Electric pulse toughening treatment method for linear friction welding joints of high-toughness titanium alloys

Abstract

The present invention discloses an electric pulse toughening treatment method for a linear friction welding joint of a high-toughness titanium alloy. The joint sample is clamped and fixed in a circuit by using a pulse power supply positive and negative electrode fixture, the positive and negative electrode fixture is made of pure copper, a digital storage oscilloscope is connected to the positive and negative electrodes of the pulse power supply, and is used to test and save pulse current related parameters. A contact surface thermometer is used to closely contact the sample surface, and the real-time temperature rise in the central area of ​​the sample is measured. The joint organization is controlled by changing variables such as pulse charging voltage, pulse frequency, and pulse time, and then air cooling is performed to obtain the final sample. The present invention realizes local control of the joint organization without affecting the parent material organization, and can greatly improve the joint toughness while ensuring good joint strength.

Description

Technical Field

[0001] The invention belongs to the technical field of electric pulse processing methods, and in particular relates to an electric pulse toughening processing method for a high-toughness titanium alloy linear friction welding joint. Background Art

[0002] High-toughness titanium alloys are mainly used in the preparation of aircraft fuselage structural parts due to their high toughness and good comprehensive mechanical properties. Linear friction welding (LFW), as an advanced solid phase welding technology, has become an important method for achieving high-quality connection of titanium alloys due to its advantages such as high welding efficiency, excellent forming quality and self-cleaning function. The titanium alloy structural parts prepared by this method are not constrained by the size of the welding section. The preformed semi-finished parts can be directly welded into an integral joint, and then the joint with the same strength as the overall structural parts can be obtained through fine processing. However, the low toughness of the joint greatly limits the use of this structural part in aircraft. This is mainly attributed to the fact that the friction extrusion force and shear force cause the dynamic recovery and recrystallization of the joint weld zone structure to form an equiaxed crystal structure. In the equiaxed structure, the crack diffusion path is straight and fast, with few branches, and the energy absorbed during the destruction process is also less, so the toughness is extremely low. As a local rapid heat treatment technology, electric pulse treatment can achieve joint microstructure regulation without affecting the parent material structure. It uses the synergistic effect of Joule thermal effect and electron wind non-thermal effect to achieve precise control of joint microstructure. The electron wind controls the growth of grains after nucleation into needle-shaped or lamellar microstructures, thereby transforming the equiaxial microstructure of the joint into an interlaced basket mesh microstructure and improving the toughness of the joint. Summary of the invention

[0003] The purpose of the present invention is to provide an electric pulse toughening treatment method for a high-toughness titanium alloy linear friction welding joint, and to significantly improve the joint toughness by regulating the TC21 titanium alloy joint structure through electric pulse treatment.

[0004] The technical solution adopted by the present invention is an electric pulse toughening treatment method for a high-toughness titanium alloy linear friction welding joint, which is specifically implemented according to the following steps:

[0005] Step 1, preparing TC21 titanium alloy linear friction welding structural parts by optimizing welding process;

[0006] Step 2: Prepare a strip sample required for electric pulse treatment on the welded joint by machining, and pretreat its surface;

[0007] Step 3, fixing the strip sample processed in step 2 between two copper electrodes of an electric pulse device;

[0008] Step 4, controlling the electric pulse treatment temperature and range by adjusting the electric pulse charging voltage, pulse frequency and pulse time;

[0009] Step 5: After the electric pulse treatment, air cool to room temperature and test the strength and toughness of the sample after the electric pulse treatment.

[0010] The present invention is also characterized in that:

[0011] The process parameter ranges of linear friction welding of TC21 titanium alloy in step 1 are: vibration frequency 30 Hz to 70 Hz, amplitude 2 mm to 5 mm, friction pressure 30 MPa to 70 MPa, upsetting pressure 50 MPa to 90 MPa, and holding time 10 s to 20 s.

[0012] The size in step 2 is 90×10×3mm 3 The surface of the sample is ground by a grinder to control the surface processing accuracy within 0.01mm.

[0013] The dimensions of the two copper electrodes in step 3 are both 240×30×3.2mm 3 , the effective distance between the two copper electrodes is 60mm.

