A method for ultrasonic vibration compression regulation of grain boundary precipitate-free zone microstructure of 7xxx series aluminum alloy and application thereof

Abstract

The application discloses a method for regulating and controlling the microstructure of a 7xxx series aluminum alloy grain boundary precipitate-free zone through ultrasonic vibration compression and application thereof, and belongs to the technical field of aluminum alloy material processing. The application aims at the technical problem that the grain boundary precipitate-free zone (PFZ) of a T6 state 7xxx series aluminum alloy is wide, and the irregular precipitate phase morphology in the PFZ leads to insufficient strength and plasticity matching. The application combines T6 heat treatment and multi-stage ultrasonic vibration compression coupling treatment, adopts a multi-process composite process of 'double-stage solid solution treatment -> intermediate precooling -> aging treatment -> multi-stage ultrasonic vibration compression coupling treatment -> low-temperature stabilization', and changes the irregular lath-shaped precipitate phase morphology in the PFZ into round granular precipitate phase, and significantly narrows the width of the PFZ. The tensile strength of the 7xxx aluminum alloy treated by the method reaches 610-624 MPa, the elongation reaches more than 20%, and the synergistic improvement of the strength and plasticity is realized.

Description

Technical Field

[0001] This invention relates to a method for controlling the microstructure of precipitate-free zones (PFZs) at grain boundaries in 7xxx series aluminum alloys using ultrasonic vibration compression and its application. Specifically, it involves a multi-stage composite process—two-stage solution treatment, pre-cooling treatment, aging treatment, multi-stage ultrasonic vibration compression coupling treatment, and low-temperature stabilization treatment—to achieve precise control over the narrowing of the PFZ width and the rounding of the morphology of precipitates within the PFZ in T6-state 7xxx series aluminum alloys, thereby simultaneously improving the alloy's strength and plasticity. This invention belongs to the field of aluminum alloy material processing technology. Background Technology

[0002] 7xxx series (Al-Zn-Mg-(Cu)) aluminum alloys are widely used in lightweight applications such as aerospace, rail transportation, and automobile manufacturing due to their superior properties, including ultra-high strength and low density. The T6 temper (peak aging) is the most commonly used heat treatment state for these alloys. Through solution treatment followed by artificial aging, a large number of dispersed η′ strengthening phases precipitate within the grains, resulting in high strength (typically reaching 500-600 MPa). However, T6 temper 7xxx series aluminum alloys suffer from a long-standing microstructural problem that limits their overall performance—the absence of precipitate-free zones (PFZs) at grain boundaries.

[0003] Precipitated zone (PFZ) is a region near grain boundaries where solute atoms (Zn, Mg, Cu) are depleted, resulting in the absence of precipitates. Its formation mechanism is related to grain boundaries acting as a "sink" for vacancies and solute atoms: during quenching and aging, supersaturated vacancies near grain boundaries diffuse and annihilate towards the grain boundaries, preventing solute atoms from forming precipitates in this region. The impact of PFZ on alloy properties is mainly reflected in the following aspects: (1) Mechanical properties: The PFZ is a soft region near the grain boundary, and its strength is much lower than that of the intragranular precipitation strengthening region. During plastic deformation, dislocation movement preferentially occurs in the PFZ, leading to strain localization, which becomes the preferred channel for crack initiation and propagation. The wider the PFZ, the worse the plasticity and the lower the toughness of the alloy.

[0004] (2) Morphology of precipitates in PFZ: PFZ is not completely free of precipitates, but contains a small amount of coarse equilibrium phases (such as η-MgZn2 phase). These precipitates often have irregular lath or needle-like morphologies, forming sharp stress concentration points near the grain boundaries, which further exacerbates the brittleness of the alloy.

[0005] (3) In terms of corrosion resistance: the potential difference between PFZ and the grain boundary precipitate leads to preferential corrosion of the grain boundary. The wider the PFZ, the higher the sensitivity to intergranular corrosion.

[0006] Therefore, the wide PFZ and irregular precipitates within the PFZ are the key microstructural causes of insufficient strength-plasticity matching and deterioration of corrosion resistance in T6-state 7xxx series alloys.

[0007] To address these issues, researchers explored various technical approaches: (1) Adjusting the aging regime: By optimizing heat treatment processes such as two-stage aging (T73, T74) and regressive aging (RRA), attempts are made to improve the grain boundary precipitation state while maintaining the strengthening effect of intragranular precipitation. For example, RRA treatment coarsens the grain boundary precipitates into a discontinuous distribution through high-temperature short-time regression, while maintaining the strengthening effect of the intragranular η′ phase. However, such methods often sacrifice 5%-15% of the strength and have limited effect on controlling the PFZ width (usually only narrowing it by 10%-20%).

[0008] (2) Microalloying: By adding trace elements such as Zr, Sc, Ag, and Er, the grain size is refined, recrystallization is inhibited, and precipitation behavior is affected, thereby indirectly improving the PFZ state. For example, the addition of Sc can form Al3Sc dispersed phase, which pins grain boundaries and inhibits PFZ widening. However, the addition of expensive alloying elements significantly increases the material cost, and the scarcity of some elements (such as Sc) limits their large-scale industrial application.

[0009] (3) Pre-deformation treatment: Before aging, a certain amount of pre-deformation (such as stretching or compression) is applied to the alloy to increase the vacancy concentration and nucleation sites by introducing dislocations, thereby promoting intragranular precipitation and inhibiting PFZ widening. However, the amount of pre-deformation is difficult to control precisely: if the amount of deformation is too small, the effect is not obvious, and if the amount of deformation is too large, it will lead to coarsening of intragranular precipitates and a decrease in strength.

[0010] (4) Vibration aging technology: Existing Chinese patents (such as CN112899592A) disclose a method for improving the stress corrosion resistance of 7xxx series aluminum alloys through vibration pretreatment. The principle is to induce micro-plastic deformation of the alloy through mechanical vibration, thereby increasing the dislocation and vacancy density and controlling the precipitation behavior during the aging process. However, this technology mainly targets the improvement of stress corrosion performance and does not involve the rounding of the morphology of precipitates in PFZ. Moreover, the vibration treatment is carried out before aging, so its ability to control the already formed PFZ is limited.

[0011] (5) Ultrasonic vibration aging: Studies have shown that applying ultrasonic vibration during aging treatment at 120℃ can improve the yield strength and elongation of 7075 aluminum alloy. However, the existing ultrasonic vibration aging technology has the following shortcomings: ① It only uses ultrasonic vibration as an auxiliary physical field in the aging process, which belongs to the category of heat treatment. The control of PFZ by ultrasonic vibration is passive and non-directional; ② It does not involve the synergistic effect of compressive load, and cannot achieve directional control of PFZ.

