Al-mg-zn aluminum alloy sheet material with excellent strength and plasticity and light weight characteristics, preparation method and use

Abstract

This invention discloses an Al-Mg-Zn aluminum alloy sheet with excellent strength, ductility, and lightweight properties, its preparation method, and applications. The alloy composition, by mass percentage, is: Mg 5.0-5.5%, Zn 1.5-2.0%, Mn 0.4-0.5%, Cu 0.1-0.3%, Sc 0.15-0.25%, Zr 0.1-0.15%, Ag 0.05-0.15%, impurities ≤0.1%, balance Al; density ≤2.63 g / cm³, tensile strength ≥470 MPa, elongation ≥23%. The preparation method includes: high-purity raw material smelting and casting → two-stage homogenization → hot rolling → intermediate annealing → cold rolling → solution treatment → single-stage aging; wherein the total reduction during hot rolling is 80-85%, the total reduction during cold rolling is 20-35%, and the single-stage aging is 120-140℃ × 16-24 h. The alloy's microstructure is characterized by: an average size of dispersed Al₃Sc particles ≤100 nm, a deformed grain area fraction ≥70%, an average size of nano-β-Al₃Mg₂ and T-Mg₃₂(Al,Zn)₄₉ composite precipitates ≤20 nm with a number density ≥1×10²³ m⁻³, and a micron-scale second phase area fraction ≤0.5% formed solely by Fe impurities. This invention simplifies the traditional two-stage aging process while still achieving simultaneous improvements in low density, high strength, and high plasticity, making it suitable for large-scale industrial applications.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy profile manufacturing technology, and in particular to an Al-Mg-Zn aluminum alloy sheet with excellent strength and light weight, its preparation method and applications. Background Technology

[0002] As a major source of carbon emissions, the transportation industry faces the challenge of lightweighting as a key pathway to achieving the strategic goals of "carbon peaking and carbon neutrality." Aluminum alloys, due to their high specific strength, low density, corrosion resistance, and recyclability, play a crucial role in transportation lightweighting. 6xxx series Al-Mg-Si alloys have a tensile strength of approximately 413 MPa and an elongation of approximately 15%; 2xxx series Al-Cu alloys can reach a strength of 531 MPa, but their elongation is only about 12%, and they exhibit poor corrosion resistance. While Al-Mg-Zn alloys possess lightweighting potential, current technologies employ two-stage aging, resulting in complex processes, limited strength-ductility matching advantages, and relatively high density. Summary of the Invention

[0003] The purpose of this invention is to provide an Al-Mg-Zn aluminum alloy sheet with excellent strength and light weight, its preparation method and uses, thereby solving the aforementioned problems in the prior art.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] An Al-Mg-Zn aluminum alloy sheet possessing both excellent strength and light weight, wherein the aluminum alloy composition, by mass percentage, comprises:

[0006] Mg: 5.0-5.5%, Zn: 1.5-2.0%, Mn: 0.4-0.5%, Cu: 0.1-0.3%, Sc: 0.15-0.25%, Zr: 0.1-0.15%, Ag: 0.05-0.15%, impurities ≤0.1%, balance Al;

[0007] The density of the aluminum alloy is ≤2.63g / cm³, the tensile strength is ≥470MPa, and the elongation is ≥23%.

[0008] Preferably, the microstructure of the aluminum alloy includes:

[0009] Dispersed submicron-sized Al3Sc particles with an average particle size ≤100nm;

[0010] The area fraction of deformed grains retained after hot rolling-cold rolling is ≥70%;

[0011] Nanoscale β-Al3Mg2 and T-Mg precipitated after single-stage aging 32 (Al,Zn) 49The composite precipitate has an average size ≤20nm and a number density ≥1×10²³m⁻³.

[0012] Preferably, the thickness of the sheet is 1.5-3mm, the total reduction in cold rolling is 20-35%, the total reduction in hot rolling is 80-85%, and the final rolling temperature is ≥300℃.

[0013] In another embodiment, a method for preparing an aluminum alloy sheet includes the following steps in sequence:

[0014] (1) Melting and casting: High-purity Al, Mg, Zn, Ag and intermediate alloys are melted under a protective atmosphere at 750-800℃, and after degassing and slag removal, they are poured into iron molds to obtain ingots;

[0015] (2) Two-stage homogenization: First, heat the furnace at 5-10℃ / min to 400-430℃ and hold for 4-8 hours, then heat it to 450-470℃ and hold for 24-28 hours, and then air cool it after removing it from the furnace.

[0016] (3) Hot rolling: After the homogenized ingot is held at 410-460℃ for 30-60 minutes, it is hot rolled in 10-15 passes with a total reduction of 80-85%. Every 2-3 passes, it is reheated in the furnace for 3-10 minutes. The final rolling temperature is ≥300℃.

