High-strength and high-plasticity 7075 aluminum alloy and preparation method thereof

Abstract

This invention provides a high-strength, high-ductility 7075 aluminum alloy and its preparation method, belonging to the field of additive manufacturing. The alloy composition, by mass percentage, is: Zn: 7.5-8.5%, Mg: 2.7-3.7%, Zr: 1.0-3.0%, Cu: 1.5-2.5%, Ti: 0.7-1.3%, Y: 0.1-0.4%, with the balance being Al and unavoidable impurities, the impurities being ≤0.02%. The alloy preparation method includes: forming under high-purity argon protection using laser powder bed melting process, solution treatment, and aging treatment. The alloy has an average grain size ≤2.1μm and a three-peak structure, consisting of columnar crystals (5%-25% area), coarse equiaxed crystals (30%-60% area), and fine equiaxed crystals (35%-55% area). The 7075 aluminum alloy possesses high-density nanoscale η-Mg(Al,Zn,Cu)2 phase (radius ≤ 19 nm), primary L12-Al3Zr phase (radius ≤ 50 nm), and secondary L12-Al3Zr phase (radius ≤ 2.9 nm). The alloy exhibits a tensile strength ≥ 515.9 MPa and an elongation ≥ 12.7%, achieving a synergistic improvement in both strength and ductility.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology, specifically relating to a high-strength, high-ductility 7075 aluminum alloy and its preparation method. Background Technology

[0002] 7075 aluminum alloy is one of the most widely used ultra-high strength aluminum alloys in commercial applications. It has high Zn, Mg, and Cu content, making it a preferred material for lightweight, high-strength load-bearing structural components, and it is highly favored in aerospace, defense, and transportation fields. However, 7075 aluminum alloy has poor weldability, a wide solidification temperature range, and is prone to hot cracking, which severely deteriorates its mechanical properties. Therefore, reducing the tendency for hot cracking and improving its strength and toughness are crucial.

[0003] To address the aforementioned problems, existing solutions primarily employ complex plastic deformation processes. However, industrial-scale production of complex plastic deformation is challenging, costly, and results in uneven strain distribution within the material, leading to significant anisotropy in mechanical properties. For example, Ding Zhiguang et al. used a semi-solid die-casting process to form Al-Zn-Mg-Cu alloys. This process required precise control of temperature, pressure, and material flowability, and was prone to defects such as porosity, inclusions, and shrinkage cavities. The resulting aluminum alloy had a tensile strength of 473 MPa and an elongation of 9%. Furthermore, existing alloys can only achieve simple structures. Forming complex structures requires large deformation processes, which place stringent demands on equipment and can lead to alloy cracking and anisotropy. Therefore, how to reduce costs, simplify processes, avoid cracking and anisotropy, produce both simple and complex structures, simultaneously improve strength and plasticity, and achieve industrial-scale production of 7075 aluminum alloys are pressing technical challenges that need to be addressed. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a high-strength, high-ductility 7075 aluminum alloy. The 7075 aluminum alloy composition, by mass percentage, is: Zn: 7.5-8.5%, Mg: 2.7-3.7%, Zr: 1.0-3.0%, Cu: 1.5-2.5%, Ti: 0.7-1.3%, Y: 0.1-0.4%, with the balance being Al and unavoidable impurities, wherein the impurities are ≤0.02%. Its preparation method includes the following steps: (1) 7075 aluminum alloy powder and ZrH2 powder are mixed at a mass ratio of 97-99:1-3, kept at 50-150℃ for 3-8 hours, ball-milled, and vacuum-dried at 50-150℃ for 3-8 hours to obtain 7075 aluminum alloy composite powder; the ball milling process is carried out at a mixing speed of 80-120 r / min and a mixing time of 1-3 hours. (2) Under the protection of high-purity argon, using an aluminum alloy plate as the substrate, the 7075 aluminum alloy composite powder obtained in step (1) is subjected to 80-500 layers of laser powder bed melting treatment, held at 400-550℃ for 0.5-3h, water quenched, and then held at 100-150℃ for 0.5-12h and water quenched again to obtain a high-strength, high-plasticity 7075 aluminum alloy; the laser powder bed melting treatment of each layer has the following characteristics: laser power of 200-300W, scanning speed of 600-1200mm / s, scanning spacing of 80-120μm, layer thickness of 20-40μm, scanning method of strip scanning, and interlayer scanning angle of 50-80°. Each layer is processed 1-4 times using different laser powder bed melting process parameters; each processing is as follows: laser power 220-280W, scanning speed 700-1000mm / s, scanning spacing 90-110μm, scanning method strip scanning, and interlayer scanning angle 60-70°; the high-strength, high-plasticity 7075 aluminum alloy has an average grain size ≤2.1μm, a three-peak structure, consisting of columnar crystals (5%-20% area), coarse equiaxed crystals (35%-55% area), and fine equiaxed crystals (35%-50% area); and also possesses high-density nanoscale η-Mg(Al, The alloy has a Zn,Cu)2 phase with a radius ≤19nm, a primary L12-Al3Zr phase with a radius ≤50nm, and a secondary L12-Al3Zr phase with a radius ≤2.9nm; the alloy has a tensile strength ≥515.9MPa and an elongation ≥12.7%; the high-strength, high-ductility 7075 aluminum alloy avoids cracking and anisotropy, and can be used for both simple and complex structures.