[0012] It is worth noting that the effects of ultrasonic vibration on the PFZ reported in existing literature are contrary to the research direction of this invention: some studies have reported an increase in PFZ width in 7xxx aluminum alloys cast by ultrasonic vibration, and an increase in PFZ width can also be observed on the surface of 7050-T7451 aluminum alloys cut by ultrasonic elliptical vibration. These studies indicate that conventional ultrasonic vibration treatment often leads to PFZ widening, while this invention achieves a significant narrowing of the PFZ.

[0013] Furthermore, while existing technologies involving simple large plastic deformation (such as rolling and compression) can improve alloy strength through grain refinement and dislocation strengthening, they often lead to a significant reduction in elongation. For example, when 7xxx aluminum alloys are subjected to impact compression treatment using a light gas gun, the strength increases to 542 MPa, but the elongation drops to 7.5%, exhibiting a typical strength-plasticity inverse relationship.

[0014] In summary, current technologies have not yet solved the problem of insufficient strength-ductility matching in T6-state 7xxx series aluminum alloys due to the wide PFZ and irregular precipitates within the PFZ. There is an urgent need for a new method that can actively, directionally, and precisely control the microstructure of the PFZ through physical field coupling without altering the main T6 process. Summary of the Invention

[0015] The purpose of this invention is to provide a method for controlling the microstructure of precipitate-free grain boundaries in 7xxx series aluminum alloys by ultrasonic vibration compression. By combining T6 heat treatment with multi-stage ultrasonic vibration compression coupling treatment, the solute atom diffusion behavior and precipitate morphology evolution within the PFZ are actively controlled by utilizing the force field coupling effect of ultrasonic vibration and compression load. This achieves controllable narrowing of the PFZ width and rounding of the precipitate morphology within the PFZ, thereby significantly improving the plasticity of the alloy without sacrificing strength and breaking the inherent strength-plasticity inversion relationship of 7xxx series aluminum alloys.

[0016] Meanwhile, the present invention provides a 7xxx series aluminum alloy material with narrowed PFZ and rounded precipitates obtained by the above method.

[0017] Meanwhile, this invention provides the application of the above-mentioned methods and materials in key load-bearing components in aerospace, rail transportation, and automotive industries.

[0018] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for controlling the microstructure of 7xxx series aluminum alloys without precipitate bands at grain boundaries using ultrasonic vibration compression, comprising the following steps: S01, Preparation of 7xxx aluminum alloy ingots: First, prepare the raw materials according to the composition of 7xxx series aluminum alloys (Zn 7%-9%, Mg 1%-3%, Cu 0.1%-0.25%, balance Al and unavoidable impurities). Place the crucible in a vacuum melting furnace preheated to 490-510℃, add the raw materials, set the temperature to 690-710℃, and hold for 25-35 minutes until the raw materials are completely melted. Then, open the melting furnace to skim off the slag and slowly stir the molten metal with a stirring spoon to ensure a uniform composition. Next, remove the mold to prepare for casting. During the casting process, ensure that the flow rate of the molten metal is uniform, and finally obtain the blocky 7xxx series aluminum alloy required for the experiment, i.e., 7xxx aluminum alloy ingot. SO2, two-stage solution treatment: The 7xxx series aluminum alloy ingots obtained from S01 were subjected to a two-stage solution treatment under a protective atmosphere. The two-stage solution treatment included: First-stage solution treatment: heating from room temperature to 240-260℃ at a heating rate of 4-6℃ / min and holding for 25-35min to eliminate residual stress in the as-cast structure; Second-stage solution treatment: The temperature is increased from the first-stage solution treatment temperature to 460-480℃ at a heating rate of 1-3℃ / min and held for 1-2 hours. This is used to eliminate macroscopic segregation of elements in the as-cast structure and achieve high solubility of alloying elements (Zn, Mg, Cu). Solution treatment was carried out under a protective atmosphere of 99.5% Ar + 0.5% H2 to prevent oxidation; After the heat preservation is completed, the alloy is immediately water quenched to 140-160℃ at a cooling rate of 190-210℃ / s, and then air-cooled to room temperature.

[0019] S03, Pre-cooling treatment: The alloy obtained from SO2 was pre-cooled at -10 to 5℃ for 10 to 30 minutes.

[0020] The purpose of pre-cooling is to lower the overall temperature of the alloy, so that the matrix is ​​in a higher supersaturated state before entering the aging stage (i.e., the actual solute concentration has a greater supersaturation relative to the equilibrium solubility at this low temperature), providing a greater driving force for the nucleation of precipitated phases during the subsequent aging process; at the same time, low-temperature pre-cooling can suppress premature precipitation near the grain boundaries in the early stage of aging, making the distribution of solute atoms in the PFZ more uniform during the subsequent aging process, and creating favorable initial conditions for the narrowing of the PFZ.

[0021] S04, Time-sensitive processing: The alloy obtained from SO3 was subjected to artificial aging treatment at 110-130℃ for 20-28 hours to obtain the T6 state alloy.

[0022] The aging treatment is carried out under nitrogen protection, and the temperature uniformity inside the furnace is controlled within ±2℃ to ensure the uniformity of the aging effect.

[0023] S05, Multi-stage ultrasonic vibration compression coupling treatment: S05a, Level 1 Low-Energy Ultrasonic Treatment: The T6 alloy obtained from S04 is placed in an ultrasonic pressing device, and a synchronous coupling treatment of compressive load and ultrasonic vibration is applied. The compressive load is applied by a press at a loading rate of 0.1-0.5 mm / min, and the stress is 50% of the yield strength of the alloy (the T6 alloy obtained from S04) at room temperature. The treatment temperature is 20-30℃. Ultrasonic vibration is started at an ultrasonic frequency of 20-40kHz and an ultrasonic energy of 400-600J. The heat and pressure treatment is carried out for 5-15 minutes. S05b, Level 2 medium-energy ultrasonic treatment: Keep the compression load and treatment temperature constant, switch the ultrasonic energy to 800-1000J within 20-40s under pressure, and continue the coupling treatment for 5-15min. S05c, Level 3 High-Energy Ultrasonic Treatment: Keep the compressive load and treatment temperature constant, switch the ultrasonic energy to 1100-1300J within 20-40 seconds under pressure, remove the compressive load after coupling treatment for 5-15 minutes, and cool to room temperature with the furnace.