[0014] When measuring the temperature in step 4, a contact surface thermometer is used, and the electric pulse processing parameter range is: charging voltage 10V~70V, pulse frequency 100Hz~300Hz, pulse time 10s~100s, root mean square current density 1×10 6 A / m 2 ~9×10 6 A / m 2 .

[0015] In step 5, the tensile specimen is used to test the joint strength, and the impact specimen is used to characterize the joint toughness, and the strength and toughness of the joint tissue corresponding to different electric pulse conditions are analyzed.

[0016] The beneficial effect of the present invention is that the present invention provides an electric pulse toughening treatment method for a high-toughness titanium alloy linear friction welding joint, which realizes local regulation of the joint structure without affecting the parent material structure, and can greatly improve the joint toughness while ensuring good joint strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the experimental process of the electric pulse toughening treatment method of the high-toughness titanium alloy linear friction welding joint of the present invention;

[0018] Figure 2 This is a microstructure diagram of the weld zone before and after the electric pulse treatment of the high-toughness titanium alloy linear friction welding joint obtained in Example 2 of the electric pulse toughening treatment method of the present invention;

[0019] Figure 3 It is a schematic diagram of the microstructure evolution of the weld zone before and after the electric pulse treatment of the joint in the electric pulse toughening treatment method of the high-toughness titanium alloy linear friction welding joint of the present invention;

[0020] Figure 4 It is a graph showing the impact toughness values ​​of the joint after different electric pulse treatments in the electric pulse toughening treatment method of the high-toughness titanium alloy linear friction welding joint of the present invention;

[0021] Figure 5 It is a diagram of the impact fracture position of the untreated joint after welding in the electric pulse toughening treatment method of the high-toughness titanium alloy linear friction welding joint of the present invention;

[0022] Figure 6 This is a diagram of the impact fracture position of the joint obtained in Example 2 of the electric pulse toughening treatment method for the high-toughness titanium alloy linear friction welding joint of the present invention;

[0023] Figure 7 This is an impact fracture morphology diagram of an untreated joint after welding in the electric pulse toughening treatment method of a high-toughness titanium alloy linear friction welding joint of the present invention;

[0024] Figure 8 This is a joint impact fracture morphology obtained in Example 2 of the electric pulse toughening treatment method for a high-toughness titanium alloy linear friction welding joint of the present invention. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] The electric pulse toughening treatment method of the high-toughness titanium alloy linear friction welding joint of the present invention is specifically implemented according to the following steps:

[0027] Step 1: Prepare a TC21 titanium alloy linear friction welding structural part by an optimal welding process, wherein the nominal composition of the TC21 titanium alloy is Ti-6Al-2Zr-2Sn-2Mo-1.5Cr-2N;

[0028] The process parameter ranges of linear friction welding of TC21 titanium alloy in step 1 are: vibration frequency 30 Hz to 70 Hz, amplitude 2 mm to 5 mm, friction pressure 30 MPa to 70 MPa, upsetting pressure 50 MPa to 90 MPa, and holding time 10 s to 20 s;

[0029] Step 2: Prepare a strip sample required for electric pulse treatment on the welded joint by machining, and pretreat its surface;

[0030] The size in step 2 is 90×10×3mm 3 , Grind the sample surface with a grinder to control the surface processing accuracy within 0.01mm;

[0031] Step 3, fixing the strip sample processed in step 2 between two copper electrodes of an electric pulse device;

[0032] The dimensions of the two copper electrodes in step 3 are both 240×30×3.2mm 3 , the effective distance between the two copper electrodes is 60 mm;

[0033] Step 4, controlling the electric pulse treatment temperature and range by adjusting the electric pulse charging voltage, pulse frequency and pulse time;

[0034] When measuring the temperature in step 4, a contact surface thermometer is used, and the electric pulse processing parameter range is: charging voltage 10V~70V, pulse frequency 100Hz~300Hz, pulse time 10s~100s, root mean square current density 1×10 6 A / m 2 ~9×10 6 A / m 2 ;

[0035] Step 5, air-cooling to room temperature after electric pulse treatment, testing the strength and toughness of the sample after electric pulse treatment, and clarifying the interdependence between joint organization and strength and toughness;

[0036] In step 5, the tensile specimen is used to test the joint strength, and the impact specimen is used to characterize the joint toughness. The strength and toughness of the joint structure under different electric pulse conditions are analyzed to clarify the dependence between the microstructure and strength and toughness of the TC21 titanium alloy joint.

