A 2xxx series aluminum alloy prepared by composite controlled rolling and its gradient strengthening method

Abstract

This invention belongs to the field of non-ferrous metal materials and processing technology, and relates to a composite controlled-rolling method for preparing 2xxx series aluminum alloys and its step-strengthened preparation method. The chemical composition, by mass percentage, is: Cu 4.2-4.8%, Mg 1.3-1.7%, Mn 0.5-0.8%, Ag 0.1-0.4%, Eu 0.05-0.20%, Yb 0.05-0.15%, Ge 0.02-0.08%, simultaneously satisfying Mn = (1 / 2Ag + Eu + 2Yb + Ge), (Yb + Eu + 2Ge) / Ag = 0.9-1.4, with the balance being Al and unavoidable impurities. The total impurity content is ≤0.1 wt.%, and the content of any single impurity component is ≤0.03%. The preparation method includes vacuum induction melting, liquid nitrogen cryogenic crushing, multi-pass temperature-controlled hot rolling, asynchronous cold rolling microstructure control, and multi-scale gradient aging strengthening. The beneficial effects of this invention are: the alloy composition is scientifically designed, and the synergistic effect of multiple strengthening phases is achieved by precisely controlling the content of each element. The innovative combination of rare earth elements, the revolutionary process design, and the innovative toughening mechanism enable the aluminum alloy prepared by this invention to meet the requirements of high-end fields for high-strength and tough materials, and it has broad market prospects 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 method for preparing 2xxx series aluminum alloys with stepped strengthening through composite controlled rolling. Background Technology

[0002] As modern aviation demands ever higher levels of flight quality, safety, and economy, the aircraft tail section, as a key component of the flight control system, bears a heavy responsibility for ensuring flight stability and control. It must not only withstand alternating loads from complex airflow but also maintain reliable performance under extreme weather conditions and high-maneuverability flight. To ensure the safety and long service life of the aircraft tail section under various operating conditions, the tail material must possess excellent fatigue resistance, outstanding corrosion resistance, and precise microstructure control. However, while traditional 2xxx series aluminum alloys exhibit good rigidity and strength, they fail to meet the basic requirements of modern aircraft tail sections in the face of increasingly complex flight environments. For example, their fatigue resistance is insufficient for long-range, high-frequency flights, their protection in corrosive environments such as humid heat and salt spray is inadequate, and the inhomogeneity of their microstructure affects their overall mechanical properties.

[0003] Composite controlled rolling, through staged temperature field regulation coupled with asymmetric shear stress generated by the difference in linear speed between the upper and lower rolls, can significantly enhance grain refinement, optimize microstructure, reduce material anisotropy, improve surface quality, and reduce intermediate annealing times to improve processing efficiency. Simultaneously, it promotes the uniform precipitation and directional distribution of rare earth elements or second phases, synergistically improving material strength, plasticity, and overall mechanical properties. Chinese invention patent application number 202011238679.X discloses a composite controlled-rolling high-strength aluminum-lithium alloy and its preparation method. Its composition, by mass percentage, is: Cu 2.7-2.8%, Li 1.7-1.9%, Mg 0.3-0.5%, Mn 0.3-0.5%, Zn 0.5-0.7%, Zr 0.08-0.12%, with the balance being Al and other unavoidable impurity elements. The composite controlled rolling method includes two parts: multi-pass temperature-controlled hot rolling and asynchronous cold rolling.

[0004] Chinese invention patent application number 113088840A discloses a composite controlled rolling process for an aluminum alloy, composed by mass percentage of Zn 5.6-6.1%, Mg 2.1-2.5%, Cu 1.2-1.6%, Mn 0.2-0.4%, Zr 0.08-0.12%, with the balance being Al and other unavoidable impurity elements. The composite controlled rolling method includes two parts: multi-pass temperature-controlled hot rolling and asynchronous cold rolling. Despite the advantages of this compositional design and processing technology, the preparation of 2xxx series aluminum alloys still faces challenges in achieving precise alloy element mass fractions and process parameters. Optimization of key Mn and Ge contents, as well as key parameters (such as protective gas composition, melting temperature, and cryogenic crushing time), is not yet mature enough. This deficiency significantly affects the consistency and stability of alloy properties, hindering the widespread application of this technology in aircraft tail section design. Therefore, further in-depth research is necessary in areas such as process optimization and composition optimization. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing 2xxx series aluminum alloys with stepped strengthening through composite controlled rolling, overcoming the shortcomings of existing technologies. By precisely controlling the alloy element ratio and optimizing the preparation process, and matching it with multi-scale gradient aging strengthening, the alloy properties are improved, achieving an integrated improvement in high strength, high toughness, and corrosion resistance. This significantly enhances the comprehensive performance of the tail fin material, strengthens its fatigue and corrosion resistance, optimizes the microstructure, and provides a solid guarantee for the reliability and high-performance operation of the aircraft tail fin, meeting the extreme requirements of high-end equipment for material performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One technical solution: A composite controlled-rolled 2xxx series aluminum alloy, whose chemical composition by mass percentage is: Cu 4.2-4.8%, Mg 1.3-1.7%, Mn 0.5-0.8%, Ag 0.1-0.4%, Eu 0.05-0.20%, Yb 0.05-0.15%, Ge 0.02-0.08%, and simultaneously satisfying Mn=1 / 2Ag+Eu+2Yb+Ge, (Yb+Eu+2Ge) / Ag=0.9-1.4, with the balance being Al and unavoidable impurities, and the total content of impurity components ≤0.1wt.%, and the content of individual impurity components ≤0.03%.

