Method for producing 7xxx-series aluminium alloy sheet and use thereof

Abstract

The application provides a preparation method and application of a 7xxx series aluminum alloy plate. The preparation method comprises the following steps: sequentially performing homogenization heat treatment, preheating, hot rolling, solid solution treatment, quenching, pre-stretching treatment and aging treatment on a 7xxx series aluminum alloy ingot to obtain the 7xxx series aluminum alloy plate. The hot rolling is divided into first stage hot rolling and second stage hot rolling according to the pass sequence, and the temperature, reduction rate and rolling speed of the hot rolling in different stages are set respectively. The first stage hot rolling adopts a small single pass reduction rate and a fast rolling speed, and the second stage hot rolling adopts a large single pass reduction rate and a slow rolling speed, so that the plate is fully dynamically recovered, the recrystallization behavior of the plate in the subsequent solid solution process is reduced, the coarse second phase is fully broken and dispersedly distributed, the recrystallization is effectively inhibited, and thus the high-performance 7xxx series aluminum alloy plate with high strength, high toughness and stress corrosion resistance is obtained.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy processing technology, and more specifically, to a method for preparing 7xxx series aluminum alloy sheets and their application. Background Technology

[0002] 7xxx series aluminum alloys, due to their excellent specific strength, good toughness, and low density, have become key materials for manufacturing critical load-bearing structural components such as aircraft frames and skins. However, recrystallization inevitably occurs during the material preparation process due to the influence of composition and processing. Recrystallization forms coarse, randomly oriented recrystallized grains, replacing the original fine, fibrous deformed structure. This microstructural transformation brings a series of adverse effects: First, the coarse recrystallized grains significantly reduce the material's strength and toughness; second, the randomly oriented grains destroy the anisotropic properties brought about by the deformed texture, leading to a sharp decrease in the material's crack propagation resistance, especially the resistance to short crack propagation, which is a critical indicator in aerospace structural component design; furthermore, the recrystallized structure is also prone to forming continuously distributed precipitates at grain boundaries, exacerbating the material's susceptibility to stress corrosion cracking. Therefore, how to effectively suppress the recrystallization process of 7xxx series aluminum alloys and obtain an unrecrystallized or partially recrystallized structure with high dislocation density and strong deformed texture has become a technical bottleneck for improving the overall performance of this series of alloys.

[0003] To reduce the recrystallization fraction in 7xxx aluminum alloys, transition metals such as Sc are typically added. These elements form dispersed particles that pin grain boundaries and dislocations, thereby hindering recrystallization nucleation and growth. While this method is the most effective, these elements are expensive, significantly increasing production costs. Numerous studies have attempted to suppress recrystallization through other methods. Chinese patent application CN105838945A discloses a method for suppressing recrystallization in sheet metal by adding Cr, Si, and rare earth elements to replace Sc. Chinese patent application CN106555065A discloses an alloying method that uses high-frequency electromagnetic oscillation in a vacuum high-frequency electromagnetic arc furnace during the casting process to uniformly disperse Ti and Zr elements, ultimately suppressing aluminum alloy recrystallization. Chinese patent application CN104018039B provides a homogenization cooling process that transfers flat ingots to a cooling chamber for strong air cooling or spray cooling, causing fine precipitates to dissolve and inhibiting their re-precipitation or coarsening, ultimately reducing the recrystallization fraction. Chinese patent application CN109022857B discloses a method for increasing the recrystallization temperature of aluminum alloys. This method involves altering the dispersion behavior of the dispersed phase through a two-stage rolling process (rolling and cold rolling), thereby inhibiting recrystallization and grain growth. While this method avoids the addition of expensive elements by adding extra processing steps or equipment, it increases the production cost due to the increased investment in equipment. Summary of the Invention

[0004] The main objective of this invention is to provide a method for preparing 7xxx series aluminum alloy sheets and their application, in order to solve the problem that 7xxx series aluminum alloys are prone to recrystallization during preparation, which leads to a decrease in strength, fracture toughness and stress corrosion resistance.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for preparing 7xxx series aluminum alloy sheet is provided, comprising the following steps: Step S1, homogenizing a 7xxx series aluminum alloy ingot with heat treatment to obtain a homogenized ingot; Step S2, preheating the homogenized ingot to obtain a preheated ingot; Step S3, feeding the preheated ingot into a hot rolling mill for hot rolling to obtain a hot-rolled sheet; wherein, the hot rolling includes n passes, where n is an integer and 6 < n < 25; the hot rolling is divided into a first-stage hot rolling and a second-stage hot rolling according to the pass sequence; the single-pass reduction rate of the first-stage hot rolling is < the single-pass reduction rate of the second-stage hot rolling; the rolling speed of the first-stage hot rolling is > the rolling speed of the second-stage hot rolling; the sheet temperature of the first-stage hot rolling is 435~455℃, and the rolling speed is 50~100m / min; the first-stage hot rolling includes The rolling process consists of two stages: Section 1 and Section 2; Section 1 comprises the first and second passes, with a single-pass reduction rate of 3-5%; Section 2 comprises the third to the (n-3)th passes, with a single-pass reduction rate of 10-15%; The second stage of hot rolling includes Sections 3 and 4; Section 3 comprises the (n-2)th and (n-1)th passes, with a plate temperature of 420-440℃, a single-pass reduction rate of 20-25%, and a rolling speed of 35-50 m / min; Section 4 comprises the nth pass, with a plate temperature of 400-420℃, a single-pass reduction rate of 15-20%, and a rolling speed of 20-35 m / min; Step S4 involves sequentially performing solution treatment, quenching, and pre-stretching on the hot-rolled plate to obtain the W51 state plate; Step S5 involves aging the W51 state plate to obtain the 7xxx series aluminum alloy plate.

