High-strength heat-resistant al-zn-mg-cu aluminum alloy and preparation method thereof

Abstract

The application discloses a high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy and a preparation method thereof, and belongs to the technical field of aluminum alloys. By optimizing the composition and component ratio of the aluminum alloy, combining the optimized process, and adding refining agent A and refining B for synergistic refining treatment, the prepared aluminum alloy can have high strength, high heat resistance and good plasticity, is significantly better than a traditional high-strength aluminum alloy (the yield reduction after baking is usually 10% to 15%), and is more suitable for occasions with high requirements for high-temperature service performance of materials, such as aerospace structural parts, new energy automobile battery trays, anti-collision beams, rail transit car bodies and the like. Compared with a traditional 7-series aluminum alloy, the alloy disclosed by the application has a significantly reduced softening degree at high temperature, and can meet increasingly stringent lightweight and safety performance requirements.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, and more specifically, to a high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy and its preparation method. Background Technology

[0002] Aluminum alloys, due to their lightweight, high specific strength, and good machinability, have been widely used in aerospace, automotive manufacturing, rail transportation, and other industrial fields. In recent years, with the continuous improvement of material performance requirements in these fields, especially the need for components to withstand higher service temperatures while maintaining lightweight properties, the development of aluminum alloys that combine high strength and excellent heat resistance has become a research hotspot.

[0003] In existing technologies, high-strength aluminum alloys are mainly divided into two categories: one is precipitation-strengthened aluminum alloys, represented by the 7xxx series (Al-Zn-Mg-Cu series), which have excellent room temperature strength but poor microstructural stability at high temperatures. The precipitated phases are prone to coarsening or phase transformation, leading to rapid softening of the material under baking or high-temperature service conditions, with a significant decrease in yield strength (typically 10%-15%). The other category is heat-resistant aluminum alloys, represented by the Al-Si series. Their eutectic silicon phase can provide certain high-temperature resistance, but often at the cost of strength, making it difficult to meet the requirements of critical load-bearing components. For example, Chinese invention patent application number CN201110243419.6 discloses a high-strength heat-resistant aluminum alloy comprising 1-5% copper, 0.5-1.0% manganese, 0.1-0.5% titanium, 0.1-0.3% iron, 0.1-0.3% silicon, 0.01-0.05% magnesium, 0.01-0.05% zinc, 0.1-0.5% zirconium, 0.01-0.05% nickel, 0.01-0.05% tin, 0.35-0.75% indium, and the balance aluminum. The aluminum alloy T5 obtained by this invention patent has a tensile strength of 150-250 MPa and an elongation of 2-8% after heat treatment. For example, Chinese patent application CN202510645570.4 discloses a high-temperature, high-strength, heat-resistant aluminum alloy. Using Al-6%Cu-1.5%Zn-0.5%Mg as the matrix, with added Mn and Cr elements, the target alloy is prepared using a medium-frequency induction heating device. After casting and machining, the aluminum alloy ingot is treated with the T6 process using JINDUN heat treatment equipment. The resulting aluminum alloy has a tensile strength as high as 418.59 MPa and a high-temperature (350℃) tensile strength of 217.30 MPa, but there is still room for improvement.

[0004] To balance strength and heat resistance, those skilled in the art have made various attempts. In terms of compositional design, the conventional method is to add trace amounts of Zr, Ti, and other elements to a high Zn and Mg content to refine the grains and increase the recrystallization temperature. However, this lacks systematic control over Si, resulting in insufficient thermal stability. For example, precipitates formed solely by Zn and Mg (such as the η' phase) coarsen rapidly above 120°C. While the introduction of a small amount of Si can form precipitates with higher thermal stability, improper control of Si content easily leads to its combination with Mg to form coarse, brittle Mg2Si phases, severely impairing the alloy's plasticity. In terms of manufacturing processes, existing technologies often employ long-duration (>24h) stepped homogenization treatments to eliminate dendrite segregation, combined with medium-temperature extrusion (380-420°C) and T6 single-stage aging. However, excessively low extrusion temperatures can lead to high deformation resistance and difficulty in forming; excessively high extrusion temperatures can easily cause abnormal grain growth; at the same time, the two-stage or multi-stage aging process used to improve heat resistance often results in a 10-15% loss in strength, which cannot meet the requirements for high performance.

