Electric pulse assisted forging process and tooling for two-phase / near-α titanium alloy

Abstract

The present invention discloses a two-phase / near-α titanium alloy electric pulse assisted reforging process and tooling, and forging a two-phase / near-α titanium alloy ingot with a coarse Widmanstatten structure (cluster domain structure composed of lamellar structure) after opening by conventional large forging ratio forging composite high-frequency short-time high-temperature electrical treatment and low-frequency long-time low-temperature electrical treatment in the low temperature section of the two-phase region to obtain a fine-grained dual-state structure titanium alloy forging billet with a high degree of spheroidization of the primary α phase and precipitation of fine lamellar α phase in the transformed β phase matrix. The two-phase / near-α titanium alloy electric pulse assisted reforging process and tooling of the present invention significantly improve the single-pass deformation spheroidization rate of the titanium alloy, reduce the reforging heating temperature and the number of fires, reduce the production cost, simplify the process flow, thereby shortening the production cycle, improving the material utilization rate, and further improving the quality of the forging billet.

Description

Technical Field

[0001] The invention relates to the technical field of metal plastic forming, and in particular to a two-phase / near-alpha titanium alloy electric pulse assisted forging process and tooling. Background Art

[0002] Near-α titanium alloys represented by TA7, TA15, TA18, and TA19 alloys and α+β titanium alloys represented by TC4, TC11, and TC17 have excellent thermal strength, thermal stability, corrosion resistance, fatigue performance, welding performance, and low fatigue crack growth rate. They are widely used in aircraft compressor blades, load-bearing bulkheads, missile rudder wings, manned spacecraft wall panels and other aerospace launch equipment structural and functional integrated components. The above-mentioned titanium alloy raw materials often need to undergo multiple hot mechanical processing before being used in parts manufacturing, which mainly includes single-phase zone blanking and two-phase zone repeated upsetting and forging. In this way, the original coarse cluster-structured Widmanstatten structure can be transformed into a fine and uniform spherical equiaxed structure, dual-state structure, and three-state structure, thereby improving the process plasticity of the raw materials, so that the final component has a better comprehensive match of strength, plasticity, fatigue performance, and fracture toughness. The main organizational evolution phenomenon that occurs during the two-phase forging process of α+β titanium alloys and near-α titanium alloys is the spheroidization of the lath α phase. The existing thermomechanical processing methods are mostly multi-pass free forging. The spheroidization efficiency of the lath α phase is low and has loading orientation dependence. The number of firings required to achieve complete spheroidization is often more than 10 times. In addition, the processing temperature window is narrow, the manufacturing process is complex, the cycle is long, and the energy consumption is high. There is an urgent need for a green, efficient, and short-process thermomechanical processing (blank opening, forging) process method.

[0003] Electric pulse processing is a fast non-equilibrium processing technology. Combining it with thermomechanical processing can accelerate the transformation of diffusion-type organization and promote the evolution of dislocation configuration under the action of electric-thermal-mechanical coupling. It can effectively improve the microstructure of the material at a lower temperature and in a very short time, significantly improve the material performance, and avoid oxidation, hydrogen absorption and other problems to the greatest extent. A large number of studies have shown that pulse current also has a significant promoting effect on the recovery and recrystallization, dislocation movement, phase transformation, precipitation phase and intermetallic compound precipitation, and twinning of metal materials, which can cause rapid recrystallization and phase transformation, refine grains, and improve organizational uniformity. This provides an effective means to effectively improve the organizational structure of lamellar organization near α-type titanium alloys and α+β-type titanium alloys and improve the comprehensive performance of materials. To this end, the present invention performs pulse current assisted deformation and pulse current treatment on the coarse lamellar structure TA15 alloy obtained by single-phase zone heat treatment and slow furnace cooling, promotes local element diffusion through the thermal and non-thermal effects of the pulse current, and stimulates dislocation movement and dislocation reaction; under the condition of relatively low cumulative deformation, the spheroidization kinetic rate can be significantly improved, the efficiency of titanium alloy forging is effectively improved, and an important theoretical basis is provided for promoting the application of new two-phase zone thermal mechanical processing technologies in the aerospace field.

[0004] In view of the above analysis, the inventors of the present invention finally obtained the present invention after a long period of research and practice. Summary of the invention

[0005] The purpose of the present invention is to solve the problems that the billet making process of lamellar two-phase / near-α titanium alloys represented by TA15 titanium alloy and TC4 alloy requires multiple high-temperature repeated reversing and severe deformation, low efficiency of grain refinement and equiaxed (spheroidizing), long reforging cycle, high energy consumption and significant material heat loss, and provides a low-cost short-process reforging process and corresponding tooling assisted by electric pulses for lamellar two-phase / near-α titanium alloys.

