A low-cost short-process high-strength high-plasticity metastable beta titanium alloy sheet and a preparation method thereof

Abstract

The application discloses a low-cost short-process high-strength high-plasticity metastable beta titanium alloy sheet and a preparation method thereof, and relates to the technical field of titanium alloy material processing and heat treatment. The heat treatment method is as follows: a metastable beta titanium alloy cold-rolled sheet is subjected to short-time solid solution treatment at 30 DEG C to 60 DEG C below a beta transformation point, a small amount of primary alpha phase and cold-rolled beta substructure are reserved, then short-time low-temperature omega phase aging treatment is carried out, beta substructure and Zr / Sn are used to induce uniform nucleation of the omega phase and limit the coarsening of the omega phase, and a dual-phase structure containing nano omega phase is obtained. Through composition and process synergy, the application solves the problem of traditional omega phase embrittlement, and realizes excellent matching of high strength and high plasticity. The yield strength of the sheet obtained after heat treatment is greater than or equal to 1050 MPa, the elongation after fracture is greater than or equal to 30%, and the strength-plasticity product is greater than or equal to 30 GPa%. The method has simple procedures, low temperature and short time, low raw material and production cost, and compact process, and is suitable for industrialized batch production.

Description

Technical Field

[0001] This invention relates to a low-cost, short-process, high-strength, high-plasticity metastable β-titanium alloy thin plate and its preparation method, belonging to the field of titanium alloy material processing and heat treatment technology. Background Technology

[0002] Metastable β-titanium alloys have become important lightweight structural materials in aerospace, defense, and high-end medical implants due to their excellent specific strength, good hardenability, excellent cold forming properties, and biocompatibility. Among these applications, titanium alloy sheets are in high demand for aircraft skins, honeycomb sandwich panels, pressure-resistant shells, and medical bone plates. However, to ensure forming capabilities and service reliability, these applications typically require the sheets to possess both high strength and high ductility—a good strength-ductility balance.

[0003] Currently, the strengthening of metastable β-titanium alloys mainly relies on the dispersed fine secondary α-phase precipitated during solution treatment and aging heat treatment. This strengthening mechanism exhibits a significant strength-plasticity inversion: while the alloy achieves high strength through α-phase strengthening, its plasticity often decreases sharply. Taking a typical metastable β-alloy as an example, when the tensile strength is increased to above 1400 MPa, the elongation after fracture is usually less than 5%, and the strength-ductility product is less than 10 GPa·%. Although complex processes such as multi-stage aging and deformation heat treatment can improve the strength-plasticity match to some extent, they suffer from drawbacks such as lengthy processes, high energy consumption, and narrow process windows, making it difficult to meet the industrial production requirements of low cost and short processes. In addition, high-performance metastable β-titanium alloys typically contain high levels of expensive alloying elements to obtain sufficient β-phase stability and heat treatment strengthening potential, resulting in high raw material costs. The high material costs severely limit the large-scale application of metastable β-titanium alloys in industrial fields.

[0004] Therefore, there is an urgent need in this field to develop a technical solution that has controllable alloy costs, a short process flow, and can effectively achieve a synergistic match between high strength and high plasticity in metastable β-titanium alloy thin plates. Summary of the Invention

[0005] To address the shortcomings of related technologies, this invention provides a low-cost, short-process, high-strength, high-plasticity metastable β-titanium alloy thin plate and its preparation method. This invention, through the synergy of composition and process, prepares titanium alloy thin plates that combine high strength and high plasticity, and has the advantages of significantly shortening the heat treatment process and time, reducing production energy consumption, effectively inhibiting the growth and coarsening of the ω phase, avoiding plasticity deterioration, and solving the problem that the strength and plasticity of metastable β-titanium alloys cannot be synergistically improved.

[0006] One of the objectives of this invention is to provide a low-cost, short-process, high-strength, high-plasticity metastable β-titanium alloy sheet. The composition of the high-strength, high-plasticity metastable β-titanium alloy sheet, by mass percentage, includes: 2.8~6.0% Mo, 1.5~3.6% Cr, 0.8~1.6% Fe, 0~2.5% Zr, and 0~1.8% Sn, satisfying 0.5%≤Zr+Sn≤3.5%, with the balance being Ti and unavoidable impurities.

[0007] More preferably, the composition of the high-strength, high-plasticity metastable β-titanium alloy sheet includes, by mass percentage: 3.5-5.5% Mo, 1.5-2.8% Cr, 0.8-1.6% Fe, 0-2.0% Zr, and 0-1.2% Sn, and satisfies 1.2% ≤ Zr + Sn ≤ 2.3%, with the balance being Ti and unavoidable impurities.

