Liquid die-forged high strength-to-toughness 7xxx aluminum alloy and method of making

Abstract

The application belongs to the field of non-ferrous metal materials and processing technology, and particularly relates to a liquid die forging high-strength and high-toughness 7xxx aluminum alloy and a preparation method thereof, characterized by the following chemical composition in percentage by mass: Zn 5.5-7.0%, Mg 2.4-2.7%, Cu 1.8-2.2%, Y 0.03-0.06%, Ce 0.01-0.03%, Mo 0.05-0.1%, N 0.01-0.03%, while satisfying Zn / Mg=2.2-2.6, (Zn+Cu) / Mg=2.9-3.4, (Y+Ce) / Mo=0.6-1.6, the balance being Al and other inevitable impurities, the total content of impurities being ≤0.1wt.%, and the content of a single impurity being ≤0.03%. The preparation method comprises melting, refining, liquid die forging forming, demolding and double-stage heat treatment. The application has the following advantages: the component design is scientific, the performance is stable, the stability and consistency of the alloy performance are ensured, the castings are well formed and the structure is uniform, the accurate control of the strengthening phase precipitation behavior is realized, and the best strength and toughness matching is obtained. The comprehensive innovation makes the aluminum alloy prepared by the application meet the requirements of high-end fields for high-strength and high-toughness materials, and has a broad market prospect and high economic value.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal materials and their processing technology, and particularly to a liquid-forged high-strength and high-toughness 7xxx aluminum alloy and its preparation method. Background Technology

[0002] As modern aircraft design demands increasingly stringent requirements for flight efficiency, fuel consumption, and safety, the spars, as the core load-bearing system of the wing, bears complex dynamic loads and must maintain excellent mechanical performance under high-intensity aerodynamic pressure and temperature fluctuations. To ensure long-term reliability and safety, spars materials must possess exceptional fatigue resistance, significant resistance to stress corrosion, and precise grain size control to ensure stability and durability under extreme environmental conditions. However, while traditional aluminum alloys exhibit excellent strength and rigidity, they fail to meet the stringent requirements of modern aircraft for comprehensive mechanical properties, low stress corrosion sensitivity, and uniform grain size. Especially under long-term repeated loading, temperature fluctuations, and corrosive environments, the fatigue performance and stress corrosion resistance of traditional aluminum alloys are often insufficient, and their large grain size affects their overall mechanical properties and structural stability. To address these challenges, liquid forging technology has emerged. With its precise control over alloy composition and process parameters, it can significantly optimize the mechanical properties of aluminum alloys, improve corrosion resistance, and refine grain structure, thereby providing higher strength, toughness, and reliability for wing spars, perfectly meeting the extreme material performance requirements of aircraft.

[0003] Liquid forging technology is a novel process that integrates the characteristics of casting and forging, possessing advantages such as a wide range of material selection, low forming deformation force, low processing energy consumption, uniform and dense microstructure of forgings, and high mechanical properties. Chinese invention patent application number 201711418983.0 discloses a liquid forging high-strength and high-toughness aluminum alloy and its liquid forging method. The alloy's composition and mass percentages are: Si 6.5-7.5%, Mg 0.25-0.35%, Cu 0.05-0.15%, Mn 0.05-0.1%, Ni 0.025-0.05%, Ti 0.005-0.01%, C 0.001-0.002%, Re 0.01-0.03%, Fe≤0.2%, with the balance being Al and other unavoidable impurity elements. The liquid forging method includes batching, melting aluminum alloy liquid, refining, degassing and slag removal, liquid forging forming and solution aging treatment.

[0004] Chinese invention patent application number 201910318385.9 discloses a liquid forging process for casting aluminum alloys and its casting process. The alloy composition, by mass percentage, is as follows: Si 7-8.0%, Cu 0.05-0.1%, Mn 0.01-0.05%, Mg 0.3-0.45%, Zn 0.11-0.17%, Fe 0.01-0.12%, with the balance being Al and unavoidable impurity elements, wherein the total amount of impurity elements is controlled below 0.05% by mass percentage. The liquid forging method includes batching, melting the aluminum alloy liquid, refining, degassing and slag removal, liquid forging forming, and solution aging treatment.

[0005] Despite the advantages of liquid forging technology, the precise control of process parameters remains a challenge in the preparation of 7xxx series aluminum alloys. Optimization of key process parameters (such as melting temperature, refining time, and filling speed) is not yet mature, which may affect the consistency and stability of alloy properties. To ensure the widespread application of this technology in spar structure manufacturing, further in-depth research is needed in process optimization and parameter control to fully unleash the potential of liquid forging. Therefore, there is an urgent need to develop a high-strength, high-toughness, and low-defect 7xxx aluminum alloy to meet the extreme material performance requirements of high-end equipment. Summary of the Invention

[0006] The purpose of this invention is to provide a liquid-forged high-strength and high-toughness 7xxx aluminum alloy and its preparation method, which overcomes the shortcomings of the prior art. By precisely controlling the alloy element ratio, optimizing the refining and degassing process, and innovatively matching the parameters of dual-stage heat treatment with liquid forging, the casting fluidity is improved, and the integrated improvement of high strength, high toughness and low defects is achieved, meeting the ultimate requirements of high-end equipment for material performance.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] One technical solution: A liquid-forged high-strength and high-toughness 7xxx aluminum alloy, whose chemical composition by mass percentage is: Zn 5.5-7.0%, Mg 2.4-2.7%, Cu 1.8-2.2%, Y 0.03-0.06%, Ce 0.01-0.03%, Mo 0.05-0.1%, N 0.01-0.03%, simultaneously satisfying Zn / Mg = 2.2-2.6, (Zn+Cu) / Mg = 2.9-3.4, (Y+Ce) / Mo = 0.6-1.6, with the balance being Al and other unavoidable impurities, the total impurity content ≤ 0.1 wt.%, and the impurity content of a single component ≤ 0.03%.