[0006] In order to solve the above technical problems, a technical solution adopted by the present invention is:

[0007] A two-phase / near-alpha titanium alloy electric pulse assisted forging process, comprising the following steps:

[0008] S1. Cutting a rectangular blank from a two-phase / near-α titanium alloy raw material and cleaning it;

[0009] S2, tightly wrapping the outer side of the titanium alloy rectangular blank with a sheath and encapsulating it;

[0010] S3, the isothermal furnace is heated to a preset deformation temperature, and the titanium alloy cuboid billet is temperature-homogenized in the isothermal furnace;

[0011] S4, the press machine presses the titanium alloy blank to a preset deformation amount at a preset strain rate to upset the titanium alloy rectangular blank;

[0012] S5, the titanium alloy rectangular blank is homogenized in the furnace and a preset pressure is maintained, and a high-frequency pulse current is applied to the titanium alloy rectangular blank for a preset power-on time;

[0013] S6, turning the titanium alloy cuboid blank over so that the longest side is parallel to the compression axis, and repeating steps S3 to S5 several times;

[0014] S7, the titanium alloy rectangular blank is cooled with the furnace and a preset pressure is maintained, and a low-frequency pulse current is applied to the titanium alloy rectangular blank for a preset power-on time;

[0015] S8, the titanium alloy cuboid billet is cooled with the furnace to a preset furnace opening temperature, and then taken out and air-cooled to room temperature;

[0016] S9, remove the outer sheath, remove trace oxide scale, and obtain the final titanium alloy billet.

[0017] Preferably, in step S1, the height-to-diameter ratio of the titanium alloy rectangular blank obtained after cutting and cleaning is 2.0 to 2.5, so as to ensure that the blank does not suffer from unstable folding and double bulging during the upsetting deformation process, and to avoid excessive changes in the contact area of ​​the upper and lower end surfaces of the titanium alloy blank coated with the brass sheath during the compression process.

[0018] Preferably, in step S2, the thickness of the brass sheath used for the titanium alloy rectangular blank is 1 / 7 to 1 / 6 of the shortest side length of the rectangular blank, and tungsten inert gas welding is used for packaging to ensure that the titanium alloy blank inside the copper sheath is deformed under sufficient three-dimensional compressive stress during the upsetting deformation process without cracking, and to prevent the brass sheath from being separated from the titanium alloy blank over a large area during the upsetting deformation process.

[0019] Preferably, in step S3, the preset deformation temperature in the isothermal furnace is 600-700° C., and the titanium alloy rectangular blank coated with the brass sheath is temperature-homogenized in the isothermal furnace for no less than 30 minutes.

[0020] Preferably, in step S4, the deformation temperature of the titanium alloy cuboid blank during the upsetting deformation process is maintained at 600-700°C, and the preset strain rate is not greater than 0.05s -1 The preset deformation amount is not more than 60%, which is used to inhibit recovery and recrystallization and ensure that the titanium alloy evenly accumulates a large amount of strain and crystal defects at the low temperature section of the two-phase region.

[0021] Preferably, in step S5, the furnace homogenization time of the titanium alloy rectangular billet after upsetting is at least 10 minutes, and the preset pressure maintained between the upper and lower anvils during the homogenization process is at least 200 MPa, so as to ensure that the upper and lower anvils are in close contact with the end surface of the titanium alloy sample coated with a brass sheath, so that no local tip discharge occurs between the upper and lower anvils and the billet during the pulse current treatment, thereby avoiding uneven current distribution inside the sample and local overburning.

[0022] The parameters of the high-frequency pulse current passed into the titanium alloy rectangular blank are: current density 15~20A / mm 2 , frequency 500Hz, pulse width 100μs, and high-frequency pulse current treatment time is 30-35s, so as to ensure sufficient local temperature rise inside the material to reach the conventional thermal deformation temperature of 900-1000℃, so as to promote the titanium alloy billet which has accumulated a large number of crystal defects after the warm deformation to undergo rapid static spheroidization, static recovery and static recrystallization and other organizational evolution phenomena under the synergistic effect of pulse current and high temperature, and efficiently reorganize the lamellar structure into equiaxed structure.

[0023] Preferably, in step S7, the cooling time of the titanium alloy rectangular blank treated with the high-frequency pulse current is at least 10 minutes, the preset pressure maintained between the upper and lower anvils during the cooling process is at least 200 MPa, and the parameters of the low-frequency pulse current passed into the titanium alloy rectangular blank are: the current density is 40 to 60 A / mm 2 , frequency is 5 Hz, pulse width is 100 μs, and low-frequency pulse current treatment time is at least 10 min, so as to ensure that the heat input and heat dissipation of the titanium alloy material are basically stable during the pulse current treatment, so that the titanium alloy billet maintains a near-equilibrium state between heat input and heat output during the pulse current treatment, and the temperature is between 600 and 650 ° C.

