Preparation method of high-toughness double-gradient aluminum alloy bar

Abstract

The invention discloses a preparation method of a high-toughness double-gradient aluminum alloy bar. The preparation method comprises the three procedures of bar rotary swaging strain gradient machining, grain size gradient pulse current treatment and precipitated phase density gradient aging treatment. According to the method, the rotary swaging gradient treatment and the short-time high-energy pulse current technology are creatively combined, and the aluminum alloy bar with the grain size distributed in a gradient increasing mode from the core to the edge is successfully constructed while rapid grain refining and complete recrystallization are achieved. And then gradient precipitation of a nanoscale precipitated phase is induced through aging treatment, and finally the high-toughness aluminum alloy material with the grain size and precipitated phase density double gradient structure is prepared.

Description

Technical Field

[0001] This invention relates to a method for preparing high-strength and high-toughness dual-gradient aluminum alloy rods. Specifically, it utilizes rotary forging to achieve strain gradient and dislocation gradient, combined with short-time high-energy pulsed current treatment to achieve grain size gradient, and finally controls the precipitate density through aging to achieve a method for preparing high-strength and high-toughness aluminum alloy rods with dual gradients in grain size and precipitate density. Background Technology

[0002] Aluminum alloys, due to their excellent comprehensive properties such as low density, high specific strength, corrosion resistance, and good machinability, have become a core material in the field of industrial lightweighting, and are widely used in aerospace structural component weight reduction, automotive lightweighting and energy saving, as well as machinery manufacturing, shipbuilding, and chemical engineering. However, the tensile strength of industrial pure aluminum is typically only 80-100 MPa. Although its elongation at break can reach about 40%, its strength and plasticity are poorly matched, making it difficult to meet the stringent requirements of high-performance structural components. With the continuous improvement of relevant industry technical standards, the development of new aluminum alloy processing technologies that combine efficient preparation with excellent mechanical properties has become a key research direction. Although traditional processing technologies are relatively mature, they generally suffer from limitations such as long production cycles and low efficiency. In contrast, short-cycle, high-efficiency aluminum alloy processing technologies show significant advantages. It is worth noting that the macroscopic properties of materials essentially depend on their microstructure. Among them, fine-grain strengthening and precipitation strengthening, as two key strengthening mechanisms, can work synergistically to significantly improve the comprehensive mechanical properties of aluminum alloys.

[0003] A literature search of existing technologies revealed that Anqing Li et al., in their article "Effect of Sc microalloying on the microstructure and mechanical properties of 2195 Al-Li alloy wire rods during hot extrusion" published in *Materials Characterization*, 2025, 229: 15503, used hot extrusion and microalloying design to refine the grains, combining grain refinement strengthening and dislocation strengthening to prepare a series of homogeneous 2195 Al-Li alloy rods, increasing the tensile strength of the material from 317 MPa to 424 MPa, but severely sacrificing plastic deformation capacity. Kaixuan Zhou et al., in their article "Preparing bulk nanocrystalline Cu-Alalloys via rotary swaging" published in *Journal of Materials Processing Technology*, 2024, 330: 118489, used rotary forging technology to prepare copper-aluminum alloy rods with significant hardness gradients. As deformation increases, strain accumulates in the core of the material and stress relaxation becomes difficult, resulting in a decreasing distribution of strain, dislocation density, and hardness from the core to the edge of the bar. After rotary forging, annealing is often used to control the gradient microstructure, optimizing plasticity while achieving high strength. However, traditional annealing methods struggle to precisely control the fine microstructure, leading to poor repeatability and stability of properties. Furthermore, the long processing time significantly extends the production cycle, resulting in decreased production efficiency and increased overall manufacturing costs.

[0004] Further research revealed that pulsed current treatment, as a high-energy-input technique, can rapidly input multi-field coupled energy (electric, thermal, and mechanical) into the material, inducing significant changes in its microstructure and macroscopic properties, thus greatly improving work efficiency. The paper "Accelerated cluster dissolution using electropulsing for ultrafastperformance regeneration" published by Shuyang Qin et al. in *Scripta Materialia*, 2020, 178: 24-28, points out that pulsed current treatment has significant advantages over traditional annealing: its second-level short-duration effect can suppress grain growth, achieving rapid recrystallization and microstructure refinement; simultaneously, it promotes the formation of high-density nanoprecipitates—increased grain boundaries provide nucleation sites, current enhances atomic migration and alters the nucleation barrier, ultimately forming fine, dispersed, stable nanoprecipitates. However, this technique is difficult to use alone to construct gradient heterogeneous materials, limiting its application scope. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention provides a method for preparing high-strength and high-toughness dual-gradient aluminum alloy rods.