[0024] The ultrasound energy mentioned above is the total input energy (E). The relationship between the total input energy (E), output power (P), and processing time (t) is E = P × t.

[0025] The output power of the ultrasonic generator of this invention is monitored in real time by a built-in power meter, and real-time power data is recorded at a sampling frequency of 500-1000Hz using a data acquisition card. The power-time curve is then integrated. The total input energy (E) is obtained. Then, the output power P is calculated using E=P×t, t=5-15min. Note that the calculated output power P is the average power. Since ultrasonic vibration is a high-frequency pulsed output of 20-40kHz, the instantaneous power is much higher than this value.

[0026] S06, Low-temperature stabilization treatment: The alloy obtained from S05 was held at -20 to -5℃ for 5 to 15 minutes, and then heated to room temperature in the furnace.

[0027] The effects of low-temperature stabilization treatment are: 1. to freeze the optimized microstructure formed during ultrasonic vibration compression treatment and prevent PFZ from widening again during the heating process; 2. to promote the uniform release of residual stress and improve tissue stability.

[0028] The 7xxx series aluminum alloys are Al-Zn-Mg-(Cu) series aluminum alloys, and their composition by weight percentage is: Zn 7%-9%, Mg 1%-3%, Cu 0.1%-0.25%, with the balance being Al and unavoidable impurities.

[0029] Mechanism of action of the present invention: This invention, based on the multi-physics field control principle of "force field coupling + temperature field synergy," achieves active and precise control of the microstructure of PFZ. Its mechanism of action is as follows: (1) Force field coupling effect between ultrasonic vibration and compressive load: The high-frequency mechanical energy of ultrasonic vibration generates an alternating stress field (20-40 kHz) in the alloy, forming periodic stress oscillations near the grain boundaries. Simultaneously, the application of a quasi-static compressive load introduces a uniaxial stress field into the alloy. The coupling of these two forces creates an asymmetric alternating stress field near the grain boundaries, which exhibits the following effects: 1. Promote the directional migration of solute atoms in PFZ: The asymmetric alternating stress field breaks the equilibrium state of solute atom distribution near the grain boundary. Through the stress-induced diffusion effect, it promotes the directional migration of Zn, Mg, and Cu atoms in PFZ towards the grain boundary, replenishing the solute concentration near the grain boundary, thereby achieving the narrowing of PFZ.

[0030] 2. Promotes the evolution of precipitated phase morphology: An asymmetric alternating stress field applies periodic shear stress to the irregular lath-shaped precipitates. Studies have shown that ultrasonic vibration can generate high concentrations of non-equilibrium vacancies (X). V (Approximately equal to 0.06) and significantly reduces the atomic diffusion activation energy, increasing the diffusion coefficient by 1-2 orders of magnitude. Under the coupled effect of ultrasonic alternating stress and compressive static stress, the precipitates in PFZ transform from high-interface-energy lath-like structures to low-interface-energy rounded granular structures through interfacial atomic rearrangement and short-range diffusion, achieving the rounding of the precipitates. Existing literature has confirmed that ultrasonic treatment can promote the transformation of the second phase in aluminum alloys from needle-like / elongated structures to granular / short rod-like structures. In this invention, the morphological evolution of the precipitates is a result of stress-induced morphological evolution as the main driver, supplemented by ultrasonic-promoted short-range diffusion.

[0031] 3. Promotes dislocation movement and recombination: The alternating stress of ultrasonic vibration causes dislocations near the grain boundary to reciprocate. This, together with the directional stress field of compressive load, promotes the recombination and annihilation of dislocations, reduces the dislocation density in the PFZ, and reduces stress concentration sources.

[0032] (2) Synergistic effect of temperature field between precooling treatment and low-temperature stabilization: Pre-cooling treatment lowers the initial temperature of the alloy before aging, increases supersaturation, and enhances the precipitation driving force near grain boundaries during aging, which is beneficial for narrowing of the PFZ. Low-temperature stabilization treatment freezes the optimized microstructure formed by ultrasonic vibration compression treatment by holding the alloy at low temperature, preventing the PFZ from widening again during the heating process.

[0033] (3) Synergistic effect of multi-process composite technology: The various processes in this invention, namely "two-stage solution treatment → pre-cooling → aging → ultrasonic vibration compression → low-temperature stabilization", exhibit synergistic effects: The two-stage solution treatment ensures high solubility of alloying elements, providing a sufficient source of solute for subsequent precipitation; Pre-cooling treatment increases the precipitation driving force, creating initial conditions for PFZ narrowing; Aging treatment resulted in a matrix microstructure in the T6 state (intracrystalline η′ strengthening phase). Ultrasonic vibration compression coupling is the core process for achieving PFZ narrowing and precipitate rounding. Low-temperature stabilization treatment froze and stabilized the optimized microstructure.

[0034] (4) The relationship between microstructure and macroscopic performance: The narrowing of PFZ reduces the size of the weak region near the grain boundary, making plastic deformation more uniform and delaying crack initiation. The rounding of precipitates within PFZ reduces stress concentration and decreases crack initiation sites; The retention of the intracrystalline η′ strengthening phase ensures a high strength level; Ultimately, this leads to a synergistic improvement in plasticity.

[0035] Secondly, the present invention provides a 7xxx series aluminum alloy material prepared by the above method, which has the following characteristics: (1) The width of the grain boundary precipitation-free zone (PFZ) is more than 30% narrower than that of the conventional T6 state (i.e., the T6 state alloy obtained by SO4 in this invention); (2) The morphology of the precipitated phase in PFZ changed from irregular lath shape to round granular shape, and the aspect ratio of the precipitated phase was ≤2.61; (3) Tensile strength ≥600MPa, elongation ≥20%.

[0036] Furthermore, the 7xxx series aluminum alloy is an Al-Zn-Mg-(Cu) aluminum alloy, which, after being treated by the method of the present invention, has a tensile strength of 610-624 MPa and an elongation of over 20%.

[0037] Thirdly, the present invention provides the application of the above-mentioned method or the above-mentioned 7xxx series aluminum alloy material in materials that combine lightweight and long service life.

[0038] The materials that combine lightweight design and long service life include materials used in aerospace, rail transportation, and the automotive industry.

[0039] Materials used in aerospace include key load-bearing components such as aircraft fuselages, wings, landing gear, rocket engine frames, and missile casings.