[0009] Technical Solution Two: A method for preparing high-strength and high-toughness 7xxx aluminum alloy by liquid forging, including melting, refining, liquid forging, demolding, and two-stage heat treatment. The specific steps are as follows: 1) Melting: The alloy components are sequentially placed into a melting furnace and heated to 700-740℃ for melting, ensuring the alloy is fully melted and uniformly mixed; 2) Refining: During the melting process, a mixed gas and powdered refining agent are used for spray refining. The refining temperature is between 720℃ and 740℃, and the refining time is 10-15 minutes, to remove gas and impurities from the molten metal, controlling the gas content to 0.2-0.3 cm³. 3 / less than 100g; 3) Liquid forging: Pour molten metal into the preheated mold, control the temperature of the molten metal at 690-720℃, control the filling speed at 0.3-0.8m / s, control the pressure at 80-150MPa, and hold the pressure for 10-30s; 4) Demolding: Demold the casting when it cools to 300-350℃; 5) Double-stage heat treatment, the steps are as follows: a) Double-stage homogenization treatment, 450-465℃ / 20-24h + 470-485℃ / 6-10h (furnace cooling); b) Solution treatment + aging treatment, 460-480℃ / 2-6h (water quenching) + 120-180℃ / 24-32h (air cooling).

[0010] Furthermore, in step 1), the alloy composition includes pure aluminum, pure copper, aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-yttrium master alloy, aluminum-cerium master alloy, aluminum-molybdenum master alloy, and aluminum nitride master alloy, wherein the aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-yttrium master alloy, aluminum-cerium master alloy, and aluminum-molybdenum master alloy are Al-10Zn, Al-10Mg, Al-2Y, Al-2Ce, and Al-5Mo, respectively; the pure aluminum has an aluminum content ≥99.9%; the pure copper has a copper content ≥99.9%; and the aluminum nitride has an aluminum content ≥99.9% and a nitrogen content ≥99.9%.

[0011] Furthermore, before the smelting furnace operates in step 1), it must be preheated to 600-650°C to ensure that the furnace is dry and free of impurities.

[0012] Furthermore, the order of adding each alloy component in step 1) is as follows: first, pure aluminum is added to the melting furnace and heated to 700°C to completely melt it; then, the temperature is controlled at 700-720°C, and pure copper and aluminum-zinc master alloys are added in sequence to completely melt them; finally, the temperature is raised to 720-740°C, and aluminum-magnesium master alloy, aluminum-yttrium master alloy, aluminum-cerium master alloy, aluminum-molybdenum master alloy, and aluminum nitride master alloy are added in sequence, and stirred for 5-10 minutes to ensure that the master alloys are completely melted and evenly distributed.

[0013] Furthermore, in step 2), the mixed gas is one of two combinations, selected according to the situation. The gas components are combined by volume percentage as follows: Combination 1): N2 (80%–90%) + Ar (0%–5%) + Cl2 (10%–20%); Combination 2): N2 (80%–90%) + Ar (10%–20%); the gas pressure is controlled at 0.3–0.4 MPa, and the flow rate is 15–40 L / min.

[0014] Furthermore, in step 2), there are two types of powder refining agents, which are selected according to the situation. The amount of refining agent used is 0.3% to 1.2% of the mass of aluminum liquid. The powder components are combined by weight percentage as follows: Combination 1): NaCl (30% to 35%) + KCl (25% to 28%) + Na3AlF6 (8% to 10%) + C2Cl6 (15% to 25%) + CeF3 (5% to 10%); Combination 2): Cl (45% to 55%) + MgCl2 (10% to 15%) + AlF3 (15% to 20%) + Na3AlF6 (10% to 12%) + CaF2 (5% to 10%).

[0015] Furthermore, in step 2), the powder refining agent is added to the molten aluminum using a powder spraying device. With the help of a mixed gas as a carrier gas, the refining agent is evenly sprayed into the bottom of the molten aluminum. The mixture is stirred for 15-20 minutes, allowed to stand for 10-15 minutes to allow impurities to float to the surface, and then the slag is removed with a slag removal tool before casting.

[0016] Furthermore, in step 3), the mold is preheated to 200-300℃ before use for 2-4 hours.

[0017] Furthermore, in step 5) the two-stage homogenization process, the temperature is raised to the second-stage homogenization temperature after the first-stage homogenization process.

