Method and system for regulating and controlling residual stress of high-strength aluminum alloy thin-wall ribbed member

Abstract

The invention discloses a method and a system for regulating and controlling residual stress of a high-strength aluminum alloy thin-wall ribbed member. The invention relates to the field of material processing, and aims to solve the problems that in the prior art, macro-micro coupling residual stress of a high-strength aluminum alloy thin-wall ribbed component is difficult to systematically and cooperatively regulate and control, and processing deformation, size out-of-tolerance and stress corrosion cracking are easily caused. The method comprises the steps that tensile preload is applied to the component, 0.2%-0.8% of global inelastic strain is generated, and unloading is carried out after load holding; high-frequency ultrasonic vibration is applied to the surface of the component, and the local alternating stress amplitude is not lower than 10% of the local residual stress value of a corresponding area; the lowest temperature is less than or equal to-150 DEG C, and the heating and cooling rate is controlled between 0.5 DEG C / min and 5 DEG C / min. After being treated by the method, the residual stress peak value of the component is obviously reduced, the dimensional stability is greatly improved, the microstructure is optimized, and the service performance is enhanced.

Description

Technical Field

[0001] This invention relates to the field of materials processing technology, and in particular to a method and system for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components. Background Technology

[0002] High-strength aluminum alloy thin-walled stiffened components, due to their high specific strength and high stiffness, are widely used in the main load-bearing structures of aerospace and other fields. During the manufacturing process, these components typically undergo critical processes such as high-temperature solution treatment and rapid quenching. However, due to uneven cooling of the cross-section and the geometric constraints of the "skeleton-skin" structure, a complex three-dimensional macroscopic residual stress field is generated inside the component. Simultaneously, the quenching process introduces high-density dislocations, vacancies, and other crystal defects, further forming a microscale lattice distortion stress field.

[0003] In existing technologies, the treatment of residual stress in such components often employs a single post-processing method. For example, mechanical tensioning is only effective for components with simple cross-sections, and it is difficult to achieve comprehensive and effective stress control for complex thin-walled stiffened components. Vibration aging is relatively simple to operate, but its effect is relatively superficial and unstable, and it cannot penetrate deep into the component to solve the problem of residual stress. Cryogenic treatment mainly targets microscopic defects and has limited ability to reduce macroscopic residual stress.

[0004] These traditional, single-method approaches cannot systematically and collaboratively address the macro-micro coupled residual stress problem in high-strength aluminum alloy thin-walled stiffened components. This leads to unpredictable "tool deflection" deformation during subsequent precision machining, resulting in dimensional deviations and severely impacting machining accuracy. More seriously, the presence of residual stress may also trigger stress corrosion cracking, significantly reducing the component's service safety and reliability. Therefore, it is necessary to propose a method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components to solve these problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components, in order to solve the problem that existing technologies cannot systematically and synergistically address the macro-micro coupled residual stress in high-strength aluminum alloy thin-walled stiffened components, which leads to subsequent processing deformation, dimensional deviations, and the risk of stress corrosion cracking.

[0006] In a first aspect, the present invention provides a method for controlling residual stress in a high-strength aluminum alloy thin-walled stiffened component, comprising: Step 1: Apply a tensile preload to the component to induce a global inelastic strain of 0.2% to 0.8%, and make the maximum equivalent stress of the component section lower than 85% of the yield strength of the material at that temperature. After holding the load for a preset time, unload the component.

[0007] Step 2: Apply high-frequency ultrasonic vibration to the surface of the component treated in Step 1. The amplitude of the local alternating stress generated by the high-frequency ultrasonic vibration shall not be less than 10% of the local residual stress value in the corresponding area of ​​the component.

[0008] Step 3: Perform programmed cryogenic thermal cycling on the components processed in Step 2. The minimum temperature of the cryogenic thermal cycling is ≤-150℃, and the heating and cooling rate is controlled between 0.5℃ / min and 5℃ / min.

[0009] Furthermore, in step one, the preset holding time t_hold and the maximum cross-sectional thickness d of the component satisfy the following relationship: t_hold≥2d, where t_hold is in minutes and d is in millimeters.

[0010] Furthermore, in step one, the unloading process adopts slow linear unloading, with an unloading rate of no more than 0.5 mm / min.

[0011] Furthermore, in step two, when the high-frequency ultrasonic vibration is applied, a robotic arm is used to hold a focused ultrasonic transducer to scan the surface of the component.

[0012] Furthermore, in step two, the scanning adopts a dual-frequency alternating mode.

[0013] Furthermore, in step two, the dual-frequency alternation mode includes 20kHz and 40kHz.

[0014] Furthermore, in step two, the path overlap rate of the scan is not less than 30%.

