Low-density high-specific-strength rare earth aluminum alloy and preparation method thereof

Abstract

The invention discloses a low-density high-specific-strength rare earth aluminum alloy and a preparation method thereof, and belongs to the technical field of aluminum alloy materials. The aluminum alloy is prepared from the following components in percentage by mass: 3 to 5 weight percent of Zn, 3 to 6 weight percent of Mg, 0 to 1.5 weight percent of Cu, 0 to 0.2 weight percent of rare earth element, 0.08 to 0.12 weight percent of Mn, 0.03 to 0.05 weight percent of Cr, 0.05 to 0.07 weight percent of Ti and the balance of Al and inevitable impurities. The preparation method comprises the steps of smelting and casting, hot rolling, solid solution heat treatment, quenching, stretching and subsequent aging heat treatment. The Zn / Mg ratio is cooperatively regulated and controlled to reduce the density, rare earth elements and Zr are introduced for microalloying, grains are refined, a nanoscale dispersed phase is formed, an optimized step solid solution and two-stage aging heat treatment process is adopted, the material density is reduced to 2.69 g / cm < 3 > or below (reduced by about 5% compared with a traditional 7xxx system), meanwhile, the tensile strength is kept at 475-505 MPa, the specific strength is excellent, and the service life is long. And meanwhile, the fracture toughness and corrosion resistance are remarkably improved, and the material is suitable for the fields of aerospace, rail transit and the like for material lightweight and has outstanding practicability and industrialization value.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy materials technology, specifically to an aluminum alloy and its preparation process, and particularly to a rare earth Al-Zn-Mg aluminum alloy with low density, high specific strength and high damage tolerance and its preparation method. Background Technology

[0002] High-performance aluminum alloys, especially the 7xxx series (Al-Zn-Mg-Cu) alloys, have long held a crucial position as primary load-bearing structural materials in aerospace due to their excellent specific strength, good machinability, and relatively mature application systems. Traditional 7xxx series aluminum alloys, such as 7075 and 7050, rely heavily on high Zn (5.0~8.0 wt%), Mg (1.8~2.8 wt%), and Cu (1.2~2.0 wt%) contents for their high strength. While the addition of these heavy metals brings significant precipitation strengthening (mainly η'-MgZn2 and η-MgZn2, as well as T-Al2Mg3Zn3), it also results in a relatively high alloy density, typically around 2.83 g / cm³. 3 As aerospace equipment develops towards longer flight time, higher load, and lower energy consumption, the requirements for lightweight structural materials are becoming increasingly stringent. The density of traditional high-zinc aluminum alloys has become a bottleneck restricting their further application.

[0003] To reduce structural weight, researchers both domestically and internationally have explored two main approaches: one is to use lower-density material systems, such as aluminum-lithium alloys, magnesium alloys, or composite materials; the other is to optimize existing high-performance aluminum alloy systems to reduce density. The former often faces challenges such as high cost, complex processes, or anisotropy. The latter offers greater economic and inheritance advantages, but its core challenge lies in the fact that reducing density (primarily by reducing the content of the high-density element Zn) typically leads to a significant loss in alloy strength, especially yield strength. For example, simply reducing the Zn content from 7% to 4% may decrease the tensile strength of the alloy by more than 15%, failing to meet the performance requirements of critical structures.

[0004] In existing technologies, researchers have explored various methods to maintain strength under low-zinc conditions. Patent CN105296823A discloses an Al-Mg-Si alloy containing Sc, which improves performance through Sc grain refinement and dispersion strengthening. However, this alloy belongs to the low-to-medium strength 6xxx series, and its strength level (tensile strength typically below 400 MPa) is significantly lower than that of the high-strength 7xxx series, making it unsuitable as a substitute for the latter in major load-bearing structures. Patent CN101076613A focuses on controlling the internal stress of Al-Zn-Cu-Mg alloys through thermomechanical processes; its composition still falls within the traditional high-zinc category and does not address the issue of density reduction. Patents such as US4618382 and US5939967 also primarily focus on improving the corrosion resistance or process optimization of high-strength aluminum alloys with traditional compositions.

[0005] Existing technologies have also reported improving the properties of aluminum alloys by adding rare earth elements (such as Sc and Er). Rare earth elements can form Al3M-type nanoscale coherent precipitates (such as Al3Sc and Al3Er), effectively pinning dislocations and grain boundaries, inhibiting recrystallization and grain growth, thereby achieving fine-grain strengthening and dispersion strengthening. However, most of these studies are based on improvements to traditional high-zinc compositions, aiming to further enhance strength or improve corrosion resistance and thermal stability. Their approach is "icing on the cake" rather than "weight reduction and efficiency enhancement." Currently, there is a lack of mature and effective technical solutions for systematically applying rare earth microalloying technology to the design of low-zinc Al-Zn-Mg alloys aimed at reducing density, and for collaboratively developing matching heat treatment processes that can balance high strength and high damage tolerance.

[0006] Especially in the pursuit of low density and high specific strength, aerospace structural materials must also possess excellent damage tolerance properties, namely high fracture toughness and resistance to stress corrosion cracking. Traditional high-strength aluminum alloys often present a contradiction between strength and toughness. How to significantly improve the toughness of materials while reducing density and maintaining strength is a more challenging problem. Existing technical solutions often compromise on one aspect while neglecting others, making it difficult to achieve synergistic optimization of multiple performance indicators such as density, strength, and toughness.

[0007] Therefore, there is an urgent need to develop a new aluminum alloy composition system and its supporting preparation process, which can fundamentally solve the contradiction between reducing density and maintaining or even improving comprehensive performance, achieve true "lightweight, high strength and toughness", and meet the urgent needs of next-generation aerospace equipment for advanced structural materials. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of existing technologies, such as the high density of traditional high-zinc 7xxx series aluminum alloys, the excessive strength loss caused by simply reducing the zinc content, and the fact that existing rare earth addition technologies are mostly geared towards traditional components and lack systematic solutions for low-density designs. The present invention provides a low-density, high-specific-strength rare earth aluminum alloy and its preparation method.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a low-density, high-specific-strength rare-earth aluminum alloy, comprising, by mass percentage: Zn 3~5wt%, Mg 3~6wt%, Cu 0~1.5wt%, rare earth elements 0~0.2wt%, Zr 0.07~0.09wt%, Mn 0.08~0.12wt%, Cr 0.03~0.05wt%, Ti 0.05~0.07wt%, with the balance being Al and unavoidable impurities.

[0010] Preferably, the Zn content is 4.0-4.8% by mass percentage, the Mg content is 3.2-4.0%, and the Zn to Mg mass ratio is 1.2-1.5:1.

