Cast-rolling-based high-strength thermal-stability Al-Zn-Mg series aluminum alloy and preparation method thereof

Abstract

The invention discloses a cast-rolling-based high-strength heat-stable Al-Zn-Mg series aluminum alloy and a preparation method thereof. The aluminum alloy is prepared from the following components in percentage by mass: 5.4 to 6.1 percent of Zn, 2.9 to 4.4 percent of Mg, 1.5 to 1.8 percent of Cu, 0.05 to 0.25 percent of Si, less than or equal to 0.20 percent of inevitable impurities and the balance of Al. The preparation method comprises the steps of smelting, double-roller cast rolling, homogenization treatment, multi-pass hot rolling, single-stage solid solution heat treatment, quenching, single-stage artificial aging treatment and the like. The aluminum alloy obtained through the method has excellent room-temperature and high-temperature mechanical properties, and the yield strength of the aluminum alloy is larger than or equal to 500 MPa under the room-temperature condition; after 100-500 hours of thermal exposure at 100-150 DEG C, the yield strength can still be kept to be larger than or equal to 470 MPa, and the attenuation rate is smaller than or equal to 10%; and the tensile strength is greater than or equal to 465 MPa when the alloy is stretched at a high temperature of 100-150 DEG C. The alloy components provided by the invention are suitable for cast rolling, the technological process is simple, the controllability is high, and the method is suitable for industrial popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy preparation technology, specifically relating to a high-strength, thermally stable Al-Zn-Mg aluminum alloy based on casting and rolling and its preparation method. Background Technology

[0002] Aluminum alloys, due to their lightweight, high strength, flexible forming and processing, and excellent corrosion resistance, occupy an important position in the aerospace, transportation, and advanced manufacturing fields. Among them, Al–Zn–Mg aluminum alloys, with their outstanding age-hardening ability and excellent comprehensive strength and toughness, are one of the most important structural materials for high-end equipment. With the continuous increase in the demand for larger, higher-speed, and longer service life, materials face more stringent requirements in terms of strength, heat resistance, cost control, and reliability.

[0003] However, existing Al–Zn–Mg alloys have significant shortcomings in the synergistic optimization of strength and plasticity, making it difficult to achieve simultaneous improvement in both. Furthermore, increasing the high-temperature strength of alloys usually inevitably weakens their room-temperature strength and plasticity, further limiting performance matching. Although high alloying can improve peak strength, its stability under medium and high-temperature conditions is extremely limited. Existing technologies show a significant decrease in yield strength of 25–60% after only ~100 hours of heat exposure at 100°C, making it difficult to simultaneously achieve both high initial strength and plasticity and high-temperature creep mechanical stability.

[0004] For example, the existing 7050-T7452 alloy also incorporates a large amount of rare earth and other precious metals and adopts a complex and time-consuming preparation process. The room temperature yield strength is ~399MPa, but after heating at 150℃ for 500h, the yield strength is only ~325MPa, with a decay rate of ~19%.

[0005] Therefore, the urgent technical challenges to be solved are how to achieve cost control through short-process preparation and avoidance of rare earth and other precious metals while reducing costs and simplifying processes, ensuring high plasticity of the alloy, and simultaneously improving the strength at both room temperature and high temperature, enhancing long-term thermal exposure stability, and synergistically optimizing the strengthening mechanism. In other words, how to achieve Al–Zn–Mg aluminum alloy system that maintains excellent mechanical properties at both room temperature and high temperature and high stability after long-term high-temperature exposure, and how to realize industrial production and provide more reliable materials for high-end structural components. Summary of the Invention

[0006] To address the aforementioned technical challenges, this invention provides a high-strength, thermally stable Al-Zn-Mg aluminum alloy based on casting and rolling. The aluminum alloy is composed of the following components by mass percentage: Zn: 5.4–6.1 wt.%, Mg: 2.9–4.4 wt.%, Cu: 1.5–1.8 wt.%, Si: 0.05–0.25 wt.%, with unavoidable impurities ≤0.20 wt.%, and the balance being Al. The alloy is prepared by batching the components according to the above mass percentages, and the preparation method includes the following steps:

[0007] (1) Under a protective gas atmosphere, commercial pure Al, pure Zn, pure Cu and Al-Si master alloy are heated to 720–765℃ until completely melted; then cooled to 650–700℃, pure Mg is added, and after melting, the mixture is held for 5–20 min, and then stirred, refined and slag removed to obtain alloy melt.