[0015] Furthermore, in step three, the cryogenic thermal cycling process has a cycle of no less than two.

[0016] Furthermore, in step three, during the low-temperature insulation stage of the cryogenic thermal cycling treatment, a static pressure of 0.5 bar to 2 bar is applied to the treatment medium.

[0017] Secondly, the present invention provides a residual stress control system for high-strength aluminum alloy thin-walled stiffened components, comprising: The macro-stress coordination unit is used to apply tensile preload to the component, causing the component to produce a global inelastic strain of 0.2% to 0.8%, and making the maximum equivalent stress of the component section lower than 85% of the yield strength of the material at that temperature. After holding the load for a preset time, the load is unloaded. The macro-stress coordination unit includes a multi-actuator coordinated loading mechanism and a clamp designed conformally to the ribs of the component.

[0018] An ultrasonic dislocation engineering unit is used to apply high-frequency ultrasonic vibration to the surface of a component treated by a macro-stress coordination unit. The amplitude of the local alternating stress generated by the high-frequency ultrasonic vibration is not less than 10% of the local residual stress value in the corresponding area of ​​the component. The ultrasonic dislocation engineering unit includes a high-power ultrasonic generator, a focusing transducer, and a six-axis robotic arm for holding the transducer and scanning the surface of the component.

[0019] A cryogenic thermodynamic coupling unit is used to perform programmed cryogenic thermal cycling treatment on components that have undergone ultrasonic dislocation engineering unit treatment. The minimum temperature of the cryogenic thermal cycling treatment is ≤-150℃, and the heating and cooling rate is controlled between 0.5℃ / min and 5℃ / min. The cryogenic thermodynamic coupling unit includes a cryogenic treatment device with programmed temperature and pressure regulation functions. The cryogenic treatment device is capable of cooling the component to -196℃ and applying a static pressure of 0.5 bar to 2 bar.

[0020] The central intelligent control system is communicatively connected to the macro-stress coordination unit, the ultrasonic dislocation engineering unit, and the cryogenic thermo-coupling unit, and is used to integrate and control the sequential and coordinated operation of each unit; the central intelligent control system includes an online stress monitoring module and a process parameter dynamic optimization module.

[0021] The beneficial effects of this invention are as follows: The method and system for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components of this invention systematically solves the problem of macro-micro coupled residual stress in high-strength aluminum alloy thin-walled stiffened components through the synergistic effect of three steps: controllable plastic coordination of the macro-stress field, ultrasonic-assisted reconstruction of the micro-dislocation structure, and deep cryogenic cycling stabilization of micro-defects and microstructure. Components treated by this invention exhibit significantly reduced peak residual stress on the surface and in the core, and a more uniform stress distribution across the entire cross-section. This effectively avoids tool deformation and dimensional deviations during subsequent precision machining, while also greatly reducing the risk of stress corrosion cracking, significantly improving the service safety and reliability of the components. Furthermore, the process of reducing residual stress also optimizes the microstructure, rationally controls the dislocation structure, and the nanoscale phase precipitation induced by cryogenic treatment provides additional precipitation strengthening, achieving a synergistic improvement in strength and toughness, further enhancing the overall performance of the components. Attached Figure Description

[0022] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of the method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components according to the present invention.

[0024] Figure 2 This is a schematic diagram illustrating the principle of residual stress control in the high-strength aluminum alloy thin-walled stiffened component of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The technical solutions provided by various embodiments of this invention will be described in detail below with reference to the accompanying drawings.

[0026] Please see Figure 1 The present invention provides a method for controlling residual stress in a high-strength aluminum alloy thin-walled stiffened component, comprising: Step 1: Apply a tensile preload to the component to induce a global inelastic strain of 0.2% to 0.8%, and make the maximum equivalent stress of the component section lower than 85% of the yield strength of the material at that temperature. After holding the load for a preset time, unload the component.

[0027] A tensile preload, below the macroscopic yield limit but sufficient to induce local microscopic yielding, is applied to the component. The purpose is not simple elastic deformation, but rather to force an inelastic redistribution of the original quenching stress field within the component by introducing controllable, directional macroscopic plastic strain. This "flattens" the high-gradient stress peaks, reducing the overall stress level to a lower and more uniform plateau. This step creates a uniform initial stress background field for subsequent, more refined micro-processing.