[0024] Preferably, in step S8, the preset furnace opening temperature is not less than 300° C. to ensure sufficient precipitation of the secondary lamellar α phase.

[0025] Also provided is a two-phase / near-α titanium alloy electric pulse assisted forging tool, which uses the two-phase / near-α titanium alloy electric pulse assisted forging process as described above, including a fixed lower die seat, an upper die seat located directly above the lower die seat and capable of vertical lifting and lowering, a lower flat anvil is fixedly arranged on the top surface of the lower die seat, an isothermal furnace insulation lower shell is coaxially fixedly arranged on the outer side of the lower flat anvil, an upper flat anvil is fixedly arranged on the bottom surface of the upper die seat and relatively arranged above the lower flat anvil, an isothermal furnace insulation upper shell that can be matched with the isothermal furnace insulation lower shell is coaxially fixedly arranged on the outer side of the upper flat anvil, and an annular heating body is fixedly arranged on the inner walls of the isothermal furnace insulation lower shell and the isothermal furnace insulation upper shell;

[0026] The side of the lower anvil is fixedly connected to a first terminal that passes through the outside of the lower insulation shell of the isothermal furnace, and the side of the upper anvil is fixedly connected to a second terminal that passes through the outside of the upper insulation shell of the isothermal furnace. The first terminal and the second terminal are respectively electrically connected to the two electrode output terminals of the pulse current generator.

[0027] Preferably, a lower heat insulation layer is provided between the top surface of the lower flat anvil and the top surface of the lower die seat, a downward elastic high-temperature resistant seal is provided between the outer side wall of the lower flat anvil and the inner side wall of the isothermal furnace insulation lower shell, and a lower lateral elastic high-temperature resistant seal is provided between the outer side of the first terminal and the side wall of the isothermal furnace insulation lower shell;

[0028] An upper insulation layer is arranged between the bottom surface of the upper flat anvil and the bottom surface of the upper mold base, an upper vertical elastic high-temperature resistant seal is arranged between the outer side wall of the upper flat anvil and the inner side wall of the isothermal furnace insulation upper shell, and an upper lateral elastic high-temperature resistant seal is arranged between the outer side of the second terminal and the side wall of the isothermal furnace insulation upper shell.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The present invention provides a low-cost short-process electric pulse-assisted forging method for a lamellar two-phase / near-α titanium alloy and a corresponding tooling structure, which solves the problems that the lamellar near-α titanium alloy and α+β (two-phase) titanium alloy represented by TA15 titanium alloy and TC4 alloy require multiple high-temperature repeated reversing and severe plastic deformation (10-15 times, one time refers to one heating and forging until the temperature of the billet drops below the forging temperature range, each time includes multiple reversing upsetting deformations, and the forging deformation temperature in the two-phase region is about 900-980°C), the deformation grain refinement and equiaxed (spheroidizing) efficiency is low under conventional deformation, and the forging cycle is long, the energy consumption is large, and the material heat loss is significant. The present invention significantly simplifies the traditional blanking hot forming steps, improves the spheroidizing efficiency of the material blanking process, and achieves the effects of low cost, short process, and low energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the process flow of the two-phase / near-α titanium alloy electric pulse assisted forging process of the present invention.

[0032] Figure 2 TA15 alloy used in the examples.

[0033] Figure 3 The present invention is a three-dimensional structural schematic diagram of a high-temperature alloy voltage-carrying disk assembled on a universal testing machine.

[0034] Figure 4 Schematic diagram of the TA15 alloy electrical compression and electrical treatment experiment in the embodiment.

[0035] Figure 5 In the embodiment, the deformation amount is 60% and the strain rate is 0.01s -1 Schematic diagram of the metallographic structure and spheroidization phenomenon of TA15 alloy under different current densities under different conditions.

[0036] Figure 6 In the embodiment, the deformation amount is 60% and the strain rate is 0.01s -1 Conditions, the average lamellar thickness and lamellar axis ratio curves of TA15 alloy lamellar α phase under different current densities.

[0037] Figure 7 The current density in the embodiment is 16A / mm 2 , strain rate is 0.01s -1 Schematic diagram of the metallographic structure and spheroidization phenomenon of TA15 alloy under different deformation amounts.

[0038] Figure 8 The current density in the embodiment is 16A / mm 2 , strain rate is 0.01s -1The average lamellar thickness and lamellar axis ratio curves of TA15 alloy lamellar α phase under different strain amounts.

[0039] Fig. 9 Dynamic spheroidization volume fraction curve of TA15 alloy after electric-assisted deformation and composite electric treatment under different true strains in the embodiment.

[0040] Fig.10 A schematic structural diagram of the two-phase / near-alpha titanium alloy electric pulse assisted forging tooling of the present invention.