[0008] (2) The alloy melt obtained in step (1) is diverted to the water-cooled copper roll gap for sub-rapid solidification casting and rolling, and then subjected to homogenization treatment, multi-pass hot rolling, single-stage solution heat treatment, quenching, and single-stage artificial aging treatment to obtain a high-strength thermally stable Al-Zn-Mg aluminum alloy based on casting and rolling.

[0009] The water-cooled copper roll gap in step (2) is 1-10mm, the linear speed of the water-cooled copper roll is 3-12m / min, the pre-gating temperature of the water-cooled copper roll is 200-400℃, the sub-rapid solidification casting and rolling is: the sub-rapid solidification cooling rate is 300-500K / s; the homogenization treatment is: holding at 400-500℃ for 1-10h; the multi-pass hot rolling is: 4-8 passes of hot rolling, holding at 200-420℃ for 5-20min before each pass, the reduction per pass is 20-25%, and the total reduction is 60-90%; the single-stage solution heat treatment is: holding at 400-500℃ for 1-5h; the single-stage artificial aging treatment is: holding at 100-160℃ for 10-40h.

[0010] The main precipitated phases and average sizes of the high-strength thermally stable Al-Zn-Mg aluminum alloy obtained in step (2) based on casting and rolling are as follows: η-type phase: diameter ~1.5-2.3nm, length ~2.4-4.6nm; T-type phase: diameter ~1.6-4.3nm; The aluminum alloy has excellent room temperature and high temperature mechanical properties: at room temperature, its yield strength is ≥500MPa; after 100-500h of heat exposure at 100℃-150℃, it can maintain a yield strength ≥470MPa and a decay rate ≤10%; under high temperature tensile conditions at 100℃-150℃, the tensile strength is ≥465MPa.

[0011] Further, the homogenization process described in step (2) is: heat treatment at 450–470℃ for 2–3 hours.

[0012] Further, the multi-pass hot rolling in step (2) is: 5-7 passes of hot rolling, with each pass held at 250-400℃ for 10-15 minutes before the pass, and the total reduction is 70-85%.

[0013] Further, the single-stage solution heat treatment in step (2) is: holding at 420–480℃ for 2–4 hours; the single-stage artificial aging treatment is: holding at 110–150℃ for 14–30 hours.

[0014] Compared with the prior art, the present invention has the following significant features and beneficial effects:

[0015] This invention achieves an Al–Zn–Mg aluminum alloy that combines high strength at room temperature, high strength at high temperature, and thermal stability after prolonged exposure to high temperatures, while maintaining high plasticity, through the synergistic design of alloy composition, component ratio, and the coupled synergistic effect of process and process parameters. Existing technologies struggle with this problem because traditional Al–Zn–Mg alloys have a single type of reinforcing phase and low element utilization. While maintaining high plasticity at room temperature, it is difficult to improve room temperature strength. Furthermore, it is difficult to simultaneously improve any two of the following: room temperature strength, high strength at high temperatures, and thermal stability after prolonged exposure to high temperatures. Existing technologies tend to exhibit significant microstructure coarsening after long-term heat exposure (100–500 h) at 100℃–150℃, resulting in a yield strength reduction rate as high as 25–60%, which is insufficient to meet high-temperature service requirements. Additionally, the tensile strength of the alloy decreases significantly at high temperatures, reaching ≤400 MPa. Existing technologies often involve adding large amounts of rare earth precious metals. While this can improve the strength and ductility of materials to a certain extent, the high-temperature strength and thermal stability after prolonged high-temperature exposure of the alloys are poor. These processes significantly increase costs. Furthermore, because alloying elements often form high-binding-energy pairings with vacancies or solute atoms, they alter the original precipitation pathways, resulting in the precipitation of large amounts of non-strengthening phases and inhibiting the full formation of strengthening phases, or causing some solute to remain within the matrix. This leads to low element utilization and poor strengthening effects. Therefore, existing technologies struggle to simultaneously improve room-temperature strength and ductility, high-temperature strength, and thermal stability after prolonged high-temperature exposure in Al–Zn–Mg alloys.

