A preparation method for improving the strength performance of 7xxx series aluminum alloy

Abstract

The application discloses a preparation method for improving the strength performance of 7xxx series aluminum alloy and belongs to the technical field of aluminum alloy material preparation. The application uses homogenization treatment + fast cooling cycle to make Zn, Mg, Cu and Cr micro-alloying elements uniformly distributed in the alloy, and CrAl7 intermetallic compound is generated in the microstructure and has a pinning effect, so that the grain boundary migration is difficult, and the recrystallized grains hinder the nucleation and growth of recrystallization. Then, a medium average strain rate and a proper hot rolling temperature are selected for rolling to obtain an organization structure in which the coarse grains are embedded in the fine grains. Finally, the material performance is further improved through pre-deformation and regression re-aging heat treatment. Through the synergistic effect of micro-alloying, homogenization treatment + fast cooling treatment, hot rolling treatment, pre-deformation and regression re-aging heat treatment, the proportion of the organization structure in which the coarse grains are embedded in the fine grains is improved, so that the strength and corrosion resistance of the 7xxx series aluminum alloy are improved.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material preparation technology, specifically relating to a preparation method for improving the strength properties of 7xxx series aluminum alloys. Background Technology

[0002] 7xxx series aluminum alloys are widely used as structural materials in transportation and aerospace environments due to their ease of machining, good corrosion resistance, high strength, heat treatability, and good weldability. However, the development of modern industry has placed higher demands on the strength properties of 7xxx series aluminum alloys.

[0003] Invention patent application CN106967910A introduces a high-strength Al-Zn-Mg aluminum alloy and its preparation method. This Al-Zn-Mg aluminum alloy exhibits a room-temperature tensile strength greater than 420 MPa, a yield strength greater than 380 MPa, and an elongation greater than 11%. It possesses advantages such as high strength, good plasticity, and excellent corrosion resistance, making it suitable for manufacturing casings for portable electronic products such as tablets and smartphones, as well as bumpers, anti-collision beams, and crossbeams for transportation vehicles such as automobiles and rail vehicles. It has broad market application prospects. However, the addition of rare earth elements increases the cost of the alloy, which is not conducive to practical production applications. While the high-strength Al-Zn-Mg aluminum alloy obtained by the process described in the above patent application can improve strength and corrosion resistance by improving processing technology and material proportions to form different microstructures or precipitates, the improvement in strength and toughness is still not ideal. Therefore, it is necessary to provide a processing technology to improve the strength and toughness of 7xxx series aluminum alloys, further expanding the application of 7xxx series aluminum alloy materials in transportation and aerospace. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention provides a preparation method for improving the strength properties of 7xxx series aluminum alloys.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for improving the strength properties of 7xxx series aluminum alloys, through optimized design of the 7xxx series aluminum alloy composition, combined with homogenization, rapid cooling, and hot rolling, achieves the optimal strength properties of the 7xxx series aluminum alloys, including the following steps:

[0007] (1) Three homogenization + rapid cooling treatment: First homogenization treatment: the alloy plate is homogenized at 280℃ for 1h; Second homogenization treatment: the alloy plate is homogenized at 400℃ for 3h; Third homogenization + rapid cooling treatment: the alloy plate is homogenized at 480℃ for 12h, and then rapidly cooled at a rate of 300℃ / s.

[0008] (2) The alloy after three homogenization and rapid cooling cycles is preheated;

[0009] (3) The preheated alloy is hot-rolled;

[0010] (4) The hot-rolled alloy is subjected to multi-stage solution treatment, quenching treatment, pre-deformation, pre-aging treatment and over-aging treatment in sequence;

[0011] The 7xxx series aluminum alloys comprise the following components by mass percentage: 5.0~6.2% Zn, 2.2~2.7% Mg, 1.2~1.6% Cu, 0.02~0.05% Cr, with the balance being Al and unavoidable impurities.

[0012] In a preferred embodiment of the present invention, the average strain rate of the hot rolling treatment is 2.1~5.1 s. -1 The deformation amount per rolling cycle is 65%.

[0013] In a preferred embodiment of the present invention, the preheating temperature is 380~440℃ and the time is 30min.

