7-series aluminum alloy and preparation method and application thereof

Abstract

The invention provides a 7-series aluminum alloy and a preparation method and application thereof. The preparation method comprises the following steps: preparing raw materials according to the components of the 7-series aluminum alloy; the raw materials are sequentially smelted and cast to obtain an aluminum alloy cast ingot; the aluminum alloy ingot is sequentially subjected to first-stage homogenization treatment at the temperature of 360-420 DEG C and second-stage homogenization treatment at the temperature of 460-480 DEG C, and an aluminum alloy ingot blank is obtained; performing deformation treatment on the aluminum alloy ingot blank to obtain an aluminum processing material; and the aluminum processing material is sequentially subjected to solution treatment and aging treatment, and the 7-series aluminum alloy is obtained. The composition content of the aluminum alloy is adjusted to reduce generation of refractory compounds, meanwhile, dispersed Mn-containing phase particles are formed through specific homogenization treatment, and the microstructure of the material is further improved through solid solution and aging treatment, so that the high strength is kept, and meanwhile, the mechanical property of the material is improved. The stress corrosion sensitivity is greatly reduced; the exfoliation corrosion resistance is improved; and the hydrogen embrittlement corrosion behavior is improved.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, and more specifically, to a 7-series aluminum alloy, its preparation method, and its application. Background Technology

[0002] 7-series aluminum alloys are widely used in aerospace, shipbuilding, and weaponry due to their high specific strength, good formability, and excellent fatigue and fracture toughness. Corrosion has been a major problem throughout the development and application of ultra-high-strength 7-series aluminum alloys. Developing new aluminum alloy products with high strength and high corrosion resistance has become a major challenge in aluminum alloy applications. The mechanism of stress corrosion cracking in 7-series high-strength aluminum alloys is very complex, influenced by many factors, and a unified theory has not yet been established. Anodic dissolution and hydrogen embrittlement are two widely accepted mechanisms, and various mechanistic models have been derived around these two mainstream mechanisms, including preferred anodic phase dissolution, slip dissolution, film rupture mechanisms, hydrogen pressure theory, weak bond theory, and Mg-H complex theory.

[0003] In recent years, with the emergence of advanced characterization techniques, stress corrosion research has progressed from macroscopic and microscopic to nanoscale and atomic scales, leading to a clearer understanding of the microscopic mechanisms of stress corrosion in 7-series aluminum alloys. The segregation of hydrogen and magnesium at grain boundaries significantly reduces the grain boundary binding energy, promoting grain boundary embrittlement and the formation of corrosion cracks. Furthermore, the absence of precipitation zones at grain boundaries can act as hydrogen diffusion channels, accelerating hydrogen migration and accumulation at grain boundaries, forming hydrogen embrittlement sources with the Mg-H segregation regions, resulting in localized stress concentration and microcrack initiation, ultimately leading to hydrogen-induced corrosion cracking. Anodic dissolution is a widely accepted stress corrosion mechanism, especially since pitting pits induced by the micro-potential difference between the second phases (MgZn2, AlFeSi, etc.) and the matrix are often the origin points for stress corrosion crack initiation. To suppress anodic dissolution and hydrogen embrittlement in aluminum alloys, the key lies in inhibiting the electrochemical corrosion process of microgalvanic cells, eliminating the electrochemical driving force for crack initiation and propagation, and reducing hydrogen supply sources. This is one of the core design concepts for developing corrosion-resistant aluminum alloys.

[0004] Currently, there are relevant patent reports on the development of high-strength and corrosion-resistant aluminum alloys. For example, patent CN116694968B discloses a 7-series high-strength and corrosion-resistant aluminum alloy and its preparation method. The aluminum alloy composition by weight percentage is Zn 6.1~6.4%, Mg 1.5~1.7%, Cu 0.25~0.35%, Fe≤0.15%, Si≤0.04%, Ti 0.03~0.08%, other impurities ≤0.15%, and the balance being Al. This patent mainly uses ultrasonic treatment of the melt to break up grains, increase the number of nuclei, refine the grains, and improve the overall performance of the alloy. However, the alloy has high requirements for casting equipment, which is not conducive to the widespread application of the alloy. Patent CN116284904B discloses a high-strength, high-toughness, corrosion-resistant, and weldable 7000 series aluminum alloy and its preparation method. The alloy composition by weight percentage is Mg 3.0%, Zn 5.0%, Cu 0.20%, Er 0.25%, Y 0.20%, Sn 0.20%, Zr 0.20%, with the balance being Al. This patent improves the alloy's corrosion resistance by adding trace elements such as Er, Y, and Sn to form dispersed double-layer core-shell nanoparticles and by controlling the Zn and Mg content to precipitate the T phase. However, the addition of expensive Sc, Er, and Y elements to the alloy is not conducive to low-cost manufacturing of the aluminum alloy.

[0005] In summary, to develop 7xxx series aluminum alloys that combine high strength and high corrosion resistance, the following technical challenges must be overcome: First, balancing alloy composition: Fine-tuning the alloy composition must meet high strength requirements while avoiding the formation of harmful phases and reducing the possibility of electrochemical corrosion. Second, controlling microstructure: Effectively controlling the microstructure through heat treatment and other means to avoid phenomena such as grain boundary embrittlement and hydrogen embrittlement is key to improving the corrosion resistance of aluminum alloys. Third, reducing costs: Using conventional elements rather than rare and expensive elements, and finding economical and efficient ways to improve the corrosion resistance of aluminum alloys, is of great significance for industrial applications.

