Extrusion method for complex cross-section titanium alloy profile

Abstract

This invention discloses an extrusion molding method for complex cross-section titanium alloy profiles, comprising the following steps: First, using sponge titanium, industrial pure aluminum, Al-V master alloy, and titanium dioxide as raw materials, the raw materials are proportioned according to the nominal composition of TC4 titanium alloy, Ti-6Al-4V, to prepare TC4 ingots; second, preparing machined billets; third, heating the machined billets to 1050~1150℃, while simultaneously preheating the extrusion cylinder, extrusion die, and extrusion pad, and lubricating the extrusion die; fourth, rapidly transferring the heated billet into the extrusion cylinder of the extrusion press for extrusion at a speed of 100-240 mm / s; fifth, pre-cutting the extruded TC4 profile, followed by hot tension straightening at a straightening temperature ≤700℃; sixth, annealing at a temperature of 710±10℃ for a holding time of 90-100 min, followed by air cooling; and finally, surface treatment to obtain TC4 titanium alloy complex cross-section profiles. The extrusion molding method for complex cross-section titanium alloy profiles of the present invention optimizes the extrusion process parameters, straightening process and heat treatment process, so that the prepared complex cross-section titanium alloy profiles can meet the standard requirements for dimensions, straightness, torsion, mechanical properties, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy material processing, and particularly to an extrusion forming method for titanium alloy profiles with complex cross-sections. Background Art

[0002] The extrusion method is the only and efficient process for preparing titanium alloy profiles with complex cross-sections that have excellent mechanical properties, high dimensional accuracy, and good surface quality. It can produce both thick-walled profiles and thin-walled profiles. Various titanium alloy profiles with complex cross-sections have been widely used as general components on military aircraft. The extrudable alloy grades include both medium-strength near-α and α+β titanium alloys and high-strength β titanium alloys. The more abundant the specifications of mature titanium alloy profile products, the wider the range of options available for the design and final production of new aircraft models. Titanium alloy profiles can be more widely used as general components in the field of industrial manufacturing, giving full play to the weight-saving advantage of titanium alloys and shortening the design and final production cycle of new aircraft models. Abroad, extruded titanium alloy profiles are basically purchased directly as off-the-shelf products. Judging from the current application requirements in various industrial fields in China, titanium alloy profiles have broad application prospects in the country.

[0003] The cross-sectional shape of titanium alloy profiles is becoming increasingly complex, the cross-sectional shape and position are more compact, and one-piece forming is required. These characteristics greatly increase the overall processing difficulty, especially in extrusion forming. In the prior art, there are already extrusion preparation methods for titanium alloy profiles. For example, a method for extruding TA15 titanium alloy T profiles (application number CN201911209811.1) discloses the main process parameters including melting, forging, extrusion, etc. Through this technical solution, the related technical problems of the existing extrusion preparation of TA15 titanium alloy T profiles can be solved, but it cannot solve the extrusion preparation of TC4 titanium alloy profiles with complex cross-sectional shapes and cannot meet the requirements of technical difficulty,成材率 (成材率 is not clear in the context, please check and provide the correct word), and production cost control.

[0004] With the development of applications, the cross-sectional shape of titanium alloy profiles tends to be more complex cross-sections, such as the "king" shape. The characteristics of the cross-sectional shape of this profile are quite different from the cross-sectional shapes of the profiles prepared in the past, and it has characteristics such as a complex cross-sectional shape, a long outer contour line, and a large linear density. In addition to the room-temperature mechanical properties, the material property indicators also require higher compressive yield strength and bearing stress. The existing extrusion methods for titanium alloy profiles are difficult to meet the standard requirements of dimensions, flatness, twist, performance, etc. for complex cross-sectional shapes.

[0005] In view of this, it is necessary to provide a new process to solve the above technical problems. Summary of the Invention

[0006] The purpose of this invention is to provide an extrusion molding method for titanium alloy profiles with complex cross-sections. By optimizing the extrusion process parameters, straightening process, and heat treatment process, the prepared titanium alloy profiles with complex cross-sections can meet the standard requirements for dimensions, straightness, torsion, and mechanical properties.