[0018] The working principle of this invention is as follows: By precisely controlling the Zn / Mg ratio, (Zn+Cu) / Mg ratio, (Y+Ce) / Mo ratio, and nitrogen content in the alloy, the mechanical properties, stress corrosion susceptibility, and grain size of the aluminum alloy are optimized, significantly improving its application performance in spar structures. Maintaining the Zn / Mg ratio between 2.2 and 2.6 helps to ensure the uniform distribution of the strengthening phase, improving the strength and toughness of the alloy. By controlling the (Zn+Cu) / Mg ratio (2.9-3.4), the corrosion resistance of the alloy is effectively improved, stress corrosion susceptibility is reduced, and service life is extended. The optimized (Y+Ce) / Mo ratio (0.6-1.6) helps to refine the grains, improve the microstructure of the alloy, and enhance the overall mechanical properties of the material. The introduction of N further refines the grain structure, improves the mechanical properties and corrosion resistance of the alloy, and avoids material degradation at high temperatures. Through this alloy composition design, the mechanical properties, corrosion resistance, and grain size of the alloy are significantly optimized, ensuring the reliability and safety of the spar in extreme environments.

[0019] This invention combines two-stage homogenization with (solution treatment + aging treatment) to achieve coupled strengthening of nano-precipitates and ultrafine grains, completing composition-process synergistic design and improving mechanical properties. Simultaneously, it employs efficient refining technology, using a Cl2-Ar mixed gas combined with rare earth refining agents to significantly reduce hydrogen content and inclusions, ensuring the purity of the molten metal. The refining and degassing process effectively removes hydrogen and non-metallic inclusions from the molten aluminum alloy, reducing porosity and inclusion defects in castings, improving the alloy's density and purity, thereby enhancing its mechanical and machinability. By optimizing liquid forging parameters, pressure-temperature-speed matching is achieved, solving the problem of poor fluidity in high-alloy aluminum liquid. Optimization of liquid forging forming process parameters results in good casting formation and dense structure, avoiding defects such as shrinkage cavities and porosity. Two-stage heat treatment can effectively eliminate casting stress, allow elements in the alloy to diffuse fully, reduce component segregation, and improve the uniformity of the alloy structure. By controlling the temperature, time, and other process parameters of solution treatment and aging treatment, the precipitation behavior of strengthening phases can be precisely controlled, thereby obtaining the best strength and toughness matching.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1) Scientifically designed composition ensures stable performance. This invention optimizes the Zn / Mg ratio within the range of 2.2-2.6 to promote the uniform distribution of the strengthening phase, thereby improving the strength and toughness of the alloy. Adjusting the (Zn+Cu) / Mg ratio to 2.9-3.4 improves corrosion resistance, significantly reduces stress corrosion sensitivity, and extends the service life of the alloy. Finely controlling the (Y+Ce) / Mo ratio between 0.6-1.6 effectively refines the grains, enhancing the overall mechanical properties and stability of the alloy. The introduction of nitrogen further improves the mechanical properties and corrosion resistance of the alloy, preventing material degradation in high-temperature environments. Furthermore, this invention strictly limits the impurity content, ensuring that the total impurities do not exceed 0.1 wt.% and the impurity content of a single component does not exceed 0.03 wt.%, effectively reducing the adverse effects of impurities on alloy performance and guaranteeing the stability and consistency of alloy performance.

[0022] 2) Optimized manufacturing process and improved casting quality: The smelting process of this invention precisely controls the feeding sequence and temperature to avoid element loss and segregation, ensuring uniform alloy composition. The use of a mixed gas and powdered refining agent for spray refining effectively removes gases and impurities, keeping the gas content at a low level and improving the density and purity of the alloy. The liquid forging process, through precise control of pouring temperature, filling speed, pressure, and holding time, eliminates defects such as shrinkage cavities and porosity, resulting in well-formed castings with a uniform microstructure.

[0023] 3) The heat treatment process is precise, resulting in excellent overall performance. This invention employs a two-stage homogenization process: the low-temperature stage dissolves some low-melting-point phases and prevents excessive grain growth, while the high-temperature stage further promotes element diffusion and the dissolution of residual phases, effectively improving the uniformity of the alloy microstructure. The solution aging treatment precisely controls temperature and time, allowing alloying elements to fully dissolve into the matrix and uniformly precipitate strengthening phases. This achieves precise control over the precipitation behavior of the strengthening phases, resulting in optimal strength and toughness matching. This comprehensive innovation enables the aluminum alloy prepared by this invention to meet the requirements of high-end fields for high-strength and high-toughness materials, possessing broad market prospects and high economic value. Attached Figure Description

[0024] Figure 1 The image shows the microstructure of the liquid-forged high-strength and high-toughness 7xxx aluminum alloy obtained in Example 1 of this invention.

[0025] Figure 2 The stress-strain curve of the liquid-forged high-strength and high-toughness 7xxx aluminum alloy obtained in Example 1 of the present invention at room temperature. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the specific embodiments used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the specific embodiments described below are some embodiments of the present invention. For those skilled in the art, other specific embodiments can be obtained based on these specific embodiments without creative effort.

[0028] The components of the embodiments of the invention described and shown in the specific embodiments herein can be arranged and designed in countless different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the specific embodiments is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0029] The alloy compositions selected in the following embodiments include pure aluminum, pure copper, aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-yttrium master alloy, aluminum-cerium master alloy, aluminum-molybdenum master alloy, and aluminum nitride master alloy. The aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-yttrium master alloy, aluminum-cerium master alloy, and aluminum-molybdenum master alloy are Al-10Zn, Al-10Mg, Al-2Y, Al-2Ce, and Al-5Mo, respectively. The pure aluminum contains ≥99.9% aluminum; the pure copper contains ≥99.9% copper; and the aluminum nitride contains ≥99.9% aluminum and ≥99.9% nitrogen. The total impurity content in the alloy composition is ≤0.1 wt.%, and the impurity content of any single component is ≤0.03%.