[0006] Therefore, how to provide a low-cost and high-efficiency preparation method for 7-series aluminum alloys, and obtain 7-series aluminum alloys that can take into account both high mechanical properties and high corrosion resistance, so as to meet the needs of modern industry for high-performance aluminum alloys, is one of the important technical problems that need to be solved in this field. Summary of the Invention

[0007] The main objective of this invention is to provide a 7-series aluminum alloy, its preparation method, and its application, in order to solve the problem that existing technologies cannot prepare 7-series aluminum alloys that combine high mechanical properties and high corrosion resistance at low cost and high efficiency.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a 7-series aluminum alloy, comprising: step S1, preparing raw materials according to the composition of a 7-series aluminum alloy; the composition of the 7-series aluminum alloy, by weight percentage, includes 7.1%~8.1% Zn, 1.8%~2.6% Mg, 1.6%~2.3% Cu, 0.2%~1.0% Mn, 0.03%~0.6% Fe, 0.01%~0.30% Si, with the balance being Al and unavoidable impurities; the raw materials are sequentially smelted and cast to obtain an aluminum alloy ingot; step S2, the aluminum alloy ingot is sequentially subjected to a first-stage homogenization treatment at a temperature of 360℃~420℃ and a second-stage homogenization treatment at a temperature of 460℃~480℃ to obtain an aluminum alloy billet; step S3, the aluminum alloy billet is subjected to a deformation treatment to obtain an aluminum processed material; step S4, the aluminum processed material is sequentially subjected to a solution treatment and an aging treatment to obtain a 7-series aluminum alloy.

[0009] Further, by weight percentage, the composition of the 7-series aluminum alloy includes 7.2%~8.0% Zn, 1.9%~2.5% Mg, 1.7%~2.2% Cu, 0.25%~0.9% Mn, 0.05%~0.25% Fe, and 0.02%~0.25% Si, with the balance being Al and unavoidable impurities; preferably, by weight percentage, the composition of the 7-series aluminum alloy includes 7.3%~7.8% Zn, 2.0% Mg, 1.7%~2.2% Cu, 0.25%~0.9% Mn, 0.05%~0.25% Fe, and 0.02%~0.25% Si, with the balance being Al and unavoidable impurities; The composition of the 7-series aluminum alloy is 2.4% Mg, 1.8% 2.1% Cu, 0.3% 0.8% Mn, 0.06% 0.20% Fe, and 0.04% 0.21% Si, with the balance being Al and unavoidable impurities. More preferably, the composition of the 7-series aluminum alloy also includes 0% 0.25% Ti, 0% 0.25% Cr, and 0% 0.25% Zr by weight, and the percentages of Ti, Cr, and Zr are not all 0 at the same time.

[0010] Furthermore, in 7-series aluminum alloys, by weight percentage, when Fe≤0.15%, 0.3%≤Mn≤0.5%; when 0.15%<Fe≤0.25%, 0.5%<Mn≤0.8%.

[0011] Furthermore, in step S2, the heat preservation temperature for the first homogenization treatment is 370℃~410℃, and the heat preservation time is 6h~12h; the heat preservation temperature for the second homogenization treatment is 465℃~475℃, and the heat preservation time is 36h~60h.

[0012] Furthermore, prior to the deformation treatment, step S3 also includes heat preservation treatment of the aluminum alloy ingot; the heat preservation treatment is carried out at 410℃~450℃ and the heat preservation treatment time is ≥4h; and / or, the forming treatment is selected from one or more of rolling treatment, forging treatment and extrusion treatment.

[0013] Further, in step S4, the heat treatment temperature is 470℃~485℃ and the heat treatment time is 2h~4h; and / or, the heat treatment temperature is 100℃~185℃ and the heat treatment time is 6h~120h, and the aging treatment is at least a two-stage aging treatment.

[0014] Furthermore, the aging treatment includes, in sequence: a first-stage aging treatment with a holding temperature of 100℃~110℃ and a holding time of 6h~12h; a second-stage aging treatment with a holding temperature of 175℃~185℃ and a holding time of 8h~12h; or, the aging treatment includes, in sequence: a first-stage aging treatment with a holding temperature of 110℃~125℃ and a holding time of 12h~48h; a second-stage aging treatment with a holding temperature of 175℃~185℃ and a holding time of 30min~60min; and a third-stage aging treatment with a holding temperature of 110℃~125℃ and a holding time of 12h~48h.

[0015] A second aspect of the present invention provides a 7-series aluminum alloy, which is prepared by the above-described method for preparing 7-series aluminum alloys.

[0016] Furthermore, the tensile strength of 7-series aluminum alloys is 620 MPa to 680 MPa; and / or, the yield strength of 7-series aluminum alloys is 580 MPa to 620 MPa; and / or, the elongation of 7-series aluminum alloys is 8% to 12%; and / or, the exfoliation corrosion resistance of 7-series aluminum alloys is ≥ EA grade; and / or, the stress corrosion susceptibility factor I of 7-series aluminum alloys is... SSRT The value was 0.001~0.04; and / or, under a stress condition of 354±0.5MPa, a C-ring stress corrosion test was conducted on 7-series aluminum alloys for 30±0.5 days, and no cracking was observed in the 7-series aluminum alloys.

[0017] The third aspect of the present invention provides an application of the above-mentioned 7-series aluminum alloy as an alloy material in the fields of aerospace, transportation, marine vessels and high-end industries.

[0018] By applying the technical solution of this invention, the composition of aluminum alloy is adjusted to reduce the formation of refractory compounds. At the same time, a specific homogenization treatment is used to form dispersed Mn-containing phase particles. Furthermore, the microstructure of the material is improved through solid solution and aging treatment. This achieves the goal of significantly improving the corrosion resistance and mechanical properties of 7-series aluminum alloys. Thus, while maintaining high strength, the technical effects of significantly reducing stress corrosion sensitivity, improving resistance to exfoliation corrosion, and improving hydrogen embrittlement corrosion behavior are achieved. Attached Figure Description

[0019] 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:

[0020] Figure 1 The scanning electron microscope (SEM) characterization results of the 7-series aluminum alloy sheet obtained in Example 1 of this invention;

[0021] Figure 2 The results of energy scattering spectroscopy (EDS) characterization of coarse refractory compounds in the aluminum matrix of the 7-series aluminum alloy sheet obtained in Example 1 of this invention;

[0022] Figure 3 The electron backscatter diffraction (EBSD) characterization results of the grain structure of the 7-series aluminum alloy sheet obtained in Example 2 of this invention;

[0023] Figure 4 The transmission electron microscope (TEM) characterization results of the 7-series aluminum alloy sheet obtained in Example 3 of the present invention;

[0024] Figure 5 The above are the SEM characterization results of the 7-series aluminum alloy sheet obtained in Comparative Example 1 of this invention.