[0007] The technical solution of this invention is:

[0008] An extrusion forming method for titanium alloy profiles with complex cross-sections includes the following steps:

[0009] Step S1: Using sponge titanium, industrial pure aluminum, Al-V master alloy, and titanium dioxide as raw materials, the raw materials are proportioned according to the nominal composition of TC4 titanium alloy Ti-6Al-4V to prepare TC4 ingots.

[0010] Step S2: Spray the surface of the ingot with forging glass protective lubricant and let it dry naturally. Heat it to 150°C above the β phase transformation temperature and hold it for 150-180 minutes. Then, perform four-stage forging on a hydraulic press to form a billet. After final forging, machine it into a polished billet. The cutting length is determined according to the extrusion ratio.

[0011] Step S3: After wiping the machined billet clean, spray it with glass protective lubricant for extrusion, heat the machined billet to 1050~1150℃, and at the same time preheat the extrusion cylinder, extrusion die and extrusion pad, and lubricate the extrusion die.

[0012] Step S4: The heated billet is quickly transferred into the extrusion cylinder of the extrusion press for extrusion. The extrusion speed is 100-240 mm / s. After the TC4 profile is extruded, it is pre-cut and then subjected to hot tension straightening. The straightening temperature is ≤700℃.

[0013] Step S5: Anneal the straightened profile at a temperature of 710±10℃ for 90-100 minutes, followed by air cooling.

[0014] Step S6 involves precision straightening followed by surface treatment to obtain a TC4 titanium alloy complex cross-section profile.

[0015] Furthermore, in step S3, the machined billet is heated using a stepped heating method. The first stage heating temperature is 1000-1050℃, held for 2-3 hours, and the second stage heating temperature is increased to 1120-1150℃, held for 1-2 hours. The temperature of the heated billet shows a gradient along the cross-section, with the outer edge temperature being higher than the core temperature.

[0016] Furthermore, in step S3, the lubricant used for the extrusion die includes a graphite-based lubricant, which comprises the following components by weight percentage:

[0017] The composition consists of 60-70% high-purity microcrystalline graphite powder, 10-15% sodium-based bentonite, 10-15% silica sol, and the remainder is water.

[0018] Further, in step S3, the extrusion cylinder, extrusion die, and extrusion pad are preheated to 400-450°C, and the inner corner area of ​​the extrusion die cross section is lubricated with a graphite-based lubricant to form a 0.2-0.5 mm graphite-based coating on its surface.

[0019] Furthermore, in step S4, after the thermal tension straightening process, a room temperature pre-stretching process is also included:

[0020] After the profile is cooled to room temperature after thermal tension straightening, it is clamped on a high-tonnage tension straightening machine, a constant tensile load is applied and held for 60-120 minutes, so that the profile as a whole produces an elastic strain of 0.2%-0.35%.

[0021] Furthermore, in step S4, after room temperature pre-stretching, a multi-point micro-straightening process is also included:

[0022] Fabricate straightening rollers that match the cross-sectional shape of the profile, and arrange multiple straightening rollers along the length of the profile;

[0023] A laser scanner is used to detect the straightness and torsion of the entire length of the profile, generating a form and position error curve;

[0024] For specific bends or twists, the corresponding straightening rollers are controlled to perform a "reverse bending" action, applying a reverse bending moment to the local area where the bend occurs, causing a small amount of plastic deformation at the corresponding position.

[0025] Furthermore, in step S5, the annealing process includes a low-temperature stress-relief annealing process: the annealing temperature is 550±10℃, the holding time is 3.5-4.5h, the furnace is cooled to below 300℃, and then air-cooled.

[0026] Furthermore, in step S4, the extrusion process is an automatically controlled process:

[0027] Install high-precision pressure sensors on the extrusion bar hydraulic system or extrusion pad to monitor the extrusion force in real time;

[0028] A non-contact infrared thermometer is installed near the extrusion cylinder inlet to monitor the actual temperature of the billet end face in real time.

