Preparation method of ultrahigh-toughness 2024 aluminum alloy

Abstract

The invention relates to a preparation method of an ultrahigh-toughness 2024 aluminum alloy. The preparation method comprises the following steps: A, providing a 2024 aluminum alloy bar which has the diameter of 30-120mm and is subjected to primary hot extrusion; b, semi-solid isothermal treatment is conducted, specifically, the 2024 aluminum alloy bar is heated to the semi-solid interval of 520-580 DEG C, heat preservation is conducted for 5-60 min, and then rapid water-cooling quenching is conducted; c, secondary hot extrusion is conducted, specifically, the 2024 aluminum alloy bar is subjected to secondary hot extrusion, the extrusion temperature is 350-450 DEG C, the extrusion speed is 0.1-4 mm / s, the extrusion ratio is (6-20): 1, a plain end die or a conical die is adopted, and air cooling or water cooling is conducted to the room temperature after extrusion; and D, directly carrying out aging treatment on the secondarily extruded aluminum alloy obtained in the step C or firstly carrying out solution treatment and then carrying out aging treatment to obtain the ultrahigh-toughness 2024 aluminum alloy. The solid solution treatment temperature is 480-510 DEG C, the solid solution treatment time is 0.5-2 hours, water-cooling quenching is carried out after the solid solution treatment, the aging treatment temperature is 140-160 DEG C, the aging treatment time is 10-20 hours, and water-cooling quenching is carried out after the aging treatment. The 2024 aluminum alloy prepared through the method has excellent tensile strength, yield strength and ductility.

Description

Technical Field

[0001] This invention relates to a method for preparing ultra-high strength and toughness 2024 aluminum alloy, belonging to the field of aluminum alloy manufacturing. Background Technology

[0002] 2024 aluminum alloy, a typical 2xxx series aluminum alloy, is widely used in aerospace, automotive manufacturing, and rail transportation due to its excellent strength, fatigue performance, and machinability. Examples include its use in aircraft skins, structural components, and high-speed train body frames. Currently, industrially produced 2024 aluminum alloy bars are mainly obtained through traditional hot extrusion and T6 heat treatment (solution + aging), with typical tensile strengths of 400-450 MPa, yield strengths of 300-350 MPa, and elongation of 20-30%. However, with the increasing demand for lightweight, high-strength materials in the aerospace field, the existing properties of 2024 alloys are insufficient to meet the requirements of extreme working conditions, such as fatigue life and corrosion resistance under higher loads. Furthermore, the traditional process contains coarse S-phase (Al₂CuMg) and T-phase, which are brittle and coarse, limiting the improvement of alloy strength and exacerbating the strength-plasticity inversion problem. Specifically, these micron-sized coarse phases deplete solute atoms, reducing matrix supersaturation and thus limiting precipitation hardening potential. Simultaneously, they act as stress concentration sources, inducing crack initiation and propagation, significantly weakening the alloy's ductility. Existing conventional methods such as casting, rolling, or extrusion are insufficient for efficiently refining these phases, necessitating novel microstructure control techniques to alleviate the strength-plasticity tradeoff. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing ultra-high strength and toughness 2024 aluminum alloy. This method combines semi-solid isothermal treatment, secondary hot extrusion, and aging or solution + aging processes to prepare ultra-high strength and toughness 2024 aluminum alloy with excellent tensile strength, yield strength, and elongation.

[0004] The technical solution adopted by this invention to achieve its objective is: a method for preparing ultra-high strength and toughness 2024 aluminum alloy, the steps of which are as follows: A. Provide 2024 aluminum alloy bars with diameters of 30-120mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; B. Semi-solid isothermal treatment: Heat the 2024 aluminum alloy bar from step A to the semi-solid range of 520-580℃, hold for 5-60 minutes, and then quickly water-quench it. The quenching medium is water at 20-80℃. C. Secondary hot extrusion: The 2024 aluminum alloy bar that has undergone semi-solid isothermal treatment is subjected to secondary hot extrusion. The extrusion temperature is 350-450℃, the extrusion speed is 0.1-4mm / s, the extrusion ratio is 6-20:1, and a flat die or a conical die is used. After extrusion, the aluminum alloy is air-cooled or water-cooled to room temperature to obtain secondary extruded aluminum alloy. D. Aging treatment or solution aging treatment: The specific operation of the aging treatment is to directly age the secondary extruded aluminum alloy obtained in step C. The aging treatment temperature is 140-160℃, the aging treatment time is 10-20h, and the aging treatment is followed by water quenching to obtain ultra-high strength and toughness 2024 aluminum alloy. The specific operation of the solution aging treatment is as follows: First, the secondary extruded aluminum alloy obtained in step C is subjected to solution treatment. The solution treatment includes placing the secondary extruded aluminum alloy obtained in step C at a temperature of 480-510℃ for 0.5-2 hours, followed by water quenching. Then, the solution-treated secondary extruded aluminum alloy is subjected to aging treatment at a temperature of 140-160℃ for 10-20 hours. After aging treatment, it is water quenched to obtain ultra-high strength and toughness 2024 aluminum alloy.