[0017] (4) Intermediate annealing: The hot-rolled plate is held at 370-400℃ for 40-80 minutes and then air-cooled;

[0018] (5) Cold rolling: Perform 5-10 cold rolling passes with a total reduction of 20-35% to obtain the required thickness;

[0019] (6) Solution treatment: Hold at 470-490℃ for 40-60 min and then quench in water. The quenching transfer time is ≤2s.

[0020] (7) Single-stage aging: keep warm at 120-140℃ for 16-24 hours and then air cool.

[0021] Preferably, the intermediate alloy in step (1) is Al-50 wt.%Cu, Al-10 wt.%Mn, Al-5 wt.%Zr, Al-2 wt.%Sc and Al-10 wt.%Ti, and all raw materials have a purity ≥99.99%.

[0022] Preferably, in step (3), the single-pass pressing amount of hot rolling is 1-2 mm and the roll speed is 5 r / min; in step (5), the single-pass pressing amount of cold rolling is 0.5-1 mm and the roll speed is 5 r / min.

[0023] Preferably, in the aluminum alloy sheet obtained by the preparation method, the area fraction of the micron-sized second phase is ≤0.5%, and the micron-sized second phase is formed only by impurity Fe, without other micron-sized phases containing Mg, Zn, or Cu.

[0024] Preferably, a single-stage aging process at 120℃ for 16 hours yields a comprehensive performance of 472±7MPa tensile strength and 23.5±0.5% elongation.

[0025] In another embodiment, aluminum alloy sheet is used in lightweight structural components for transportation vehicles, including automotive body panels, rail vehicle body panels, or aircraft cabin interior trim panels.

[0026] The beneficial effects of this invention are:

[0027] 1. This invention, through rational composition design and preparation process, achieves an excellent combination of microstructure characteristics. Instead of forming coarse, micron-sized second phases that could potentially act as crack initiation sources, the alloy precipitates a large number of fine, dispersed Al3Sc particles. These dispersed particles significantly hinder the migration of dislocations and grain boundaries during hot deformation and solution treatment, thereby effectively refining the grains and preserving the deformed structure. The abundant dislocations within the deformed grains not only provide numerous nucleation sites for the precipitated phases during aging but also serve as rapid diffusion channels for alloying elements, promoting the formation of high-density β-Al3Mg2 phase and T-Mg phase. 32 (Al, Zn) 49 Synergistic precipitation of phases. The optimized combination of the above-mentioned microstructures significantly improves the strength-ductility matching properties of the alloy. In addition, the alloy composition system and preparation process used in this invention have good scalability and can meet the needs of large-scale industrial production and commercial applications.

[0028] 2. This invention, through optimized composition design and preparation process, successfully developed a novel Al-Mg-Zn alloy that combines high strength and ductility with low density. Compared to 6xxx series aluminum alloys, which are known for their balance between strength and ductility, the Al-Mg-Zn alloy of this invention exhibits superior overall performance in both strength and ductility matching. Even compared to high-strength 2xxx series aluminum alloys, its strength is only slightly lower, but it has a significant advantage in ductility. Simultaneously, the alloy's density is only 2.63 g / cm³, significantly lower than traditional aluminum alloy systems, including 2xxx series (2.75–2.84 g / cm³) and 6xxx series (2.69–2.72 g / cm³) alloys, demonstrating a unique advantage of combining lightweight with excellent strength-ductility matching. Attached Figure Description

[0029] Figure 1 This is a graph showing the mechanical tensile test results of the Al-Mg-Zn alloy in the aged state provided in Example 1 of the present invention;

[0030] Figure 2 This is a submicron-scale microstructure diagram of the Al-Mg-Zn alloy in its aged state provided in Example 1 of the present invention;

[0031] Figure 3 This is a graph showing the grain distribution (a) and statistical results (b) of the Al-Mg-Zn alloy in the aged state provided in Example 1 of the present invention.

[0032] Figure 4 These are microstructure images of the Al-Mg-Zn alloy in its aged state provided in Example 1 of the present invention; (a) tensile fracture surface; (b) interior of the alloy, magnified view showing elemental segregation of the extremely small micron second phase;

[0033] Figure 5 This describes the distribution of aged nano-precipitates and elemental segregation in the Al-Mg-Zn alloy provided in Example 1 of the present invention.