[0040] The beneficial effects of the above technical solution adopted in this invention are: (1) Microstructure innovation - the first realization of PFZ narrowing and precipitate rounding: This invention is the first to discover that applying a coupled treatment of ultrasonic vibration and compressive loading to T6-state 7xxx series aluminum alloys, combined with the synergistic effect of precooling and low-temperature stabilization, can transform the morphology of precipitates within the PFZ (precipitate zone) from irregular lamellar shapes to rounded granules, and significantly narrow the PFZ width (by more than 30%). This discovery provides a novel approach to the microstructure control of the PFZ in 7xxx series aluminum alloys, and stands in stark contrast to the PFZ widening effect reported in existing literature, demonstrating remarkable non-obviousness.

[0041] (2) Significant performance improvement: The Al-Zn-Mg-(Cu) aluminum alloy treated by the method of this invention achieves a tensile strength of 610-624 MPa and an elongation of over 20%. Compared with the existing light gas gun impact compression technology (542 MPa, 7.5%), this invention significantly improves the strength level while increasing the elongation by 167%, effectively breaking the strength-plasticity inversion relationship of 7xxx series aluminum alloys.

[0042] The Al-Zn-Mg-(Cu) aluminum alloy treated by the method of this invention has a morphology of precipitated phases in the PFZ that changes from irregular lath-like to rounded granular (with an aspect ratio of about 1.68-2.61) and the PFZ width is significantly narrowed (about 28-32 nm).

[0043] (3) The process system is highly systematic and has a large degree of controllability: This invention employs a multi-stage composite process of "two-stage solid solution → pre-cooling → aging → multi-stage ultrasonic vibration compression → low-temperature stabilization". The parameters of each stage can be independently adjusted and can be flexibly matched according to different alloy compositions and performance requirements, thus having a wide range of applicability and process window.

[0044] (4) Good process compatibility: This invention adds pre-cooling, ultrasonic vibration compression and low-temperature stabilization processes to the T6 heat treatment process without changing the core concept of the T6 main process. It requires little modification to existing T6 production lines and is easy to implement for industrial application.

[0045] (5) Economic and environmental protection: This invention does not require the addition of expensive and rare alloying elements such as Sc and Ag, resulting in low material costs and simple recycling, which meets the requirements of green manufacturing and sustainable development.

[0046] This invention discloses a method for controlling the microstructure of precipitate-free grain boundaries (PFZs) in 7xxx series aluminum alloys using ultrasonic vibration compression and its application, belonging to the field of aluminum alloy material processing technology. Addressing the technical problem of wide PFZs and irregular morphology of precipitates within PFZs leading to insufficient strength-ductility matching in T6-state 7xxx series aluminum alloys, this invention combines T6 heat treatment with multi-stage ultrasonic vibration compression coupling treatment. Employing a multi-step composite process of "two-stage solution treatment → intermediate pre-cooling → aging treatment → multi-stage ultrasonic vibration compression coupling treatment → low-temperature stabilization," the morphology of precipitates within PFZs is transformed from irregular lamellar shapes to rounded granules (aspect ratio approximately 1.68-2.61), and the PFZ width is significantly narrowed (approximately 28-32 nm). The 7xxx aluminum alloys treated using this method achieve a tensile strength of 610-624 MPa and an elongation exceeding 20%, achieving a synergistic improvement in strength and ductility. This invention achieves precise and controllable optimization of the PFZ microstructure through the coupling of the force field of ultrasonic vibration and compressive load, combined with the synergistic control of the temperature field. This solution requires no expensive alloying elements, offers flexible and adjustable processes, and is suitable for critical load-bearing components in aerospace, rail transportation, and other industries. Attached Figure Description

[0047] Figure 1 This is a flowchart of the multi-process composite process of the present invention; Figure 2 This is a schematic diagram of the microstructure evolution of PFZ before and after ultrasonic vibration compression treatment according to the present invention, wherein (a) is the conventional T6 state (PFZ is wide, and the precipitate is irregularly plate-like), and (b) is after treatment according to the present invention (PFZ is narrowed, and the precipitate is rounded and granular). Figure 3 This is a diagram showing the dimensions and shape of the tensile specimen. Figure 4 These are the original characterization spectra of the embodiments and comparative examples of the present invention. Detailed Implementation

[0048] The following description, in conjunction with the accompanying drawings and embodiments of the present invention, will further clarify the objectives, technical solutions, and advantages of the present invention. The specific embodiments described are merely illustrative and are not intended to limit the scope of the invention. Example 1:

[0049] This embodiment provides a method for controlling the microstructure of 7xxx aluminum alloy grain boundaries without precipitates by ultrasonic vibration compression.

[0050] An Al-Zn-Mg-(Cu) alloy sample with dimensions of 10×40×1.5mm was prepared.

[0051] The composition of the Al-Zn-Mg-(Cu) alloy is as follows: Zn content is 7.14wt%, Mg content is 1.73wt%, Cu content is 0.22wt%, and the balance is Al and unavoidable impurities.

[0052] like Figure 1 As shown, a method for controlling the microstructure of Al-Zn-Mg-(Cu) alloy grain boundaries without precipitation bands by ultrasonic vibration compression includes the following steps: S01, Preparation of Al-Zn-Mg-(Cu) alloy ingots: First, based on the composition of 7xxx series aluminum alloy (Zn content 7.14wt%, Mg content 1.73wt%, Cu content 0.22wt%, balance Al and unavoidable impurities), prepare the raw materials. Place the crucible in a vacuum melting furnace preheated to 500℃, add the raw materials, set the temperature to 700℃, and hold for 30 minutes until the raw materials are completely melted. Then, open the melting furnace to skim off the slag and slowly stir the molten metal with a stirring spoon to ensure a uniform distribution of its composition. Next, remove the mold to prepare for casting. During the casting process, ensure that the flow rate of the molten metal is uniform, and finally obtain the block-shaped 7xxx series aluminum alloy required for the experiment. SO2, two-stage solution treatment: The Al-Zn-Mg-(Cu) alloy ingot obtained in SO1 was subjected to a two-stage solution treatment under a protective atmosphere of 99.5%Ar + 0.5%H2; First stage of solid solution treatment: Heat from room temperature to 250℃ at a heating rate of 5℃ / min and hold for 30min; Second stage of solution treatment: heating from 250℃ to 470℃ at a heating rate of 2℃ / min, and holding at that temperature for 1.5h; After the heat preservation is completed, the alloy is immediately water quenched to 150°C at a cooling rate of 200°C / s, and then air-cooled to room temperature.