[0028] This invention employs a high-rigidity, multi-actuator coordinated specialized tensioning machine, equipped with a hydraulically expanded or modular mechanical locking clamp designed conformally to the ribs of the component, ensuring uniform load transfer and preventing localized crushing. The loading path uses a displacement control mode, and the target strain (ε_target) is calibrated based on finite element simulation and actual measurements, satisfying: 0.2% ≤ ε_target ≤ 0.8%, and ensuring that the maximum equivalent stress at the most critical section of the component does not exceed 85% of its yield strength at that temperature. The preset holding time t_hold is related to the section thickness d, and the preset holding time t_hold and the maximum section thickness d of the component satisfy the following relationship: t_hold ≥ 2d, where t_hold is in minutes and d is in millimeters. Unloading must be performed using slow linear unloading, with a rate ≤ 0.5 mm / min.

[0029] Step 2: Apply high-frequency ultrasonic vibration to the surface of the component treated in Step 1. The amplitude of the local alternating stress generated by the high-frequency ultrasonic vibration shall not be less than 10% of the local residual stress value in the corresponding area of ​​the component.

[0030] A high-frequency (>20kHz) ultrasonic energy field is applied to the macroscopic stress field that has already been "peak-shaving and valley-filling". The core mechanism has two aspects: first, utilizing the acoustic plasticity effect, i.e., the superposition of high-frequency alternating stress and residual stress, reduces the critical shear stress for dislocation slip, promoting the directional slip, multiplication, and reorganization of dislocations, thereby releasing lattice distortion energy; second, utilizing the microscopic plastic rheology generated near the material surface by ultrasonic cavitation and rheological effects to further homogenize surface stress. This step aims to "domesticate" and reconstruct the dislocation substructure. When the high-frequency ultrasonic vibration is applied, a robotic arm holds a focusing ultrasonic transducer to scan the surface of the component. The scanning adopts a dual-frequency alternating mode. The dual-frequency alternating mode includes frequencies of 20kHz and 40kHz or higher. The path overlap rate of the scan is not less than 30%.

[0031] Specifically, this invention employs a high-power ultrasonic generator exceeding 2kW, combined with a focused transducer and a six-axis robotic arm, to achieve adaptive scanning of complex curved surfaces. A variable-frequency scanning mode, such as alternating between 20kHz and 40kHz, is used to excite dislocation responses of different depths and scales. The ultrasonic amplitude A is crucial and must satisfy: σ_acoustic(≈E) β A ω)≥0.1 σ_yield(local), where σ_acoustic refers to the amplitude of alternating stress generated locally in the material by high-frequency ultrasonic vibration, E is Young's modulus, β is the material nonlinear coefficient, ω is the angular frequency, and ω represents the yield strength of the material in the corresponding region of the component under local conditions. The scanning speed v and overlap rate η must satisfy: v(mm / s)≤f λ / 10, where f is the frequency, λ is the wavelength, and η≥30%, to ensure uniform coverage of the energy field.

[0032] Step 3: Perform programmed cryogenic thermal cycling on the components processed in Step 2. The minimum temperature of the cryogenic thermal cycling is ≤-150℃, and the heating and cooling rate is controlled between 0.5℃ / min and 5℃ / min.

[0033] This invention involves programmed cryogenic cycling of components that have undergone macroscopic coordination and dislocation reconstruction. Different phases and grains with different orientations in the material exhibit varying shrinkage coefficients at extremely low temperatures, generating microscopic thermal mismatch stress that drives further movement and annihilation of dislocations. Cryogenic treatment promotes the migration of supersaturated vacancies to wells such as dislocation lines and grain boundaries, pinning dislocations and simultaneously "freezing" the optimized defect structure, enhancing microstructural stability. The extremely low temperature treatment effectively suppresses atomic thermal diffusion, thereby locking in the stress relief results achieved in the first two steps. The cryogenic thermal cycling process consists of at least two cycles. During the low-temperature holding phase of the cryogenic thermal cycling process, a static pressure of 0.5 bar to 2 bar is applied to the treatment medium.

[0034] Specifically, this invention employs a cryogenic treatment system with high-precision (±1℃) temperature control and programmable pressure (0-10 bar) regulation. At least two complete thermal cycles are performed. A typical cycle is: room temperature, decreasing to -80℃ at 2℃ / min (inducing partial phase change), holding at this temperature for 30 min, decreasing to -196℃ (liquid nitrogen) at 1℃ / min, holding at this temperature for 120 min, recovering to -80℃ at 0.5℃ / min, and then recovering to room temperature at 1℃ / min. A hydrostatic liquid nitrogen pressure of 0.5-2 bar can be applied to provide gentle hydrostatic stress, aiding microscopic plastic flow.

[0035] The above three-step process should be integrated into a manufacturing unit equipped with a data bus. The central controller, based on the component's three-dimensional model, material database, and online stress monitoring data, such as using an ultrasonic or X-ray online thickness gauge to invert stress, dynamically optimizes the process parameters of steps one to three, realizing closed-loop intelligent control of measurement, modeling, processing, and verification.

