Liquid die forging high-toughness 7xxx aluminum alloy and preparation method thereof

Abstract

The invention belongs to the technical field of non-ferrous metal materials and processing thereof, and particularly relates to a liquid die forging high-toughness 7xxx aluminum alloy and a preparation method thereof, and is characterized in that the liquid die forging high-toughness 7xxx aluminum alloy comprises the following chemical components in percentage by mass: 5.5-7.0% of Zn, 2.4-2.7% of Mg, 1.8-2.2% of Cu, 0.03-0.06% of Y, 0.01-0.03% of Ce, 0.05-0.1% of Mo, 0.01-0.03% of N, and the balance of Al and other inevitable impurities which meet the conditions that the ratio of Zn to Mg is 2.2-2.6, the ratio of (Zn + Cu) to Mg is 2.9-3.4, the ratio of (Y + Ce) to Mo is 0.6-1.6, the total content of impurity components is less than or equal to 0.1 wt.%, and the content of single component impurity is less than or equal to 0.03 The preparation method comprises the steps of smelting, refining, liquid forging forming, demolding and two-stage heat treatment. The alloy has the beneficial effects that the composition design is scientific, the performance is stable, and the stability and consistency of the alloy performance are guaranteed; the casting is good in molding and uniform in structure; the precise regulation and control of the precipitation behavior of the strengthening phase are realized, and the optimal obdurability matching is obtained. Through comprehensive innovation, the prepared aluminum alloy can meet the requirements of high-end fields for high-strength and high-toughness materials, and the aluminum alloy has wide market prospects and high economic value.

Description

Technical Field

[0001] The present invention relates to the technical field of non-ferrous metal materials and their processing, and particularly to a liquid forging high-strength and tough 7xxx aluminum alloy and a preparation method thereof. Background Art

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

[0003] The liquid forging technology is a new process that combines the characteristics of casting and forging. It has the advantages of a wide range of material selection, small forming deformation force, low processing energy consumption, uniform and dense structure of forgings, and high mechanical properties. The Chinese invention patent with the application number 201711418983.0 discloses a liquid forging high-strength and tough aluminum alloy and its liquid forging method. Its composition and mass percentage 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%, and the balance is Al and inevitable other impurity elements. The liquid forging method includes batching, melting aluminum alloy liquid, refining and degassing and slag removal, liquid forging forming, and solution aging treatment.

[0004] The Chinese invention patent with the application number 201910318385.9 discloses a liquid die forging processed cast aluminum alloy and its casting process, which is composed of the following components by mass percentage: 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%; the balance is Al and inevitable impurity elements, and the total amount of impurity elements is controlled below 0.05% by mass percentage. The liquid die forging method includes batching, melting aluminum alloy liquid, refining for degassing and slag removal, liquid die forging forming and solution aging treatment.

[0005] Although the liquid die forging technology has these advantages, it still faces challenges in the precise control of process parameters in the preparation of 7xxx series aluminum alloys. The optimization of key process parameters (such as melting temperature, refining time, filling speed, etc.) is not yet mature enough, which may affect the consistency and stability of alloy properties. To ensure the wide application of this technology in the manufacture of wing beam structures, in-depth research needs to be carried out in process optimization and parameter control in the future to fully release the potential of liquid die forging. Therefore, there is an urgent need to develop a 7xxx aluminum alloy with high strength, high toughness and low defects to meet the extreme requirements of high-end equipment for material properties. Summary of the Invention

[0006] The purpose of the present invention is to provide a liquid die forging high-strength and high-toughness 7xxx aluminum alloy and its preparation method, to overcome the deficiencies of the prior art, and to improve the casting fluidity, realize the integrated improvement of high strength, high toughness and low defects, and meet the extreme requirements of high-end equipment for material properties by precisely regulating the alloy element ratio, optimizing the refining and degassing process, and innovatively matching the parameters of double-stage heat treatment and liquid die forging.

[0007] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0008] Technical solution one: A liquid die forging high-strength and high-toughness 7xxx aluminum alloy, whose chemical composition is composed of the following by mass percentage: 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 is Al and other inevitable impurities, the total content of impurity components ≤ 0.1 wt.%, and the content of each single-component impurity ≤ 0.03%.