[0037] Example 1

[0038] The electric pulse toughening treatment method for high-toughness titanium alloy linear friction welding joint is specifically implemented in the following steps:

[0039] Step 1: Prepare TC21 titanium alloy linear friction welding structural parts by optimizing welding process. The process parameter range of TC21 titanium alloy linear friction welding is vibration frequency: 35 Hz, amplitude 4 mm, friction pressure 60 MPa, top forging pressure 80 MPa, and holding time 10 s.

[0040] Step 2: Prepare the strip sample required for electric pulse treatment on the welded joint by machining, and pretreat its surface. The sample size is 90×10×3mm 3 , Grind the sample surface with a grinder to control the surface processing accuracy within 0.01mm;

[0041] Step 3: Fix the strip sample processed in step 2 between two copper electrodes of the electric pulse device. The dimensions of the two copper electrodes are 240×30×3.2 mm. 3 , fix the treated sample between two copper electrodes, and the effective distance between the copper electrodes is 60mm.

[0042] Step 4: Control the temperature and range of the electric pulse treatment by adjusting the electric pulse charging voltage, pulse frequency and pulse time; the electric pulse treatment parameter range is: charging voltage is 50V, pulse frequency is 190Hz, pulse time is 70s, root mean square current density is 6.35×10 6 A / m 2 .

[0043] Step 5. After electric pulse treatment, air cool to room temperature, test the strength and toughness of the sample after electric pulse treatment, clarify the interdependence between joint structure and strength and toughness, use tensile specimens to test joint strength, and then use impact specimens to characterize joint toughness, and analyze the strength and toughness of the joint structure corresponding to different electric pulse conditions.

[0044] Example 2

[0045] The electric pulse toughening treatment method for high-toughness titanium alloy linear friction welding joint is specifically implemented in the following steps:

[0046] Step 1: Prepare TC21 titanium alloy linear friction welding structural parts by optimizing welding process. The process parameter range of TC21 titanium alloy linear friction welding is vibration frequency: 70 Hz, amplitude 3 mm, friction pressure 40 MPa, top forging pressure 50 MPa, and holding time 15 s.

[0047] Step 2: Prepare the strip sample required for electric pulse treatment on the welded joint by machining, and pretreat its surface. The sample size is 90×10×3mm 3 , Grind the sample surface with a grinder to control the surface processing accuracy within 0.01mm;

[0048] Step 3: Fix the strip sample processed in step 2 between two copper electrodes of the electric pulse device. The dimensions of the two copper electrodes are 240×30×3.2 mm. 3 , fix the treated sample between two copper electrodes, and the effective distance between the copper electrodes is 60mm.

[0049] Step 4: Control the temperature and range of the electric pulse treatment by adjusting the electric pulse charging voltage, pulse frequency and pulse time; the electric pulse treatment parameter range is: charging voltage is 50V, pulse frequency is 220Hz, pulse time is 70s, and root mean square current density is 7.07×10 6 A / m 2 .

[0050] Step 5. After electric pulse treatment, air cool to room temperature, test the strength and toughness of the sample after electric pulse treatment, clarify the interdependence between joint structure and strength and toughness, use tensile specimens to test joint strength, and then use impact specimens to characterize joint toughness, and analyze the strength and toughness of the joint structure corresponding to different electric pulse conditions.

[0051] Example 3

[0052] The electric pulse toughening treatment method for high-toughness titanium alloy linear friction welding joint is specifically implemented in the following steps:

[0053] Step 1: Prepare TC21 titanium alloy linear friction welding structural parts by optimizing welding process. The process parameter range of TC21 titanium alloy linear friction welding is vibration frequency: 40 Hz, amplitude 3.5 mm, friction pressure 50 MPa, top forging pressure 60 MPa, and holding time 13 s.

[0054] Step 2: Prepare the strip sample required for electric pulse treatment on the welded joint by machining, and pretreat its surface. The sample size is 90×10×3mm 3 , Grind the sample surface with a grinder to control the surface processing accuracy within 0.01mm;

[0055] Step 3: Fix the strip sample processed in step 2 between two copper electrodes of the electric pulse device. The dimensions of the two copper electrodes are 240×30×3.2 mm. 3 , fix the treated sample between two copper electrodes, and the effective distance between the copper electrodes is 60mm.