[0008] Technical Solution Two: A method for preparing 2xxx series aluminum alloys with stepped strengthening through composite controlled rolling, including vacuum induction melting, liquid nitrogen cryogenic crushing, multi-pass temperature-controlled hot rolling, asynchronous cold rolling microstructure control, and multi-scale gradient aging strengthening. The specific operation steps are as follows:

[0009] 1) Vacuum induction melting: Take the alloy components and put them into the melting furnace in sequence, blow in Ar+CH4 protective gas, heat to 730℃-750℃, add powder refining agent, stir for 5-10 minutes to remove impurities in the metal solution, and ensure that the alloy is fully dissolved and uniformly mixed. After removing the slag with a slag removal tool, cast into 300mm thick flat ingots.

[0010] 2) Liquid nitrogen cryogenic treatment: Place the thick flat ingot in a liquid nitrogen environment for 2-4 hours and blow in Ar+CH4 protective gas to prevent oxidation;

[0011] 3) Multi-pass temperature-controlled hot rolling: The thick flat ingot is heated to 420℃-450℃ and rolled to 20mm in 5 passes. The deformation per pass is 20-25%. The final rolling temperature should be 360℃-400℃. The temperature needs to be controlled after each rolling and water mist cooling is used.

[0012] 4) Asynchronous cold rolling microstructure control: The rolling path is 45° cross rolling, with intermediate annealing at 260℃ for 1 hour; the final plate thickness is 2.5 mm;

[0013] 5) Multi-scale gradient aging strengthening: supersaturated solution treatment, 510℃×(0.75-1)h in salt bath furnace, water quenching, pre-aging at 110℃ for 4-6 hours; gradient aging at 150℃→170℃→190℃, holding at each stage for 2 hours; final aging at 210℃ for 4 hours, water cooling to room temperature.

[0014] Furthermore, in step 1), the alloy composition is selected from pure aluminum, pure copper, aluminum-magnesium master alloy, aluminum-manganese master alloy, aluminum-ytterbium master alloy, aluminum-silver master alloy, aluminum-germanium master alloy, and aluminum-europium master alloy, wherein the master alloys are Al-10Mg, Al-10Mn, Al-5Yb, Al-10Ag, Al-10Ge, and Al-5Eu, respectively; the pure aluminum has an aluminum content ≥99.9%; and the pure copper has a copper content ≥99.9%.

[0015] Furthermore, before the induction melting furnace operates in step 1), it is necessary to preheat the furnace to 600-650°C to ensure that the furnace is dry and free of impurities.

[0016] Furthermore, in step 1), the order of adding each alloy component is as follows: first, pure aluminum is added to a vacuum induction melting furnace and heated to 700°C to completely melt it. Then, the temperature is controlled at 700-720°C, and pure copper, aluminum-magnesium master alloy, aluminum-manganese master alloy, aluminum-ytterbium master alloy, aluminum-silver master alloy, aluminum-germanium master alloy, and aluminum-europium master alloy are added in sequence.

[0017] Furthermore, in step 1), the powder refining agent is added to the molten aluminum using a powder spraying device. With Ar+CH4 protective gas as the carrier gas, the refining agent is evenly sprayed into the bottom of the molten aluminum. After stirring, it is allowed to stand for 10-15 minutes to allow impurities to float to the surface. The amount of powder refining agent is 0.3% to 1.2% of the mass of the molten aluminum. The amount of CH4 accounts for 0.5% of the total volume of the Ar+CH4 mixed gas.

[0018] Furthermore, the powder refining agent in step 1) is composed of the following components by weight percentage: NaCl (28%~32%) + KCl (25%~30%) + Na2CO3 (10%~15%) + K2TiF6 (8%~12%) + CeO2 (5%~8%) + BaCO3 (3%~5%).

[0019] Furthermore, in step 3), the water mist cooling rate is greater than 80°C / s.

[0020] Furthermore, the total deformation of the cross-rolling in step 4) is 85%.

[0021] Furthermore, in step 5), the cooling rate of water quenching is >500℃ / s, and multi-stage aging strengthening should be carried out immediately after solution treatment.

[0022] The working principle of this invention is as follows: By precisely controlling the alloy composition and the proportional formulas Mn=(1 / 2Ag+Eu+2Yb+Ge) and (Yb+Eu+2Ge) / Ag=0.9-1.4, the strength, toughness, and corrosion resistance of aluminum alloys are optimized, significantly improving their application performance in tail fin structures. Ag can synergistically enhance stacking fault energy with rare earth elements, improving the fatigue and fracture properties of the alloy. Yb can refine grains, giving the alloy higher strength. In the formula Mn=(1 / 2Ag+Eu+2Yb+Ge), the appropriate addition of Mn can inhibit recrystallization, maintain high strength and hardness, and improve fatigue resistance, wear resistance, high-temperature dimensional stability, and softening resistance. In the formula (Yb+Eu+2Ge) / Ag=0.9-1.4, the appropriate addition of Eu can solidify atoms, agglomerate subgrain boundaries, generate dislocation pinning strengthening, and improve fatigue performance. The addition of Ge can inhibit the agglomeration of impurity phases, making the alloy structure more uniform and its properties more complete. Through this alloy composition design, the mechanical properties, corrosion resistance, and fatigue resistance of the alloy are significantly optimized, ensuring the reliability and safety of the aircraft tail fin in extreme environments.