[0009] Technical Solution 2: A preparation method of a liquid die forging high-strength and tough 7xxx aluminum alloy, including melting, refining, liquid die forging forming, demoulding, and double-stage heat treatment. The specific operations are as follows: 1) Melting: Take the alloy composition raw materials and put them into the melting furnace in sequence, heat to 700 - 740 °C for melting to fully melt the alloy and make it evenly mixed; 2) Refining: During the melting process, carry out spray refining with a mixed gas and a powder refining agent. The refining temperature is 720 °C - 740 °C, and the refining time is 10 - 15 min to remove the gas and impurities in the molten metal, and control the gas content within 0.2 - 0.3 cm 3 / 100 g or less; 3) Liquid die forging forming: Pour the molten metal into the preheated mold. The temperature of the molten metal is controlled at 690 - 720 °C, the filling speed is controlled at 0.3 - 0.8 m / s, the pressure is controlled at 80 - 150 MPa, and the pressure holding time is 10 - 30 s; 4) Demoulding: When the casting cools to 300 - 350 °C, carry out the demoulding operation; 5) Double-stage heat treatment, the steps are as follows: a) Double-stage homogenization treatment, 450 - 465 °C / 20 - 24 h + 470 - 485 °C / 6 - 10 h (furnace cooling); b) Solution treatment + aging treatment, 460 - 480 °C / 2 - 6 h (water quenching) + 120 - 180 °C / 24 - 32 h (air cooling).

[0010] Further, the alloy composition selection 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. Among them, 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 aluminum content in the pure aluminum is ≥99.9%; the copper content in the pure copper is ≥99.9%; the aluminum content in the aluminum nitride is ≥99.9%, and the nitrogen content is ≥99.9%.

[0011] Further, before the melting furnace in step 1) works, it is necessary to preheat the melting furnace to 600 - 650 °C to ensure that the furnace is dry and free of impurities.

[0012] Further, the addition sequence of each alloy component in step 1) is: First, add pure aluminum to the melting furnace and heat 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, 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 min to ensure that the master alloy is completely melted and evenly distributed.

[0013] Further, the mixed gas in step 2) is of two combinations, which are 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] Further, there are two types of powder refining agents in step 2), which are selected according to the situation. The dosage of the refining agent is 0.3% - 1.2% of the mass of the aluminum liquid. The powder components are combined by weight percentage as follows: Combination 1): NaCl (30% - 35%) + KCl (25% - 28%) + Na3AlF6 (8% - 10%) + C2Cl6 (15% - 25%) + CeF3 (5% - 10%); Combination 2): Cl (45% - 55%) + MgCl2 (10% - 15%) + AlF3 (15% - 20%) + Na3AlF6 (10% - 12%) + CaF2 (5% - 10%).

[0015] Further, the powder refining agent in step 2) is added into the aluminum liquid through a powder spraying device. With the mixed gas as the carrier gas, the refining agent is evenly sprayed into the bottom of the aluminum liquid, stirred for 15 - 20 min, and left standing for 10 - 15 min to make the impurities float. After removing the floating slag with a slag skimming tool, casting is carried out.

[0016] Further, before use, the mold in step 3) is preheated to 200 - 300 °C for 2 - 4 h.

[0017] Further, in the two - stage homogenization treatment in step 5), after the first - stage homogenization treatment, the temperature is raised to the second - stage homogenization temperature along with the furnace.

[0018] The working principle of the present invention is as follows: By precisely regulating the ratios of Zn / Mg, (Zn + Cu) / Mg, (Y + Ce) / Mo in the alloy and the nitrogen content, the mechanical properties, stress corrosion sensitivity, and grain size of the aluminum alloy are optimized, significantly enhancing its application performance in the spar structure. Keeping the Zn / Mg ratio between 2.2 - 2.6 helps 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, the stress corrosion sensitivity is reduced, and the service life is extended. The optimized (Y + Ce) / Mo ratio (0.6 - 1.6) helps 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 deterioration 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] The present invention combines double-stage homogenization + (solution treatment + aging treatment), which can achieve the coupled strengthening of nano-precipitation phases and ultrafine grains, complete the collaborative design of composition - process, and improve the mechanical properties. At the same time, an efficient refining technology is adopted, with the combined use of Cl2 - Ar mixed gas and rare earth refining agent, significantly reducing the hydrogen content and inclusions, ensuring the purity of the molten metal. The refining and degassing process can effectively remove hydrogen and non-metallic inclusions in the aluminum alloy liquid, reduce porosity and inclusion defects in the casting, improve the density and purity of the alloy, thereby improving the mechanical properties and processing performance of the alloy. Through the optimization of liquid forging parameters, the pressure - temperature - speed matching is achieved, solving the problem of poor fluidity of highly alloyed aluminum liquid. The optimization of liquid forging forming process parameters results in good casting forming and dense structure, avoiding defects such as shrinkage cavities and porosity; double-stage heat treatment can effectively eliminate casting stress, enable the elements in the alloy to fully diffuse, reduce composition segregation, and improve the tissue uniformity of the alloy. By controlling process parameters such as the temperature and time of solution treatment and aging treatment, the precipitation behavior of strengthening phases can be precisely regulated, thereby obtaining the best strength-toughness matching.