[0014] As a preferred embodiment of the present invention, the multi-stage solution treatment specifically involves holding at 450°C for 40 minutes, then holding at 490°C for 30 minutes, and finally holding at 550°C for 20 minutes.

[0015] In a preferred embodiment of the present invention, the quenching treatment uses CL-1 organic quenching agent as the quenching medium.

[0016] In a preferred embodiment of the present invention, the deformation amount of the pre-deformation is 3%.

[0017] As a preferred embodiment of the present invention, the pre-aging treatment is performed at 125°C for 20 minutes, followed by heat preservation for 1 hour.

[0018] In a preferred embodiment of the present invention, the over-aging treatment is carried out at a temperature of 190°C to 230°C for 4 hours.

[0019] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention uses homogenization + rapid cooling treatment to ensure that microalloying elements are uniformly distributed in the alloy. Simultaneously, the generated CrAl7 intermetallic compound has a pinning effect in the microstructure, making grain boundary migration difficult. This significantly refines the recrystallized grains, hindering the nucleation and growth process of recrystallization, thus strengthening the alloy. Then, rolling is performed at a moderate average strain rate and an appropriate hot rolling temperature to obtain a microstructure in which coarse grains are embedded within fine grains. Finally, pre-deformation and regression re-aging heat treatment further improve the material properties. Through the synergistic effect of microalloying, three homogenization treatments + rapid cooling, hot rolling, pre-deformation, and regression re-aging heat treatment, the proportion of coarse grains embedded within fine grains is increased, thereby achieving the goal of improving the strength properties of 7xxx series aluminum alloys. This invention yields aluminum alloy sheets with excellent comprehensive properties such as strength and elongation. Furthermore, the preparation method has advantages such as relatively simple production process, low cost, and ease of implementation. Attached Figure Description

[0020] Figure 1 Preparation process to improve the strength properties of 7xxx series aluminum alloys. Detailed Implementation

[0021] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Example 1

[0022] Table 1. Chemical composition (wt%) of the aluminum-zinc-magnesium-copper-chromium alloy in this embodiment.

[0023]

[0024] The preparation method of the high-strength 7xxx series aluminum alloy described in this embodiment specifically includes the following steps:

[0025] (1) The alloy is smelted, cast and homogenized according to the composition in Table 1. The alloy is heated to 800℃~850℃ to melt. After the alloy is completely melted, it is stirred, refined and impurity removed to obtain the alloy melt.

[0026] (2) After the alloy melt obtained in step (1) is kept at 750°C for 30 minutes, it is poured into a preheated mold to form an aluminum alloy ingot with a thickness of 100 mm.

[0027] (3) The aluminum alloy ingot obtained in step (2) is circulated with air using a high-power axial flow fan. First homogenization treatment: the alloy plate is homogenized at 280℃ for 1h; second homogenization treatment: the alloy plate is homogenized at 400℃ for 3h; third homogenization + rapid cooling treatment: the alloy plate is homogenized at 480℃ for 12h, and then rapidly cooled at a rate of 300℃ / s to make all elements uniformly distributed.

[0028] (4) The alloy was processed into a sample of 80mm×50mm×10mm, and placed at room temperature for 1 hour. Then it was preheated to 380℃ for 30 minutes. The preheated sample was then rolled in a single pass on a d300mm×300mm twin-roll mill with a deformation of 65% and an average strain rate of 2.1 s. -1 After rolling, the sample is placed in cold water to cool it in order to preserve its deformed microstructure.

[0029] (5) Then it is heated and subjected to a multi-stage solution treatment with parameters of 450℃×40min+490℃×30min+550℃×20min, followed by quenching in CL-1 organic quenching agent.

[0030] (6) The sample after solution quenching was immediately placed on an electro-hydraulic servo fatigue testing machine for 3% pre-deformation treatment. The pre-deformed aluminum alloy was immediately placed in an oil bath furnace at 125℃ for 20 minutes of pre-aging treatment, and then placed in a constant temperature vacuum chamber for 1 hour.