[0005] Further, in step (1), the 7075 aluminum alloy powder and ZrH2 powder are mixed at a mass ratio of 98-99:1-2 and then kept at 80-120℃ for 4-6 hours.

[0006] Further, the 7075 aluminum alloy composite powder is obtained after vacuum drying at 80-120℃ for 4-6 hours as described in step (1).

[0007] Further, the ball milling process described in step (1) involves a mixing speed of 90-110 r / min and a mixing time of 1.5-2 h.

[0008] Further, the high-strength, high-plasticity 7075 aluminum alloy obtained by holding at 450-500℃ for 1-2 hours, water quenching, and then holding at 110-130℃ for 1-10 hours and water quenching in step (2) is obtained.

[0009] Further, the laser powder bed melting process for each layer described in step (2) is as follows: the laser power is 220-280W, the scanning speed is 800-1000mm / s, the scanning interval is 90-110μm, the layer thickness is 25-35μm, the scanning method is strip scanning, and the interlayer scanning angle is 60-70°. The laser powder bed melting process parameters for each layer are as follows: the laser power is 230-270W, the scanning speed is 800-900mm / s, the scanning interval is 95-105μm, the scanning method is strip scanning, and the interlayer scanning angle is 63-68°.

[0010] Furthermore, the high-strength, high-plasticity 7075 aluminum alloy described in step (2) has an average grain size of 1-2 μm and a three-peak structure, consisting of columnar crystals with an area ratio of 7%-18%, coarse equiaxed crystals with an area ratio of 38%-52%, and fine equiaxed crystals with an area ratio of 40%-48%. It also has a high-density nanoscale η-Mg(Al, Zn, Cu)2 phase with a radius of 10-18 nm, a primary L12-Al3Zr phase with a radius of 30-48 nm, and a secondary L12-Al3Zr phase with a radius of 1-2.5 nm.

[0011] Compared with the prior art, the advantages of the present invention are: This invention, through the synergistic regulation of component interactions, proportions, processes, and process parameters, significantly reduces alloy addition costs, simplifies processes, avoids cracking and anisotropy, achieves short processes, and can produce both simple and complex structures, as well as enabling industrial-scale production, without employing complex processes such as large deformation. The beneficial effects are as follows: Compared with the prior art, the high-strength, high-ductility 7075 aluminum alloy obtained by the present invention avoids cracking and anisotropy, can achieve both simple and complex structures, and simultaneously improves strength and ductility, with tensile strength ≥515.9MPa and elongation after fracture ≥12.7%. 2. Existing technologies generally refine grains through processes such as plasma sintering, extrusion, and surface mechanical rolling. However, the degree of grain refinement is limited, resulting in poor alloy surface quality and difficulty in forming complex components. For example, Lian Junmao et al. used surface mechanical rolling (SMRT) to produce 7075 aluminum alloy. SMRT could not form complex internal structures, and the alloy had a single equiaxed crystal structure, with an average grain size of 5.4 μm after five SMRT passes. In contrast, this invention, through the synergistic control of component interactions, proportions, processes, and process parameters, forms a primary L12-Al3Zr phase (radius ≤ 50 nm) with an average grain size ≤ 2.1 μm. It also achieves a three-peak structure: columnar crystals (5%-25% area), coarse equiaxed crystals (30%-60% area), and fine equiaxed crystals (35%-55% area). This avoids cracking and anisotropy, enabling both simple and complex structures to be formed. Employing a short-time solution treatment and aging process, this heat treatment consumes low energy and is suitable for efficient and green manufacturing scenarios. Simultaneously, high-density nanoscale reinforcing phases, secondary L12-Al3Zr phase (radius ≤ 2.9 nm) and η-Mg(Al, Zn, Cu)2 phase (radius ≤ 19 nm), precipitate after heat treatment. This invention simultaneously improves the alloy's strength and ductility, with a tensile strength ≥ 515.9 MPa and elongation ≥ 12.7%, achieving a synergistic improvement in strength and ductility compared to existing 7075 aluminum alloys. It is particularly suitable for the low-cost, high-efficiency mass production requirements of lightweight, complex structural components in the aerospace field. Attached Figure Description

