Segregation-free high-strength and large-specification Ti6Al6V2Sn titanium alloy forge piece and preparation method thereof

Abstract

The invention belongs to the technical field of titanium alloy material processing, and relates to a segregation-free, high-strength and large-specification Ti6Al6V2Sn titanium alloy forge piece and a preparation method thereof. The thickness of the titanium alloy forge piece manufactured through the method ranges from 350 mm to 420 mm, the width of the titanium alloy forge piece ranges from 420 mm to 470 mm, and the length of the titanium alloy forge piece ranges from 3200 mm to 4400 mm. The method comprises the specific steps that firstly, raw materials of a titanium alloy forge piece are placed in a vacuum consumable smelting furnace, and a Ti6Al6V2Sn cast ingot is prepared through multiple times of smelting; the pretreated cast ingot is sequentially subjected to cogging forging, intermediate forging and finished product forging, and then a finished product forging stock is obtained; and finally, the finished forging stock is subjected to solid solution aging heat treatment, then straightening and machining are sequentially conducted, and the Ti6Al6V2Sn titanium alloy forge piece is obtained and has good strength and plasticity comprehensive performance and can be applied to the high-end equipment manufacturing and key industrial field.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy material processing technology, and relates to a high-strength, segregation-free Ti6Al6V2Sn titanium alloy forging prepared by free forging and its preparation method. Background Technology

[0002] Titanium alloys, with their lightweight, high strength, corrosion resistance, and wear resistance, play a vital role in aerospace, marine engineering, weaponry, and petrochemical industries. Ti6Al6V2Sn titanium alloy is a (α+β) two-phase titanium alloy developed from Ti6Al4V titanium alloy by adding β-stabilizing elements V, Fe, and Cu, and the neutral element Sn. Compared to Ti6Al4V titanium alloy, Ti6Al6V2Sn titanium alloy exhibits superior heat treatment strengthening properties and tensile strength, while also possessing good hardenability and thermal stability, thus offering significant advantages in large-scale structural components. However, due to limitations in the smelting process, the equilibrium distribution coefficients of Cu and Fe differ significantly from those of Ti, leading to compositional segregation and the formation of β-spot defects during Ti6Al6V2Sn titanium alloy processing. These defects result in deterioration of the internal microstructure uniformity and decreased batch stability, severely impacting the performance and service life of Ti6Al6V2Sn titanium alloy as large-scale forgings. Therefore, Ti6Al6V2Sn titanium alloy is currently often used to manufacture small components such as plates, small forgings, bars, or fasteners, which is difficult to meet the application requirements of large-scale structural forgings, and seriously restricts the application prospects of Ti6Al6V2Sn titanium alloy in high-end fields such as aerospace and marine engineering.

[0003] Therefore, there is an urgent need to develop a large-size Ti6Al6V2Sn titanium alloy forging and its preparation method to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and propose a segregation-free, high-strength, large-size Ti6Al6V2Sn alloy forging and its preparation method. First, in the composition design of the Ti6Al6V2Sn titanium alloy, this method replaces elemental copper and iron with binary intermediate alloys such as titanium-copper and titanium-iron, and reduces the Cu and Fe content in the alloy, thereby reducing segregation and β-spot defects generated during the smelting process. Second, during the forging process, a forging mode combining multi-fire upsetting and two-phase region reversing upsetting is used to optimize the microstructure and metal flow direction, obtaining a uniform and fine forging microstructure, compensating for the decrease in mechanical properties of the forging caused by the reduction in Cu and Fe content. Finally, a composite heat treatment process of high-temperature water-cooled solution treatment and aging in the upper two-phase region is adopted to further improve the strength of the large-size Ti6Al6V2Sn titanium alloy forging while retaining a certain degree of plasticity. This method involves partially dissolving the primary α-phase inside the alloy forging billet at high temperatures, forming a high proportion of metastable β-phase in the matrix, while retaining a suitable amount of primary α-phase as nucleation sites. In the subsequent low-temperature aging heat treatment stage, a large amount of the metastable β-phase inside the forging billet decomposes, forming a significant number of secondary α-phases. Through ingot composition design, a forging mode combining large deformation upsetting and reversing upsetting, and a composite heat treatment process of high-temperature water-cooled solution treatment followed by aging, high-strength, high-grade Ti6Al6V2Sn titanium alloy forgings with no segregation, uniform microstructure, and significant engineering implications are ultimately produced.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention discloses a high-strength, segregation-free Ti6Al6V2Sn titanium alloy forging, wherein the thickness of the Ti6Al6V2Sn titanium alloy forging is 350~420mm, the width is 420~470mm, the length is 3200~4400mm, and its room temperature tensile strength is ≥1035MPa, the specified plastic elongation strength is ≥965MPa, and the elongation is ≥12%.

[0006] Secondly, this invention discloses a method for preparing segregation-free, high-strength, and high-grade Ti6Al6V2Sn titanium alloy forgings, comprising the following steps: S1. Sponge titanium, titanium-copper alloy, aluminum-vanadium alloy, titanium-iron alloy, TiO2, titanium-tin alloy and aluminum are pressed into consumable electrodes. The consumable electrodes are then subjected to vacuum consumable arc melting, followed by trimming and machining to obtain Ti6Al6V2Sn ingots. S2. A coating is applied to the surface of the Ti6Al6V2Sn ingot to obtain a pretreated ingot. The pretreated ingot is then subjected to forging, intermediate forging and finished product forging in sequence to obtain a finished forged billet. S3. The finished forging billet is subjected to solution aging heat treatment, and then straightened and machined in sequence to finally obtain the Ti6Al6V2Sn titanium alloy forging.

[0007] Specifically, in S1, the finishing process involves removing the riser and the bottom of the molten ingot obtained after vacuum melting; the purpose of the machining is to remove the oxide scale on the surface of the molten ingot to obtain a Ti6Al6V2Sn ingot with a clean surface that meets the subsequent forging conditions.