[0025] Figure 6 The above are the EDS characterization results of coarse refractory compounds in the aluminum matrix of the 7-series aluminum alloy sheet obtained in Comparative Example 1 of this invention. Detailed Implementation

[0026] 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 embodiments.

[0027] As described in the background section, there is a problem in the existing technology that it is impossible to prepare 7-series aluminum alloys that combine high mechanical properties and high corrosion resistance at low cost and high efficiency. To address the aforementioned technical problems, the first aspect of this invention provides a method for preparing 7-series aluminum alloys, comprising: step S1, preparing raw materials according to the composition of 7-series aluminum alloys; by weight percentage, the composition of the 7-series aluminum alloy includes 7.1%~8.1% Zn, 1.8%~2.6% Mg, 1.6%~2.3% Cu, 0.2%~1.0% Mn, 0.03%~0.6% Fe, 0.01%~0.30% Si, with the balance being Al and unavoidable impurities; the raw materials are sequentially smelted and cast to obtain an aluminum alloy ingot; step S2, the aluminum alloy ingot is sequentially subjected to a first-stage homogenization treatment at a temperature of 360℃~420℃ and a second-stage homogenization treatment at a temperature of 460℃~480℃ to obtain an aluminum alloy billet; step S3, the aluminum alloy billet is subjected to deformation treatment to obtain an aluminum processed material; step S4, the aluminum processed material is sequentially subjected to solution treatment and aging treatment to obtain a 7-series aluminum alloy.

[0028] This invention, based on a precise combination of specific chemical composition formulations and heat treatment processes, achieves a comprehensive and synergistic improvement in the corrosion resistance and mechanical properties of 7-series aluminum alloys. Specifically:

[0029] Firstly, regarding the control of the elemental composition: by setting the Zn content between 7.1% and 8.1%, the Mg content between 1.8% and 2.6%, and the Cu content between 1.6% and 2.3%, this invention effectively balances the strength and corrosion resistance of the alloy. Zn and Mg are the main elements forming the η phase (MgZn2), which is the primary source of strength in 7-series aluminum alloys. Cu helps promote η phase precipitation, increasing alloy strength, and improves corrosion resistance by reducing the potential difference between the precipitated phase and the aluminum matrix. The proportional relationship between elements is crucial to alloy performance; excessively high or low content can lead to performance degradation. For example, too much Zn increases the brittleness of the material, while insufficient Mg makes it difficult to form enough η phase for strengthening. The Mn content of 0.2% to 1.0% aims to improve the corrosion behavior of the alloy by controlling the phase types of refractory compounds and forming dispersed Mn phase particles. In the 7-series aluminum alloy provided by this invention, Mn interacts with Fe, reducing the harmful effects of Fe, forming more stable compounds, and reducing the possibility of electrochemical corrosion. Meanwhile, the dispersed Mn phase particles can adsorb hydrogen atoms in the alloy, reducing hydrogen segregation at grain boundaries and lowering the risk of hydrogen embrittlement cracking.

[0030] Secondly, regarding the preparation process: In the preparation method provided by this invention, a two-stage homogenization treatment is incorporated. The first-stage homogenization treatment is carried out at 360℃~420℃, and the second-stage treatment is carried out at 460℃~480℃. This treatment helps to eliminate component segregation in the alloy, promotes uniform element distribution, and forms a more stable microstructure. Through high-temperature and long-term holding, the refractory phase (or insoluble phase) in the alloy can be fully dissolved, reducing stress concentration points. Furthermore, after the aluminum processed material is obtained through deformation treatment, a solution treatment is performed to facilitate rapid cooling to room temperature under conditions where the alloying elements are fully dissolved, thus preserving the supersaturated state of solute atoms in the matrix. The subsequent aging treatment is carried out at a lower temperature to allow the supersaturated solute atoms to precipitate and form strengthening phases, such as η and T phases. By controlling the temperature and time of the solution and aging treatments, the type, size, and distribution of the precipitated phases can be controlled, thereby optimizing the alloy properties.

[0031] Finally, regarding the reaction mechanism in the preparation process provided by this invention: First, the interaction between Mn and Fe: Mn and Fe form more stable compounds, such as Al6(Fe,Mn), etc. The electrochemical corrosion potential of these compounds is closer to that of the matrix, thereby reducing the micro-cell effect in the alloy and lowering the risk of stress corrosion cracking (SCC). Second, the formation and distribution of Mn phase particles: During the two-stage homogenization process, the formation and distribution of Mn phase particles can effectively suppress the recrystallization process, reduce the generation of recrystallization grain boundaries, and reduce the number of corrosion channels. On the other hand, it captures hydrogen atoms in the alloy aggregate, reducing the possibility of hydrogen atoms segregating towards grain boundaries and lowering the risk of hydrogen embrittlement. Third, solid solution and precipitation strengthening: After solid solution treatment, supersaturated solute atoms (such as Zn, Mg, Cu) in the alloy precipitate during the aging process to form strengthening phases, such as η phase and T phase. The formation of these phases not only improves the strength of the alloy but also improves its corrosion resistance, especially reducing the susceptibility to SCC.

[0032] In summary, the above-mentioned method for preparing 7-series aluminum alloys provided by this invention achieves the goal of significantly improving corrosion resistance while maintaining the high strength of 7-series aluminum alloys by precisely controlling the alloy composition, including the content of Zn, Mg, Cu, Mn and Fe and Si impurity elements, combined with specific heat treatment processes such as two-stage homogenization, solution treatment and aging treatment.

[0033] It should be noted that the composition of the 7-series aluminum alloys provided by this invention does not include rare earth elements. Generally speaking, the addition of rare earth elements can refine the grain size and reduce the degree of recrystallization. However, in the alloy formulation provided by this invention, rare earth elements may form refractory composite phases with elements such as Cu and Fe, which may become stress concentration points and thus affect the corrosion resistance and crack propagation resistance of the resulting 7-series aluminum alloys.