[0029] Establish a digital twin model of the extrusion process, and use the ideal extrusion pressure-displacement curve simulated by the digital twin model as a baseline, and set an upper and lower limit for allowable fluctuations;

[0030] During the extrusion process, the actual extrusion force curve is compared with the reference line in real time. If the measured extrusion force continuously exceeds the upper limit, it is determined that the metal fluidity has deteriorated or the temperature is too low. The control system slightly increases the extrusion speed to compensate for the temperature with deformation heat. If the measured extrusion force continuously falls below the lower limit, it is determined that the billet temperature is too high and there is a risk of overheating. The control system slightly reduces the extrusion speed.

[0031] Furthermore, the cross-sectional shape of the titanium alloy profile is a "king" shape.

[0032] Compared with the prior art, the extrusion forming method of the complex cross-section titanium alloy profile provided by the present invention has the following beneficial effects:

[0033] First, the extrusion forming method of the complex cross-section titanium alloy profile provided by the present invention, through the synergistic effect of the extrusion process, straightening process and heat treatment process, enables the prepared complex cross-section titanium alloy profile to meet the standard requirements such as dimensions, flatness, twist, mechanical properties, etc.

[0034] Second, the extrusion forming method of the complex cross-section titanium alloy profile provided by the present invention, by optimizing the extrusion process, straightening process and heat treatment process, can reduce the residual stress of the profile, prevent dimensional creep during long-term storage or processing, and is particularly suitable for aerospace precision structural parts with extremely high requirements for long-term dimensional stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0036] Figure 1 It is a cross-sectional schematic diagram of the titanium alloy profile in Embodiment 1 of the present invention;

[0037] Figure 2 It is a cross-sectional schematic diagram of the titanium alloy profile in Embodiment 2 of the present invention;

[0038] Figure 3 It is the metallographic diagram of the titanium alloy profiles in Embodiment 1 and Embodiment 5 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the following further explains the specific embodiments of the present invention.

[0040] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0041] Taking the extrusion forming method of titanium alloy profiles with a "king" - shaped complex cross - section as an example, the extrusion forming method of titanium alloy profiles with a complex cross - section is elaborated in detail. The cross - section of the profile is "king" - shaped, with characteristics such as a complex cross - section shape, a long outer contour line, and a large linear density. In addition to the mechanical properties at room temperature, the material performance index also requires a relatively high compressive yield strength and bearing stress.

[0042] Example 1

[0043] The structure of the titanium alloy profile with a complex cross - section in this example is as Figure 1 shown.

[0044] An extrusion forming method for titanium alloy profiles with a complex cross - section includes the following steps:

[0045] Step S1: Using sponge titanium, industrial pure aluminum, Al - V master alloy, and titanium dioxide as raw materials, each raw material is proportioned according to the nominal composition of TC4 titanium alloy Ti - 6Al - 4V. A self - consumable electrode block of TC4 titanium alloy is prepared by an oil press, and a TC4 ingot is obtained through 2 - time melting in a VAR furnace, and the vacuum degree before melting and the vacuum degree in the stable stage of the last melting meet the index requirements.

[0046] Step S2: Spray a glass protective lubricant for forging on the surface of the ingot and let it dry naturally. Heat it in a box - type resistance furnace to 150℃ above the β - phase transformation temperature, keep it warm for 180 min, and perform four - pass forging on an oil press to obtain a bar blank with a diameter of Φ370×Lmm. The blooming temperature is 50℃ - 60℃ above the β - phase transformation point, the intermediate forging temperature is 60 - 70℃ above the β - phase transformation point, the round - off temperature is 50 - 60℃ below the phase transformation point, keep it warm for 180 min, and after final forging, machine - process it into a turned - up bar blank. The cutting length is determined according to the extrusion ratio, and the extrusion ratio λ = 12 - 15.

[0047] Hot - working in the β - phase region can ensure plasticity and reduce the deformation ability.

[0048] Step S3: After wiping the turned - up bar blank clean, spray a glass protective lubricant for extrusion, heat it to 1050 - 1150℃ using an industrial frequency induction furnace, and at the same time pre - heat the extrusion cylinder, extrusion die, and extrusion pad to 450℃, and use a lubricant to lubricate the extrusion die.