[0008] Another objective of this invention is to provide a low-cost, short-process method for preparing high-strength, high-ductility, metastable β-titanium alloy thin plates, specifically comprising the following steps: (1) Batching and smelting: Weigh the high-strength, high-plasticity metastable β-titanium alloy thin plate raw materials according to the proportion, and perform vacuum self-consumption smelting on the raw materials to obtain alloy ingots.

[0009] (2) Cross-β phase region forging: The alloy ingot is subjected to cross-phase region multi-fire multi-directional forging in the β phase region and the α+β two-phase region to obtain titanium alloy forging billet.

[0010] (3) Hot rolling: The titanium alloy forging billet is hot rolled in multiple passes to obtain titanium alloy hot-rolled plate.

[0011] (4) Cold rolling: The hot-rolled titanium alloy sheet is cold-rolled in multiple passes to obtain a cold-rolled titanium alloy sheet.

[0012] (5) Heat treatment: The cold-rolled titanium alloy sheet is subjected to distributed heat treatment, as follows: Short-time solution treatment: Cold-rolled titanium alloy sheet is solution treated and then cooled to obtain solution-treated titanium alloy sheet.

[0013] Low-temperature ω-phase aging treatment: The titanium alloy sheet after solution treatment is aged and then cooled to obtain a high-strength, high-plasticity metastable β-titanium alloy sheet.

[0014] More preferably, in step (1), the vacuum degree of the vacuum self-consumable melting is 0.01~0.08 Pa, and the melting current density is 25~30 A / mm. 2 Vacuum self-consumption melting is performed 3 to 5 times.

[0015] Preferably, the cumulative deformation of the multi-fire multi-directional forging in step (2) is 50-65%.

[0016] More preferably, the forging temperature of the β phase region in step (2) is set to be 35~65℃ higher than the β transformation point, and the forging temperature of the α+β two-phase region is set to be 25~35℃ lower than the β transformation point.

[0017] Preferably, the temperature of the multi-pass hot rolling in step (3) is 720~760℃, and the cumulative deformation is 75%~80%.

[0018] More preferably, the thickness of the hot-rolled titanium alloy sheet in step (3) is 5~10mm.

[0019] Preferably, in step (4), the deformation amount of each pass of the multi-pass cold rolling is ≤10%, and the cumulative deformation amount is 65~90%.

[0020] More preferably, the thickness of the cold-rolled titanium alloy sheet in step (4) is <2.5 mm.

[0021] Preferably, the solution treatment conditions in step (5) are: 30~60℃ below the β transformation point (Tβ), and the temperature is held for 5~25 minutes; the cooling method is water quenching.

[0022] Preferably, the aging treatment conditions in step (5) are: 130~160℃, heat preservation for 20~45min; and the cooling method is air cooling.

[0023] Mechanism of the invention: This invention is based on the [Mo] equivalent design criterion and d- The electronic alloy design method utilizes the synergistic combination of Mo, Cr, and Fe elements to reduce the amount of precious metal Mo while ensuring a uniform supersaturated β phase after solution treatment. During low-temperature aging, a sufficient quantity of isothermal ω phase precipitates. Simultaneously, neutral Zr and Sn are used to reduce the mismatch between the ω phase and the β matrix, further refining and uniformly distributing the ω phase while maintaining its volume fraction. In terms of processing, the synergistic effect of short-time solution treatment (performed in the α+β dual-phase region) and subsequent low-temperature aging treatment retains a certain amount of fine primary α phase to suppress β grain growth, while also preserving the high-density dislocation β substructure generated by cold rolling deformation. These substructures effectively suppress the coarsening and growth of the ω phase during subsequent low-temperature aging, strictly controlling its size within the 1.5~3nm range. Ultimately, the strength is significantly improved by relying on the nanoscale ω phase, while avoiding the plasticity deterioration caused by ω phase coarsening, achieving a balance between high strength and high plasticity, reducing alloy costs, and shortening the heat treatment process.