[0008] Specifically, the nominal weight of the Ti6Al6V2Sn titanium alloy forging is preferably 3000 kg and 4500 kg.

[0009] Specifically, in S1, the sponge titanium is preferably 0A grade sponge titanium; the aluminum-vanadium alloy is preferably AlV65 alloy; and the aluminum material is preferably aluminum briquettes.

[0010] Specifically, the vacuum self-consuming arc melting operation is preferably performed 2 to 3 times; More specifically, the vacuum self-consuming arc melting is a conventional and mature process for this target titanium alloy in the field, and belongs to the existing well-known technology, so it will not be described in detail here; More specifically, the target composition range of the Ti6Al6V2Sn titanium alloy forging is as follows: Al: 5.00%~6.00%, V: 5.00%~6.00%, Sn: 1.5%~2.5%, Fe: 0.35%~1.00%, Cu: 0.35%~1.00%, C≤0.10%, N≤0.08%, H≤0.015%, O:≤0.20%, Y≤0.005%, single impurity element≤0.1% and total impurity elements≤0.4%, with the balance being Ti.

[0011] Specifically, in S2, the coating is mainly used for protection during the billet forging process. It is preferably made of protective coating of model TB1200-16. The coating can prevent hydrogen evolution and oxygen absorption of the ingot at high temperature.

[0012] Specifically, after the finished forging billet is taken out of the furnace, it needs to be quickly transferred to a circulating cooling water tank for solution heat treatment. Preferably, the transfer operation time is ≤30s to ensure that the finished forging billet enters the solution heat treatment process at a high temperature and avoids the solution effect being affected by the temperature drop.

[0013] Specifically, in S3, after the solution aging heat treatment process is completed, the straightening treatment is carried out using the residual heat from the furnace of the finished forging billet, so as to achieve a seamless connection between heat treatment and straightening treatment and avoid secondary heating that would lead to increased energy consumption and grain growth.

[0014] Specifically, in S3, the machining process preferably uses a heavy-duty gantry milling machine, sawing machine, or end milling machine to machine the finished forging billet after heat treatment, requiring a single-sided milling amount of ≥6mm to ensure that the Ti6Al6V2Sn titanium alloy forging has a smooth surface and is free of defects such as cracks.

[0015] Specifically, in S3, after the machining is completed, ultrasonic testing is used to ensure that there are no internal cracks in the Ti6Al6V2Sn titanium alloy forging. The test results must meet the AA grade requirements in GB / T5193, and the other indicators must meet the AMS 4979H standard.

[0016] Specifically, the maximum upper limit of the holding time range for each process stage of the Ti6Al6V2Sn titanium alloy forging described in this application is determined after extending the holding time; that is to say, the longest holding time actually performed in each stage cannot exceed this upper limit value of the corresponding stage.

[0017] Further, in S2, the initial forging includes a single-stage upsetting and drawing forging process, wherein the upsetting and drawing forging steps include: first heating the pretreated ingot to 800℃~850℃ and holding it at that temperature for 60~150 min; then, within 120~240 min, heating the pretreated ingot to (T... β +150)℃~(T β The blank is heated to +250℃ and held for 120~550 minutes before the first forging. After forging, it is air-cooled and polished to obtain the primary forging blank.

[0018] Specifically, the first forging preferentially adopts two upsetting and two drawing processes. Through large deformation and repeated upsetting and drawing deformation, the coarse as-cast structure inside the ingot is broken and defects such as porosity and shrinkage cavities inside the ingot are eliminated, laying a uniform microstructure foundation for subsequent forming forging. More specifically, in S2, after one upsetting and one drawing, the ingot needs to be returned to the furnace for heat preservation. The purpose is to prevent the temperature from dropping and the ingot's deformation resistance from increasing during the forging process, which could lead to defects such as cracking on the surface of the forging billet. More specifically, the holding temperature of the remelting process is relatively high (T). β +150)℃~(T β The temperature is reduced by 30-50°C (+250°C), preferably to 1100°C, and the holding time is 30-90 minutes, so as to ensure that the forging billet maintains a high temperature during the forging process and reduce the deformation resistance.

[0019] Specifically, in order to optimize the performance of the Ti6Al6V2Sn titanium alloy forging, the first heating temperature of the pretreated ingot is preferably 850℃, and the second heating temperature is preferably 1150℃.

[0020] Specifically, the preferred tool for the grinding process is a grinding wheel, which is used to grind down defective areas generated during the forging process to ensure that the surface of the forging is free of cracks.

[0021] Furthermore, in S2, the initial forging temperature of the first forging is ≥900℃, and the final forging temperature is ≥850℃.

[0022] Further, in S2, the intermediate forging includes one-pass intermediate high-temperature upsetting forging, four to six-pass intermediate low-temperature upsetting forging, and post-forging treatment, wherein: The intermediate high-temperature upsetting forging step includes: heating the primary forging billet to 800℃~850℃ and holding it at that temperature for 60~120 minutes; then, within 90~210 minutes, heating the primary forging billet to (T... β +50)℃~(T β After being heated to +200℃ and held at that temperature for 180~700min, the second forging, air cooling, and grinding were carried out sequentially to obtain the second forging billet. The 4-6 heat-passing intermediate low-temperature upsetting and drawing forging processes all include a heating stage and a forging stage. The heating stage includes the following steps: heating the forging billet obtained in the previous step to 800℃~850℃ and holding it at that temperature for 60~150 minutes; then, heating the forging billet from the previous heat-passing process to (T) within 60~210 minutes. β -30)℃~(T β -80)℃ and hold at that temperature for 240~920min; the forging stage includes several reversing upsetting and drawing operations; after 4~6 rounds of intermediate low temperature upsetting and drawing forging are completed, the third forging billet is obtained; The post-forging treatment steps include: sequentially air-cooling and grinding the third forging billet to obtain an intermediate forging billet.

