A friction welding weld surface strengthening method based on high temperature ultrasonic shot peening

Abstract

The present invention belongs to the technical field of metal surface strengthening, and in particular relates to a method for strengthening the surface of a friction welding weld based on high-temperature ultrasonic shot peening. Two parts to be welded are welded to obtain a friction-welded part B; the friction-welded part B is treated to make the surface of the friction-welded part B smooth; the surface of the friction-welded part B is cleaned to obtain a welded part C to be strengthened; the welded part C to be strengthened is fixed in an adaptive clamping device, which is placed in a well-type heating furnace. The ultrasonic shot peening equipment is fitted to the welded part C to be strengthened, and the ultrasonic shot peening parameters are set; the ultrasonic shot peening equipment is turned on, and the shot is driven to repeatedly impact the weld surface from different directions to complete the high-temperature ultrasonic shot peening treatment, thereby obtaining a strengthened welded part D. The yield strength of the weld material is effectively reduced by the high-temperature environment, and the high-frequency mechanical energy drives the shot to perform high-energy impact on the weld surface, thereby increasing the fatigue strength of the friction welding weld by more than 50%.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal surface strengthening, and in particular relates to a friction welding weld surface strengthening method based on high-temperature ultrasonic shot peening. Background Art

[0002] Friction-welded aeroengine parts (such as blisks and turbine disks) operate under high temperatures, pressures, and high rotational speeds. The high residual tensile stresses generated during friction welding can cause fatigue initiation and propagation in welded joints, leading to fatigue failure. While traditional mechanical shot peening can improve weld fatigue resistance by creating a residual compressive stress layer through shot impact, it has the following limitations: 1) Risk of surface damage: Shot peening can cause craters on the part surface, significantly increasing surface roughness and potentially creating new stress concentration sources, weakening the strengthening effect. 2) Residual compressive stresses generated by traditional mechanical shot peening are prone to relaxation at high temperatures, significantly reducing the strengthening effect of traditional shot peening. 3) Difficulty in treating complex structures: Traditional mechanical shot peening is difficult to achieve uniform strengthening on certain complex structural parts, resulting in the formation of blind spots. 4) Environmental and energy issues: Traditional shot peening relies on a high-pressure gas source, generating metal dust and noise pollution. Shot peening equipment is bulky, energy-intensive, and difficult to integrate with other process equipment. Therefore, a new surface strengthening technology is needed to address these issues of traditional mechanical shot peening. Summary of the Invention

[0003] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a friction welding weld surface strengthening method based on high-temperature ultrasonic shot peening, which impacts the weld surface from all directions. This continuous and repeated multi-directional high strain rate impact will cause severe plastic deformation on the weld surface, effectively inhibiting surface damage and avoiding the generation of microcracks that are easily generated by traditional mechanical shot peening, thereby achieving high reliability and long service life of friction welding joints.

[0004] The specific technical solutions are as follows:

[0005] A friction welding weld surface strengthening method based on high-temperature ultrasonic shot peening comprises the following steps:

[0006] Step 1: Weld the two parts a and b to be welded according to the process parameters to obtain the friction welded part B;

[0007] Step 2: Processing the friction welded part B obtained in step 1 to make the surface of the friction welded part B smooth;

[0008] Step 3: Clean the surface of the friction welded part B processed in step 2 to obtain the welded part C to be strengthened;

[0009] Step 4: Fix the welded part C to be strengthened obtained in step 3 in an adaptive clamping device;

[0010] Step 5: Place the adaptive clamping device with the welded part C to be strengthened in a pit-type heating furnace equipped with an infrared thermometer, set the target strengthening temperature, and then heat to the target strengthening temperature;

[0011] Step 6: After step 5 is completed, place the ultrasonic shot peening equipment on the welded part C to be strengthened and set the ultrasonic shot peening parameters;

[0012] Step 7: Turn on the ultrasonic shot peening equipment and drive the projectiles to repeatedly impact the weld surface of the welded part C to be strengthened from different directions to complete the high-temperature ultrasonic shot peening treatment. After the high-temperature ultrasonic shot peening is completed, the friction weld is kept to slowly cool to room temperature, and finally the welded part D after high-temperature ultrasonic shot peening is obtained.

[0013] In step 2, the semi-molten metal overflowing around the weld is removed using a mechanical grinding or milling tool.