[0016] (1) Compared with the prior art, the inventiveness of this invention lies in achieving the following beneficial effects simultaneously: First, it promotes the supersaturated solid solution of solute elements in the matrix and inhibits the formation of coarse Fe-containing second phases (impurities), thereby effectively reducing central segregation, allowing more solute elements to participate in the nucleation and growth of nanoscale strengthening phases, improving element utilization, and thus obtaining higher strengthening effects with lower alloy content; Second, existing Al-Zn-Mg alloys mainly precipitate η-type phase (MgZn2) as the strengthening phase (average size: diameter ≥ 4nm; length ≥ 6nm). This phase will coarsen under long-term heating, resulting in a significant reduction in alloy strength. This invention breaks through the bottleneck of the prior art and regulates the high-density and finer η-type phase (MgZn2), wherein the η-type phase has a diameter of ~1.5-2.3nm and a length of ~2.4-4.6nm; at the same time, it also obtains a high-density and finer T-type phase (Mg 32 (Al,Zn,Cu) 49 The diameter of this phase is ~1.6-4.3 nm. No literature reports on the T-type phase have been found in the prior art. This invention achieves a synergistic effect between the two phases through a composite structure where a high-density, fine η-type phase and a T-type phase coexist: dual-phase precipitation strengthening provides high strength at room temperature, while the composite structure of the T-type and η-type phases inhibits phase coarsening and significantly improves thermal stability. Therefore, the alloy of this invention, while maintaining a simple process and low cost, and ensuring high plasticity, still achieves room temperature high strength, high temperature high strength, and thermal stability after long-term high-temperature heat exposure, far exceeding that of existing technologies.

[0017] (2) The aluminum alloy obtained by this invention achieves high strength at room temperature, high strength at high temperature, and thermal stability after long-term high-temperature heat exposure while ensuring high plasticity. This results in a simultaneous improvement in comprehensive performance, breaking through the technical bottleneck of the prior art where it is difficult to improve any two properties simultaneously. The performance indicators obtained by this invention are significantly better than those obtained by the prior art. Through the interaction between alloying elements, the ratio, the process, and the synergistic effect of process parameters, this invention achieves high element utilization and multi-phase synergy, resulting in excellent comprehensive performance: room temperature yield strength ≥ 500 MPa; yield strength ≥ 470 MPa after heat exposure at 100℃-150℃ for 100h-500h; yield strength decay rate ≤ 10%, which is significantly better than the decay rate of 25-60% in the prior art. It can also ensure high strength after high-temperature tensile testing at 100℃-150℃, with a tensile strength ≥ 465 MPa. In other words, the alloy obtained by this invention not only has high plasticity, but also achieves high strength at room temperature, low strength decay rate at high temperature (after high-temperature exposure), and high strength at high temperature. In summary, this invention simultaneously improves room temperature strength and plasticity while also possessing excellent high-temperature strength and a low strength decay rate after high-temperature heat exposure. It can maintain stable and excellent comprehensive performance under extreme conditions such as high-temperature service and heat exposure, which is far superior to the results of existing technologies in any high-temperature scenario. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the embodiments.

[0019] Example 1

[0020] An Al-5.7Zn-3.2Mg-1.7Cu-0.12Si alloy (composed of the following components by mass percentage: Zn: 5.7%, Mg: 3.2%, Cu: 1.7%, Si: 0.12%, unavoidable impurities ≤ 0.20%, balance Al) is prepared by the following steps:

[0021] (1) According to the alloy composition ratio, under a protective gas atmosphere, commercial pure Al, pure Zn, pure Cu and Al-Si master alloy are heated to 730°C until completely melted; then cooled to 680°C, pure Mg is added, and after melting, the mixture is kept at the temperature for 15 minutes, and then stirred, refined and slag removed to obtain the alloy melt.

[0022] (2) The alloy melt obtained in step (1) is diverted to the water-cooled copper roll gap for sub-rapid solidification casting and rolling. The water-cooled copper roll gap is 3.2 mm, the linear speed of the water-cooled copper roll is 8 m / min, and the temperature of the water-cooled copper roll pre-gating channel is 250 °C to obtain aluminum alloy strip. The aluminum alloy strip is homogenized: held at 450 °C for 2 h, hot rolled in 6 passes: held at 250 °C for 10 min before each pass, the reduction in each pass is 20%, and the total reduction is 74%. Then, it undergoes single-stage solution heat treatment: held at 470 °C for 3.5 h, quenched, and single-stage artificial aging treatment to obtain high-strength, heat-resistant Al-5.7Zn-3.2Mg-1.7Cu-0.12Si aluminum alloy. The sub-rapid solidification is: the cooling rate is 300 K / s, and the single-stage artificial aging treatment is: held at 150 °C for 15 h.