[0034] Figure 6 The images provided in Example 1 of this invention are high-resolution transmission electron microscope images (a1-a4) of the aged nanoprecipitate crystal structure of Al-Mg-Zn alloy, as well as inverse Fourier transform images and calibration structures corresponding to b1-4. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] Reference Figures 1 to 6 The Al-Mg-Zn aluminum alloy sheet shown here combines excellent strength and ductility with lightweight properties. The composition of the aluminum alloy, by mass percentage, includes:

[0037] Mg: 5.0-5.5%, Zn: 1.5-2.0%, Mn: 0.4-0.5%, Cu: 0.1-0.3%, Sc: 0.15-0.25%, Zr: 0.1-0.15%, Ag: 0.05-0.15%, impurities ≤0.1%, balance Al;

[0038] The density of the aluminum alloy is ≤2.63g / cm³, the tensile strength is ≥470MPa, and the elongation is ≥23%.

[0039] Reference Figures 1 to 6As shown, this invention provides an Al-Mg-Zn aluminum alloy sheet that combines excellent strength and ductility with lightweight properties. The aluminum alloy comprises, by mass percentage: 5.0% to 5.5% magnesium, 1.5% to 2.0% zinc, 0.4% to 0.5% manganese, 0.1% to 0.3% copper, 0.15% to 0.25% scandium, 0.1% to 0.15% zirconium, 0.05% to 0.15% silver, with total impurities not exceeding 0.1%, and the balance being aluminum. The aluminum alloy has a density not exceeding 2.63 g / cm³, a tensile strength not less than 470 MPa, and an elongation not less than 23%.

[0040] like Figure 1 As shown, the tensile stress-strain curve of the aluminum alloy under single-stage aging exhibits continuous and uniform plastic deformation characteristics, with no significant stress drop before necking. The measured tensile strength is 472±7 MPa and the elongation is 23.5±0.5%, indicating that the alloy possesses both high strength and high plasticity.

[0041] like Figure 2 As shown, the alloy's submicron-scale microstructure contains a large number of dispersed Al3Sc particles with an average size of no more than 100 nanometers, which are associated with regions of high dislocation density. These particles precipitate during the homogenization stage and pin grain boundaries and dislocations during subsequent hot rolling and solution treatment, significantly inhibiting recrystallization nucleation and thus preserving the deformed grain structure.

[0042] like Figure 3 a and Figure 3 As shown in b, the grain orientation distribution diagram and statistical results indicate that after hot rolling-cold rolling-solution, the area fraction of deformed grains is not less than 70%, and the recrystallized region accounts for only a small amount. The residual deformed structure stores high-density dislocations, providing nucleation sites for subsequent nano-precipitates and serving as a rapid diffusion channel for solute atoms.

[0043] like Figure 4 As shown in a, the alloy matrix is ​​almost entirely a solid solution phase, with only trace amounts of micron-sized second phase formed by impurity iron. Figure 4 Numerous dimples are visible at the tensile fracture surface, with virtually no second-phase particles inside, indicating very few crack initiation sites, which is beneficial for maintaining high plasticity.

[0044] like Figure 5 As shown in the dark-field image obtained by transmission electron microscopy, after single-stage aging treatment, high-density nanophases precipitate within the crystal, with an average size not exceeding 20 nanometers and a number density not less than 1 × 10²³ per cubic meter. These nanophases are uniformly distributed within the crystal and in the dislocation network, forming a reinforcing framework.

[0045] like Figure 6 The high-resolution transmission electron microscopy and inverse Fourier transform calibration results show that the nano-precipitated phases are β-Al3Mg2 and T-Mg. 32(Al,Zn) 49 The composite structure, with the two alternating or coexisting distributions, provides a synergistic strengthening effect by hindering dislocation movement through coherent strain and interface; at the same time, due to its extremely small size, dislocations can still be sheared or bypassed, maintaining a high elongation.

[0046] In conclusion, Figures 1 to 6 Joint evidence shows that the present invention obtains low-density, high-strength, and high-plasticity Al-Mg-Zn aluminum alloy sheets through a reasonable composition window, Sc-Zr-Ag microalloying, and single-stage aging process. The microstructure and mechanical properties of the sheets are significantly superior to those of the prior art.

[0047] Preferably, the microstructure of the aluminum alloy includes:

[0048] Dispersed submicron-sized Al3Sc particles with an average particle size ≤100nm;

[0049] The area fraction of deformed grains retained after hot rolling-cold rolling is ≥70%;

[0050] Nanoscale β-Al3Mg2 and T-Mg precipitated after single-stage aging 32 (Al,Zn) 49 The composite precipitate has an average size ≤20nm and a number density ≥1×10²³m⁻³.