[0023] Specifically, the reversing upsetting operation is preferably performed twice, in the corresponding heat treatment during the intermediate low-temperature upsetting forging. The purpose is to change the direction of the metal flow lines inside the forging billet through reversing upsetting, thereby achieving a uniform internal structure.

[0024] Specifically, the intermediate high-temperature upsetting and drawing forging preferably employs a two-upsetting and two-drawing process. After one upsetting and one drawing are completed, the ingot needs to be returned to the furnace for heat preservation. The heat preservation temperature is (T). β +50)℃~(T β +200)℃, and the heat preservation time is 30~120min.

[0025] Specifically, the intermediate low-temperature upsetting and drawing forging in the 4th to 6th firing stages preferably employs two upsetting and two drawing stages. After each upsetting and drawing operation is completed, the ingot needs to be returned to the furnace for heat preservation. The heat preservation temperature is (T). β -30)℃~(T β -80)℃, heat preservation time is 60~180min.

[0026] More specifically, during the final drawing process of the intermediate low-temperature upsetting forging, the forging billet needs to be squared. Preferably, the cross-section of the forging billet after squarening is □550mm. More specifically, if the intermediate low-temperature forging adopts 4-stage upsetting and drawing, then reverse upsetting and drawing is adopted in the 3rd and 4th stages, and the forging billet is drawn and squared in the 4th stage. If the intermediate low-temperature forging adopts 5-stage upsetting and drawing, then reverse upsetting and drawing is adopted in the 3rd and 4th stages, and the forging billet is drawn and squared in the 5th stage. If the intermediate low-temperature forging adopts 6-stage upsetting and drawing, then reverse upsetting and drawing is adopted in the 4th and 5th stages, and the forging billet is drawn and squared in the 6th stage.

[0027] Specifically, in order to optimize the performance of the Ti6Al6V2Sn titanium alloy forgings, during the intermediate high-temperature upsetting and drawing forging process, the first heating temperature is preferably 850℃, and the second heating temperature is preferably 1080~1100℃; during the intermediate low-temperature upsetting and drawing forging process, the first heating temperature is preferably 800℃, and the second heating temperature is preferably 850~885℃.

[0028] Furthermore, the initial forging temperature of the intermediate high-temperature upsetting forging is ≥800℃, and the final forging temperature is ≥750℃; the initial forging temperature of each heat in the intermediate low-temperature upsetting forging is ≥750℃, and the final forging temperature is ≥700℃.

[0029] Further, in S2, the finished product forging includes a final drawing forging, the final drawing forging step comprising: heating the intermediate forging billet to 800℃~850℃ and holding it at that temperature for 60~120 minutes; subsequently, heating the intermediate forging billet to (T) within 60~180 minutes. β -30)℃~(T β The forged billet is heated to -80℃ and held for 210–570 min before being drawn, straightened, and air-cooled to obtain the finished forging billet.

[0030] Specifically, in order to optimize the performance of the Ti6Al6V2Sn titanium alloy forging, the first heating temperature during the final single-heat drawing forging process is preferably 800℃, and the second heating temperature is preferably 850~875℃.

[0031] Furthermore, the total deformation during the initial forging process is 80%–90%, the total deformation during the intermediate high-temperature upsetting forging process is 80%–90%, the total deformation during each heat of the intermediate low-temperature upsetting forging process is 70%–80%, and the total deformation during the finished product forging process is 30%–50%.

[0032] Furthermore, the initial forging temperature of the elongation forging is ≥750℃, and the final forging temperature is ≥700℃.

[0033] Furthermore, in S3, the solution heat treatment temperature is 850℃~900℃ and the holding time is 2~3h, and the aging heat treatment temperature is 450℃~600℃ and the holding time is 6~8h.

[0034] Specifically, the solution heat treatment temperature is preferably 890°C, and the holding time is preferably 3 hours; the aging heat treatment temperature is preferably 538°C, and the holding time is preferably 8 hours.

[0035] Compared with the prior art, the present invention has the following beneficial effects: First, in terms of composition design, this invention uses titanium-copper and titanium-iron binary intermediate alloys as raw material additives and reduces the content of Cu and Fe elements, which can effectively reduce defects such as β spots caused by compositional segregation in the ingot, and provide a stable Ti6Al6V2Sn ingot for subsequent forging processes.

[0036] Secondly, this invention employs a large deformation multi-fire upsetting and drawing process, and introduces a reversing upsetting and drawing process. This ensures sufficient deformation of the casting and avoids localized heating during the processing of Ti6Al6V2Sn titanium alloy by controlling the forging process parameters. This achieves grain refinement and optimized metal flow lines in the internal structure of the forging, resulting in a forging with a uniform structure. This solves the problem that conventional upsetting and drawing forging easily leads to coarse internal structure and significant grain orientation, which greatly reduces the comprehensive mechanical properties of large-size Ti6Al6V2Sn forgings. At the same time, a composite heat treatment process of high-temperature solution treatment and low-temperature aging is used to further improve the strength of the forging while retaining its high and stable plasticity.

[0037] Third, the large-size Ti6Al6V2Sn titanium alloy forgings prepared by this invention have a thickness of 350~420 mm, a width of 420~470 mm, and a length of 3200~4400 mm. They exhibit good microstructure uniformity, good batch stability, and excellent comprehensive performance, meeting the technical requirements and further expanding the application fields of large-size Ti6Al6V2Sn titanium alloy forgings. Simultaneously, while ensuring the aforementioned large dimensions, the forgings achieve excellent synergy between microstructure and mechanical properties: the low-magnification microstructure is free of crack defects, and the microstructure is a uniform, fine, and equiaxed structure without elemental segregation; its room-temperature mechanical properties are excellent, specifically, tensile strength ≥1035 MPa, specified plastic elongation strength ≥965 MPa, and elongation ≥12%. Attached Figure Description

[0038] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a flowchart of the preparation method of the Ti6Al6V2Sn titanium alloy forgings according to the present invention; Figure 2 This is a low-magnification microstructure diagram of the large-sized Ti6Al6V2Sn titanium alloy forging with dimensions of 355×420×3500mm in Example 1. Figure 3 The image shows the microstructure of the large-sized Ti6Al6V2Sn titanium alloy forging with dimensions of 355×420×3500mm in Example 1. Figure 4 This is a low-magnification microstructure image of the large-size Ti6Al6V2Sn titanium alloy forging of 355×470×3200mm in Example 2; Figure 5 The image shows the microstructure of the large-sized Ti6Al6V2Sn titanium alloy forging of 355×470×3200mm in Example 2.