[0030] Before operating the smelting furnace, it is necessary to preheat the furnace to 600-650℃ to ensure that the furnace is dry and free of impurities.

[0031] The mold should be preheated to 200-300℃ for 2-4 hours before use.

[0032] In the two-stage homogenization process, the temperature is raised to the second-stage homogenization temperature after the first-stage homogenization process.

[0033] Example 1

[0034] A liquid-forged high-strength and high-toughness 7xxx aluminum alloy has the following chemical composition by mass percentage: Zn 7.0%, Mg 2.7%, Cu 2.1%, Y 0.06%, Ce 0.02%, Mo 0.05%, N 0.02%, Zn / Mg = 2.6, (Zn+Cu) / Mg = 3.37, (Y+Ce) / Mo = 1.6, with the balance being Al and other unavoidable impurities.

[0035] The preparation method of Example 1 includes melting, refining, liquid forging, demolding, and two-stage heat treatment. The specific operations are as follows:

[0036] 1) Smelting: Take the raw materials of the alloy composition and put them into the smelting furnace in sequence. The order of adding each alloy composition is as follows: First, add pure aluminum into the smelting furnace and heat it to 700℃ to melt it completely; then, control the temperature at 720℃ and add pure copper and aluminum-zinc master alloy in sequence to melt it completely; finally, raise the temperature to 740℃ and add aluminum-zirconium master alloy, aluminum-scandium master alloy and aluminum-magnesium master alloy in sequence, stir for 10 minutes to ensure that the master alloy is completely melted and evenly distributed.

[0037] 2) Refining: During the smelting process, a mixed gas and powdered refining agent are used for spray refining at a temperature of 720℃ for 15 minutes to remove gases and impurities from the molten metal, controlling the gas content to below 0.3 cm³ / 100g. The mixed gas used has a volume percentage composition of 85% N₂ + 5% Ar + 10% Cl₂, a gas pressure controlled at 0.3 MPa, and a flow rate of 30 L / min. The powdered refining agent used has a mass percentage composition of:

[0038] The refining agent consists of 35% NaCl, 25% KCl, 10% Na3AlF6, 20% C2Cl6, and 10% CeF3, and the amount of refining agent used is 0.7% of the mass of the molten aluminum. The powdered refining agent is added to the molten aluminum through a powder spraying device. Using the mixed gas as a carrier gas, the refining agent is evenly sprayed into the bottom of the molten aluminum. The mixture is stirred for 15 minutes, allowed to stand for 15 minutes to allow impurities to float to the surface, and then the slag is removed with a slag removal tool before casting.

[0039] 3) Liquid forging: Pour molten metal into the preheated mold. The temperature of the molten metal is controlled at 700℃, the filling speed is controlled at 0.6m / s, the pressure is controlled at 80MPa, and the holding time is 30s.

[0040] 4) Demolding: Demolding is performed when the casting cools to 300℃;

[0041] 5) Two-stage heat treatment: a) Two-stage homogenization treatment, 460℃ / 20h + 480℃ / 10h (furnace cooling); b) Solution treatment + aging treatment, 470℃ / 2h (water quenching) + 120℃ / 32h (air cooling).

[0042] Example 1 describes the flow performance testing process during refining as follows: 1) The uniform flowability of the alloy is tested using a pressure sensor array method. During the casting and filling process, the data acquisition system records the pressure data measured by each pressure sensor in real time and calculates the uniformity index UI; 2) The flowability is quantitatively characterized using a spiral flowability test method. After the liquid aluminum alloy solidifies and cools in the mold, the length of the spiral sample from the starting point to the final stopping position of the liquid metal is directly measured, and the filling rate is calculated.

[0043] The room temperature mechanical properties, stress corrosion resistance, grain size, and flowability test results (UI, filling rate) of the castings obtained in Example 1 are shown in Table 1. The performance test results of the castings obtained in Examples 1-7 and Comparative Examples 1-2 of this invention are shown in Table 1.

[0044] Example 2

[0045] A liquid-forged high-strength and high-toughness 7xxx aluminum alloy has the following chemical composition by mass percentage: Zn 6.5%, Mg 2.6%, Cu 1.8%, Y 0.04%, Ce 0.03%, Mo 0.07%, N 0.02%, Zn / Mg = 2.5, (Zn+Cu) / Mg = 3.19, (Y+Ce) / Mo = 1, with the balance being Al and other unavoidable impurities.

[0046] The preparation method of Example 2 includes melting, refining, liquid forging, demolding, and two-stage heat treatment. The specific operations are as follows:

[0047] 1) Smelting: Take the raw materials of the alloy composition and put them into the smelting furnace in sequence. The order of adding each alloy composition is as follows: First, add pure aluminum into the smelting furnace and heat it to 700℃ to melt it completely; then, control the temperature at 720℃ and add pure copper and aluminum-zinc master alloy in sequence to melt it completely; finally, raise the temperature to 740℃ and add aluminum-zirconium master alloy, aluminum-scandium master alloy and aluminum-magnesium master alloy in sequence, stir for 10 minutes to ensure that the master alloy is completely melted and evenly distributed.