[0024] This invention utilizes short-time solution treatment in the α+β two-phase region to retain a certain volume fraction of fine primary α phase, effectively suppressing β grain growth and obtaining a uniform and fine α+β two-phase microstructure. Simultaneously, it preserves the high-density dislocation β substructure introduced by cold rolling. The solution treatment is performed within the α+β two-phase region, resulting in a two-phase microstructure composed of primary α phase and β matrix phase, while intentionally retaining the β substructure introduced by cold rolling deformation. These substructures provide high-density, uniform nucleation sites for the precipitation of the ω phase during subsequent low-temperature aging, effectively suppressing the growth and coarsening of the ω phase and confining its size to the nanoscale. Low-temperature aging treatment causes coherent isothermal ω phase nanoparticles to precipitate uniformly and diffusely within the β matrix.

[0025] This invention abandons the traditional solution aging process and innovatively adopts a short-process heat treatment scheme of short-time solution aging + low-temperature aging. It utilizes nano-sized fine ω particles to significantly improve strength, while avoiding plasticity deterioration by preserving the β substructure and precisely controlling the microstructure.

[0026] This method innovates synergistically from two aspects: alloy composition design and heat treatment process. On the one hand, it controls alloy costs by selecting low-cost alloying elements and reducing the amount of expensive alloying elements. On the other hand, it creatively employs a synergistic combination of short-time solid solution treatment in the α+β dual-phase region and ultra-short-time low-temperature ω-phase aging to purposefully retain the β substructure introduced by cold rolling deformation and utilize it to regulate the precipitation behavior of the ω phase. This achieves a breakthrough in plasticity retention while obtaining the high strength contribution of the ω phase. Furthermore, the innovative process significantly shortens the heat treatment process and time, reduces production energy consumption, and facilitates the industrial-scale mass production of sheet metal.

[0027] The beneficial effects of this invention are: (1) This invention inhibits β grain growth through the synergistic effect of cold rolling and short-term solid solution phase in the two-phase region, while introducing high-density small-angle grain boundaries within the β grains to form a fine β subcrystalline structure. The β subcrystalline structure provides extremely high-density uniform nucleation sites for the ω phase, significantly increasing the nucleation rate of the ω phase. A large number of fine ω phase particles compete for limited solute atoms before growth. At the same time, the addition of Zr / Sn can further promote the uniform and high-density nucleation of the ω phase and significantly inhibit its growth. The synergistic effect of the β substructure and Zr / Sn effectively confines the ω particles in the β matrix to the ultrafine nanoscale of 1.5nm~3nm. The interaction between the ultrafine coherent ω phase particles and dislocations is mainly through-cutting, which can provide a significant strengthening increment while avoiding strong local stress concentration due to the extremely small particle size and extremely uniform distribution, thus maximizing the preservation of the uniform plastic deformation capability of the β matrix and the α phase. This is different from the mechanism by which long-term solid solution in the traditional β single-phase region leads to the disappearance of substructure, local coarsening of the ω phase, and embrittlement.

[0028] (2) The preparation method of this invention only includes smelting, forging, hot rolling, cold rolling, and two heat treatment processes. The solution treatment time is only 5~25 min, and the aging time is only 20~45 min. The process is short, and the aging temperature is only 130℃~160℃, which is much lower than the 500℃~600℃ of traditional α phase aging, significantly reducing energy consumption and production cycle. At the same time, the alloy composition uses low-cost elements such as Cr and Fe with low Mo content, effectively controlling raw material costs. The process window is wide, the equipment requirements are low, and it is easy to achieve batch application on existing titanium alloy production lines.

[0029] (3) The typical microstructure of the titanium alloy thin plate finally prepared by the method of the present invention is: short rod-shaped primary α phase + β matrix containing high-density dislocation substructure and ultrafine nano ω phase. While ensuring a yield strength ≥1050MPa, the elongation after fracture is stable at over 30%, and the strength-ductility product can reach over 33GPa·%, successfully breaking through the bottleneck of the traditional metastable β titanium alloy strength-ductility inversion, and achieving an excellent synergistic match between high strength and high ductility.

[0030] (4) In the titanium alloy microstructure after short-time solid solution treatment in the α+β dual-phase region of the present invention, the volume fraction of the primary α phase is 15%~25%, the α phase is in the shape of short rods with an aspect ratio of about 6~8.5; the β matrix contains high density of small-angle grain boundaries, and the average grain size of the β subgrains is 4~10μm; in the titanium alloy microstructure after low-temperature ω phase aging treatment, the average size of the isothermal ω phase nanoparticles precipitated in the β matrix is ​​1.5~3nm, and the volume fraction is 20%~35%. Attached Figure Description

[0031] Figure 1 The microstructure of the low-cost, short-process, high-strength, high-ductility metastable β-titanium alloy sheet prepared in Example 1 of this invention is shown in the EBSD diagram. Figure 1 (a) shows the EBSD phase distribution diagram. Figure 1 (b) shows the grain boundary orientation difference distribution of EBSD.