[0051] Preferred, such as Figure 2 , Figure 3 , Figure 5 and Figure 6 As shown, the microstructure of the aluminum alloy sheet of the present invention simultaneously possesses the following three characteristics, and the synergistic effect of these three characteristics enables the material to achieve an excellent balance of tensile strength not less than 470 MPa and elongation not less than 23% while maintaining a density not higher than 2.63 g / cm³:

[0052] First, submicron-sized Al3Sc particles are dispersed and precipitated during homogenization and thermal processing. Figure 2 High-magnification scanning electron microscopy images show that these particles are spherical or ellipsoidal, with an average size of no more than 100 nm, and are uniformly distributed within the grains and near the grain boundaries. Due to the co-inclusion of Sc and Zr, Zr inhibits the coarsening and aggregation of Al3Sc at high temperatures, allowing it to maintain its nanoscale size during subsequent hot rolling and solution treatment stages. This continuously pins grain boundaries and dislocations, significantly inhibiting recrystallization nucleation and grain growth.

[0053] second, Figure 3 Orientation imaging diagram of a and its statistical results ( Figure 3(b) indicates that after hot rolling-cold rolling and solution treatment, the area fraction of deformed grains in the alloy is not less than 70%, and the recrystallized region accounts for only a small amount. The residual deformed structure stores a large number of dislocations, which become rapid diffusion channels for solute atoms and nucleation sites for precipitated phases during single-stage aging, providing a structural basis for the subsequent high-density precipitation of nano-strengthening phases.

[0054] third, Figure 5 Transmission electron microscopy images show that after single-stage aging, high-density nano-precipitates appear in the crystal, with an average size of no more than 20 nm. Figure 6 High-resolution images and their inverse Fourier transform calibration confirmed that these precipitates are β-Al3Mg2 and T-Mg. 32 (Al,Zn) 49 Alternating or symbiotic distributions form a composite strengthening structure. Statistical analysis using dark-field imaging shows a number density of no less than 1×10²³ m⁻³. The nanoscale β phase provides coherent strain strengthening, while the T phase generates interfacial strengthening; together, they hinder dislocation movement, thus significantly improving the alloy's strength. Simultaneously, due to the extremely small size and uniform distribution of the precipitated phases, dislocations can still bypass or shear, maintaining high plasticity.

[0055] The three microscopic features mentioned above work together: Al3Sc particles inhibit recrystallization and preserve the deformed structure; the high dislocation density in the deformed structure promotes the uniform and high-density precipitation of the nano-β+T phase; and the micron-sized second phase is fully eliminated due to the composition design and homogenization-solution process. Figure 4 (Almost no particles are observed within the dimples on the fracture surface), reducing crack initiation sources and further ensuring elongation. Thus, the alloy achieves a simultaneous improvement in high strength and high plasticity under low-density conditions.

[0056] Preferably, the thickness of the sheet is 1.5-3mm, the total reduction in cold rolling is 20-35%, the total reduction in hot rolling is 80-85%, and the final rolling temperature is ≥300℃.

[0057] Preferred, such as Figure 3 and Figure 4 As shown, the finished thickness of the aluminum alloy sheet of the present invention is controlled within the range of 1.5 mm to 3 mm; in its preparation process, the cold rolling stage adopts 5 to 10 continuous rolling passes, with a cumulative total reduction of 20% to 35% to ensure surface quality and dimensional accuracy; the hot rolling stage is set with 10 to 15 passes, with a cumulative total reduction of 80% to 85%, and the final rolling temperature is not lower than 300℃. Figure 3 The grain orientation distribution diagram of a shows that, under the above combination of rolling parameters, the grains in the thickness direction of the plate are significantly elongated along the rolling direction, forming a high-density deformation energy storage, which provides a structural basis for the uniform nucleation of nano-precipitates in the subsequent solid solution-aging stage; Figure 4The tensile fracture morphology shows that the dimple size of the 2 mm thick sample is uniformly distributed, without delamination or intergranular cracking, confirming that the rolling window can achieve both high density and high plasticity in the thickness range of 1.5-3 mm.

[0058] In another embodiment, a method for preparing an aluminum alloy sheet includes the following steps in sequence:

[0059] (1) Melting and casting: High-purity Al, Mg, Zn, Ag and intermediate alloys are melted under a protective atmosphere at 750-800℃, and after degassing and slag removal, they are poured into iron molds to obtain ingots;

[0060] (2) Two-stage homogenization: First, heat the furnace at 5-10℃ / min to 400-430℃ and hold for 4-8 hours, then heat it to 450-470℃ and hold for 24-28 hours, and then air cool it after removing it from the furnace.

[0061] (3) Hot rolling: After the homogenized ingot is held at 410-460℃ for 30-60 minutes, it is hot rolled in 10-15 passes with a total reduction of 80-85%. Every 2-3 passes, it is reheated in the furnace for 3-10 minutes. The final rolling temperature is ≥300℃.