[0023] The prepared Al-5.7Zn-3.2Mg-1.7Cu-0.12Si alloy has a yield strength of approximately 520 MPa at room temperature; after 500 h of heat exposure at 150 °C, the yield strength is approximately 476 MPa, with a yield strength decay rate of approximately 8.4%; and under high-temperature tensile testing at 150 °C, the tensile strength is 480 MPa, demonstrating excellent long-term thermal stability.

[0024] Example 2

[0025] An Al-5.5Zn-4.1Mg-1.6Cu-0.15Si alloy (composed of the following components by mass percentage: Zn: 5.5%, Mg: 4.1%, Cu: 1.6%, Si: 0.15%, unavoidable impurities ≤ 0.20%, balance Al) is prepared by the following steps:

[0026] (1) According to the alloy composition ratio, under a protective gas atmosphere, commercial pure Al, pure Zn, pure Cu and Al-Si master alloy are heated to 750°C until completely melted; then cooled to 670°C, pure Mg is added, and after melting, the mixture is kept at the temperature for 10 minutes, and then stirred, refined and slag removed to obtain the alloy melt.

[0027] (2) The alloy melt obtained in step (1) is diverted to the water-cooled copper roll gap for sub-rapid solidification casting and rolling. The water-cooled copper roll gap is 5.5 mm, the linear speed of the water-cooled copper roll is 10 m / min, and the temperature of the water-cooled copper roll pre-gating channel is 300 °C to obtain aluminum alloy strip. The aluminum alloy strip is homogenized: held at 460 °C for 3 h, hot rolled in 5 passes: held at 400 °C for 10 min before each pass, the reduction in each pass is 25%, and the total reduction is 76%. Then, it undergoes single-stage solution heat treatment: held at 475 °C for 2 h, quenched, and single-stage artificial aging treatment to obtain high-strength, heat-resistant Al-5.5Zn-4.1Mg-1.6Cu-0.15Si aluminum alloy. The sub-rapid solidification is: the cooling rate is 400 K / s, and the single-stage artificial aging treatment is: held at 120 °C for 22 h.

[0028] The prepared Al-5.5Zn-4.1Mg-1.6Cu-0.15Si alloy has a yield strength of approximately 515 MPa at room temperature; after 500 h of heat exposure at 100℃, the yield strength is approximately 502 MPa, with a yield strength decay rate of approximately 2.5%; and under high-temperature tensile testing at 100℃, the tensile strength is 507 MPa, demonstrating excellent long-term thermal stability.

[0029] Example 3

[0030] An Al-5.7Zn-3.5Mg-1.5Cu-0.20Si alloy (composed of the following components by mass percentage: Zn: 5.7%, Mg: 3.5%, Cu: 1.5%, Si: 0.20%, unavoidable impurities ≤ 0.20%, balance Al) is prepared by the following steps:

[0031] (1) According to the alloy composition ratio, under a protective gas atmosphere, commercial pure Al, pure Zn, pure Cu and Al-Si master alloy are heated to 720°C until completely melted; then cooled to 680°C, pure Mg is added, and after melting, the mixture is kept at the temperature for 20 minutes, and then stirred, refined and slag removed to obtain the alloy melt.

[0032] (2) The alloy melt obtained in step (1) is diverted to the water-cooled copper roll gap for sub-rapid solidification casting and rolling. The water-cooled copper roll gap is 4.8 mm, the linear speed of the water-cooled copper roll is 12 m / min, and the temperature of the water-cooled copper roll pre-gating channel is 400 °C to obtain aluminum alloy strip. The aluminum alloy strip is homogenized: held at 470 °C for 2.5 h, hot rolled in 7 passes: held at 350 °C for 15 min before each pass, the reduction in each pass is 20%, and the total reduction is 79%. Then, it undergoes single-stage solution heat treatment: held at 480 °C for 2.5 h, quenched, and single-stage artificial aging treatment to obtain a high-strength, heat-resistant Al-5.5Zn-3.5Mg-1.5Cu-0.20Si alloy. The sub-rapid solidification is: the cooling rate is 450 K / s, and the single-stage artificial aging treatment is: held at 110 °C for 30 h.