[0032] Figure 2 Transmission electron microscopy (TEM) image of a low-cost, short-process, high-strength, high-ductility metastable β-titanium alloy thin plate prepared in Example 1 of this invention; wherein... Figure 2 Image (a) shows the bright-field image from a transmission electron microscope and the selected area electron diffraction pattern corresponding to the β matrix. Figure 2 In Figure (a), (b) is the dark field image of the ω phase corresponding to Figure (a).

[0033] Figure 3 The table shows a comparison of the room temperature tensile stress-strain curves of metastable β-titanium alloy thin plates in Examples 1 and 4 and Comparative Examples 2 and 3 of this invention. Detailed Implementation

[0034] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. In the embodiments and comparative examples of this invention, unless otherwise specified, all chemical reagents used were commercially available analytical grade reagents. The Ti-60Mo master alloy (i.e., a titanium-molybdenum master alloy with a molybdenum content of 60% by mass) used in the embodiments and comparative examples of this invention was prepared using conventional smelting methods.

[0035] Example 1 A low-cost, short-process method for preparing high-strength, high-ductility metastable β-titanium alloy thin plates, specifically including the following steps: (1) Batching and smelting: Sponge titanium, Ti-60Mo master alloy, pure chromium sheet, pure iron granules, pure zirconium granules, and pure tin granules were weighed according to the proportion. The composition of the raw materials, by mass percentage, included: 3.5% Mo, 2.8% Cr, 1.6% Fe, 1.5% Zr, 0.8% Sn, with the balance being Ti and unavoidable impurities. After the raw materials were mixed evenly, they were pressed into blocks of different shapes. The blocks were welded into electrodes using a vacuum plasma welding box and then smelted in a vacuum arc remelting furnace (VAR) at a current density of 25 A / mm. 2 The vacuum degree was 0.08 Pa, and the alloy ingot was repeatedly melted five times to obtain a uniform alloy ingot. The β transformation point Tβ of the alloy ingot was determined by metallographic method to be about 815℃.

[0036] (2) Cross-β phase region forging: Set the β phase region to 950℃ and the α+β two-phase region to 780℃. Perform cross-phase region multi-fire multi-directional forging in the β phase region and the α+β two-phase region in stages, with a cumulative deformation of 60%, in order to break the original coarse as-cast structure and obtain titanium alloy forging billet.

[0037] (3) Hot rolling: The titanium alloy forging billet is hot rolled in multiple passes at 730℃, with a cumulative deformation of about 78%, to obtain a titanium alloy hot-rolled plate with a thickness of 5mm.

[0038] (4) Cold rolling: The hot-rolled titanium alloy sheet is cold-rolled in multiple passes at room temperature, with a deformation of 8% per pass and a cumulative deformation of 65%, to obtain a cold-rolled titanium alloy sheet with a thickness of 1.8 mm.

[0039] (5) Heat treatment: The cold-rolled titanium alloy sheet is subjected to distributed heat treatment, as follows: Short-time solution treatment in the α+β two-phase region: Cold-rolled titanium alloy sheet was solution treated at 760℃ for 10 min, and then water-quenched to room temperature to obtain the solution-treated titanium alloy sheet.

[0040] Low-temperature ω-phase aging treatment: The solution-treated titanium alloy sheet is placed in a circulating hot air furnace and aged at 145℃ for 40 minutes, and then air-cooled to room temperature to obtain a high-strength, high-plasticity metastable β-titanium alloy sheet.

[0041] Figure 1 This is a microstructure image of the 1.8 mm titanium alloy sheet after heat treatment prepared in Example 1. Figure 1 From (a), it can be concluded that the microstructure consists of short rod-shaped primary α phase and β matrix, with the α phase having a volume fraction of approximately 18% and an aspect ratio of approximately 7.2. Figure 1 From (b), it can be concluded that the β matrix contains a high proportion of small-angle grain boundaries, and the average size of the β subgrains is about 6 μm.

[0042] Figure 2 The TEM microstructure of the 1.8 mm titanium alloy sheet prepared in Example 1 after heat treatment. Figure 2 The TEM bright-field image in (a) and the corresponding electron diffraction of the selected β matrix show that the β phase contains a high-density isothermal ω phase. Figure 2 The corresponding dark field image in (b) confirms that a large number of coherent isothermal ω phase particles with a size of about 1.8 nm are uniformly dispersed in the β matrix, with a volume fraction of about 28%.