[0036] This invention also provides a residual stress control system for high-strength aluminum alloy thin-walled stiffened components, used to implement the above-mentioned method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components, including: The macro-stress coordination unit is used to apply tensile preload to the component, causing the component to produce a global inelastic strain of 0.2% to 0.8%, and making the maximum equivalent stress of the component section lower than 85% of the yield strength of the material at that temperature. After holding the load for a preset time, the load is unloaded. The macro-stress coordination unit includes a multi-actuator coordinated loading mechanism and a clamp designed conformally to the ribs of the component.

[0037] An ultrasonic dislocation engineering unit is used to apply high-frequency ultrasonic vibration to the surface of a component treated by a macro-stress coordination unit. The amplitude of the local alternating stress generated by the high-frequency ultrasonic vibration is not less than 10% of the local residual stress value in the corresponding area of ​​the component. The ultrasonic dislocation engineering unit includes a high-power ultrasonic generator, a focusing transducer, and a six-axis robotic arm for holding the transducer and scanning the surface of the component.

[0038] A cryogenic thermodynamic coupling unit is used to perform programmed cryogenic thermal cycling treatment on components that have undergone ultrasonic dislocation engineering unit treatment. The minimum temperature of the cryogenic thermal cycling treatment is ≤-150℃, and the heating and cooling rate is controlled between 0.5℃ / min and 5℃ / min. The cryogenic thermodynamic coupling unit includes a cryogenic treatment device with programmed temperature and pressure regulation functions. The cryogenic treatment device is capable of cooling the component to -196℃ and applying a static pressure of 0.5 bar to 2 bar.

[0039] The central intelligent control system is communicatively connected to the macro-stress coordination unit, the ultrasonic dislocation engineering unit, and the cryogenic thermo-coupling unit, and is used to integrate and control the sequential and coordinated operation of each unit; the central intelligent control system includes an online stress monitoring module and a process parameter dynamic optimization module.

[0040] Figure 2 This is a schematic diagram illustrating the principle of residual stress control in the high-strength aluminum alloy thin-walled stiffened component of the present invention. From left to right, the thin-walled stiffened plate is clamped and pre-stretched (deformation amount 0.5%–0.8%, parameter range 0.2%–0.8%) to achieve macroscopic stress redistribution. Subsequently, ultrasonic high-frequency vibration and surface scanning are performed to promote dislocation reconstruction and surface stress homogenization. Then, liquid nitrogen deep cryogenic cycle treatment is performed to stabilize defects and microstructure. Finally, the residual stress peak value is reduced, the stress distribution is more uniform, the processing deformation is reduced, and the dimensional stability is improved.

[0041] In summary, this invention first addresses the main contradictions at the macroscopic level, then refines them at the mesoscopic / microscopic level, and finally achieves stabilization at the atomic scale. This sequential approach avoids the problem that reverse processing might lead to the destruction of the optimized microstructure by macroscopic plastic deformation. The tensile prestress determines the material's subsequent sensitivity to ultrasound, and the dislocation structure formed after ultrasound treatment directly affects the kinetics of vacancy pinning and phase transformation during cryogenic treatment. These parameters need to be optimized collaboratively through system experiments and multi-scale modeling. After treatment with this invention, AA7050-T7451 type components show significantly improved residual stress reduction depth and uniformity. The peak residual stress on the surface and in the core is reduced by ≥90%, the standard deviation of stress across the entire cross-section decreases by ≥70%, and the stress distribution changes from a "saddle-shaped" distribution after quenching to a near-horizontal "platform-shaped" distribution. Regarding dimensional stability, after subsequent milling, the maximum deformation can be controlled within 0.05 mm / m, an improvement of an order of magnitude compared to traditional single-process methods. The microstructure was also significantly optimized. TEM observation showed that dislocations transformed from a tangled state after quenching to a clear dislocation wall / cellular structure. Cryogenic treatment induced uniformly dispersed nanoscale η' phase precipitation, which brought additional precipitation strengthening while relieving stress, achieving a synergistic improvement in strength and toughness. The service performance of the components also performed excellently, with the stress corrosion threshold K_ISCC increasing by more than 30% and high-cycle fatigue life increasing by 1-2 orders of magnitude.

[0042] The following describes in detail the residual stress control method for high-strength aluminum alloy thin-walled stiffened components of the present invention with reference to several embodiments.

[0043] Example 1: 7050-T7451 aluminum alloy wing rib stringer for aviation.

[0044] This embodiment focuses on a 7050-T7451 aluminum alloy wing rib stringer component of a certain type of aircraft wing. This component is a typical "U"-shaped cross-section ribbed structure with a maximum wall thickness of 8mm, a rib height of 25mm, and a total length of 1800mm. After solution hardening, this component exhibits severe "saddle-shaped" residual stress distribution, with a peak surface compressive stress of -180MPa and a peak core tensile stress of +210MPa, posing an extremely high risk of deformation during subsequent processing.