[0014] In step three, the surface of the friction-welded part B obtained in step two is cleaned by decontamination and polishing.

[0015] In step five, the target strengthening temperature is selected according to the material setting, and the target strengthening temperature is controlled below the recrystallization temperature of the friction welding weld material.

[0016] In step five, when the welded part C to be strengthened is heated to the target strengthening temperature, the pit-type heating furnace controls the heating rate and slowly heats it. After heating to the target strengthening temperature, it is kept warm for half an hour to ensure that the temperature inside and outside the welded part C to be strengthened is uniform.

[0017] In step six, the ultrasonic shot peening equipment is mounted upwardly to clamp the weld of the welded part C to be strengthened.

[0018] In step seven, during the shot peening process, a pit-type heating furnace equipped with an infrared thermometer heats the welded part C to be strengthened, maintaining the temperature inside the furnace at the target strengthening temperature and monitoring the weld surface temperature in real time, so that the dynamic fluctuation of the heating temperature is controlled within ±10°C.

[0019] In step seven, after the welded part C to be strengthened is strengthened by high-temperature ultrasonic shot peening, it is slowly cooled in a pit-type heating furnace by controlling the cooling rate until it cools to room temperature.

[0020] The beneficial effects of the present invention are:

[0021] The present invention combines a high-temperature environment with ultrasonic shot peening strengthening technology. After the welded parts to be strengthened are heated to an appropriate temperature, the ultrasonic shot peening equipment converts electrical energy into a high-frequency electrical signal (>20kHz), which is converted into mechanical vibrations by the ultrasonic transducer of the ultrasonic shot peening equipment. The amplitude is then amplified by the amplitude transformer in the ultrasonic shot peening equipment, and finally the projectiles (smooth spherical steel balls, glass beads, ceramic beads) are impacted at a frequency of tens of thousands of times per second, so that they achieve instantaneous high speed and impact the weld surface from all directions. This continuous and repeated multi-directional high-strain rate impact will cause severe plastic deformation on the weld surface. The high temperature environment reduces the yield strength of the weld and thus intensifies the plastic deformation of the weld surface, which in turn causes significant residual compressive stress on the weld surface, and the grains on the weld surface will gradually be refined to the nanometer level.

[0022] Compared with traditional mechanical shot peening, high-temperature ultrasonic shot peening strengthening technology has the following advantages: 1. Stability of the strengthening layer. High-temperature ultrasonic shot peening promotes the proliferation of dislocations through the thermomechanical coupling effect. The residual compressive stress layer and nanocrystals formed have a low thermal relaxation rate and a slow growth rate at high temperature; it effectively inhibits surface damage, and the high-temperature environment improves the plasticity of the material, avoiding the generation of microcracks that are prone to traditional mechanical shot peening; 2. Adaptability to complex structures. Compared with traditional mechanical shot peening that relies on large pneumatic devices, the projectile ejection trajectory is limited, and the coverage of complex curved surfaces or inner cavities is uneven, making it difficult to handle complex structures. High-temperature ultrasonic shot peening equipment adopts a handheld or robotic arm integrated design with a small size. It can operate flexibly in small spaces or large workpieces. The projectiles of high-temperature ultrasonic shot peening can achieve multi-directional impact through high-frequency vibration, and can penetrate into grooves, holes, welds and other areas that cannot be covered by mechanical shot peening, and have good adaptability to complex structures; 3. High-temperature ultrasonic shot peening projectiles use less, are recyclable, and have no dust pollution.

[0023] This application innovatively applies high-temperature ultrasonic shot peening technology to the field of friction welding weld strengthening. By creating a high-temperature environment, it effectively reduces the yield strength of the weld material and uses high-frequency mechanical energy to drive the projectile to deliver high-energy impact to the weld surface. Experimental data shows that this technology can form a residual compressive stress field on the weld surface with a depth of up to 1mm, a value more than twice that of traditional shot peening. It also achieves a higher shot coverage rate than traditional processes, thereby more effectively eliminating residual tensile stress in the weld. More significantly, this technology can refine the weld surface grains to the nanometer level (<100nm), increasing the fatigue strength of friction welds by more than 50%, and its overall strengthening effect is more than 10% higher than that of traditional shot peening.