[0023] This invention combines liquid nitrogen cryogenic treatment with multi-scale gradient aging strengthening technology. Through multi-stage temperature control, it achieves the synergistic distribution of nano-strengthening phases and sub-nanometer atomic clusters, completing a deep match between alloy composition design, microstructure control, and processing technology, thus overcoming the challenge of synergistic optimization of high strength and corrosion resistance. Simultaneously, it employs asynchronous cold rolling and temperature-controlled rolling technologies, significantly improving dislocation density and microstructure orientation strength through strain gradient design and dynamic recrystallization suppression, forming a gradient nanostructure with ultrafine grains on the surface and a high-density dislocation network retained in the core, achieving a simultaneous improvement in material strength and plasticity. The liquid nitrogen cryogenic process utilizes the rapid quenching effect under ultra-low temperature conditions to effectively suppress the diffusion and segregation of rare earth elements, ensuring the uniform distribution of ternary atomic clusters at an ultrafine scale and completely blocking the formation of coarse and brittle phases. Asynchronous rolling, through a composite strain mode, establishes multi-scale microstructure characteristics in the plate, strengthening the interface pinning effect. The multi-scale gradient aging process, based on a specific combination of temperature and time, precisely controls the size, distribution, and coherence of the main strengthening phase, activating the synergistic strengthening mechanism of multiple types of precipitated phases, ultimately achieving a combination of ultra-high strength and good ductility. Salt spray testing verifies that this process can significantly reduce intergranular corrosion sensitivity, enabling the material to maintain excellent corrosion resistance in harsh environments, successfully overcoming the typical failure problem of high-strength aluminum alloys.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1) Collaborative innovation in composition design leads to significant breakthroughs in overall performance. This invention constructs a ternary synergistic system of rare earth elements europium (Eu), silver (Ag), and ytterbium (Yb), fully leveraging the lattice distortion effect of ultra-large atomic radius rare earth elements. Combined with the targeted purification function of non-metallic element germanium (Ge), it achieves efficient coupling between the strengthening phase and the matrix at the atomic scale. The introduction of Eu significantly enhances dislocation pinning ability, while Ag's electron cloud regulation effect inhibits the diffusion and agglomeration of rare earth elements, forming ultrafine atomic clusters and completely eliminating the risk of brittle intermetallic compound formation. Ge preferentially combines with impurities to form coherent nanophases, blocking the coarsening path of harmful phases and significantly improving corrosion resistance while maintaining high strength. The multi-component synergistic design takes into account both strengthening and purification mechanisms, breaking through the bottleneck of the traditional aluminum alloy's inverted strength-toughness-corrosion resistance performance.

[0026] 2) Compatible and optimized preparation process with precise and efficient microstructure control: This invention, while fully utilizing the original cryogenic rolling process, achieves cross-scale optimization of the microstructure through precise control of element ratios. During the casting process, the synergistic effect of rare earth elements and Ag refines the dendritic structure and improves compositional uniformity; during the temperature-controlled rolling stage, the lattice distortion effect of Eu promotes dislocation proliferation and storage, forming a high-strength microstructure; the two-stage aging process achieves precise control of the size and distribution of the strengthening phase through stepwise temperature-time regulation. The high adaptability of the process parameters throughout the entire process ensures that the alloy achieves the synergistic strengthening effect of nanoscale precipitates and ultrafine grains without the need for complex equipment modifications; 3) Excellent performance-cost balance with broad industrial application prospects: Through a disruptive rare earth element substitution strategy and a combination of trace high-efficiency elements, performance leaps are achieved at extremely low addition levels. The synergistic effect of Eu and Ag partially replaces precious metal elements, significantly reducing material costs; the impurity targeting and fixation technology of Ge element reduces subsequent purification processes and improves production yield. The resulting alloy possesses ultra-high strength, excellent formability, and resistance to corrosion in extreme environments, making it particularly suitable for fields with stringent requirements for comprehensive material performance, such as ultra-high-speed rail transportation and aerospace. It provides a novel material solution for addressing the challenge of synergistic lightweighting and long service life in high-end equipment. Attached Figure Description

[0027] Figure 1 The image shows the IPF (Intensity Per Frame) of the high-strength and high-toughness 2xxx aluminum alloy obtained in Example 1 of this invention.