[0012] Figure 1 (a) and (b) are optical microscope comparison images of high-strength, high-ductility 7075 aluminum alloy 1 obtained in Example 1 and high-strength, high-ductility 7075 aluminum alloy 2 obtained in Example 2, respectively. Figure 2 The tensile stress-strain curves are for the high-strength, high-ductility 7075 aluminum alloy 1 obtained in Example 1 and the high-strength, high-ductility 7075 aluminum alloy 2 obtained in Example 2. Detailed Implementation

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto. Unless otherwise specified, the experimental materials and related equipment involved in the following embodiments and comparative examples can be obtained commercially. Example 1

[0014] A high-strength, high-ductility 7075 aluminum alloy 1, with the following composition by mass percentage: Zn: 7.93%, Mg: 3.07%, Zr: 2.5%, Cu: 2.17%, Ti: 0.99%, Y: 0.26%, with the balance being Al and unavoidable impurities, wherein the impurities are ≤0.02%; its preparation method includes the following steps: (1) 7075 aluminum alloy powder and ZrH2 powder were mixed at a mass ratio of 99:1, kept at 110℃ for 5 hours, ball-milled, and vacuum dried at 110℃ for 5 hours to obtain 7075 aluminum alloy composite powder; the ball milling process was carried out at a mixing speed of 95 r / min and a mixing time of 2 hours. Under the protection of high-purity argon, using an aluminum alloy plate as the substrate, the 7075 aluminum alloy composite powder obtained in step (1) was subjected to 300 layers of laser powder bed melting treatment, held at 480℃ for 1.5h, water quenched, and then held at 110℃ for 4h and water quenched again to obtain high-strength, high-plasticity 7075 aluminum alloy 1. The macroscopic metallographic image of the formed alloy 1 is shown below. Figure 1 As shown in (a), there are no cracks, no anisotropy, and the forming quality is good. The laser powder bed melting process for each layer is as follows: laser power is 280W, scanning speed is 900mm / s, scanning spacing is 90μm, layer thickness is 32μm, scanning method is strip scanning, and interlayer scanning angle is 65°. Each layer is processed once using different laser powder bed melting process parameters; each processing is as follows: laser power is 280W, scanning speed is 900mm / s, scanning spacing is 90μm, scanning method is strip scanning, and interlayer scanning angle is 65°. The high-strength, high-plasticity zirconium-containing 7075 aluminum alloy 1 has an average grain size of 2.0μm and a three-peak structure: columnar crystals (7.6% area), coarse equiaxed crystals (51.7% area), and fine equiaxed crystals (40.7% area). The mechanical properties of alloy 1 are as follows: Figure 2 As shown, the tensile strength is 534.8 MPa and the elongation is 12.7%. Example 2

[0015] High-strength, high-ductility 7075 aluminum alloy 2, by mass percentage, comprises: Zn: 7.85%, Mg: 3.12%, Zr: 2.0%, Cu: 2.13%, Ti: 0.98%, Y: 0.27%, with the balance being Al and unavoidable impurities, wherein the impurities are ≤0.02%; its preparation method includes the following steps: 7075 aluminum alloy powder and ZrH2 powder were mixed at a mass ratio of 98:2, kept at 100℃ for 6 hours, ball-milled, and vacuum-dried at 100℃ for 6 hours to obtain 7075 aluminum alloy composite powder; the ball milling process was carried out at a mixing speed of 100 r / min for 1.5 hours. Under the protection of high-purity argon gas, using an aluminum alloy plate as the substrate, the 7075 aluminum alloy composite powder obtained in step (1) was subjected to 350 layers of laser powder bed melting treatment, held at 470℃ for 1 hour, water quenched, and then held at 120℃ for 8 hours and water quenched again to obtain high-strength, high-plasticity 7075 aluminum alloy 2. The macroscopic metallographic image of the formed alloy 2 is shown below. Figure 1 As shown in (b), there are no cracks, no anisotropy, and the forming quality is good. The laser powder bed melting process for each layer is as follows: laser power is 260W, scanning speed is 800mm / s, scanning spacing is 100μm, layer thickness is 30μm, scanning method is strip scanning, and the interlayer scanning angle is 67°. Each layer is processed twice using different laser powder bed melting process parameters; each processing is as follows: laser power is 260W, scanning speed is 800mm / s, scanning spacing is 100μm, scanning method is strip scanning, and the interlayer scanning angle is 67°. The high-strength, high-plasticity 7075 aluminum alloy 2 has an average grain size of 2.1μm and a three-peak structure: columnar crystals (15.0% area), coarse equiaxed crystals (40.6% area), and fine equiaxed crystals (44.4% area). The mechanical properties of alloy 2 are as follows: Figure 2 As shown, the tensile strength is 515.9 MPa and the elongation is 16.6%.