[0045] Step 1: Macro-stress coordination.

[0046] A 600-ton tensioning machine with four actuators operating in a synchronized and coordinated manner, coupled with modular mechanical locking fixtures conforming to the stiffeners of the component, was employed. Based on finite element simulation and pre-analysis of the component's 3D model, the target strain ε_target was set to 0.45%. Loading was performed using a displacement-controlled mode at a loading rate of 1.2 mm / min. Once the target displacement was reached, a hold-load phase was initiated. Based on the component's maximum cross-sectional thickness d = 8 mm, the hold-load time t_hold ≥ 2d = 16 minutes was calculated; in this embodiment, the actual hold-load time was set to 20 minutes. After the hold-load phase, slow linear unloading was employed at a rate of 0.3 mm / min, significantly lower than the upper limit of 0.5 mm / min, to fully release the elastic aftereffects.

[0047] After treatment, the global stress field of the component was significantly harmonized. X-ray diffraction analysis showed that the maximum equivalent stress in the cross-section was reduced to 72% of the material's yield strength in this state (approximately 450 MPa), i.e., below approximately 324 MPa. The "saddle-shaped" peak of the stress distribution was flattened by about 40%, creating a uniform initial stress background field for subsequent treatment.

[0048] Step 2: Ultrasonic dislocation engineering.

[0049] A 3kW high-power ultrasonic generator, equipped with a 25mm diameter focusing transducer, was used to adaptively scan the component surface using a six-axis robotic arm. A dual-frequency alternating scanning mode of 20kHz and 40kHz was employed, switching between frequencies after each scan, for a total of four cycles. The scan path overlap rate was set to 35% to ensure uniform energy field coverage. The ultrasonic amplitude A was dynamically adjusted according to the formula σ_acoustic(≈EβAω)≥0.1σ_yield(local). For 7050 aluminum alloy, E≈71.7GPa, β was pre-calibrated to 0.35, ω was taken as 2π×20kHz or 40kHz, and the local yield strength σ_yield(local) was taken as 450MPa. The calculated minimum required amplitude A was approximately 3.5μm (20kHz) and 1.8μm (40kHz). In actual control, the system dynamically maintains the amplitude within the ranges of 4-5 μm (20 kHz) and 2-3 μm (40 kHz) based on feedback from online stress monitoring. The scanning speed v is set to 3 mm / s, satisfying v ≤ f. Constraints of λ / 10 (at 20kHz, wavelength λ≈5mm, f) λ / 10 = 10 mm / s).

[0050] After treatment, transmission electron microscopy revealed a significant change in the dislocation morphology near the surface of the component. The high-density tangled dislocations after quenching transformed into clear dislocation walls and cellular structures, indicating that the acoustic plasticity effect effectively promoted dislocation rearrangement and annihilation. The residual stress on the surface was further homogenized, with the compressive stress fluctuation range reduced to within ±15 MPa.

[0051] Step 3: Cryogenic thermodynamic coupling treatment.

[0052] The component was placed in a high-precision, programmable cryogenic treatment system and subjected to three complete thermal cycles. The process parameters for each cycle were as follows: Cool from room temperature to -80°C at a rate of 2°C / min and hold for 30 minutes (to induce partial re-dissolution of the GP zone).

[0053] Continue cooling to -196℃ (liquid nitrogen environment) at a rate of 1℃ / min, and hold for 180 minutes. During the holding period, apply a static pressure of 1.2 bar to the liquid nitrogen medium through a programmable control system.

[0054] The temperature is raised to -80℃ at a rate of 0.8℃ / min, and then warmed back to room temperature at a rate of 1.5℃ / min.

[0055] Treatment effect evaluation: After a complete three-step process, the components undergo comprehensive testing: Residual stress: The peak residual stress on the surface and in the core decreased to the range of -12MPa to +18MPa, a reduction of more than 90%. The standard deviation of stress across the entire cross section decreased from approximately 65MPa in the original state to 16MPa, a reduction of 75%. The stress distribution exhibits a near-horizontal "plateau" shape.

[0056] Dimensional stability: After subsequent 0.5mm precision milling, the maximum deformation of the component is 0.03mm / m, which is far better than the 0.3-0.5mm / m of traditional single process treatment.

[0057] Microstructure: TEM observations showed that the dislocation structure evolved into a uniform cellular substructure, and a large number of diffusely distributed nanoscale η' precipitates were observed, with sizes between 5 and 15 nm, and the number density was increased by about 30% compared with the traditional T7451 state.