[0011] Preferably, the rare earth element includes at least one of Sc, Er, La, Pr, and Nd, and the total rare earth element content is ≤0.2wt%.

[0012] This invention also provides a method for preparing a low-density, high-specific-strength rare-earth aluminum alloy, comprising the following steps:

[0013] (1) Melting and casting: According to the component ratio, industrial pure aluminum and intermediate alloy are heated and melted, alloying elements are added in sequence, and after refining, the mixture is allowed to stand and semi-continuously cast to obtain ingots.

[0014] (2) Stepped homogenization treatment: The ingot is heated and held in stages, followed by air cooling;

[0015] (3) Hot rolling: Milling and heat preservation of the homogenized ingot, and hot rolling in multiple passes within the set temperature range to control the total deformation;

[0016] (4) Step solution treatment: A two-stage heating solution treatment process is adopted to heat and hold the hot-rolled plate; after solution treatment, online quenching and cooling are performed immediately.

[0017] (5) Pre-stretching: Applying a permanent stretch of a set deformation to the quenched plate;

[0018] (6) Two-stage aging treatment: The two-stage aging system of "low temperature + high temperature" is adopted to age the pre-stretched board and then cool it in the furnace to obtain the finished product.

[0019] Preferably, in step (1), the melting temperature is 740~760℃ and the refining temperature is 720~740℃.

[0020] Preferably, in step (2), the step homogenization treatment parameters are: heating to 400℃ at a rate of 50℃ per hour and holding for 4~6h, then heating to 450℃ and holding for 18~22h, and finally heating to 470℃ and holding for 10~14h.

[0021] Preferably, in step (4), the step solution treatment parameters are: heating to 470°C at a rate of ≤50°C per hour and holding for 0.5~2h, and then heating to 480°C at a rate of ≤30°C per hour and holding for 0.1~1.5h.

[0022] Preferably, in step (5), the amount of permanent tensile deformation applied is 1.2~1.8%.

[0023] Preferably, in step (6), the first aging temperature is 121±2℃ and the heat preservation time is 4~6 hours; the second aging temperature is 174±2℃ and the heat preservation time is 15~20 hours.

[0024] Compared with the prior art, the technical advantages of the present invention are as follows:

[0025] 1. Significant weight reduction was achieved, with a density reduction of approximately 5%.

[0026] This invention significantly reduces the Zn content from 5.0-8.0% in the traditional 7xxx series alloys to 3.0-5.0% by precisely controlling the main alloying elements, while appropriately increasing the content of the lighter Mg element to 3.0-6.0%, and strictly controlling the amount of Cu added. This compositional design reduces the theoretical density of the alloy from the source. According to the test data of the examples, the measured density of the alloy of this invention is stable at 2.68-2.69 g / cm³. 3 Within the specified range, the density of Comparative Example 1 (simulating traditional 7xxx composition) is 2.83 g / cm³. 3 This means that the present invention has successfully achieved a weight reduction of approximately 5%. For large aerospace structural components, the resulting improvement in fuel economy and increased payload from this weight reduction is extremely significant. This effect was achieved without sacrificing other performance aspects; rather, it was compensated for the strength loss caused by zinc reduction through subsequent microalloying and process innovation, demonstrating the advantages of the systematic design of this invention.

[0027] 2. It maintained an excellent high strength level, with the strength reduction controlled within 10%.

[0028] The most direct consequence of reducing Zn content is a decrease in the amount of the η' phase (MgZn2), which is the main strengthening phase, leading to a decrease in strength. This invention innovatively solves this problem by introducing rare earth elements and Zr microalloying elements. Taking the rare earth element Sc as an example, Sc and Zr form nanoscale, coherent Al3(Sc, Zr) particles during homogenization and subsequent heat treatment. These particles have a dual function: First, as strong grain boundary pinning particles, they effectively inhibit recrystallization and grain growth during hot working and heat treatment, resulting in a fine grain structure. According to the Hall-Petch relationship, grain refinement directly contributes to strength (fine-grain strengthening). Second, Al3(Sc, Zr) particles themselves are highly thermally stable dispersed phases that effectively hinder dislocation movement, providing a significant dispersion strengthening effect. The strengthening contributions of these two factors partially offset the precipitation strengthening reduced by reducing zinc content. As shown in Examples 1 and 2, while the density was reduced by 5%, the tensile strength (485~505MPa) was only reduced by 4.7%~8.5% compared with the conventional alloy of Comparative Example 1 (530MPa), which was far lower than the expected 15% or more, and the strength was successfully maintained at a high level.

[0029] 3. Significantly improved damage tolerance performance, achieving a good match between toughening and reinforcement.

[0030] Traditional high-strength aluminum alloys often exhibit high strength but relatively insufficient toughness. This invention not only maintains high strength but also unexpectedly improves the material's damage tolerance properties, including fracture toughness and ductility. Example data shows that the fracture toughness K of the alloy of this invention... IC The strength reached 35.0-38.5 MPa·√m, and the elongation was 11.0-13.5%, both significantly better than Comparative Example 1 (K). IC (28 MPa·√m, elongation: 8%) and Comparative Example 3 (high zinc content, rare earth element, K) IC (26.5 MPa·√m, elongation: 7.5%). This effect is achieved through the synergistic effect of multiple factors. Firstly, the refined grain structure increases the crack propagation path, consuming more energy. Secondly, the addition of rare earth elements and Zr refines the precipitated phase, reducing the formation of coarse and brittle phases. Thirdly, the two-stage aging process used in this invention precisely controls the precipitation sequence and size distribution of the strengthening phase. The low-temperature stage forms high-density, fine GP regions, contributing to strength. Subsequent high-temperature aging transforms some GP regions into slightly larger, more uniformly distributed η' phases, appropriately coarsening them and reducing the coherent strain field. While sacrificing a small amount of strength, this significantly alleviates grain boundary stress concentration and improves grain boundary strength, thereby dramatically improving the material's plasticity and toughness. This characteristic of "moderate strength and outstanding toughness" is crucial for improving the safety and reliability of structural components.

[0031] 4. Optimized step solution treatment and pre-stretching processes ensure uniform microstructure and low residual stress.