[0041] In the figure: 1. lower die base; 2. upper die base; 3. lower flat anvil; 4. isothermal furnace insulation lower shell; 5. upper flat anvil; 6. isothermal furnace insulation upper shell; 7. heating body; 8. first terminal; 9. second terminal; 10. pulse current generator; 11. lower insulation layer; 12. lower vertical elastic high temperature resistant seal; 13. lower lateral elastic high temperature resistant seal; 14. upper insulation layer; 15. upper vertical elastic high temperature resistant seal; 16. upper lateral elastic high temperature resistant seal; 17. terminal; 18. bolt; 100. titanium alloy rectangular blank; 200. brass sheath. DETAILED DESCRIPTION

[0042] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0043] The technical solution of the present application is described in detail below in conjunction with a specific experimental process.

[0044] The TA15 alloy raw material used in this experiment is TA15 alloy bar provided by Taidaxing Metal Processing Factory in Baoji High-tech Zone, with a diameter of 50mm and a β phase complete transformation temperature between 985℃ and 990℃. The original billet was kept at 1020℃ for 35min and furnace cooled to obtain the β annealed lamellar structure (such as Figure 2 As shown in the figure, it can be seen that the flake-like α phase is distributed in clusters or bundles in the coarse β grains, the β grain boundaries are clearly visible, and some α phases have a growth trend from the β grain boundaries to the grains. The orientations of the flake-like α phases in different clusters in the grains are different, and the thickness of the flakes is about , the thickness of the α-lamellar structure near the grain boundary is about .

[0045] The electric pulse assisted compression and electric treatment test was carried out on a WDW-100H universal testing machine equipped with a self-designed high-temperature alloy voltage plate (such as Figure 3 As shown in the figure), the pulse current is output by a 10kA-150V single pulse power generator, and the power-on compression process is shown in the schematic diagram Figure 4As shown, a Fluke infrared thermal imager is used to take infrared images and record temperature data.

[0046] See also Figure 1 , a two-phase / near-alpha titanium alloy electric pulse assisted forging process, comprising the following steps:

[0047] S1. Cut a rectangular blank from the two-phase / near-α titanium alloy raw material of the widmanstattenite structure (cluster domain structure composed of lamellar structure) after blanking to remove the oxide scale and oil stains remaining on the surface. Preferably, in this step, the height-to-diameter ratio of the titanium alloy rectangular blank obtained after cutting and cleaning is 2.0-2.5 to ensure that the blank does not fold or double bulge during the upsetting deformation process, and to avoid excessive changes in the contact area of ​​the upper and lower end surfaces of the titanium alloy blank coated with the brass sheath during the compression process.

[0048] In this embodiment, the initial TA15 rod is cut into a cylindrical specimen of ∅10mm×15mm, ensuring that the upper and lower end faces are horizontal and parallel and perpendicular to the side faces. The surface needs to be processed smoothly to further reduce the effect of end face friction on deformation.

[0049] S2, tightly wrap the outer side of the titanium alloy rectangular blank with a brass sheath, and weld and package it. Preferably, in this step, the thickness of the brass sheath used for the titanium alloy rectangular blank is 1 / 7 to 1 / 6 of the shortest side length of the rectangular blank, and tungsten inert gas welding is used for welding and packaging to ensure that the titanium alloy blank inside the copper sheath is deformed under sufficient three-dimensional compressive stress during the upsetting deformation process without cracking, and to prevent the brass sheath from being separated from the titanium alloy blank over a large area during the upsetting deformation process.

[0050] S3, heat the isothermal furnace to a preset deformation temperature, place the titanium alloy rectangular blank coated with a brass sheath between the upper and lower anvils (high temperature alloy voltage plate) of the press in the isothermal furnace, and equalize the temperature with the furnace. Preferably, in this step, the preset deformation temperature in the isothermal furnace is 600-700°C, and the time for the titanium alloy rectangular blank coated with a brass sheath to equalize the temperature with the furnace in the isothermal furnace is 30 minutes. During the test, the sample is placed at the center of the lower anvil, and the upper anvil is adjusted to contact with the upper surface of the sample and pre-tightened. The conductive cable of the pulse current generator is tightly connected to the wiring terminals on the upper and lower anvils of the universal testing machine through bolts and nuts to conduct the pulse current. At the same time, the upper and lower anvils are separated from other parts of the universal testing machine by insulating materials to prevent the current from flowing into other instruments, thereby damaging the instruments or causing safety accidents.

[0051] S4, the titanium alloy blank after temperature equalization is pressed down by a flat anvil on a press machine at a preset strain rate to a preset deformation amount, and the titanium alloy rectangular blank coated with a brass sheath is upset. Preferably, in this step, the deformation temperature of the titanium alloy rectangular blank during the upsetting deformation process is maintained at 600-700°C, and the preset strain rate is 0.05s -1 The preset deformation amount is 60% to inhibit recovery and recrystallization, ensuring that the titanium alloy evenly accumulates a large amount of strain and crystal defects at the low temperature section of the two-phase region.