[0043] Figure 3 The dark solid line represents the room temperature tensile stress-strain curve of the 1.8 mm titanium alloy sheet prepared in Example 1 after heat treatment. Uniaxial room temperature tensile tests were conducted on a universal testing machine (LS5105) at a tensile rate of 0.5 mm / min according to GB / T 228.1 standard. The test results show that the sheet obtained in Example 1 of this invention has a yield strength of 1106 MPa, an elongation at break of 31.4%, and a strength-ductility product of 34.7 GPa·s.

[0044] Example 2 A low-cost, short-process method for preparing high-strength, high-ductility metastable β-titanium alloy thin plates, specifically including the following steps: (1) Batching and smelting: Weigh out the raw materials of sponge titanium, Ti-60Mo master alloy, pure chromium sheet, pure iron granules and pure zirconium granules according to the proportion. The composition of the raw materials by mass percentage includes: 4.5% Mo, 2.2% Cr, 1.2% Fe, 2% Zr, with the balance being Ti and unavoidable impurities. After mixing the raw materials evenly, press them into blocks of different shapes. Use a vacuum plasma welding box to weld the blocks into electrodes and place them in a vacuum arc remelting furnace (VAR) for smelting. The smelting current density is 30A / mm. 2 The alloy ingot was repeatedly melted three times under a vacuum of 0.01 Pa to obtain a uniform alloy ingot. The β transformation point Tβ of the alloy ingot was determined to be approximately 805℃ by metallographic method.

[0045] (2) Cross-β phase region forging: Set the β phase region to 950℃ and the α+β two-phase region to 780℃. Perform cross-phase region multi-fire multi-directional forging in the β phase region and the α+β two-phase region in stages. The cumulative deformation is 60%, and the original coarse as-cast structure is broken to obtain titanium alloy forging billet.

[0046] (3) Hot rolling: The titanium alloy forging billet is hot rolled in multiple passes at 755℃, with a cumulative deformation of about 75%, to obtain a titanium alloy hot-rolled plate with a thickness of 10mm.

[0047] (4) Cold rolling: The hot-rolled titanium alloy sheet is cold-rolled in multiple passes at room temperature, with a deformation of 5% per pass and a cumulative deformation of 85%, to obtain a cold-rolled titanium alloy sheet with a thickness of 1.5 mm.

[0048] (5) Heat treatment: The cold-rolled titanium alloy sheet is subjected to distributed heat treatment, as follows: Short-time solution treatment in the α+β two-phase region: Cold-rolled titanium alloy sheet was solution treated at 775℃ for 5 minutes, and then water-quenched to room temperature to obtain the solution-treated titanium alloy sheet.

[0049] Low-temperature ω-phase aging treatment: The solution-treated titanium alloy sheet is placed in a circulating hot air furnace and aged at 130℃ for 25 minutes, and then air-cooled to room temperature to obtain a high-strength, high-plasticity metastable β-titanium alloy sheet.

[0050] Using the same microstructure characterization analysis as in Example 1, the microstructure of the heat-treated 1.5 mm titanium alloy sheet prepared in Example 2 consisted of short rod-shaped primary α phase and β matrix. The α phase had a volume fraction of approximately 21% and an aspect ratio of approximately 6.9. The β matrix contained a high proportion of small-angle grain boundaries, with an average β subgrain size of approximately 5.7 μm. TEM characterization confirmed that a large number of coherent isothermal ω phase particles with a size of approximately 1.5 nm were uniformly dispersed within the β matrix, with a volume fraction of approximately 25%.

[0051] Using the same mechanical testing conditions as in Example 1, the yield strength of the plate was 1082 MPa, the elongation at break was 30.7%, and the strength-ductility product was 33.2 GPa·s.

[0052] Example 3 A low-cost, short-process method for preparing high-strength, high-ductility metastable β-titanium alloy thin plates, specifically including the following steps: (1) Batching and smelting: Weigh out the raw materials of sponge titanium, Ti-60Mo master alloy, pure chromium sheet, pure iron granules and pure tin granules according to the proportion. The composition of the raw materials by mass percentage includes: 5.5% Mo, 1.6% Cr, 0.8% Fe, 1.2% Sn, with the balance being Ti and unavoidable impurities. After mixing the raw materials evenly, press them into blocks of different shapes. Use a vacuum plasma welding box to weld the blocks into electrodes and place them in a vacuum arc remelting furnace (VAR) for smelting. The smelting current density is 28A / mm. 2 The alloy ingot was repeatedly melted three times under a vacuum of 0.05 Pa to obtain a uniform alloy ingot. The β transformation point Tβ of the alloy ingot was determined to be approximately 805℃ by metallographic method.