[0056] Step 4: Control the temperature and range of the electric pulse treatment by adjusting the electric pulse charging voltage, pulse frequency and pulse time; the electric pulse treatment parameter range is: charging voltage is 50V, pulse frequency is 250Hz, pulse time is 60s, and root mean square current density is 7.36×10 6 A / m 2 .

[0057] Step 5. After electric pulse treatment, air cool to room temperature, test the strength and toughness of the sample after electric pulse treatment, clarify the interdependence between joint structure and strength and toughness, use tensile specimens to test joint strength, and then use impact specimens to characterize joint toughness, and analyze the strength and toughness of the joint structure corresponding to different electric pulse conditions.

[0058] Example 4

[0059] The electric pulse toughening treatment method for high-toughness titanium alloy linear friction welding joint is specifically implemented in the following steps:

[0060] Step 1: Prepare TC21 titanium alloy linear friction welding structural parts by optimizing welding process. The process parameter range of TC21 titanium alloy linear friction welding is vibration frequency: 50 Hz, amplitude 3 mm, friction pressure 50 MPa, top forging pressure 70 MPa, and holding time 15 s.

[0061] Step 2: Prepare the strip sample required for electric pulse treatment on the welded joint by machining, and pretreat its surface. The sample size is 90×10×3mm 3 , Grind the sample surface with a grinder to control the surface processing accuracy within 0.01mm;

[0062] Step 3: Fix the strip sample processed in step 2 between two copper electrodes of the electric pulse device. The dimensions of the two copper electrodes are 240×30×3.2 mm. 3 , fix the treated sample between two copper electrodes, and the effective distance between the copper electrodes is 60mm.

[0063] Step 4: Control the temperature and range of the electric pulse treatment by adjusting the electric pulse charging voltage, pulse frequency and pulse time; the electric pulse treatment parameter range is: charging voltage is 50V, pulse frequency is 250Hz, pulse time is 70s, and root mean square current density is 7.28×10 6 A / m 2 .

[0064] Step 5. After electric pulse treatment, air cool to room temperature, test the strength and toughness of the sample after electric pulse treatment, clarify the interdependence between joint structure and strength and toughness, use tensile specimens to test joint strength, and then use impact specimens to characterize joint toughness, and analyze the strength and toughness of the joint structure corresponding to different electric pulse conditions.

[0065] Figure 1 This is a schematic diagram of the electric pulse toughening treatment method for high-toughness titanium alloy linear friction welding joints. The experiment uses an electroplastic pulse device to perform electric pulse treatment on the TC21 linear friction welding joint. The joint sample is clamped and fixed in the circuit using a pulse power supply positive and negative electrode fixture. The positive and negative electrode fixtures are made of pure copper and have a size of 240×30×3.2mm. 3 ; Connect the digital storage oscilloscope to the positive and negative electrodes of the pulse power supply to test and save the pulse current related parameters; use a contact surface thermometer to closely contact the sample surface to measure the real-time temperature rise in the center area of ​​the sample. By changing the variables such as pulse charging voltage, pulse frequency and pulse time, the joint structure is regulated, and then air cooling is performed to obtain the final sample.

[0066] Figure 2 This is the microstructure diagram of the weld area before and after the electric pulse treatment of the joint obtained in Example 2. Figure 2 (a) is the microstructure of the weld zone of the untreated joint after welding. The original equiaxed crystal structure is clearly visible, and the grain boundary is a long strip of primary α phase. A large number of secondary α′ phases and residual β phases are dispersed inside the grains. After electric pulse treatment, the original equiaxed crystals in the weld zone disappear, the primary α phase at the grain boundary transforms into lamellar, and the spherical dispersed particles in the crystal transform into needle-shaped. The microstructure transformation process is shown in Figure 2. Figure 3As shown, an interlocking basket structure is formed on the β matrix.

[0067] Figure 4 This is a comparison chart of the strength and toughness of the joint after different electric pulse treatments in the electric pulse toughening treatment method of the high-toughness titanium alloy linear friction welding joint of the present invention. The impact toughness values ​​of the joints obtained in Examples 1 to 4 are in the range of 45 J / cm 2 ~60J / cm 2 , the strength range is 915MPa~1009MPa, and the strength and toughness of the joint after electric pulse treatment can reach more than 85% of the strength and toughness of TC21 parent material. Example 2 After electric pulse treatment, the joint toughness reaches 90.5% of the parent material toughness value, and the joint strength reaches 87% of the parent material strength value. The joint toughness after electric pulse treatment is 138.4% higher than that of the welded joint.