[0028] Figure 2 The image shown is a SAED diagram of the high-strength and high-toughness 2xxx aluminum alloy obtained by liquid forging in Example 1 of this invention. Detailed Implementation

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The alloy compositions selected in the following embodiments include pure aluminum, pure copper, aluminum-magnesium master alloy, aluminum-manganese master alloy, aluminum-ytterbium master alloy, aluminum-silver master alloy, aluminum-germanium master alloy, and aluminum-europium master alloy, wherein the master alloys are Al-10Mg, Al-10Mn, Al-5Yb, Al-10Ag, Al-10Ge, and Al-5Eu, respectively. The pure aluminum contains ≥99.9% aluminum, and the pure copper contains ≥99.9% copper. The total impurity content in the alloy composition is ≤0.1 wt.%, and the impurity content of any single component is ≤0.03%. The order of adding each alloy is as follows: First, pure aluminum is added to a vacuum induction melting furnace and heated to 700℃ to melt it completely. Then, the temperature is controlled at 700-720℃, and pure copper, aluminum-magnesium master alloy, aluminum-manganese master alloy, aluminum-ytterbium master alloy, aluminum-silver master alloy, aluminum-germanium master alloy, and aluminum-europium master alloy are added in sequence. Ar + 0.5% CH4 protective gas is blown in, and finally the temperature is raised to 730℃-750℃ and stirred for 10 minutes to ensure that the alloy is fully dissolved and uniformly mixed.

[0033] Before operating the smelting furnace, it must be preheated to 600-650℃ to ensure the furnace is dry and free of impurities. For multi-scale gradient aging strengthening, multi-stage aging strengthening should be performed immediately after solution treatment. The amount of CH4 in the Ar+CH4 protective gas should account for 0.5% of the total volume of the Ar+CH4 mixture.

[0034] Example 1

[0035] A composite controlled-rolled 2xxx series aluminum alloy has the following chemical composition by mass percentage: Cu 4.5%, Mg 1.5%, Mn 0.515%, Yb 0.12%, Ag 0.25%, Ge 0.05%, Eu 0.10%, which conforms to Mn = (1 / 2Ag + Eu + 2Yb + Ge) and (Yb + Eu + 2Ge) / Ag = 1.28, with the balance being Al and other unavoidable impurities.

[0036] A method for preparing 2xxx series aluminum alloys with stepped strengthening through composite controlled rolling includes vacuum induction melting, liquid nitrogen cryogenic crushing, multi-pass temperature-controlled hot rolling, asynchronous cold rolling microstructure control, and multi-scale gradient aging strengthening. The specific operation steps are as follows:

[0037] 1) Vacuum induction melting: Take the alloy components and put them into the melting furnace in sequence, and blow in Ar+CH4 protective gas. Heat to 730℃, add each alloy in sequence, add refining agent, the content of which is 0.3% of the mass of aluminum liquid, stir for 5 minutes to remove impurities in the metal solution, so as to ensure that the alloy is fully dissolved and uniformly mixed, and cast into 300mm thick flat ingots.

[0038] 2) Liquid nitrogen cryogenic treatment: Place the 300mm thick flat ingot in a liquid nitrogen environment (-194℃) for 2 hours, and blow in Ar+CH4 protective gas to prevent oxidation. Keep it at this temperature for 2 hours to refine the dendrites.

[0039] 3) Multi-pass temperature-controlled hot rolling: The thick flat ingot is heated to 420℃ and rolled to 20mm in 5 passes. The deformation per pass is 20%, and the final rolling temperature is 360℃. The temperature needs to be controlled after each rolling, and water mist cooling is used with a cooling rate of more than 80℃ / s.

[0040] 4) Asynchronous cold rolling microstructure control: The rolling path is 45° cross rolling, with intermediate annealing at 260℃ for 1 hour; the final plate thickness is 2.5 mm; the total deformation of cross rolling is 85%;

[0041] 5) Multi-scale gradient aging strengthening: supersaturated solution treatment, 510℃×0.75h in a salt bath furnace, water quenching, cooling rate of water quenching >500℃ / s, pre-aging at 110℃ for 4 hours, multi-stage aging strengthening should be carried out immediately after solution treatment; gradient aging at 150℃→170℃→190℃, holding at each stage for 2 hours; final aging at 210℃ for 4 hours, water cooling to room temperature.

[0042] The process for detecting the thermal expansion coefficient and conductivity parameters of the alloy is as follows: 1) The alloy is processed into a sample of a specific size (such as a slender rod) and placed in a thermal expansion instrument. Under program control, the sample is heated at a certain heating rate, and the change in sample length with temperature is measured in real time using a high-precision displacement sensor. The thermal expansion coefficient is calculated according to the definition formula α=(1 / L0)×(dL / dT) (L0 is the initial length, dL / dT is the rate of change of length with temperature). 2) Four probes are arranged in a straight line and make good contact with the surface of the alloy sample. A constant current is passed through the two outer probes, and the voltage is measured on the two inner probes. The resistivity of the sample is calculated according to a specific formula based on the measured voltage and current values, and then the conductivity is obtained.

[0043] The results of the greenhouse mechanical properties, stress corrosion resistance, coefficient of thermal expansion and conductivity of the workpiece obtained in Example 1 are shown in Table 1.