[0049] When heating the billet in a power frequency induction furnace, the heating coils are evenly arranged along the length of the billet, and the billet is heated to 1050~1150℃ in one go. The actual temperature at both ends of the billet is monitored in real time by an infrared thermometer and fed back to the induction furnace control system to ensure that the temperature remains stable within the target range. The entire heating process is carried out under argon protection to prevent excessive oxidation.

[0050] The lubricant used to lubricate the extrusion die is a glass lubricant.

[0051] Step S4: Quickly transfer the heated billet into the extrusion cylinder of the extrusion press for extrusion. The extrusion speed is set to 150-240 mm / s, and the transfer time should be controlled to be as short as possible (<15s). After the TC4 profile is extruded, it is pre-cut and then subjected to constant tensile straightening on a tension straightener. The straightening temperature should not exceed 700℃, and the heating rate is controlled to be a gradient increase of 50℃ at intervals.

[0052] The extrusion speed of 150-240 mm / s can balance production efficiency and avoid surface cracks; the short billet transfer time can prevent excessive temperature drop of the billet, which would lead to insufficient filling.

[0053] In this embodiment, the straightening temperature is ≤700℃ (in the α+β phase region) to avoid excessive growth of β grains, and deformation is eliminated by utilizing high-temperature plasticity. The thermal tension straightening stretch is 0.5-1.2%, which can effectively eliminate longitudinal bending without causing excessive plastic deformation.

[0054] Step S5: Anneal the straightened profile at a temperature of 710±10℃ for 90-100 minutes, followed by air cooling.

[0055] This annealing process effectively eliminates stress, stabilizes the microstructure, and achieves an optimal balance between strength and plasticity.

[0056] Step S6: After annealing, check the straightness and torsion, then perform fine straightening on a tension straightening machine without setting a stretch. The surface of the finely straightened profile is then treated to obtain a TC4 titanium alloy complex section profile.

[0057] Example 2

[0058] The structure of the complex cross-section titanium alloy profile in this embodiment is as follows: Figure 2 As shown.

[0059] An extrusion forming method for titanium alloy profiles with complex cross-sections includes the following steps:

[0060] Step S1: Using sponge titanium, industrial pure aluminum, Al-V master alloy and titanium dioxide as raw materials, each raw material is proportioned according to the nominal composition of TC4 titanium alloy Ti-6Al-4V. TC4 titanium alloy consumable electrode blocks are prepared by hydraulic press and TC4 ingots are obtained by two meltings in VAR furnace. The vacuum degree before melting and the vacuum degree during the stabilization stage of the last melting meet the index requirements.

[0061] Step S2: Spray the surface of the ingot with forging glass protective lubricant and let it dry naturally. Heat it in a box-type resistance furnace to 150°C above the β phase transformation temperature and hold for 180 minutes. Perform four-stage forging on a hydraulic press to form a Φ370×Lmm billet. The initial forging temperature is 50°C~60°C above the β phase transformation point, the intermediate forging temperature is 60~70°C above the β phase transformation point, the rounding temperature is 50°C below the phase transformation point, and the holding time is 150 minutes. After final forging, machine it into a polished billet. The cutting length is determined according to the extrusion ratio.

[0062] Step S3: After wiping the machined billet clean, spray it with glass protective lubricant for extrusion, heat it to 1100-1120℃ using an electric resistance furnace, and at the same time preheat the extrusion cylinder, extrusion die, and extrusion pad to 400℃, and lubricate the extrusion die with lubricant.

[0063] Step S4: Quickly transfer the heated billet into the extrusion cylinder of the extrusion press for extrusion. The extrusion speed is set to 200-240 mm / s, and the transfer time should be controlled to be as short as possible. After the TC4 profile is extruded, it is pre-cut and then subjected to constant tensile straightening on a tension straightener. The straightening temperature should not exceed 700℃, and the heating rate is controlled to be a gradient increase of 50℃ at intervals.

[0064] Step S5: Anneal the straightened profile at a temperature of 710±10℃ for 90-100 minutes, followed by air cooling.

