Double-peak heterostructure 6061 aluminum alloy and preparation method thereof

Abstract

The invention belongs to the technical field of alloy preparation, and particularly discloses a double-peak heterostructure 6061 aluminum alloy and a preparation method thereof.The preparation method comprises the following steps that S1, solution treatment is conducted, specifically, the as-cast 6061 aluminum alloy is subjected to solution treatment for 4 h at the temperature of 560 DEG C, water quenching is conducted to the room temperature, and the as-cast 6061 aluminum alloy is cut into thin plates; s2, deep cooling rolling treatment is conducted, specifically, the thin plate obtained in the S2 is sequentially cooled and rolled; s3, short-time annealing treatment is conducted, specifically, annealing is conducted for 5 min at 200 DEG C, and oil cooling is conducted to the room temperature; and S4, aging treatment is conducted, specifically, artificial aging is conducted for 1-32 h at the temperature of 120-180 DEG C, and the 6061 aluminum alloy is obtained. According to the 6061 aluminum alloy with the double-peak heterostructure and the preparation method of the 6061 aluminum alloy with the double-peak heterostructure, the double-peak heterostructure of fine recrystallized grains and coarse deformed grains is obtained, then the size and the volume fraction of second-phase particles are regulated and controlled, the strengthening mechanism of the 6061 aluminum alloy with the double-peak heterostructure is disclosed, and synchronous improvement of the strength and plasticity of the 6061 aluminum alloy is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy preparation, and particularly to a 6061 aluminum alloy with a bimodal heterogeneous structure and a preparation method thereof. Background Art

[0002] The 6061 aluminum alloy is a typical heat-treatable aluminum alloy. Due to its good formability, weldability, machinability, medium strength and high plasticity, it is widely used in key components in the fields of aerospace, automotive and robotics. As key components in aerospace, automotive and robotics, excellent strength and plasticity matching are required. The mechanical properties of key components of the 6061 aluminum alloy mainly depend on the grain size of the alloy matrix and the size and volume fraction of the second phase. Although traditional solution + aging treatment or solution + cold rolling + aging processes can improve the strength of the alloy, they are at the cost of sacrificing the plasticity of the alloy. Therefore, how to prepare 6061 aluminum alloy materials with the optimal strength and plasticity matching remains a key engineering problem faced by the fields of aerospace, automotive and robotics.

[0003] In recent years, it has been found that if there are two significantly different grain distributions of fine grains and coarse grains in metal materials at the same time, this structure can significantly optimize the mechanical properties such as strength, plasticity and toughness of the material through unique interface effects and deformation mechanisms. Therefore, how to construct a bimodal heterogeneous structure in the 6061 aluminum alloy is an important way to solve the strength and plasticity matching of the 6061 aluminum alloy.

[0004] In order to improve the mechanical properties of the 6061 aluminum alloy, a series of new preparation technologies have been proposed in recent years, such as thermomechanical treatment (TMT), laser shock peening (LSP), accumulative roll bonding (ARB), high-pressure cold spraying (HPCS) and cryorolling (CR). The LSP technology can improve the strength of the 6061 aluminum alloy by inducing the precipitation of second-phase particles and refining grains in the aluminum alloy matrix, but the elongation of the alloy is reduced to a certain extent. For the ARB technology, the tensile strength of the alloy processed by ARB will increase with the increase of the number of ARB cycles, but the elongation of the alloy is only about 5%, which is far lower than the application requirements in the fields of aerospace, automotive and robotics. The strength of the 6061 aluminum alloy treated by the HPCS technology has not been significantly improved. In summary, these existing processing technologies can greatly improve the strength of the alloy, but it is difficult to synergistically improve the plasticity of the alloy. Therefore, how to develop a simple new processing technology to prepare a bimodal heterogeneous structure in the 6061 aluminum alloy to achieve the synergistic improvement of the strength and plasticity of the 6061 aluminum alloy is of great significance to the development of the fields of aerospace, automotive and robotics. Summary of the Invention

[0005] The object of the present invention is to provide a 6061 aluminum alloy with a bimodal heterogeneous structure and a preparation method thereof. By means of severe cold rolling + short-time annealing, a bimodal heterogeneous structure composed of fine recrystallized grains and coarse deformed grains is obtained inside the 6061 aluminum alloy. Then, the size and volume fraction of the second-phase particles (Mg2Si) are regulated through aging treatment, and the strengthening mechanism of the 6061 aluminum alloy with a bimodal heterogeneous structure is revealed, so as to simultaneously improve the strength and plasticity of the 6061 aluminum alloy.