[0044] Example 2

[0045] A method for preparing 2xxx series aluminum alloys with stepped strengthening by composite controlled rolling, wherein the chemical composition by mass percentage is: Cu 4.8%, Mg 1.44%, Mn 0.78%, Yb 0.15%, Ag 0.4%, Ge 0.08%, Eu 0.20%, which conforms to Mn=(1 / 2Ag+Eu+2Yb+Ge) and (Yb+Eu+2Ge) / Ag=1.275, with the balance being Al and other unavoidable impurities.

[0046] A method for preparing 2xxx series aluminum alloys with stepped strengthening through composite controlled rolling includes vacuum induction melting, liquid nitrogen cryogenic crushing, multi-pass temperature-controlled hot rolling, asynchronous cold rolling microstructure control, and multi-scale gradient aging strengthening. The specific operation steps are as follows:

[0047] 1) Vacuum induction melting: Take the alloy components and put them into the melting furnace in sequence, and blow in Ar+CH4 protective gas. Heat to 740℃, add each alloy in sequence, add refining agent, content 0.5%, stir for 8 minutes to remove impurities in the metal solution, so as to ensure that the alloy is fully dissolved and uniformly mixed, and cast into 300mm thick flat ingots.

[0048] 2) Liquid nitrogen cryogenic treatment: Place the 300mm thick flat ingot in a liquid nitrogen environment (-194℃) for 3 hours, and blow in Ar+CH4 protective gas to prevent oxidation. Keep it at this temperature for 3 hours to refine the dendrites.

[0049] 3) Multi-pass temperature-controlled hot rolling: The thick flat ingot is heated to 430℃ and rolled to 20mm in 5 passes. The deformation per pass is 25%, and the final rolling temperature is 370℃. The temperature needs to be controlled after each rolling, and water mist cooling is used with a cooling rate greater than 80℃ / s.

[0050] 4) Asynchronous cold rolling microstructure control: The rolling path is 45° cross rolling, with intermediate annealing at 260℃ for 1 hour; the final plate thickness is 2.5 mm; the total deformation of cross rolling is 85%;

[0051] 5) Multi-scale gradient aging strengthening: supersaturated solution treatment, 510℃×0.75h in a salt bath furnace, water quenching, cooling rate of water quenching >500℃ / s, pre-aging at 110℃ for 5 hours, multi-stage aging strengthening should be carried out immediately after solution treatment; gradient aging at 150℃→170℃→190℃, holding at each stage for 2 hours; final aging at 210℃ for 4 hours, water cooling to room temperature.

[0052] The measurement process for the coefficient of thermal expansion and conductivity of the alloy obtained in Example 2 is the same as that in Example 1.

[0053] The results of the greenhouse mechanical properties, stress corrosion resistance, coefficient of thermal expansion and conductivity of the workpiece obtained in Example 2 are shown in Table 1.

[0054] Example 3

[0055] A composite controlled-rolled 2xxx series aluminum alloy has the following chemical composition by mass percentage: Cu 4.2%, Mg 1.3%, Mn 0.6%, Yb 0.13%, Ag 0.3%, Ge 0.04%, Eu 0.15%, which conforms to Mn = (1 / 2Ag + Eu + 2Yb + Ge) and (Yb + Eu + 2Ge) / Ag = 1.2, with the balance being Al and other unavoidable impurities.

[0056] A method for preparing 2xxx series aluminum alloys with stepped strengthening through composite controlled rolling includes vacuum induction melting, liquid nitrogen cryogenic crushing, multi-pass temperature-controlled hot rolling, asynchronous cold rolling microstructure control, and multi-scale gradient aging strengthening. The specific operation steps are as follows:

[0057] 1) Vacuum induction melting: Take the alloy components and put them into the melting furnace in sequence, and blow in Ar+CH4 protective gas. Heat to 750℃, add each alloy in sequence, add refining agent, content 0.7%, stir for 10 minutes to remove impurities in the metal solution, so as to ensure that the alloy is fully dissolved and uniformly mixed, and cast into 300mm thick flat ingots.

[0058] 2) Liquid nitrogen cryogenic treatment: Place the 300mm thick flat ingot in a liquid nitrogen environment (-194℃) for 4 hours, and blow in Ar+CH4 protective gas to prevent oxidation. Keep it at this temperature for 4 hours to refine the dendrites.

[0059] 3) Multi-pass temperature-controlled hot rolling: The thick flat ingot is heated to 440℃ and rolled to 20mm in 5 passes. The deformation per pass is 25%, and the final rolling temperature is 380℃. The temperature needs to be controlled after each rolling, and water mist cooling is used with a cooling rate greater than 80℃ / s.

[0060] 4) Asynchronous cold rolling microstructure control: The rolling path is 45° cross rolling, with intermediate annealing at 260℃ for 1 hour; the final plate thickness is 2.5 mm; the total deformation of cross rolling is 85%;

[0061] 5) Multi-scale gradient aging strengthening: supersaturated solution treatment, 510℃×1h in salt bath furnace, water quenching, water quenching cooling rate>500℃ / s, pre-aging at 110℃ for 5 hours, multi-stage aging strengthening should be carried out immediately after solution treatment; gradient aging at 150℃→170℃→190℃, holding at each stage for 2 hours; final aging at 210℃ for 4 hours, water cooling to room temperature.