[0041] Figure 6 This is a low-magnification microstructure image of the large-sized Ti6Al6V2Sn titanium alloy forging with dimensions of 420×445×4400mm in Example 3. Figure 7 The image shows the microstructure of the large-sized Ti6Al6V2Sn titanium alloy forging with dimensions of 420×445×4400mm in Example 3. Figure 8 The microstructure of the large-sized Ti6Al6V2Sn titanium alloy forging with dimensions of 355×420×3500mm in Comparative Example 1 is shown in low magnification. Figure 9 Microstructure of the large-sized Ti6Al6V2Sn titanium alloy forging with dimensions of 355×420×3500mm in Comparative Example 1. Figure 10 Microstructure of the large-sized Ti6Al6V2Sn titanium alloy forging with dimensions of 355×470×3200mm in Comparative Example 2. Figure 11 The image shows the microstructure of the large-sized Ti6Al6V2Sn titanium alloy forging with dimensions of 355×470×3200mm in Comparative Example 2. Detailed Implementation

[0042] Exemplary embodiments will now be described in detail. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples consistent with some aspects of the invention as detailed in the appended claims.

[0043] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0044] Example 1 like Figure 1 As shown, this invention provides a method for preparing segregation-free, high-strength, large-size Ti6Al6V2Sn titanium alloy forgings, comprising the following steps: S1. According to the target alloy composition ratio of the Ti6Al6V2Sn titanium alloy forging, take 0A grade sponge titanium, AlV65 alloy, aluminum briquettes, titanium-tin alloy, titanium-iron alloy and titanium-copper alloy, mix the raw materials and press them into consumable electrodes, and then perform two VAR melting processes on the consumable electrodes to obtain primary ingots. After removing the risers and ingot bottoms of the primary ingots, remove the oxide scale on the surface of the primary ingots by machining to obtain Ti6Al6V2Sn ingots.

[0045] Specifically, the actual weight of the Ti6Al6V2Sn ingot is 2946 kg, and the phase transformation point (T) is... β The temperature was 937℃.

[0046] S2. A TB1200-16 coating is applied to the surface of the Ti6Al6V2Sn ingot to obtain a pretreated ingot. Subsequently, the ingot undergoes rough forging, intermediate forging, and final forging in sequence, specifically as follows: The initial forging process includes a single upsetting and drawing forging. In this stage, the pretreated ingot is heated to 850°C in a natural gas furnace and held for 150 minutes. Then, within 120 minutes, the pretreated ingot is heated to 1087°C and held for 120 minutes before being removed from the furnace. The pretreated ingot is then upset and drawn once using a 45 / 50MN high-speed forging mill before being returned to the furnace. The holding temperature during return is 1007°C, and the holding time is 60 minutes. The upsetting and drawing operation is then performed again, and the forged billet is air-cooled and polished to obtain the primary forged billet.

[0047] Specifically, the upsetting and drawing forging process employs large deformation to fully break the as-cast structure, and the total deformation in this process is 90%, with a final forging temperature of 897℃.

[0048] The intermediate forging process includes, in sequence, one intermediate high-temperature upsetting and drawing forging, three intermediate low-temperature upsetting and drawing forging, and post-forging treatment, wherein: The first intermediate high-temperature upsetting and drawing forging process involves heating the primary forging billet to 825°C in a natural gas furnace and holding it at that temperature for 90 minutes. Then, within 150 minutes, the primary forging billet is heated to 997°C and held at that temperature for 180 minutes before being removed from the furnace. The primary forging billet is then upset and drawn once using a 45 / 50MN fast forging unit and returned to the furnace. At this time, the temperature for holding it in the furnace is 987°C and the holding time is 80 minutes. Subsequently, a second upsetting and drawing process is performed, and the forged billet is air-cooled and polished in sequence to obtain the first intermediate forging billet.

[0049] Specifically, the total deformation during the first intermediate high-temperature upsetting and drawing forging process is 85%, and the final forging temperature is 793℃.

[0050] The first intermediate low-temperature upsetting and drawing forging process involves heating the first intermediate forging billet to 825°C in an electric furnace and holding it at that temperature for 60 minutes. Then, within 210 minutes, the first intermediate forging billet is heated to 857°C and held at that temperature for 920 minutes before being removed from the furnace. The first intermediate forging billet is then subjected to one upsetting and one drawing forging process using a 45 / 50MN fast forging unit, and then returned to the furnace for holding (holding temperature is 857°C, holding time is 180 minutes). Subsequently, a second upsetting and drawing process is performed, and the forged billet is air-cooled and polished to obtain the second intermediate forging billet.

[0051] Specifically, the total deformation during the first intermediate low-temperature upsetting and drawing forging process is 80%, and the final forging temperature is 715℃.