[0005] The reaction principle of this invention is as follows: The initial microstructure of the commercial 2024 aluminum alloy bar provided in step A, which underwent hot extrusion according to GB / T 3191-2019, consists of coarse S-phase (Al2CuMg) and T-phase distributed in an α-Al matrix. After semi-solid isothermal treatment and rapid quenching in step B, the extremely high cooling rate achieves a large degree of supercooling, thereby increasing the growth rate of the eutectic. At the same time, it also greatly shortens the atomic diffusion distance. Under the combined effect of these two factors, a uniformly distributed nanoscale S-phase lamellar eutectic is formed at the grain boundaries. Specifically, the high-temperature local melting in the semi-solid region promotes solute redistribution, and the rapid water-cooling quenching follows the solidification theory (supercooling). ΔT = T m - T , T m Melting point T (actual temperature), high supercooling increases growth rate. R ∝ ΔT Meanwhile, atomic diffusion coefficient D ∝ exp(-Q / RT) ( Q To activate energy, R The gas constant is... T The high cooling rate limits the temperature, causing Cu and Mg atoms to rapidly solidify into fine lamellar phases rather than coarse bulk phases at the grain boundaries; step C, secondary hot extrusion, further breaks down these nanocrystalline eutectic phases, due to the Gibbs-Thomson effect (chemical potential difference). Δμ = 2γΩ / r , γ For interface energy, Ω Atomic volume rThe coarsening process, involving both the radius of curvature and Ostwald ripening (dissolution of small particles and transfer to larger particles), results in the formation of spherical submicron particles. These particles are more easily dissolved than traditional coarse S phases, thus increasing the solute atom concentration in the matrix. The specific mechanism is as follows: high shear stress and thermal activation increase the dissolution threshold in the high-curvature region at the edge of the lamellar structure, generating a concentration gradient that drives solute diffusion from the high-curvature region to the low-curvature region, promoting spheroidization and size homogenization. Step D, the aging treatment, utilizes the residual solute atoms in the extruded state and the high dislocation density (solute atoms diffuse more efficiently along dislocation channels, resulting in a higher channel diffusion coefficient). D p >> Bulk diffusion coefficient D b To promote the precipitation of the S' phase, or to further enhance the degree of solid solution through solution treatment followed by aging, a higher density of fine precipitated phases can be achieved. High-density dispersed S' phases are precipitated through the Orowan mechanism (critical stress). τ ∝ √ f / λ , f It is the volume fraction. λ The spherical submicron S-phase strengthens the dislocations during deformation, effectively pinning them and promoting uniform dislocation accumulation. Furthermore, the spherical submicron S-phase reduces the local strain gradient, suppressing recrystallization induced by particle-induced nucleation (PSN requires high dislocation density to lower the nucleation barrier, but the spherical phase reduces stress concentration and dislocation multiplication), thus preserving a coarse-grained region with high dislocation density. This optimized bimodal grain structure possesses excellent ability to maintain strain hardening. Ultimately, this significantly improves the alloy's strength and ductility, achieving high strength and toughness in commercially available 2024 aluminum alloys.

[0006] I. For commercial 2024 aluminum alloy bars, a semi-solid isothermal treatment and secondary hot extrusion were introduced to achieve the transformation from coarse second phase to nanoscale lamellar eutectic and then to submicron particles, without the need for additional alloying, resulting in low cost. This process refines the second phase size by more than 50% through semi-solid local melting and rapid quenching, while secondary extrusion promotes the breakup and spheroidization of the nanolamellar eutectic, reducing stress concentration caused by the irregular edges of the second phase. Furthermore, the refined spherical S phase is more easily dissolved during solid solution treatment, thereby increasing the solute saturation and subsequently increasing the density of precipitated phases, ultimately leading to a significant increase in alloy strength.

[0007] Second, it offers two pathways: aging and solution + aging, flexibly adapting to different industrial needs. The aging pathway simplifies the process and controls costs, while the solution + aging pathway further optimizes performance. This coupling process can reduce the size of the second phase to the submicron level and highly spheroidize it under thermomechanical processing conditions, coupling high-density precipitation and bimodal grain structure to achieve tensile strength of 450-605MPa, yield strength of 350-520MPa, and elongation of 10-25%, far exceeding the 438MPa strength and 30% elongation obtained by the traditional process (secondary extrusion + solution aging treatment), breaking the dilemma of strength-plasticity trade-off.

[0008] III. The strengthening mechanisms include Orowan bypass strengthening of the S' precipitate, load transfer of the spherical S phase, and contributions from the high-density dislocation structure; the improvement in plasticity stems from the relief of stress concentration by spherical particles (stress concentration factor). K T ∝ √a / r , a For defect size, r For the tip radius, sphericity increases r The non-recrystallization zone accommodates deformation and prevents crack propagation. This method requires no change in composition, allows for flexible and easily controllable processing parameters, is suitable for large-scale industrial production, and has significant engineering application potential.

[0009] Furthermore, the diameter of the 2024 aluminum alloy rod in step A of the present invention is 35-100mm.

[0010] Tests have verified that this size range ensures stable semi-solid behavior and subsequent processability.