[0062] The measurement process for the coefficient of thermal expansion and conductivity of the alloy obtained in Example 3 is the same as that in Example 1.

[0063] The results of the greenhouse mechanical properties, stress corrosion resistance, coefficient of thermal expansion and conductivity of the workpiece obtained in Example 3 are shown in Table 1.

[0064] Example 4

[0065] A method for preparing 2xxx series aluminum alloys with stepped strengthening by composite controlled rolling, wherein the chemical composition by mass percentage is: Cu 4.6%, Mg 1.6%, Mn 0.59%, Yb 0.10%, Ag 0.3%, Ge 0.06%, Eu 0.18%, which conforms to Mn=(1 / 2Ag+Eu+2Yb+Ge) and (Yb+Eu+2Ge) / Ag=1.33, with the balance being Al and other unavoidable impurities.

[0066] A method for preparing 2xxx series aluminum alloys with stepped strengthening through composite controlled rolling includes vacuum induction melting, liquid nitrogen cryogenic crushing, multi-pass temperature-controlled hot rolling, asynchronous cold rolling microstructure control, and multi-scale gradient aging strengthening. The specific operation steps are as follows:

[0067] 1) Vacuum induction melting: Take the alloy components and put them into the melting furnace in sequence, and blow in Ar+CH4 protective gas. Heat to 750℃, add each alloy in sequence, add refining agent, 1% content, stir for 10 minutes to remove impurities in the metal solution, so as to ensure that the alloy is fully dissolved and uniformly mixed, and cast into 300mm thick flat ingots.

[0068] 2) Liquid nitrogen cryogenic treatment: Place the 300mm thick flat ingot in a liquid nitrogen environment (-194℃) for 2.5 hours, and blow in Ar+CH4 protective gas to prevent oxidation. Keep it at this temperature for 2.5 hours to refine the dendrites.

[0069] 3) Multi-pass temperature-controlled hot rolling: The thick flat ingot is heated to 450℃ and rolled to 20mm in 5 passes. The deformation per pass is 22%, and the final rolling temperature is 390℃. The temperature needs to be controlled after each rolling, and water mist cooling is used with a cooling rate greater than 80℃ / s.

[0070] 4) Asynchronous cold rolling microstructure control: The rolling path is 45° cross rolling, with intermediate annealing at 260℃ for 1 hour; the final plate thickness is 2.5 mm; the total deformation of cross rolling is 85%;

[0071] 5) Multi-scale gradient aging strengthening: supersaturated solution treatment, 510℃×1h in salt bath furnace, water quenching, water quenching cooling rate>500℃ / s, pre-aging at 110℃ for 6 hours, multi-stage aging strengthening should be carried out immediately after solution treatment; gradient aging at 150℃→170℃→190℃, holding at each stage for 2 hours; final aging at 210℃ for 4 hours, water cooling to room temperature.

[0072] The thermal expansion coefficient and electrical conductivity of the alloy obtained in Example 4 are obtained through the same process as in Example 1.

[0073] The results of the greenhouse mechanical properties, stress corrosion resistance, coefficient of thermal expansion and conductivity of the workpiece obtained in Example 4 are shown in Table 1.

[0074] Example 5

[0075] A method for preparing 2xxx series aluminum alloys with stepped strengthening by composite controlled rolling, wherein the chemical composition by mass percentage is: Cu 4.3%, Mg 1.4%, Mn 0.58%, Yb 0.1%, Ag 0.3%, Ge 0.04%, Eu 0.19%, which conforms to Mn=(1 / 2Ag+Eu+2Yb+Ge) and (Yb+Eu+2Ge) / Ag=1.23, with the balance being Al and other unavoidable impurities.

[0076] The preparation method of Example 5 is the same as that of Example 1, except that:

[0077] Step 1) Vacuum induction melting: Take the alloy components and put them into the melting furnace in sequence, and blow in Ar + CH4 protective gas. Heat to 750°C, add each alloy in sequence, add refining agent, content 1.2%, stir for 10 minutes to remove impurities in the metal solution, and ensure that the alloy is fully dissolved and uniformly mixed. Cast into 300mm thick flat ingots.

[0078] Step 3) Multi-pass temperature-controlled hot rolling: Heat the thick flat ingot to 450℃, roll it to 20mm in 5 passes, with a single deformation of 25%, and a final rolling temperature of 400℃. Control the temperature after each rolling and use water mist cooling with a cooling rate greater than 80℃ / s.

[0079] Step 5) Multi-scale gradient aging strengthening: supersaturated solution treatment, 510℃×0.9h in a salt bath furnace, water quenching, cooling rate of water quenching >500℃ / s, pre-aging at 110℃ for 5 hours, multi-stage aging strengthening should be carried out immediately after solution treatment; gradient aging at 150℃+170℃+190℃, holding at each stage for 2 hours; final aging at 210℃ for 4 hours, water cooling to room temperature.

[0080] The measurement process for the coefficient of thermal expansion and conductivity of the alloy obtained in Example 5 is the same as that in Example 1.

[0081] The results of the greenhouse mechanical properties, stress corrosion resistance, coefficient of thermal expansion and conductivity of the workpiece obtained in Example 5 are shown in Table 1.