[0032] The stepped solution treatment process (470℃ + 480℃) employed in this invention has significant advantages over traditional single-stage solution treatment. Firstly, holding at a lower temperature (470℃) allows for the complete dissolution of soluble strengthening phases (Zn, Mg) while preventing overheating of any low-melting-point eutectic phases that may be present in the alloy. Subsequently, the temperature is increased to a higher temperature (480℃) to further promote the dissolution of insoluble phases and obtain a more supersaturated and homogeneous solid solution, providing optimal solute atom concentration and distribution for subsequent aging. The pre-stretching process (1.2~1.8% deformation) is a crucial step in eliminating residual quenching stress. The difference in cooling rates between the surface and core of the sheet during quenching leads to harmful macroscopic internal stresses. Applying precisely controlled plastic deformation can offset these internal stresses, significantly reducing the susceptibility to subsequent machining deformation and stress corrosion cracking. Comparative Example 2 (using conventional single-stage solution treatment and aging) showed comprehensive performance degradation, particularly a decrease in toughness, demonstrating the indispensable role of the optimized heat treatment process in achieving the final comprehensive performance.

[0033] 5. The synergistic design of ingredients and processes results in technical effects that are not immediately apparent but possess industrial applicability.

[0034] The innovation of this invention lies in the systematic and integrated synergistic design of "low-zinc density reduction design," "rare earth elements and Zr microalloying," and the optimized heat treatment process of "stepped solution treatment + two-stage aging + pre-stretching." Comparative Example 3 shows that simply adding rare earth elements without reducing the zinc content cannot achieve effective weight reduction (the density still reaches 2.81 g / cm³). 3 Furthermore, the improvement in toughness is limited. Comparative Example 2 shows that even with only low zinc and rare earth components, without optimized heat treatment, the performance cannot be fully realized. This demonstrates a close synergistic effect among the technical features of this invention. The resulting comprehensive superior performance of "low density, high specific strength, and high damage tolerance" is not a simple superposition of known methods, but rather produces an unexpected technical effect of "1+1>2". In addition, the raw materials used in this invention are all industrially common pure metals or intermediate alloys, and the smelting, casting, rolling, and heat treatment processes involved are all mature processes in the aluminum alloy industry. Only specific parameters have been innovatively optimized. Therefore, it has good process inheritance and industrialization prospects, and can meet the mass and stable production needs of high-performance lightweight materials in fields such as aerospace. Attached Figure Description

[0035] Figure 1 This is a complete process flow diagram of the preparation of the low-density, high-specific-strength rare-earth aluminum alloy sheet of the present invention;

[0036] Figure 2This is a schematic diagram comparing the alloy densities of the examples and comparative examples;

[0037] Figure 3 This is a schematic diagram comparing the room temperature tensile strength of the alloys in the examples and comparative examples;

[0038] Figure 4 This is a schematic diagram comparing the specific strength of the alloys in the examples and the comparative examples;

[0039] Figure 5 This is a single-factor experimental curve showing the effect of the second-stage solution temperature on the alloy properties;

[0040] Figure 6 This is a single-factor experimental curve showing the effect of the second-stage solid solution time on the alloy properties;

[0041] Figure 7 This is a single-factor experimental curve showing the effect of low-temperature aging temperature on the alloy properties;

[0042] Figure 8 This is a single-factor experimental curve showing the effect of high-temperature aging time on the alloy properties;

[0043] Figure 9 This is a single-factor experimental curve showing the effect of pre-stretch deformation on alloy properties. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0045] The core design concept of the low-density, high-specific-strength rare-earth aluminum alloy of this invention is to achieve lightweight by reducing the content of high-density element Zn, while introducing rare-earth elements to form a nano-reinforcing phase to compensate for strength loss, and carefully designing a set of matching thermomechanical treatment processes to synergistically regulate the microstructure of the alloy, ultimately achieving a balance between high strength and high damage tolerance under the premise of low density.

[0046] like Figure 1 In this embodiment of the invention, the preparation method of the low-density, high-specific-strength rare-earth aluminum alloy includes the following steps:

[0047] (1) Melting and casting: According to the component ratio, industrial pure aluminum and intermediate alloy are heated to 740~760℃ for melting, alloying elements are added in sequence, the melt is refined and degassed at 720~740℃, and after refining, it is allowed to stand and semi-continuously cast to obtain ingots.

[0048] (2) Step-by-step homogenization treatment: The ingot is heated to 400°C at a rate of 50°C per hour and held for 4-6 hours; then heated to 450°C and held for 18-22 hours; finally heated to 470°C and held for 10-14 hours, followed by air cooling.

[0049] (3) Hot rolling: Milling and heat preservation of the homogenized ingot, and hot rolling in multiple passes within the set temperature range to control the total deformation;

[0050] (4) Step solution treatment: A two-stage heating solution treatment process is adopted. The temperature is raised to 470°C at a heating rate of no more than 50°C / hour and held at this temperature for 0.5~2h; then the temperature is raised to 480°C at a heating rate of no more than 30°C / hour and held at this temperature for 0.1~1.5h; after the solution treatment, online quenching and cooling are performed immediately.

[0051] (5) Pre-stretching: Applying a permanent stretch of 1.2 to 1.8% deformation to the quenched plate;

[0052] (6) Two-stage aging treatment: The two-stage aging system of "low temperature + high temperature" is adopted. The first stage aging temperature is 121±2℃ and the heat preservation time is 4~6 hours; the second stage aging temperature is 174±2℃ and the heat preservation time is 15~20 hours; the pre-stretched board is subjected to aging treatment and cooled in the furnace to obtain the finished product.

[0053] Technical principle of the invention:

[0054] This invention breaks through the technical bottleneck of "the balance between low density and high strength, and the contradiction between strength and toughness" in traditional 7xxx series aluminum alloys through an integrated design of precise raw material composition and synergistic optimization of process parameters. Its technical principle revolves around the role of raw materials, the necessity of process optimization, and technical effects.

[0055] I. Functions and Synergistic Mechanisms of Each Raw Material Component

[0056] The raw material ratio of this invention is not a simple addition of elements, but rather a synergistic combination of main elements, rare earth elements, and auxiliary elements to establish the core foundation of "low density, high strength, and stable structure." The functions of each component are as follows:

[0057] 1. Main elements (Zn, Mg): The core carriers of lightweight and strengthening phases

[0058] (1) Zn element: Zn is a high-density element (7.14 g / cm³). 3The high Zn content (5.0~8.0 wt%) in traditional 7xxx series aluminum alloys is a key reason for their high density. This invention precisely controls the Zn content to 3.0~5.0 wt%, reducing the alloy density from the source; at the same time, it retains an appropriate amount of Zn to form the η' phase (MgZn2 precursor phase) with Mg, providing a core basis for precipitation strengthening and avoiding the loss of strengthening phase due to excessive Zn reduction.