[0065] Step S6: After annealing, check the straightness and torsion, then perform fine straightening on a tension straightening machine without setting a stretch. The surface of the finely straightened profile is then treated to obtain a TC4 titanium alloy complex section profile.

[0066] The TC4 titanium alloy complex section profiles prepared in Examples 1-2 meet the standard requirements for dimensional accuracy, straightness, and torsion; their room temperature tensile properties, compressive properties, and load-bearing stress also meet the standard requirements. The performance parameters of Examples 1-2 are shown in Table 1.

[0067] Table 1: Properties of TC4 titanium alloy complex section profiles prepared in Examples 1-2

[0068] Tensile strength (MPa) A Z Compressive yield strength (MPa) Support fracture strength (MPa) Support yield strength (MPa) Example 1 977 16% 29% 940 1656 1360 Example 2 979 18% 28% 945 1662 1383

[0069] Example 3: Optimization of the extrusion process

[0070] The structure of the complex cross-section titanium alloy profile in this embodiment is the same as in Embodiment 1. A method for extruding a complex cross-section titanium alloy profile includes the following steps:

[0071] Step S1: Using sponge titanium, industrial pure aluminum, Al-V master alloy and titanium dioxide as raw materials, each raw material is proportioned according to the nominal composition of TC4 titanium alloy Ti-6Al-4V. TC4 titanium alloy consumable electrode blocks are prepared by hydraulic press and TC4 ingots are obtained by two meltings in VAR furnace. The vacuum degree before melting and the vacuum degree during the stabilization stage of the last melting meet the index requirements.

[0072] Step S2: Spray the surface of the ingot with forging glass protective lubricant and let it dry naturally. Heat it in a box-type resistance furnace to 150°C above the β phase transformation temperature and hold for 180 minutes. Perform four-stage forging on a hydraulic press to form a Φ370×Lmm billet. The initial forging temperature is 50°C~60°C above the β phase transformation point, the intermediate forging temperature is 60~70°C above the β phase transformation point, the rounding temperature is 50~60°C below the phase transformation point, and the holding time is 180 minutes. After final forging, machine it into a polished billet. The cutting length is determined according to the extrusion ratio.

[0073] Step S3: After cleaning the machined billet, spray it with glass protective lubricant for extrusion, heat it to 1080-1150℃ using an electric resistance furnace, and at the same time preheat the extrusion cylinder, extrusion die, and extrusion pad to 450℃, and lubricate the extrusion tools with lubricant.

[0074] When heating the billet in a power frequency induction furnace, a stepped heating method is adopted. The first stage heating temperature is 1000-1050℃, held for 2 hours, and the second stage heating temperature is increased to 1120-1150℃, held for 1 hour. After heating, the billet temperature exhibits a gradient along the cross-section, with the outer edge temperature higher than the core temperature. The actual temperature at both ends of the billet is monitored in real time using an infrared thermometer, and feedback is sent to the induction furnace control system to ensure that the temperature remains stable within the target range. The entire heating process is carried out under argon protection to prevent excessive oxidation.

[0075] Under conventional heating conditions, the flow velocity of metal varies significantly across different parts of the mold cross-section. The flow is rapid in the center and thick-walled areas, while the flow is slow at the edges, thin walls, and inner corners due to high frictional resistance and rapid cooling. This results in a "tongue-shaped" flow pattern in the profile, causing insufficient filling and inconsistent lengths of the ribs, and generating significant lateral tensile stress internally. This embodiment employs a gradient heating method, which solves the problem of uniform metal flow.

[0076] Through finite element simulation, the area on the die where metal flow is most difficult is determined to be the inner corner area of the "king" - shaped cross - section. Therefore, when lubricating the extrusion die in this embodiment, a slender spray gun is used to spray a layer of graphite - based lubricant with a thickness of 0.2 - 0.5 mm on the die hole surface in the inner corner area, and glass - based lubricant is applied to other areas of the die according to the conventional method. The graphite - based lubricant includes the following components by weight percentage:

[0077] 65% high - purity microcrystalline graphite powder, 12% sodium - bentonite, 10% silica sol, and the balance is water. This lubricant can form a stable, continuous lubricating film with an extremely low friction coefficient at high temperatures.