[0053] S03, Pre-cooling treatment: The alloy obtained from SO2 was pre-cooled at 0℃ for 20 min.

[0054] S04, Time-sensitive processing: The alloy obtained from SO3 was subjected to artificial aging treatment at 120℃ for 24 hours to obtain the T6 state alloy. The aging treatment was carried out under nitrogen protection, using a nitrogen circulation system (flow rate of 0.8 m³ / s). 3 ( / h) Ensure that the temperature uniformity inside the furnace is controlled within ±2℃.

[0055] S05, Ultrasonic vibration compression coupling treatment: The T6 alloy obtained from S04 was placed in an ultrasonic pressing device, and a synchronous coupling treatment of compressive load and ultrasonic vibration was applied. The compressive load was applied by a press at a loading rate of 0.5 mm / min, the stress was 50% of the yield strength of the alloy at room temperature, and the treatment temperature was 25℃; ultrasonic vibration was started at an ultrasonic frequency of 20 kHz and an ultrasonic energy of 500 J, and the heat and pressure treatment was carried out for 10 min. Keep the compression load and processing temperature constant, switch the ultrasonic energy to 900J within 30 seconds under pressure, and continue the coupling process for 10 minutes. Keeping the compression load and processing temperature constant, the ultrasonic energy was switched to 1200J within 30 seconds under pressure and coupled for 10 minutes before the compression load was removed and the furnace was cooled to room temperature.

[0056] S06, Low-temperature stabilization treatment: The alloy obtained from S05 was held at -10℃ for 10 minutes, and then heated to room temperature in the furnace.

[0057] The Al-Zn-Mg-(Cu) alloy treated by the method in this embodiment has a tensile strength of 624 MPa and an elongation of 20%. Figure 2 and Figure 4 As shown, compared with the conventional T6 state, the width of the PFZ narrowed from 46 nm to 30 nm, and the morphology of the precipitated phase in the PFZ changed from irregular lamellar shape to rounded granular shape (the aspect ratio of the precipitated phase decreased from 3.12 to 1.68).

[0058] Example 2:

[0059] This embodiment provides a method for controlling the microstructure of 7xxx aluminum alloy grain boundaries without precipitates by ultrasonic vibration compression.

[0060] An Al-Zn-Mg-(Cu) alloy sample with dimensions of 10×40×1.5mm was prepared.

[0061] The composition of the Al-Zn-Mg-(Cu) alloy is as follows: Zn content is 7.14wt%, Mg content is 1.73wt%, Cu content is 0.22wt%, and the balance is Al and unavoidable impurities.

[0062] A method for controlling the microstructure of Al-Zn-Mg-(Cu) alloy grain boundaries without precipitation bands by ultrasonic vibration compression includes the following steps: S01, Preparation of Al-Zn-Mg-(Cu) alloy ingots: First, prepare the raw materials based on the composition of the 7xxx series aluminum alloy. Place the crucible in a vacuum melting furnace preheated to 490℃, add the raw materials, set the temperature to 690℃, and hold for 25 minutes until the raw materials are completely melted. Then, open the melting furnace to skim off the slag and slowly stir the molten metal with a stirring spoon to ensure a uniform distribution of its composition. Next, remove the mold to prepare for casting. During the casting process, ensure that the flow rate of the molten metal is uniform, and finally obtain the block-shaped 7xxx series aluminum alloy required for the experiment. SO2, two-stage solution treatment: The Al-Zn-Mg-(Cu) alloy ingot obtained in SO1 was subjected to a two-stage solution treatment under a protective atmosphere of 99.5%Ar + 0.5%H2; First stage of solid solution treatment: Heat from room temperature to 250℃ at a heating rate of 5℃ / min and hold for 30min; Second stage of solution treatment: heating from 250℃ to 470℃ at a heating rate of 2℃ / min, and holding at that temperature for 1.5h; After the heat preservation is completed, the alloy is immediately water quenched to 150°C at a cooling rate of 200°C / s, and then air-cooled to room temperature.

[0063] S03, Pre-cooling treatment: The alloy obtained from SO2 was pre-cooled at 0℃ for 20 min.

[0064] S04, Time-sensitive processing: The alloy obtained from SO3 was subjected to artificial aging treatment at 120℃ for 24 hours to obtain the T6 state alloy. The aging treatment was carried out under nitrogen protection, using a nitrogen circulation system (flow rate of 0.8 m³ / s). 3 ( / h) Ensure that the temperature uniformity inside the furnace is controlled within ±2℃.

[0065] S05, Ultrasonic vibration compression coupling treatment: The T6 alloy obtained from S04 was placed in an ultrasonic pressing device, and a synchronous coupling treatment of compressive load and ultrasonic vibration was applied. The compressive load was applied by a press at a loading rate of 0.5 mm / min, the stress was 50% of the yield strength of the alloy at room temperature, and the treatment temperature was 25℃; ultrasonic vibration was started at an ultrasonic frequency of 20 kHz and an ultrasonic energy of 400 J, and the heat and pressure treatment was carried out for 10 min. Keep the compression load and processing temperature constant, switch the ultrasonic energy to 800J within 30 seconds under pressure, and continue coupling processing for 10 minutes. Keeping the compression load and processing temperature constant, the ultrasonic energy was switched to 1100J within 30 seconds under pressure and coupled for 10 minutes before the compression load was removed and the furnace was cooled to room temperature.

[0066] S06, Low-temperature stabilization treatment: The alloy obtained from S05 was held at -10℃ for 10 minutes, and then heated to room temperature in the furnace.

[0067] The Al-Zn-Mg-(Cu) alloy treated by the method in this embodiment has a tensile strength of 618 MPa and an elongation of 21%. Compared with the conventional T6 state, the PFZ width is narrowed from 46 nm to 32 nm, and the morphology of the precipitates within the PFZ changes from irregular lamellar shapes to rounded granular shapes (the aspect ratio of the precipitates decreases from 3.12 to 1.83). Figure 4 (As shown).

[0068] Example 3:

[0069] This embodiment provides a method for controlling the microstructure of 7xxx aluminum alloy grain boundaries without precipitates by ultrasonic vibration compression.

[0070] An Al-Zn-Mg-(Cu) alloy sample with dimensions of 10×40×1.5mm was prepared.

[0071] The composition of the Al-Zn-Mg-(Cu) alloy is as follows: Zn content is 7.14wt%, Mg content is 1.73wt%, Cu content is 0.22wt%, and the balance is Al and unavoidable impurities.