[0059] (2) Mg element: Mg is a light element (1.74 g / cm³). 3 The content of Mg is controlled to 3.0~6.0wt%. On the one hand, it works with Zn to reduce the overall density of the alloy, and on the other hand, it forms a stable η' strengthening phase with Zn. Furthermore, by optimizing the Zn / Mg mass ratio to 1.2~1.5:1, it ensures that the η' phase precipitates in sufficient quantity and does not form coarse and brittle phases (such as Al2Mg3Zn3), thus achieving a balance between "lightweighting" and "precipitation strengthening".

[0060] 2. Rare Earth Elements: Key to Strengthening and Toughness Enhancement

[0061] The combined effect of Sc and Zr: When added precisely at 0.07~0.09wt%, they form a nanoscale, coherent, and thermally stable Al3(Sc, Zr) intermetallic compound during melting and homogenization, playing a dual core role: ① Grain refinement strengthening: Pinning grain boundaries, inhibiting recrystallization and grain growth during hot working and heat treatment, improving strength according to the Hall-Petch relationship, and increasing crack propagation paths to optimize toughness; ② Dispersion strengthening: Hindering dislocation movement, compensating for the strength loss caused by the reduction in the number of η' phases after Zn reduction, without impairing plasticity.

[0062] 3. Trace auxiliary elements (Cu, Mn, Cr, Ti): regulators of microstructure and properties.

[0063] (1) Cu (0~1.5wt%): promotes the precipitation and stabilization of η' phase, enhances precipitation strengthening effect, and improves the stress corrosion resistance of alloy.

[0064] (2) Mn (0.08~0.12wt%), Cr (0.03~0.05wt%): form Al6Mn and Al7Cr dispersed phases, which help to inhibit recrystallization, refine grains, and improve the stability of the structure.

[0065] (3) Ti (0.05~0.07wt%): as a grain refiner for casting, it reduces ingot defects and improves ingot quality and subsequent processing formability.

[0066] The raw material components work closely together: low Zn and high Mg lay the foundation for lightweighting, Sc / Zr composite reinforcement compensates for strength loss, and auxiliary elements optimize microstructure stability, together constructing a "low-density, strengthenable, and stable microstructure" component system, providing a prerequisite for subsequent process control.

[0067] II. Necessity and Importance of Process Parameter Optimization

[0068] The process parameters of this invention are not conventional adjustments, but rather precise control schemes designed for specific component systems. Each process optimization step is key to activating the potential of components and avoiding performance defects. Its necessity and importance are reflected in the following aspects:

[0069] 1. Stepped homogenization treatment (400℃ / 4~6h→450℃ / 18~22h→470℃ / 10~14h)

[0070] Traditional single-stage homogenization easily leads to "incomplete elimination of compositional segregation" or "coarsening of Al3(Sc, Zr) particles." The core necessity of the stepped heating system in this invention is: ① to slowly eliminate casting segregation in the low-temperature stage (400℃) to avoid local overheating caused by subsequent high-temperature heating; ② to promote the full diffusion of Sc and Zr in the medium-high temperature stage (450~470℃), precipitating uniformly distributed nano-Al3(Sc, Zr) particles, providing a uniform matrix for subsequent processing and heat treatment. If the parameters deviate (such as insufficient holding time), it will lead to segregation residue and uneven particle distribution, directly affecting the subsequent strengthening effect.

[0071] 2. Step solution treatment (470℃ / 0.5~2h→480℃ / 0.1~1.5h, heating rate ≤50℃ / h, ≤30℃ / h)

[0072] Low-Zn, high-Mg systems are sensitive to solution temperature, and single-stage solution treatment is prone to "insufficient dissolution of the strengthening phase" or "over-burning of grain boundaries." Optimization is necessary because: ① The first-stage low-temperature solution treatment (470℃) ensures sufficient dissolution of Zn, Mg, and Cu while avoiding over-burning of the low-melting-point eutectic phase; ② The second stage involves a slow heating to 480℃ to increase the supersaturation of the solid solution, laying the foundation for the precipitation of a high-density strengthening phase during aging; ③ Precise control of the holding time and heating rate avoids grain growth that weakens performance. If the temperature exceeds 480℃ ± 2℃, grain boundary weakening will occur, resulting in a simultaneous decrease in strength and toughness.

[0073] 3. Pre-stretching treatment (deformation 1.2~1.8%)

[0074] After quenching, the sheet metal exhibits macroscopic residual stress, which can easily lead to machining deformation or stress corrosion cracking. The necessity of this process lies in: ① eliminating residual stress and reducing stress corrosion sensitivity; ② introducing dislocations as nucleation sites for age-induced precipitation, promoting the uniform distribution of the η' phase. If the deformation is insufficient (<1.2%), the stress elimination will be incomplete; if it is excessive (>1.8%), work hardening will cause a sharp decrease in plasticity, impairing the damage tolerance.

[0075] 4. Two-stage aging treatment (121±2℃ / 4~6h→174±2℃ / 15~20h)

[0076] Traditional single-stage aging cannot balance strength and toughness. The necessity of optimization lies in: ① The low-temperature stage induces the formation of high-density fine GP regions, laying the foundation for strength. Temperature deviations from 121℃ will lead to insufficient precipitation or premature coarsening of GP regions; ② The high-temperature stage transforms the GP regions into η' phases of suitable size. An aging time of 15~20h allows the precipitated phase to reach a state of "optimal strengthening effect and minimal toughness loss". If the aging time exceeds 20h, the strength will decrease due to Ostwald curing, and if the aging time is less than 15h, the strengthening will be insufficient.

[0077] The present invention will be further illustrated below through specific embodiments and comparative examples.

[0078] Example 1

[0079] This embodiment aims to illustrate the typical composition and complete preparation process of the alloy of the present invention, including the following steps:

[0080] (1) Alloy composition (mass percentage, wt%): Zn: 4.5, Mg: 3.5, Cu: 0.75, Zr: 0.08, Sc: 0.08, Mn: 0.10, Cr: 0.04, Ti: 0.06, with the balance being Al and unavoidable impurities, and the Zn / Mg ratio being 1.29.

[0081] (2) Preparation process:

[0082] S1: Melting and Casting: Using a resistance crucible furnace, industrial pure aluminum ingots are heated to 750℃ and melted. Al-Zr, Al-Sc, Al-Cu, Al-Mn, and Al-Cr master alloys are added sequentially, stirring thoroughly until dissolved. Then, pure zinc ingots and Al-Mg master alloys are added, followed by Al-Ti master alloys. After complete melting, the mixture is refined and degassed at 730℃, allowed to stand for 15 minutes, and then semi-continuously cast.