[0053] (2) Cross-β phase region forging: Set the β phase region to 950℃ and the α+β two-phase region to 780℃. The alloy ingot is subjected to cross-phase region multi-fire multi-directional forging in the β phase region and the α+β two-phase region in stages. The cumulative deformation is 55%, and the original coarse as-cast structure is broken to obtain titanium alloy forging billet.

[0054] (3) Hot rolling: The titanium alloy forging billet is hot rolled in multiple passes at 740℃, with a cumulative deformation of about 75%, to obtain a titanium alloy hot-rolled plate with a thickness of 6mm.

[0055] (4) Cold rolling: The hot-rolled titanium alloy sheet is cold-rolled in multiple passes at room temperature, with a deformation of 5% per pass and a cumulative deformation of 80%, to obtain a cold-rolled titanium alloy sheet with a thickness of 1.2 mm.

[0056] (5) Heat treatment: The cold-rolled titanium alloy sheet is subjected to distributed heat treatment, as follows: Short-time solution treatment in the α+β dual-phase region: Cold-rolled titanium alloy sheet was solution treated at 765℃ for 15 minutes, and then water-quenched to room temperature to obtain the solution-treated titanium alloy sheet.

[0057] Low-temperature ω-phase aging treatment: The solution-treated titanium alloy sheet is placed in a circulating hot air furnace and aged at 150℃ for 25 minutes, and then air-cooled to room temperature to obtain a high-strength, high-plasticity metastable β-titanium alloy sheet.

[0058] Using the same microstructure characterization analysis as in Example 1, the microstructure of the heat-treated 1.2 mm titanium alloy sheet prepared in Example 3 consisted of short rod-shaped primary α phase and β matrix. The α phase had a volume fraction of approximately 17% and an aspect ratio of approximately 7.8. The β matrix contained a high proportion of small-angle grain boundaries, with an average β subgrain size of approximately 7.4 μm. TEM characterization confirmed that a large number of coherent isothermal ω phase particles with a size of approximately 1.6 nm were uniformly dispersed within the β matrix, with a volume fraction of approximately 27%.

[0059] Using the same test conditions as in Example 1, the yield strength of the sheet was 1093 MPa, the elongation at break was 30.9%, and the strength-ductility product was 33.7 GPa·s.

[0060] Example 4 A low-cost, short-process method for preparing high-strength, high-ductility metastable β-titanium alloy thin plates, specifically including the following steps: (1) Batching and smelting: Weigh out the following raw materials according to the proportions: sponge titanium, Ti-60Mo master alloy, pure chromium sheet, pure iron granules, pure zirconium granules, and pure tin granules. The composition of these raw materials, by mass percentage, includes: 3.5% Mo, 2.2% Cr, 1.6% Fe, 1.5% Zr, and 0.8% Sn, with the balance being Ti and unavoidable impurities. After mixing the raw materials evenly, press them into blocks of different shapes. Use a vacuum plasma welding box to weld the blocks into electrodes, and place them in a vacuum arc remelting furnace (VAR) for smelting. The smelting current density is 25 A / mm. 2 The alloy ingot was repeatedly melted five times under a vacuum of 0.01 Pa to obtain a uniform alloy ingot. The β transformation point Tβ of the alloy ingot was determined to be approximately 815℃ by metallographic analysis.

[0061] (2) Cross-β phase region forging: Set the β phase region to 950℃ and the α+β two-phase region to 780℃. Perform cross-phase region multi-fire multi-directional forging in the β phase region and the α+β two-phase region in stages. The cumulative deformation is 65%, and the original coarse as-cast structure is broken to obtain titanium alloy forging billet.

[0062] (3) Hot rolling: The titanium alloy forging billet is hot rolled in multiple passes at 750℃, with a cumulative deformation of about 80%, to obtain a titanium alloy hot-rolled plate with a thickness of 5mm.

[0063] (4) Cold rolling: The hot-rolled titanium alloy sheet is cold-rolled in multiple passes at room temperature, with a deformation of 3% per pass and a cumulative deformation of 90%, to obtain a cold-rolled titanium alloy sheet with a thickness of 0.5 mm.