[0006] Further, in step S1, the 7xxx series aluminum alloy ingot includes Al, Zn, Mg, Cu and unavoidable impurities. By weight percentage, the sum of Zn, Mg and Cu is 9~14wt%, the weight percentage of a single impurity is ≤0.05wt%, the total weight percentage of impurities is ≤0.15wt%, and the balance is Al; and / or, the homogenization heat treatment temperature is 465~490℃ and the time is 30~60h.

[0007] Further, in step S1, the weight ratio of Zn to Mg in the 7xxx series aluminum alloy ingot is (3.2~5):1; and / or, the weight ratio of Cu to Mg in the 7xxx series aluminum alloy ingot is (0.6~1.12):1.

[0008] Furthermore, the preheating temperature is 440~460℃ and the time is 60~120min; and / or, the total deformation of the first stage hot rolling and the second stage hot rolling is 75~90%.

[0009] Furthermore, hot rolling includes n passes, where n is an integer and 11 ≤ n ≤ 17.

[0010] Furthermore, the single-pass reduction rate of the first-stage hot rolling is less than that of the second-stage hot rolling, with a difference of 6-21%; and / or, the rolling speed of the first-stage hot rolling is greater than that of the second-stage hot rolling, with a difference of 10-65 m / min.

[0011] Further, in step S4, the solution treatment temperature is 465~480℃ and the time is 180~330min; and / or, the quenching treatment is water quenching at a water temperature of 10~50℃; and / or, the stretching amount of the pre-stretching treatment is 1.5~3%.

[0012] Further, in step S5, the aging process includes a first aging process and a second aging process performed sequentially; wherein, the temperature of the first aging process is 115~125℃ and the time is 6~12h; the temperature of the second aging process is 150~160℃ and the time is 10~30h.

[0013] According to another aspect of the present invention, a 7xxx series aluminum alloy sheet is provided, which is obtained by the above-described method for preparing the 7xxx series aluminum alloy sheet.

[0014] Furthermore, the thickness of the 7xxx series aluminum alloy sheet is 40~100mm; and / or, the recrystallization fraction of the 7xxx series aluminum alloy sheet is 1.59~10%.

[0015] By applying the technical solution of this invention, 7xxx series aluminum alloy ingots are sequentially subjected to homogenization heat treatment, preheating, hot rolling, solution treatment, quenching, pre-stretching, and artificial aging to obtain 7xxx series aluminum alloy plates. The hot rolling process is divided into a first-stage hot rolling and a second-stage hot rolling. By employing segmented gradient process control in the hot rolling process—that is, the first-stage hot rolling uses a smaller single-pass reduction rate and a faster rolling speed, while the second-stage hot rolling uses a larger single-pass reduction rate and a slower rolling speed—the plate undergoes sufficient dynamic recovery during multi-pass rolling, weakening the dislocation density accumulation introduced by plastic deformation, consuming the energy stored during plate deformation, and reducing the driving force required for recrystallization during subsequent solution treatment. Simultaneously, the coarse second phase in the ingot is fully broken up and uniformly dispersed under gradually increasing deformation conditions, effectively suppressing recrystallization. This invention achieves a recrystallization fraction of ≤10% by controlling the hot rolling temperature gradient, optimizing the deformation amount in each pass, matching the rolling speed gradient, and precisely controlling the final rolling temperature, thereby obtaining high-strength, high-toughness, and stress corrosion-resistant high-performance 7xxx series aluminum alloy sheets. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 An EBSD (electron backscattering diffraction) microstructure of a 7xxx series aluminum alloy sheet according to Embodiment 1 of the present invention is shown.

[0018] Figure 2 An EBSD microstructure diagram of a 7xxx series aluminum alloy sheet according to Embodiment 2 of the present invention is shown.

[0019] Figure 3 An EBSD microstructure diagram of a 7xxx series aluminum alloy sheet according to Embodiment 3 of the present invention is shown.

[0020] Figure 4 An EBSD microstructure diagram of a 7xxx series aluminum alloy sheet according to Comparative Example 1 is shown.