[0062] (4) Intermediate annealing: The hot-rolled plate is held at 370-400℃ for 40-80 minutes and then air-cooled;

[0063] (5) Cold rolling: Perform 5-10 cold rolling passes with a total reduction of 20-35% to obtain the required thickness;

[0064] (6) Solution treatment: Hold at 470-490℃ for 40-60 min and then quench in water. The quenching transfer time is ≤2s.

[0065] (7) Single-stage aging: keep warm at 120-140℃ for 16-24 hours and then air cool.

[0066] In another embodiment, a method for preparing the Al-Mg-Zn aluminum alloy sheet with excellent strength and light weight is described, with the following steps and process window: Figures 1 to 6 As shown:

[0067] (1) Smelting and casting: Refer to Figure 2 Under an argon protective atmosphere at 750℃ to 800℃, high-purity aluminum, magnesium, zinc, and silver with a purity of not less than 99.99% and intermediate alloys Al-50 wt.%Cu, Al-10 wt.%Mn, Al-5 wt.%Zr, Al-2 wt.%Sc, and Al-10 wt.%Ti are added to a graphite crucible. After complete melting, argon is blown to remove gas, and electromagnetic stirring is used to remove slag. Then, the mixture is poured into a cast iron mold to obtain an ingot without macroscopic segregation.

[0068] (2) Two-stage homogenization: First, heat the temperature to 400°C to 430°C at a rate of 5°C to 10°C per minute and hold for 4 to 8 hours to eliminate the low melting point eutectic; then continue to heat the temperature to 450°C to 470°C and hold for 24 to 28 hours to allow the residual non-equilibrium phase to fully dissolve and then air-cool the furnace.

[0069] (3) Hot rolling: such as Figure 3 As shown, the homogenized ingot is held in a box furnace at 410°C to 460°C for 30 to 60 minutes, and then hot rolled for 10 to 15 passes, with a total reduction of 80% to 85%. After every 2 to 3 passes of rolling, the ingot is returned to the furnace and held for 3 to 10 minutes to control the final rolling temperature to be no less than 300°C, so as to ensure sufficient accumulation of deformation energy.

[0070] (4) Intermediate annealing: After the hot-rolled plate is held at 370°C to 400°C for 40 to 80 minutes, it is air-cooled to eliminate work hardening and provide a redistributed dislocation network for subsequent cold rolling.

[0071] (5) Cold rolling: Perform 5 to 10 cold rolling passes, with a total reduction of 20% to 35%, to obtain finished sheet metal with a thickness of 1.5 mm to 3 mm.

[0072] (6) Solid solution: such as Figure 4 The cold-rolled sheet is held at 470℃ to 490℃ for 40 to 60 minutes, followed by water quenching. The quenching transfer time does not exceed 2 seconds to suppress recrystallization and retain a high dislocation density.

[0073] (7) Single-level time limit: such as Figure 5 and Figure 6 The solution-treated board is kept at 120℃ to 140℃ for 16 to 24 hours, and then air-cooled to room temperature; at this time, nano-sized β-Al3Mg2 and T-Mg 32 (Al,Zn) 49 The composite precipitates are distributed in a high-density and uniform manner, with an average size ≤20 nm, a number density ≥1×10²³ m⁻³, and a micron-sized second phase area fraction ≤0.5%.

[0074] Preferably, the selection and purity control of the intermediate alloy in step (1) ensures stable yields of Sc, Zr, and Ag elements in the ingot, providing a compositional basis for the subsequent formation of Al3Sc dispersed particles and the synergistic strengthening of nano-precipitates, such as... Figure 2 As shown.

[0075] Preferably, the intermediate alloy in step (1) is Al-50 wt.%Cu, Al-10 wt.%Mn, Al-5 wt.%Zr, Al-2 wt.%Sc and Al-10 wt.%Ti, and all raw materials have a purity ≥99.99%.

[0076] Preferably, in step (3), the single-pass pressing amount of hot rolling is 1-2 mm and the roll speed is 5 r / min; in step (5), the single-pass pressing amount of cold rolling is 0.5-1 mm and the roll speed is 5 r / min.

[0077] Preferably, in the aluminum alloy sheet obtained by the preparation method, the area fraction of the micron-sized second phase is ≤0.5%, and the micron-sized second phase is formed only by impurity Fe, without other micron-sized phases containing Mg, Zn, or Cu.

[0078] Preferably, a single-stage aging process at 120℃ for 16 hours yields a comprehensive performance of 472±7MPa tensile strength and 23.5±0.5% elongation.