[0052] Both the second and third intermediate low-temperature upsetting forging processes are performed using an electric furnace. Specifically, the second intermediate forging billet is heated to 825°C and held for 90 minutes; then, within 60 minutes, it is heated to 857°C and held for 920 minutes before being removed from the furnace. The second and third intermediate low-temperature upsetting forging processes are then performed using a 45 / 50MN fast forging mill. Both the second and third intermediate low-temperature upsetting forging processes employ reverse upsetting forging. Specifically, during the second intermediate low-temperature upsetting process... During the drawing and forging process, the second intermediate billet is forged by side upsetting and then held in the furnace at a temperature of 857°C for 180 minutes. After that, it is taken out of the furnace and subjected to side upsetting and skewing forging and surface grinding to obtain the third intermediate billet. During the third intermediate low-temperature upsetting and drawing forging process, the third intermediate billet is forged by side upsetting and then held in the furnace at a temperature of 857°C for 118 minutes. After that, it is taken out of the furnace and subjected to side upsetting and skewing forging. During the skewing process, it is squared to a size of □550×2055 mm, then air-cooled and 100% surface-ground to finally obtain the intermediate billet.

[0053] Specifically, the final forging temperature of the second intermediate low-temperature upsetting forging is 742°C, and the final forging temperature of the third intermediate low-temperature upsetting forging is 728°C.

[0054] Specifically, the total deformation during the second and third intermediate low-temperature upsetting and drawing forging processes is 80%.

[0055] The finished product forging includes post-forging treatment, in which a drawing process is performed on the intermediate forging billet. Specifically, the intermediate forging billet is heated to 800°C in an electric furnace and held for 90 minutes; then, within 60 minutes, the intermediate forging billet is heated to 857°C and held for 210 minutes before being removed from the furnace. A 45 / 50MN high-speed forging mill is then used to draw the intermediate forging billet, elongating its dimensions from □550×2055 mm to [the desired size]. mm, to obtain the finished forging billet.

[0056] Specifically, the post-forging treatment is performed during the final forging process, in which the elongation deformation is 50% and the final forging temperature is 790℃.

[0057] S3. The box-type resistance furnace is heated to 900℃, and the finished forging billet is placed in the box-type resistance furnace and subjected to solution heat treatment at 900℃. After the finished forging billet is held at this temperature for 3 hours, it is removed from the furnace and transferred to a circulating cooling water tank for water cooling to obtain the first finished forging. Subsequently, the first finished forging is heated to 450℃ in the box-type resistance furnace and held at this temperature for 6 hours before being removed from the furnace. Then, it is air-cooled to complete the aging heat treatment, finally obtaining the second finished forging. The residual heat of the second finished forging is used to straighten it to ensure that its curvature is ≤3mm / m. Finally, the straightened second finished forging is milled using a heavy-duty gantry milling machine to obtain the finished titanium alloy forging.

[0058] Specifically, the milling standard for the second finished forging after straightening is as follows: the minimum milling amount on one side in the thickness direction is 6.5 mm, and the minimum milling amount on one side in the width direction is 11 mm, so as to ensure that 100% of the surface defects of the second finished forging after straightening are removed. Specifically, the dimensions of the finished titanium alloy forging after machining are as follows: mm, surface roughness Ra≤1.6μm.

[0059] To determine the quality of the finished titanium alloy forgings, this embodiment utilizes a handheld ultrasonic testing device to perform 100% ultrasonic testing. The testing results show that the finished titanium alloy forgings ultimately meet the AA grade requirements of GB / T 5193. Figures 2-3 The diagram shown is a microstructure of the large-size Ti6Al6V2Sn titanium alloy forging with dimensions of 355×420×3500mm obtained in this embodiment.

[0060] Example 2 The preparation method in this embodiment is the same as that in Example 1, except that: In S1, the actual weight of the Ti6Al6V2Sn ingot obtained is 2970 kg, and the phase transformation point (T) is... β The temperature is 942℃.

[0061] In S2, the specific process parameters for the upsetting and drawing forging are as follows: the pretreated ingot is heated to 825°C and held for 100 minutes; then, within 180 minutes, the pretreated ingot is heated to 1142°C and held for 300 minutes before being taken out of the furnace; then, the pretreated ingot is upset and drawn once using a 45 / 50MN fast forging unit and returned to the furnace. At this time, the furnace holding temperature is 1082°C and the holding time is 30 minutes. Specifically, the total deformation during the upsetting and drawing forging process is 85%, and the final forging temperature is 903℃.

[0062] In S2, the intermediate forging process sequentially includes one intermediate high-temperature upsetting forging, four intermediate low-temperature upsetting forging, and post-forging treatment.

[0063] Specifically, in the intermediate high-temperature upsetting and drawing forging, the primary forging billet is heated to 850°C and held for 60 minutes; then, within 90 minutes, the primary forging billet is heated to 1062°C and held for 450 minutes before being taken out of the furnace; the holding temperature for the return to the furnace after one upsetting and drawing is 1072°C and the holding time is 30 minutes. In the first intermediate low-temperature upsetting and drawing forging, the first intermediate forging billet is heated to 800°C and held for 90 minutes. Then, within 60 minutes, the first intermediate forging billet is heated to 912°C and held for 600 minutes before being taken out of the furnace. The holding temperature after one upsetting and one drawing is 887°C and the holding time is 120 minutes. Before the second intermediate low-temperature upsetting and drawing forging, the second intermediate forging billet needs to be heated to 825°C and held for 60 minutes; then, within 210 minutes, the second intermediate forging billet is heated to 912°C and held for 600 minutes before being taken out of the furnace. In the second intermediate low-temperature upsetting and drawing forging, the second intermediate billet is forged by axial upsetting and side drawing, and then put back into the furnace for heat preservation (the heat preservation temperature is 912℃ and the heat preservation time is 125min). After that, it is taken out of the furnace for side upsetting and axial drawing forging to obtain the third intermediate forging billet. In the third intermediate low-temperature upsetting and drawing forging, the third intermediate forging billet needs to be heated to 825°C and held for 60 minutes. Then, within 210 minutes, the third intermediate forging billet is heated to 912°C and held for 600 minutes before being taken out of the furnace. The third intermediate forging billet is then side-upset and drawn by a shaft and then returned to the furnace for holding (holding temperature is 912°C and holding time is 180 minutes). After that, it is taken out of the furnace for side upsetting and shaft drawing forging, and then air-cooled and surface-polished in sequence to obtain the fourth intermediate forging billet. In the fourth intermediate low-temperature upsetting and drawing forging, the fourth intermediate forging billet is heated to 850°C and held for 60 minutes. Then, within 60 minutes, the fourth intermediate forging billet is heated to 862°C and held for 240 minutes before being taken out of the furnace. The fourth forging billet is then upset and drawn once using a 45 / 50MN fast forging unit and then returned to the furnace for holding (holding temperature is 862°C and holding time is 60 minutes). It is then upset and drawn again and squared to a size of □550×2070mm. After that, it is air-cooled and 100% surface-polished to finally obtain the intermediate forging billet.