[0072] A method for controlling the microstructure of Al-Zn-Mg-(Cu) alloy grain boundaries without precipitation bands by ultrasonic vibration compression includes the following steps: S01, Preparation of Al-Zn-Mg-(Cu) alloy ingots: First, prepare the raw materials based on the composition of the 7xxx series aluminum alloy. Place the crucible in a vacuum melting furnace preheated to 510℃, add the raw materials, set the temperature to 710℃, and hold for 35 minutes until the raw materials are completely melted. Then, open the melting furnace to skim off the slag and slowly stir the molten metal with a stirring spoon to ensure a uniform distribution of its composition. Next, remove the mold to prepare for casting. During the casting process, ensure that the flow rate of the molten metal is uniform, and finally obtain the block-shaped 7xxx series aluminum alloy required for the experiment. SO2, two-stage solution treatment: The Al-Zn-Mg-(Cu) alloy ingot obtained in SO1 was subjected to a two-stage solution treatment under a protective atmosphere of 99.5%Ar + 0.5%H2; First stage of solid solution treatment: Heat from room temperature to 250℃ at a heating rate of 5℃ / min and hold for 30min; Second stage of solution treatment: heating from 250℃ to 470℃ at a heating rate of 2℃ / min, and holding at that temperature for 1.5h; After the heat preservation is completed, the alloy is immediately water quenched to 150°C at a cooling rate of 200°C / s, and then air-cooled to room temperature.

[0073] S03, Pre-cooling treatment: The alloy obtained from SO2 was pre-cooled at 0℃ for 20 min.

[0074] S04, Time-sensitive processing: The alloy obtained from SO3 was subjected to artificial aging treatment at 120℃ for 24 hours to obtain the T6 state alloy. The aging treatment was carried out under nitrogen protection, using a nitrogen circulation system (flow rate of 0.8 m³ / s). 3 ( / h) Ensure that the temperature uniformity inside the furnace is controlled within ±2℃.

[0075] S05, Ultrasonic vibration compression coupling treatment: The T6 alloy obtained from S04 was placed in an ultrasonic pressing device, and a synchronous coupling treatment of compressive load and ultrasonic vibration was applied. The compressive load was applied by a press at a loading rate of 0.5 mm / min, the stress was 50% of the yield strength of the alloy at room temperature, and the treatment temperature was 25℃; ultrasonic vibration was started at an ultrasonic frequency of 20 kHz and an ultrasonic energy of 600 J, and the heat and pressure treatment was carried out for 10 min. Keep the compression load and processing temperature constant, switch the ultrasonic energy to 1000J within 30 seconds under pressure, and continue the coupling process for 10 minutes. Keeping the compression load and processing temperature constant, the ultrasonic energy was switched to 1300J within 30 seconds under pressure and coupled for 10 minutes before the compression load was removed and the furnace was cooled to room temperature.

[0076] S06, Low-temperature stabilization treatment: The alloy obtained from S05 was held at -10℃ for 10 minutes, and then heated to room temperature in the furnace.

[0077] The Al-Zn-Mg-(Cu) alloy treated by the method in this embodiment has a tensile strength of 610 MPa and an elongation of 21%. Compared with the conventional T6 state, the PFZ width is narrowed from 46 nm to 28 nm, and the morphology of the precipitates within the PFZ changes from irregular lamellar shapes to rounded granules (the aspect ratio of the precipitates decreases from 3.12 to 2.0). Figure 4 (As shown).

[0078] Example 4:

[0079] This embodiment provides a method for controlling the microstructure of 7xxx aluminum alloy grain boundaries without precipitates by ultrasonic vibration compression.

[0080] An Al-Zn-Mg-(Cu) alloy sample with dimensions of 10×40×1.5mm was prepared.

[0081] The composition of the Al-Zn-Mg-(Cu) alloy is as follows: Zn content is 7wt%, Mg content is 1wt%, Cu content is 0.1wt%, and the balance is Al and unavoidable impurities.

[0082] A method for controlling the microstructure of Al-Zn-Mg-(Cu) alloy grain boundaries without precipitation bands by ultrasonic vibration compression includes the following steps: S01, Preparation of Al-Zn-Mg-(Cu) alloy ingots: First, prepare the raw materials based on the composition of the 7xxx series aluminum alloy. Place the crucible in a vacuum melting furnace preheated to 510℃, add the raw materials, set the temperature to 710℃, and hold for 35 minutes until the raw materials are completely melted. Then, open the melting furnace to skim off the slag and slowly stir the molten metal with a stirring spoon to ensure a uniform distribution of its composition. Next, remove the mold to prepare for casting. During the casting process, ensure that the flow rate of the molten metal is uniform, and finally obtain the block-shaped 7xxx series aluminum alloy required for the experiment. SO2, two-stage solution treatment: The Al-Zn-Mg-(Cu) alloy ingot obtained in SO1 was subjected to a two-stage solution treatment under a protective atmosphere of 99.5%Ar + 0.5%H2; First stage of solid solution treatment: Heat from room temperature to 240℃ at a heating rate of 4℃ / min and hold for 25min; Second stage of solid solution treatment: heating from 240℃ to 460℃ at a heating rate of 1℃ / min, and holding at that temperature for 1 hour; After the heat preservation was completed, the alloy was immediately water quenched to 140°C at a cooling rate of 190°C / s, and then air-cooled to room temperature.

[0083] S03, Pre-cooling treatment: The alloy obtained from SO2 was pre-cooled at -10℃ for 10 min.

[0084] S04, Time-sensitive processing: The alloy obtained from SO3 was subjected to artificial aging treatment at 110℃ for 20 hours to obtain the T6 state alloy. The aging treatment was carried out under nitrogen protection, using a nitrogen circulation system (flow rate of 0.8 m³ / s). 3 ( / h) Ensure that the temperature uniformity inside the furnace is controlled within ±2℃.

[0085] S05, Ultrasonic vibration compression coupling treatment: The T6 alloy obtained from S04 was placed in an ultrasonic pressing device, and a synchronous coupling treatment of compressive load and ultrasonic vibration was applied. The compressive load was applied by a press at a loading rate of 0.1 mm / min, the stress was 50% of the yield strength of the alloy at room temperature, and the treatment temperature was 20℃; ultrasonic vibration was started at an ultrasonic frequency of 40 kHz and an ultrasonic energy of 500 J, and the heat and pressure treatment was carried out for 5 min. Keep the compression load and processing temperature constant, switch the ultrasonic energy to 850J within 20 seconds under pressure, and continue coupling processing for 5 minutes. Keeping the compression load and processing temperature constant, the ultrasonic energy was switched to 1150J within 20 seconds under pressure, and after coupling treatment for 5 minutes, the compression load was removed and the furnace was cooled to room temperature.