[0079] Preferred, such as Figures 2 to 6 As shown, the intermediate alloy in step (1) is specifically Al-50 wt.%Cu, Al-10 wt.%Mn, Al-5 wt.%Zr, Al-2 wt.%Sc and Al-10 wt.%Ti, and all raw materials have a purity ≥99.99%. This combination ensures that the yield of Sc, Zr and Ag elements in the melt is stable, forming dispersed Al3Sc particles, which lays the foundation for subsequent microstructure control.

[0080] Preferably, in step (3), the single-pass pressing amount of hot rolling is controlled at 1-2 mm, and the roll speed is set to 5 r / min; in step (5), the single-pass pressing amount of cold rolling is controlled at 0.5-1 mm, and the roll speed is also 5 r / min. This low-speed and low-pressing strategy makes the surface quality of the plate excellent, while maintaining a uniform distribution of deformation energy storage, which is beneficial to the retention of high dislocation density in the subsequent solid solution stage.

[0081] Preferred, such as Figure 4 As shown, in the aluminum alloy sheet obtained by the preparation method, the area fraction of the micron-sized second phase is ≤0.5%, and the micron-sized second phase is formed only by impurity Fe, without any micron-sized phase containing Mg, Zn, or Cu; this feature significantly reduces the probability of crack initiation and improves the elongation.

[0082] Preferred, such as Figure 1 As shown, single-stage aging at 120℃ for 16 h can achieve a comprehensive performance of tensile strength of 472±7 MPa and elongation of 23.5±0.5%. This process window simplifies the traditional two-stage aging process while still achieving a synergistic breakthrough in high strength and high plasticity.

[0083] In another embodiment, aluminum alloy sheet is used in lightweight structural components for transportation vehicles, including automotive body panels, rail vehicle body panels, or aircraft cabin interior trim panels.

[0084] In another embodiment, such as Figure 1 , Figure 4 and Figure 5 As shown, the Al-Mg-Zn aluminum alloy sheet, which combines excellent strength and ductility with lightweight properties, is used in lightweight structural components for transportation vehicles. These structural components include automotive body panels, rail vehicle body panels, or aircraft cabin interior trim panels, all of which share the common requirement of significantly reducing weight while maintaining strength and rigidity, thereby improving energy efficiency and reducing emissions.

[0085] Specifically, the aluminum alloy sheet exhibits excellent plastic deformation capacity during the forming stage due to its density not exceeding 2.63 grams per cubic centimeter, tensile strength not less than 470 MPa, and elongation not less than 23%. The structural components are formed by stamping and bending.

[0086] Example 1

[0087] The composition of the newly developed Al-Mg-Zn alloy, expressed as a percentage by mass, is as follows: Mg content 5.46 wt%, Zn content 1.86%, Mn content 0.45%, Cu content 0.18%, Sc content 0.19%, Zr content 0.12%, Ag content 0.09%, impurity content less than 0.1%, with the balance being Al. The preparation method is as follows:

[0088] Smelting and Casting: High-purity Al, Mg, Zn lumps and Ag powder (99.99%), along with master alloys (Al–50wt.%Cu, Al–10wt.%Mn, Al–5wt.%Zr, Al–2wt.%Sc, and Al–10wt.%Ti), are used as raw materials and smelted in a vacuum induction furnace. The raw materials are placed in a graphite crucible, and then, under an argon protective atmosphere, the current is increased to completely melt the raw materials, at which point the temperature is raised to 780℃. Subsequent blowing, stirring, and slag removal operations are performed, and the mixture is poured into a cast iron mold with dimensions of 20mm×20mm×100mm to form an alloy ingot.

[0089] Homogenization treatment: The alloy ingot is placed in a box furnace for homogenization treatment. The furnace temperature is increased to 430°C at a rate of 10°C / min, and then held for 6 hours to initially eliminate the low-melting-point second phase. Subsequently, the temperature is increased to 460°C at a rate of 10°C / min, and then held for 24-28 hours to eliminate the non-equilibrium eutectic structure. After being removed from the furnace and air-cooled, the surface is milled to a thickness of 18 mm.

[0090] Deformation: After homogenization and milling, the ingot is placed in a box furnace at 430℃ and held for 40 minutes before hot rolling. The initial rolling temperature is 430℃, and the final rolling temperature is not lower than 300℃. The roll speed is 5 r / min, the reduction per pass is 1~2 mm, and the holding time is 5 minutes after every two passes. The final thickness of the hot-rolled plate is 2.8 mm, and the total deformation is 84.4%. Subsequently, it is held in a furnace at 375℃ for 75 minutes and then air-cooled, followed by cold rolling at a roll speed of 5 r / min and a reduction per pass of 1 mm. The final thickness of the cold-rolled plate is 2 mm, and the total deformation is 28.6%.