[0064] Specifically, the post-forging process parameters are as follows: the intermediate forging billet is heated to 850°C and held for 120 minutes; then, within 120 minutes, the intermediate forging billet is heated to 912°C and held for 390 minutes before being removed from the furnace; and then, a 45 / 50MN fast forging mill is used to elongate the intermediate forging billet, so that the billet size is elongated from □550×2070mm to [the desired value]. mm, to obtain the finished forging billet.

[0065] More specifically, in S2, the total deformation during the intermediate high-temperature upsetting and drawing forging process is 80%, and the final forging temperature is 785℃; the total deformation during the first intermediate low-temperature upsetting and drawing forging process is 70%, and the final forging temperature is 739℃; the total deformation during the second intermediate low-temperature upsetting and drawing forging process is 71%, and the final forging temperature is 716℃; the total deformation during the third intermediate low-temperature upsetting and drawing forging process is 70%, and the final forging temperature is 733℃; the total deformation during the fourth intermediate low-temperature upsetting and drawing forging process is 75%, and the final forging temperature is 736℃; and the total deformation during the post-forging treatment process is 39.5%.

[0066] In S3, the solution heat treatment temperature is 850℃ and the holding time is 2.5h; in the aging heat treatment, the temperature of the box-type resistance furnace is 525℃ and the holding time is 7h. The final dimensions of the titanium alloy forging product obtained in this embodiment are as follows: mm, such as Figures 4-5 The diagram shown is a microstructure of the titanium alloy forging.

[0067] Example 3 The preparation method in this embodiment is the same as that in Example 1, except that: In S1, 0A grade sponge titanium, AlV65 alloy, aluminum briquettes, titanium-tin alloy, titanium-iron alloy and titanium-copper alloy are weighed out respectively, and the raw materials are mixed and pressed into consumable electrodes. After the consumable electrodes are subjected to three VAR melting processes, Ti6Al6V2Sn ingots are obtained.

[0068] Specifically, the nominal weight of the Ti6Al6V2Sn ingot is 4500 kg, the actual weight is 4412 kg, and the phase transformation point is 937℃.

[0069] In S2, the specific process parameters for the upsetting and drawing forging are as follows: the pretreated ingot is heated to 800°C and held for 60 minutes; then, within 240 minutes, the pretreated ingot is heated to 1187°C and held for 550 minutes before being taken out of the furnace; then, the pretreated ingot is upset and drawn once using a 45 / 50MN fast forging unit and returned to the furnace. At this time, the furnace heating temperature is 1137°C and the holding time is 90 minutes. Specifically, the total deformation during the upsetting and drawing forging process is 80%, and the final forging temperature is 865℃.

[0070] In S2, the intermediate forging process sequentially includes one intermediate high-temperature upsetting forging, five intermediate low-temperature upsetting forging, and post-forging treatment.

[0071] Specifically, in the intermediate high-temperature upsetting and drawing forging, the primary forging billet is heated to 825°C and held for 120 minutes; then, within 210 minutes, the primary forging billet is heated to 1137°C and held for 700 minutes before being taken out of the furnace; the holding temperature for the return to the furnace after one upsetting and drawing is 1117°C and the holding time is 120 minutes. In the first and second low-temperature upsetting and drawing forging processes, the corresponding forging billets obtained in the previous process are heated to 850°C and held for 150 minutes. Then, within 150 minutes, the corresponding forging billets obtained in the previous process are heated to 887°C and held for 240 minutes before being taken out of the furnace. After one upsetting and one drawing, the billets are returned to the furnace for holding at 907°C for 60 minutes. Before the third intermediate low-temperature upsetting and drawing forging, the third intermediate forging billet obtained from the second intermediate low-temperature upsetting and drawing forging needs to be heated to 850°C and held for 150 minutes; then, within 150 minutes, the third intermediate forging billet is heated to 887°C and held for 240 minutes before being taken out of the furnace. In the third upsetting and drawing forging process, the third intermediate billet is forged by side upsetting and drawing on a shaft and then placed back into the furnace for heat preservation (the heat preservation temperature is 887°C and the heat preservation time is 60 min); then it is taken out of the furnace for side upsetting and shaft drawing forging to obtain the fourth intermediate forging billet. In the fourth upsetting and drawing forging process, the fourth intermediate forging billet is heated to 800°C and held for 150 minutes. Then, within 210 minutes, the fourth intermediate forging billet is heated to 907°C and held for 920 minutes before being taken out of the furnace. After being side-upset and drawn by shaft, it is returned to the furnace for holding (holding temperature is 907°C, holding time is 180 minutes). Then, it is taken out of the furnace for side upsetting and shaft drawing forging, followed by air cooling and surface grinding to obtain the fifth intermediate forging billet. In the fifth upsetting and drawing forging process, the fifth intermediate forging billet is heated to 850°C and held for 150 minutes. Then, within 70 minutes, the fifth intermediate forging billet is heated to 867°C and held for 250 minutes before being removed from the furnace. The fifth forging billet is then upset and drawn once using a 45 / 50MN fast forging unit and then returned to the furnace for holding (holding temperature is 867°C, holding time is 90 minutes). It is then upset and drawn again, and squared to a size of □550×3110mm. After air cooling and 100% surface grinding, the intermediate forging billet is finally obtained.