[0011] Furthermore, the semi-solid temperature range of the semi-solid isothermal treatment in step B of the present invention is 530-560℃, and the holding time is 10-45min.

[0012] Experimental results show that the above semi-solid isothermal treatment parameters can avoid large-scale overmelting or insufficient refinement of layer thickness, and achieve optimal nanoscale eutectic formation of layers.

[0013] Furthermore, in step B of the present invention, the quenching medium for water-cooled quenching is water at 25-60°C.

[0014] Experiments have verified that the above-mentioned water temperature range significantly inhibits cracking and effectively preserves supersaturated solid solution.

[0015] Furthermore, in step C of the present invention, the extrusion temperature of the secondary hot extrusion is 380-420℃, the extrusion speed is 0.3-0.6mm / s, the extrusion ratio is 8-15:1, a conical die is used, and the material is water-cooled to room temperature after extrusion.

[0016] Experiments have verified that the above hot extrusion parameters can ensure uniform deformation and submicron particle distribution.

[0017] Furthermore, the cooling method after extrusion in step C of the present invention is water cooling, and the cooling medium is room temperature water.

[0018] Furthermore, in step D of the present invention, the aging temperature or solution aging treatment is 145-155℃ and the aging time is 12-18h.

[0019] Experiments have verified that the above-mentioned aging treatment temperature and time can achieve peak hardness and ensure the uniform precipitation of high-density S'.

[0020] Furthermore, the solution treatment in step D of the present invention includes placing the secondary extruded aluminum alloy obtained in step C at a temperature of 490-505℃ for 0.8-1.5h and then water quenching.

[0021] Experiments have verified that the above-mentioned solution temperature and time can ensure the maximum spheroidization and dissolution of S, thereby maximizing the degree of solution. Attached Figure Description

[0022] Figure 1 The tensile curve of the ultra-high strength and toughness 2024 aluminum alloy prepared in Embodiment 1 of the present invention is shown.

[0023] Figure 2 The image shows the microstructure of a 2024 aluminum alloy bar after semi-solid isothermal treatment according to Embodiment 1 of the present invention, where (b) is a magnified view of (a).

[0024] Figure 3 The image shows the microstructure of the secondary extruded aluminum alloy after secondary hot extrusion in Embodiment 1 of the present invention, where (b) is a magnified view of (a).

[0025] Figure 4 Transmission electron microscopy (TEM) images and energy-dispersive X-ray spectroscopy (EDS) elemental mapping analysis of the 2024 aluminum alloy prepared in this comparative example and Example 5 are shown. (a) is a bright-field TEM image of the aluminum alloy prepared in the comparative example; (b) is the EDS elemental mapping of the corresponding region of (a), including (b1) Al, (b2) Cu, (b3) Mg, and (b4) Mn; (c) is a bright-field TEM image of the aluminum alloy prepared in Example 5; and (d) is the EDS elemental mapping of the corresponding region of (c), including (d1) Al, (d2) Cu, (d3) Mg, and (d4) Mn.

[0026] Figure 5TEM images and selected area electron diffraction (SAED) analysis of the precipitates of the 2024 aluminum alloy prepared in this comparative example and Example 5 are shown. (a) shows the morphology of the precipitates of the aluminum alloy prepared in the comparative example; (b) shows the SAED pattern of the marked area in (a); (c) shows the morphology of the precipitates of the aluminum alloy prepared in Example 5; and (d) shows the SAED pattern of the marked area in (c). Detailed Implementation

[0027] Comparative Example A method for preparing 2024 aluminum alloy, as a comparison with the present invention, comprises the following steps (without a semi-solid isothermal treatment step, directly performing secondary hot extrusion and solution aging treatment to simulate the traditional process): A. Provide 2024 aluminum alloy bars with a diameter of 50mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; C. Secondary hot extrusion: The 2024 aluminum alloy bar from step A is subjected to secondary hot extrusion at a temperature of 400℃, an extrusion speed of 0.4mm / s, and an extrusion ratio of 10:1. A conical die is used, and the bar is water-cooled to room temperature after extrusion to obtain a secondary extruded aluminum alloy. D. Solution aging treatment: The specific operation of the solution aging treatment is as follows: first, the secondary extruded aluminum alloy obtained in step C is subjected to solution treatment. The solution treatment includes placing the secondary extruded aluminum alloy obtained in step C at a temperature of 500°C for 1 hour, followed by water quenching. Then, the solution-treated secondary extruded aluminum alloy is subjected to aging treatment at a temperature of 150°C for 15 hours. After aging treatment, it is water quenched to obtain 2024 aluminum alloy.