[0034] Further, by weight percentage, the composition of the 7-series aluminum alloy includes 7.2%~8.0% Zn, 1.9%~2.5% Mg, 1.7%~2.2% Cu, 0.25%~0.9% Mn, 0.05%~0.25% Fe, and 0.02%~0.25% Si, with the balance being Al and unavoidable impurities; preferably, by weight percentage, the composition of the 7-series aluminum alloy includes 7.3%~7.8% Zn, 2.0%~2.4% Mg, 1.8%~2.1% Cu, 0.3%~0.8% Mn, 0.06%~0.20% Fe, and 0.04%~0.21% Si, with the balance being Al and unavoidable impurities. In the aforementioned progressively optimized alloy formulations, by narrowing the content range of the main strengthening elements, the formation of the η and T phases can be controlled more precisely, and the performance fluctuations caused by excess or deficiency of elements can be reduced more effectively. In particular, the progressive optimization of the Mn content range can further enhance the control of the types of refractory compounds and the trapping of hydrogen atoms, reducing the risk of electrochemical corrosion and hydrogen embrittlement. Stricter control of Fe and Si impurities can further reduce the formation of the Fe phase and other harmful phases, more effectively reducing the micro-cell effect in the resulting 7-series aluminum alloys, and ultimately achieving a more significant balance between mechanical properties and corrosion resistance.

[0035] To further optimize the microstructure and form a dispersed strengthening phase, the preferred composition of the 7-series aluminum alloy, by weight percentage, includes 0-0.25% Ti (more preferably 0.05%-0.25% by weight), 0-0.25% Cr (more preferably 0.05%-0.25% by weight), and 0-0.25% Zr, wherein the percentages of Ti, Cr, and Zr are not simultaneously 0. In particular, Zr can form a stable Al3Zr phase with Al at a specific addition amount (0.05%-0.20%), thus acting as a nucleating agent during the preparation process, further refining the grains, reducing recrystallization, and ultimately significantly optimizing the strength and corrosion resistance of the resulting 7-series aluminum alloy.

[0036] In 7-series aluminum alloys, by weight percentage, it is preferred that when Fe ≤ 0.15%, Mn ≤ 0.5%; and when 0.15% < Fe ≤ 0.25%, it is preferred that Mn ≤ 0.8%. This preferred combination of Mn and Fe percentages can more effectively promote the formation of a relatively stable composite phase (such as Al6(Fe,Mn) phase) between Fe and Mn, thereby significantly reducing active sites that act as corrosion sources. Furthermore, it is further preferred that the weight percentage ratio of Fe to Mn in the 7-series aluminum alloy be 1:(3~5). This preferred scheme means that the present invention establishes a clear content relationship between Fe and Mn, and adaptively adjusts the Mn content based on the Fe content, thereby more precisely controlling the micro-cell effect between refractory compounds and the aluminum matrix in the alloy, reducing the probability of SCC (sulfur-induced corrosion cracking), and also helping to suppress hydrogen embrittlement, ultimately better synergistically improving the mechanical properties and corrosion resistance of the resulting 7-series aluminum alloy.

[0037] To achieve a more uniform distribution of elements, more effectively reduce harmful phases at grain boundaries, and further optimize the microstructure to provide a more uniform matrix for subsequent processing, step S2 is further optimized as follows: the holding temperature for the first-stage homogenization treatment is 370℃~410℃, and the holding time is 6h~12h; the holding temperature for the second-stage homogenization treatment is 465℃~475℃, and the holding time is 36h~60h. In the above-mentioned preferred two-stage homogenization process, considering the dispersion precipitation and dissolution temperature of coarse phases in the alloy, the first-stage homogenization treatment is preferably held at a temperature range of 370℃~410℃ for 6~12 hours, thereby forming a uniformly distributed fine dispersed phase. The subsequent second-stage homogenization treatment at 465℃~475℃ for 36~60 hours can effectively eliminate the compositional segregation and large-size compounds (such as MgZn2 and Al2Mg3Zn3) formed by alloying elements during solidification, thereby more effectively reducing stress concentration points and improving the plasticity, corrosion resistance and processing performance of the resulting 7-series alloys.

[0038] Before the deformation process, step S3 also includes heat preservation treatment of the aluminum alloy billet; the heat preservation treatment is carried out at 410℃~450℃ and the heat preservation time is ≥4h. In practical applications, the deformation treatment can be selected from one or more of rolling, forging and extrusion, and the resulting aluminum processed material can be sheet, forging or extrusion.

[0039] Further, in step S4, the preferred holding temperature for the solution treatment is 470℃~485℃ (more preferably 472℃~482℃), and the holding time is 2h~4h, so as to further promote the complete dissolution of solute elements (such as Zn, Mg, Cu), forming a more stable supersaturated solid solution, and preparing better conditions for subsequent aging treatment. Ultimately, a more uniform strengthening phase is formed in the aluminum matrix, further synergistically optimizing its mechanical properties and corrosion resistance. For the aging treatment, the preferred holding temperature is 100℃~185℃, and the holding time is 6h~120h, and the aging treatment is at least a two-stage aging treatment. Through two-stage or multi-stage aging treatment, the type, size, and distribution of precipitated phases can be more precisely controlled, reducing the coarse precipitate phenomenon that may be caused by single aging, thereby significantly reducing the brittleness and corrosion cracking of the obtained 7-series aluminum alloy.

[0040] To obtain more corrosion-resistant 7-series aluminum alloys, in several typical embodiments, the aging treatment includes, sequentially: a first-stage aging treatment at a holding temperature of 100℃~110℃ and a holding time of 6h~12h; and a second-stage aging treatment at a holding temperature of 175℃~185℃ and a holding time of 8h~12h. In other typical embodiments, the aging treatment includes, sequentially: a first-stage aging treatment at a holding temperature of 110℃~125℃ and a holding time of 12h~48h; a second-stage aging treatment at a holding temperature of 175℃~185℃ and a holding time of 30min~60min; and a third-stage aging treatment at a holding temperature of 110℃~125℃ and a holding time of 12h~48h.

[0041] A second aspect of this invention provides a 7-series aluminum alloy prepared by the aforementioned method. By precisely controlling the alloy composition and combining optimized homogenization, solution treatment, and aging processes, the 7-series aluminum alloy obtained by this invention achieves a good balance between high strength and high corrosion resistance. It should be noted that due to the complex structural changes and crystal formation during the preparation process, as well as the special characteristics of alloy materials and limitations of existing testing and characterization methods, a comprehensive quantitative characterization of the complex microstructure and metallographic features of the aforementioned 7-series aluminum alloy is difficult. However, performance test results have already shown that the aforementioned 7-series aluminum alloy obtained by this invention can better balance high mechanical properties and superior corrosion resistance.