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

[0021] 1) The component design is scientific, and the performance takes into account stability. In the present invention, by optimizing the Zn / Mg ratio within the range of 2.2 - 2.6, the uniform distribution of the strengthening phase is promoted, and the strength and toughness of the alloy are improved; by adjusting the (Zn + Cu) / Mg ratio to 2.9 - 3.4, the corrosion resistance is improved, the stress corrosion sensitivity is significantly reduced, and the service life of the alloy is extended; by precisely controlling the (Y + Ce) / Mo ratio between 0.6 and 1.6, the grain is effectively refined, and the overall mechanical properties and stability of the alloy are enhanced; the introduction of nitrogen further improves the mechanical properties and corrosion resistance of the alloy, and avoids the deterioration of the material in high-temperature environments. In addition, the present invention strictly limits the impurity content, ensuring that the total impurity content does 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 the alloy performance and ensuring the stability and consistency of the alloy performance;

[0022] 2) The preparation process is optimized, and the quality of the casting is improved. The melting process of the present invention precisely controls the feeding sequence and temperature, avoids element burning loss and segregation, ensures uniform alloy composition, and uses a mixed gas and powder refining agent with a combined composition for blowing refining, which can effectively remove gases and impurities, control the gas content at a low level, and improve the density and purity of the alloy. The liquid die forging process eliminates defects such as shrinkage cavities and porosity by precisely controlling the pouring temperature, filling speed, pressure, and holding time, making the casting well-formed and the structure uniform;

[0023] 3) The heat treatment process is precise, and the comprehensive performance is excellent. The present invention adopts a two-stage homogenization treatment. In the low-temperature stage, part of the low-melting-point phase is dissolved and excessive grain growth is avoided. In the high-temperature stage, element diffusion and the dissolution of the remaining phase are further promoted, effectively improving the uniformity of the alloy structure. The solution aging treatment precisely controls the temperature and time, enabling alloy elements to fully dissolve into the matrix and uniformly precipitate strengthening phases, achieving precise control of the precipitation behavior of the strengthening phases and obtaining the best strength-ductility matching. The comprehensive innovation enables the aluminum alloy prepared by the present invention to meet the requirements of high-strength and high-ductility materials in high-end fields, and has broad market prospects and high economic value. Brief Description of the Drawings

[0024] Figure 1 It is a microstructural photograph of the liquid die forging high-strength and high-ductility 7xxx aluminum alloy obtained in Example 1 of the present invention;

[0025] Figure 2 It is the stress-strain curve at room temperature of the liquid die forging high-strength and high-ductility 7xxx aluminum alloy obtained in Example 1 of the present invention. Detailed Description of the Invention

[0026] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments.

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the specific examples required for the description of the specific embodiments or the prior art. Obviously, the specific examples described below are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other specific examples can be obtained based on these specific examples.

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

[0029] In the following embodiments, the alloy components selected 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. Among them, 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 aluminum content in the pure aluminum is ≥99.9%; the copper content in the pure copper is ≥99.9%; the aluminum content in the aluminum nitride is ≥99.9%, and the nitrogen content is ≥99.9%. The total content of impurity components in the alloy components is ≤0.1 wt.%, and the impurity content of a single component is ≤0.03%.

[0030] Before the melting furnace works, it is necessary to preheat the melting furnace to 600 - 650 °C to ensure that the furnace is dry and free of impurities.