[0028] The alloy prepared in this comparative example has a tensile strength of 438 MPa, a yield strength of 320 MPa, and an elongation of 30.0%. Compared with the embodiments of the present invention, this alloy has lower strength and higher elongation, reflecting the strength-plasticity inversion problem caused by the coarse second phase in traditional processes, which cannot achieve a synergy between high strength and reasonable plasticity. Example 1

[0029] A method for preparing ultra-high strength and toughness 2024 aluminum alloy, the steps of which are as follows: A. Provide 2024 aluminum alloy bars with a diameter of 50mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; B. Semi-solid isothermal treatment: The 2024 aluminum alloy bar from step A is heated to the semi-solid range of 540℃, held for 20 minutes, and then rapidly water-cooled and quenched. The quenching medium is water at 40℃. C. Secondary hot extrusion: The 2024 aluminum alloy bar, which has undergone semi-solid isothermal treatment, is subjected to secondary hot extrusion at a temperature of 400℃, an extrusion speed of 0.4mm / s, and an extrusion ratio of 10:1. A conical die is used, and the extruded material is water-cooled to room temperature to obtain a secondary extruded aluminum alloy. D. Solution aging treatment: The specific operation of the solution aging treatment is to first perform solution treatment on the secondary extruded aluminum alloy obtained in step C. The solution treatment includes placing the secondary extruded aluminum alloy obtained in step C at a temperature of 500°C for 1 hour, followed by water quenching. Then, the solution-treated secondary extruded aluminum alloy is subjected to aging treatment at a temperature of 150°C for 15 hours. After aging treatment, it is water quenched to obtain ultra-high strength and toughness 2024 aluminum alloy.

[0030] The alloy prepared in this example has a tensile strength of 542 MPa, a yield strength of 398 MPa, and an elongation of 15.8%.

[0031] Figure 1 The figure shows the tensile curve of the ultra-high strength and toughness 2024 aluminum alloy prepared in Example 1 of this invention. As can be seen from the figure, the stress-strain curve of the alloy exhibits a high strain hardening rate, with a final tensile strength of 542 MPa, a yield strength of 398 MPa, and an elongation of 15.8%. This performance improvement stems from the nanoscale S-phase lamellar eutectic formed after semi-solid isothermal treatment (see...). Figure 2 These eutectic particles are broken and coarsened into submicron spherical particles during the secondary hot extrusion process (see...). Figure 3 These particles promote the uniform diffusion of solute atoms (such as Cu and Mg) through the Gibbs-Thomson effect, increasing the supersaturation in the matrix. In subsequent solution aging treatment, the high-density S' phase (fine precipitates of Al2CuMg) pins dislocations through the Orowan mechanism, hindering dislocation movement and thus significantly enhancing strength. Simultaneously, the spherical submicron S phase reduces the local strain gradient, suppresses recrystallization induced by particle-induced nucleation (PSN) mechanisms, retains high dislocation density regions, and promotes uniform dislocation accumulation and strain hardening. This avoids the strength-plasticity inversion problem caused by the coarse second phase in traditional 2024 alloys, achieving strength while maintaining a reasonable elongation.

[0032] Figure 2The image shows the SEM image of the microstructure of a 2024 aluminum alloy bar after semi-solid isothermal treatment according to Embodiment 1 of the present invention, where (b) is a magnified view of (a). As can be seen from the image, after the initial coarse S phase (Al2CuMg) and T phase were held at 540℃ for 20 min, a uniformly distributed nanoscale S phase lamellar eutectic was formed at the grain boundaries through high-temperature partial melting in the semi-solid region and rapid water quenching (40℃ water). These lamellars are approximately 50-200 nm thick and exhibit a continuous network distribution. Based on solidification theory, this structure formation benefits from the large supercooling during the quenching process: the extremely high cooling rate increases the eutectic growth rate and shortens the atomic diffusion distance, causing Cu and Mg atoms to rapidly solidify into fine lamellars at the grain boundaries, rather than coarse blocky phases. Compared to traditional coarse phases, this nanoscale eutectic phase is easier to crush and dissolve in subsequent processes, increasing the solid solution concentration of solute atoms in the matrix, thereby providing more nucleation sites for aging precipitation and ultimately contributing to the strengthening of the alloy.

[0033] Figure 3 The image shows the SEM image of the microstructure of the secondary extruded aluminum alloy after secondary hot extrusion according to Embodiment 1 of the present invention, where (b) is a magnified view of (a). As can be seen from the image, the nanoscale lamellar eutectic is further broken up and coarsened under the conditions of 400℃ and an extrusion ratio of 10:1, forming spherical submicron S-phase particles with a diameter of approximately 0.2-0.8 μm. These particles are uniformly dispersed in the α-Al matrix. This transformation originates from the high shear stress and thermal activation during the extrusion process: the Gibbs-Thomson effect increases the curvature of the small-sized lamellars, promoting dissolution and reprecipitation; simultaneously, the Ostwald aging mechanism drives the dissolution of small particles and their transfer to larger particles, achieving particle spheroidization and size homogenization. These submicron particles are more easily dissolved in the solution treatment compared to the initial coarse phase, increasing the supersaturated solid solubility of Cu and Mg in the matrix. During aging, these solute atoms diffuse efficiently along dislocation channels, forming a high-density fine S' phase, enhancing the Orowan bypass strengthening mechanism. In addition, spherical particles reduce crack initiation sources, improve plasticity, and ensure that the alloy still has good elongation at high strength. Example 2