[0031] (7) Finally, an aging treatment was performed at 190℃ for 4 hours. The tensile strength and elongation of the final aluminum alloy are shown in Table 2. The proportion of coarse grains embedded in fine grains was obtained from the EBSD grain boundary diagram of the sample.

[0032] Table 2

[0033] Example 2

[0034] Table 3 Chemical composition (wt%) of the aluminum-zinc-magnesium-copper-chromium alloy in this embodiment.

[0035]

[0036] The preparation method of the high-strength 7xxx series aluminum alloy described in this embodiment specifically includes the following steps:

[0037] (1) The alloy is smelted, cast and homogenized according to the composition in Table 3. The alloy is heated to 800℃~850℃ to melt. After the alloy is completely melted, it is stirred, refined and impurity removed to obtain the alloy melt.

[0038] (2) After the alloy melt obtained in step (1) is kept at 750°C for 30 minutes, it is poured into a preheated mold to form an aluminum alloy ingot with a thickness of 100 mm.

[0039] (3) The aluminum alloy ingot obtained in step (2) is circulated with air using a high-power axial flow fan. First homogenization treatment: the alloy plate is homogenized at 280℃ for 1h; second homogenization treatment: the alloy plate is homogenized at 400℃ for 3h; third homogenization + rapid cooling treatment: the alloy plate is homogenized at 480℃ for 12h, and then rapidly cooled at a rate of 300℃ / s to make all elements uniformly distributed.

[0040] (4) The alloy was processed into a sample of 80mm×50mm×10mm, and placed at room temperature for 1 hour. Then it was preheated to 410℃ for 30 minutes. The preheated sample was then rolled in a single pass on a d300mm×300mm twin-roll mill with a deformation of 65% and an average strain rate of 3.9 s. -1 After rolling, the sample is placed in cold water to cool it in order to preserve its deformed microstructure.

[0041] (5) Then it is heated and subjected to a multi-stage solution treatment with parameters of 450℃×40min+490℃×30min+550℃×20min, followed by quenching in CL-1 organic quenching agent.

[0042] (6) The sample after solution quenching was immediately placed on an electro-hydraulic servo fatigue testing machine for 3% pre-deformation treatment. The pre-deformed aluminum alloy was immediately placed in an oil bath furnace at 125℃ for 20 minutes of pre-aging treatment, and then placed in a constant temperature vacuum chamber for 1 hour.

[0043] (7) Finally, an aging treatment was performed with parameters of 210℃×4h. The tensile strength and elongation of the final aluminum alloy are shown in Table 4. The proportion of coarse grains embedded in fine grains in the microstructure was obtained from the EBSD grain boundary diagram of the sample.

[0044] Table 4

[0045] Example 3

[0046] Table 5. Chemical composition (wt%) of the aluminum-zinc-magnesium-copper-chromium alloy in this embodiment.

[0047]

[0048] The preparation method of the high-strength 7xxx series aluminum alloy described in this embodiment specifically includes the following steps:

[0049] (1) The alloy is smelted, cast and homogenized according to the composition in Table 5. The alloy is heated to 800℃~850℃ to melt. After the alloy is completely melted, it is stirred, refined and impurity removed to obtain the alloy melt.

[0050] (2) After the alloy melt obtained in step (1) is kept at 750°C for 30 minutes, it is poured into a preheated mold to form an aluminum alloy ingot with a thickness of 100 mm.

[0051] (3) The aluminum alloy ingot obtained in step (2) is circulated with air using a high-power axial flow fan. First homogenization treatment: the alloy plate is homogenized at 280℃ for 1h; second homogenization treatment: the alloy plate is homogenized at 400℃ for 3h; third homogenization + rapid cooling treatment: the alloy plate is homogenized at 480℃ for 12h, and then rapidly cooled at a rate of 300℃ / s to make all elements uniformly distributed.

[0052] (4) The alloy was processed into a sample of 80mm×50mm×10mm, and placed at room temperature for 1 hour. Then it was preheated to 380℃ for 30 minutes. The preheated sample was then rolled in a single pass on a d300mm×300mm twin-roll mill with a deformation of 65% and an average strain rate of 5.1 s. -1 After rolling, the sample is placed in cold water to cool it in order to preserve its deformed microstructure.