[0021] Figure 5 The EBSD microstructure of a 7xxx series aluminum alloy sheet according to Comparative Example 2 is shown.

[0022] Figure 6 The EBSD microstructure of the 7xxx series aluminum alloy sheet according to Comparative Example 3 is shown. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] The rolling process induces intense plastic deformation in the sheet metal, resulting in the accumulation of a large amount of deformation energy within it. This energy is the core driving force for recrystallization during subsequent solution heat treatment, and it has a decisive influence on the nucleation and growth processes of recrystallization. On the other hand, the coarse second-phase particles are not coherent with the matrix, and during deformation, a strong lattice distortion region is formed around these coarse second-phase particles. The subgrains in this region vary in size and have a large orientation difference, with a high dislocation density within the subgrains. This provides a large driving force for subgrain boundary migration, promoting recrystallization nucleation.

[0025] As described in the background section of this invention, existing technologies suffer from the problem that 7xxx series aluminum alloys are prone to recrystallization during preparation, leading to a decrease in strength, toughness, and stress corrosion resistance. To address this issue, in a typical embodiment of this invention, a method for preparing 7xxx series aluminum alloy sheets is provided, comprising the following steps: Step S1, homogenizing a 7xxx series aluminum alloy ingot with heat treatment to obtain a homogenized ingot; Step S2, preheating the homogenized ingot to obtain a preheated ingot; Step S3, hot rolling the preheated ingot into a hot rolling mill to obtain a hot-rolled sheet; wherein the hot rolling includes n passes, where n is an integer and 6 < n < 25; the hot rolling is divided into a first-stage hot rolling and a second-stage hot rolling according to the pass order; the single-pass reduction rate of the first-stage hot rolling is < the single-pass reduction rate of the second-stage hot rolling; the rolling speed of the first-stage hot rolling is > the rolling speed of the second-stage hot rolling; the sheet temperature of the first-stage hot rolling is 435~455℃, and the rolling speed is 50~100m / min; the first-stage hot rolling... The process includes two stages: Stage 1 and Stage 2; Stage 1 consists of the first and second passes, with a single-pass reduction rate of 3-5%; Stage 2 consists of the third to the (n-3)th passes, with a single-pass reduction rate of 10-15%; Stage 2 hot rolling includes Stage 3 and Stage 4; Stage 3 consists of the (n-2)th and (n-1)th passes, with a plate temperature of 420-440℃, a single-pass reduction rate of 20-25%, and a rolling speed of 35-50 m / min; Stage 4 consists of the nth pass, with a plate temperature of 400-420℃, a single-pass reduction rate of 15-20%, and a rolling speed of 20-35 m / min; Step S4 involves sequentially performing solution treatment, quenching, and pre-stretching on the hot-rolled plate to obtain the W51 state plate; Step S5 involves aging the W51 state plate to obtain the 7xxx series aluminum alloy plate.

[0026] This invention controls the microstructure of 7xxx series aluminum alloy sheets through a hot rolling process under specific conditions. First, the 7xxx series aluminum alloy ingot is subjected to homogenization heat treatment, which allows the unevenly distributed alloying elements in the as-cast state to fully diffuse at high temperature, eliminates dendritic segregation, and promotes the dissolution of low-melting-point eutectic phases into the matrix, resulting in an ingot with stable composition and uniform microstructure.

[0027] Then, the homogenized ingot is preheated and enters the hot rolling process, which employs a two-stage, four-interval gradient control process. Specifically, the first stage of hot rolling is the biting and main deformation stage, divided into two intervals. Interval 1 (passes 1-2, biting period): a small deformation of 3%~5% is used for biting to ensure the billet is smoothly bitten into the rolls, avoiding slippage and initial cracking. Interval 2 (pass 3 to the end of the first stage): after successful biting, the deformation of a single pass is immediately increased to 10%~15% for rapid, large-reduction rolling.

[0028] In the early stages of conventional plate rolling, to ensure smooth ingot "biting," the first 3-5 passes typically employ a "small deformation amount + gradual increase" method to ensure the billet smoothly bites into the rolls and avoids slippage and initial cracking. However, this leads to an increase in the total number of subsequent deformation passes, a decrease in the final rolling temperature, and ultimately a higher recrystallization content in the plate. This invention limits the temperature and rolling speed in a coordinated manner, effectively reducing the above problems and thus enabling the number of passes in interval one to be reduced to 2.

[0029] Compared to conventional processes that require 4-5 passes to achieve maximum deformation (i.e., interval one occurs in passes 1-4 or 1-5), this invention completes the bite-in process in just the first 2 passes, gradually entering the maximum deformation state from the 3rd pass onwards. With a constant total deformation, the larger deformation per pass effectively reduces the total number of rolling passes and shortens the total rolling time, thereby significantly reducing the temperature drop of the billet during rolling and keeping the sheet material within a relatively high temperature window.