[0005] Therefore, how to overcome the technical bottleneck of achieving both high strength and high heat resistance through precise composition design and process optimization, and obtain an aluminum alloy material that simultaneously possesses high tensile strength, high heat resistance, and good plasticity, is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] Based on this, in order to solve one of the above-mentioned technical problems, the present invention provides a high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy and its preparation method, the specific technical solution of which is as follows: A high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy, wherein the aluminum alloy comprises the following chemical composition by mass percentage: Zn 6.5%~7.8%, Mg 1.8%~2.8%, Cu 0.9%~1.5%, Si 0.10%~0.25%, Ti 0.03%~0.08%, Zr 0.10%~0.20%, with the balance being Al and unavoidable impurities.

[0007] Furthermore, the Al-Zn-Mg-Cu aluminum alloy comprises the following chemical composition by mass percentage: Zn 6.9%, Mg 2.4%, Cu 1.2%, Si 0.2%, Ti 0.05%, Zr 0.15%, with the balance being Al and unavoidable impurities.

[0008] Furthermore, the Al-Zn-Mg-Cu aluminum alloy has a tensile strength ≥600MPa, a yield strength ≥570MPa, and an elongation ≥13%; after simulated baking treatment at 185℃ for 30min, the yield strength is ≥550MPa with a reduction of ≤5%.

[0009] In addition, the present invention also provides a method for preparing a high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy, the method comprising the following steps: S1. Pure aluminum, pure zinc, pure magnesium, Al-Cu master alloy, Al-Si master alloy, Al-Ti master alloy and Al-Zr master alloy are added to a melting furnace for melting. After all materials are melted, they are stirred evenly to obtain aluminum alloy melt. S2. Introduce protective gas to refine and degas the aluminum alloy melt, and remove slag after standing to obtain refined aluminum alloy melt. S3. The refined alloy melt is subjected to semi-continuous casting to obtain an ingot; S4. The ingot is subjected to homogenization treatment at a temperature of 470℃~480℃ for 20h~28h, followed by cooling. S5. Preheat the homogenized ingot to 380℃~440℃, and at the same time preheat the extrusion die to 400℃~420℃, and then perform hot extrusion at a speed of 0.5mm / s~1.5 mm / s. S6. Immediately after extrusion, the extruded material is cooled online to room temperature, and then stretched and straightened to obtain the Al-Zn-Mg-Cu aluminum alloy.

[0010] Further, in step S2, the refining process includes a first refining process and a second refining process; and in the first refining process, refining agent A, accounting for 1% to 3% of the mass of the aluminum alloy melt, is added, and the refining process is carried out at 700℃ to 720℃ for 20 min to 30 min; in the second refining process, refining agent B, accounting for 0.5% to 1% of the mass of the aluminum alloy melt, is added, and the refining process is carried out at 680℃ to 700℃ for 10 min to 15 min.

[0011] Further, in step S2, the refining agent A is composed of potassium fluoroaluminate, hexachloroethane and sodium carbonate in a weight ratio of (1~5):(1~3):(1~4).

[0012] The refining agent B is rare earth-doped cryolite, and the rare earth doping content in the rare earth-doped cryolite is 0.05%~0.1%, and the rare earth is Ce.

[0013] Furthermore, in step S3, the temperature of the semi-continuous casting is 680℃~720℃, the casting speed is 25mm / min~50mm / min, and the cooling water pressure is 0.05MPa~0.12MPa.

[0014] Furthermore, in step S4, the heating rate of the homogenization treatment is 3℃ / min~10℃ / min, and air cooling is used after heat preservation.

[0015] Furthermore, in step S5, the temperature difference between the ingot and the mold is controlled to be ≤20℃.

[0016] Furthermore, in step S6, the online cooling method is water cooling, spraying, or air mist cooling, and the cooling rate is ≥60℃ / s; the straightening amount of the tension straightening is 1%~1.5%.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention optimizes the composition and component ratio of aluminum alloys, combined with an optimized process, to produce aluminum alloys that balance high strength, high heat resistance, and good plasticity, significantly outperforming traditional high-strength aluminum alloys (whose yield strength after baking typically decreases by 10%~15%). This makes them more suitable for applications requiring high-temperature performance, such as aerospace structural components, new energy vehicle battery trays, crash beams, and rail transit vehicle bodies. Compared to traditional 7-series aluminum alloys, the alloy of this invention exhibits significantly reduced softening at high temperatures, meeting increasingly stringent requirements for lightweighting and safety performance.