[0024] Based on these technical advantages, this achievement provides a clear technical path for surface strengthening of friction-welded aero-engine parts. The application of this technology will significantly improve the reliability of key engine components and effectively reduce lifecycle maintenance costs, thus possessing significant engineering value in promoting the high-performance and sustainable development of aero-engine equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the structure of parts after friction welding in the present invention;

[0026] Figure 2 Schematic diagram of the structure of the adaptive clamping device for clamping the welded part C to be strengthened in the present invention;

[0027] Figure 3 This is a schematic diagram of the structure in which the welded part C to be strengthened is placed in a pit-type heating furnace for heating in the present invention;

[0028] Figure 4 Schematic diagram of high temperature ultrasonic shot peening process;

[0029] Figure 5 This is a schematic diagram of the parts after high-temperature ultrasonic shot peening;

[0030] Figure 6 This is a shot peening time-arc height relationship curve in this embodiment;

[0031] Among them, 1. Part a to be welded; 2. Part b to be welded; 3. Part B after friction welding; 4. Part C to be strengthened and welded; 5. Part D to be welded after strengthening; 6. Adaptive clamping device; 7. Well-type heating furnace; 8. Ultrasonic shot peening equipment. DETAILED DESCRIPTION

[0032] In order to better explain the present invention and facilitate understanding, the technical solutions and effects of the present invention are described in detail below with reference to the accompanying drawings through specific implementation methods.

[0033] This example discloses a friction welding seam surface strengthening method based on high-temperature ultrasonic shot peening. It is used to strengthen the weld surface of friction welded parts. In this example, the welded parts a1 and b2 are rectangular TC4 titanium alloy test pieces measuring 13 mm by 8 mm by 40 mm. The welding parameters are: vibration frequency of 40 Hz, amplitude of 2 mm, friction pressure of 70 MPa, friction time of 15 s, forging pressure of 140 MPa, and forging time of 10 s.

[0034] Step 1: The welding surfaces of the two parts a1 and b2 to be welded are machined (such as milling, turning) and cleaned to ensure that the joint surfaces are free of scratches and contamination. After that, the two parts a1 and b2 to be welded are clamped in the fixture of the friction welding workbench and welded according to the above process parameters (basic parameters of vibration frequency, amplitude, friction pressure, friction time, upsetting pressure, and upsetting time) to obtain the friction welded part B3, as shown in the figure. Figure 1 As shown;

[0035] Step 2: Use mechanical grinding or milling tools to remove the semi-molten metal (welding flash, such as welding burrs) overflowing from the friction welded part B3 obtained in step 1. Figure 1 As shown) make the surface of part B3 smooth after friction welding;

[0036] Step 3: Clean the surface of the friction welded part B3 after removing the flash in step 2, for example, by decontamination and polishing, to ensure that the roughness is ≤ 0.8 μm, and obtain the welded part C4 to be strengthened. Figure 2 As shown;

[0037] Among them, after cleaning, an appearance inspection is carried out to observe the uniformity of weld formation and surface smoothness, and to detect whether there are defects such as cracks and pores. If the appearance inspection is qualified and there are no visible defects, the weld appearance quality is judged to be qualified, and the welded part to be strengthened C4 is obtained. If it is unqualified, treatment measures need to be taken. If there are significant defects (incomplete penetration, pores), repair welding is required.

[0038] Step 4: Fix the welded part C4 to be strengthened obtained in step 3 in the adaptive clamping device 6 (model 1200ag-1005050-hs), ensuring that the clamp can be adaptively adjusted when the workpiece is extended at high temperature, such as Figure 2 As shown;

[0039] Step 5: Place the adaptive clamping device 6 with the welded part C4 to be strengthened into a pit-type heating furnace 7 (model RJ2-80-12) equipped with an infrared thermometer, set the target strengthening temperature to 450°C (usually controlled below the metal recrystallization temperature), and keep the temperature for half an hour after reaching the target strengthening temperature to ensure uniform temperature inside and outside the welded part C4. Figure 3 As shown;

[0040] The target strengthening temperature is precisely set based on the material, meaning it must be below the recrystallization temperature of the friction weld material. Ultrasonic shot peening below the recrystallization temperature not only reduces the yield strength of the weld, effectively minimizing surface damage while enhancing the shot peening effect, but also prevents grain growth and relaxation of residual compressive stresses. Furthermore, the high temperature effectively releases residual tensile stresses introduced during the friction welding process. Different temperatures are selected for high-temperature ultrasonic shot peening depending on the material, such as around 450°C for titanium alloys, around 600°C for nickel-based alloys, and around 150°C for aluminum alloys. When heating the welded part C4 to the target strengthening temperature, it should be slowly heated in a pit-type heating furnace 7 using a controlled heating rate (≤10°C / min). A gradient heating process is employed to avoid thermal stress concentration. The pit-type heating furnace 7 is an open structure, allowing the surface of the welded part C4 to be exposed to direct sunlight.