[0006] This method involves performing a rotary forging gradient treatment on aluminum rods, resulting in a gradient characteristic of decreasing strain, dislocation density, and hardness from the core to the edge of the rod. Then, rapid recrystallization and microstructure refinement are achieved through short-duration, high-energy pulsed currents, resulting in fully recrystallized aluminum rods with a gradient distribution of grain size. Finally, aging treatment is used to control the precipitate density, thus preparing a high-strength and high-toughness aluminum alloy material with dual gradients in grain size and precipitate density.

[0007] This invention is achieved through the following technical solution: A method for preparing high-strength and high-toughness dual-gradient aluminum alloy rods includes the following steps: (1) Pre-treat the surface of the aluminum alloy rod to remove oil and oxide film, and polish until the bright metal substrate is exposed; (2) Strain gradient processing of bar forging: The pretreated aluminum alloy bars are placed in a rotary forging machine for large deformation processing. Radial forging and axial rotation processing are performed using a grinding wheel. The axial rotation speed is 10~1000 rad / min, the bite speed is 10~1000 mm / s, the hammering time is 0.001~10 s, the time interval between two hammerings is 0.001~10 s, and the diameter reduction per pass is 0.001~10 mm. (3) Grain size gradient pulse current treatment: After reaching the specified pressure, take out the bar after the large deformation processing in step (2), remove the surface oil, and use short-time high-energy pulse current to refine the grains and rapidly recrystallize the bar; wherein, the output voltage is set to 0.01~100 V, the pulse time is set to 10~1000 ms, the number of pulse treatments is 1~100 times, and a fully recrystallized aluminum bar with a gradient distribution of grain size is obtained; (4) Aging treatment of precipitated phase density gradient: The aluminum rod obtained in step (3) is placed in a heat treatment furnace for aging treatment. The aging temperature is 100~200℃ and the aging time is 1~100 hours. Finally, a high-strength and high-toughness aluminum alloy material with dual gradients of grain size and precipitate density is obtained.

[0008] A high-strength and high-toughness dual-gradient aluminum alloy rod prepared based on the above method.

[0009] This invention has significant advantages over existing technologies: 1. This invention innovatively combines rotary forging gradient treatment with short-time high-energy pulsed current technology, achieving rapid grain refinement and complete recrystallization while successfully constructing aluminum alloy rods with a gradient grain size distribution from the center to the edge. Subsequently, aging treatment induces the gradient precipitation of nanoscale precipitates, ultimately producing a high-strength and tough aluminum alloy material with a dual gradient structure of grain size and precipitate density.

[0010] 2. This invention obtains a gradient material with a continuously changing microstructure through rotary forging gradient processing. Its soft region ensures excellent plasticity, while the hard region provides high strength, thus achieving a good match between high strength and high plasticity.

[0011] 3. This invention uses high-energy instantaneous pulse current technology to replace traditional annealing heat treatment, which can complete the complete recrystallization process of the material in a very short time and effectively refine the grains. At the same time, it works in synergy with rotary forging gradient treatment to achieve a gradient distribution of grain size, which significantly improves the comprehensive mechanical properties of aluminum alloys.

[0012] 4. This invention utilizes high-energy instantaneous pulse current technology to achieve refined and controllable regulation of the material's microstructure by precisely controlling the process temperature and processing time, thereby improving the excellent comprehensive performance stability of aluminum alloys.

[0013] 5. Compared with traditional heat treatment processes, the present invention significantly shortens the production cycle, significantly improves production efficiency, and has strong industrial continuity, making it easier to meet the needs of large-scale industrial applications. Attached Figure Description

[0014] Figure 1The following are schematic diagrams of the processing flow for the embodiments: 1) Schematic diagram of rotary forging strain gradient processing; 2) Schematic diagram of grain size gradient pulse processing; 3) Schematic diagram of precipitate density gradient aging processing; Figure 2 Schematic diagram of microstructure evolution for the embodiment; 1) Initial microstructure; 2) Strain and dislocation gradient microstructure; 3) Grain size gradient distribution microstructure; 4) Dual gradient microstructure; Figure 3 Comparison of tensile properties between homogeneous aluminum alloys with grain size gradients and double-gradient grain size precipitation (traditional annealing) and pulse-treated aluminum alloys; Figure 4 Figure showing the differences in grain size and precipitate density of aluminum alloys after heat treatment under different strains; Among them: 1 is the pressure roller, 2 is the forging hammer, 3 is the forging die, 4 is the pulse power supply, 5 is the fixed copper electrode, 6 is the pulse oscilloscope, and 7 is the heat treatment furnace. Detailed Implementation

[0015] Referring to the accompanying drawings, the embodiments of the present invention will be described in detail below. These embodiments are implemented based on the technical solutions of the present invention, and detailed implementation methods and specific operation processes are given. However, the scope of protection of the present invention is not limited to the following embodiments.