[0018] 2. This invention employs a homogenization treatment at 470℃~480℃ for 20h~28h, combined with air cooling, to effectively eliminate dendritic segregation and coarse second phases. Subsequently, the ingot is preheated to 380℃~440℃ and the die to 400℃~420℃ for hot extrusion, with the extrusion speed controlled at 0.5mm / s~1.5mm / s. Particularly preferred is controlling the temperature difference between the ingot and die to ≤20℃ (isothermal extrusion), which effectively reduces surface cracking tendency, promotes dynamic recrystallization, and refines the grain structure. Furthermore, immediate online cooling at a rate ≥60℃ / s (preferably water cooling) after extrusion effectively suppresses the growth of precipitated phases and preserves the supersaturated solid solution state. This synergistic effect promotes the formation of high-density, uniformly distributed nanoscale strengthening phases in the aluminum alloy during the extrusion state.

[0019] 3. This invention optimizes the refining process. In the first refining process, refining agent A, composed of potassium fluoroaluminate, hexachloroethane, and sodium carbonate, is added. Potassium fluoroaluminate effectively dissolves the Al2O3 film, hexachloroethane slowly releases chlorine to remove hydrogen, and sodium carbonate decomposes to generate CO2 bubbles for further physical hydrogen removal. The three components work synergistically to significantly improve the effect. In the second refining process, rare earth-doped cryolite (Ce as the rare earth element, with a doping amount of 0.05%~0.1%) is added as refining agent B. Rare earth-doped cryolite not only has excellent slag and degassing capabilities, but also the residual trace amounts of Ce (ppm level) are uniformly distributed at grain boundaries and dislocations, which acts as grain boundary pinning and increases the recrystallization temperature, thereby synergistically improving the high-temperature thermal stability of the alloy. Compared with traditional refining agents, this not only significantly reduces the hydrogen content of the melt and reduces inclusions, but also provides the alloy with additional rare earth microalloying effects. Attached Figure Description

[0020] The invention will be further understood from the following description taken in conjunction with the accompanying drawings. The components in the drawings are not necessarily drawn to scale, but rather the emphasis is on illustrating the principles of the embodiments. In different views, the same reference numerals designate corresponding parts.

[0021] Figure 1 This is a schematic diagram of the metallographic structure of a high-strength and heat-resistant aluminum alloy according to Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of the metallographic structure of the aluminum alloy in Comparative Example 1 of the present invention. Figure 3 This is a schematic diagram of the metallographic structure of the aluminum alloy in Comparative Example 5 of the present invention. Figure 4 This is a schematic diagram of the metallographic structure of the aluminum alloy in Comparative Example 8 of the present invention. Figure 5 This is an electronic image of the microstructure of a high-strength, heat-resistant aluminum alloy according to Embodiment 1 of the present invention; Figure 6 This is an energy dispersive spectroscopy (EDS) analysis diagram of a high-strength, heat-resistant aluminum alloy according to Embodiment 1 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] One embodiment of the present invention provides a high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy, wherein the Al-Zn-Mg-Cu aluminum alloy comprises the following chemical composition by mass percentage: Zn 6.5%~7.8%, Mg 1.8%~2.8%, Cu 0.9%~1.5%, Si 0.10%~0.25%, Ti 0.03%~0.08%, Zr 0.10%~0.20%, with the balance being Al and unavoidable impurities.

[0025] In one embodiment, the Al-Zn-Mg-Cu aluminum alloy comprises the following chemical composition by mass percentage: Zn 6.9%, Mg 2.4%, Cu 1.2%, Si 0.2%, Ti 0.05%, Zr 0.15%, with the balance being Al and unavoidable impurities.

[0026] In one embodiment, the Al-Zn-Mg-Cu aluminum alloy has a tensile strength ≥600MPa, a yield strength ≥570MPa, and an elongation ≥13%; after simulated baking treatment at 185℃ for 30min, the yield strength is ≥550MPa and the reduction is ≤5%.