[0048] 2) Refining: During the smelting process, a mixed gas and powdered refining agent are used for spray refining at a temperature of 730℃ for 12 minutes to remove gases and impurities from the molten metal, controlling the gas content to 0.3 cm³. 3 / less than 100g; the mixed gas used has a volume percentage composition of 87% N2 + 3% Ar + 10% Cl2, the gas pressure is controlled at 0.3MPa, and the flow rate is 30L / min; the powder refining agent used has a mass percentage composition of:

[0049] The refining agent consists of 35% NaCl, 25% KCl, 10% Na3AlF6, 20% C2Cl6, and 10% CeF3, and the amount of refining agent used is 0.7% of the mass of the molten aluminum. The powdered refining agent is added to the molten aluminum through a powder spraying device. Using the mixed gas as a carrier gas, the refining agent is evenly sprayed into the bottom of the molten aluminum. The mixture is stirred for 15 minutes, allowed to stand for 15 minutes to allow impurities to float to the surface, and then the slag is removed with a slag removal tool before casting.

[0050] 3) Liquid forging: Pour molten metal into the preheated mold. The temperature of the molten metal is controlled at 710℃, the filling speed is controlled at 0.7m / s, the pressure is controlled at 85MPa, and the holding time is 20s.

[0051] 4) Demolding: Demolding is performed when the casting cools to 300℃;

[0052] 5) Two-stage heat treatment: a) Two-stage homogenization treatment, 460℃ / 20h + 480℃ / 10h (furnace cooling); b) Solution treatment + aging treatment, 470℃ / 2h (water quenching) + 120℃ / 32h (air cooling).

[0053] The flow performance testing process in Example 2 during the refining process is the same as in Example 1.

[0054] The room temperature mechanical properties, stress corrosion resistance, grain size, and flowability (UI, filling rate) of the castings obtained in Example 2 are shown in Table 1, which shows the performance test results of the castings obtained in Examples 1-7 and Comparative Examples 1-2 of this invention.

[0055] Example 3

[0056] A liquid-forged high-strength and high-toughness 7xxx aluminum alloy has the following chemical composition by mass percentage: Zn 5.6%, Mg 2.4%, Cu 1.8%, Y 0.05%, Ce 0.01%, Mo 0.08%, N 0.01%, Zn / Mg = 2.33, (Zn+Cu) / Mg = 3.08, (Y+Ce) / Mo = 0.75, with the balance being Al and other unavoidable impurities.

[0057] The preparation method of Example 3 includes melting, refining, liquid forging, demolding, and two-stage heat treatment. The specific operations are as follows:

[0058] 1) Smelting: Take the raw materials of the alloy composition and put them into the smelting furnace in sequence. The order of adding each alloy composition is as follows: First, add pure aluminum into the smelting furnace and heat it to 700℃ to melt it completely; then, control the temperature at 720℃ and add pure copper and aluminum-zinc master alloy in sequence to melt it completely; finally, raise the temperature to 740℃ and add aluminum-zirconium master alloy, aluminum-scandium master alloy and aluminum-magnesium master alloy in sequence, stir for 10 minutes to ensure that the master alloy is completely melted and evenly distributed.

[0059] 2) Refining: During the smelting process, a mixed gas and powdered refining agent are used for spray refining at a temperature of 740℃ for 8 minutes to remove gases and impurities from the molten metal, controlling the gas content to 0.3 cm³. 3 / less than 100g; the mixed gas used has a volume percentage composition of 80% N2 + 5% Ar + 15% Cl2, the gas pressure is controlled at 0.3MPa, and the flow rate is 20L / min; the powder refining agent used has a mass percentage composition of:

[0060] The refining agent consists of 32% NaCl, 28% KCl, 10% Na3AlF6, 25% C2Cl6, and 5% CeF3, and the amount of refining agent used is 0.9% of the mass of the molten aluminum. The powdered refining agent is added to the molten aluminum through a powder spraying device. Using the mixed gas as a carrier gas, the refining agent is evenly sprayed into the bottom of the molten aluminum. The mixture is stirred for 10 minutes, allowed to stand for 15 minutes to allow impurities to float to the surface, and then the slag is removed with a slag removal tool before casting.

[0061] 3) Liquid forging: Pour molten metal into the preheated mold. The temperature of the molten metal is controlled at 690℃, the filling speed is controlled at 0.4m / s, the pressure is controlled at 100MPa, and the holding time is 30s.

[0062] 4) Demolding: Demolding is performed when the casting cools to 350℃;

[0063] 5) Two-stage heat treatment: a) Two-stage homogenization treatment, 465℃ / 22h + 485℃ / 8h (furnace cooling); b) Solution treatment + aging treatment, 475℃ / 2h (water quenching) + 150℃ / 24h (air cooling).

[0064] The flow performance test process in Example 3 during the refining process is the same as in Example 1.

[0065] The room temperature mechanical properties, stress corrosion resistance, grain size, and flowability (UI, filling rate) of the castings obtained in Example 3 are shown in Table 1, which shows the performance test results of the castings obtained in Examples 1-7 and Comparative Examples 1-2 of this invention.

[0066] Example 4

[0067] A liquid-forged high-strength and high-toughness 7xxx aluminum alloy has the following chemical composition by mass percentage: Zn 5.5%, Mg 2.5%, Cu 1.8%, Y 0.03%, Ce 0.03%, Mo 0.1%, N 0.01%, Zn / Mg = 2.2, (Zn+Cu) / Mg = 2.92, (Y+Ce) / Mo = 0.6, with the balance being Al and other unavoidable impurities.