[0031] The mold is preheated to 200 - 300 °C for 2 - 4 h before use.

[0032] In the double-stage homogenization treatment, after the first-stage homogenization treatment, the temperature is raised to the second-stage homogenization temperature with the furnace.

[0033] Example 1

[0034] A liquid forging high-strength and high-toughness 7xxx aluminum alloy, the chemical composition of which is composed of the following mass percentages: 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, and the balance is Al and other inevitable impurities.

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

[0036] 1) Melting: The raw materials of alloy components are sequentially put into a melting furnace. The addition order of each alloy component is as follows: First, pure aluminum is added to the melting furnace and heated to 700 °C to make it completely melt; Subsequently, the temperature is controlled at 720 °C, and pure copper and aluminum-zinc master alloy are sequentially added to make them completely melt; Finally, the temperature is raised to 740 °C, and aluminum-zirconium master alloy, aluminum-scandium master alloy and aluminum-magnesium master alloy are sequentially added, and stirred for 10 min to ensure that the master alloy is completely melted and evenly distributed;

[0037] 2) Refining: During the melting process, blowing refining is carried out using a mixed gas and a powder refining agent. The refining temperature is 720 °C and the refining time is 15 min to remove the gas and impurities in the molten metal and control the gas content below 0.3 cm3 / 100 g; The mixed gas used is composed of 85% N2 + 5% Ar + 10% Cl2 by volume percentage, the gas pressure is controlled at 0.3 MPa, and the flow rate is 30 L / min; The powder refining agent used is composed of:

[0038] 35% NaCl + 25% KCl + 10% Na3AlF6 + 20% C2Cl6 + 10% CeF3, and the dosage of the refining agent is 0.7% of the mass of the aluminum liquid; The powder refining agent is added to the aluminum liquid through a powder spraying device, and with the help of the mixed gas as a carrier gas, the refining agent is evenly sprayed into the bottom of the aluminum liquid, stirred for 15 min, and left standing for 15 min to make the impurities float, and the floating slag is removed with a slag skimming tool and then casting is carried out;

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

[0040] 4) Demolding: When the casting is cooled to 300 °C, the demolding operation is carried out;

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

[0042] The process of fluidity performance test in the refining process of Example 1 is as follows: 1) The pressure sensor array method is used to test the uniform fluidity of the alloy. During the pouring 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 spiral fluidity test method is used to quantitatively characterize the fluidity. After the liquid aluminum alloy solidifies and cools in the mold, the length of the spiral specimen from the starting point to the final stop position of the liquid metal is directly measured, and the filling rate is calculated.

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

[0044] Example 2

[0045] A liquid forging high-strength and tough 7xxx aluminum alloy, whose chemical composition by mass percentage is: 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, and the balance is Al and other inevitable impurities.

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

[0047] 1) Melting: The alloy component raw materials are successively put into a melting furnace. The addition order of each alloy component is: First, pure aluminum is added to the melting furnace and heated to 700 °C to completely melt it; subsequently, the temperature is controlled at 720 °C, and pure copper and aluminum-zinc master alloy are successively added to completely melt them; finally, the temperature is raised to 740 °C, and aluminum-zirconium master alloy, aluminum-scandium master alloy, and aluminum-magnesium master alloy are successively added, and stirred for 10 min to ensure that the master alloy is completely melted and evenly distributed;

[0048] 2) Refining: During the melting process, blowing refining is carried out using a mixed gas and a powder refining agent. The refining temperature is 730 °C, and the refining time is 12 min to remove the gas and impurities in the molten metal, and the gas content is controlled below 0.3 cm 3 / 100 g; the mixed gas used is composed of 87% N2 + 3% Ar + 10% Cl2 by volume percentage, the gas pressure is controlled at 0.3 MPa, and the flow rate is 30 L / min; the powder refining agent used is composed of:

[0049] 35% NaCl + 25% KCl + 10% Na3AlF6 + 20% C2Cl6 + 10% CeF3, and the dosage of the refining agent is 0.7% of the mass of the aluminum liquid; the powder refining agent is added to the aluminum liquid through a powder spraying device, and with the help of the mixed gas as the carrier gas, the refining agent is evenly sprayed into the bottom of the aluminum liquid, stirred for 15 min, and left standing for 15 min to make the impurities float, and then the floating slag is removed with a slag skimming tool before casting;

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

[0051] 4) Demolding: When the casting cools to 300 °C, the demolding operation is carried out;

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

[0053] The process of testing the flowability during the refining process of Example 2 is the same as that of Example 1.