[0086] S06, Low-temperature stabilization treatment: The alloy obtained from S05 was held at -20℃ for 5 minutes, and then heated to room temperature in the furnace.

[0087] The Al-Zn-Mg-(Cu) alloy treated by the method in this embodiment has a tensile strength of 615 MPa and an elongation of 23%. Compared with the conventional T6 state, the PFZ width is narrowed from 46 nm to 30 nm, and the morphology of the precipitates within the PFZ changes from irregular lamellar shapes to rounded granules (the aspect ratio of the precipitates decreases from 3.12 to 2.2). Figure 4 (As shown).

[0088] Example 5:

[0089] This embodiment provides a method for controlling the microstructure of 7xxx aluminum alloy grain boundaries without precipitates by ultrasonic vibration compression.

[0090] An Al-Zn-Mg-(Cu) alloy sample with dimensions of 10×40×1.5mm was prepared.

[0091] The composition of the Al-Zn-Mg-(Cu) alloy is as follows: Zn content is 9wt%, Mg content is 3wt%, Cu content is 0.25wt%, and the balance is Al and unavoidable impurities.

[0092] A method for controlling the microstructure of Al-Zn-Mg-(Cu) alloy grain boundaries without precipitation bands by ultrasonic vibration compression includes the following steps: S01, Preparation of Al-Zn-Mg-(Cu) alloy ingots: First, prepare the raw materials based on the composition of the 7xxx series aluminum alloy. Place the crucible in a vacuum melting furnace preheated to 500℃, add the raw materials, set the temperature to 700℃, and hold for 30 minutes until the raw materials are completely melted. Then, open the melting furnace to skim off the slag and slowly stir the molten metal with a stirring spoon to ensure a uniform distribution of its composition. Next, remove the mold to prepare for casting. During the casting process, ensure that the flow rate of the molten metal is uniform, and finally obtain the block-shaped 7xxx series aluminum alloy required for the experiment. SO2, two-stage solution treatment: The Al-Zn-Mg-(Cu) alloy ingot obtained in SO1 was subjected to a two-stage solution treatment under a protective atmosphere of 99.5%Ar + 0.5%H2; First stage of solid solution treatment: Heat from room temperature to 260℃ at a heating rate of 6℃ / min and hold for 35min; Second stage of solid solution treatment: heating from 260℃ to 480℃ at a heating rate of 3℃ / min, and holding at that temperature for 2 hours; After the heat preservation was completed, the alloy was immediately water quenched to 160°C at a cooling rate of 210°C / s, and then air-cooled to room temperature.

[0093] S03, Pre-cooling treatment: The alloy obtained from SO2 was pre-cooled at 5℃ for 30 minutes.

[0094] S04, Time-sensitive processing: The alloy obtained from SO3 was subjected to artificial aging treatment at 130℃ for 28 hours to obtain the T6 state alloy. The aging treatment was carried out under nitrogen protection, using a nitrogen circulation system (flow rate of 0.8 m³ / s). 3 ( / h) Ensure that the temperature uniformity inside the furnace is controlled within ±2℃.

[0095] S05, Ultrasonic vibration compression coupling treatment: The T6 alloy obtained from S04 was placed in an ultrasonic pressing device, and a synchronous coupling treatment of compressive load and ultrasonic vibration was applied. The compressive load was applied by a press at a loading rate of 0.3 mm / min, the stress was 50% of the yield strength of the alloy at room temperature, and the treatment temperature was 30℃; ultrasonic vibration was started at an ultrasonic frequency of 30 kHz and an ultrasonic energy of 450 J, and the heat and pressure treatment was carried out for 15 min. Keep the compression load and processing temperature constant, switch the ultrasonic energy to 950J within 40 seconds under pressure, and continue coupling processing for 15 minutes. Keeping the compression load and processing temperature constant, the ultrasonic energy was switched to 1250J within 40 seconds under pressure and coupled for 15 minutes before the compression load was removed and the furnace was cooled to room temperature.

[0096] S06, Low-temperature stabilization treatment: The alloy obtained from S05 was held at -5℃ for 15 minutes, and then heated to room temperature in the furnace.

[0097] The Al-Zn-Mg-(Cu) alloy treated by the method in this embodiment has a tensile strength of 611 MPa and an elongation of 20%. Compared with the conventional T6 state, the PFZ width is narrowed from 46 nm to 28 nm, and the morphology of the precipitates within the PFZ changes from irregular lamellar shapes to rounded granular shapes (the aspect ratio of the precipitates decreases from 3.12 to 2.61) (e.g. Figure 4 (As shown).

[0098] Comparative Example 1:

[0099] The difference between this comparative example and Example 1 is that in S05, energy level switching is not performed; instead, a constant ultrasonic energy of 500 J is used for continuous treatment for 30 minutes. In this comparative example, the tensile strength is 552 MPa, the elongation is 18%, the PFZ width changes from 46 nm to 79 nm, and the aspect ratio of the precipitated phase within the PFZ changes from 3.12 to 3.67 (e.g., ...). Figure 4 (As shown).

[0100] Comparative Example 2: The difference between this comparative example and Example 1 is that S05 only has two energy increments (i.e., 500J to 900J), lacking a third high-energy ultrasonic curing treatment. In this comparative example, the tensile strength is 579MPa, the elongation is 15%, the PFZ width changes from 46nm to 53nm, and the aspect ratio of the precipitated phase within the PFZ changes from 3.12 to 2.81 (e.g., ...). Figure 4 (As shown).

[0101] Comparative Example 3:

[0102] The difference between this comparative example and Example 1 is that the S05 ultrasonic vibration compression coupling treatment and the S06 low-temperature stabilization treatment are not performed. Furthermore, only the first-stage solution treatment is performed, omitting the second-stage solution treatment. In this comparative example, the tensile strength is 525 MPa, the elongation is 11%, the PFZ width changes from 46 nm to 81 nm, and the aspect ratio of the precipitated phase within the PFZ changes from 3.12 to 4.12 (e.g., ...). Figure 4 (As shown).