[0006] To achieve the above object, the present invention provides a preparation method of a 6061 aluminum alloy with a bimodal heterogeneous structure, comprising the following steps:

[0007] S1. Solution treatment: subjecting as-cast 6061 aluminum alloy to solution treatment at 560 °C for 4 h and then water quenching to room temperature, and cutting it into thin plates;

[0008] S2. Severe cold rolling treatment: sequentially cooling and rolling the thin plates obtained in S2 for multiple times;

[0009] S3. Short-time annealing treatment: annealing at 200 °C for 5 min and then oil cooling to room temperature;

[0010] S4. Aging treatment: performing artificial aging at 120 °C - 180 °C for 1 - 32 h to obtain the 6061 aluminum alloy.

[0011] Preferably, in S1, the molar ratio of Mg and Si in the as-cast 6061 aluminum alloy is 1.8 - 1.9.

[0012] Preferably, in S1, the as-cast 6061 aluminum alloy comprises the following components in parts by weight:

[0013] Mg 1.01 wt.%, Si 0.56 wt.%, Ti 0.01 wt.%, Fe 0.21 wt.%, Cu 0.21 wt.%, Mn 0.03 wt.%, Zn 0.01 wt.%, Cr 0.18 wt.%, and the balance is Al.

[0014] Preferably, S1 is specifically:

[0015] Placing the as-cast 6061 aluminum alloy in a muffle furnace heated to 560 °C, holding for 4 h, then water cooling to room temperature, and cutting it into thin plates with a length of 160 mm, a width of 60 mm, and a thickness of 6.5 mm.

[0016] Preferably, in S2, the cooling is specifically:

[0017] Immersing the thin plates in liquid nitrogen for 10 - 20 min until the temperature of the thin plates reaches the liquid nitrogen temperature.

[0018] Preferably, in S2, the rolling is specifically:

[0019] Each deformation is 10% until 70% of the designed deformation is reached.

[0020] Preferably, in S5, the aging treatment is specifically as follows:

[0021] Artificially age at 120 °C for 1 - 32 h to obtain 6061 aluminum alloy.

[0022] Preferably, in S5, the aging treatment is specifically as follows:

[0023] Artificially age at 120 °C for 20 h to obtain 6061 aluminum alloy.

[0024] The present invention also provides a 6061 aluminum alloy with a bimodal heterogeneous structure.

[0025] Therefore, by adopting the above 6061 aluminum alloy with a bimodal heterogeneous structure and its preparation method, the beneficial effects of the present invention are as follows:

[0026] (1) Through deep cold rolling + short - time annealing, the present invention obtains a bimodal heterogeneous structure composed of fine recrystallized grains and coarse deformed grains inside the 6061 aluminum alloy. By utilizing this structure, through unique interface effects and deformation mechanisms, the strength and plasticity of the 6061 aluminum alloy are improved, enabling the simultaneous improvement of the strength and plasticity of the 6061 aluminum alloy material, and the comprehensive performance is excellent.

[0027] (2) By performing aging heat treatment on the 6061 aluminum alloy with a bimodal heterogeneous structure, the present invention regulates the size and volume fraction of the second - phase particles (Mg2Si) through aging treatment, clarifies the dynamic relationship between the dislocation density and the second - phase volume fraction, and reveals the strengthening mechanism of the heterogeneous structure, dislocation density, second - phase, etc. on the 6061 aluminum alloy. Through process optimization, the limitation of traditional strengthening relying only on the Mg2Si second - phase is broken through, thereby achieving the simultaneous increase in the strength and plasticity of the 6061 aluminum alloy.

[0028] (3) The method by which the present invention enables the 6061 aluminum alloy to obtain a bimodal heterogeneous structure through solution treatment + short - time annealing + aging treatment has the advantages of low cost, simple process, and convenient operation.

[0029] (4) The present invention provides an idea for preparing a bimodal heterogeneous structure in other series of aluminum alloys.