[0064] (5) Heat treatment: The cold-rolled titanium alloy sheet is subjected to distributed heat treatment, as follows: Short-time solution treatment in the α+β two-phase region: Cold-rolled titanium alloy sheet was solution treated at 770℃ for 25 minutes, and then water-quenched to room temperature to obtain the solution-treated titanium alloy sheet.

[0065] Low-temperature ω-phase aging treatment: The solution-treated titanium alloy sheet is placed in a circulating hot air furnace and aged at 155℃ for 20 minutes, and then air-cooled to room temperature to obtain a high-strength, high-plasticity metastable β-titanium alloy sheet.

[0066] Using the same microstructure characterization analysis as in Example 1, the microstructure of the heat-treated 0.5 mm titanium alloy sheet prepared in Example 4 consisted of short rod-shaped primary α phase and β matrix. The α phase had a volume fraction of approximately 19% and an aspect ratio of approximately 6.1. The β matrix contained a high proportion of small-angle grain boundaries, with an average β subgrain size of approximately 4.8 μm. TEM characterization confirmed that a large number of coherent isothermal ω phase particles with a size of approximately 1.9 nm were uniformly dispersed within the β matrix, with a volume fraction of approximately 25%.

[0067] Figure 3 The light-colored solid line represents the room temperature tensile stress-strain curve of the 0.5 mm titanium alloy sheet prepared in Example 4 after heat treatment. Using the same test conditions as in Example 1, the sheet's yield strength was 1120 MPa, its elongation at break was 30.0%, and its strength-ductility product was 33.6 GPa·s.

[0068] Comparative Example 1 Metastable β-titanium alloy sheets were prepared using the same raw materials and methods as in Example 1. The only difference was that the heat treatment conditions in this comparative example were as follows: the cold-rolled titanium alloy sheet was first subjected to a solution treatment at 830°C for 1 hour, then water-quenched to room temperature, and subsequently subjected to the same low-temperature aging treatment as in Example 1.

[0069] Under the same mechanical testing conditions as in Example 1, the yield strength of the sheet was 1099 MPa, the elongation at break was 6.2%, and the strength-ductility product was 6.8 GPa·%. Microstructural analysis showed that in the thin sheet prepared by the method described in Comparative Example 1, the ω phase in the β matrix was significantly coarsened, and preferentially precipitated along the grain boundaries to form a continuous brittle network. This fully demonstrates that prolonged solid solution treatment in the β single-phase region eliminates substructures and leads to grain coarsening, thereby causing ω embrittlement and resulting in a sharp deterioration in the plasticity of the sheet.

[0070] Comparative Example 2 Metastable β-titanium alloy thin plates were prepared using the same raw materials and methods as in Example 1. The only difference was that the heat treatment conditions in this comparative example were as follows: solution treatment was performed in the same manner as in Example 1, followed by holding at 540°C for 4 hours and then air cooling to room temperature (i.e., using the traditional α-phase aging process).

[0071] Using the same mechanical test conditions as in Example 1, Figure 3 The dark dashed line represents the room temperature tensile stress-strain curve of the 1.8 mm titanium alloy sheet prepared in Comparative Example 2. The sheet has a yield strength of 1320 MPa, an elongation at break of 4.3%, and a strength-ductility product of 5.6 GPa·%. This indicates that α-precipitation strengthening can significantly improve strength, but the ductility loss caused by α-phase strengthening is also extremely severe, making it difficult to achieve a good balance between strength and ductility.

[0072] Comparative Example 3 Metastable β-titanium alloy sheets were prepared using the same raw materials and methods as in Example 1. The only difference was that the heat treatment conditions in this comparative example were: the cold-rolled titanium alloy sheet was solution treated at 760°C for 10 minutes, and then water-quenched to room temperature without any aging treatment.

[0073] Using the same mechanical test conditions as in Example 1, Figure 3 The light-colored dashed line represents the room-temperature tensile stress-strain curve of the 1.8 mm titanium alloy sheet prepared in Comparative Example 1. The sheet has a yield strength of 820 MPa, an elongation at break of 36.2%, and a strength-ductility product of 29.7 GPa·%. The yield strength is too low with only solution treatment, making it difficult to meet the high-strength performance requirements of the sheet, thus demonstrating the necessity of low-temperature ω-phase aging strengthening.