[0027] In addition, the present invention also provides a method for preparing a high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy, the method comprising the following steps: S1. Pure aluminum, pure zinc, pure magnesium, Al-Cu master alloy, Al-Si master alloy, Al-Ti master alloy and Al-Zr master alloy are added to a melting furnace for melting. After all materials are melted, they are stirred evenly to obtain aluminum alloy melt. S2. Introduce protective gas to refine and degas the aluminum alloy melt, and remove slag after standing to obtain refined aluminum alloy melt. S3. The refined alloy melt is subjected to semi-continuous casting to obtain an ingot; S4. The ingot is subjected to homogenization treatment at a temperature of 470℃~480℃ for 20h~28h, followed by cooling. S5. Preheat the homogenized ingot to 380℃~440℃, and at the same time preheat the extrusion die to 400℃~420℃, and then perform hot extrusion at a speed of 0.5mm / s~1.5 mm / s. S6. Immediately after extrusion, the extruded material is cooled online to room temperature, and then stretched and straightened to obtain the Al-Zn-Mg-Cu aluminum alloy.

[0028] In one embodiment, in step S1, the melting temperature is 720°C to 760°C.

[0029] In one embodiment, in step S2, the protective gas is nitrogen.

[0030] In one embodiment, step S2 includes a first refining process and a second refining process; and in the first refining process, refining agent A, accounting for 1% to 3% of the mass of the aluminum alloy melt, is added, and the refining process is carried out at 700℃ to 720℃ for 20 min to 30 min; in the second refining process, refining agent B, accounting for 0.5% to 1% of the mass of the aluminum alloy melt, is added, and the refining process is carried out at 680℃ to 700℃ for 10 min to 15 min.

[0031] In one embodiment, in step S2, the refining agent A is composed of potassium fluoroaluminate, hexachloroethane and sodium carbonate in a weight ratio of (1~5):(1~3):(1~4).

[0032] The refining agent B is rare earth-doped cryolite, and the rare earth doping content in the rare earth-doped cryolite is 0.05%~0.1%, and the rare earth is Ce.

[0033] In one embodiment, in step S3, the temperature of the semi-continuous casting is 680℃~720℃, the casting speed is 25mm / min~50mm / min, and the cooling water pressure is 0.05MPa~0.12MPa.

[0034] In one embodiment, in step S4, the heating rate of the homogenization process is 3℃ / min to 10℃ / min, and air cooling is used after heat preservation.

[0035] In one embodiment, in step S5, the difference between the ingot temperature and the mold temperature is controlled to be ≤20°C.

[0036] In one embodiment, in step S6, the online cooling method is water cooling, spraying or air mist cooling, and the cooling rate is ≥60℃ / s; the straightening amount of the tension straightening is 1%~1.5%.

[0037] The above scheme optimizes the composition and component ratio of aluminum alloys, and combines it with process improvements to prepare aluminum alloys that can comprehensively balance mechanical properties and heat resistance, thus having better application value.

[0038] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments.

[0039] Example 1: The high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy of this embodiment comprises the following chemical composition by mass percentage: Zn 6.9%, Mg 2.4%, Cu 1.2%, Si 0.2%, Ti 0.05%, Zr 0.15%, with the balance being Al and unavoidable impurities; A method for preparing a high-strength, heat-resistant Al-Zn-Mg-Cu aluminum alloy includes the following steps: S1. Pure aluminum, pure zinc, pure magnesium, Al-Cu master alloy, Al-Si master alloy, Al-Ti master alloy and Al-Zr master alloy are added to a melting furnace for melting. The melting process is carried out at 760℃. After all materials are melted, the mixture is stirred evenly to obtain aluminum alloy melt. S2. Nitrogen gas is introduced to subject the aluminum alloy melt to a first refining treatment and a second refining treatment. In the first refining treatment, refining agent A, accounting for 2% of the mass of the aluminum alloy melt, is added, and the refining treatment is carried out at 720°C for 30 minutes. In the second refining treatment, refining agent B, accounting for 0.5% of the mass of the aluminum alloy melt, is added, and the refining treatment is carried out at 680°C for 15 minutes. After degassing, the melt is allowed to stand and then the slag is removed to obtain the refined aluminum alloy melt. The refining agent A is composed of potassium fluoroaluminate, hexachloroethane and sodium carbonate in a weight ratio of 5:3:2; the refining agent B is rare earth-doped cryolite, and the rare earth doping content in the rare earth-doped cryolite is 0.05%, and the rare earth is Ce. S3. The refined alloy melt is subjected to semi-continuous casting at a temperature of 700°C, a casting speed of 30 mm / min, and a cooling water pressure of 0.10 MPa to obtain an ingot; S4. The ingot is homogenized by heating it to 475°C at a heating rate of 5°C / min and holding it at that temperature for 24 hours, followed by air cooling. S5. Preheat the homogenized ingot to 410°C, and at the same time preheat the extrusion die to 400°C, and then perform hot extrusion at a speed of 0.6 mm / s. S6. Immediately after extrusion, the extruded material is cooled online at a rate ≥60℃ / s until it reaches room temperature. Then, it is stretched and straightened with a straightening amount of 1.5% to obtain the Al-Zn-Mg-Cu aluminum alloy.