[0091] Solution treatment: The plate is placed in a box furnace at 470℃ for 60 minutes for solution treatment, followed by water quenching, with a quenching transfer time of less than 2 seconds.

[0092] Aging treatment: The solution-treated board is placed in a box furnace at 120°C for 16 hours of aging treatment, and then air-cooled to room temperature.

[0093] Three standard tensile specimens were prepared using the above-described preparation process. The mechanical properties obtained were a tensile strength of 472±7 MPa and an elongation of 23.5±0.5%. The three sets of stress-strain curves obtained are shown below. Figure 1 As shown. The density was measured using an MSA324S densitometer, and the result was 2.63 g / cm³.

[0094] Example 1 exhibits an excellent balance of strength and plasticity, which is attributed to the superior microstructure formed by the combined effects of alloy composition and processing technology. Figure 2 The submicron-scale microstructure of the Al-Mg-Zn alloy prepared in Example 1 in its aged state is shown, revealing a large number of fine Al3Sc dispersed particles and a rich dislocation network. This is mainly due to the addition of Sc and Zr elements: Sc promotes the precipitation of Al3Sc particles during homogenization, while Zr inhibits the growth and aggregation of Al3Sc particles during homogenization, thereby forming dispersed Al3Sc particles that effectively hinder grain boundary and dislocation migration during hot deformation and solution treatment. Figure 3 Figures a and 3b respectively illustrate the grain distribution and statistical results of the aged alloy in Example 1. They show significant orientation differences in the grains, with fine grains and extremely low recrystallization. Simultaneously, a large number of deformed grains remain, further demonstrating that the dispersed Al3Sc particles significantly hinder grain boundary and dislocation migration during hot deformation and solution treatment, resulting in a large accumulation of dislocations within the alloy. This provides abundant nucleation sites for the formation of nano-precipitates during aging. Typically, the degree of recrystallization during solution treatment is mutually constrained by the degree of solution solubility of the second phase; low recrystallization often implies insufficient solution solubility. However, Figure 4The microstructure of the aged state in Example 1 shown in Figure a indicates that the alloy matrix is ​​almost entirely composed of a solid solution phase, exhibiting extremely high solid solubility. The trace amounts of micron-sized second phase are solely due to Fe impurities. Therefore, the dispersed Al3Sc particles enable the novel Al-Mg-Zn alloy to maintain high solid solubility while achieving extremely low recrystallization. This high solid solubility further promotes the formation of nano-precipitates during the aging process. Furthermore, since micron-sized second phases typically serve as the starting point for crack initiation and propagation, the extremely low content of micron-sized second phases in the novel Al-Mg-Zn alloy is beneficial for maintaining good alloy plasticity. Figure 4 b shows the micron-scale microstructure of the tensile fracture surface of the alloy in Example 1 under aging conditions. Numerous dimples of varying sizes are visible, and these dimples contain almost no second phase. This further verifies that the micron-sized second phase significantly reduces the tendency for crack initiation and propagation, thus contributing to high plasticity. The high strength of the alloy mainly originates from the high-density nano-precipitates. Figure 5 The distribution and elemental segregation of the nano-precipitates in the aged alloy of Example 1 are shown. Due to the large number of dislocations and high solid solubility within the alloy, and the presence of Mn, Cu, and Ag elements that promote precipitation, the alloy formed a large number of Zn- and Mg-rich nano-precipitates. The structural analysis results are as follows... Figure 6 As shown, these precipitated phases are not single phases, but rather a combination of β-Al3Mg2 phase and T-Mg32(Al,Zn)49 phase, which synergistically contribute to the high strength of the alloy. This excellent microstructure matching is not achieved in other Al-Mg-Zn alloys.

[0095] In summary, through the combined effects of alloy composition and processing, the novel Al-Mg-Zn alloy exhibits excellent strength and ductility, with a density of only 2.63 g / cm³, significantly lower than that of current commercial aluminum alloys such as Al-Cu (2.75–2.84 g / cm³) and Al-Mg-Si (2.69–2.72 g / cm³). Therefore, it combines excellent strength and ductility with lightweight properties. Since the elements contained in the novel Al-Mg-Zn alloy are inexpensive and the processing is simple, it can be used for large-scale industrial production and lightweighting of transportation vehicles, and holds promise for replacing some commercial aluminum alloys.

[0096] By adopting the above-disclosed technical solution of this invention, the following beneficial effects are obtained:

[0097] Low density: with a density of ≤2.63g / cm³, it is lighter than traditional 6xxx series (2.69-2.72g / cm³) and 2xxx series (2.75-2.84g / cm³) aluminum alloys, resulting in an additional weight reduction of 3-8%.