[0082] Example 6

[0083] A method for preparing 2xxx series aluminum alloys with stepped strengthening by composite controlled rolling, wherein the chemical composition by mass percentage is: Cu 4.7%, Mg 1.6%, Mn 0.645%, Yb 0.12%, Ag 0.35%, Ge 0.07%, Eu 0.16%, conforming to Mn=(1 / 2Ag+Eu+2Yb+Ge) and (Yb+Eu+2Ge) / Ag=1.2, with the balance being Al and other unavoidable impurities.

[0084] The preparation method of Example 6 is the same as that of Example 1, except that:

[0085] Step 1) Vacuum induction melting: Take the alloy components and put them into the melting furnace in sequence, and blow in Ar + CH4 protective gas. Heat to 730°C, add each alloy in sequence, add refining agent, content 1.3%, stir for 10 minutes to remove impurities in the metal solution, and ensure that the alloy is fully dissolved and uniformly mixed. Cast into 300mm thick flat ingots.

[0086] Step 3) Multi-pass temperature-controlled hot rolling: Heat the thick flat ingot to 420℃, roll it to 20mm in 5 passes, with a single deformation of 25%, and a final rolling temperature of 390℃. After each rolling, the temperature needs to be controlled and water mist cooling is used with a cooling rate greater than 80℃ / s.

[0087] The measurement process for the coefficient of thermal expansion and conductivity of the alloy obtained in Example 6 is the same as that in Example 1.

[0088] The results of the greenhouse mechanical properties, stress corrosion resistance, coefficient of thermal expansion and conductivity of the workpiece obtained in Example 6 are shown in Table 1.

[0089] Comparative Example 1

[0090] The preparation method of Comparative Example 1 is the same as that of Example 1, except that the mass percentage of each component is different:

[0091] Its chemical composition by mass percentage is: Cu 4.4%, Mg 1.5%, Mn 0.51%, Yb 0.09%, Ag 0.28%, Ge 0.05%, Eu 0.14%, Mn = (1 / 2Ag + Eu + 2Yb + Ge)(Yb + Eu + 2Ge) / Ag = 1.18, with the balance being Al and other unavoidable impurities.

[0092] Step 2) Conventional cooling: After the melt is poured, it is allowed to cool naturally to room temperature without liquid nitrogen cryogenic treatment;

[0093] The test results of the greenhouse mechanical properties, stress corrosion resistance, coefficient of thermal expansion and electrical conductivity of the workpiece obtained in Comparative Example 1 are shown in Table 1.

[0094] Comparative Example 2

[0095] The preparation method of Comparative Example 2 is the same as that of Example 1, except that the mass percentage of each component is different:

[0096] Its chemical composition by mass percentage is: Cu 4.9%, Mg 1.1%, Mn 0.57%, Yb 0.05%, Ag 0.4%, Ge 0.07%, Eu 0.2%, Mn = (1 / 2Ag + Eu + 2Yb + Ge) and (Yb + Eu + 2Ge) / Ag = 0.975, with the balance being Al and other unavoidable impurities.

[0097] Step 1) Smelting: Use ordinary refining process (N2 protection, no Cl2 gas added), refining agent dosage 0.5%;

[0098] The test results of the greenhouse mechanical properties, stress corrosion resistance, coefficient of thermal expansion and conductivity of the workpiece obtained in Comparative Example 2 are shown in Table 1.

[0099] Table 1

[0100]

[0101] As shown in Table 1, this invention achieves a comprehensive improvement in the performance of high-strength and high-toughness 2xxx series aluminum alloys through scientific and precise alloy composition design, composite rolling control, and synergistic optimization of step strengthening. A high-strength, high-toughness, and corrosion-resistant aluminum alloy material system is constructed through the coupling effect of rare earth element atomic radius gradient design and non-metallic hybridization reactions. Utilizing the ultra-large atomic radius of europium (Eu) and the synergistic effect of electron orbitals of silver (Ag) and ytterbium (Yb), a stable atomic cluster structure is constructed at the nanoscale, significantly enhancing dislocation pinning ability and grain boundary stability. Simultaneously, the targeted impurity purification mechanism of germanium (Ge) eliminates brittle phase segregation. Based on complete compatibility with existing cryogenic rolling processes, through multi-level strengthening network design of atomic clusters and precipitated phases and precise control of lattice distortion energy, the inverse relationship of strength-plasticity-corrosion resistance in traditional aluminum alloys is broken, exhibiting excellent comprehensive performance matching in the field of aircraft tail fins. This system achieves a leapfrog improvement in the basic properties of materials while maintaining process economy through the functional combination of rare earth elements and the in-situ conversion strategy of impurity elements, providing a revolutionary solution for the manufacturing of next-generation aircraft tail fins.

[0102] 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 composite controlled-rolled 2xxx series aluminum alloy, characterized in that, Its chemical composition by mass percentage is as follows: Cu 4.2-4.8%, Mg 1.3-1.7%, Mn 0.5-0.8%, Ag 0.1-0.4%, Eu 0.05-0.20%, Yb 0.05-0.15%, Ge 0.02-0.08%, and simultaneously satisfies Mn=1 / 2Ag+Eu+2Yb+Ge, (Yb+Eu+2Ge) / Ag=0.9-1.4, with the balance being Al and unavoidable impurities, and the total content of impurity components ≤0.1wt.%, and the content of individual impurity components ≤0.03%.