[0052] S5, homogenize the titanium alloy rectangular blank after upsetting with the furnace, maintain a preset pressure between the upper and lower anvils during the homogenization process, and pass a high-frequency pulse current to the titanium alloy rectangular blank after upsetting through the power supply terminal connected to the pulse current generator between the upper and lower anvils until the preset power-on time. Preferably, in this step, the homogenization time of the titanium alloy rectangular blank after upsetting with the furnace is 10min, and the preset pressure maintained between the upper and lower anvils during the homogenization process is 200MPa, so as to ensure that the upper and lower anvils are in close contact with the end face of the titanium alloy sample coated with the brass sheath, so that no local tip discharge occurs between the upper and lower anvils and the blank during the pulse current treatment, so as to avoid uneven current distribution and local overburning inside the sample.

[0053] The parameters of the high-frequency pulse current passed into the titanium alloy rectangular blank are: current density 15~20A / mm 2 , frequency 500Hz, pulse width 100μs, and high-frequency pulse current treatment time is 30-35s, so as to ensure sufficient local temperature rise inside the material to reach the conventional thermal deformation temperature of 900-1000℃, so as to promote the titanium alloy billet which has accumulated a large number of crystal defects after the warm deformation to undergo rapid static spheroidization, static recovery and static recrystallization and other organizational evolution phenomena under the synergistic effect of pulse current and high temperature, and efficiently reorganize the lamellar structure into equiaxed structure.

[0054] S6, turning over the titanium alloy cuboid blank treated with high-frequency pulse current so that the longest side is parallel to the compression axis, and repeating the high-frequency pulse power-on and pressurized upsetting operations of steps S3 to S5 2 to 3 times;

[0055] S7. Cool the titanium alloy rectangular blank treated with multiple high-frequency pulse currents with the furnace. During the cooling process, a preset pressure is maintained between the upper and lower anvils. A low-frequency pulse current is passed through the power terminals of the pulse current generator connected between the upper and lower anvils to treat the titanium alloy rectangular blank treated with high-frequency pulse current until the preset power-on time. Preferably, in this step, the cooling time of the titanium alloy rectangular blank treated with high-frequency pulse current with the furnace is 10 minutes. During the cooling process, the preset pressure maintained between the upper and lower anvils is 200MPa. The parameters of the low-frequency pulse current passed into the titanium alloy rectangular blank are: the current density is 40 to 60A / mm 2 , frequency is 5 Hz, pulse width is 100 μs, and low-frequency pulse current treatment time is 10 min, which is used to ensure that the heat input and heat dissipation of the titanium alloy material are basically stable during the pulse current treatment, so that the titanium alloy billet maintains a near-equilibrium state between heat input and heat output during the pulse current treatment, and the temperature is between 600 and 650 °C.

[0056] S8. Turn off the heating system, and allow the titanium alloy rectangular blank treated with low-frequency pulse current to cool to a preset furnace opening temperature, then open the furnace, take out the blank, and air-cool it to room temperature; preferably, in this step, the preset furnace opening temperature is 300°C to ensure sufficient precipitation of the secondary lamellar α phase.

[0057] S9. The outer copper sheath of the cooled titanium alloy rectangular blank is removed by mechanical stripping, and trace oxide scale is removed by pickling to obtain the final titanium alloy blank.

[0058] The specific test of this embodiment mainly includes electric assisted compression and low-frequency high-current electrical treatment of lamellar structure TA15 titanium alloy under different deformation amounts, deformation rates and different current densities, to explore the spheroidization law of electric-thermal-mechanical coupling treatment of lamellar structure TA15 titanium alloy under the action of pulse current. The electric assisted compression deformation parameters are selected as follows:

[0059] (1) Current density: 10A / mm 2 , 12A / mm 2 , 14A / mm 2 , 16A / mm 2 ;

[0060] (2) Deformation: 20%, 40%, 60%;

[0061] (3) Strain rate: 0.005s -1 、0.01s -1 、0.02s -1 ;

[0062] The low-frequency pulse current treatment time is 10 minutes, and the pulse current density is 40A / mm 2, frequency is 5Hz, pulse width is 100μs.

[0063] The evolution law of TA15 titanium alloy lamellar structure under different pulse current densities is as follows Figure 5 As shown in the figure, when the strain rate is 0.01s -1 When the deformation is 60%, with the increase of current density, the initial lamella α in the large deformation zone begins to break, and lamella bending and lamella separation occur in some areas. The lamella thickness decreases and the degree of spheroidization increases. In quantitative metallographic analysis, the aspect ratio of the α phase is used to determine the thickness of the lamella. This value is less than or equal to 2.5 as the criterion for determining spheroidized tissue. The dynamic spheroidization of lamellar α tissue is mainly reflected by the number of spheroidized α phases, the average axial ratio of α phases, the initial lamellar orientation, and the degree of tissue homogenization.

