upsetting, drawing and squaring. Some fires can adopt reversing upsetting and drawing, wherein the upsetting rate of each fire is 15 mm / s to 30 mm / s, the drawing rate is 60 mm / s to 80 mm / s, and the drawing feed amount is 200 mm to 300 mm. 2 to 3 upsetting and drawing are completed in each forging fire, and a β structure with a grain size of 10 mm to 20 mm is finally obtained.

4. The method for preparing a low-cost, high-performance TC6 titanium alloy large-size forging plate according to claim 1, characterized in that: In the S2, 2 to 4 fires of upsetting and drawing forging are first performed, and the forging methods of each fire are upsetting, drawing square, drawing flat square and inverted octagonal, and a low-high forging process is adopted, wherein 1 to 2 fires are heated to 20°C to 60°C below the phase change point, and the holding time is 5h to 9h, and 1 to 2 fires are heated to 30°C to 150°C above the phase change point, and the holding time is 4h to 8h. The upsetting and forging ratio of each fire is controlled between 1.4 and 4.8, 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 fire forgings are carried out. The forging method of each fire is upsetting and flat square drawing. The forging ratio of each fire is controlled between 1.2~2.

8. The deformation during drawing is controlled at 25%~50%, the drawing rate is 60mm / s~80mm / s, and the drawing feed is 200mm~300mm.

5. The method for preparing a low-cost, high-performance TC6 titanium alloy large-size forging plate according to claim 1, characterized in that: In the above S3, stepwise heating is adopted to 10°C to 40°C above the phase transformation point, and the holding time is 2h to 3.5h, followed by one-time drawing forging, with a straight drawing deformation of 20% to 45%, to obtain a uniform and fine β structure with a grain size of 1mm to 2mm.

6. The method for preparing a low-cost, high-performance TC6 titanium alloy large-size forging plate according to claim 1, characterized in that: In the above 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.

7. The method for preparing a low-cost, high-performance TC6 titanium alloy large-size forging plate according to claim 1, characterized in that: In the above-mentioned S4, the forging method is straight drawing, each heating is performed to 20°C to 70°C below the phase transformation point, the holding time is 3h to 6h, and the drawing deformation is controlled between 5% and 15%.

8. The method for preparing a low-cost, high-performance TC6 titanium alloy large-size forging plate according to claim 1, characterized in that: In the above S4, the initial forging temperature of each two-phase region forging is 100°C to 200°C below the phase transformation point, and the final forging temperature is 150°C to 300°C below the phase transformation point.

9. The method for preparing a low-cost, high-performance TC6 titanium alloy large-size forging plate according to claim 1, characterized in that: In S5, the forging blank is first heated to 870°C to 920°C, kept at this temperature for 1h to 2h, and then air-cooled. It is then heated to 550°C to 600°C, kept at this temperature for 2h to 5h, and then air-cooled to obtain a heat-treated forging blank, which is then machined into a finished forged plate in the final delivery state.

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