[0042] In several preferred embodiments, the tensile strength of the 7-series aluminum alloy is 620 MPa to 680 MPa; and / or, the yield strength of the 7-series aluminum alloy is 580 MPa to 620 MPa; and / or, the elongation of the 7-series aluminum alloy is 8% to 12%; and / or, the exfoliation corrosion resistance of the 7-series aluminum alloy is ≥ EA level; and / or, the stress corrosion susceptibility factor of the 7-series aluminum alloy is I. SSRTThe tensile strength is 0.001~0.04; and / or, under a stress condition of 354±0.5MPa, a C-ring stress corrosion test was conducted on the 7-series aluminum alloy for 30±0.5 days, and no cracking was observed in the 7-series aluminum alloy. That is to say, the 7-series aluminum alloy prepared by the method provided by this invention not only possesses superior tensile strength, yield strength, and elongation, but also exhibits superior corrosion resistance in various environments.

[0043] A third aspect of this invention provides an application of the aforementioned 7-series aluminum alloys as alloy materials in the aerospace, transportation, marine vessel, and high-end industrial fields. Through the above-described preparation method and optimized composition design, the 7-series aluminum alloy materials prepared by this invention exhibit excellent corrosion resistance and good machinability while maintaining high strength. These performance characteristics make them an ideal choice for fields with extremely demanding requirements for alloy materials.

[0044] 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.

[0045] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0046] Example 1

[0047] A method for preparing 7-series aluminum alloys:

[0048] (1) Smelt and prepare 7-series aluminum alloys with the following composition: 7.5% Zn, 2.2% Mg, 2.0% Cu, 0.5% Mn, 0.1% Zr, 0.12% Fe, 0.10% Si, with the balance being Al and unavoidable impurities (the content and relationship of the above components are as shown in Table 1). Aluminum alloy ingots are obtained by smelting, degassing, removing inclusions, and semi-continuous casting of the raw materials of aluminum alloy materials.

[0049] (2) The obtained aluminum alloy ingot was kept at 400℃ for 8 hours for the first homogenization treatment, and then kept at 475℃ for 48 hours for the second homogenization treatment.

[0050] (3) After homogenization treatment, the aluminum alloy ingot is kept at 420℃ for 4 hours and then hot rolled to obtain aluminum alloy sheet.

[0051] (4) The obtained aluminum alloy sheet was kept at 473℃ for 3 hours for solution quenching treatment; the solution-quenched aluminum alloy sheet was subjected to three-stage aging treatment. The first stage aging treatment temperature was 120℃ and the holding time was 24 hours, the second stage aging treatment temperature was 180℃ and the holding time was 40 minutes, and the third stage aging treatment temperature was 120℃ and the holding time was 24 hours, thereby obtaining an ultra-high strength corrosion-resistant 7-series aluminum alloy sheet.

[0052] The SEM characterization results of the obtained 7-series aluminum alloy sheets are shown in the figure. Figure 1 In the figure, the gray areas represent the aluminum matrix, while the white highlighted areas represent coarse, refractory compounds within the aluminum matrix. These coarse, refractory compounds were characterized by EDS, and the results are shown below. Figure 2 .

[0053] Example 2

[0054] A method for preparing 7-series aluminum alloys:

[0055] (1) A 7-series aluminum alloy with the following composition was prepared by smelting: 7.3% Zn, 2.0% Mg, 1.8% Cu, 0.3% Mn, 0.13% Zr, 0.06% Fe, 0.04% Si, with the balance being Al and unavoidable impurities (the content and relationship of the above components are shown in Table 1). The raw materials of the aluminum alloy were processed by smelting, degassing, removing inclusions and semi-continuous casting to obtain aluminum alloy ingots.

[0056] (2) The obtained aluminum alloy ingot was kept at 370℃ for 12h for the first homogenization treatment, and then kept at 465℃ for 36h for the second homogenization treatment.

[0057] (3) After homogenization treatment, the aluminum alloy ingot is kept at 410℃ for 5 hours and then hot rolled to obtain aluminum alloy sheet.

[0058] (4) The obtained aluminum alloy sheet was kept at 472℃ for 4 hours for solution quenching treatment; the solution quenched aluminum alloy sheet was subjected to three-stage aging treatment. The first stage aging treatment temperature was 110℃ and the holding time was 48 hours, the second stage aging treatment temperature was 175℃ and the holding time was 60 minutes, and the third stage aging treatment temperature was 110℃ and the holding time was 48 hours, thereby obtaining an ultra-high strength corrosion resistant 7-series aluminum alloy sheet.

[0059] The EBSD analysis diagram of the grain structure of the obtained 7-series aluminum alloy sheet is shown below. Figure 3 .

[0060] Example 3

[0061] A method for preparing 7-series aluminum alloys:

[0062] (1) A 7-series aluminum alloy with the following composition was prepared by smelting: 8.1% Zn, 2.4% Mg, 2.2% Cu, 0.5% Mn, 0.11% Zr, 0.10% Fe, 0.11% Si, with the balance being Al and unavoidable impurities (the content and relationship of the above components are as shown in Table 1). The raw materials of the aluminum alloy were processed by smelting, degassing, removing inclusions and semi-continuous casting to obtain aluminum alloy ingots.

[0063] (2) The obtained aluminum alloy ingot was kept at 410℃ for 6 hours for the first homogenization treatment, and then kept at 465℃ for 60 hours for the second homogenization treatment.

[0064] (3) After homogenization treatment, the aluminum alloy ingot is kept at 450℃ for 4 hours and then hot rolled to obtain aluminum alloy sheet.

[0065] (4) The obtained aluminum alloy sheet was kept at 482℃ for 2 hours for solution quenching treatment; the solution-quenched aluminum alloy sheet was subjected to three-stage aging treatment. The first stage aging treatment temperature was 125℃ and the holding time was 24 hours, the second stage aging treatment temperature was 185℃ and the holding time was 30 minutes, and the third stage aging treatment temperature was 125℃ and the holding time was 24 hours, thereby obtaining an ultra-high strength corrosion-resistant 7-series aluminum alloy sheet.