[0064] When the current density is 10A / mm 2 When the sample is compressed, the maximum temperature is about 605.2℃, and the sample is crushed in the late compression period due to the low current density and large deformation. Figure 5 As can be seen in (a), the original β grains remain relatively intact, the boundaries between the β grain boundaries and the initial α lamellae are clearly visible, and the orientations of adjacent α lamellae are significantly different. The thickness of the α lamellae in the β grains is relatively large and still maintains a large lamellae axis ratio. The α lamellae are almost not broken or spheroidized, and only a small part of the organization has lamellae bending.

[0065] from Figure 5 It can be seen from (b) that when the current density is 12A / mm 2 When the original β grains no longer exist, the boundaries of the initial α sheets gradually become blurred, the orientation differences between different sheets gradually disappear, and the α sheets show a trend of being arranged parallel to the direction 45° apart from the compression direction. In the middle area of ​​the shear band, some coarse α sheets are broken, and the α sheets with an orientation close to the compression axis are bent to a certain extent, and the average axial ratio of the α phase tends to decrease.

[0066] from Figure 5 It can be seen from (c) that when the current density is 14A / mm 2 When the α-lamellar boundary almost disappears, the lamella separation phenomenon becomes more obvious, and fine equiaxed α-structures with a diameter of about 3-4 mm appear between the separated lamellae. The thickness of the lamellae at the center of the shear band is further reduced, the degree of bending of the lamellae on both sides of the center of the shear band increases, the average axial ratio of the α-phase is further reduced, and the spheroidization rate of the lamellae α-phase has reached 39.7%.

[0067] from Figure 5 As can be seen from (d), when the current density reaches 16A / mm 2When the shear band is 0.5mm, almost all α lamellae are broken and separated, and some are still bent. The axial ratio of the α lamellae in the middle of the shear band is greatly reduced, the number of equiaxed α grains is significantly increased, the orientation difference between different lamellae is almost gone, the spheroidization rate of the lamellae α phase has reached 51.2%, and the specific current density is 14A / mm 2 The spheroidization rate increased by nearly 22% and the specific current density was 14A / mm 2 The spheroidization rate increased by nearly 43%.

[0068] It can be seen that with the continuous increase of current density, the separation and bending of the α phase of the lamellae become more obvious, the orientation difference between different lamellae gradually disappears, and the average lamellae thickness and lamellae axis ratio show a downward trend, indicating that the increase of current density promotes the thinning of the lamellae and the spheroidization process. The average lamellae thickness is thinned by 1.7μm (such as Figure 6 As shown in (a) in the figure), the lamellae axis ratio is reduced by 1.15 (as shown in Figure 6 (as shown in (b) in the figure).

[0069] like Figure 7 As shown, the current density is 16A / mm 2 , strain rate is 0.01s -1 The metallographic structure and spheroidization law of TA15 alloy under different deformation amounts are shown in Figure 2. Figure 7 The corresponding deformations of (a), (b) and (c) are 20%, 40% and 60% respectively. Figure 8 As shown, the current density is 16A / mm 2 , strain rate is 0.01s -1 The average lamellar thickness and lamellar axis ratio of the TA15 alloy lamellar α phase under different strains. It can be seen that with the increase of the electric-assisted deformation, the average thickness of the lamellar α decreases, and the degree of equiaxed lamellar α increases. When the strain is 1.85, the average lamellar thickness is only 2.37μm, the lamellar axis ratio is the smallest at 2.27, and the spheroidization is more significant.

[0070] like Fig. 9 As shown, it is the dynamic spheroidization volume fraction of TA15 alloy after electric-assisted deformation and composite electric treatment under different true strains. It can be seen that the spheroidization rate is significantly increased under the assistance of pulse current, which proves that the technical solution of the present invention has significant practicality.

[0071] See also Fig.10 The present invention also provides a two-phase / near-α titanium alloy electric pulse assisted forging tool, which uses the two-phase / near-α titanium alloy electric pulse assisted forging process as described above, including a fixed lower die base 1, and an upper die base 2 located directly above the lower die base 1 and capable of vertical lifting and lowering, the lower die base 1 corresponds to the support platform of an existing universal testing machine, and the upper die base 2 corresponds to the power output end of the existing universal testing machine.