[0078] Step S4: Rapidly transfer the heated billet into the extrusion cylinder of the extruder for extrusion. The transfer time should be controlled as short as possible, and the extrusion speed is set at 150 - 240 mm / s. After the extruded TC4 profile is pre - cut, it is subjected to hot tension straightening with a constant tensile amount on a tension straightening machine. The straightening temperature should not exceed 700°C, and the heating rate is controlled to increase the temperature at a gradient of 50°C intervals;

[0079] Step S5: Anneal the straightened profile. The annealing temperature is 710 ± 10°C, the holding time is 90 - 100 min, and it is air - cooled;

[0080] Step S6: After annealing, check the flatness and twist, and then perform fine straightening on the tension straightening machine without setting a tensile amount. After the surface of the finely - straightened profile is treated, a TC4 titanium alloy complex - cross - section profile is obtained.

[0081] Compared with Embodiment 1 and Embodiment 2, in this embodiment, through gradient heating of the billet, metal flow can be promoted, and local lubrication can reduce resistance. The two work together to ensure that the flow rates of each part of the metal tend to be consistent when filling the die. This makes the lengths of each rib of the extruded "king" - shaped profile flush, the cross - section profile clear, and at the same time significantly reduces the internal stress generated by uneven flow.

[0082] Embodiment 4: Optimize the straightening process

[0083] Based on Embodiment 3, this embodiment optimizes the straightening process in Step S4. Specifically, the straightening process includes: hot tension straightening process, room - temperature pre - stretching process, and multi - point micro - straightening process. Among them, the hot tension straightening process is the same as that in Embodiment 3;

[0084] The room temperature pre-stretching process involves cooling the thermally tension-straightened profile to room temperature, clamping it in a high-tonnage tension straightener, applying a constant tensile load, and holding it for 60-120 minutes. This induces an elastic strain of 0.2%-0.35% throughout the profile. The corresponding tensile stress is approximately 20%-35% of the material's yield strength (Rp0.2) (approximately 160-280 MPa for TC4). This process, through a creep mechanism, relaxes and homogenizes the unevenly distributed residual stress (especially peak stress) within the profile.

[0085] The multi-point micro-correction process involves:

[0086] Fabricate straightening rollers that match the cross-sectional shape of the profile, and arrange multiple straightening rollers along the length of the profile;

[0087] A laser scanner is used to detect the straightness and torsion of the entire length of the profile, generating a form and position error curve;

[0088] For specific bends or twists, the corresponding straightening rollers are controlled to perform a "reverse bending" action, applying a reverse bending moment to the local area where the bend occurs, causing a small amount of plastic deformation at the corresponding position.

[0089] The multi-point micro-correction process does not set an overall stretching amount; it only performs "surgical" precise correction on the unqualified local areas.

[0090] In this embodiment, the straightening process synergistically controls both macroscopic and microscopic residual stress. Room temperature pre-stretching homogenizes the overall stress level, while multi-point micro-straightening precisely eliminates local deformation, ultimately yielding a profile with extremely high dimensional stability, laying the foundation for subsequent precision machining.

[0091] Example 5: Optimization of the heat treatment process

[0092] This embodiment optimizes the heat treatment process in step S5 based on embodiment 4.

[0093] Conventional annealing (700°C, as in Example 1) is primarily intended to achieve the target mechanical properties through recrystallization and microstructure adjustment, but it is not thorough enough for eliminating the micro-stress introduced by straightening (especially multi-point micro-straightening).

[0094] Therefore, in this embodiment, a low-temperature stress-relief annealing process is added after the conventional annealing process. The stress-relief annealing regime is as follows: annealing temperature is 550±10℃, holding time is 4h, furnace cooling is carried out to below 300℃, and then air cooling is performed.

[0095] This temperature is lower than the recrystallization temperature of the TC4 alloy and will not significantly change its microstructure and mechanical properties. However, when held at this temperature for a long time, the atomic diffusion ability is enhanced, which is sufficient to fully release the elastic strain (i.e., residual stress) within the microscopic region through the recovery mechanism. The slow furnace cooling process is to prevent the generation of new thermal stress due to rapid cooling.