[0033] The prepared Al-5.7Zn-3.5Mg-1.5Cu-0.20Si alloy has a yield strength of approximately 510 MPa at room temperature; after 100 h of heat exposure at 150 °C, the yield strength is approximately 495 MPa, with a yield strength decay rate of approximately 2.9%; and under high-temperature tensile testing at 150 °C, the tensile strength is 470 MPa, demonstrating excellent long-term thermal stability.

[0034] Example 4

[0035] An Al-5.9Zn-3.8Mg-1.8Cu-0.25Si alloy (composed of the following components by mass percentage: Zn: 5.9%, Mg: 3.8%, Cu: 1.8%, Si: 0.25%, unavoidable impurities ≤ 0.20%, balance Al) is prepared by the following steps:

[0036] (1) According to the alloy composition ratio, under a protective gas atmosphere, commercial pure Al, pure Zn, pure Cu and Al-Si master alloy are heated to 750°C until completely melted; then cooled to 690°C, pure Mg is added, and after melting, the mixture is kept at the temperature for 15 minutes, and then stirred, refined and slag removed to obtain the alloy melt.

[0037] (2) The alloy melt obtained in step (1) is diverted to the water-cooled copper roll gap for sub-rapid solidification casting and rolling. The water-cooled copper roll gap is 1.5 mm, the linear speed of the water-cooled copper roll is 11 m / min, and the temperature of the water-cooled copper roll pre-gating channel is 350 °C to obtain aluminum alloy strip. The aluminum alloy strip is homogenized: held at 450 °C for 3 h, hot rolled in 5 passes: held at 400 °C for 10 min before each pass, the reduction in each pass is 25%, and the total reduction is 77%. Then, it undergoes single-stage solution heat treatment: held at 475 °C for 2 h, quenched, and single-stage artificial aging treatment to obtain a high-strength, heat-resistant Al-5.9Zn-3.8Mg-1.8Cu-0.25Si alloy. The sub-rapid solidification is: the cooling rate is 480 K / s, and the single-stage artificial aging treatment is: held at 130 °C for 18 h.

[0038] The prepared Al-5.9Zn-3.8Mg-1.8Cu-0.25Si alloy has a yield strength of approximately 522 MPa at room temperature; after 500 h of heat exposure at 150 °C, the yield strength is approximately 480 MPa, with a yield strength decay rate of approximately 8.0%; and under high-temperature tensile testing at 150 °C, the tensile strength is 475 MPa, demonstrating excellent long-term thermal stability.

[0039] Example 5

[0040] An Al-6.1Zn-4.2Mg-1.7Cu-0.22Si alloy (composed of the following components by mass percentage: Zn: 6.1%, Mg: 4.2%, Cu: 1.7%, Si: 0.22%, unavoidable impurities ≤ 0.20%, balance Al) is prepared by the following steps:

[0041] (1) According to the alloy composition ratio, under a protective gas atmosphere, commercial pure Al, pure Zn, pure Cu and Al-Si master alloy are heated to 760°C until completely melted; then cooled to 685°C, pure Mg is added, and after melting, the mixture is kept at the temperature for 20 minutes, and then stirred, refined and slag removed to obtain the alloy melt.

[0042] (2) The alloy melt obtained in step (1) is diverted to the water-cooled copper roll gap for sub-rapid solidification casting and rolling. The water-cooled copper roll gap is 9.3 mm, the linear speed of the water-cooled copper roll is 9 m / min, and the temperature of the water-cooled copper roll pre-gating channel is 380℃ to obtain aluminum alloy strip. The aluminum alloy strip is homogenized: held at 465℃ for 2 h, hot rolled in 7 passes: held at 380℃ for 15 min before each pass, the reduction in each pass is 25%, and the total reduction is 85%. Then, it undergoes single-stage solution heat treatment: held at 470℃ for 4 h, quenched, and single-stage artificial aging treatment to obtain a high-strength, heat-resistant Al-6.1Zn-4.2Mg-1.7Cu-0.22Si alloy. The sub-rapid solidification is: the cooling rate is 300 K / s, and the single-stage artificial aging treatment is: held at 150℃ for 16 h.

[0043] The prepared Al-6.1Zn-4.2Mg-1.7Cu-0.22Si alloy has a yield strength of approximately 518 MPa at room temperature; after 500 h of heat exposure at 130℃, the yield strength is approximately 495 MPa, with a yield strength decay rate of approximately 4.4%; and under high-temperature tensile testing at 130℃, the tensile strength is 488 MPa, demonstrating excellent long-term thermal stability.