[0016] Comparative Example 1 Journal Title: Journal of Manufacturing Processes, Year: 2025, Authors: Jinbing Hu, Yuting Wan, Wenjie He, Liang Qi, Title: Effect of teardrop-shaped protrusions and Sc micro-additions on resulting microstructure and tensile behavior of Al-Ce-Sc alloy fabricated by additive friction stir deposition. Using hot-extruded Al-12Ce-0.45Sc alloy as raw material, Al-Ce-Sc alloy (by mass percentage: Ce: 12%, Sc: 0.45%, balance Al) was prepared by additive friction stir deposition. Specific process parameters were: rotational speed 350 rpm, feed rate 114 mm / min, axial pressure 12 kN, preheating time 25 seconds, and preheating temperature 140℃. The Al-Ce-Sc alloy (by mass percentage, Ce: 12%, Sc: 0.45%, balance Al) was solution-treated at 630℃ for 0.5h and then aged at 300℃ for 5h. After aging, the alloy mainly contained spherical Al3Ce phase and Al3Zr phase. The mechanical properties of the alloy were: tensile strength of 234.4 MPa and elongation of 9.3%.

[0017] In Comparative Example 1, the rare earth element content was 12.45%. In this embodiment of the invention, the only rare earth element is Y, and the content is ≤0.4%. The rare earth element content in Comparative Example 1 is ≥31 times that of this invention. The unit price of Sc in Comparative Example 1 is about 10-20 times that of Y, and the content is 0.45%. The element with a relatively large content in this embodiment of the invention is Zn, and the Zn content is ≤8.5%. In Comparative Example 1, the Ce content is 12%, and the price of Ce is about 1.4-1.5 times that of Zn. The price of Zn added in this invention is equivalent to the price of 5.9% Ce in the Comparative Example. The price of Ce is approximately 2.0-2.5 times that of Mg, and approximately 3.1-4.3 times that of Zr. Therefore, the total cost of Comparative Example 1 is approximately 1.5-2 times that of the highest alloy addition in this invention, making Comparative Example 1 significantly more expensive than the raw material cost of this invention. Furthermore, the heat treatment temperatures of Comparative Example 1 (630℃ solution treatment, 300℃ aging) are higher than those of this invention (470℃ solution treatment, 120℃ aging), resulting in higher energy consumption. Additionally, the surface quality of the sample obtained using friction stir deposition additive manufacturing in Comparative Example 1 is poor, making it difficult to form components with complex internal structures. The average grain size of the alloy in Comparative Example 1 is 5.7 μm, exhibiting a single equiaxed crystal structure, while the average grain size of the alloy in this invention is ≤2.1 μm and exhibits a three-peak structure. The average grain size of the alloy in this invention is smaller than that of the alloy in Comparative Example 1. The aluminum alloy obtained in Comparative Example 1 has a tensile strength of 234.4 MPa and an elongation of 9.3%. The mechanical properties of the alloy obtained in Comparative Example 1, such as strength and plasticity, are significantly lower than the minimum properties of the alloy obtained in this invention.

[0018]

[0019] Compared to the comparative example, this invention synergistically improves both strength and plasticity, solving the industry-wide problems of hot cracking and toughening of 7075 aluminum alloy. Furthermore, the component ratios and process parameters differ in each embodiment of this invention, resulting in varying performance. This demonstrates that the superior effects achieved by this invention are not determined by a single component, ratio, process, or process parameter, but rather by the synergistic regulation of component interactions, elemental ratios, processes, and process parameters. Moreover, the simultaneous improvement of alloy strength and plasticity can only be achieved within the scope of the claims of this invention.