[0072] A lower flat anvil 3 is fixedly arranged on the top surface of the lower die base 1, and an isothermal furnace insulation lower shell 4 is coaxially fixedly arranged on the outer side of the lower flat anvil 3. An upper flat anvil 5 is fixedly arranged on the bottom surface of the upper die base 2 and is relatively arranged above the lower flat anvil 3. The lower flat anvil 3 and the upper flat anvil 5 are both made of Figure 3 The high temperature alloy is shown as a voltage plate. The lower anvil 3 and the lower die base 1, and the upper anvil 5 and the upper die base 2 are connected by T-bolts. The outer side of the upper anvil 5 is coaxially fixed with an isothermal furnace insulation upper shell 6 that can be matched with the isothermal furnace insulation lower shell 4, and an annular heating body 7 is fixed on the inner wall of the isothermal furnace insulation lower shell 4 and the isothermal furnace insulation upper shell 6. Specifically, connecting flanges are fixedly provided on the outer circular side surfaces of the lower anvil 3 and the upper anvil 5, and the bottom center position of the isothermal furnace insulation lower shell 4 is located above the connecting flange of the lower anvil 3 and is fixed by bolt connection. The top center position of the isothermal furnace insulation upper shell 6 is movably overlapped above the connecting flange of the upper anvil 5. When the power output end of the universal testing machine drives the upper anvil 5 to move downward, the upper anvil 5 gradually approaches the lower anvil 3, and the isothermal furnace insulation upper shell 6 synchronously approaches the isothermal furnace insulation lower shell 4 and matches with it, forming a closed insulation space outside the upper anvil 5 and the lower anvil 3, and then the isothermal furnace is built outside the forming working position of the universal testing machine. After the heating body 7 is powered on, the insulation space can be quickly heated and stabilized within a preset temperature range. After the isothermal furnace insulation upper shell 6 and the isothermal furnace insulation lower shell 4 match, the upper anvil 5 can continue to move downward and approach the lower anvil 3, and press the titanium alloy rectangular blank coated with a brass sheath placed on the top surface of the lower anvil 3. After the power-on compression deformation is completed, the power output end of the universal testing machine drives the upper anvil 5 upward, releases the pressure on the blank, and overlaps with the top center position of the isothermal furnace insulation upper shell 6 again, and then lifts the isothermal furnace insulation upper shell 6 upward and separates it from the isothermal furnace insulation lower shell 4 to complete the furnace opening operation.

[0073] The side of the lower anvil 3 is fixedly connected with a first terminal 8 that penetrates the outside of the isothermal furnace insulation lower shell 4, and the side of the upper anvil 5 is fixedly connected with a second terminal 9 that penetrates the outside of the isothermal furnace insulation upper shell 6. The first terminal 8 and the second terminal 9 are respectively electrically connected to the two electrode output ends of the pulse current generator 10. Specifically, the ends of the first terminal 8 and the second terminal 9 are respectively fixedly connected with the terminal 17 through the bolt 18, and the two terminal 17 are respectively connected to the two output electrodes of the pulse current generator 10 through cables, so that the pulse current is passed through the titanium alloy rectangular blank coated with the brass sheath through the upper anvil 5 and the lower anvil 3 as the guide end.

[0074] Preferably, in order to improve the isothermal insulation effect, minimize energy loss, and ensure the uniform temperature in the isothermal furnace, a lower insulation layer 11 is provided between the top surface of the lower flat anvil 3 and the top surface of the lower die seat 1, a downward vertical elastic high temperature resistant seal 12 is provided between the outer wall of the lower flat anvil 3 and the inner wall of the isothermal furnace insulation lower shell 4, and a lower lateral elastic high temperature resistant seal 13 is provided between the outer side of the first terminal 8 and the side wall of the isothermal furnace insulation lower shell 4. An upper insulation layer 14 is provided between the bottom surface of the upper flat anvil 5 and the bottom surface of the upper die seat 2, an upper vertical elastic high temperature resistant seal 15 is provided between the outer side wall of the upper flat anvil 5 and the inner side wall of the isothermal furnace insulation upper shell 6, and an upper lateral elastic high temperature resistant seal 16 is provided between the outer side of the second terminal 9 and the side wall of the isothermal furnace insulation upper shell 6. By providing a sealing and heat-insulating structure at each connection position, the sealing and heat-insulating properties inside the isothermal furnace are improved while ensuring the movement function.