[0066] The TEM characterization results of the obtained 7-series aluminum alloy plates are shown in the figure. Figure 4 The gray-white areas in the image represent the aluminum matrix, while the black areas represent the intracrystalline dispersed phase. Compare this image with... Figure 2 Analysis shows that, by controlling the two-stage homogenization temperature and holding time, the embodiments of the present invention obtain dispersed Mn-containing dispersed phase particles, which not only inhibit recrystallization and regulate the microstructure, reducing the number of corrosion channels, but also inhibit the segregation of hydrogen atoms at the grain boundaries, thus reducing the occurrence of hydrogen embrittlement cracking.

[0067] Example 4

[0068] A method for preparing 7-series aluminum alloys:

[0069] (1) A 7-series aluminum alloy with the following composition was prepared by smelting: 7.4% Zn, 2.2% Mg, 2.1% Cu, 0.8% Mn, 0.08% Zr, 0.20% Fe, 0.21% Si, with the balance being Al and unavoidable impurities (the content and relationship of the above components are as shown in Table 1). The raw materials of the aluminum alloy were processed by smelting, degassing, removing inclusions and semi-continuous casting to obtain aluminum alloy ingots.

[0070] (2) The obtained aluminum alloy ingot was kept at 360℃ for 12h for the first homogenization treatment, and then kept at 468℃ for 60h for the second homogenization treatment.

[0071] (3) After homogenization treatment, the aluminum alloy ingot is kept at 430℃ for 6 hours and then hot rolled to obtain aluminum alloy sheet.

[0072] (4) The obtained aluminum alloy sheet was kept at 472℃ for 2 hours for solution quenching treatment; the aluminum alloy sheet after solution quenching treatment was subjected to two-stage aging treatment. The first stage aging treatment temperature was 107℃ and the holding time was 8 hours, and the second stage aging treatment temperature was 177℃ and the holding time was 10 hours, thereby obtaining ultra-high strength corrosion resistant 7-series aluminum alloy sheet.

[0073] Example 5

[0074] A method for preparing 7-series aluminum alloys:

[0075] (1) Smelt and prepare 7-series aluminum alloys with the following composition: 8.1% Zn, 2.1% Mg, 1.9% Cu, 0.6% Mn, 0.12% Zr, 0.17% Fe, 0.2% Si, with the balance being Al and unavoidable impurities (the content and relationship of the above components are as shown in Table 1). Aluminum alloy ingots are obtained by smelting, degassing, removing inclusions, and semi-continuous casting of the raw materials of aluminum alloy materials.

[0076] (2) The obtained aluminum alloy ingot was kept at 420℃ for 6 hours for the first homogenization treatment, and then kept at 480℃ for 36 hours for the second homogenization treatment.

[0077] (3) After homogenization treatment, the aluminum alloy ingot is kept at 430℃ for 4 hours and then hot rolled to obtain aluminum alloy sheet.

[0078] (4) The obtained aluminum alloy sheet was kept at 482℃ for 4 hours for solution quenching treatment; the aluminum alloy sheet after solution quenching treatment was subjected to two-stage aging treatment. The first stage aging treatment temperature was 110℃ and the holding time was 6 hours, and the second stage aging treatment temperature was 175℃ and the holding time was 12 hours, thereby obtaining ultra-high strength corrosion resistant 7-series aluminum alloy sheet.

[0079] Example 6

[0080] A method for preparing 7-series aluminum alloys:

[0081] (1) Smelt and prepare 7-series aluminum alloys with the following composition: 7.8% Zn, 2.3% Mg, 2.0% Cu, 0.4% Mn, 0.11% Zr, 0.08% Fe, 0.06% Si, with the balance being Al and unavoidable impurities (the content and relationship of the above components are shown in Table 1). Aluminum alloy ingots are obtained by smelting, degassing, removing inclusions, and semi-continuous casting of the raw materials of aluminum alloy materials.

[0082] (2) The obtained aluminum alloy ingot was kept at 400℃ for 8 hours for the first homogenization treatment, and then kept at 477℃ for 48 hours for the second homogenization treatment.

[0083] (3) After homogenization treatment, the aluminum alloy ingot is kept at 420℃ for 6 hours and then hot rolled to obtain aluminum alloy sheet.

[0084] (4) The obtained aluminum alloy sheet was kept at 475℃ for 3 hours for solution quenching treatment; the aluminum alloy sheet after solution quenching treatment was subjected to two-stage aging treatment. The first stage aging treatment temperature was 100℃ and the holding time was 12 hours, and the second stage aging treatment temperature was 185℃ and the holding time was 8 hours, thereby obtaining ultra-high strength corrosion resistant 7-series aluminum alloy sheet.

[0085] Example 7

[0086] A method for preparing 7-series aluminum alloys:

[0087] The only difference between this embodiment and Embodiment 1 is the composition of the 7-series aluminum alloy, as detailed in Table 1.

[0088] Example 8

[0089] A method for preparing 7-series aluminum alloys:

[0090] The only difference between this embodiment and Embodiment 1 is the composition of the 7-series aluminum alloy, as detailed in Table 1.

[0091] Example 9

[0092] A method for preparing 7-series aluminum alloys:

[0093] The only difference between this embodiment and embodiment 1 is that in step (2), the heat preservation temperature of the first homogenization treatment is changed to 360°C, and the heat preservation temperature of the second homogenization treatment is changed to 460°C.

[0094] Example 10

[0095] A method for preparing 7-series aluminum alloys:

[0096] The only difference between this embodiment and embodiment 1 is that in step (2), the heat preservation temperature of the first homogenization treatment is changed to 420°C, and the heat preservation temperature of the second homogenization treatment is changed to 480°C.

[0097] Example 11

[0098] A method for preparing 7-series aluminum alloys:

[0099] The only difference between this embodiment and embodiment 1 is that in step (4), the heat preservation temperature of the solution treatment is changed to 470°C.