[0072] More specifically, in S2, the total deformation during the intermediate high-temperature upsetting and drawing forging process is 90%, and the final forging temperature is 813℃; the total deformation during the first intermediate low-temperature upsetting and drawing forging process is 75.5%, and the final forging temperature is 730℃; the total deformation during the second intermediate low-temperature upsetting and drawing forging process is 75.5%, and the final forging temperature is 716℃; the total deformation during the third intermediate low-temperature upsetting and drawing forging process is 75%, and the final forging temperature is 733℃; the total deformation during the fourth intermediate low-temperature upsetting and drawing forging process is 80%, and the final forging temperature is 729℃; the total deformation during the fifth intermediate low-temperature upsetting and drawing forging process is 76.5%, and the final forging temperature is 742℃; and the total deformation during the post-forging treatment process is 30%.

[0073] Specifically, the post-forging process parameters are as follows: the intermediate forging billet is heated to 825°C and held for 60 minutes; then, within 180 minutes, the intermediate forging billet is heated to 887°C and held for 570 minutes before being removed from the furnace. A 45 / 50MN fast forging mill is then used to elongate the intermediate forging billet, increasing its dimensions from □550×3110 mm to [missing value]. mm, to obtain the finished forging billet.

[0074] In S3, the solution heat treatment temperature is 875℃ and the holding time is 2h; in the aging heat treatment, the temperature of the box-type resistance furnace is 600℃ and the holding time is 8h. The final dimensions of the titanium alloy forging product obtained in this embodiment are as follows: mm, such as Figures 6-7 The diagram shown is a microstructure of the finished titanium alloy forging.

[0075] This specification further provides microstructure diagrams, room temperature mechanical property test results, and ultrasonic test results of the segregation-free, high-strength, large-size Ti6Al6V2Sn titanium alloy forgings prepared in Examples 1-3, specifically: Depend on Figure 2 , Figure 4 , Figure 6As can be seen from the low-magnification morphology and microstructure images of the titanium alloy forgings prepared in Examples 1-3, the low-magnification microstructure of the titanium alloy forgings prepared in Examples 1-3 is free of cracks, pores, metallic or non-metallic inclusions, and there are no segregated bright blocks or bright streaks or other defects visible to the naked eye.

[0076] Figure 3 , Figure 5 , Figure 7 The microstructure shown is the structure formed by processing the α+β two-phase region of the titanium alloy forging. As can be observed from the microstructure diagram, there are no complete original β grain boundaries in the titanium alloy forgings prepared in Examples 1-3. The microstructure types are equiaxed α and elongated α, and there is no continuous network α.

[0077] Table 1 shows the room temperature mechanical properties and ultrasonic testing results of the titanium alloy forgings prepared in Examples 1-3, as detailed below: Table 1 Mechanical properties and ultrasonic test results of titanium alloy forgings In Table 1, L represents the sampling direction as longitudinal, T represents the sampling direction as transverse, and STA represents the heat treatment state of the forging as solution-treated and aged. As can be seen from the data in Table 1, the mechanical properties of the titanium alloy forgings obtained in Examples 1 to 3 are uniformly distributed and have significant allowances, and the ultrasonic testing levels all meet the technical standard requirements.

[0078] Comparative Example 1 The difference between the preparation method in this comparative example and that in Example 1 is: The intermediate forging in this comparative example includes a first intermediate high-temperature upsetting and a second intermediate low-temperature upsetting, and no reversing upsetting is set in the second intermediate low-temperature upsetting.

[0079] The total deformation during the first upsetting and drawing forging process is 86%, and the final forging temperature is 880℃; the total deformation during the intermediate high-temperature upsetting and drawing forging process is 87%, and the final forging temperature is 800℃; the total deformation during the first intermediate low-temperature upsetting and drawing forging process is 75%, and the final forging temperature is 722℃; the total deformation during the second intermediate low-temperature upsetting and drawing forging process is 75%, and the final forging temperature is 728℃.

[0080] The low-magnification microstructure and microstructure of the titanium alloy forgings obtained in this comparative example are shown in the following figures. Figures 8-9 As shown, from the low-magnification topography image (such as...) Figure 8 As can be seen, its low-magnification microstructure does not show cracks, pores, metallic or non-metallic inclusions, nor does it show segregation bright spots, bright streaks or other defects visible to the naked eye; Its high-magnification tissue map (e.g.) Figure 9Although the microstructure is formed by processing in the α+β two-phase region, the grains have been significantly broken and there are no complete original β grain boundaries, which can meet the basic requirements of the technical standards. However, there are still significant disadvantages. Specifically, the microstructure is dominated by elongated α phase, and the elongated α phase is obviously oriented, resulting in prominent anisotropy of the microstructure. At the same time, the α phase is not completely broken, which is not conducive to the uniformity of mechanical properties and the matching of strength and toughness of the forging. There is still considerable room for improvement.

[0081] In summary, the intermediate forging process described in this application, which employs increased heat treatment and reverse upsetting, can effectively improve the uniformity of the mechanical properties of the finished titanium alloy forgings, optimize their strength-toughness matching, and enhance their fatigue resistance and service stability.

[0082] Comparative Example 2 The difference between the preparation method in this comparative example and that in Example 2 is: In the Ti6Al6V2Sn ingot preparation stage, copper wire was used as the raw material for Cu element addition and iron nails were used as the raw material for Fe element addition to replace the titanium-copper alloy and titanium-iron alloy used in Example 2.

[0083] The microstructure of the titanium alloy forgings obtained in this comparative example is shown in the figure below. Figure 10 , Figure 11 As shown, the high-magnification microstructure of the titanium alloy forging is an α+β two-phase region. The original β grains are fully broken and there are no continuous grain boundaries α. The microstructure consists of transformed β matrix, equiaxed α phase and elongated α phase. However, the content of primary α phase in some areas is low, only 4.5%, which directly reflects the obvious segregation in its microstructure, which is not conducive to the uniformity control of the mechanical properties of the forging.