[0040] Example 2: The high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy of this embodiment comprises the following chemical composition by mass percentage: Zn 6.9%, Mg 2.4%, Cu 1.2%, Si 0.2%, Ti 0.05%, Zr 0.15%, with the balance being Al and unavoidable impurities; A method for preparing a high-strength, heat-resistant Al-Zn-Mg-Cu aluminum alloy includes the following steps: S1. Pure aluminum, pure zinc, pure magnesium, Al-Cu master alloy, Al-Si master alloy, Al-Ti master alloy and Al-Zr master alloy are added to a melting furnace for melting. The melting process is carried out at 760℃. After all materials are melted, the mixture is stirred evenly to obtain aluminum alloy melt. S2. Nitrogen gas is introduced to subject the aluminum alloy melt to a first refining treatment and a second refining treatment. In the first refining treatment, refining agent A, accounting for 2% of the mass of the aluminum alloy melt, is added, and the refining treatment is carried out at 720°C for 30 minutes. In the second refining treatment, refining agent B, accounting for 0.5% of the mass of the aluminum alloy melt, is added, and the refining treatment is carried out at 680°C for 15 minutes. After degassing, the melt is allowed to stand and then the slag is removed to obtain the refined aluminum alloy melt. The refining agent A is composed of potassium fluoroaluminate, hexachloroethane and sodium carbonate in a weight ratio of 5:3:2; the refining agent B is rare earth-doped cryolite, and the rare earth doping content in the rare earth-doped cryolite is 0.05%, and the rare earth is Ce. S3. The refined alloy melt is subjected to semi-continuous casting at a temperature of 700°C, a casting speed of 30 mm / min, and a cooling water pressure of 0.10 MPa to obtain an ingot; S4. The ingot is homogenized by heating it to 475°C at a heating rate of 5°C / min and holding it at that temperature for 24 hours, followed by air cooling. S5. Preheat the homogenized ingot to 440°C, and at the same time preheat the extrusion die to 420°C, and then perform hot extrusion at a speed of 0.8 mm / s. S6. Immediately after extrusion, the extruded material is cooled online at a rate ≥60℃ / s until it reaches room temperature. Then, it is stretched and straightened with a straightening amount of 1.5% to obtain the Al-Zn-Mg-Cu aluminum alloy.

[0041] Example 3: The high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy of this embodiment comprises the following chemical composition by mass percentage: Zn 6.9%, Mg 2.4%, Cu 1.2%, Si 0.2%, Ti 0.05%, Zr 0.15%, with the balance being Al and unavoidable impurities; A method for preparing a high-strength, heat-resistant Al-Zn-Mg-Cu aluminum alloy includes the following steps: S1. Pure aluminum, pure zinc, pure magnesium, Al-Cu master alloy, Al-Si master alloy, Al-Ti master alloy and Al-Zr master alloy are added to a melting furnace for melting. The melting process is carried out at 760℃. After all materials are melted, the mixture is stirred evenly to obtain aluminum alloy melt. S2. Nitrogen gas is introduced to subject the aluminum alloy melt to a first refining treatment and a second refining treatment. In the first refining treatment, refining agent A, accounting for 2% of the mass of the aluminum alloy melt, is added, and the refining treatment is carried out at 700°C for 30 minutes. In the second refining treatment, refining agent B, accounting for 0.6% of the mass of the aluminum alloy melt, is added, and the refining treatment is carried out at 685°C for 15 minutes. After degassing, the melt is allowed to stand and then the slag is removed to obtain the refined aluminum alloy melt. The refining agent A is composed of potassium fluoroaluminate, hexachloroethane and sodium carbonate in a weight ratio of 4:3:3; the refining agent B is rare earth-doped cryolite, and the rare earth doping content in the rare earth-doped cryolite is 0.06%, and the rare earth is Ce. S3. The refined alloy melt is subjected to semi-continuous casting at a temperature of 700°C, a casting speed of 30 mm / min, and a cooling water pressure of 0.10 MPa to obtain an ingot; S4. The ingot is homogenized by heating it to 475°C at a heating rate of 5°C / min and holding it at that temperature for 24 hours, followed by air cooling. S5. Preheat the homogenized ingot to 440°C, and at the same time preheat the extrusion die to 420°C, and then perform hot extrusion at a speed of 0.8 mm / s. S6. Immediately after extrusion, the extruded material is cooled online at a rate of 60°C / s until it reaches room temperature. Then, it is stretched and straightened with a straightening amount of 1.5% to obtain the Al-Zn-Mg-Cu aluminum alloy.