[0096] The dimensional accuracy, flatness, and twist of the complex-section profiles of TC4 titanium alloy prepared in Examples 3 - 5 meet the standard requirements; the tensile properties, compressive properties, and bearing stress at room temperature meet the standard requirements.

[0097] Compared with Examples 1 - 2, Examples 3 - 5 further control the residual stress of the profiles, prevent dimensional creep during long-term storage or processing, and optimize the uniformity of the flow of each rib of the "king" - shaped cross-section, which is particularly suitable for aerospace precision structural parts with extremely high requirements for long-term dimensional stability.

[0098] Compare the properties of the complex-section titanium alloy profiles prepared in Example 5 with those in Example 1. The methods and results are as follows:

[0099] 1. Residual stress: The surface residual stress was measured by X-ray diffraction method. The stress value of the product in Example 5 was reduced by more than 60% compared with that in Example 1.

[0100] 2. Long-term dimensional stability: After placing the profiles of Example 5 and Example 1 for 6 months and measuring, the change in flatness of the profile in Example 5 < 0.05 mm / m, while the change in flatness of the profile in Example 1 was 0.1 - 0.15 mm / m.

[0101] 3. Cross-section tissue uniformity: Observed under a metallurgical microscope (as Figure 3 shown), compared with Example 1, the grain size at each rib of the profile in Example 5 was more uniform, with a difference within 1 grade.

[0102] In the present invention, in order to improve the high consistency and stability of product quality and increase the成材率 (成材率 is not clear in Chinese, assuming it means "yield rate"), the extrusion process is designed as an automatic control process. The control method is as follows:

[0103] Install a high-precision pressure sensor on the extrusion rod hydraulic system or the extrusion pad to monitor the extrusion pressure in real time;

[0104] Install a non-contact infrared thermometer near the entrance of the extrusion cylinder to monitor the actual temperature of the billet end face in real time;

[0105] Establish a digital twin model of the extrusion process, and use the ideal extrusion pressure - displacement curve simulated by the digital twin model as the reference line, and set upper and lower limits for allowable fluctuations;

[0106] During the extrusion process, the actual extrusion force curve is compared with the reference line in real time. If the measured extrusion force continuously exceeds the upper limit, it is judged that the metal fluidity becomes poor or the temperature is too low, and the control system slightly increases the extrusion speed to compensate for the temperature with the deformation heat. If the measured extrusion force continuously falls below the lower limit, it is judged that the billet temperature is too high and there is a risk of overheating, and the control system slightly reduces the extrusion speed.

[0107] Through the real-time online monitoring and feedback control process, the standard deviation of the performance fluctuations of the profiles in the same batch is reduced by about 30%. Due to more precise process control, defects such as drawing cracks and insufficient filling are reduced, and the comprehensive成材率 is increased by about 5%.

[0108] The extrusion forming method of the complex-section titanium alloy profile of the present invention solves the forming and performance problems of the "king"-shaped complex-section TC4 profile through the synergistic effect of the extrusion process, the straightening process and the heat treatment process, and can be applied to the forming of other complex-section titanium alloy profiles.

[0109] The above has made a detailed description of the embodiments of the present invention, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations made to these embodiments without departing from the principle and spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for extruding titanium alloy profiles with complex cross-sections, characterized in that, Includes the following steps: Step S1: Using sponge titanium, industrial pure aluminum, Al-V master alloy, and titanium dioxide as raw materials, the raw materials are proportioned according to the nominal composition of TC4 titanium alloy Ti-6Al-4V to prepare TC4 ingots. Step S2: Spray the surface of the ingot with forging glass protective lubricant and let it dry naturally. Heat it to 150°C above the β phase transformation temperature and hold it for 150-180 minutes. Then, perform four-stage forging on a hydraulic press to form a billet. After final forging, machine it into a polished billet. The cutting length is determined according to the extrusion ratio. Step S3: After wiping the machined billet clean, spray it with glass protective lubricant for extrusion, heat the machined billet to 1050~1150℃, and at the same time preheat the extrusion cylinder, extrusion die and extrusion pad, and lubricate the extrusion die. Step S4: The heated billet is quickly transferred into the extrusion cylinder of the extrusion press for extrusion. The extrusion speed is 100-240 mm / s. After the TC4 profile is extruded, it is pre-cut and then subjected to hot tension straightening. The straightening temperature is ≤700℃. Step S5: Anneal the straightened profile at a temperature of 710±10℃ for 90-100 minutes, followed by air cooling. Step S6 involves precision straightening followed by surface treatment to obtain a TC4 titanium alloy complex cross-section profile.