[0030] When the final three passes of rolling are completed, the second stage of hot rolling begins. Due to the fewer passes and smaller temperature drop in the earlier stages, the slab still maintains a relatively high temperature. In this stage, a larger deformation amount and a lower rolling speed than in the first stage of hot rolling are used, which allows the deformation to fully penetrate from the surface of the plate to the core. This ensures uniform deformation in the thickness direction of the thick plate (finished specifications 40~100mm), achieving full deformation transfer and avoiding only surface deformation while energy accumulates in the core.

[0031] Furthermore, the constraints on deformation amount, rolling speed, and temperature at this stage produce a significant synergistic effect. Typically, towards the end of rolling, the temperature difference between the slab surface and core gradually increases. Traditional processes involving low temperature, high speed, and large deformation can lead to significant differences in microstructure at different thicknesses of the slab, and also result in insufficient release of the high energy stored during deformation. This method addresses this issue by combining high-temperature conditions in the last three passes with a slow strain rate. High temperature increases the atomic diffusion rate, while a slow rate extends the deformation time, allowing dislocations to fully climb and cancel each other out, resulting in dynamic recovery and energy release. This dynamic recovery process can consume a large amount of deformation energy accumulated during plastic deformation, thus significantly reducing the thermodynamic driving force for recrystallization nucleation during subsequent solution heating. It also avoids the phenomenon of sufficient surface rolling but insufficient core rolling, common in traditional thick-plate rolling processes. Simultaneously, the large deformation amount allows for the thorough breaking down and refinement of coarse secondary phases (such as the Al7Cu2Fe phase) remaining in the ingot, preventing these coarse particles from acting as particle-induced nucleation (PSN) sites to induce local recrystallization during subsequent high-temperature processes.

[0032] Furthermore, in the second stage of hot rolling, based on the parameters in interval three, the parameters in interval four are further adjusted to obtain a limited parameter range. This adjustment is based on the overall increase in temperature and the limited rolling speed and deformation amount mentioned above in this method. It can significantly improve the coordination between temperature, rolling speed and deformation amount. Thus, under the rolling process with the parameters in the above range, the specifications of the rolled plate can still be flexibly adjusted to obtain the rolled plate with the specified dimensions and precision.

[0033] Finally, the hot-rolled sheet is solution-quenched to form a supersaturated solid solution. The quenched sheet is then pre-stretched to eliminate residual stress and ensure flatness. Simultaneously, an appropriate number of movable dislocations are introduced to provide preferential heterogeneous nucleation sites for subsequent aging precipitation. Finally, aging treatment is performed, and by controlling the nucleation, growth, and coarsening processes of the precipitated phases, 7xxx series aluminum alloy sheets are obtained.

[0034] This invention, by controlling key process parameters in the hot rolling process, enables aluminum alloy sheets to achieve a significant reduction in recrystallization driving force during the solution treatment process by weakening the concentration of deformation energy storage, breaking down coarse second phases, and uniformly dispersing them, without adding expensive rare metals such as Sc, or adding new equipment and processing steps. This reduces the recrystallization fraction to below 10%. The process of this invention is suitable for large-scale industrial continuous production, is low-cost and highly efficient, and can significantly improve the strength, toughness, and stress corrosion resistance of 7xxx series aluminum alloy sheets for aerospace applications, solving the technical bottleneck of low-cost recrystallization suppression in the industry.

[0035] In a preferred embodiment, the 7xxx series aluminum alloy ingot comprises Al, Zn, Mg, Cu, and unavoidable impurities. By weight percentage, the sum of Zn, Mg, and Cu is 9-14 wt%, the weight percentage of a single impurity is ≤0.05 wt%, the total weight percentage of impurities is ≤0.15 wt%, and the balance is Al. And / or, the homogenization heat treatment temperature is 465-490°C, and the time is 30-60 h.

[0036] Using 7xxx series aluminum alloys with the above-mentioned composition can further promote the fine distribution of precipitated phases during aging, making it easier for the matrix to achieve stronger mechanical properties while maintaining good plasticity. Controlling the total amount and individual impurity content within the above-mentioned ranges can further improve the fracture toughness of the sheet metal. Maintaining the homogenization heat treatment temperature and time within the above-mentioned ranges can further promote the full diffusion of alloying elements, which is more conducive to eliminating as-cast segregation and making the second phase distribution more uniform, thus better facilitating deformation energy storage during subsequent hot rolling.

[0037] In some embodiments, the 7xxx series aluminum alloy ingots, by weight percentage, comprise 8-10 wt.% Zn, 1.3-2 wt.% Cu and 1.8-2.5 wt.% Mg, with the balance being Al and unavoidable impurities, wherein the weight percentage of a single impurity is ≤0.05 wt% and the total weight percentage of impurities is ≤0.15 wt%.