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

[0055] Example 3

[0056] A liquid forging high-strength and tough 7xxx aluminum alloy, its chemical composition by mass percentage is: 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, and the balance is Al and other inevitable impurities.

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

[0058] 1) Melting: Take the alloy composition raw materials and put them into the melting furnace in turn. The addition order of each alloy component is: First, add pure aluminum to the melting furnace and heat it to 700 °C to make it completely melt; Subsequently, control the temperature at 720 °C and add pure copper and aluminum-zinc master alloy in turn to make them completely melt; Finally, raise the temperature to 740 °C, add aluminum-zirconium master alloy, aluminum-scandium master alloy and aluminum-magnesium master alloy in turn, and stir for 10 min to ensure that the master alloy is completely melted and evenly distributed;

[0059] 2) Refining: During the melting process, mixed gas and powder refining agent are used for blowing refining. The refining temperature is 740 °C and the refining time is 8 min to remove the gas and impurities in the molten metal, and the gas content is controlled below 0.3 cm 3 / 100 g; The mixed gas used is composed of 80% N2 + 5% Ar + 15% Cl2 by volume percentage, the gas pressure is controlled at 0.3 MPa, and the flow rate is 20 L / min; The powder refining agent used is composed of:

[0060] 32% NaCl + 28% KCl + 10% Na3AlF6 + 25% C2Cl6 + 5% CeF3. The dosage of the refining agent is 0.9% of the mass of the molten aluminum. The powder refining agent is added into the molten aluminum through a powder spraying device. With the help of a mixed gas as the carrier gas, the refining agent is evenly sprayed into the bottom of the molten aluminum, stirred for 10 min, and left standing for 15 min to make the impurities float. After removing the floating slag with a slag skimming tool, casting is carried out.

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

[0062] 4) Demolding: When the casting cools to 350 °C, the demolding operation is carried out.

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

[0064] The flowability test process of Example 3 during the refining process is the same as that of Example 1.

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

[0066] Example 4

[0067] A liquid die forging high-strength and tough 7xxx aluminum alloy, whose chemical composition is in 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, and the balance is Al and other inevitable impurities.

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

[0069] 1) Melting: Take the alloy composition raw materials and put them into the melting furnace in sequence. The addition sequence of each alloy component is: First, add pure aluminum into the melting furnace and heat it to 700 °C to completely melt it; then, control the temperature at 720 °C and add pure copper and aluminum-zinc master alloy in sequence to completely melt them; finally, raise the temperature to 740 °C and add aluminum-zirconium master alloy, aluminum-scandium master alloy, and aluminum-magnesium master alloy in sequence, and stir for 10 min to ensure that the master alloy completely melts and is evenly distributed.

[0070] 2) Refining: During the smelting process, mixed gas and powder refining agent are used for blowing refining. The refining temperature is 730 °C and the refining time is 10 min to remove gases and impurities in the molten metal, so that the gas content is controlled below 0.3 cm 3 / 100 g; The mixed gas used is composed of 87% N2 + 3% Ar + 10% Cl2 by volume percentage, the gas pressure is controlled at 0.3 MPa, and the flow rate is 25 L / min; The powder refining agent used is composed of

[0071] 35% NaCl + 26% KCl + 9% Na3AlF6 + 22% C2Cl6 + 8% CeF3. The dosage of the refining agent is 1.2% of the mass of the aluminum liquid; The powder refining agent is added into the aluminum liquid through a powder spraying device. With the mixed gas as the carrier gas, the refining agent is evenly sprayed into the bottom of the aluminum liquid, stirred for 15 min, and left standing for 15 min to make the impurities float up. After removing the floating slag with a slag skimming tool, casting is carried out;

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

[0073] 4) Demolding: When the casting cools to 350 °C, demolding operation is carried out;

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

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

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

[0077] Example 5

[0078] A liquid die forging high-strength and tough 7xxx aluminum alloy, whose chemical composition is composed of: 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, and the balance is Al and other inevitable impurities.