Claims

1. A high-strength, high-ductility 7075 aluminum alloy, characterized in that: The 7075 aluminum alloy composition, by mass percentage, is: Zn: 7.5-8.5%, Mg: 2.7-3.7%, Zr: 1.0-3.0%, Cu: 1.5-2.5%, Ti: 0.7-1.3%, Y: 0.1-0.4%, with the balance being Al and unavoidable impurities, wherein the impurities are ≤0.02%. Its preparation method includes the following steps: (1) 7075 aluminum alloy powder and ZrH2 powder are mixed at a mass ratio of 97-99:1-3, kept at 50-150℃ for 3-8 hours, ball-milled, and vacuum-dried at 50-150℃ for 3-8 hours to obtain 7075 aluminum alloy composite powder; the ball milling process is carried out at a mixing speed of 80-120 r / min and a mixing time of 1-3 hours. (2) Under the protection of high-purity argon, using an aluminum alloy plate as the substrate, the 7075 aluminum alloy composite powder obtained in step (1) is subjected to 80-500 layers of laser powder bed melting treatment, held at 400-550℃ for 0.5-3h, water quenched, and then held at 100-150℃ for 0.5-12h and water quenched again to obtain a high-strength, high-plasticity 7075 aluminum alloy; the laser powder bed melting treatment of each layer has the following characteristics: laser power of 200-300W, scanning speed of 600-1200mm / s, scanning spacing of 80-120μm, layer thickness of 20-40μm, scanning method of strip scanning, and interlayer scanning angle of 50-80°. Each layer is processed 1-4 times using different laser powder bed melting process parameters; each processing is as follows: laser power 220-280W, scanning speed 700-1000mm / s, scanning spacing 90-110μm, scanning method strip scanning, and interlayer scanning angle 60-70°; the high-strength, high-plasticity 7075 aluminum alloy has an average grain size ≤2.1μm, a three-peak structure, consisting of columnar crystals (5%-20% area), coarse equiaxed crystals (35%-55% area), and fine equiaxed crystals (35%-50% area); and also possesses high-density nanoscale η-Mg(Al, The alloy has a Zn, Cu)2 phase with a radius ≤19nm, a primary L12-Al3Zr phase with a radius ≤50nm, and a secondary L12-Al3Zr phase with a radius ≤2.9nm; the alloy has a tensile strength ≥515.9MPa and an elongation ≥12.7%; the high-strength, high-ductility 7075 aluminum alloy avoids cracking and anisotropy, and can be used for both simple and complex structures.

2. The high-strength, high-ductility 7075 aluminum alloy according to claim 1, characterized in that, In step (1), 7075 aluminum alloy powder and ZrH2 powder are mixed at a mass ratio of 98-99:1-2 and then kept at 80-120℃ for 4-6 hours.

3. The high-strength, high-ductility 7075 aluminum alloy according to claim 1, characterized in that, The 7075 aluminum alloy composite powder is obtained by vacuum drying at 80-120℃ for 4-6 hours as described in step (1).

4. The high-strength, high-ductility 7075 aluminum alloy according to claim 1, characterized in that, The ball milling process described in step (1) involves a mixing speed of 90-110 r / min and a mixing time of 1.5-2 h.

5. The high-strength, high-ductility 7075 aluminum alloy according to claim 1, characterized in that, Step (2) describes the process of holding the aluminum alloy at 450-500℃ for 1-2 hours, water quenching, and then holding it at 110-130℃ for 1-10 hours and water quenching again to obtain a high-strength, high-plasticity 7075 aluminum alloy.

6. The high-strength, high-ductility 7075 aluminum alloy according to claim 1, characterized in that, The laser powder bed melting process for each layer described in step (2) is as follows: laser power is 220-280W, scanning speed is 800-1000mm / s, scanning spacing is 90-110μm, layer thickness is 25-35μm, scanning method is strip scanning, and interlayer scanning angle is 60-70°. The laser powder bed melting process parameters for each layer are as follows: laser power is 230-270W, scanning speed is 800-900mm / s, scanning spacing is 95-105μm, scanning method is strip scanning, and interlayer scanning angle is 63-68°.

7. The high-strength, high-ductility 7075 aluminum alloy according to claim 1, characterized in that, The high-strength, high-plasticity 7075 aluminum alloy described in step (2) has an average grain size of 1-2 μm and a three-peak structure, consisting of columnar crystals with an area ratio of 7%-18%, coarse equiaxed crystals with an area ratio of 38%-52%, and fine equiaxed crystals with an area ratio of 40%-48%. It also has a high-density nanoscale η-Mg(Al, Zn, Cu)2 phase with a radius of 10-18 nm, a primary L12-Al3Zr phase with a radius of 30-48 nm, and a secondary L12-Al3Zr phase with a radius of 1-2.5 nm.

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