[0038] To further promote the fine distribution of precipitated phases during the aging process and make it easier for the matrix to obtain stronger mechanical properties while maintaining good plasticity, in a preferred embodiment, in step S1, the weight ratio of Zn to Mg in the 7xxx series aluminum alloy ingot is (3.2~5):1; and / or, the weight ratio of Cu to Mg in the 7xxx series aluminum alloy ingot is (0.6~1.12):1.

[0039] In a preferred embodiment, the preheating temperature is 440~460℃, and the time is 60~120min; and / or, the total deformation of the first-stage hot rolling and the second-stage hot rolling is 75~90%. Preheating temperature and time within the above range can further promote a uniform transition of the internal temperature field of the ingot, which is more conducive to a smooth transition of deformation resistance during hot rolling and reduces the difference in microstructure between the surface and the core. Total deformation within the above range can further improve the accumulation efficiency of dislocation density in the matrix, allowing for more complete second-phase fragmentation and a more overall coordinated distribution of deformation energy storage, thereby making it easier to suppress recrystallization of the alloy.

[0040] To further refine the control of the hot rolling process and more easily obtain alloy plates with high dimensional accuracy, in a preferred embodiment, the hot rolling includes n passes, where n is an integer and 11≤n≤17.

[0041] In a preferred embodiment, the single-pass reduction rate of the first-stage hot rolling is less than the single-pass reduction rate of the second-stage hot rolling, with a difference of 6-21%; and / or, the rolling speed of the first-stage hot rolling is greater than the rolling speed of the second-stage hot rolling, with a difference of 10-65 m / min.

[0042] The second-stage hot rolling process, employing lower speeds and greater deformation, allows the slab to undergo sufficient dynamic recovery during rolling to release stored energy. This reduces the thermodynamic driving force for recrystallization nucleation during subsequent solution heating, thus lowering the recrystallization fraction. Simultaneously, it ensures consistent deformation between the surface and core of the slab.

[0043] In a preferred embodiment, in step S4, the solution treatment temperature is 465~480℃, and the time is 180~330 min; and / or, the quenching treatment is water quenching at a water temperature of 10~50℃. The solution temperature and time being within the above range can further promote the sufficient dissolution of the second phase into the matrix. Limiting the water quenching temperature to the above range can further improve the controllability of the cooling rate, resulting in a more fully supersaturated solid solution.

[0044] In a preferred embodiment, in step S4, the stretching amount of the pre-stretching treatment is 1.5~3%; and / or, in step S5, the aging treatment includes a first aging treatment and a second aging treatment performed sequentially; wherein, the temperature of the first aging treatment is 115~125℃ and the time is 6~12h; the temperature of the second aging treatment is 150~160℃ and the time is 10~30h.

[0045] Pre-stretching within the aforementioned range can further promote the gradual release of residual stress and reduce the disturbance of local strain concentration to the deformed structure. The aforementioned two-stage aging process can further promote the uniform nucleation of fine precipitates, making it easier for solute atoms to orderly agglomerate near dislocations, resulting in a more overall coordinated strengthening effect and enhancing the comprehensive properties of the material without significantly sacrificing plasticity.

[0046] In a preferred embodiment, the thickness of the 7xxx series aluminum alloy sheet is 40~100mm; and / or, the recrystallization fraction of the 7xxx series aluminum alloy sheet is 1.59~10%. Due to the above preparation method, the fibrous deformed structure can be significantly preserved while the recrystallization fraction of the sheet is reduced, resulting in a simultaneous improvement in the material's strength, toughness, and stress corrosion resistance, meeting high requirements for overall performance. Especially for thick sheets, this process effectively ensures the consistency of microstructure and properties between the core and the surface.

[0047] Typical, but not limiting, temperatures for the first-stage hot rolling of the sheet metal are 435℃, 437℃, 439℃, 442℃, 444℃, 446℃, 448℃, 451℃, 453℃, 455℃, or any two of these values. Rolling speeds for the first-stage hot rolling are 50 m / min, 56 m / min, 61 m / min, 67 m / min, 72 m / min, 78 m / min, 83 m / min, 89 m / min, 94 m / min, 100 m / min, or any two of these values. Single-pass reduction rates for interval one are 3.0%, 3.2%, 3.4%, 3.7%, 3.9%, 4.1%, 4.3%, 4.6%, 4.8%, 5.0%, or any two of these values. The single-pass reduction rate for interval two is 10.0%, 10.6%, 11.1%, 11.7%, 12.2%, 12.8%, 13.3%, 13.9%, 14.4%, 15.0%, or a range of values ​​consisting of any two points.