[0034] A method for preparing ultra-high strength and toughness 2024 aluminum alloy, the steps of which are as follows: A. Provide 2024 aluminum alloy bars with a diameter of 80mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; B. Semi-solid isothermal treatment: Heat the 2024 aluminum alloy bar from step A to the semi-solid range of 550°C, hold for 12 minutes, and then quickly water-quench it. The quenching medium is water at 50°C. C. Secondary hot extrusion: The 2024 aluminum alloy bar that has undergone semi-solid isothermal treatment is subjected to secondary hot extrusion at a temperature of 390℃, an extrusion speed of 0.5mm / s, and an extrusion ratio of 12:1. A flat die is used, and the extrusion is followed by air cooling to room temperature to obtain a secondary extruded aluminum alloy. D. Time-sensitive processing: The specific operation of the aging treatment is to directly age the secondary extruded aluminum alloy obtained in step C. The aging treatment temperature is 148℃ and the aging treatment time is 16h. After aging treatment, the alloy is water-cooled and quenched to obtain ultra-high strength and toughness 2024 aluminum alloy.

[0035] The alloy prepared in this example has a tensile strength of 480 MPa, a yield strength of 390 MPa, and an elongation of 18.0%. Example 3

[0036] A method for preparing ultra-high strength and toughness 2024 aluminum alloy, the steps of which are as follows: A. Provide 2024 aluminum alloy bars with a diameter of 100mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; B. Semi-solid isothermal treatment: Heat the 2024 aluminum alloy bar from step A to the semi-solid range of 535℃, hold for 10 minutes, and then quickly water-quench it. The quenching medium is water at 30℃. C. Secondary hot extrusion: The 2024 aluminum alloy bar, which has undergone semi-solid isothermal treatment, is subjected to secondary hot extrusion at a temperature of 410℃, an extrusion speed of 0.3mm / s, and an extrusion ratio of 9:1. A conical die is used, and the extruded material is water-cooled to room temperature to obtain a secondary extruded aluminum alloy. D. Solution aging treatment: The specific operation of the solution aging treatment is as follows: first, the secondary extruded aluminum alloy obtained in step C is subjected to solution treatment. The solution treatment includes placing the secondary extruded aluminum alloy obtained in step C at a temperature of 495°C for 1.2 hours, followed by water quenching. Then, the solution-treated secondary extruded aluminum alloy is subjected to aging treatment at a temperature of 152°C for 14 hours. After aging treatment, it is water quenched to obtain ultra-high strength and toughness 2024 aluminum alloy.

[0037] The alloy prepared in this example has a tensile strength of 560 MPa, a yield strength of 470 MPa, and an elongation of 14.5%. Example 4

[0038] A method for preparing ultra-high strength and toughness 2024 aluminum alloy, the steps of which are as follows: A. Provide 2024 aluminum alloy bars with a diameter of 40mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; B. Semi-solid isothermal treatment: Heat the 2024 aluminum alloy bar from step A to the semi-solid range of 545℃, hold for 35 minutes, and then quickly water-quench it. The quenching medium is water at 45℃. C. Secondary hot extrusion: The 2024 aluminum alloy bar that has undergone semi-solid isothermal treatment is subjected to secondary hot extrusion at a temperature of 380℃, an extrusion speed of 0.4mm / s, and an extrusion ratio of 11:1. A flat die is used, and the extruded aluminum alloy is air-cooled or water-cooled to room temperature to obtain a secondary extruded aluminum alloy. D. Time-sensitive processing: The specific operation of the aging treatment is to directly age the secondary extruded aluminum alloy obtained in step C. The aging treatment temperature is 150℃ and the aging treatment time is 15h. After aging treatment, it is water-cooled and quenched to obtain ultra-high strength and toughness 2024 aluminum alloy.

[0039] The alloy prepared in this example has a tensile strength of 460 MPa, a yield strength of 370 MPa, and an elongation of 20.0%. Example 5

[0040] A method for preparing ultra-high strength and toughness 2024 aluminum alloy, the steps of which are as follows: A. Provide 2024 aluminum alloy bars with a diameter of 120mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; B. Semi-solid isothermal treatment: Heat the 2024 aluminum alloy bar from step A to the semi-solid range of 530°C, hold for 15 minutes, and then quickly water-quench it. The quenching medium is water at 60°C. C. Secondary hot extrusion: The 2024 aluminum alloy bar, which has undergone semi-solid isothermal treatment, is subjected to secondary hot extrusion at a temperature of 420℃, an extrusion speed of 0.6mm / s, and an extrusion ratio of 15:1. A conical die is used, and the extruded material is water-cooled to room temperature to obtain a secondary extruded aluminum alloy. D. Solution aging treatment: The specific operation of the solution aging treatment is as follows: first, the secondary extruded aluminum alloy obtained in step C is subjected to solution treatment. The solution treatment includes placing the secondary extruded aluminum alloy obtained in step C at a temperature of 490°C for 1.5 hours, followed by water quenching. Then, the solution-treated secondary extruded aluminum alloy is subjected to aging treatment at a temperature of 145°C for 18 hours. After aging treatment, it is water quenched to obtain ultra-high strength and toughness 2024 aluminum alloy.