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

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

[0081] 2) Refining: During the melting process, spray refining is carried out using a mixed gas and a powder refining agent. The refining temperature is 730 °C and the refining time is 15 min to remove the gas and impurities in the molten metal, and control the gas content within 0.2 cm 3 / 100 g or less; the mixed gas used is composed of 80% N2 + 0% Ar + 20% Cl2 by volume percentage, the gas pressure is controlled at 0.4 MPa, and the flow rate is 30 L / min; the powder refining agent used is composed of the following by mass percentage:

[0082] 30% NaCl + 25% KCl + 10% Na3AlF6 + 25% C2Cl6 + 10% CeF3, and the dosage of the refining agent is 0.8% of the mass of the aluminum liquid; the powder refining agent is added to the aluminum liquid through a powder spraying device, and with the mixed gas as the carrier gas, the refining agent is evenly sprayed into the bottom of the aluminum liquid, stirred for 15 min, and left standing for 15 min to make the impurities float up. After removing the floating slag with a slag skimming tool, casting is carried out;

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

[0084] 4) Demoulding: When the casting cools to 300 °C, carry out the demoulding operation;

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

[0086] The flowability test process of Example 5 during the refining process is the same as that of 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 are the performance test results of the castings obtained in Examples 1-7 and Comparative Examples 1-2 of the present invention.

[0088] Example 6

[0089] The mass percentages of the components and the preparation method of Example 6 are the same as those of 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 consists of 45% KCl + 15% MgCl2 + 20% AlF3 + 12% Na3AlF6 + 8% CaF2, and the dosage of the refining agent is 1% of the mass of the molten aluminum;

[0092] In step 5), the heat treatment process: 1) Double-stage homogenization treatment, 455 °C / 22 h + 475 °C / 6 h (furnace cooling); 2) Solution treatment + aging treatment, 475 °C / 6 h (water quenching) + 120 °C / 32 h (air cooling).

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

[0094] Example 7

[0095] The mass percentages of the components and the preparation method of Example 7 are the same as those of 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 dosage of the refining agent is 0.7% of the mass of the molten aluminum.

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

[0099] The room temperature mechanical properties, stress corrosion resistance, grain size, and fluidity 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 the present invention.

[0100] Comparative Example 1

[0101] The preparation method of Comparative Example 1 was the same as that of Example 1, except that the chemical components were composed of, by mass percentage: Zn 5.0, Mg 3.0, Cu 1.7, Y 0.02, Ce 0.01, Mo 0.12, N 0.04, and the balance was Al and other inevitable impurities.

[0102] In step 3), liquid die forging forming: Pour the molten metal into the preheated mold. The temperature of the molten metal was controlled at 680 °C, the filling speed was controlled at 0.4 m / s, the pressure was controlled at 75 MPa, and the pressure holding time was 40 s;

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

[0104] Comparative Example 2

[0105] The preparation method of Comparative Example 2 was the same as that of Example 1, except that the chemical components were composed of, by mass percentage: Zn 7.5, Mg 2.0, Cu 1.5, Y 0.07, Ce 0.04, Mo 0.04, and the balance was Al and other inevitable impurities.

[0106] In step 3), liquid die forging forming: Pour the molten metal into the preheated mold. The temperature of the molten metal was controlled at 695 °C, the filling speed was controlled at 0.5 m / s, the pressure was controlled at 110 MPa, and the pressure holding time was 20 s;

[0107] The test results of the room temperature mechanical properties, stress corrosion resistance, grain size, and fluidity (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 can be seen from Table 1, through the synergistic optimization of scientific and precise alloy composition design, liquid die forging forming, and two-stage heat treatment, the present invention has achieved a comprehensive improvement in the properties of high-strength and tough 7xxx aluminum alloys. The reasonable control of key ratios such as Zn / Mg, (Zn + Cu) / Mg, and (Y + Ce) / Mo in the alloy not only promotes the dispersion precipitation of strengthening phases, improves the strength and plasticity of the alloy, but also effectively reduces the stress corrosion sensitivity and refines the grain structure. The liquid die forging process, with its high-pressure rapid filling and dense solidification mechanism, significantly improves the tissue uniformity and forming quality of the casting, and enhances the consistency of the overall mechanical properties. The two-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 has good toughness and corrosion resistance under high-strength conditions, indicating that the material system of the present invention has significant application value and promotion potential in the field of aviation structures.