[0030] The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments. Description of the Drawings

[0031] Figure 1It is the test result diagram of Embodiment 1 of the present invention, where (a) is the IPF diagram, (b) is the recrystallized grain diagram, (c) is the second-phase particle volume distribution diagram, (d) is the KAM diagram, (e) is the tensile engineering stress-strain curve, and (f) is the mechanical property statistical diagram;

[0032] Figure 2 It is the test result diagram of Embodiment 2 of the present invention, where (a) is the IPF diagram, (b) is the recrystallized grain diagram, (c) is the second-phase particle volume distribution diagram, (d) is the KAM diagram, (e) is the tensile engineering stress-strain curve, and (f) is the mechanical property statistical diagram;

[0033] Figure 3 It is the test result diagram of Embodiment 3 of the present invention, where (a) is the IPF diagram, (b) is the recrystallized grain diagram, (c) is the second-phase particle volume distribution diagram, (d) is the KAM diagram, (e) is the tensile engineering stress-strain curve, and (f) is the mechanical property statistical diagram;

[0034] Figure 4 It is the test result diagram of Embodiment 4 of the present invention, where (a) is the IPF diagram, (b) is the recrystallized grain diagram, (c) is the second-phase particle volume distribution diagram, (d) is the KAM diagram, (e) is the tensile engineering stress-strain curve, and (f) is the mechanical property statistical diagram;

[0035] Figure 5 It is the test result diagram of Comparative Example 1 of the present invention, where (a) is the tensile engineering stress-strain curve and (b) is the mechanical property statistical diagram. Detailed implementation manners

[0036] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0038] A as-cast 6061 aluminum alloy, commercially available, is a 6061 aluminum alloy rich in Mg with a molar ratio of Mg / Si of 1.804. The chemical composition of this 6061 aluminum alloy is as follows:

[0039] Mg 1.01wt.%, Si 0.56wt.%, Ti 0.01wt.%, Fe 0.21wt.%, Cu 0.21wt.%, Mn 0.03wt.%, Zn 0.01wt.%, Cr 0.18wt.%, and the balance is Al.

[0040] Embodiment 1

[0041] A 6061 aluminum alloy with bimodal heterogeneous structure and its preparation method include the following steps:

[0042] S1. Solution treatment: Place the as-cast 6061 aluminum alloy in a muffle furnace heated to 560 °C, hold for 4 h, then water-cool to room temperature, and cut it into thin plates with a length of 160 mm, a width of 60 mm, and a thickness of 6.5 mm.

[0043] S2. Deep cold rolling treatment: Perform multi-pass rolling on the thin plates obtained in S1, with a deformation of 10% for each pass. Before the first rolling, soak the thin plates in liquid nitrogen for 20 min, then quickly transfer them to the rolling mill for rolling. After each rolling, soak the thin plates in liquid nitrogen for 10 min until 70% of the experimentally designed deformation is reached.

[0044] S3. Short-time annealing treatment: Anneal at 200 °C for 5 min, then oil-cool to room temperature.

[0045] S4. Aging treatment: Perform artificial aging at 120 °C for 12 h to obtain the 6061 aluminum alloy, denoted as PA120-12.

[0046] Example 2

[0047] The difference from Example 1 is that in S5. Aging treatment: Perform artificial aging at 120 °C for 20 h to obtain the 6061 aluminum alloy, denoted as PA120-20.

[0048] Example 3

[0049] The difference from Example 1 is that in S5. Aging treatment: Perform artificial aging at 120 °C for 32 h to obtain the 6061 aluminum alloy, denoted as PA120-32.

[0050] Example 4

[0051] The difference from Example 1 is that in S5. Aging treatment: Perform artificial aging at 180 °C for 1 h to obtain the 6061 aluminum alloy, denoted as PA180-1.

[0052] Example 5

[0053] The difference from Example 1 is that in S5. Aging treatment: Perform artificial aging at 150 °C for 7 h to obtain the 6061 aluminum alloy, denoted as PA150-7.

[0054] Comparative Example 1

[0055] A 6061 aluminum alloy and its preparation method are as follows:

[0056] (1) Solution treatment: The as-cast 6061 aluminum alloy was placed in a muffle furnace heated to 560 °C, held for 4 h, and then water-cooled to room temperature. It was cut into thin plates with a length of 160 mm, a width of 60 mm, and a thickness of 6.5 mm.