[0041] The alloy prepared in this example has a tensile strength of 605 MPa, a yield strength of 520 MPa, and an elongation of 10.0%.

[0042] Figure 4Transmission electron microscopy (TEM) images and corresponding energy-dispersive X-ray spectroscopy (EDS) elemental distribution maps of 2024 aluminum alloys prepared by the comparative example (traditional secondary extrusion + solution aging treatment) and Example 5 (semi-solid isothermal treatment + secondary hot extrusion + solution aging treatment). In the figure, (a) is a bright-field TEM image of the conventional process; (b) shows the EDS elemental distribution of the corresponding region in (a), including (b1) Al, (b2) Cu, (b3) Mg, and (b4) Mn; (c) is a bright-field TEM image of Example 5; and (d) shows the EDS elemental distribution of the corresponding region in (c), including (d1) Al, (d2) Cu, (d3) Mg, and (d4) Mn. This figure, by comparing the morphology and elemental distribution of the second phase under the two processes, reveals the synergistic effect of microstructure refinement on the uniformity of solute distribution and mechanical properties. Figure 4 (a) As can be seen, under traditional industrial processing conditions, the α-Al matrix contains coarse, irregular blocky intermetallic compounds, labeled as the S phase (Al₂CuMg) and T phase, with dimensions reaching several micrometers, sharp edges, and a banded distribution along the extrusion direction. These coarse phases easily cause stress concentration, and their stress concentration factor can be expressed as… K t ≈1+2 a / r ,in a For defect size, r For the radius of curvature, smaller r lead to K t Increased solute concentration promotes microcrack nucleation and reduces material ductility. EDS spectra (b) further show that Cu and Mg are significantly enriched in the coarse phase (Figs. (b2), (b3)), while the solute concentration is lower in the Al-dominated region (Fig. (b1)), and Mn is locally enriched in the T phase (Fig. (b4)). This distribution exhibits a clear solute gradient and the presence of solute-depleted zones (SDZs), whose formation is controlled by diffusion processes and follows Fick's second law. ,in D The bulk diffusion coefficient is approximately 10 at the commonly used solution temperature (500℃). -13 m 2 / s, long diffusion path and low rate, resulting in solute flux The insufficiency makes it difficult to achieve homogenization, which limits the quantity and distribution of precipitated phases during subsequent aging. In contrast, Figure 4(c) As shown in Example 5, after semi-solid isothermal treatment (530℃ for 15 min) and secondary extrusion (420℃, extrusion ratio 15:1), the coarse second phase was significantly refined and broken into submicron-sized particles (approximately 0.2–0.8 μm in diameter), with a more uniform distribution. This structural transformation originates from the breakage and spheroidization of the nanolamellae eutectic formed during the SSIT process during thermal deformation. The combined effects of the Gibbs–Thomson effect and Ostwald ripening promote the dissolution of high-curvature regions and solute redistribution, ultimately achieving uniform particle size and a spherical morphology. The spherical particles effectively alleviate stress concentration and improve the material's toughness. EDS spectra (d) show that Cu and Mg are still enriched in the refined particles, but the gradient is gentler (Figs. (d2), (d3)), the SDZ range is significantly reduced, and the Mn distribution is more uniform (Fig. (d4)). This uniform solute distribution is beneficial for increasing the matrix supersaturation, providing conditions for the subsequent formation of high-density precipitates.

[0043] In summary, Figure 4 This invention elucidates the problems of solute inhomogeneity and stress concentration caused by coarse phases in traditional processes at the microscopic scale, and demonstrates how the process of this invention achieves efficient solute utilization and improved deformation coordination through second-phase refinement and spheroidization. In Example 5, this structural optimization, combined with Orowan strengthening and load transfer mechanisms, enables the alloy to maintain a 10% elongation while increasing its tensile strength to 605 MPa, successfully overcoming the strength-plasticity trade-off limitation.

[0044] Figure 5 This study presents the TEM morphology and selected area electron diffraction (SAED) analysis of the precipitates in 2024 aluminum alloys prepared in the T6 aging state, as shown in Comparative Example (conventional secondary extrusion + solution aging) and Example 5 (semi-solid isothermal treatment + secondary hot extrusion + solution aging). (a) is the TEM image of the precipitates in the aluminum alloy prepared in the comparative example; (b) is... Figure 4 (a) is the SAED spectrum of the area marked by the yellow circle; (c) is the TEM image of the precipitated phase of the aluminum alloy prepared in Example 5; (d) is the SAED spectrum of the area marked in (c). This figure reveals, at the nanoscale, significant differences in the density, morphology, and crystal structure of the precipitated phase under the two processes, elucidating the precipitation strengthening effect and the matching mechanism of strength and plasticity in the alloy. Figure 5 (a) As can be seen, under conventional conditions, the precipitated phase is mainly composed of needle-like or plate-like S′ phases (Al2CuMg metastable phases), which are sparsely distributed, have low density, are hundreds of nanometers in size, have large spacing, and are mostly attached to the coarse secondary phase heterogeneous nucleation. This sparse distribution is attributed to the localized decrease in supersaturation caused by the aforementioned solute-depleted zone (SDZ), and the nucleation rate is controlled by classical nucleation theory: Where Δ G As a nucleation barrier, a decrease in solute concentration will increase Δ. GThis inhibits the formation of a large amount of precipitates. Simultaneously, the low bulk diffusion coefficient leads to coarsening of the precipitates, weakening the Orowan strengthening mechanism. SAED pattern (b) shows diffraction spots obtained along the