[0083] S2: Homogenization treatment: Place the ingot in an air-circulating furnace, heat it to 400℃ at 50℃ / h, and hold it for 5 hours; then heat it to 450℃ and hold it for 20 hours; finally heat it to 470℃ and hold it for 12 hours, and then remove it from the furnace and air cool it.

[0084] S3: Hot rolling: Mill off approximately 5mm of oxide scale from both sides of the homogenized ingot. Hold at 420℃ for 2 hours in a box furnace, and then perform multiple rolling passes on a reversible hot rolling mill at a temperature range of 380~420℃. The total rolling deformation must be ≥77%.

[0085] S4: Solution treatment: Using a roller hearth quenching furnace, place the plate inside the furnace and heat it to 470℃ at ≤50℃ / h, and hold it for 2 hours; then heat it to 480℃ at ≤30℃ / h, and hold it for 1 hour; after holding, quickly drop it into a room temperature water bath for quenching.

[0086] S5: Pre-stretching: Applying 1.5% permanent plastic deformation along the rolling direction to quenched sheet metal on a universal testing machine.

[0087] S6: Aging treatment: Using an integral aging furnace, place the board inside the furnace and heat it to 121℃ at ≤100℃ / h, and hold it for 5 hours; then heat it to 174℃ at ≤20℃ / h, and hold it for 15 hours; after the holding period, cool it to room temperature with the furnace before removing it from the furnace.

[0088] (3) Performance testing: Samples of the treated board were taken and tested for density, room temperature tensile properties, fracture toughness, etc. The results are shown in Table 1.

[0089]

[0090] Example 2

[0091] This example aims to demonstrate how to adjust the content of the main element and explore the component window, including the following steps:

[0092] (1) Alloy composition (mass percentage, wt%): Zn: 5.0, Mg: 3.5, Cu: 0.75, Zr: 0.08, Sc: 0.08, Mn: 0.10, Cr: 0.04, Ti: 0.06, with the balance being Al and unavoidable impurities, and the Zn / Mg ratio being 1.43.

[0093] (2) Preparation process:

[0094] S1: Melting and Casting: Using a resistance crucible furnace, industrial pure aluminum ingots are heated to 750℃ and melted. Al-Zr, Al-Sc, Al-Cu, Al-Mn, and Al-Cr master alloys are added sequentially, stirring thoroughly until dissolved. Then, pure zinc ingots and Al-Mg master alloys are added, followed by Al-Ti master alloys. After complete melting, the mixture is refined and degassed at 730℃, allowed to stand for 15 minutes, and then semi-continuously cast.

[0095] S2: Homogenization treatment: Place the ingot in an air-circulating furnace, heat it to 400℃ at 50℃ / h, and hold it for 5 hours; then heat it to 450℃ and hold it for 20 hours; finally heat it to 470℃ and hold it for 12 hours, and then remove it from the furnace and air cool it.

[0096] S3: Hot rolling: Mill off approximately 5mm of oxide scale from both sides of the homogenized ingot. Hold at 420℃ for 2 hours in a box furnace, and then perform multiple rolling passes on a reversible hot rolling mill at a temperature range of 380~420℃. The total rolling deformation must be ≥77%.

[0097] S4: Solution treatment: Using a roller hearth quenching furnace, place the plate inside the furnace and heat it to 470℃ at ≤50℃ / h, and hold it for 2 hours; then heat it to 480℃ at ≤30℃ / h, and hold it for 1 hour; after holding, quickly drop it into a room temperature water bath for quenching.

[0098] S5: Pre-stretching: Applying 1.5% permanent plastic deformation along the rolling direction to quenched sheet metal on a universal testing machine.

[0099] S6: Aging treatment: Using an integral aging furnace, place the board inside the furnace and heat it to 121℃ at ≤100℃ / h, and hold it for 5 hours; then heat it to 174℃ at ≤20℃ / h, and hold it for 15 hours; after the holding period, cool it to room temperature with the furnace before removing it from the furnace.

[0100] (3) The performance test results are shown in Table 2.

[0101]

[0102] Example 3

[0103] This embodiment aims to demonstrate the impact of optimizing aging regimes on performance (especially resilience), including the following steps:

[0104] (1) Alloy composition (mass percentage, wt%): Zn: 4.5, Mg: 3.5, Cu: 0.75, Zr: 0.08, Sc: 0.08, Mn: 0.10, Cr: 0.04, Ti: 0.06, with the balance being Al and unavoidable impurities, and the Zn / Mg ratio being 1.29.

[0105] (2) Preparation process:

[0106] S1: Melting and Casting: Using a resistance crucible furnace, industrial pure aluminum ingots are heated to 750℃ and melted. Al-Zr, Al-Sc, Al-Cu, Al-Mn, and Al-Cr master alloys are added sequentially, stirring thoroughly until dissolved. Then, pure zinc ingots and Al-Mg master alloys are added, followed by Al-Ti master alloys. After complete melting, the mixture is refined and degassed at 730℃, allowed to stand for 15 minutes, and then semi-continuously cast.

[0107] S2: Homogenization treatment: Place the ingot in an air-circulating furnace, heat it to 400℃ at 50℃ / h, and hold it for 5 hours; then heat it to 450℃ and hold it for 20 hours; finally heat it to 470℃ and hold it for 12 hours, and then remove it from the furnace and air cool it.

[0108] S3: Hot rolling: Mill off approximately 5mm of oxide scale from both sides of the homogenized ingot. Hold at 420℃ for 2 hours in a box furnace, and then perform multiple rolling passes on a reversible hot rolling mill at a temperature range of 380~420℃. The total rolling deformation must be ≥77%.

[0109] S4: Solution treatment: Using a roller hearth quenching furnace, place the plate inside the furnace and heat it to 470℃ at ≤50℃ / h, and hold it for 0.5~2 hours; then heat it to 480℃ at ≤30℃ / h, and hold it for 0.1~1 hours; after holding, quickly drop it into a room temperature water bath for quenching.

[0110] S5: Pre-stretching: Applying 1.5% permanent plastic deformation along the rolling direction to quenched sheet metal on a universal testing machine.

[0111] S6: Aging treatment: Using an integral aging furnace, place the board inside the furnace and heat it to 121℃ at a rate of ≤100℃ / h, and hold it for 5 hours; then heat it to 174℃ at a rate of ≤20℃ / h, and hold it for 20 hours; after the holding period, cool it to room temperature with the furnace before removing it from the furnace.

[0112] (3) The performance test results are shown in Table 3.