[0058] Mechanical properties: The yield strength increased from 455MPa in the original state to 482MPa, the tensile strength increased from 525MPa to 545MPa, and the elongation remained above 9%.

[0059] Service performance: The stress corrosion threshold value K_ISCC increased from approximately 25 MPa·m in the original state. 1 / 2 Increased to 34 MPa·m 1 / 2 This represents an increase of 36%. High-cycle fatigue (R=0.1, maximum stress 400MPa) life increased from approximately 5×10⁻⁶. 5 Cycles increased to 2.3 × 10 6 Cycles, nearly 5 times faster.

[0060] Example 2: High-strength Al-Zn-Mg-Cu alloy wall panel components.

[0061] This embodiment relates to a high-strength aluminum alloy (grade 7A85) wall panel component based on the Al-Zn-Mg-Cu system used in spacecraft compartments. The component is a curved wall panel with reinforcing ribs, measuring 1200mm × 800mm, with a maximum wall thickness of 15mm (located at the intersection of the reinforcing ribs) and a minimum wall thickness of 3mm (in the skin area). After solution treatment and aging, due to the large difference in wall thickness, the residual stress distribution after quenching is extremely uneven, with compressive stress in the skin area reaching -120MPa and tensile stress at the intersection of the ribs reaching +280MPa.

[0062] Step 1: Macro-stress coordination.

[0063] An 800-ton specialized tensile testing machine with six actuators working together is equipped with a hydraulically swellable adaptive clamp. This clamp automatically expands according to the rib contour of the component, ensuring uniform clamping and load transfer for complex curved surfaces. Based on high-precision finite element simulation, the target strain ε_target is determined to be 0.65%. Considering the maximum cross-sectional thickness of the component d=15mm, the holding time t_hold is set to 35 minutes (≥2d=30 minutes). The loading rate is controlled at 1.0mm / min, and the unloading rate is strictly implemented at 0.2mm / min.

[0064] Key data after processing: The maximum equivalent stress at the most critical section of the component (where the stiffeners intersect) is 78% of the material's yield strength (approximately 470 MPa), or approximately 367 MPa. The global stress peak was reduced by about 45%, creating favorable conditions for subsequent ultrasonic treatment.

[0065] Step 2: Ultrasonic dislocation engineering.

[0066] A 5kW high-power ultrasonic generator, equipped with a 35mm diameter focusing transducer, was used, mounted by a six-axis robotic arm, for isometric scanning of complex curved surfaces. An alternating scanning mode of 20kHz, 30kHz, and 40kHz was employed to excite dislocation responses at different depth scales. The scan path overlap rate was set to 40%. The ultrasonic amplitude was dynamically adjusted to ensure σ_acoustic ≥ 0.1. σ_yield(local) is used to control the amplitude within the range of 3-6 μm, taking into account the differences in yield strength of materials in different regions. The scanning speed v is optimized based on frequency and wavelength and set to 2-4 mm / s.

[0067] After processing, electron backscattering diffraction analysis showed that the local orientation difference distribution in the near-surface region of the component became more uniform, indicating that the intracrystalline dislocation structure was effectively reconstructed. The residual compressive stress in the skin region was homogenized from -120 MPa to the range of -25 to -35 MPa, and the residual tensile stress at the rib intersection decreased from +280 MPa to the range of +30 to +45 MPa, with the stress gradient significantly mitigated.

[0068] Step 3: Cryogenic thermodynamic coupling treatment.

[0069] For the complex wall thickness structure of this component, four deep cryogenic cycles were designed, and the key parameters for each cycle are as follows: Cooling program: from room temperature to -80℃ at 1.5℃ / min, hold for 45 minutes; then cool to -196℃ at 0.8℃ / min, hold for 240 minutes.

[0070] Static pressure application: During the -196℃ insulation stage, a static pressure of 1.5 bar is applied to the liquid nitrogen medium and maintained throughout the entire insulation process.

[0071] Temperature rise program: slowly rise to -80℃ at 0.5℃ / min, then return to room temperature at 1.0℃ / min.

[0072] Treatment effect evaluation: Residual stress: After final treatment, the peak residual stress of the entire component ranged from -8MPa to +12MPa, a reduction of over 95%. The standard deviation of stress across the entire cross section decreased from approximately 72MPa in the original state to 11MPa, a reduction of 85%.

[0073] Dimensional stability: After subsequent five-axis machining, the maximum deformation is 0.045 mm / m, which meets the requirements for precision assembly of spacecraft (≤0.1 mm / m).

[0074] Microstructure: High-resolution transmission electron microscopy revealed a clear dislocation wall structure with a spacing of approximately 200-300 nm. Cryogenic treatment induced the uniform precipitation of a large number of fine η' phases (2-8 nm), while the number of coarse η phases (>50 nm) was significantly reduced.