[0068] The preparation method of Example 4 includes melting, refining, liquid forging, demolding, and two-stage heat treatment. The specific operations are as follows:

[0069] 1) Smelting: Take the raw materials of the alloy composition and put them into the smelting furnace in sequence. The order of adding each alloy composition is as follows: First, add pure aluminum into the smelting furnace and heat it to 700℃ to melt it completely; then, control the temperature at 720℃ and add pure copper and aluminum-zinc master alloy in sequence to melt it completely; finally, raise the temperature to 740℃ and add aluminum-zirconium master alloy, aluminum-scandium master alloy and aluminum-magnesium master alloy in sequence, stir for 10 minutes to ensure that the master alloy is completely melted and evenly distributed.

[0070] 2) Refining: During the smelting process, a mixed gas and powdered refining agent are used for spray refining at a temperature of 730℃ for 10 minutes to remove gases and impurities from the molten metal, controlling the gas content to 0.3 cm³. 3 / less than 100g; the mixed gas used has a volume percentage composition of 87% N2 + 3% Ar + 10% Cl2, the gas pressure is controlled at 0.3MPa, and the flow rate is 25L / min; the powder refining agent used has a mass percentage composition of:

[0071] The amount of refining agent 35% NaCl + 26% KCl + 9% Na3AlF6 + 22% C2Cl6 + 8% CeF3 is 1.2% of the mass of aluminum liquid. The powdered refining agent is added to the aluminum liquid through a powder spraying device. With the help of the mixed gas as the carrier gas, the refining agent is evenly sprayed into the bottom of the aluminum liquid. Stir for 15 minutes, let stand for 15 minutes to allow the impurities to float to the surface, remove the slag with a slag removal tool, and then cast.

[0072] 3) Liquid forging: Pour molten metal into the preheated mold. The temperature of the molten metal is controlled at 720℃, the filling speed is controlled at 0.8m / s, the pressure is controlled at 150MPa, and the holding time is 30s.

[0073] 4) Demolding: Demolding is performed when the casting cools to 350℃;

[0074] 5) Two-stage heat treatment: a) Two-stage homogenization treatment, 450℃ / 24h + 470℃ / 10h (furnace cooling); b) Solution treatment + aging treatment, 460℃ / 4h (water quenching) + 180℃ / 32h (air cooling).

[0075] The flow performance test process in Example 4 during the refining process is the same as in Example 1.

[0076] The room temperature mechanical properties, stress corrosion resistance, grain size, and flowability (UI, filling rate) of the castings obtained in Example 4 are shown in Table 1, which shows the performance test results of the castings obtained in Examples 1-7 and Comparative Examples 1-2 of this invention.

[0077] Example 5

[0078] A liquid-forged high-strength and high-toughness 7xxx aluminum alloy has the following chemical composition by mass percentage: Zn 6.0%, Mg 2.5%, Cu 2.2%, Y 0.05%, Ce 0.03%, Mo 0.06%, N 0.03%, Zn / Mg = 2.4, (Zn+Cu) / Mg = 3.28, (Y+Ce) / Mo = 1.33, with the balance being Al and other unavoidable impurities.

[0079] The preparation method of Example 5 includes melting, refining, liquid forging, demolding, and two-stage heat treatment. The specific operations are as follows:

[0080] 1) Smelting: Take the raw materials of the alloy composition and put them into the smelting furnace in sequence. The order of adding each alloy composition is as follows: First, add pure aluminum into the smelting furnace and heat it to 700℃ to melt it completely; then, control the temperature at 720℃ and add pure copper and aluminum-zinc master alloy in sequence to melt it completely; finally, raise the temperature to 740℃ and add aluminum-zirconium master alloy, aluminum-scandium master alloy and aluminum-magnesium master alloy in sequence, stir for 10 minutes to ensure that the master alloy is completely melted and evenly distributed.

[0081] 2) Refining: During the smelting process, a mixed gas and powdered refining agent are used for spray refining at a temperature of 730℃ for 15 minutes to remove gases and impurities from the molten metal, controlling the gas content to 0.2 cm³. 3 / less than 100g; the mixed gas used has a volume percentage composition of 80% N2 + 0% Ar + 20% Cl2, the gas pressure is controlled at 0.4MPa, and the flow rate is 30L / min; the powder refining agent used has a mass percentage composition of:

[0082] The refining agent consists of 30% NaCl, 25% KCl, 10% Na3AlF6, 25% C2Cl6, and 10% CeF3, and the amount of refining agent used is 0.8% of the mass of the molten aluminum. The powdered refining agent is added to the molten aluminum through a powder spraying device. Using the mixed gas as a carrier gas, the refining agent is evenly sprayed into the bottom of the molten aluminum. The mixture is stirred for 15 minutes, allowed to stand for 15 minutes to allow impurities to float to the surface, and then the slag is removed with a slag removal tool before casting.

[0083] 3) Liquid forging: Pour molten metal into the preheated mold. The temperature of the molten metal is controlled at 690℃, the filling speed is controlled at 0.6m / s, the pressure is controlled at 120MPa, and the holding time is 30s.

[0084] 4) Demolding: Demolding is performed when the casting cools to 300℃;

[0085] 5) Two-stage heat treatment: a) Two-stage homogenization treatment, 455℃ / 22h + 475℃ / 6h (furnace cooling); b) Solution treatment + aging treatment, 475℃ / 6h (water quenching) + 120℃ / 32h (air cooling).