[0084] In summary, this application uses titanium-copper alloys and titanium-iron alloys to replace the copper and iron elements added separately in the traditional alloy preparation process, which has a significant effect on suppressing microstructure segregation.

[0085] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0086] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A high-strength, segregation-free Ti6Al6V2Sn titanium alloy forging, characterized in that, The Ti6Al6V2Sn titanium alloy forging has a thickness of 350~420mm, a width of 420~470mm, a length of 3200~4400mm, and a room temperature tensile strength ≥1035MPa, a specified plastic elongation strength ≥965MPa, and an elongation ≥12%.

2. A method for preparing a segregation-free, high-strength, high-specification Ti6Al6V2Sn titanium alloy forging according to claim 1, characterized in that, Includes the following steps: S1. Sponge titanium, titanium-copper alloy, aluminum-vanadium alloy, titanium-iron alloy, TiO2, titanium-tin alloy and aluminum are pressed into consumable electrodes. The consumable electrodes are then subjected to vacuum consumable arc melting, followed by trimming and machining to obtain Ti6Al6V2Sn ingots. S2. A coating is applied to the surface of the Ti6Al6V2Sn ingot to obtain a pretreated ingot. The pretreated ingot is then subjected to forging, intermediate forging and finished product forging in sequence to obtain a finished forged billet. S3. The finished forging billet is subjected to solution aging heat treatment, and then straightened and machined in sequence to finally obtain the finished titanium alloy forging.

3. The method for preparing a segregation-free, high-strength, high-specification Ti6Al6V2Sn titanium alloy forging according to claim 2, characterized in that, In S2, the initial forging includes a single-stage upsetting and drawing forging process. The upsetting and drawing forging steps include: first heating the pretreated ingot to 800℃~850℃ and holding it at that temperature for 60~150 minutes; then, within 120~240 minutes, heating the pretreated ingot to (T... β +150)℃~(T β The blank is heated to +250℃ and held for 120~550 minutes before the first forging. After forging, it is air-cooled and polished to obtain the primary forging blank.

4. The method for preparing a segregation-free, high-strength, high-specification Ti6Al6V2Sn titanium alloy forging according to claim 3, characterized in that, In S2, the initial forging temperature of the first forging is ≥900℃, and the final forging temperature is ≥850℃.

5. The method for preparing a segregation-free, high-strength, high-specification Ti6Al6V2Sn titanium alloy forging according to claim 2, characterized in that, In S2, the intermediate forging includes one-stage intermediate high-temperature upsetting forging, four to six-stage intermediate low-temperature upsetting forging, and post-forging treatment, wherein: The intermediate high-temperature upsetting forging step includes: heating the primary forging billet to 800℃~850℃ and holding it at that temperature for 60~120 minutes; then, within 90~210 minutes, heating the primary forging billet to (T... β +50)℃~(T β After being heated to +200℃ and held at that temperature for 180~700min, the second forging, air cooling, and grinding were carried out sequentially to obtain the second forging billet. The 4-6 heat-passing intermediate low-temperature upsetting and drawing forging processes all include a heating stage and a forging stage. The heating stage includes the following steps: heating the forging billet obtained in the previous step to 800℃~850℃ and holding it at that temperature for 60~150 minutes; then, heating the forging billet from the previous heat-passing process to (T) within 60~210 minutes. β -30)℃~(T β -80)℃ and hold at that temperature for 240~920min; the forging stage includes several reversing upsetting and drawing operations, and the forging billet is squared during the last intermediate low temperature forging process; after 4~6 intermediate low temperature upsetting and drawing forgings are completed, the third forging billet is obtained. The post-forging treatment steps include: sequentially air-cooling and grinding the third forging billet to obtain an intermediate forging billet.

6. The method for preparing a segregation-free, high-strength, high-specification Ti6Al6V2Sn titanium alloy forging according to claim 5, characterized in that, The initial forging temperature of the intermediate high-temperature upsetting forging is ≥800℃, and the final forging temperature is ≥750℃; the initial forging temperature of each heat in the intermediate low-temperature upsetting forging is ≥750℃, and the final forging temperature is ≥700℃.

7. The method for preparing a segregation-free, high-strength, high-specification Ti6Al6V2Sn titanium alloy forging according to claim 5, characterized in that, In S2, the finished product forging includes a final drawing forging, the steps of which include: heating the intermediate forging billet to 800℃~850℃ and holding it at that temperature for 60~120 minutes; subsequently, heating the intermediate forging billet to (T) within 60~180 minutes. β -30)℃~(T β After being heated to -80℃ and held at that temperature for 210~570 minutes, the billet is then subjected to drawing forging, straightening, and air cooling in sequence to obtain the finished forging billet.

8. The method for preparing a segregation-free, high-strength, high-specification Ti6Al6V2Sn titanium alloy forging according to claim 7, characterized in that, The total deformation during the initial forging process is 80% to 90%; the total deformation during the intermediate high-temperature upsetting forging process is 80% to 90%; the total deformation during each heat of the intermediate low-temperature upsetting forging process is 70% to 80%; and the total deformation during the finished product forging process is 30% to 50%.

9. The method for preparing a segregation-free, high-strength, high-specification Ti6Al6V2Sn titanium alloy forging according to claim 7, characterized in that, The initial forging temperature of the final drawing forging is ≥750℃, and the final forging temperature is ≥700℃.

10. The method for preparing a segregation-free, high-strength, high-specification Ti6Al6V2Sn titanium alloy forging according to claim 2, characterized in that, In S3, the solution heat treatment temperature is 850℃~900℃ and the holding time is 2~3h, and the aging heat treatment temperature is 450℃~600℃ and the holding time is 6~8h.

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