[0044] Example 6

[0045] An Al-6.1Zn-2.9Mg-1.7Cu-0.12Si alloy (composed of the following components by mass percentage: Zn: 6.1%, Mg: 2.9%, Cu: 1.7%, Si: 0.12%, unavoidable impurities ≤ 0.20%, balance Al) is prepared by the following steps:

[0046] (1) According to the alloy composition ratio, under a protective gas atmosphere, commercial pure Al, pure Zn, pure Cu and Al-Si master alloy are heated to 730°C until completely melted; then cooled to 700°C, pure Mg is added, and after melting, the mixture is kept at the temperature for 15 minutes, and then stirred, refined and slag removed to obtain the alloy melt.

[0047] (2) The alloy melt obtained in step (1) is diverted to the water-cooled copper roll gap for sub-rapid solidification casting and rolling. The water-cooled copper roll gap is 6.5 mm, the linear speed of the water-cooled copper roll is 10 m / min, and the temperature of the water-cooled copper roll pre-gating channel is 350℃ to obtain aluminum alloy strip. The aluminum alloy strip is then homogenized: held at 460℃ for 2 h, and hot rolled in 7 passes: held at 250℃ for 15 min before each pass, with a reduction of 20% per pass and a total reduction of 79%. Then, it undergoes a single-stage solution heat treatment: held at 470℃. After 2 hours of quenching and single-stage artificial aging treatment, a high-strength, heat-resistant Al-6.1Zn-3.3Mg-1.7Cu-0.12Si alloy is obtained. The sub-rapid solidification involves a cooling rate of 400 K / s, and the single-stage artificial aging treatment involves holding at 120℃ for 26 hours. The average grain diameter of the obtained aluminum alloy is ~31 μm. The main precipitated phases and their average sizes are: η-type phase: diameter ~1.8 nm, length ~3.5 nm; T-type phase: diameter ~2.5 nm. Compared with existing technologies, the aluminum alloy obtained by this invention has finer and more uniform grain size; the main strengthening phases are also finer and more uniformly distributed.

[0048] The prepared Al-6.1Zn-2.9Mg-1.7Cu-0.12Si alloy has a yield strength of approximately 520 MPa at room temperature; after 500 h of heat exposure at 150 °C, the yield strength is approximately 472 MPa, with a yield strength decay rate of approximately 9.2%; and under high-temperature tensile testing at 150 °C, the tensile strength is 482 MPa, demonstrating excellent long-term thermal stability.

[0049] Comparative Example 1

[0050] Journal title: "Transactions of Nonferrous Metals Society of China", Year: 2009, Pages: 1405-1409, Authors: SHEN Kai et al., Title: "TEM study on microstructures and properties of 7050 aluminum alloy during thermal exposure". Page 1, "Experimental", Paragraph 1: The material used was commercial 7050 aluminum alloy, composed of the following components by mass percentage: Zn: 6.24%, Mg: 2.26%, Cu: 2.32%, Mn: 0.10%, Cr: 0.01%, Zr: 0.1%, Ti: 0.13%, Fe: 0.07%, Si: 0.15%, balance Al. Commercial 7050 aluminum alloy was solution treated at 470℃ for 50 min and at 485℃ for 1.5 h, followed by water quenching, pre-deformation of 1%-3%, pre-aging at 120℃ for 6 h, and then aging at 165℃ for 18 h to obtain the final aluminum alloy. The yield strength of the obtained aluminum alloy was ~490 MPa, and after heating at 150℃ for 500 h, the yield strength was ~329 MPa, with a yield strength attenuation rate of ~32.8%.

[0051] The data above shows that the alloy content used in Comparative Example 1 is not within the scope of protection of the claims of this invention. The contents of Zn and Cu are higher than those of the alloys obtained in all embodiments of this invention. Furthermore, elements not used in this invention—Mn, Cr, Zr, and Ti—were added, and their prices are higher than those added in the alloys of the embodiments. Therefore, the production cost of Comparative Example 1 is higher, and the process and process parameters used are different from those of this invention. According to prior art reports, for Al-Zn-Mg aluminum alloys, the addition of Mn, Cr, Zr, and Ti can refine the grains and improve the high-temperature microstructure and precipitate stability. Based on prior art calculations, the high-temperature performance of the alloy in Comparative Example 1 should be higher than that of this invention. However, the mechanical properties of the alloy in Comparative Example 1 are lower than those of all embodiments of this invention, and its stability under long-term high-temperature storage is also lower than that of the embodiments of this invention. Therefore, compared with the prior art, this invention achieves a significantly improved technical effect.