[0086] The flow performance test process in Example 5 during the refining process is the same as in Example 1.

[0087] The room temperature mechanical properties, stress corrosion resistance, grain size, and flowability test results (UI, filling rate) of the castings obtained in Example 5 are shown in Table 1, which shows the performance test results of the castings obtained in Examples 1-7 and Comparative Examples 1-2 of this invention.

[0088] Example 6

[0089] The mass percentages of each component and the preparation method in Example 6 are the same as in Example 1, except that:

[0090] In step 2), the mixed gas consists of 90% N2 + 10% Ar, the gas pressure is controlled at 0.3 MPa, and the flow rate is 30 L / min;

[0091] In step 3), the powder refining agent is composed of 45% KCl + 15% MgCl2 + 20% AlF3 + 12% Na3AlF6 + 8% CaF2, and the amount of refining agent used is 1% of the mass of aluminum liquid.

[0092] Step 5) Heat treatment process: 1) Two-stage homogenization treatment, 455℃ / 22h + 475℃ / 6h (furnace cooling); 2) Solution treatment + aging treatment, 475℃ / 6h (water quenching) + 120℃ / 32h (air cooling).

[0093] The room temperature mechanical properties, stress corrosion resistance, grain size, and flowability test results (UI, filling rate) of Example 6 are shown in Table 1.

[0094] Example 7

[0095] The mass percentages of each component and the preparation method in Example 7 are the same as in Example 1, except that:

[0096] In step 2), the mixed gas consists of 80% N2 + 20% Ar, the gas pressure is controlled at 0.4 MPa, and the flow rate is 40 L / min.

[0097] In step 3), the powder refining agent consists of 55% KCl + 10% MgCl2 + 15% AlF3 + 10% Na3AlF6 + 10% CaF2, and the amount of refining agent used is 0.7% of the mass of aluminum liquid.

[0098] In step 5), the heat treatment process is as follows: 1) Two-stage homogenization treatment, 465℃ / 22h + 485℃ / 8h (furnace cooling); 2) Solution treatment + aging treatment, 475℃ / 2h (water quenching) + 150℃ / 24h (air cooling).

[0099] The room temperature mechanical properties, stress corrosion resistance, grain size, and flowability test results (UI, filling rate) of Example 7 are shown in Table 1, which shows the performance test results of the castings obtained in Examples 1-7 and Comparative Examples 1-2 of this invention.

[0100] Comparative Example 1

[0101] The preparation method of Comparative Example 1 is the same as that of Example 1, except that the chemical components are composed of the following mass percentages: Zn 5.0, Mg 3.0, Cu 1.7, Y 0.02, Ce 0.01, Mo 0.12, N 0.04, with the balance being Al and other unavoidable impurities.

[0102] In step 3), liquid forging: pour molten metal into the preheated mold, control the temperature of the molten metal at 680℃, control the filling speed at 0.4m / s, control the pressure at 75MPa, and hold the pressure for 40s;

[0103] The room temperature mechanical properties, stress corrosion resistance, grain size, and flowability test results (UI, filling rate) of Comparative Example 1 are shown in Table 1.

[0104] Comparative Example 2

[0105] The preparation method of Comparative Example 2 is the same as that of Example 1, except that the chemical components are composed of the following mass percentages: Zn 7.5, Mg 2.0, Cu 1.5, Y 0.07, Ce 0.04, Mo 0.04, with the balance being Al and other unavoidable impurities.

[0106] In step 3), liquid forging is performed by pouring molten metal into the preheated mold. The temperature of the molten metal is controlled at 695°C, the filling speed is controlled at 0.5 m / s, the pressure is controlled at 110 MPa, and the holding time is 20 s.

[0107] The room temperature mechanical properties, stress corrosion resistance, grain size, and flowability test results (UI, filling rate) of Comparative Example 2 are shown in Table 1, which shows the performance test results of the castings obtained in Examples 1-7 and Comparative Examples 1-2 of the present invention.

[0108] Table 1

[0109]

[0110] As shown in Table 1, this invention achieves a comprehensive improvement in the performance of high-strength and high-toughness 7xxx aluminum alloys through scientific and precise alloy composition design, synergistic optimization of liquid forging and dual-stage heat treatment. The rational control of key ratios such as Zn / Mg, (Zn+Cu) / Mg, and (Y+Ce) / Mo in the alloy not only promotes the dispersed precipitation of strengthening phases, improving the alloy's strength and plasticity, but also effectively reduces stress corrosion sensitivity and refines the grain structure. The liquid forging process, with its high-pressure rapid filling and dense solidification mechanism, significantly improves the uniformity of the casting's structure and forming quality, enhancing the consistency of overall mechanical properties. The dual-stage heat treatment process, through multi-stage homogenization and precise solution aging control, makes the precipitation behavior of strengthening phases more controllable and the strengthening effect more significant, ensuring that the alloy still possesses good toughness and corrosion resistance under high-strength conditions. This indicates that the material system of this invention has significant application value and promotion potential in the field of aerospace structures.