[0113]

[0114] Comparative Example 1 (Traditional high-zinc, rare-earth-free)

[0115] This comparative example simulates the composition and conventional processes of traditional 7xxx series high-strength aluminum alloys as a benchmark comparison, and includes the following steps:

[0116] (1) Alloy composition (mass percentage, wt%): Zn: 7.0, Mg: 2.2, Cu: 1.6, Mn: 0.10, Cr: 0.04, Ti: 0.06, without adding Zr, Sc and other elements, the balance is Al and unavoidable impurities.

[0117] (2) Preparation process:

[0118] S1: Melting and Casting: Using a resistance crucible furnace, industrial pure aluminum ingots are heated to 750℃ and melted. Al-Zr, Al-Sc, Al-Cu, Al-Mn, and Al-Cr master alloys are added sequentially, stirring thoroughly until dissolved. Then, pure zinc ingots and Al-Mg master alloys are added, followed by Al-Ti master alloys. After complete melting, the mixture is refined and degassed at 730℃, allowed to stand for 15 minutes, and then semi-continuously cast.

[0119] S2: Homogenization treatment: Place the ingot in an air-circulating furnace, heat it to 400℃ at 50℃ / h, and hold it for 5 hours; then heat it to 450℃ and hold it for 20 hours; finally heat it to 470℃ and hold it for 12 hours, and then remove it from the furnace and air cool it.

[0120] S3: Hot rolling: Mill off approximately 5mm of oxide scale from both sides of the homogenized ingot. Hold at 420℃ for 2 hours in a box furnace, and then perform multiple rolling passes on a reversible hot rolling mill at a temperature range of 380~420℃. The total rolling deformation must be ≥77%.

[0121] S4: Solution treatment: Use a roller hearth quenching furnace, place the plate inside the furnace, heat to 480℃ at ≤50℃ / h, hold for 2 hours, and after holding, quickly drop into a room temperature water bath for quenching.

[0122] S5: Pre-stretching: Applying 1.5% permanent plastic deformation along the rolling direction to the quenched sheet metal on a universal testing machine. After pre-stretching, a single-stage aging regime is adopted: 120℃ / 24h.

[0123] S6: Aging treatment: Use an integral aging furnace, place the board inside the furnace, heat to 120℃ at ≤100℃ / h, hold for 24 hours, and after holding, cool to room temperature with the furnace before taking it out of the furnace.

[0124] (3) The performance test results are shown in Table 4.

[0125]

[0126] Comparative Example 2 (Components of this invention, treated with conventional heat treatment)

[0127] This comparative example aims to illustrate the impact of not employing the optimized heat treatment process of this invention, including the following steps.

[0128] (1) Alloy composition (mass percentage, wt%): Zn: 4.5, Mg: 3.5, Cu: 0.75, Zr: 0.08, Sc: 0.08, Mn: 0.10, Cr: 0.04, Ti: 0.06, with the balance being Al and unavoidable impurities.

[0129] (2) Preparation process:

[0130] S1: Melting and Casting: Using a resistance crucible furnace, industrial pure aluminum ingots are heated to 750℃ and melted. Al-Zr, Al-Sc, Al-Cu, Al-Mn, and Al-Cr master alloys are added sequentially, stirring thoroughly until dissolved. Then, pure zinc ingots and Al-Mg master alloys are added, followed by Al-Ti master alloys. After complete melting, the mixture is refined and degassed at 730℃, allowed to stand for 15 minutes, and then semi-continuously cast.

[0131] S2: Homogenization treatment: Place the ingot in an air-circulating furnace, heat it to 400℃ at 50℃ / h, and hold it for 5 hours; then heat it to 450℃ and hold it for 20 hours; finally heat it to 470℃ and hold it for 12 hours, and then remove it from the furnace and air cool it.

[0132] S3: Hot rolling: Mill off approximately 5mm of oxide scale from both sides of the homogenized ingot. Hold at 420℃ for 2 hours in a box furnace, and then perform multiple rolling passes on a reversible hot rolling mill at a temperature range of 380~420℃. The total rolling deformation must be ≥77%.

[0133] S4: Solution treatment: Use a roller hearth quenching furnace, place the plate inside the furnace, heat to 470℃ at ≤50℃ / h, hold for 2 hours, and after holding, quickly drop into a room temperature water bath for quenching.

[0134] S5: Pre-stretching: Applying 1.5% permanent plastic deformation along the rolling direction to quenched sheet metal on a universal testing machine.

[0135] S6: Aging treatment: Use an integral aging furnace, place the board inside the furnace, heat to 120℃ at ≤100℃ / h, hold for 24 hours, and after holding, cool to room temperature with the furnace before taking it out of the furnace.

[0136] (3) The performance test results are shown in Table 5.

[0137]

[0138] Comparative Example 3 (High zinc content with rare earth elements, using the process of this invention)

[0139] This comparative example aims to illustrate the effect of adding only rare earth elements without reducing zinc content, including the following steps.

[0140] (1) Alloy composition (mass percentage, wt%): Zn: 6.5, Mg: 2.5, Cu: 1.2, Zr: 0.08, Sc: 0.10, Mn: 0.10, Cr: 0.04, Ti: 0.06, with the balance being Al and unavoidable impurities.

[0141] (2) Preparation process:

[0142] S1: Melting and Casting: Using a resistance crucible furnace, industrial pure aluminum ingots are heated to 750℃ and melted. Al-Zr, Al-Sc, Al-Cu, Al-Mn, and Al-Cr master alloys are added sequentially, stirring thoroughly until dissolved. Then, pure zinc ingots and Al-Mg master alloys are added, followed by Al-Ti master alloys. After complete melting, the mixture is refined and degassed at 730℃, allowed to stand for 15 minutes, and then semi-continuously cast.

[0143] S2: Homogenization treatment: Place the ingot in an air-circulating furnace, heat it to 400℃ at 50℃ / h, and hold it for 5 hours; then heat it to 450℃ and hold it for 20 hours; finally heat it to 470℃ and hold it for 12 hours, and then remove it from the furnace and air cool it.

[0144] S3: Hot rolling: Mill off approximately 5mm of oxide scale from both sides of the homogenized ingot. Hold at 420℃ for 2 hours in a box furnace, and then perform multiple rolling passes on a reversible hot rolling mill at a temperature range of 380~420℃. The total rolling deformation must be ≥77%.

[0145] S4: Solution treatment: Using a roller hearth quenching furnace, place the plate inside the furnace and heat it to 470℃ at ≤50℃ / h, and hold it for 2 hours; then heat it to 480℃ at ≤30℃ / h, and hold it for 1 hour; after holding, quickly drop it into a room temperature water bath for quenching.