[0048] Typical, but not limiting, plate temperatures in Zone 3 are 420℃, 422℃, 424℃, 427℃, 429℃, 431℃, 433℃, 436℃, 438℃, 440℃, or any two of these values. Single-pass reduction rates in Zone 3 are 20.0%, 20.6%, 21.0%, 21.7%, 22.0%, 22.8%, 23.0%, 24.0%, 24.4%, 25.0%, or any two of these values. Rolling speeds in Zone 3 are 35m / min, 37m / min, 38m / min, 40m / min, 42m / min, 43m / min, 45m / min, 47m / min, 48m / min, 50m / min, or any two of these values. The plate temperature in interval four is 400℃, 402℃, 404℃, 407℃, 409℃, 411℃, 413℃, 416℃, 418℃, 420℃, or any two of these values. The single-pass reduction rate in interval four is 15.0%, 15.6%, 16.0%, 16.7%, 17.0%, 17.8%, 18.0%, 19.0%, 19.4%, 20.0%, or any two of these values. The rolling speed in interval four is 20m / min, 22m / min, 23m / min, 25m / min, 27m / min, 28m / min, 30m / min, 32m / min, 33m / min, 35m / min, or any two of these values.

[0049] Typically, but not restrictively, the single-pass reduction rate of the first-stage hot rolling is less than that of the second-stage hot rolling, with a difference of 6%, 8%, 9%, 11%, 13%, 14%, 16%, 18%, 19%, 21%, or any two of these values ​​within a range. The rolling speed of the first-stage hot rolling is greater than that of the second-stage hot rolling, with a difference of 10 m / min, 16 m / min, 22 m / min, 28 m / min, 34 m / min, 41 m / min, 47 m / min, 53 m / min, 59 m / min, 65 m / min, or any two of these values ​​within a range.

[0050] Typical, but not limiting, weight ratios of Zn to Mg in 7xxx series aluminum alloy ingots are 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4.0:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1, 5.0:1, or any range of two such ratios. Weight ratios of Cu to Mg in 7xxx series aluminum alloy ingots are 0.60:1, 0.66:1, 0.72:1, 0.77:1, 0.83:1, 0.89:1, 0.95:1, 1.00:1, 1.06:1, 1.12:1, or any range of two such ratios.

[0051] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0052] Example 1

[0053] Step S1: Homogenize the 7xxx series aluminum alloy ingot with a size of 420mm×1320mm by holding it at 475℃ for 30h to obtain a homogenized ingot. The composition of the ingot is shown in Table 1.

[0054] Step S2: Preheat the homogenized ingot to 460°C and hold for 90 minutes to obtain the hot-rolled sheet.

[0055] Step S3: The preheated ingot is fed into a hot rolling mill for hot rolling to obtain the hot-rolled sheet; specific parameters are shown in Tables 2 and 3.

[0056] Step S4: The hot-rolled sheet is solution treated at 475℃ for 180 minutes, and then water-quenched at 35℃ to obtain the quenched sheet. Within 4 hours after quenching, the quenched sheet is pre-stretched to eliminate residual stress, with a stretching amount of 2.5%, to obtain the W51 state sheet.

[0057] Step S5: The W51 state plate is first kept at 120℃ for 6 hours for the first aging treatment, and then heated to 160℃ for 10 hours for the second aging treatment to obtain a 7xxx series aluminum alloy plate with a thickness of 40mm.

[0058] Example 2

[0059] Step S1: Homogenize the 7xxx series aluminum alloy ingot with a size of 420mm×1320mm by holding it at 470℃ for 40h to obtain a homogenized ingot. The composition of the ingot is shown in Table 1.

[0060] Step S2: Preheat the homogenized ingot to 450°C and hold for 70 minutes to ensure that the ingot is fully heated and obtain the preheated ingot.

[0061] Step S3: The preheated ingot is fed into a hot rolling mill for hot rolling to obtain the hot-rolled sheet; specific parameters are shown in Tables 2 and 3.

[0062] Step S4: The hot-rolled sheet is solution treated at 475℃ for 240 minutes, and then water-quenched at 35℃ to obtain the quenched sheet. Within 4 hours after quenching, the quenched sheet is pre-stretched to eliminate residual stress, with a stretching amount of 2.5%, to obtain the W51 state sheet.

[0063] Step S5: The W51 state plate is first kept at 120℃ for 6 hours for the first aging treatment, and then heated to 155℃ for 20 hours for the second aging treatment to obtain a 7xxx series aluminum alloy plate with a thickness of 60mm.

[0064] Example 3

[0065] Step S1: Homogenize the 7xxx series aluminum alloy ingot with a size of 420mm×1320mm by holding it at 465℃ for 50h to obtain a homogenized ingot. The composition of the ingot is shown in Table 1.

[0066] Step S2: Preheat the homogenized ingot to 440°C and hold for 60 minutes to ensure that the ingot is fully heated and obtain the preheated ingot.

[0067] Step S3: The preheated ingot is fed into a hot rolling mill for hot rolling to obtain the hot-rolled sheet; specific parameters are shown in Tables 2 and 3.

[0068] Step S4: The hot-rolled sheet is solution treated at 475℃ for 330 minutes, and then water-quenched at 35℃ to obtain the quenched sheet. Within 4 hours after quenching, the quenched sheet is pre-stretched to eliminate residual stress, with a stretching amount of 2.5%, to obtain the W51 state sheet.