[0098] High strength and plasticity matching: tensile strength ≥470MPa, elongation ≥23%, which exceeds the performance balance point of typical 6xxx series (413 MPa / 15%) and 2xxx series (531 MPa / 12%), reducing the wall thickness design of structural components and improving the safety factor.

[0099] Process simplification: Single-stage aging (120℃×16h) replaces the traditional two-stage aging, shortening the production cycle by more than 30%, reducing energy consumption and equipment occupation, and is suitable for direct switching of existing aluminum alloy rolling production lines.

[0100] Organizational advantages: Al3Sc particles + high dislocation density + nano β+T composite precipitates provide synergistic reinforcement, with micron-sized second phase ≤0.5% and formed only by impurity Fe, eliminating crack initiation sources and achieving both high strength and high toughness.

[0101] Cost controllable: The total addition of Sc, Zr, and Ag is less than 0.5%, and conventional intermediate alloys are used, eliminating the need for expensive equipment and enabling large-scale, low-cost commercial production.

[0102] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing Al-Mg-Zn aluminum alloy sheets with both excellent strength and plasticity and lightweight properties, characterized in that, The components of aluminum alloy, by weight percentage, include: Mg: 5.0-5.5%, Zn: 1.5-2.0%, Mn: 0.4-0.5%, Cu: 0.1-0.3%, Sc: 0.15-0.25%, Zr: 0.1-0.15%, Ag: 0.05-0.15%, impurities ≤0.1%, balance Al; The aluminum alloy has a density ≤2.63g / cm³, tensile strength ≥470MPa, and elongation ≥23%. The microstructure of the aluminum alloy includes: Dispersed submicron-sized Al3Sc particles, the average particle size being ≤100nm; The area fraction of deformed grains retained after hot rolling-cold rolling is ≥70%; Nanoscale β-Al3Mg2 and T-Mg precipitated after single-stage aging 32 (Al,Zn) 49 A composite precipitate, wherein the average size of the precipitate is ≤20 nm and the number density is ≥1×10²³ m⁻³; the method includes the following steps: (1) Melting and casting: High-purity Al, Mg, Zn, Ag and intermediate alloys are melted under a protective atmosphere at 750-800℃, and after degassing and slag removal, they are poured into iron molds to obtain ingots; (2) Two-stage homogenization: First, heat the furnace at 5-10℃ / min to 400-430℃ and hold for 4-8 hours, then heat it to 450-470℃ and hold for 24-28 hours, and then air cool it after removing it from the furnace. (3) Hot rolling: After the homogenized ingot is held at 410-460℃ for 30-60 minutes, it is hot rolled in 10-15 passes with a total reduction of 80-85%. Every 2-3 passes, it is reheated in the furnace for 3-10 minutes. The final rolling temperature is ≥300℃. (4) Intermediate annealing: The hot-rolled plate is held at 370-400℃ for 40-80 minutes and then air-cooled; (5) Cold rolling: Perform 5-10 cold rolling passes with a total reduction of 20-35% to obtain the required thickness; (6) Solution treatment: Hold at 470-490℃ for 40-60 min and then quench in water. The quenching transfer time is ≤2s. (7) Single-stage aging: keep warm at 120-140℃ for 16-24 hours and then air cool.

2. The method according to claim 1, characterized in that, The intermediate alloy in step (1) is Al-50 wt.%Cu, Al-10 wt.%Mn, Al-5 wt.%Zr, Al-2 wt.%Sc and Al-10 wt.%Ti, and all raw materials have a purity ≥99.99%.

3. The method according to claim 2, characterized in that, In step (3), the single-pass pressing amount of hot rolling is 1-2 mm, and the roll speed is 5 r / min; in step (5), the single-pass pressing amount of cold rolling is 0.5-1 mm, and the roll speed is 5 r / min.

4. The method according to claim 3, characterized in that, In the aluminum alloy sheet obtained by the method, the area fraction of the micron-sized second phase is ≤0.5%, and the micron-sized second phase is formed only by impurity Fe and does not contain other micron-sized phases containing Mg, Zn, or Cu.

5. The method according to claim 4, characterized in that, The single-stage aging process involves holding the product at 120℃ for 16 hours.

6. The method according to claim 4, characterized in that, The aluminum alloy sheet has a thickness of 1.5-3mm, a total reduction of 20-35% during cold rolling, a total reduction of 80-85% during hot rolling, and a final rolling temperature of ≥300℃.

7. The use of the aluminum alloy sheet prepared by the method according to any one of claims 1-6 in lightweight structural components of transportation vehicles, wherein the structural components include automotive body panels, rail transit vehicle body panels, or aircraft cabin interior trim panels.

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