2. The extrusion forming method for complex cross-section titanium alloy profiles according to claim 1, characterized in that, In step S3, the blank is heated in a stepped manner. The first stage heating temperature is 1000-1050℃ and held for 2-3 hours. The second stage heating temperature is raised to 1120-1150℃ and held for 1-2 hours.

3. The extrusion forming method for complex cross-section titanium alloy profiles according to claim 1, characterized in that, In step S3, the lubricant used for the extrusion die includes a graphite-based lubricant, which comprises the following components by weight percentage: The composition consists of 60-70% high-purity microcrystalline graphite powder, 10-15% sodium-based bentonite, 10-15% silica sol, and the remainder is water.

4. The extrusion forming method for complex cross-section titanium alloy profiles according to claim 3, characterized in that, In step S3, the extrusion cylinder, extrusion die and extrusion pad are preheated to 400-450°C, and the inner corner area of ​​the extrusion die cross section is lubricated with graphite-based lubricant to form a 0.2-0.5 mm graphite-based coating on its surface.

5. The extrusion forming method for complex cross-section titanium alloy profiles according to claim 1, characterized in that, In step S4, after the thermal tension straightening process, a room temperature pre-stretching process is also included: After the profile is cooled to room temperature after thermal tension straightening, it is clamped on a high-tonnage tension straightening machine, a constant tensile load is applied and held for 60-120 minutes, so that the profile as a whole produces an elastic strain of 0.2%-0.35%.

6. The extrusion forming method for complex cross-section titanium alloy profiles according to claim 5, characterized in that, In step S4, after room temperature pre-stretching, a multi-point micro-straightening process is also included: Fabricate straightening rollers that match the cross-sectional shape of the profile, and arrange multiple straightening rollers along the length of the profile; A laser scanner is used to detect the straightness and torsion of the entire length of the profile, generating a form and position error curve; For specific bends or twists, the corresponding straightening rollers are controlled to perform a "reverse bending" action, applying a reverse bending moment to the local area where the bend occurs, causing a small amount of plastic deformation at the corresponding position.

7. The extrusion forming method for complex cross-section titanium alloy profiles according to claim 1, characterized in that, In step S5, after the annealing treatment, a low-temperature stress-relief annealing process is also included: the annealing temperature is 550±10℃, the holding time is 3.5-4.5h, the furnace is cooled to below 300℃, and then air-cooled.

8. The extrusion forming method for complex cross-section titanium alloy profiles according to claim 1, characterized in that, In step S4, the extrusion process is an automatically controlled process: Install a high-precision pressure sensor on the extrusion rod hydraulic system or the extrusion pad to monitor the extrusion pressure in real time; Install a non-contact infrared thermometer near the entrance of the extrusion cylinder to monitor the actual temperature of the billet end face in real time; Establish a digital twin model of the extrusion process, and use the ideal extrusion pressure-displacement curve simulated by the digital twin model as the reference line, and set upper and lower limits for allowable fluctuations; During the extrusion process, compare the actual extrusion pressure curve with the reference line in real time. If the measured extrusion pressure continuously exceeds the upper limit, it is judged that the metal fluidity has deteriorated or the temperature is too low, and the control system slightly increases the extrusion speed to compensate for the temperature with deformation heat; if the measured extrusion pressure continuously falls below the lower limit, it is judged that the billet temperature is too high and there is a risk of overheating, and the control system slightly reduces the extrusion speed.

9. The extrusion forming method for complex cross-section titanium alloy profiles according to any one of claims 1-8, characterized in that, The cross-sectional shape of the titanium alloy profile is "king" shaped.

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