[0041] Step 6: If Figure 4 As shown, after step 5 is completed, the ultrasonic shot peening equipment 8 (model UPM-5040) is clamped from above to the weld of the welded part C4 to be strengthened, ensuring that the edge of the ultrasonic shot peening equipment 8 is in contact with the welded part C4 to be strengthened. The ultrasonic shot peening parameters are set (3 mm diameter steel shot, 20 kHz ultrasonic frequency, 25 μm ultrasonic amplitude, 8 mm shot distance, 1 minute shot time, 200 shots);

[0042] The method for determining the shot peening time of the weld surface of the titanium alloy rectangular parallelepiped test block in this embodiment is as follows:

[0043] After step 5 is completed, the standard A-type Almen test piece is fixed on the weld surface area of ​​the welded part C4 to be strengthened. Then, the nozzle of the storage chamber of the ultrasonic shot peening equipment 8 is vertically aligned with the weld, ensuring that the edge of the equipment is in close contact with the surface of the welded part C4 to be strengthened. The shot peening parameters are set: 3mm diameter steel shot, 200 shots, 20kHz ultrasonic frequency, 25μm amplitude, and 8mm shot distance.

[0044] Shot peening tests of different durations were conducted in groups. After each shot peening, the test pieces were removed and the arc height value caused by the single-side shot peening deformation was accurately measured using an Almen arc height measuring instrument (unit: mm, 0.20A indicates that the arc height of the A-type test piece is 0.20mm); Figure 6 As shown, by plotting the relationship between shot peening time and arc height (saturation curve), the saturation point is determined—the critical point where the arc height increase is ≤10% when the shot peening time is doubled. In this example, the saturation point corresponds to a shot peening intensity of 0.20A, and the time required to reach this intensity is 1 minute. During this process, the Almen coupon coverage must be verified by fluorescence tracing to be ≥98% (in this case, 100% coverage is required).

[0045] After confirming the saturation point, the final process parameters were set based on an intensity value of 0.20A. The Almen test piece was removed, and ultrasonic shot peening was performed on the weld surface of the welded component C4 to be strengthened. The entire process strictly adhered to the requirements of the HB / Z 26-2021 standard for shot peening intensity control, coverage verification, and process consistency. The shot peening time in this embodiment was ultimately determined to be 1 minute. When shot peening other materials, the shot peening time can be determined according to the above method to set the ultrasonic peening parameters. Under the same conditions, the shot peening time is fixed and does not need to be repeatedly determined.

[0046] In addition, the nozzle of the shot storage chamber of the ultrasonic shot peening equipment 8 is 8 mm away from the surface of the welded part C4 to be strengthened, that is, the shot peening distance is 8 mm; the ultrasonic shot peening equipment 8 is upward (for ease of understanding, Figure 4 The welded part C4 to be strengthened is placed under the ultrasonic shot peening equipment 8. In fact, the welded part C4 to be strengthened is placed above the ultrasonic shot peening equipment 8) and is attached to the welded part C4 to be strengthened. After the shot peening is completed, the shot automatically falls back into the shot storage room; the shot and amplitude parameters need to be selected according to the material, such as steel shot for titanium alloy, ceramic shot or glass shot for aluminum alloy, and ceramic shot or steel shot for high-temperature alloy.

[0047] Step 7: Turn on the ultrasonic shot peening equipment 8, drive the projectiles to repeatedly hit the weld surface of the welded part C4 to be strengthened from different directions, and the weld surface produces plastic deformation during the high-temperature ultrasonic shot peening strengthening process, and finally completes the high-temperature ultrasonic shot peening treatment, such as Figure 4 As shown in the figure; after the high temperature ultrasonic shot peening is completed, the friction weld is kept to cool slowly to room temperature to avoid the generation of additional residual tensile stress, and finally the welded part D5 after high temperature ultrasonic shot peening is obtained, as shown in the figure. Figure 5 shown.