[0111] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A liquid-forged high-strength and high-toughness 7xxx aluminum alloy, characterized in that, Its chemical composition by mass percentage is as follows: Zn 5.5-7.0%, Mg 2.4-2.7%, Cu 1.8-2.2%, Y 0.03-0.06%, Ce 0.01-0.03%, Mo 0.05-0.1%, N 0.01-0.03%, while satisfying Zn / Mg=2.2-2.6, (Zn+Cu) / Mg=2.9-3.4, (Y+Ce) / Mo=0.6-1.6, with the balance being Al and other unavoidable impurities. The total content of impurity components is ≤0.1%, and the content of each individual impurity component is ≤0.03%.

2. The method for preparing a high-strength and high-toughness 7xxx aluminum alloy by liquid forging according to claim 1, characterized in that, The process includes melting, refining, liquid forging, demolding, and two-stage heat treatment. The specific steps are as follows: 1) Melting: Take the raw materials of the alloy composition and put them into the melting furnace in sequence, heat them to 700-740℃ for melting, so that the alloy is fully melted and uniformly mixed; 2) Refining: During the smelting process, a mixed gas and powdered refining agent are used for spray refining. The refining temperature is 720℃~740℃, and the refining time is 10-15 minutes to remove gases and impurities from the molten metal, controlling the gas content to 0.2-0.3 cm³. 3 Less than 100g; 3) Liquid forging: Pour molten metal into the preheated mold. The temperature of the molten metal is controlled at 690-720℃, the filling speed is controlled at 0.3-0.8m / s, the pressure is controlled at 80-150MPa, and the holding time is 10-30s. 4) Demolding: Demolding is performed when the casting cools to 300-350℃; 5) Two-stage heat treatment, the steps are as follows: a) Two-stage homogenization treatment, 450-465℃ / 20-24h + 470-485℃ / 6-10h + furnace cooling; b) Solution treatment + aging treatment, 460-480℃ / 2-6h + water quenching + 120-180℃ / 24-32h + air cooling.

3. The method for preparing a high-strength and high-toughness 7xxx aluminum alloy by liquid forging according to claim 2, characterized in that, The alloy composition selected in step 1) includes pure aluminum, pure copper, aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-yttrium master alloy, aluminum-cerium master alloy, aluminum-molybdenum master alloy, and aluminum nitride master alloy. The aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-yttrium master alloy, aluminum-cerium master alloy, and aluminum-molybdenum master alloy are Al-10Zn, Al-10Mg, Al-2Y, Al-2Ce, and Al-5Mo, respectively. The pure aluminum has an aluminum content ≥99.9%, and the pure copper has a copper content ≥99.9%.

4. The method for preparing a high-strength and high-toughness 7xxx aluminum alloy by liquid forging according to claim 2, characterized in that, Before operating the smelting furnace in step 1), the furnace must be preheated to 600-650°C to ensure that the furnace is dry and free of impurities.

5. The method for preparing a high-strength and high-toughness 7xxx aluminum alloy by liquid forging according to claim 2, characterized in that, The order of adding each alloy component in step 1) is as follows: First, add pure aluminum to the melting furnace and heat it to 700°C to completely melt it; then, control the temperature at 700-720°C and add pure copper and aluminum-zinc master alloy in sequence to completely melt them; finally, raise the temperature to 720-740°C and add aluminum-magnesium master alloy, aluminum-yttrium master alloy, aluminum-cerium master alloy, aluminum-molybdenum master alloy and aluminum nitride master alloy in sequence, and stir for 5-10 minutes to ensure that the master alloys are completely melted and evenly distributed.

6. The method for preparing a high-strength and high-toughness 7xxx aluminum alloy by liquid forging according to claim 2, characterized in that, In step 2), the mixed gas is a combination of two types, selected according to the situation. The gas components are combined by volume percentage as follows: Combination 1): N2 80%~90% + Ar 0%~5% + Cl2 10%~20%; Combination 2): N2 80%~90% + Ar 10%~20%; The gas pressure is controlled at 0.3~0.4MPa, and the flow rate is 15~40L / min.

7. The method for preparing a high-strength and high-toughness 7xxx aluminum alloy by liquid forging according to claim 2, characterized in that, In step 2), there are two types of powder refining agents, which are selected according to the situation. The amount of refining agent used is 0.3% to 1.2% of the mass of the molten aluminum. The powder components are combined by weight percentage as follows: Combination 1): NaCl 30%~35% + KCl 25%~28% + Na3AlF6 8%~10% + C2Cl6 20%~25% + CeF3 5%~10%; Combination 2): KCl 45%~55% + MgCl2 10%~15% + AlF3 15%~20% + Na3AlF6 10%~12% + CaF2 5%~10%.

8. The method for preparing a liquid-forged high-strength and high-toughness 7xxx aluminum alloy according to claim 2, characterized in that, In step 2), the powder refining agent is added to the molten aluminum through a powder spraying device. Using a mixed gas as a carrier gas, the refining agent is evenly sprayed into the bottom of the molten aluminum. The mixture is stirred for 15-20 minutes, then left to stand for 10-15 minutes to allow impurities to float to the surface. The slag is then removed with a slag removal tool before casting.

9. The method for preparing a high-strength and high-toughness 7xxx aluminum alloy by liquid forging according to claim 2, characterized in that, In step 3), the mold is preheated to 200-300℃ before use for 2-4 hours.

10. The method for preparing a high-strength and high-toughness 7xxx aluminum alloy by liquid forging according to claim 2, characterized in that, In step 5), the two-stage homogenization process involves heating the furnace to the second-stage homogenization temperature after the first-stage homogenization process.

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