[0052] In summary, compared with existing technologies, this invention, through the synergistic design of alloy composition, the coupling and synergistic effect of component ratio, process, and process parameters, results in an alloy with finer and more uniformly distributed precipitated strengthening phases than existing technologies. While ensuring high plasticity at room temperature, it yields Al–Zn–Mg alloys with high strength and high thermal stability at both room temperature and high temperatures (the alloys maintain high mechanical properties and thermal stability even after prolonged exposure to high temperatures and retain high strength during high-temperature use). Furthermore, the different component ratios and process parameters used in each embodiment result in different alloy properties and microstructures. This demonstrates that the superior effects obtained by this invention are not determined by a single component, process, or process parameter, but rather by the interaction of components, the synergistic control of component ratio, process, and process parameters. Moreover, only within the scope of protection of the claims of this invention can such significantly improved technical effects be achieved.

Claims

1. A high-strength, thermally stable Al–Zn–Mg aluminum alloy based on casting and rolling, characterized in that: The aluminum alloy is composed of the following components by mass percentage: Zn: 5.4–6.1 wt.%, Mg: 2.9–4.4 wt.%, Cu: 1.5–1.8 wt.%, Si: 0.05–0.25 wt.%, with unavoidable impurities totaling ≤0.20 wt.%, and the balance being Al; the alloy is prepared by batching the components according to the above mass percentages, and the preparation method includes the following steps: (1) Under a protective gas atmosphere, commercial pure Al, pure Zn, pure Cu and Al-Si master alloy are heated to 720–765℃ until completely melted; then cooled to 650–700℃, pure Mg is added, and after melting, the mixture is held for 5–20 min, and then stirred, refined and slag removed to obtain alloy melt. (2) The alloy melt obtained in step (1) is diverted to the water-cooled copper roll gap for sub-rapid solidification casting and rolling, and then subjected to homogenization treatment, multi-pass hot rolling, single-stage solution heat treatment, quenching, and single-stage artificial aging treatment to obtain a high-strength thermally stable Al-Zn-Mg aluminum alloy based on casting and rolling. The water-cooled copper roll gap in step (2) is 1-10mm, the linear speed of the water-cooled copper roll is 3-12m / min, the pre-gating temperature of the water-cooled copper roll is 200-400℃, the sub-rapid solidification casting and rolling is: the sub-rapid solidification cooling rate is 300-500K / s; the homogenization treatment is: holding at 400-500℃ for 1-10h; the multi-pass hot rolling is: 4-8 passes of hot rolling, holding at 200-420℃ for 5-20min before each pass, the reduction per pass is 20-25%, and the total reduction is 60-90%; the single-stage solution heat treatment is: holding at 400-500℃ for 1-5h; the single-stage artificial aging treatment is: holding at 100-160℃ for 10-40h. The main precipitated phases and average sizes of the high-strength thermally stable Al-Zn-Mg aluminum alloy obtained in step (2) based on casting and rolling are as follows: η-type phase: diameter ~1.5-2.3nm, length ~2.4-4.6nm; T-type phase: diameter ~1.6-4.3nm; The aluminum alloy has excellent room temperature and high temperature mechanical properties and high thermal stability: at room temperature, its yield strength is ≥500MPa; after 100-500h of heat exposure at 100℃-150℃, it can maintain a yield strength ≥470MPa and a decay rate ≤10%; under high temperature tensile conditions at 100℃-150℃, the tensile strength is ≥465MPa.

2. The high-strength, thermally stable Al-Zn-Mg aluminum alloy based on casting and rolling according to claim 1, characterized in that: The homogenization process described in step (2) is to keep the temperature at 450–470℃ for 2–3 hours.

3. The high-strength, thermally stable Al-Zn-Mg aluminum alloy based on casting and rolling according to claim 1, characterized in that: The multi-pass hot rolling in step (2) is: 5-7 passes of hot rolling, with each pass held at 250-400℃ for 10-15 minutes before the pass, and the total reduction is 70-85%.

4. The high-strength, thermally stable Al-Zn-Mg aluminum alloy based on casting and rolling according to claim 1, characterized in that: The single-stage solution heat treatment in step (2) is: holding at 420–480℃ for 2–4 hours; the single-stage artificial aging treatment is: holding at 110–150℃ for 14–30 hours.