[0048] Among them, such as Figure 4 As shown, the shot is ejected in the direction of the arrow under the action of high-frequency mechanical vibration and is shot towards the weld surface from different directions; during the shot peening process, the pit-type heating furnace 7 with an infrared thermometer heats the weld part C4 to be strengthened, so that the temperature in the furnace is maintained at the target strengthening temperature and the weld surface temperature is monitored in real time, so that the dynamic fluctuation of the heating temperature is controlled within ±10°C.

[0049] Furthermore, after high-temperature ultrasonic shot peening, welded part C4 undergoes a slow cooling process in a pit-type heating furnace 7 using a controlled cooling rate (≤10°C / min) until it reaches room temperature. This prevents thermal stress from forming in the friction weld. X-ray diffractometers are used to measure the surface residual stress of the friction weld after strengthening. The surface residual stress is required to reach 60% of the yield strength. If this does not meet the requirement, high-temperature ultrasonic shot peening may be repeated.

[0050] The present invention can be operated according to this method for different structural parts.

Claims

1. A friction welding weld surface strengthening method based on high temperature ultrasonic shot peening, characterized in that: The following steps are involved: Step 1: Weld the two parts a and b to be welded according to the process parameters to obtain the friction welded part B; Step 2: Processing the friction welded part B obtained in step 1 to make the surface of the friction welded part B smooth; Step 3: Clean the surface of the friction welded part B processed in step 2 to obtain the welded part C to be strengthened; Step 4: Fix the welded part C to be strengthened obtained in step 3 in an adaptive clamping device; Step 5: Place the adaptive clamping device with the welded part C to be strengthened in a pit-type heating furnace equipped with an infrared thermometer, set the target strengthening temperature, and then heat to the target strengthening temperature; Step 6: After step 5 is completed, place the ultrasonic shot peening equipment on the welded part C to be strengthened and set the ultrasonic shot peening parameters; Step 7: Turn on the ultrasonic shot peening equipment and drive the projectile to repeatedly impact the weld surface of the welded part C to be strengthened from different directions to complete the high-temperature ultrasonic shot peening treatment. After the high-temperature ultrasonic shot peening is completed, the friction weld is kept to slowly cool to room temperature, and finally the welded part D after high-temperature ultrasonic shot peening is obtained.

2. The method for strengthening the surface of a friction welding seam based on high-temperature ultrasonic shot peening according to claim 1, characterized in that: In step 2, the semi-molten metal overflowing around the weld is removed using a mechanical grinding or milling tool.

3. The method for strengthening the surface of a friction welding seam based on high temperature ultrasonic shot peening according to claim 1, characterized in that: In step three, the surface of the friction-welded part B obtained in step two is cleaned by decontamination and polishing.

4. The method for strengthening the surface of a friction welding seam based on high temperature ultrasonic shot peening according to claim 1, characterized in that: In step five, the target strengthening temperature is selected according to the material setting, and the target strengthening temperature is controlled below the recrystallization temperature of the friction welding weld material.

5. The method for strengthening the surface of friction welding seams based on high temperature ultrasonic shot peening according to claim 1, characterized in that: In step five, when the welded part C to be strengthened is heated to the target strengthening temperature, the pit-type heating furnace controls the heating rate and slowly heats it. After heating to the target strengthening temperature, it is kept warm for half an hour to ensure that the temperature inside and outside the welded part C to be strengthened is uniform.

6. The method for strengthening the surface of a friction welding seam based on high temperature ultrasonic shot peening according to claim 1, characterized in that: In step six, the ultrasonic shot peening equipment is mounted upwardly to clamp the weld of the welded part C to be strengthened.

7. The method for strengthening the surface of friction welding seams based on high temperature ultrasonic shot peening according to claim 1, characterized in that: In step seven, during the shot peening process, a pit-type heating furnace equipped with an infrared thermometer heats the welded part C to be strengthened, maintaining the temperature inside the furnace at the target strengthening temperature and monitoring the weld surface temperature in real time, so that the dynamic fluctuation of the heating temperature is controlled within ±10°C.

8. The method for strengthening the surface of friction welding seams based on high temperature ultrasonic shot peening according to claim 1, characterized in that: In step seven, after the welded part C to be strengthened is strengthened by high-temperature ultrasonic shot peening, it is slowly cooled in a pit-type heating furnace by controlling the cooling rate until it cools to room temperature.

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