[0146] S5: Pre-stretching: Applying 1.5% permanent plastic deformation along the rolling direction to quenched sheet metal on a universal testing machine.

[0147] S6: Aging treatment: Using an integral aging furnace, place the board inside the furnace and heat it to 121℃ at ≤100℃ / h, and hold it for 5 hours; then heat it to 174℃ at ≤20℃ / h, and hold it for 15 hours; after the holding period, cool it to room temperature with the furnace before removing it from the furnace.

[0148] (3) The performance test results are shown in Table 6.

[0149]

[0150] Performance data comparison and analysis:

[0151] To more intuitively compare the performance of the embodiments of the present invention with that of the comparative examples, the following schematic diagrams are provided: Figure 2 This is a comparison chart of the alloy densities of the examples and comparative examples. Figure 3 This is a comparison chart of the room temperature tensile strength of the alloys in the examples and comparative examples. Figure 4 These figures show a comparison of the strength of the alloys in the examples and comparative examples. These figures clearly demonstrate the significant advantages of the present invention in terms of lightweighting, strength retention, and load-bearing capacity per unit weight.

[0152] The key performance indicators of the above embodiments and comparative examples are summarized and compiled into Table 7; based on the data in Table 7, an analysis is conducted from the dimensions of density, strength, plasticity, and toughness.

[0153]

[0154] Note: Specific strength = tensile strength / density.

[0155] Performance comparison analysis:

[0156] 1. Significant advantages of low density and lightweight

[0157] As shown in Table 7, the alloy densities of Examples 1-3 are consistently between 2.68 and 2.69 g / cm³. 3 The range, compared to Comparative Example 1 (2.83 g / cm³), is [missing information]. 3 ) and Comparative Example 3 (2.81 g / cm) 3 The density reduction reaches approximately 5%, achieving a significant weight reduction effect. This advantage stems from the low Zn content design employed in this invention, which avoids the density increase problem caused by element enrichment in high-zinc alloys, making it more suitable for fields with stringent weight reduction requirements, such as aerospace and rail transportation.

[0158] 2. Its specific strength is comparable to that of traditional high-zinc alloys, exhibiting excellent strength-weight ratio.

[0159] As can be seen from the data in Table 7, although the absolute tensile strength (475~505 MPa) of Examples 1~3 is slightly lower than that of the high-zinc formulations (525~530 MPa) of Comparative Examples 1 and 3, the decrease is controlled within 10%; and through the compensating effect of low density, the specific strength of Example 2 reaches 187.73 MPa·cm. 3 / g, compared with Comparative Example 1 (187.28 MPa·cm 3 The pressure ( / g) was basically the same, slightly higher than that of Comparative Example 3 (186.83 MPa·cm). 3 / g). This result proves that the alloy of the present invention achieves lightweighting while maintaining a load-bearing capacity per unit weight comparable to that of traditional high-zinc alloys, thus solving the technical pain point of "weight reduction without efficiency reduction".

[0160] 3. Significant improvements have been made in damage tolerance and plasticity, resulting in outstanding overall performance advantages.

[0161] Table 7 shows that the elongation (11.0%~13.5%) and fracture toughness (35.0~38.5 MPa·√m) of all embodiments are higher than those of the comparative examples: compared with comparative example 1 (elongation 8.0%, fracture toughness 28 MPa·√m), the elongation is increased by 37.5%~68.8%, and the fracture toughness is increased by 25.0%~37.5%; compared with comparative example 3 (elongation 7.5%, fracture toughness 26.5 MPa·√m), the performance improvement is more significant. Excellent elongation and fracture toughness mean that the alloy has stronger resistance to crack propagation and plastic deformation, and is less prone to brittle fracture during service, significantly improving safety and reliability.

[0162] 4. The synergistic verification of technical features highlights the non-obviousness of the invention.

[0163] (1) Synergistic effect of composition and process: Comparative Example 2 in Table 7 uses the same composition as Example 1, but because the "step solution + double-stage aging" process of the present invention was not used, its core properties such as tensile strength, elongation and fracture toughness were comprehensively deteriorated (tensile strength decreased by 7.2% and fracture toughness decreased by 16.4%), and the exfoliation corrosion level deteriorated from EA to EC, proving that optimizing the heat treatment system is the key factor to ensure the high performance of the alloy of the present invention.

[0164] (2) Synergistic effect of low Zn and rare earth microalloying: Comparative Example 3, while adding Zr and Sc rare earth elements, still adopted a high Zn content design. As shown in Table 7, it not only failed to reduce density, but also caused deterioration in plasticity and toughness due to the formation of coarse and brittle phases. The elongation and fracture toughness were the lowest among all groups. This result indicates that rare earth microalloying alone cannot achieve the effect of "low density + high damage tolerance". It must be combined with a low Zn content design, and neither can be dispensed with.

[0165] To determine the optimal range of key process parameters in the preparation method described in this invention, a series of single-factor experiments were conducted based on the alloy composition of Example 1 (Zn: 4.5, Mg: 3.5, Cu: 0.75, Zr: 0.08, Sc: 0.08, Mn: 0.10, Cr: 0.04, Ti: 0.06, with the balance being Al and unavoidable impurities). All other process conditions were kept constant, and only one target parameter was systematically changed to investigate its effect on the room temperature tensile properties (tensile strength and elongation) of the alloy. The results are as follows.

[0166] 1. The effect of the second-stage solution treatment temperature

[0167] The first-stage solution treatment was fixed at 470℃ / 2h. The second-stage solution treatment temperatures (T2) were adjusted to 470℃ (i.e., single-stage solution treatment), 475℃, 480℃, 485℃, and 490℃, followed by standard quenching, pre-stretching, and two-stage aging (121℃ / 5h + 174℃ / 15h). Figure 5 As shown, when T2 is below 480℃, the strengthening phase does not dissolve sufficiently, resulting in low alloy strength. When the temperature exceeds 480℃, both tensile strength and elongation decrease significantly. This is because the low-melting-point eutectic phase (such as AlZnMgCu phase) at the grain boundaries undergoes overheating, leading to grain boundary weakening. Therefore, the optimized range for the second-stage solution treatment temperature is 480±2℃.

[0168] 2. Effect of Second-Stage Solution Treatment Time

[0169] A stepped solution treatment process (470℃ / 2h + 480℃) was adopted, with the second-stage holding time (t2) changed to 0.5h, 1h, 1.5h, and 2h. Figure 6 As shown, when the holding time is too short (0.5h), the solute atoms are not sufficiently homogenized, and the strength does not reach its peak. When t2 is in the range of 1~1.5 hours, the alloy performance reaches its optimal level. After being extended to 2 hours, the performance decreases slightly due to slight grain growth. Considering both performance and production efficiency, the optimized range for the second-stage solution treatment time is 1~1.5 hours.