[0069] Step S5: First, the W51 state plate is kept at 120℃ for 6 hours for the first aging treatment, and then the temperature is raised to 150℃ and kept at 150℃ for 30 hours for the second aging treatment, to obtain a 7xxx series aluminum alloy plate with a thickness of 100mm.

[0070] Examples 4 to 5

[0071] The difference from Example 1 is that the hot rolling process parameters are different in step S3, as shown in Tables 2 and 3.

[0072] Example 6

[0073] The difference from Example 1 is that,

[0074] In step S1, the homogenization heat treatment temperature is 490℃ and the time is 60h;

[0075] In step S2, the preheating temperature is 440℃ and the time is 120min;

[0076] In step S4, the solution treatment temperature is 465℃ and the time is 330 min; the water quenching temperature is 10℃, and the stretching amount of the pre-stretching treatment is 1.5%.

[0077] In step S5, the temperature for the first aging treatment is 115℃ and the time is 12h.

[0078] Example 7

[0079] The difference from Example 1 is that,

[0080] In step S4, the solution treatment temperature is 480℃ and the time is 180 min; the water quenching temperature is 50℃, and the stretching amount of the pre-stretching treatment is 3%;

[0081] In step S5, the temperature for the first aging treatment is 125℃ and the time is 7h.

[0082] Comparative Example 1

[0083] The difference from Example 1 is that,

[0084] In step S2, the preheating temperature is 420℃ and the time is 80 minutes;

[0085] The hot rolling process parameters differ in steps S3 and S4, as detailed in Tables 2 and 3.

[0086] Comparative Example 2

[0087] The difference from Comparative Example 1 is that the hot rolling process parameters are different in steps S3 to S4, as shown in Tables 2 and 3.

[0088] Comparative Example 3

[0089] The difference from Comparative Example 1 is that,

[0090] In step S2, the preheating temperature is 400℃ and the time is 80min;

[0091] The hot rolling process parameters differ in steps S3 and S4, as detailed in Tables 2 and 3.

[0092] Performance testing:

[0093] The aluminum alloy materials obtained in the above embodiments and comparative examples were analyzed and tested as follows, and the results are shown in Table 4.

[0094] 1. Recrystallization fraction: EBSD was used to analyze the microstructure, and HKL Channel 5 software was used to process the recrystallization degree of the head and tail microstructures. The grain boundary orientation difference angle was set to 2°~15°, that is, grains with a grain boundary angle greater than 15° were considered fully recrystallized grains, grains with a grain boundary angle of 2°~15° were considered incompletely recrystallized substructures, and grains with a grain boundary angle less than 2° were considered deformed microstructures.

[0095] 2. Mechanical strength: GB / T 16865 Test specimens and methods for tensile testing of wrought aluminum, magnesium and their alloy products.

[0096] 3. Fracture toughness: HB 5487-1996 Test method for fracture toughness of aluminum alloys.

[0097] 4. Stress corrosion resistance: HB 5259-1983 Stress corrosion test method for C-ring of aluminum alloy.

[0098] Table 1

[0099]

[0100] Table 2

[0101]

[0102] In Tables 2 and 3, " / " means "same as Example 1".

[0103] Table 3

[0104]

[0105] Table 4

[0106]

[0107] The EBSD microstructures of the 7xxx series aluminum alloy sheets in Examples 1 to 3 are shown below. Figures 1 to 3As can be seen, the sheet material exhibits a predominantly fibrous recovery structure with a low recrystallization ratio. The EBSD microstructure diagrams of the 7xxx series aluminum alloy sheets from Comparative Examples 1 to 3 are shown below. Figures 4 to 6 It can be seen that there are a large number of lath-like recrystallized structures in the plate.

[0108] Therefore, it can be seen that 7xxx series aluminum alloy ingots are subjected to homogenization heat treatment, preheating, hot rolling, solution treatment, quenching, pre-stretching, and artificial aging in sequence to obtain 7xxx series aluminum alloy plates. The hot rolling is divided into first-stage hot rolling and second-stage hot rolling according to the number of passes. By adopting segmented gradient process control in the hot rolling process, that is, the first-stage hot rolling adopts a small and medium single-pass reduction rate and a relatively fast rolling speed, while the second-stage hot rolling adopts a larger single-pass reduction rate and a slower rolling speed, so that the plate can fully undergo dynamic recovery during the multi-pass rolling process, weaken the dislocation density accumulation introduced by plastic deformation, consume the energy stored in the plate during the deformation process, reduce the driving force required for the recrystallization behavior of the plate during the subsequent solution treatment process, and at the same time, the coarse second phase in the ingot is fully broken up and uniformly dispersed under the gradually increasing deformation conditions, so as to effectively inhibit recrystallization. This invention achieves a recrystallization fraction of ≤10% by controlling the hot rolling temperature gradient, optimizing the deformation amount in each pass, matching the rolling speed gradient, and precisely controlling the final rolling temperature, thereby obtaining high-strength, high-toughness, and stress corrosion-resistant high-performance 7xxx series aluminum alloy sheets.