[0103] Comparative Example 4:

[0104] The difference between this comparative example and Example 1 is that a light gas gun was used to perform impact compression treatment (3 MPa) on the Al-Zn-Mg-(Cu) alloy, instead of the S05 ultrasonic vibration compression coupling treatment of the present invention. In this comparative example, the tensile strength is 542 MPa, and the elongation is 7.5%. The PFZ width changed from 46 nm to 73 nm, and the aspect ratio of the precipitated phase within the PFZ changed from 3.12 to 3.22 (e.g., ...). Figure 4(As shown). Detailed data on the high-performance aluminum alloys obtained in Examples 1-5 and Comparative Examples 1-4 of the present invention are shown in Table 1 below.

[0105] Table 1. Performance of Aluminum Alloys

[0106] Main testing methods: Mechanical property testing: Tensile tests were conducted on a CMT5105 electronic tensile testing machine. The tensile rate at room temperature was 0.5 mm / min. The dimensions and shape of the tensile specimens are as follows: Figure 3 As shown, the samples were cut directly from the sheet and profile according to the dimensions shown in the diagram using wire electrical discharge machining (EDM). All samples were taken from the center of the specimen. After appropriate heat treatment, the obtained samples were polished with fine sandpaper to remove the surface hardened layer produced by the wire electrical discharge machining.

[0107] The method for testing the yield strength of T6 alloy is as follows: by performing a tensile test on the sample, the stress-strain curve is obtained. The yield strength is the value read from the ordinate of the intersection point of the curve and the line parallel to the stress-strain curve whose origin is shifted 0.2% to the right along the elastic straight line segment. This value is the yield strength of the T6 alloy.

[0108] Transmission electron microscopy (TEM) analysis: This study employed a JEM-F200 (TF-HR) field emission transmission electron microscope (FET) manufactured in Japan to characterize the nanoscale features of materials at an accelerating voltage of 200 kV. Samples used for TEM observation were first mechanically thinned to approximately 70 μm, then punched into standard circular wafers with a diameter of 3 mm. These wafers were then ion-milled using a Gatan PIPS II 695 precision ion thinner to obtain electron beam transparent regions. The mechanically thinned samples were further thinned using a dual-jet electrolytic thinning method. A mixture of 30 vol% nitric acid and 70 vol% methanol was used as the electrolyte, and the thinning temperature was controlled below -25°C to ensure thinning efficiency and sample quality.

[0109] The final prepared TEM sample was observed under a JEM-F200 electron microscope using bright-field / dark-field imaging and selected area electron diffraction analysis. Using DigitalMicrograph (or Gatan Microscopy Suite) image analysis software, the particle size, aspect ratio, and other parameters of the precipitated phase in the acquired microscopic images were systematically statistically and quantitatively analyzed.

[0110] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0111] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0112] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the microstructure of 7xxx series aluminum alloys without precipitate zones at grain boundaries using ultrasonic vibration compression, characterized in that: Includes the following steps: S01, to prepare 7xxx aluminum alloy ingots; SO2, two-stage solution treatment: The S01 7xxx series aluminum alloy ingots were subjected to a two-stage solution treatment under a protective atmosphere; The two-stage solution treatment includes: First stage of solid solution treatment: raise the temperature from room temperature to 240-260℃ at a heating rate of 4-6℃ / min, and hold for 25-35min; Second stage of solution treatment: Increase the temperature from the first stage of solution treatment to 460-480℃ at a heating rate of 1-3℃ / min, and hold for 1-2 hours; After the heat preservation is completed, the alloy is immediately water quenched to 140-160℃ at a cooling rate of 190-210℃ / s, and then air-cooled to room temperature. S03, Pre-cooling treatment: The alloy obtained from SO2 was pre-cooled at -10-5℃ for 10-30 min. S04, Time-sensitive processing: The alloy obtained from SO3 was subjected to artificial aging treatment at 110-130℃ for 20-28 hours to obtain the T6 state alloy. S05, Multi-stage ultrasonic vibration compression coupling treatment: S05a, Level 1 Low-Energy Ultrasonic Treatment: The T6 state alloy obtained from S04 is placed in an ultrasonic pressing device, and a synchronous coupling treatment of compressive load and ultrasonic vibration is applied. The compressive load is applied by a press at a loading rate of 0.1-0.5 mm / min, the stress is 50% of the yield strength of the T6 alloy obtained by SO4 at room temperature, and the treatment temperature is 20-30℃; ultrasonic vibration is started, the ultrasonic frequency is 20-40 kHz, the ultrasonic energy is 400-600 J, and the heat and pressure treatment is carried out for 5-15 min. S05b, Level 2 medium-energy ultrasonic treatment: Keep the compression load and treatment temperature constant, switch the ultrasonic energy to 800-1000J within 20-40s under pressure, and continue the coupling treatment for 5-15min. S05c, Level 3 High-Energy Ultrasonic Treatment: Keep the compressive load and treatment temperature constant, switch the ultrasonic energy to 1100-1300J within 20-40 seconds under pressure, remove the compressive load after coupling treatment for 5-15 minutes, and cool to room temperature with the furnace. S06, Low-temperature stabilization treatment: The alloy obtained from S05 was held at -20 to -5℃ for 5 to 15 minutes, and then heated to room temperature in the furnace.

2. The method according to claim 1, characterized in that: In S01, the 7xxx aluminum alloy ingot has the following composition by weight percentage: Zn 7%-9%, Mg 1%-3%, Cu 0.1%-0.25%, with the balance being Al and unavoidable impurities.

3. The method according to claim 1, characterized in that: In SO2, both-stage solution treatments were carried out under a protective atmosphere of 99.5% Ar + 0.5% H2.

4. The method according to claim 1, characterized in that: In S04, the aging treatment is carried out under nitrogen protection, and the temperature uniformity inside the furnace is controlled within ±2℃.

5. The 7xxx series aluminum alloy obtained by the method according to any one of claims 1-4, characterized in that: In 7xxx series aluminum alloys, the width of the grain boundary precipitate-free zone (PFZ) is 28-32 nm; the morphology of the precipitates in the grain boundary PFZ changes from irregular lath-like to rounded granular, and the aspect ratio of the precipitates is ≤2.

61.

6. The 7xxx series aluminum alloy according to claim 5, characterized in that: The tensile strength of 7xxx series aluminum alloys reaches 610-624MPa, and the elongation reaches over 20%.

7. The application of the 7xxx series aluminum alloy according to claim 5 in materials that combine lightweight and long service life.

8. The application according to claim 7, characterized in that: Materials that combine lightweight design with long service life include materials for aerospace, rail transportation, and the automotive industry.

9. The application according to claim 8, characterized in that: Materials used in aerospace include aircraft fuselages, wings, landing gear, rocket engine frames, or missile casings.

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