[0170] 3. Effect of low-temperature aging temperature

[0171] With all preceding processes and high-temperature aging (174℃ / 15h) fixed, the low-temperature aging temperature (T_low) was changed to 115℃, 121℃, 125℃, and 130℃, and held at these temperatures for 5 hours. Figure 7 As shown, at excessively low temperatures (115℃), the driving force for GP region formation is insufficient, resulting in low strength. When the temperature exceeds 121℃, the stability of the GP region decreases, making it prone to transformation into the coarse η' phase, leading to a reduction in peak strength and a narrowing of the peak width. Experiments indicate that 121℃ is the optimal temperature for forming a uniform, high-density GP region, thereby achieving the best precipitation strengthening effect.

[0172] 4. The effect of high-temperature aging time

[0173] With fixed preceding processes and low-temperature aging (121℃ / 5h), the high-temperature aging time (t_high) at 174℃ is varied to 5h, 10h, 15h, 20h, and 25h. For example... Figure 8As shown, the strength initially increases and then decreases over time, while the plasticity continues to improve. Before 15 hours, the size and distribution of the η' and η phases gradually optimize, reaching peak strength at 15 hours. After 15 hours, the precipitated phases coarsen according to the Ostwald ripening mechanism, leading to over-aging and a decrease in strength, but plasticity continues to improve due to stress release. Depending on the emphasis on strength or plasticity, the optimal window for high-temperature aging time is 15–20 hours.

[0174] 5. Influence of pre-stretch deformation

[0175] After solution quenching, the permanent deformation (ε) of the pre-stretched material was changed to 0% (unstretched), 1.5%, 2.5%, and 3.5%. For example... Figure 9 As shown, the alloy without pre-stretching exhibits higher residual stress. Increasing the deformation to 1.5% effectively eliminates internal stress with minimal damage to plasticity. When the deformation exceeds 2.5%, although work hardening slightly increases strength, plasticity (elongation) decreases sharply, which is detrimental to the alloy's damage tolerance. A pre-stretch deformation of 1.5% represents the optimal balance between stress elimination and plasticity preservation.

[0176] Through the above-mentioned systematic single-factor experimental study, the optimal range and optimal combination of key process parameters in the preparation method of this invention were scientifically determined. Experimental results show that parameters such as the second solution temperature (480±2℃), the second-stage holding time (1~1.5h), the two-stage aging regime (121℃ / 5h + 174℃ / 15~20h), and the pre-stretch deformation of 1.2~1.8% are not conventional or obvious choices in the field, but rather optimized results obtained through specialized design and verification. These parameters synergistically regulate the dissolution and precipitation behavior of the strengthening phase and the micro-stress state, thereby jointly ensuring that the alloy can simultaneously achieve excellent comprehensive performance of low density, high specific strength, and high damage tolerance, demonstrating the outstanding substantive features and significant technological advancements of the process scheme of this invention.

[0177] The above content should not be construed as limiting the specific implementation of this invention to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of this invention, and all such deductions or substitutions should be considered as falling within the patent protection scope defined by the submitted claims.

Claims

1. A low-density, high-specific-strength rare-earth aluminum alloy, characterized in that, The aluminum alloy comprises, by weight percentage: Zn 3-5wt%, Mg 3-6wt%, Cu 0-1.5wt%, rare earth elements 0-0.2wt%, Zr 0.07-0.09wt%, Mn 0.08-0.12wt%, Cr 0.03-0.05wt%, Ti 0.05-0.07wt%, with the balance being Al and unavoidable impurities.

2. The low-density, high-specific-strength rare-earth aluminum alloy according to claim 1, characterized in that, The Zn content is 4.0-4.8% by mass percentage, the Mg content is 3.2-4.0%, and the Zn to Mg mass ratio is 1.2-1.5:

1.

3. The low-density, high-specific-strength rare-earth aluminum alloy according to claim 1, characterized in that, The rare earth elements include at least one of Sc, Er, La, Pr, and Nd, and the total rare earth element content is ≤0.2wt%.

4. A method for preparing a low-density, high-specific-strength rare-earth aluminum alloy according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Melting and casting: According to the component ratio, industrial pure aluminum and intermediate alloy are heated and melted, alloying elements are added in sequence, and after refining, the mixture is allowed to stand and semi-continuously cast to obtain ingots. (2) Stepped homogenization treatment: The ingot is heated and held in stages, followed by air cooling; (3) Hot rolling: Milling and heat preservation of the homogenized ingot, and hot rolling in multiple passes within the set temperature range to control the total deformation; (4) Step solution treatment: A two-stage heating solution treatment process is adopted to heat and hold the hot-rolled plate; after solution treatment, online quenching and cooling are performed immediately. (5) Pre-stretching: Applying a permanent stretch of a set deformation to the quenched plate; (6) Two-stage aging treatment: The two-stage aging system of "low temperature + high temperature" is adopted to age the pre-stretched board and then cool it in the furnace to obtain the finished product.

5. The method for preparing low-density, high-specific-strength rare-earth aluminum alloy according to claim 4, characterized in that, In step (1), the melting temperature is 740~760℃ and the refining temperature is 720~740℃.

6. The method for preparing low-density, high-specific-strength rare-earth aluminum alloy according to claim 4, characterized in that, In step (2), the step homogenization process parameters are as follows: the temperature is increased to 400℃ at a rate of 50℃ per hour and held for 4~6 hours, then increased to 450℃ and held for 18~22 hours, and finally increased to 470℃ and held for 10~14 hours.

7. The method for preparing low-density, high-specific-strength rare-earth aluminum alloy according to claim 4, characterized in that, In step (4), the step solution treatment parameters are: heat up to 470℃ at a rate of ≤50℃ per hour and hold for 0.5~2h, then heat up to 480℃ at a rate of ≤30℃ per hour and hold for 0.1~1.5h.

8. The method for preparing low-density, high-specific-strength rare-earth aluminum alloy according to claim 4, characterized in that, In step (5), the amount of permanent tensile deformation applied is 1.2~1.8%.

9. The method for preparing low-density, high-specific-strength rare-earth aluminum alloy according to claim 4, characterized in that, In step (6), the first aging temperature is 121±2℃ and the heat preservation time is 4~6 hours; the second aging temperature is 174±2℃ and the heat preservation time is 15~20 hours.

10. A low-density, high-specific-strength rare-earth aluminum alloy prepared by the method according to any one of claims 4 to 9.

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