[0109] Furthermore, it can be seen that the overall effect is better when all process parameters are within the preferred range of the present invention.

[0110] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing 7xxx series aluminum alloy sheets, characterized in that, Includes the following steps: Step S1: The 7xxx series aluminum alloy ingot is subjected to homogenization heat treatment to obtain a homogenized ingot. Step S2: Preheat the homogenized ingot to obtain a preheated ingot; Step S3: The preheated ingot is fed into a hot rolling mill for hot rolling to obtain a hot-rolled sheet; wherein, The hot rolling process includes n passes, where n is an integer and 6 < n < 25; the hot rolling process is divided into a first-stage hot rolling process and a second-stage hot rolling process according to the pass sequence; the single-pass reduction rate of the first-stage hot rolling process is less than the single-pass reduction rate of the second-stage hot rolling process; the rolling speed of the first-stage hot rolling process is greater than the rolling speed of the second-stage hot rolling process. The temperature of the hot-rolled plate in the first stage is 435~455℃, and the rolling speed is 50~100m / min; the first stage of hot rolling includes zone one and zone two; zone one is the first and second passes, and the single-pass reduction rate of zone one is 3~5%; zone two is the third to the (n-3)th passes, and the single-pass reduction rate of zone two is 10~15%; The second stage of hot rolling includes interval three and interval four; interval three is the (n-2)th and (n-1)th passes, the plate temperature in interval three is 420~440℃, the single-pass reduction rate is 20~25%, and the rolling speed is 35~50m / min; interval four is the nth pass, the plate temperature in interval four is 400~420℃, the single-pass reduction rate is 15~20%, and the rolling speed is 20~35m / min; Step S4: The hot-rolled sheet is subjected to solution treatment, quenching and pre-stretching treatment in sequence to obtain W51 state sheet. Step S5: The W51 state plate is subjected to aging treatment to obtain the 7xxx series aluminum alloy plate.

2. The method for preparing 7xxx series aluminum alloy sheet according to claim 1, characterized in that, In step S1 The 7xxx series aluminum alloy ingots comprise Al, Zn, Mg, Cu, and unavoidable impurities. By weight percentage, the sum of Zn, Mg, and Cu is 9-14 wt%, the weight percentage of a single impurity is ≤0.05 wt%, the total weight percentage of the impurities is ≤0.15 wt%, and the balance is Al; and / or, The homogenization heat treatment is performed at a temperature of 465~490℃ for a time of 30~60h.

3. The method for preparing 7xxx series aluminum alloy plates according to claim 2, characterized in that, In step S1 In the 7xxx series aluminum alloy ingots, the weight ratio of Zn to Mg is (3.2~5):1; and / or, In the 7xxx series aluminum alloy ingot, the weight ratio of Cu to Mg is (0.6~1.12):

1.

4. The method for preparing 7xxx series aluminum alloy sheets according to claim 1 or 2, characterized in that, The preheating temperature is 440~460℃, and the time is 60~120min; and / or, The total deformation of the first stage hot rolling and the second stage hot rolling is 75-90%.

5. The method for preparing 7xxx series aluminum alloy sheet according to claim 1 or 2, characterized in that, The hot rolling process includes n passes, where n is an integer and 11 ≤ n ≤ 17.

6. The method for preparing 7xxx series aluminum alloy sheet according to claim 1 or 2, characterized in that, The single-pass reduction rate of the first stage hot rolling is less than the single-pass reduction rate of the second stage hot rolling, with a difference of 6-21%; and / or, The rolling speed of the first stage hot rolling is greater than that of the second stage hot rolling, with a difference of 10~65m / min.

7. The method for preparing 7xxx series aluminum alloy sheets according to claim 1 or 2, characterized in that, In step S4 The solution treatment is performed at a temperature of 465~480℃ for a time of 180~330 min; and / or, The quenching treatment is water quenching at a water temperature of 10~50℃; and / or, The stretching amount of the pre-stretching treatment is 1.5~3%.

8. The method for preparing 7xxx series aluminum alloy sheet according to claim 1 or 2, characterized in that, In step S5, the aging process includes a first aging process and a second aging process performed sequentially; wherein, the temperature of the first aging process is 115~125℃ and the time is 6~12h; the temperature of the second aging process is 150~160℃ and the time is 10~30h.

9. A 7xxx series aluminum alloy sheet, characterized in that, The 7xxx series aluminum alloy sheet is obtained by the preparation method according to any one of claims 1 to 8.

10. The 7xxx series aluminum alloy sheet according to claim 9, characterized in that, The thickness of the 7xxx series aluminum alloy sheet is 40~100mm; and / or, The recrystallization fraction of the 7xxx series aluminum alloy sheet is 1.59~10%.

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