[0057] (2) Severe cold rolling treatment: The thin plates obtained in S1 were subjected to multi-pass rolling, with a deformation of 10% per pass. Before the first rolling, the thin plates were immersed in liquid nitrogen for 20 min, and then quickly transferred to a rolling mill for rolling. After each rolling, the thin plates were immersed in liquid nitrogen for 10 min until 70% of the experimentally designed deformation was reached.

[0058] (3) Aging treatment: Artificial aging was carried out at 120 °C for 20 h to obtain 6061 aluminum alloy, denoted as CR-PA120-20.

[0059] Experimental tests

[0060] 1. Structure analysis

[0061] The 6061 aluminum alloy prepared in Examples 1-4 was subjected to structure analysis. The fracture morphology of the tensile specimens was characterized by a scanning electron microscope. The microstructure of the 6061 aluminum alloy was characterized by an electron backscatter diffraction (EBSD) instrument, and the longitudinal (RD×ND plane) cross-section was also characterized. The EBSD detector was Oxford C-swift, and the test voltage was 20 kV. The samples were polished with argon ions using an IM4000+ ion milling machine system, and the scanning step was 0.84 μm. The results are shown in Figures 1-4 (a)-(d) below.

[0062] As can be seen from Figures 1-4 (a) below, solute atoms began to aggregate at the grain boundaries in the initial stage of aging treatment, forming fine second-phase particles. As the maximum aging time increased, the volume fraction of the second-phase particles gradually increased, and when the maximum aging time was reached, the volume fraction of the second-phase particles reached a peak ( Figure 2 (a) below). As the holding time increased, the volume fraction of the second-phase particles gradually dissolved. At the same time, as can be seen from Figure 4 (a) below, under the aging conditions of 180 °C - 1 h, more second-phase particles and some recrystallized grains could still be observed, which might be related to the aging temperature.

[0063] As can be seen from Figures 1-4 (b) below, as the maximum aging time increased, the content of recrystallized grains gradually increased, and the increase in aging temperature did not promote the increase in the content of recrystallized grains. It was further verified that the bimodal heterogeneous structure composed of deformed grains and recrystallized grains was helpful for improving the subsequent strength-ductility matching ability.

[0064] During the aging process of 6061 aluminum alloy, the precipitation sequence in the second stage is: GP zone → β'' → β' → β. In the early stage of aging treatment, there are a large number of unsaturated concentration vacancies in the material. Solute atoms rapidly diffuse into these unsaturated vacancies to form GP zones rich in solute atoms. At this time, the size of the GP zones is small, with a complete lattice with the parent phase, and the contribution to strength is small. When the aging temperature is low, atomic diffusion is difficult, which is not conducive to the aggregation of solute atoms. With the extension of aging time, the diffusion of solute atoms becomes more obvious, and the GP zones rapidly grow into needle-shaped or rod-shaped β'' phases. The crystal structure of the β'' phase is a c-axis monoclinic structure. The β'' phase is a very important strengthening stage in 6-series aluminum alloys and is also the main stage for the increase in material strength. With the extension of time, the β'' phase gradually coarsens and forms a semi-coherent β' transition phase with the matrix. The contribution of β' to the relative strength of its alloy is lower than that of the β'' phase. With the extension of aging time, the transition stage finally transforms into a β phase inconsistent with the matrix. At this time, the β phase is more stable, and the strength of the alloy tends to be stable. In this study, the β phase is Mg2Si particles. 20 h and 1 h are the peak aging times at 120 °C and 180 °C, respectively. When the aging temperature is 120 °C, the total volume fraction of the second phase first increases and then decreases with the extension of aging time. The total integral content of the second phase is the highest at 120 °C - 12 h, among which the content of Mg2Si particles is the highest. From Figures 1-4 As shown in (d) of 14 , after severe cold deformation, the dislocation density of 6061 aluminum alloy gradually decreases with the extension of annealing time and aging time. To quantitatively analyze the change law of dislocation density, the average geometrically necessary dislocation (GND) density of 6061 aluminum alloy under different conditions is calculated. When the aging temperature is 120 °C, the dislocation density gradually decreases from 1.76×10 -2 to 1.53×10 14 with the extension of time. Under the aging condition of 180 °C - 1 h, the dislocation density reaches the lowest value of 1.27×10 -2 . 14 -2

[0065] 2. Mechanical property testing

[0066] The mechanical properties of the 6061 aluminum alloy prepared in Examples 1 - 4 and Comparative Example 1 were tested. A tensile test was carried out using an MTS810 universal testing machine at a constant tensile speed of 1 mm / min. The engineering stress-strain curves of the tensile tests are as shown in (e) of Figures 1-4 and (a) of Figure 5 . Statistical analysis was carried out on the yield strength, tensile strength, and elongation. The results are as shown in (f) of Figures 1-4 and (b) of Figure 5 .