[0100] Example 12

[0101] A method for preparing 7-series aluminum alloys:

[0102] The only difference between this embodiment and embodiment 1 is that in step (4), the heat preservation temperature of the solution treatment is changed to 485°C.

[0103] Example 13

[0104] A method for preparing 7-series aluminum alloys:

[0105] The only difference between this embodiment and embodiment 1 is that in step (4), the conditions of the three-stage aging treatment are changed to: the first-stage aging treatment temperature is 105℃ and the holding time is 56h, the second-stage aging treatment temperature is 190℃ and the holding time is 20min, and the third-stage aging treatment temperature is 130℃ and the holding time is 10h.

[0106] Example 14

[0107] A method for preparing 7-series aluminum alloys:

[0108] The only difference between this embodiment and embodiment 1 is that in step (4), the conditions for the three-stage aging treatment are changed to: the first-stage aging treatment temperature is 130℃ and the holding time is 10h; the second-stage aging treatment temperature is 170℃ and the holding time is 90min; and the third-stage aging treatment temperature is 105℃ and the holding time is 56h.

[0109] Example 15

[0110] A method for preparing 7-series aluminum alloys:

[0111] The only difference between this embodiment and embodiment 4 is that in step (4), the conditions for the two-stage aging treatment are changed to: the temperature of the first-stage aging treatment is 105℃ and the holding time is 14h, and the temperature of the second-stage aging treatment is 190℃ and the holding time is 6h.

[0112] Example 16

[0113] A method for preparing 7-series aluminum alloys:

[0114] The only difference between this embodiment and embodiment 4 is that in step (4), the conditions for the two-stage aging treatment are changed to: the temperature of the first-stage aging treatment is 115°C and the holding time is 5h, and the temperature of the second-stage aging treatment is 170°C and the holding time is 14h.

[0115] Comparative Example 1

[0116] A method for preparing 7-series aluminum alloys:

[0117] The only difference between this comparative example and Example 1 is the composition of the 7-series aluminum alloy, as detailed in Table 1.

[0118] The SEM characterization results of the obtained 7-series aluminum alloy sheets are shown in the figure. Figure 5 In the figure, the gray areas represent the aluminum matrix, while the white highlighted areas represent coarse, refractory compounds within the aluminum matrix. These coarse, refractory compounds were characterized by EDS, and the results are shown below. Figure 6 .

[0119] Will Figure 5 , Figure 6 Compared with the sample obtained in Example 1 Figure 1 , Figure 2 In comparison, the embodiments of the present invention optimize the chemical composition of refractory compounds by reasonably controlling the content of the microalloying element Mn, thereby reducing the potential difference between the refractory compounds and the matrix and reducing corrosion cracking caused by refractory compounds.

[0120] Comparative Example 2

[0121] A method for preparing 7-series aluminum alloys:

[0122] The only difference between this comparative example and Example 1 is the composition of the 7-series aluminum alloy, as detailed in Table 1.

[0123] Comparative Example 3

[0124] A method for preparing 7-series aluminum alloys:

[0125] The only difference between this comparative example and Example 4 is the composition of the 7-series aluminum alloy, as detailed in Table 1.

[0126] Comparative Example 4

[0127] A method for preparing 7-series aluminum alloys:

[0128] The only difference between this comparative example and Example 1 is that the first-level homogenization process was not performed in step (2).

[0129] Comparative Example 5

[0130] A method for preparing 7-series aluminum alloys:

[0131] The only difference between this comparative example and Example 1 is that the second-level homogenization process was not performed in step (2).

[0132] Comparative Example 6

[0133] A method for preparing 7-series aluminum alloys:

[0134] The only difference between this comparative example and Example 1 is that in step (2), the heat preservation temperature of the first homogenization treatment is changed to 460°C, and the heat preservation temperature of the second homogenization treatment is changed to 520°C.

[0135] Comparative Example 7

[0136] A method for preparing 7-series aluminum alloys:

[0137] The only difference between this comparative example and Example 1 is that in step (2), the heat preservation temperature of the first homogenization treatment is changed to 280°C, and the heat preservation temperature of the second homogenization treatment is changed to 450°C.

[0138] Table 1

[0139]

[0140] The elemental composition of the examples and comparative examples not shown in the table is consistent with that of Example 1 (or Example 4).

[0141] Test methods

[0142] Tensile strength, yield strength, and elongation: obtained according to GB / T 228.1-2021.

[0143] Exfoliation corrosion: Tested according to GB / T 22639-2022.

[0144] Stress corrosion susceptibility factor I SSRT : Tested according to GB / T 22640-2023.

[0145] Stress corrosion test of C-ring specimens under 354MPa stress conditions: The test results were obtained according to GB / T 22640-2023, and the test duration was 30 days.

[0146] The aluminum alloy samples obtained from each embodiment and comparative example were subjected to the above tests, and the results are shown in Table 2.

[0147] Table 2

[0148]

[0149] As can be seen from the above description, compared with the comparative examples, the embodiments of the present invention, through precise control of alloy composition and combined with optimized homogenization, solution treatment, and aging processes, achieve a good balance between high strength and high corrosion resistance in 7-series aluminum alloys. The resulting 7-series aluminum alloys not only possess superior tensile strength, yield strength, and elongation, but also exhibit exceptionally superior corrosion resistance in various environments.

[0150] Specifically, in each embodiment:

[0151] Comparing Examples 4 to 6, 9 and 10 with Examples 1 to 3, it can be seen that in step S2, by optimizing the temperature and time parameters of the first-stage homogenization treatment and the second-stage homogenization treatment, a more uniform distribution of each element can be achieved, while more effectively reducing the harmful phases at the grain boundaries, and promoting further optimization of the microstructure, providing a more uniform matrix for subsequent processing, and ultimately significantly improving the plasticity, corrosion resistance and processing performance of the obtained 7-series alloy.

[0152] Comparing Examples 7 and 8 with Example 1, it can be seen that by optimizing the content of Fe and Mn, the formation of a relatively stable composite phase (such as Al6(Fe,Mn) phase) of Fe and Mn can be promoted more effectively, thereby significantly reducing the active sites that act as corrosion sources. Simultaneously, the micro-cell effect between refractory compounds and the aluminum matrix in the alloy can be more precisely controlled, reducing the probability of SCC (sulfurized cracking) and also helping to suppress hydrogen embrittlement, ultimately resulting in a better synergistic improvement in the mechanical properties and corrosion resistance of the obtained 7-series aluminum alloy.