2. The method for preparing a stepped strengthening process of a composite controlled-rolled 2xxx series aluminum alloy according to claim 1, characterized in that, The processes include vacuum induction melting, cryogenic crushing with liquid nitrogen, multi-pass temperature-controlled hot rolling, asynchronous cold rolling microstructure control, and multi-scale gradient aging strengthening. The specific operation steps are as follows: 1) Vacuum induction melting: Take the alloy components and put them into the melting furnace in sequence, blow in Ar+CH4 protective gas, heat to 730℃-750℃, add powder refining agent, stir for 5-10 minutes to remove impurities in the metal solution, and ensure that the alloy is fully dissolved and uniformly mixed. After removing the slag with a slag removal tool, cast into 300mm thick flat ingots. 2) Liquid nitrogen cryogenic treatment: Place the thick flat ingot in a liquid nitrogen environment for 2-4 hours and blow in Ar+CH4 protective gas to prevent oxidation; 3) Multi-pass temperature-controlled hot rolling: The thick flat ingot is heated to 420℃-450℃ and rolled to 20mm in 5 passes. The deformation per pass is 20-25%. The final rolling temperature should be 360℃-400℃. The temperature needs to be controlled after each rolling and water mist cooling is used. 4) Asynchronous cold rolling microstructure control: The rolling path is 45° cross rolling, with intermediate annealing at 260℃ for 1 hour; the final plate thickness is 2.5 mm; 5) Multi-scale gradient aging strengthening: supersaturated solution treatment, 510℃×(0.75-1)h in salt bath furnace, water quenching, pre-aging at 110℃ for 4-6 hours; gradient aging at 150℃→170℃→190℃, holding at each stage for 2 hours; final aging at 210℃ for 4 hours, water cooling to room temperature.

3. The method for preparing a stepped strengthening process of a composite controlled-rolled 2xxx series aluminum alloy according to claim 2, characterized in that, The alloy composition selected in step 1) includes pure aluminum, pure copper, aluminum-magnesium master alloy, aluminum-manganese master alloy, aluminum-ytterbium master alloy, aluminum-silver master alloy, aluminum-germanium master alloy, and aluminum-europium master alloy, wherein the master alloys are Al-10Mg, Al-10Mn, Al-5Yb, Al-10Ag, Al-10Ge, and Al-5Eu, respectively; the aluminum content in the pure aluminum is ≥99.9%; and the copper content in the pure copper is ≥99.9%.

4. The method for preparing a stepped strengthening process of a composite controlled-rolled 2xxx series aluminum alloy according to claim 2, characterized in that, Before the induction melting furnace operates in step 1), it is necessary to preheat the furnace to 600-650℃ to ensure that the furnace is dry and free of impurities.

5. The method for preparing a stepped strengthening process of a composite controlled-rolled 2xxx series aluminum alloy according to claim 2, characterized in that, In step 1), the order of adding each alloy component is as follows: first, pure aluminum is added to a vacuum induction melting furnace and heated to 700°C to completely melt it. Then, the temperature is controlled at 700-720°C, and pure copper, aluminum-magnesium master alloy, aluminum-manganese master alloy, aluminum-ytterbium master alloy, aluminum-silver master alloy, aluminum-germanium master alloy, and aluminum-europium master alloy are added in sequence.

6. The method for preparing a stepped strengthening process of a composite controlled-rolled 2xxx series aluminum alloy according to claim 2, characterized in that, In step 1), the powdered refining agent is added to the molten aluminum using a powder spraying device. With Ar+CH4 protective gas as the carrier gas, the refining agent is evenly sprayed into the bottom of the molten aluminum. After stirring, it is allowed to stand for 10-15 minutes to allow impurities to float to the surface. The amount of powdered refining agent is 0.3% to 1.2% of the mass of the molten aluminum. The amount of CH4 accounts for 0.5% of the total volume of the Ar+CH4 mixture.

7. The method for preparing a stepped strengthening process of a composite controlled-rolled 2xxx series aluminum alloy according to claim 2, characterized in that, The powder refining agent in step 1) is composed of the following components by weight percentage: NaCl (28%~32%) + KCl (25%~30%) + Na2CO3 (10%~15%) + K2TiF6 (8%~12%) + CeO2 (5%~8%) + BaCO3 (3%~5%).

8. The method for preparing a stepped strengthening process of a composite controlled-rolled 2xxx series aluminum alloy according to claim 2, characterized in that, In step 3), the water mist cooling rate is greater than 80℃ / s.

9. The method for preparing a stepped strengthening process of a composite controlled-rolled 2xxx series aluminum alloy according to claim 2, characterized in that, The total deformation during cross-rolling in step 4) is 85%.

10. The method for preparing a stepped strengthening process of a composite controlled-rolled 2xxx series aluminum alloy according to claim 2, characterized in that, In step 5), the water quenching cooling rate is >500℃ / s, and multi-stage aging strengthening should be carried out immediately after solution treatment.

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