[0067] From​​Figures 1-4 (e) and (f) in Figure 5 It can be seen that after solution treatment + deep cold rolling treatment + short-time annealing treatment + aging treatment, the yield strength and ultimate tensile strength of the aluminum alloy are 433 MPa and 446 MPa respectively, which are significantly higher than those of the aluminum alloy after solution treatment + deep cold rolling treatment + aging treatment. This is mainly because the high-density dislocations and other micro-nano structures generated after rolling of the aluminum alloy jointly improve the strength of the material, but the elongation level is low. The strength of the aluminum alloy decreases. After annealing at 200 °C for 5 minutes, the elongation increases to a certain extent. This is because partial recrystallization occurs in the aluminum alloy at this time, and the stored energy of the deformed structure is released to a certain extent. At the same time, it can be clearly seen that under the aging condition of 120 °C, with the increase of aging time, the yield strength and tensile strength show a trend of increasing first and then decreasing. Under the aging condition of 120 °C - 20 h, the yield strength and tensile strength of the aluminum alloy are 415 MPa and 446 MPa respectively, which are higher than the peak aging conditions at other different temperatures. This is because the content of the second phase in the alloy is the highest at this time and its distribution is more dispersed. These dispersed second-phase particles have a more significant hindering effect on the movement of dislocations.

[0068] In summary, the aluminum alloy only subjected to solution treatment + deep cold rolling treatment + 120 °C - 20 h aging treatment does not have a heterogeneous structure. Therefore, it has high strength and poor plasticity. By constructing a heterogeneous structure through solution treatment + deep cold rolling treatment + short-time annealing treatment + aging treatment and optimizing the parameters of the aging treatment, an excellent strength-ductility matching can be obtained.

[0069] The alloy strengthening mechanism is as follows:

[0070] The strength of the alloy after thermomechanical treatment has been improved to a certain extent, which is caused by precipitation strengthening, dislocation strengthening and grain refinement strengthening. Different contributions can be summarized by the expression of the total yield strength.

[0071] According to the EBSD results, the density value of the dislocations (GND) is calculated, and then the strengthening contribution (σ disl ) of the dislocations to the yield strength (σ Y ) is calculated. The work-hardening effect is closely related to the dislocation density. The greater the dislocation density of the alloy, the greater the contribution to the yield strength. As can be seen from (d) in Figures 1-4 , after severe cold deformation, with the extension of aging time, the dislocation density of the sample gradually decreases. This is mainly due to the obvious precipitation behavior of the second phase during the aging process of the alloy. Therefore, with the extension of aging time, the dislocation density continuously decreases, and the contribution to the yield strength also becomes smaller. The work-hardening effect of the alloy is the strongest at the peak aging of 120 - 20 h, and the work-hardening effect of the alloy is the weakest under the aging condition of 180 - 1 h.

[0072] During the aging process of 6061 aluminum alloy, a large number of second phases will precipitate. The strength and hardness of the alloy depend on the size and quantity of the precipitates, and the size and quantity of the precipitates are affected by the aging temperature and aging time. In the present invention, the precipitated phase after aging treatment is mainly Mg2Si particles. For Mg2Si particles, they are the equilibrium phase during the aging process of 6061 aluminum alloy, usually in the shape of particles or spheres, and maintain an incoherent relationship with the matrix Al. For incoherent second-phase particles, when a slip dislocation encounters an incoherent particle within its slip plane, the slip dislocation can bypass the particle without shearing it and form a dislocation loop around the particle. The strengthening effect (σ P ) of the non-deformable precipitate on the yield strength (σ Y ) can be calculated by the Orowan bypass mechanism. It can be seen therefrom that the higher the volume fraction of Mg2Si particles and the smaller the average size, the more obvious the bypass strengthening effect of Mg2Si particles. As shown in (c) of Figures 1-4 , at 120 - 12 h, the content of Mg2Si particles in the sample is the highest. From the above analysis, it can be seen that the increase in the yield strength of the specimen under the aging condition of 120 - 20 h is mainly due to the contribution of precipitation strengthening, especially the effect of shear strengthening of deformable particles is more obvious.