[0153] Comparing Examples 11 and 12 with Example 1, it can be seen that in step S4, by optimizing the solution treatment temperature, the solute elements (such as Zn, Mg, and Cu) can be further promoted to completely dissolve, forming a more stable supersaturated solid solution, thus preparing better conditions for subsequent aging treatment. Ultimately, a more uniform strengthening phase is formed in the aluminum matrix, further synergistically optimizing its mechanical properties and corrosion resistance.

[0154] Comparing Examples 13 and 14 with Example 1 (or comparing Examples 15 and 16 with Example 4), it can be seen that in step S4, by further optimizing the parameters of the aging treatment, the type, size and distribution of the precipitates can be more precisely controlled, reducing the coarse precipitates that may be caused by single aging, thereby significantly reducing the brittleness and corrosion cracking of the obtained 7-series aluminum alloy.

[0155] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0156] 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 a 7-series aluminum alloy, characterized in that, include: Step S1: Prepare raw materials according to the composition of the 7-series aluminum alloy; The composition of the 7-series aluminum alloy, by weight percentage, includes 7.1%~8.1% Zn, 1.8%~2.6% Mg, 1.6%~2.3% Cu, 0.2%~1.0% Mn, 0.03%~0.6% Fe, and 0.01%~0.30% Si, with the balance being Al and unavoidable impurities; the raw materials are sequentially smelted and cast to obtain aluminum alloy ingots; Step S2: The aluminum alloy ingot is subjected to a first-stage homogenization treatment at a temperature of 360℃~420℃ and a second-stage homogenization treatment at a temperature of 460℃~480℃ to obtain an aluminum alloy ingot billet. Step S3: The aluminum alloy ingot is deformed to obtain aluminum processed material; In step S4, the aluminum processed material is subjected to solution treatment and aging treatment in sequence to obtain the 7-series aluminum alloy.

2. The method for preparing 7-series aluminum alloys according to claim 1, characterized in that, By weight percentage, the composition of the 7-series aluminum alloy includes 7.2% to 8.0% Zn, 1.9% to 2.5% Mg, 1.7% to 2.2% Cu, 0.25% to 0.9% Mn, 0.05% to 0.25% Fe, 0.02% to 0.25% Si, with the balance being Al and unavoidable impurities; Preferably, by weight percentage, the composition of the 7-series aluminum alloy includes 7.3%~7.8% Zn, 2.0%~2.4% Mg, 1.8%~2.1% Cu, 0.3%~0.8% Mn, 0.06%~0.20% Fe, 0.04%~0.21% Si, with the balance being Al and unavoidable impurities; More preferably, the composition of the 7-series aluminum alloy further includes 0-0.25% Ti, 0-0.25% Cr and 0-0.25% Zr by weight percentage, and the percentage content of Ti, Cr and Zr is not simultaneously 0.

3. The method for preparing 7-series aluminum alloys according to claim 1 or 2, characterized in that, In the 7-series aluminum alloys, by weight percentage, when Fe≤0.15%, 0.3%≤Mn≤0.5%; when 0.15%<Fe≤0.25%, 0.5%<Mn≤0.8%.

4. The method for preparing 7-series aluminum alloys according to any one of claims 1 to 3, characterized in that, In step S2 The heat preservation temperature for the first-stage homogenization treatment is 370℃~410℃, and the heat preservation time is 6h~12h; The second-stage homogenization treatment is held at a temperature of 465℃~475℃ for 36h~60h.

5. The method for preparing 7-series aluminum alloys according to any one of claims 1 to 4, characterized in that, Before the deformation process, step S3 further includes heat preservation treatment of the aluminum alloy ingot; The heat preservation treatment is carried out at 410℃~450℃, and the heat preservation treatment time is ≥4h; and / or, The deformation treatment is selected from one or more of rolling, forging, and extrusion.

6. The method for preparing 7-series aluminum alloys according to any one of claims 1 to 5, characterized in that, In step S4 The solution treatment is performed at a temperature of 470℃~485℃ for 2h~4h; and / or, The aging treatment is performed at a temperature of 100℃ to 185℃ for 6 hours to 120 hours, and the aging treatment is at least a two-stage aging treatment.

7. The method for preparing 7-series aluminum alloys according to any one of claims 1 to 6, characterized in that, The aging process includes the following steps performed sequentially: a first-stage aging process with a holding temperature of 100℃~110℃ and a holding time of 6h~12h; and a second-stage aging process with a holding temperature of 175℃~185℃ and a holding time of 8h~12h. or, The aging process includes the following steps performed sequentially: a first-stage aging process with a holding temperature of 110℃~125℃ and a holding time of 12h~48h; and a second-stage aging process with a holding temperature of 175℃~185℃ and a holding time of 30min~60min. And a third-level aging treatment with a heat preservation temperature of 110℃~125℃ and a heat preservation time of 12h~48h.

8. A 7-series aluminum alloy, characterized in that, The 7-series aluminum alloy is prepared by the method for preparing 7-series aluminum alloy according to any one of claims 1 to 7.

9. The 7-series aluminum alloy according to claim 8, characterized in that, The tensile strength of the 7-series aluminum alloy is 620 MPa to 680 MPa; and / or, The yield strength of the 7-series aluminum alloy is 580 MPa to 620 MPa; and / or, The elongation of the 7-series aluminum alloy is 8%~12%; and / or, The exfoliation corrosion resistance of the 7-series aluminum alloys is ≥ EA level; and / or, The stress corrosion susceptibility factor I of the 7-series aluminum alloy SSRT The value is 0.001 to 0.04; and / or, Under a stress condition of 354±0.5MPa, the 7-series aluminum alloy was subjected to a C-ring stress corrosion test for 30±0.5 days, and no cracking was observed in the 7-series aluminum alloy.

10. The application of the 7-series aluminum alloy as described in claim 8 or 9 as an alloy material in the aerospace, transportation, marine vessel, and high-end industrial fields.

Images