[0042] Comparative Examples 1-10: Compared with Example 1, Comparative Examples 1-10 differ in that the Si content or extrusion process parameters are different, as shown in Table 1 below. Otherwise, they are the same as Example 1.

[0043] Table 1: Comparative Examples 1-10 with different Si contents or extrusion process parameters

[0044] Comparative Example 11: The difference between Comparative Example 11 and Example 1 is that the refining agent A in Comparative Example 11 is potassium fluoroaluminate alone, while the rest is the same as in Example 1.

[0045] Comparative Example 12: The difference between Comparative Example 12 and Example 1 is that the refining agent A in Comparative Example 12 is a single hexachloroethane, while the rest is the same as in Example 1.

[0046] Comparative Example 13: The difference between Comparative Example 13 and Example 1 is that the refining agent A in Comparative Example 13 is sodium carbonate alone, while the rest is the same as in Example 1.

[0047] Comparative Example 14: The difference between Comparative Example 14 and Example 1 is that Comparative Example 14 did not add refining agent A, that is, only refining agent B was added, and it was refined at 700°C for 30 minutes. Otherwise, it was the same as Example 1.

[0048] Comparative Example 15: The difference between Comparative Example 15 and Example 1 is that Comparative Example 15 did not add refining agent B, that is, only refining agent A was added, and it was refined at 700°C for 30 minutes. Otherwise, it was the same as Example 1.

[0049] The aluminum alloy samples prepared in Examples 1-3 and the aluminum alloy samples prepared in Comparative Examples 1-15 were subjected to performance tests. The mechanical properties were in accordance with GB / T16865-2023, and the heat resistance was as follows: the aluminum alloy samples prepared in Examples 1-3 and the aluminum alloy samples prepared in Comparative Examples 1-15 were baked at 185℃ for 30 min, and then the mechanical properties of the samples were tested. The results are shown in Table 2 below.

[0050] Table 2: Performance Test Results

[0051] Analysis of the data in Table 2 shows that changing the Si content results in several effects. When the Si content is 0%, although the room temperature strength is high, the yield strength decreases significantly after baking. The lack of Si elements leads to the formation of thermally stable precipitates, primarily relying on the η' phase, which is prone to coarsening at high temperatures, resulting in insufficient thermal stability. When the Si content is 0.2%, the synergistic effect of the process described in this application allows for the formation of nanoscale Si-containing precipitates (such as Mg2Si or Si-containing η phases), effectively pinning dislocations and improving thermal stability. When the Si content is 0.4%, excessive Si leads to the precipitation of coarse brittle Mg2Si phases, weakening the matrix strength. Simultaneously, it consumes Mg elements, reducing the amount of the main reinforcing phase η', resulting in lower strength and thermal stability compared to Example 1. When the Si content is 0.6%, the brittle phase increases, impairing both plasticity and strength. This indicates that adding an appropriate amount of Si (0.10%~0.25%) allows Si elements to act as effective heterogeneous nucleation cores, promoting the precipitation of more dispersed and finer η' (MgZn2) reinforcing phases in the early stages of aging after solution treatment. These fine pre-precipitated phases exhibit higher thermal stability, suppressing over-aging during subsequent baking (185℃ / 30min), slowing down the coarsening of the strengthening phase or its transformation to the equilibrium phase η (MgZn2), thus better maintaining strength. Secondly, Si can form highly thermally stable ternary or quaternary intermetallic compounds with elements such as Mg and Cu in the alloy, for example, potentially forming the AlFeMnSi phase or the Si-containing Q phase (AlCuMgSi). These Si-containing phases are very stable at baking temperatures, pinning grain boundaries and subgrain boundaries, suppressing dislocation movement and recrystallization, and hindering grain coarsening and softening processes at high temperatures. The microalloying of Si not only optimizes the precipitation behavior of the strengthening phase but also interacts with other components in the formulation system by forming a stable, heat-resistant phase, exhibiting better strength and thermal stability under specific processes.