[0074] The yield strength of the various thicknesses of titanium alloy sheets prepared in Examples 1-4 all reached over 1050 MPa, the elongation at break was all above 30%, and the strength-ductility product exceeded 33 GPa·%, which fully demonstrates that the α+β dual-phase short-time solution treatment combined with low-temperature ω-phase aging process of the present invention can significantly improve the material strength while retaining good plastic deformation capacity, thus achieving an excellent synergistic match between high strength and high plasticity. In contrast, Comparative Example 1, due to solution treatment in the β single-phase region, eliminated the cold-rolled substructure and coarsened the β grains; during the subsequent low-temperature aging process, the ω-phase precipitated in the β matrix became significantly coarser, leading to ω embrittlement and a sharp deterioration in the plasticity of the sheet. Comparative Example 2 used a traditional α-phase aging process instead of low-temperature ω-phase aging treatment, resulting in the formation of short rod-shaped primary α-phase, needle-shaped secondary α-phase, and β matrix in the microstructure of the titanium alloy sheet. Although the precipitation of the secondary α-phase can improve the strength of the material, the resulting loss of plasticity is also extremely severe, making it difficult to achieve a good strength-ductility match. Comparative Example 3, due to only undergoing short-term solid solution treatment in the α+β two-phase region, did not precipitate a high-density ω phase in the microstructure to enhance the strength of the titanium alloy, resulting in a low yield strength of the titanium alloy sheet, which is difficult to meet the high strength performance requirements of the sheet.

[0075] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A low-cost, short-process, high-strength, high-ductility, metastable β-titanium alloy sheet, characterized in that, The composition of the high-strength, high-plasticity metastable β-titanium alloy sheet, by mass percentage, includes: 2.8~6.0% Mo, 1.5~3.6% Cr, 0.8~1.6% Fe, 0~2.5% Zr, and 0~1.8% Sn, satisfying 0.5%≤Zr+Sn≤3.5%, with the balance being Ti and unavoidable impurities.

2. The low-cost, short-process method for preparing high-strength, high-plasticity metastable β-titanium alloy thin plates according to claim 1, characterized in that, Specifically, the following steps are included: (1) Batching and smelting: Weigh the high-strength and high-plasticity metastable β-titanium alloy sheet raw materials according to the proportion, and perform vacuum self-consumption smelting on the raw materials to obtain alloy ingots; (2) Cross-β phase region forging: The alloy ingot is subjected to cross-phase region multi-fire multi-directional forging in the β phase region and the α+β two-phase region in stages to obtain titanium alloy forging billet; (3) Hot rolling: The titanium alloy forging billet is hot rolled in multiple passes to obtain a hot-rolled titanium alloy plate; (4) Cold rolling: The hot-rolled titanium alloy sheet is cold-rolled in multiple passes to obtain a cold-rolled titanium alloy sheet; (5) Heat treatment: The cold-rolled titanium alloy sheet is subjected to distributed heat treatment, as follows: Short-time solution treatment: Cold-rolled titanium alloy sheet is solution treated and then cooled to obtain solution-treated titanium alloy sheet; Low-temperature ω-phase aging treatment: The titanium alloy sheet after solution treatment is aged and then cooled to obtain a high-strength, high-plasticity metastable β-titanium alloy sheet.

3. The low-cost, short-process method for preparing high-strength, high-plasticity metastable β-titanium alloy thin plates according to claim 2, characterized in that, The cumulative deformation of the multi-fire, multi-directional forging in step (2) is 50-65%.

4. The low-cost, short-process method for preparing high-strength, high-plasticity metastable β-titanium alloy thin plates according to claim 2, characterized in that, The temperature of the multi-pass hot rolling in step (3) is 720~760℃, and the cumulative deformation is 75%~80%.

5. The low-cost, short-process method for preparing high-strength, high-ductility, metastable β-titanium alloy thin plates according to claim 2, characterized in that, In step (4), the deformation amount of each pass of the multi-pass cold rolling is ≤10%, and the cumulative deformation amount is 60~90%.

6. The low-cost, short-process method for preparing high-strength, high-plasticity metastable β-titanium alloy thin plates according to claim 2, characterized in that, The conditions for solution treatment in step (5) are: 30~60℃ below the β transformation point, and holding for 5~25 min; the cooling method is water quenching.

7. The low-cost, short-process method for preparing high-strength, high-ductility, metastable β-titanium alloy thin plates according to claim 2, characterized in that, The conditions for the aging treatment in step (5) are: heat preservation at 130~160℃ for 20~45 minutes; the cooling method is air cooling.

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