[0075] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A two-phase / near-α titanium alloy electric pulse assisted forging process, characterized in that: The following steps are involved: S1. Cutting a rectangular blank from a two-phase / near-α titanium alloy raw material and cleaning it; S2, tightly wrapping the outer side of the titanium alloy rectangular blank with a sheath and encapsulating it; S3, the isothermal furnace is heated to a preset deformation temperature, and the titanium alloy cuboid billet is temperature-homogenized in the isothermal furnace; S4, the press machine presses the titanium alloy blank to a preset deformation amount at a preset strain rate to upset the titanium alloy rectangular blank; The deformation temperature of the titanium alloy cuboid billet during the upsetting deformation process is maintained at 600~700℃, and the preset strain rate is not more than 0.05s -1 , the preset deformation is not more than 60%; S5, the titanium alloy rectangular blank is homogenized in the furnace and a preset pressure is maintained, and a high-frequency pulse current is passed through the titanium alloy rectangular blank for a preset power-on time; The furnace homogenization time of the titanium alloy cuboid billet after upsetting is at least 10 minutes, the preset pressure maintained during the homogenization process is at least 200MPa, and the parameters of the high-frequency pulse current passed into the titanium alloy cuboid billet are: current density 15-20A / mm 2 , frequency 500Hz, pulse width 100μs, high-frequency pulse current treatment time is 30~35s; S6, turning the titanium alloy cuboid blank over so that the longest side is parallel to the compression axis, and repeating steps S3 to S5 several times; S7, the titanium alloy rectangular blank is cooled with the furnace and a preset pressure is maintained, and a low-frequency pulse current is applied to the titanium alloy rectangular blank for a preset power-on time; The cooling time of the titanium alloy cuboid billet treated with high-frequency pulse current is at least 10 minutes. The preset pressure maintained during the cooling process is at least 200MPa. The parameters of the low-frequency pulse current passed into the titanium alloy cuboid billet are: current density is 40-60A / mm 2 , the frequency is 5Hz, the pulse width is 100μs, and the low-frequency pulse current treatment time is at least 10min; S8, the titanium alloy cuboid billet is cooled with the furnace to a preset furnace opening temperature, and then taken out and air-cooled to room temperature; S9, remove the outer sheath, remove trace oxide scale, and obtain the final titanium alloy billet.

2. A two-phase / near-α titanium alloy electric pulse assisted forging process as claimed in claim 1, characterized in that: In step S1, the height-to-diameter ratio of the titanium alloy cuboid blank obtained after cutting and cleaning is 2.0-2.

5.

3. A two-phase / near-α titanium alloy electric pulse assisted forging process as claimed in claim 1 or 2, characterized in that: In step S2, the thickness of the sheath used for the titanium alloy cuboid blank is 1 / 7 to 1 / 6 of the shortest side length of the cuboid, and tungsten inert gas arc welding is used for welding and packaging.

4. A two-phase / near-α titanium alloy electric pulse assisted forging process as claimed in claim 1, characterized in that: In step S3, the preset deformation temperature in the isothermal furnace is 600-700° C., and the titanium alloy rectangular blank is kept in the isothermal furnace for a temperature equalization time of not less than 30 minutes.

5. The two-phase / near-α titanium alloy electric pulse assisted forging process according to claim 1, characterized in that: In step S8, the preset furnace opening temperature is not less than 300°C.

6. A two-phase / near-α titanium alloy electric pulse assisted forging tool, using the two-phase / near-α titanium alloy electric pulse assisted forging process as described in any one of claims 1 to 5, comprising a fixed lower die seat, and an upper die seat located directly above the lower die seat and capable of vertical lifting, characterized in that: A lower flat anvil is fixedly arranged on the top surface of the lower die seat, an isothermal furnace insulation lower shell is coaxially fixedly arranged on the outer side of the lower flat anvil, an upper flat anvil is fixedly arranged on the bottom surface of the upper die seat and is relatively arranged above the lower flat anvil, an isothermal furnace insulation upper shell that can be matched with the isothermal furnace insulation lower shell is coaxially fixedly arranged on the outer side of the upper flat anvil, and an annular heating body is fixedly arranged on the inner walls of the isothermal furnace insulation lower shell and the isothermal furnace insulation upper shell; The side of the lower anvil is fixedly connected to a first terminal that passes through the outside of the lower insulation shell of the isothermal furnace, and the side of the upper anvil is fixedly connected to a second terminal that passes through the outside of the upper insulation shell of the isothermal furnace. The first terminal and the second terminal are respectively electrically connected to the two electrode output terminals of the pulse current generator.

7. A two-phase / near-α titanium alloy electric pulse assisted forging tool as claimed in claim 6, characterized in that: A lower heat insulation layer is arranged between the top surface of the lower flat anvil and the top surface of the lower die seat, a downward elastic high-temperature resistant sealing body is arranged between the outer side wall of the lower flat anvil and the inner side wall of the isothermal furnace insulation lower shell, and a lower lateral elastic high-temperature resistant sealing body is arranged between the outer side of the first terminal and the side wall of the isothermal furnace insulation lower shell; An upper insulation layer is arranged between the bottom surface of the upper flat anvil and the bottom surface of the upper mold base, an upper vertical elastic high-temperature resistant seal is arranged between the outer side wall of the upper flat anvil and the inner side wall of the isothermal furnace insulation upper shell, and an upper lateral elastic high-temperature resistant seal is arranged between the outer side of the second terminal and the side wall of the isothermal furnace insulation upper shell.

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