[0075] Mechanical properties: Yield strength increased from 460 MPa to 478 MPa, tensile strength increased from 540 MPa to 565 MPa, and elongation remained above 8.5%. Fracture toughness K_IC increased from 28 MPa·m¹ / ² to 32 MPa·m¹ / ².

[0076] Service performance: The stress corrosion threshold value K_ISCC is increased by more than 35%, and the high-cycle fatigue life is increased by about 1.5 orders of magnitude.

[0077] Example 3: Complex integral reinforced thin-walled frame component.

[0078] This embodiment addresses a rigid frame component with a complex, irregular cross-section, made of AA7085 aluminum alloy. The component measures 800mm × 600mm, and its cross-section consists of multiple "T"-shaped and "L"-shaped ribs, ranging from a minimum thickness of 2.5mm to a maximum thickness of 12mm. The overall structural stiffness distribution is extremely uneven. After quenching, the residual stress distribution is extremely complex, with localized tensile stress peaks reaching +320MPa, making subsequent processing highly susceptible to severe warping deformation.

[0079] Step 1: Macro-stress coordination.

[0080] A 1000-ton tensile system employing eight actuators for intelligent coordinated loading is equipped with modular, combined mechanical locking fixtures. These fixture modules can be flexibly combined and independently locked according to the rib configuration of different areas of the component. Based on multi-scale finite element simulation and a process database, the target strain ε_target is set to 0.55%. Given a maximum cross-sectional thickness d=12mm, the holding time t_hold is set to 28 minutes (≥2d=24 minutes). Loading is controlled by displacement at a rate of 0.8mm / min, while the unloading rate is strictly controlled at 0.25mm / min.

[0081] Post-treatment stress testing showed that the maximum equivalent stress at the most critical section of the component was 82% of the material's yield strength (approximately 480 MPa), or approximately 394 MPa. Multiple high-gradient peaks in the original stress field were effectively flattened, resulting in a global stress level reduction of approximately 50%.

[0082] Step 2: Ultrasonic dislocation engineering.

[0083] A dual-channel 4kW+4kW ultrasonic generator system, equipped with two focusing transducers with different radii of curvature (R25mm and R40mm), is employed. Dual robotic arms work collaboratively to perform differentiated scanning of the planar region of the component and the rounded corner region at the root of the rib. A three-frequency alternating mode of 20kHz, 35kHz, and 50kHz is used, with a scan path overlap rate set to 45%. The ultrasonic amplitude is dynamically adjusted in zones based on the local material yield strength and geometric characteristics, with the amplitude controlled at 3-5μm in the planar region and 2-4μm in the rounded corner region at the root of the rib (to prevent over-processing damage). The scanning speed v is set to 2-5mm / s in each zone.

[0084] After treatment, atomic force microscopy revealed a uniform distribution of nanoscale plastic rheological traces on the component surface. Residual stress analysis showed that the surface stress difference was reduced from approximately 280 MPa before treatment to less than 45 MPa, indicating a significant improvement in stress distribution uniformity.

[0085] Step 3: Cryogenic thermodynamic coupling treatment.

[0086] To address the complex cross-sectional features of this component, five deep cryogenic cycles were performed to fully release the micro-stress in different geometric regions. Key process parameters: Cooling procedure: rapidly reduce the temperature to -80℃ at 2.5℃ / min (to induce martensitic phase transformation stress release), hold for 60 minutes; then slowly reduce the temperature to -196℃ at 0.6℃ / min, hold for 300 minutes.

[0087] Static pressure application: During the heat preservation stage, a static pressure of 2.0 bar (the upper limit of this embodiment) is applied to enhance the hydrostatic stress-assisted microplastic flow effect.

[0088] Temperature rise program: Rise to -80℃ at an ultra-slow rate of 0.5℃ / min, then return to room temperature at a rate of 0.8℃ / min to ensure full tissue stabilization.

[0089] Treatment effect evaluation: Residual stress: The peak residual stress of the entire component is controlled within the range of -5MPa to +8MPa, with a reduction of over 97%. The standard deviation of stress across the entire cross section decreases from approximately 85MPa in the original state to 10MPa, a reduction of 88%. The stress distribution exhibits an ideal "zero-stress" plateau shape.

[0090] Dimensional stability: After subsequent precision milling, the maximum deformation is only 0.02 mm / m, achieving near-deformation-free machining.