[001] zone axis of the Al matrix, revealing T-Al. 20 The presence of superstructure spots such as Cu2Mn3, accompanied by diffraction fringes, confirms the cubic structure of the T-phase and the orthorhombic structure of the S′-phase. However, the weak diffraction intensity indicates poor coherence and uneven distribution of the precipitated phases with the matrix. These structural characteristics limit the strength of conventionally processed specimens (438 MPa). Although recrystallization softening contributes a relatively high elongation of 30%, the coarse phases easily become crack initiation sites, resulting in poor synergy between strength and plasticity.

[0045] In comparison, Figure 5 (c) shows that after processing with the present invention, the S′ phase density is significantly increased, exhibiting fine needle-like structures that are uniformly dispersed in the matrix with spacing reduced to tens of nanometers. This high-density precipitation originates from the refinement and dissolution of the second phase achieved through the synergistic effect of SSIT and hot extrusion, effectively increasing the matrix supersaturation and promoting uniform nucleation. The high dislocation density in the non-recrystallization region provides more nucleation sites for the precipitation, and the diffusion of dislocation channels accelerates solute migration, promoting rapid growth of the precipitated phase. The circled area in Figure (c) shows dense precipitate clusters, reflecting uniform solute distribution without significant local depletion. The corresponding SAED pattern (d) shows sharp diffraction spots, confirming it as the S-Al2CuMg phase. The clear diffraction fringes indicate a good coherent relationship between the S′ phase and the aluminum matrix, strengthening the pinning effect of the coherent strain field on dislocations and enhancing the contribution of the Orowan bypass mechanism. Furthermore, Figure 4 (c) The retained low-angle grain boundaries (LAGB) contribute to dislocation accumulation and strain hardening, maintaining the ability to undergo plastic deformation.

[0046] In Example 5, the high-density precipitated phase is relieved through load transfer and stress concentration with the spheroidized second phase. K t By combining the reduction of tensile strength with the elongation of 10%, an excellent performance match of 605 MPa and 10% was finally achieved, successfully breaking through the traditional inverse relationship between strength and plasticity. Figure 5 From the perspective of precipitation behavior, traditional processes are limited by long diffusion paths and low flux, making it difficult to achieve high-density uniform precipitation. However, this invention, through the synergistic control of semi-solid isothermal treatment and thermomechanical processing, achieves nanoscale optimization of the precipitated phase without adjusting the alloy composition, providing a feasible path for the development of high-performance 2xxx series aluminum alloys. Example Six A method for preparing ultra-high strength and toughness 2024 aluminum alloy, the steps of which are as follows: A. Provide 2024 aluminum alloy bars with a diameter of 30mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; B. Semi-solid isothermal treatment: Heat the 2024 aluminum alloy bar from step A to the semi-solid range of 520℃, hold for 40 minutes, and then quickly water-quench it. The quenching medium is water at 20℃. C. Secondary hot extrusion: The 2024 aluminum alloy bar, which has undergone semi-solid isothermal treatment, is subjected to secondary hot extrusion at a temperature of 350℃, an extrusion speed of 0.1mm / s, and an extrusion ratio of 6:1. A flat die is used, and the extrusion is followed by air cooling to room temperature to obtain a secondary extruded aluminum alloy. D. Time-sensitive processing: The specific operation of the aging treatment is to directly age the secondary extruded aluminum alloy obtained in step C. The aging treatment temperature is 140℃ and the aging treatment time is 20h. After the aging treatment, the alloy is water-cooled and quenched to obtain ultra-high strength and toughness 2024 aluminum alloy.

[0047] The alloy prepared in this example has a tensile strength of 430 MPa, a yield strength of 350 MPa, and an elongation of 25.0%. Example 7

[0048] A method for preparing ultra-high strength and toughness 2024 aluminum alloy, the steps of which are as follows: A. Provide 2024 aluminum alloy bars with a diameter of 60mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; B. Semi-solid isothermal treatment: Heat the 2024 aluminum alloy bar from step A to the semi-solid range of 580℃, hold for 10 minutes, and then quickly water-quench it. The quenching medium is water at 80℃. C. Secondary hot extrusion: The 2024 aluminum alloy bar that has undergone semi-solid isothermal treatment is subjected to secondary hot extrusion at a temperature of 450℃, an extrusion speed of 1mm / s, an extrusion ratio of 20:1, and a conical die. After extrusion, the bar is water-cooled to room temperature to obtain a secondary extruded aluminum alloy. D. Solution aging treatment: The specific operation of the solution aging treatment is as follows: first, the secondary extruded aluminum alloy obtained in step C is subjected to solution treatment. The solution treatment includes placing the secondary extruded aluminum alloy obtained in step C at a temperature of 510°C for 0.5 hours, followed by water quenching. Then, the solution-treated secondary extruded aluminum alloy is subjected to aging treatment at a temperature of 160°C for 10 hours. After aging treatment, it is water quenched to obtain ultra-high strength and toughness 2024 aluminum alloy.