[0068] Figure 5 This is a diagram of the impact fracture position of the untreated joint after welding in the electric pulse toughening treatment method of the high-toughness titanium alloy linear friction welding joint of the present invention. It can be seen from the figure that the crack initiation zone of the original welded joint is in the center of the weld, and it extends approximately linearly along the thermally affected zone. The shear lip zone breaks in the center of the weld, and the entire crack propagation path is slightly deflected.

[0069] Figure 6 This is a diagram of the impact fracture position of the joint obtained in Example 2 of the electric pulse toughening treatment method for the high-toughness titanium alloy linear friction welding joint of the present invention. It can be seen from the figure that after the electric pulse heat treatment, the joint crack propagation path is very tortuous, which can be roughly divided into four stages I to IV, and the propagation path presents two deflections of approximately 90°.

[0070] Figure 7 This is the impact fracture morphology of the untreated joint after welding in the electric pulse toughening treatment method of the high-toughness titanium alloy linear friction welding joint of the present invention. It can be seen from the figure that the crack initiation zone ( Figure 7 a) There are obvious cleavage planes and tearing edges, and the crack extension zone ( Figure 7 b) The fracture is mainly along the crystal, with many icicle-like small planes and very shallow dimples distributed in the shear lip area. Therefore, the original welded joint is a typical brittle fracture mode.

[0071] Figure 8 This is the impact fracture morphology of the joint obtained in Example 2 of the electric pulse toughening treatment method for the high-toughness titanium alloy linear friction welding joint of the present invention. It can be seen from the figure that after the electric pulse treatment, the crack initiation zone ( Figure 8 a) Crack extension zone ( Figure 8 b) and shear lip area ( Figure 8 c) are composed of a large number of dimples, and there are no cleavage planes and tearing edges in the crack propagation zone, which is a typical ductile fracture mode.

[0072] The toughness of the TC21 titanium alloy joint obtained after the above electric pulse treatment reaches 90.5% of the toughness of the parent material, and the joint strength reaches 87% of the strength of the parent material, indicating that the thermal / non-thermal synergistic effect of electric pulses can effectively regulate the joint structure and simultaneously improve the strength and toughness of the joint, which has important theoretical significance and engineering application value.

Claims

1. An electric pulse toughening treatment method for a high-toughness titanium alloy linear friction welding joint, characterized in that: Follow the steps below to implement it: Step 1, preparing TC21 titanium alloy linear friction welding structural parts by welding process; Step 2: Prepare a strip sample required for electric pulse treatment on the welded joint by machining, and pretreat its surface; Step 3, fixing the strip sample processed in step 2 between two copper electrodes of an electric pulse device; Step 4, controlling the electric pulse treatment temperature and range by adjusting the electric pulse charging voltage, pulse frequency and pulse time; Step 5, air-cooling to room temperature after the electric pulse treatment, and testing the strength and toughness of the sample after the electric pulse treatment; The process parameter ranges of linear friction welding of TC21 titanium alloy in step 1 are: vibration frequency 30 Hz~70 Hz, amplitude 2 mm~5 mm, friction pressure 30 MPa~70 MPa, upsetting pressure 50 MPa~90 MPa, and holding time 10 s~20 s; The temperature in step 4 is measured using a contact surface thermometer, and the electric pulse processing parameter range is: charging voltage 10V~70V, pulse frequency 100Hz~300Hz, pulse time 10s~100s, root mean square current density 1×10 6 A / m 2 ~9×10 6 A / m 2 ; The dimensions in step 2 are 90×10×3 mm 3 , Grind the sample surface with a grinder to control the surface processing accuracy within 0.01mm; The dimensions of the two copper electrodes in step 3 are both 240×30×3.2 mm 3 , the effective distance between the two copper electrodes is 60mm.

2. The electric pulse toughening treatment method for a high-toughness titanium alloy linear friction welding joint according to claim 1 is characterized in that: In step 5, the tensile test specimen is used to test the joint strength, and the impact test specimen is used to characterize the joint toughness, and the strength and toughness of the joint tissue corresponding to different electric pulse conditions are analyzed.

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