[0091] Microstructure: Transmission electron microscopy revealed that the dislocation structure evolved into a highly ordered network of dislocation cells / walls, with a cell size of approximately 150-250 nm. Cryogenic treatment induced uniform and dispersed precipitation of the η' phase, and the transformation of some GP regions to the η' phase was also observed. The width of the non-precipitated precipitate band at the grain boundaries was significantly narrowed, which is beneficial for improving stress corrosion resistance.

[0092] Mechanical properties: Yield strength increased from 475 MPa to 495 MPa, tensile strength increased from 550 MPa to 575 MPa, and elongation remained above 8%. Fracture toughness K_IC increased from 30 MPa·m. 1 / 2 Increased to 34 MPa·m 1 / 2 .

[0093] Service performance: The stress corrosion threshold value K_ISCC is increased by 42%, and the high-cycle fatigue life is increased by more than two orders of magnitude.

[0094] The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention.

Claims

1. A method for controlling residual stress in a high-strength aluminum alloy thin-walled stiffened component, characterized in that, include: Step 1: Apply a tensile preload to the component to induce a global inelastic strain of 0.2% to 0.8%, and make the maximum equivalent stress of the component section lower than 85% of the yield strength of the material at that temperature. After holding the load for a preset time, unload the load. Step 2: Apply high-frequency ultrasonic vibration to the surface of the component treated in Step 1, wherein the amplitude of the local alternating stress generated by the high-frequency ultrasonic vibration is not less than 10% of the local residual stress value in the corresponding area of ​​the component; Step 3: Perform programmed cryogenic thermal cycling on the components processed in Step 2. The minimum temperature of the cryogenic thermal cycling is ≤-150℃, and the heating and cooling rate is controlled between 0.5℃ / min and 5℃ / min.

2. The method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components according to claim 1, characterized in that, In step one, the preset holding time t_hold and the maximum cross-sectional thickness d of the component satisfy the following relationship: t_hold ≥ 2d, where t_hold is in minutes and d is in millimeters.

3. The method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components according to claim 1, characterized in that, In step one, the unloading process adopts slow linear unloading, with an unloading rate of no more than 0.5 mm / min.

4. The method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components according to claim 1, characterized in that, In step two, when the high-frequency ultrasonic vibration is applied, a robotic arm is used to hold a focused ultrasonic transducer to scan the surface of the component.

5. The method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components according to claim 4, characterized in that, In step two, the scanning adopts a dual-frequency alternating mode.

6. The method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components according to claim 5, characterized in that, In step two, the dual-frequency alternation mode includes 20kHz and 40kHz.

7. The method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components according to claim 4, characterized in that, In step two, the overlap rate of the scanned paths is not less than 30%.

8. The method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components according to claim 4, characterized in that, In step three, the cryogenic thermal cycling process has a cycle of no less than two.

9. The method for controlling residual stress in high-strength aluminum alloy thin-walled stiffened components according to claim 4, characterized in that, In step three, during the low-temperature insulation stage of the cryogenic thermal cycling treatment, a static pressure of 0.5 bar to 2 bar is applied to the treatment medium.

10. A residual stress control system for high-strength aluminum alloy thin-walled stiffened components, characterized in that, include: The macro-stress coordination unit is used to apply tensile preload to the component, so that the component generates a global inelastic strain of 0.2% to 0.8%, and the maximum equivalent stress of the component section is lower than 85% of the yield strength of the material at that temperature. After holding the load for a preset time, the load is unloaded. The macro-stress coordination unit includes a multi-actuator coordinated loading mechanism and a fixture designed conformally to the component ribs; An ultrasonic dislocation engineering unit is used to apply high-frequency ultrasonic vibration to the surface of a component treated by a macro-stress coordination unit. The local alternating stress amplitude generated by the high-frequency ultrasonic vibration is not less than 10% of the local residual stress value in the corresponding area of ​​the component. The ultrasonic dislocation engineering unit includes a high-power ultrasonic generator, a focusing transducer, and a six-axis robotic arm for holding the transducer and scanning the surface of the component. A cryogenic thermal coupling unit is used to perform programmed cryogenic thermal cycling treatment on components that have undergone ultrasonic dislocation engineering unit treatment. The minimum temperature of the cryogenic thermal cycling treatment is ≤-150℃, and the heating and cooling rate is controlled between 0.5℃ / min and 5℃ / min. The cryogenic thermal coupling unit includes a cryogenic treatment device with programmed temperature and pressure regulation functions. The cryogenic treatment device is capable of cooling the component to -196℃ and applying a static pressure of 0.5 bar to 2 bar. The central intelligent control system is communicatively connected to the macro-stress coordination unit, the ultrasonic dislocation engineering unit, and the cryogenic thermo-coupling unit, and is used to integrate and control the sequential and coordinated operation of each unit; the central intelligent control system includes an online stress monitoring module and a process parameter dynamic optimization module.

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