[0049] The alloy prepared in this example has a tensile strength of 580 MPa, a yield strength of 490 MPa, and an elongation of 12.0%. Example 8

[0050] A method for preparing ultra-high strength and toughness 2024 aluminum alloy, the steps of which are as follows: A. Provide 2024 aluminum alloy bars with a diameter of 70mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; B. Semi-solid isothermal treatment: Heat the 2024 aluminum alloy bar from step A to the semi-solid range of 560°C, hold for 18 minutes, and then quickly water-quench it. The quenching medium is water at 30°C. C. Secondary hot extrusion: The 2024 aluminum alloy bar, which has undergone semi-solid isothermal treatment, is subjected to secondary hot extrusion at a temperature of 400℃, an extrusion speed of 0.5mm / s, and an extrusion ratio of 8:1. A flat die is used, and the extrusion is followed by air cooling to room temperature to obtain a secondary extruded aluminum alloy. D. Time-sensitive processing: The specific operation of the aging treatment is to directly age the secondary extruded aluminum alloy obtained in step C. The aging treatment temperature is 155℃ and the aging treatment time is 12h. After aging treatment, it is water-cooled and quenched to obtain ultra-high strength and toughness 2024 aluminum alloy.

[0051] The alloy prepared in this example has a tensile strength of 450 MPa, a yield strength of 360 MPa, and an elongation of 22.0%.

Claims

1. A method for preparing ultra-high strength and toughness 2024 aluminum alloy, comprising the following steps: A. Provide 2024 aluminum alloy bars with diameters of 30-120mm that have undergone one hot extrusion in accordance with GB / T 3191-2019; B. Semi-solid isothermal treatment: Heat the 2024 aluminum alloy bar from step A to the semi-solid range of 520-580℃, hold for 5-60 minutes, and then quickly water-quench it. The quenching medium is water at 20-80℃. C. Secondary hot extrusion: The 2024 aluminum alloy bar that has undergone semi-solid isothermal treatment is subjected to secondary hot extrusion. The extrusion temperature is 350-450℃, the extrusion speed is 0.1-4mm / s, the extrusion ratio is 6-20:1, and a flat die or a conical die is used. After extrusion, the aluminum alloy is air-cooled or water-cooled to room temperature to obtain secondary extruded aluminum alloy. D. Aging treatment or solution aging treatment: The specific operation of the aging treatment is to directly age the secondary extruded aluminum alloy obtained in step C. The aging treatment temperature is 140-160℃, the aging treatment time is 10-20h, and the aging treatment is followed by water quenching to obtain ultra-high strength and toughness 2024 aluminum alloy. The specific operation of the solution aging treatment is as follows: First, the secondary extruded aluminum alloy obtained in step C is subjected to solution treatment. The solution treatment includes placing the secondary extruded aluminum alloy obtained in step C at a temperature of 480-510℃ for 0.5-2 hours, followed by water quenching. Then, the solution-treated secondary extruded aluminum alloy is subjected to aging treatment at a temperature of 140-160℃ for 10-20 hours. After aging treatment, it is water quenched to obtain ultra-high strength and toughness 2024 aluminum alloy.

2. The method for preparing an ultra-high strength and toughness 2024 aluminum alloy according to claim 1, characterized in that: The diameter of the 2024 aluminum alloy rod in step A is 35-100mm.

3. The method for preparing an ultra-high strength and toughness 2024 aluminum alloy according to claim 1, characterized in that: The semi-solid temperature range for the semi-solid isothermal treatment in step B is 530-560℃, and the holding time is 10-45 minutes.

4. The method for preparing an ultra-high strength and toughness 2024 aluminum alloy according to claim 1, characterized in that: The quenching medium for water-cooled quenching in step B is water at 25-60℃.

5. The method for preparing an ultra-high strength and toughness 2024 aluminum alloy according to claim 1, characterized in that: The extrusion temperature of the secondary hot extrusion in step C is 380-420℃, the extrusion speed is 0.3-0.6mm / s, the extrusion ratio is 8-15:1, a conical die is used, and the material is water-cooled to room temperature after extrusion.

6. The method for preparing an ultra-high strength and toughness 2024 aluminum alloy according to claim 1, characterized in that: The cooling method after extrusion in step C is water cooling, and the cooling medium is room temperature water.

7. The method for preparing an ultra-high strength and toughness 2024 aluminum alloy according to claim 1, characterized in that: The aging temperature in step D, or solution aging treatment, is 145-155℃, and the aging time is 12-18h.

8. The method for preparing an ultra-high strength and toughness 2024 aluminum alloy according to claim 1, characterized in that: The solution treatment in step D, the solution aging treatment, includes placing the secondary extruded aluminum alloy obtained in step C at a temperature of 490-505℃ for 0.8-1.5h and then water quenching.

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