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

Claims

1. A liquid forging 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, the balance being Al and other inevitable impurities, the total content of impurity components ≤ 0.1 wt.%, and the content of individual component impurities ≤ 0.03%.

2. The preparation method of a liquid die forging high-strength and tough 7xxx aluminum alloy according to claim 1, characterized in that, It includes melting, refining, liquid die forging forming, demoulding, and double-stage heat treatment. The specific operations are as follows: 1) Melting: Take the alloy component raw materials and put them into the melting furnace in sequence, heat to 700 - 740 °C for melting, so that the alloy is fully melted and uniformly mixed; 2) Refining: During the smelting process, mixed gas and powder refining agent are used for blowing refining. The refining temperature is 720°C - 740°C, and the refining time is 10 - 15 minutes to remove gases and impurities in the molten metal, so that the gas content is controlled below 0.2 - 0.3 cm 3 / 100g; 3) Liquid die forging forming: Pour the molten metal into the preheated mold, control the temperature of the molten metal at 690 - 720 °C, the filling speed at 0.3 - 0.8 m / s, the pressure at 80 - 150 MPa, and the pressure holding time at 10 - 30 s; 4) Demoulding: When the casting cools to 300 - 350 °C, carry out the demoulding operation; 5) Double-stage heat treatment, the steps are as follows: a) Double-stage homogenization treatment, 450 - 465 °C / 20 - 24 h + 470 - 485 °C / 6 - 10 h (furnace cooling); b) Solution treatment + aging treatment, 460 - 480 °C / 2 - 6 h (water quenching) + 120 - 180 °C / 24 - 32 h (air cooling).

3. The preparation method of a liquid die forging high-strength and tough 7xxx aluminum alloy according to claim 2, wherein, In step 1), the selection of alloy components 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. Among them, 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 aluminum content in the pure aluminum ≥ 99.9%; the copper content in the pure copper ≥ 99.9%; the aluminum content in the aluminum nitride ≥ 99.9%, and the nitrogen content ≥ 99.9%.

4. The preparation method of a liquid die forging high-strength and high-toughness 7xxx aluminum alloy according to claim 2, wherein Before the melting furnace in step 1) works, it is necessary to preheat the melting furnace to 600 - 650 °C to ensure that the furnace is dry and free of impurities.

5. The preparation method of a liquid die forging high-strength and tough 7xxx aluminum alloy according to claim 2, characterized in that, The addition sequence of each alloy component in step 1) is: First, add pure aluminum to the melting furnace and heat to 700 °C to make it completely melt; subsequently, control the temperature at 700 - 720 °C, and add pure copper and aluminum-zinc master alloy in sequence to make them completely melt; 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 min to ensure that the master alloy is completely melted and evenly distributed.

6. The preparation method of a liquid die forging high-strength and tough 7xxx aluminum alloy according to claim 2, characterized in that, In step 2), the mixed gas is two types of 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.

7. The preparation method of a liquid die forging high-strength and tough 7xxx aluminum alloy 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 dosage of the refining agent is 0.3% - 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 (15% - 25%) + CeF3 (5% - 10%); Combination 2): Cl (45% - 55%) + MgCl2 (10% - 15%) + AlF3 (15% - 20%) + Na3AlF6 (10% - 12%) + CaF2 (5% - 10%).

8. The preparation method of a liquid die forging high-strength and tough 7xxx aluminum alloy according to claim 2, wherein, In step 2), the powder refining agent is added into the molten aluminum through a powder spraying device. With the help of a mixed gas as the carrier gas, the refining agent is evenly sprayed into the bottom of the molten aluminum, stirred for 15 - 20 min, and left standing for 10 - 15 min to make the impurities float. After removing the floating slag with a slag skimming tool, casting is carried out.

9. The preparation method of a liquid die forging high-strength and tough 7xxx aluminum alloy according to claim 2, characterized in that, In step 3), the mold is preheated to 200 - 300 °C before use for 2 - 4 h.

10. The preparation method of a liquid die forging high-strength and tough 7xxx aluminum alloy according to claim 2, characterized in that, In the two-stage homogenization treatment in step 5), after the first-stage homogenization treatment, it is heated in the furnace to the second-stage homogenization temperature.

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