[0073] As is well known, high-angle grain boundaries (≥15°) can effectively prevent the movement of mobile dislocations from one crystal to an adjacent crystal, thereby increasing the strength of metallic materials. That is to say, the finer the grain size, the greater the contribution of grain refinement (σ gb ) to the yield strength (σ Y ). As can be seen from (b) of Figures 1-4 , the average grain size of 6061 aluminum alloy aged at 120 °C for 20 h is 81.45 μm, which is the smallest grain size under all aging treatment conditions. Therefore, under the aging treatment of 120 °C for 20 h, the contribution of grain refinement to the yield strength is the greatest.

[0074] Therefore, the present invention adopts the above-mentioned 6061 aluminum alloy with a bimodal heterogeneous structure and its preparation method. By deep cold rolling + short-time annealing, a bimodal heterogeneous structure of fine recrystallized grains and coarse deformed grains is obtained inside the 6061 aluminum alloy. Then, the size and volume fraction of the second-phase particles (Mg2Si) are regulated by aging treatment, and the strengthening mechanism of the 6061 aluminum alloy with a bimodal heterogeneous structure is revealed to achieve the simultaneous improvement of the strength and plasticity of the 6061 aluminum alloy.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions of the present invention or make equivalent replacements, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of 6061 aluminum alloy with bimodal heterogeneous structure, characterized in that, It includes the following steps: S1. Solution treatment: The as-cast 6061 aluminum alloy is subjected to solution treatment at 560 °C for 4 h and then water quenched to room temperature, and cut into thin plates; S2. Deep cold rolling treatment: The thin plates obtained in S2 are cooled and rolled in sequence, and repeated multiple times; S3. Short-time annealing treatment: Anneal at 200 °C for 5 min, and then oil cool to room temperature; S4. Aging treatment: Artificial aging is carried out at 120 °C - 180 °C for 1 - 32 h to obtain the 6061 aluminum alloy.

2. The preparation method of 6061 aluminum alloy with bimodal heterogeneous structure according to claim 1, characterized in that, In S1, the molar ratio of Mg and Si in the as-cast 6061 aluminum alloy is 1.8 - 1.

9.

3. The preparation method of 6061 aluminum alloy with bimodal heterogeneous structure according to claim 1, characterized in that, In S1, the as-cast 6061 aluminum alloy includes the following components by weight: Mg 1.01 wt.%, Si 0.56 wt.%, Ti 0.01 wt.%, Fe 0.21 wt.%, Cu 0.21 wt.%, Mn 0.03 wt.%, Zn 0.01 wt.%, Cr 0.18 wt.%, and the balance is Al.

4. The preparation method of 6061 aluminum alloy with bimodal heterogeneous structure according to claim 1, characterized in that, S1 specifically is: Place the as-cast 6061 aluminum alloy in a muffle furnace heated to 560 °C, keep it warm for 4 h, then water cool to room temperature, and cut it into thin plates with a length of 160 mm, a width of 60 mm, and a thickness of 6.5 mm.

5. The preparation method of 6061 aluminum alloy with bimodal heterogeneous structure according to claim 1, characterized in that, In S2, the cooling specifically is: Immerse the thin plate in liquid nitrogen for 10 - 20 min until the temperature of the thin plate reaches the liquid nitrogen temperature.

6. The preparation method of 6061 aluminum alloy with bimodal heterogeneous structure according to claim 1, characterized in that, In S2, the rolling specifically is: The deformation per pass is 10% until 70% of the designed deformation is reached.

7. The preparation method of 6061 aluminum alloy with bimodal heterogeneous structure according to claim 1, characterized in that: In S5, the aging treatment specifically is: Artificial aging is carried out at 120 °C for 1 - 32 h to obtain the 6061 aluminum alloy.

8. The preparation method of 6061 aluminum alloy with bimodal heterogeneous structure according to claim 7, characterized in that: In S5, the aging treatment specifically is: Artificial aging is carried out at 120 °C for 20 h to obtain the 6061 aluminum alloy.

9. A 6061 aluminum alloy prepared by the preparation method of the 6061 aluminum alloy with a bimodal heterogeneous structure according to any one of claims 1 - 8.

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