[0016] Example 1

[0017] like Figure 1 and Figure 2 As shown, this invention takes 6061 aluminum alloy bars as an example, providing detailed implementation methods and specific operations. The following embodiment involves three steps: First, the 6061 aluminum bars are subjected to a rotary forging gradient treatment, so that the bar exhibits a decreasing gradient in strain, dislocation density, and hardness from the core to the edge; then, short-time high-energy pulsed current is used to rapidly achieve grain refinement and recrystallization, resulting in a fully recrystallized aluminum bar with a gradient distribution of grain size; finally, the precipitate density is controlled by aging to prepare a high-strength and high-toughness aluminum alloy material with dual gradients in grain size and precipitate density, wherein: Step 1: Pre-treat the surface of the 6061 aluminum alloy bar to remove oil and oxide film, and polish until the bright metal substrate is exposed.

[0018] Step 2: The pretreated 6061 aluminum alloy bar billet is placed into a rotary forging mill for large deformation processing. The axial rotation speed is 200 rad / min, the feed rate is controlled at approximately 15 mm / s, the diameter reduction per pass is 0.4 mm, the hammering time is 0.0038 s, and the time interval between two hammerings is 0.042 s. As the rotary forging strain increases, the surface roughness of the material gradually decreases and eventually stabilizes at approximately 0.4 μm.

[0019] Step 3: Remove the forged bar and remove surface oil. Use pulsed current to refine the grains and rapidly recrystallize the bar. Set the output voltage to 5 V, the pulse time to 240 ms, and the pulse treatment to 1 time to obtain a fully recrystallized aluminum bar with a gradient grain size distribution.

[0020] Step 4: Place the aluminum rod obtained in Step 3 into a heat treatment furnace for aging treatment at a temperature of 175°C for 6 hours. Finally, a high-strength and high-toughness aluminum alloy material with dual gradients in grain size and precipitate density is obtained.

[0021] The core of this invention lies in proposing a design concept for a "dual-gradient" aluminum alloy material and its corresponding preparation method. It primarily involves preparing aluminum alloy bars with strain gradients through rotary forging, followed by recrystallization via pulsed processes and aging to control precipitates, thereby preparing a high-strength and tough aluminum alloy material with dual gradients in grain size and precipitate density.

[0022] In this invention, the dual-gradient material further synergistically controls the grain size and precipitate density, such as... Figure 3 As shown, this method significantly improves the strength of aluminum alloys while maintaining good plasticity, providing an effective way to optimize the overall performance of aluminum alloys.

[0023] Furthermore, compared to traditional heat treatment, pulsed current treatment can significantly improve material strength while maintaining or enhancing its ductility. Its controllability is also more stable, which is particularly crucial for achieving gradient structures. Therefore, using pulsed current annealing to prepare aluminum alloys with a dual gradient structure in terms of grain size and precipitates can further synergistically optimize their strength and ductility, thereby expanding the application potential of this type of alloy.

[0024] Under different strain conditions, annealing or aging treatments will produce significant differences in grain size and precipitate density in aluminum alloy materials, such as... Figure 4 As shown. This invention utilizes rotary forging to create a strain gradient in an aluminum rod, while simultaneously controlling pulse and aging processes to prepare a high-strength, high-toughness aluminum alloy material with dual gradients in grain size and precipitate density. For example... Figure 4 As shown, due to the differences in recrystallization kinetics and precipitation response in different strain regions, significant differences in grain size and precipitate density will form inside the material when annealing or aging is performed under different strains.

Claims

1. A method of producing a high-ductility dual-gradient aluminum alloy rod, characterized by, The process includes three steps: bar forging strain gradient processing, grain size gradient pulse current treatment, and precipitate density gradient aging treatment; specifically: (1) Strain gradient processing of bar forging: The surface-pretreated aluminum alloy bars are placed into a rotary forging machine for large deformation processing, and radial forging and axial rotation processing are performed using a grinding wheel. (2) Grain size gradient pulse current treatment: After the large deformation processing in step (1), the surface oil stains of the bar are removed and short-time high-energy pulse current treatment is performed. The output voltage is 0.01~100 V, the pulse time is set to 10~1000 ms, and the number of pulse treatments is 1~100 times to obtain a fully recrystallized aluminum bar with a gradient distribution of grain size. (3) The aluminum rod obtained in step (2) is placed in a heat treatment furnace for aging treatment, and finally a high-strength and high-toughness aluminum alloy material with dual gradients of grain size and precipitate density is obtained.

2. The method for preparing high-strength and high-toughness dual-gradient aluminum alloy rods as described in claim 1, characterized in that, In step (1), during radial forging and axial rotation processing, the axial rotation speed is 10~1000 rad / min, the bite speed is 10~1000 mm / s, the hammering time is 0.001~10 s, the time interval between two hammerings is 0.001~10 s, and the diameter reduction per pass is 0.001~10 mm.

3. The method of producing a high toughness dual gradient aluminum alloy rod according to claim 1, wherein In step (3), the aging treatment temperature is 100~200℃ and the time is 1~100 hours.

4. A high-strength and high-toughness dual-gradient aluminum alloy rod prepared according to any one of claims 1-3.

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