[0052] In addition, by comparing Example 1 with Comparative Examples 11-15, the present invention introduces refining agent A and refining agent B into the process, which work synergistically to improve the purification effect of aluminum alloy melt, which helps to increase the mechanical properties of aluminum alloy. Furthermore, the residual trace Ce element pins the grain boundaries, which also helps to improve thermal stability.

[0053] In addition, combined Figures 1-6 Further analysis and demonstration of the technical solution of the present invention.

[0054] Figure 1 This is a schematic diagram of the metallographic structure of a high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the metallographic structure of the Al-Zn-Mg-Cu aluminum alloy of Comparative Example 1 of the present invention; Figure 3 This is a schematic diagram of the metallographic structure of the Al-Zn-Mg-Cu aluminum alloy of Comparative Example 5 of the present invention; Figure 4This is a schematic diagram of the metallographic structure of the Al-Zn-Mg-Cu aluminum alloy in Comparative Example 8 of this invention; comparative analysis shows that... Figure 1 (Example 1, Si=0.2%, extrusion temperature 410℃) The microstructure is the most uniform and fine, with clear grain boundaries and no obvious coarse and brittle phases. The intragranular precipitates are diffusely distributed. This is attributed to the appropriate addition of Si promoting the formation of fine Si-containing heat-resistant phases, and the dynamic recrystallization refinement achieved by combining with the optimized extrusion process. Figure 2 (Comparative Example 1, Si=0%, extrusion temperature 380℃) Although the grains are relatively fine, there is a lack of effective thermally stable phases at the grain boundaries, which makes them prone to softening at high temperatures. Figure 3 (Comparative Example 5, Si=0.4%, extrusion temperature 380℃) and Figure 4 (Comparative Example 8, Si=0.6%, extrusion temperature 380℃) A large number of coarse, blocky or needle-like brittle Mg2Si phases were observed, becoming more severe with increasing Si content. Some grains grew abnormally, and the precipitated phases were unevenly distributed, which is the direct cause of the decrease in strength and plasticity and the deterioration of thermal stability. In summary, this invention, by controlling Si at 0.10%~0.25% and using a suitable extrusion process, obtained a uniform and fine grain structure and a dispersed nanoscale reinforcing phase, thus achieving an excellent balance between high strength and high heat resistance.

[0055] Figure 5 This is an electronic image of the microstructure of a high-strength, heat-resistant aluminum alloy according to Embodiment 1 of the present invention. Figure 6 The energy dispersive spectroscopy (EDS) analysis diagram of a high-strength and heat-resistant aluminum alloy in Embodiment 1 of the present invention is shown in Table 3 below.

[0056] Table 3: Spectrum 42

[0057] From Table 3, Figure 5 as well as Figure 6 Analysis reveals that the thermally stable phase of this invention is an Al-Mg-Si-Zn phase. This phase is uniformly distributed in the form of nano- or submicron-sized dispersed particles within the grains and at grain boundaries, without the formation of coarse brittle Mg2Si phases. It effectively pins dislocations and inhibits grain boundary slip. Simultaneously, it maintains structural stability during high-temperature baking (185℃ / 30min), slows down the coarsening rate of the η' phase, thereby synergistically improving the yield strength retention rate of the alloy (reduction after baking ≤5.0%). Figure 5 and Figure 6 Together, they verified that the Al-Mg-Si-Zn heat-resistant phase induced by controlling Si at 0.10%~0.25% is a key microstructure feature that combines high strength and excellent thermal stability.

[0058] In summary, this invention provides a high-strength, heat-resistant aluminum alloy and its preparation method. Through meticulous design of the alloy composition, the contents of elements such as Zn, Mg, Cu, Si, Ti, and Zr are controlled within specific ranges, particularly limiting the Si content to a narrow window of 0.10%~0.25%. Combined with multi-stage refining, homogenization treatment, high-temperature rapid extrusion, and online cooling processes, the technical contradiction of achieving both strength and heat resistance in traditional high-strength aluminum alloys is successfully resolved. Specifically, the introduction of rare-earth doped cryolite in the refining step efficiently purifies the melt while ensuring uniform residue of trace Ce elements, which acts as grain boundary pinning and recrystallization inhibition, further improving the alloy's high-temperature thermal stability. The final prepared aluminum alloy has a tensile strength ≥600MPa, a yield strength ≥570MPa, and an elongation ≥13%. After simulated baking at 185℃ / 30min, the yield strength is ≥550 MPa with a decrease of ≤5.0%, demonstrating significantly superior overall performance compared to existing technologies. This invention has a wide process window, controllable cost, and is easy to industrialize. It can be widely used in fields such as aerospace, new energy vehicles, and rail transportation, which have stringent requirements for lightweight and high-temperature service performance. It has extremely high practical value and market prospects.

[0059] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A high-strength, heat-resistant Al-Zn-Mg-Cu aluminum alloy, characterized in that, The aluminum alloy comprises the following chemical composition by mass percentage: Zn 6.5%~7.8%, Mg 1.8%~2.8%, Cu 0.9%~1.5%, Si 0.10%~0.25%, Ti 0.03%~0.08%, Zr 0.10%~0.20%, with the balance being Al and unavoidable impurities.

2. The aluminum alloy according to claim 1, characterized in that, The aluminum alloy comprises the following chemical composition by weight percentage: Zn 6.9%, Mg 2.4%, Cu 1.2%, Si 0.2%, Ti 0.05%, Zr 0.15%, with the balance being Al and unavoidable impurities.

3. The aluminum alloy according to claim 1, characterized in that, The aluminum alloy has a tensile strength ≥600MPa, a yield strength ≥570MPa, and an elongation ≥13%. After simulated baking treatment at 185℃ for 30 minutes, the yield strength can still be maintained at ≥550 MPa with a reduction of ≤5%.

4. A method for preparing a high-strength, heat-resistant Al-Zn-Mg-Cu aluminum alloy, characterized in that, The preparation method is used to prepare the high-strength and heat-resistant aluminum alloy as described in any one of claims 1 to 3, and the preparation method includes the following steps: S1. Pure aluminum, pure zinc, pure magnesium, Al-Cu master alloy, Al-Si master alloy, Al-Ti master alloy and Al-Zr master alloy are added to a melting furnace for melting. After all materials are melted, they are stirred evenly to obtain aluminum alloy melt. S2. Introduce protective gas to refine and degas the aluminum alloy melt, and remove slag after standing to obtain refined aluminum alloy melt. S3. The refined alloy melt is subjected to semi-continuous casting to obtain an ingot; S4. The ingot is subjected to homogenization treatment at a temperature of 470℃~480℃ for 20h~28h, followed by cooling. S5. Preheat the homogenized ingot to 380℃~440℃, and at the same time preheat the extrusion die to 400℃~420℃, and then perform hot extrusion at a speed of 0.5mm / s~1.5 mm / s. S6. Immediately after extrusion, the extruded material is cooled online to room temperature, and then stretched and straightened to obtain a high-strength and heat-resistant Al-Zn-Mg-Cu aluminum alloy.

5. The preparation method according to claim 4, characterized in that, In step S2, the refining process includes a first refining process and a second refining process; and in the first refining process, refining agent A, accounting for 1% to 3% of the mass of the aluminum alloy melt, is added, and the refining process is carried out at 700℃ to 720℃ for 20 min to 30 min; in the second refining process, refining agent B, accounting for 0.5% to 1% of the mass of the aluminum alloy melt, is added, and the refining process is carried out at 680℃ to 700℃ for 10 min to 15 min.

6. The preparation method according to claim 5, characterized in that, In step S2, the refining agent A is composed of potassium fluoroaluminate, hexachloroethane and sodium carbonate in a weight ratio of (1~5):(1~3):(1~4). The refining agent B is rare earth-doped cryolite, and the rare earth doping content in the rare earth-doped cryolite is 0.05%~0.1%, and the rare earth is Ce.

7. The preparation method according to claim 4, characterized in that, In step S3, the temperature of the semi-continuous casting is 680℃~720℃, the casting speed is 25mm / min~50mm / min, and the cooling water pressure is 0.05MPa~0.12MPa.

8. The preparation method according to claim 4, characterized in that, In step S4, the heating rate for homogenization is 3℃ / min to 10℃ / min, and air cooling is used after heat preservation.

9. The preparation method according to claim 4, characterized in that, In step S5, the temperature difference between the ingot and the mold is controlled to be ≤20℃.

10. The preparation method according to claim 4, characterized in that, In step S6, the online cooling method is water cooling, spraying or air mist cooling, and the cooling rate is ≥60℃ / s; the straightening amount of the tension straightening is 1%~1.5%.

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