[0053] (5) Then it is heated and subjected to a multi-stage solution treatment with parameters of 450℃×40min+490℃×30min+550℃×20min, followed by quenching in CL-1 organic quenching agent.

[0054] (6) The sample after solution quenching was immediately placed on an electro-hydraulic servo fatigue testing machine for 3% pre-deformation treatment. The pre-deformed aluminum alloy was immediately placed in an oil bath furnace at 125℃ for 20 minutes of pre-aging treatment, and then placed in a constant temperature vacuum chamber for 1 hour.

[0055] (7) Finally, an aging treatment was performed at 230℃ for 4 hours. The tensile strength and elongation of the final aluminum alloy are shown in Table 6. The proportion of coarse grains embedded in fine grains was obtained from the EBSD grain boundary diagram of the sample.

[0056] Table 6

[0057]

[0058] Comparative Example 1

[0059] The only difference between the preparation method of the high-strength 7xxx series aluminum alloy described in this comparative example and Example 1 is that the hot rolling temperature is 340℃ and the average hot rolling strain rate is 1.2s. -1 The tensile strength and elongation of the final aluminum alloy are shown in Table 7. The proportion of coarse grains embedded in fine grains in the microstructure was obtained from the EBSD grain boundary diagram of the sample.

[0060] Table 7

[0061]

[0062] A comparison of Comparative Example 1 and Example 1 shows that the hot rolling temperature and average strain rate are crucial for improving the strength of the material. In Examples 1-3, the hot rolling temperature was 380~440℃, and the average strain rate was 2.1~5.1s. -1 This results in the coarse grain boundaries forming a relatively independent, embedded distribution around several layers of fine grains, thereby increasing the strength and elongation of the aluminum alloy.

[0063] Comparative Example 2

[0064] The only difference between the preparation method of the high-strength 7xxx series aluminum alloy described in this comparative example and Example 2 is that pre-deformation treatment, pre-aging treatment, and over-aging treatment are not performed. The tensile strength and elongation of the final aluminum alloy are shown in Table 8. The proportion of coarse grains embedded in fine grains in the microstructure is obtained from the EBSD grain boundary diagram of the sample.

[0065] Table 8

[0066]

[0067] By comparing Comparative Example 2 with Examples 1-3, Example 2 underwent a regression re-aging heat treatment, that is, after the alloy underwent solution treatment and pre-aging treatment, it underwent over-aging treatment and held at a temperature for a period of time, which can further increase its yield and tensile strength. The pre-deformation treatment can suppress the negative effects of natural aging to a certain extent, and the over-aging treatment can improve its strength, thereby increasing the strength of the aluminum alloy.

[0068] Comparative Example 3

[0069] The only difference between the preparation method of the high-strength 7xxx series aluminum alloy described in this comparative example and that in Example 3 is the chemical composition of the aluminum-zinc-magnesium-copper-chromium alloy. The chemical composition of the alloy in this comparative example is shown in Table 9. The tensile strength and elongation of the finally obtained aluminum alloy are shown in Table 10. The proportion of coarse grains embedded in fine grains in the microstructure was obtained from the EBSD grain boundary diagram of the sample.

[0070] Table 9 Chemical composition (wt%) of the comparative aluminum-zinc-magnesium-copper-chromium alloy

[0071]

[0072] Table 10

[0073]

[0074] The CrAl7 intermetallic compound formed in the aluminum plate has a pinning effect in the microstructure, making grain boundary migration difficult. It can significantly refine the recrystallized grains, hindering the nucleation and growth process of recrystallization, thus strengthening the alloy to a certain extent. It can also improve the toughness of the alloy and reduce the sensitivity to stress corrosion cracking, thereby improving the strength of the 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 the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing 7xxx series aluminum alloys with improved strength properties, characterized in that, By optimizing the composition of 7xxx series aluminum alloys, and combining three homogenization processes with rapid cooling, hot rolling, multi-stage solution treatment, quenching, pre-deformation, pre-aging, and over-aging treatments, the optimal strength performance of 7xxx series aluminum alloys is achieved. This includes the following steps: (1) Three homogenization and rapid cooling treatments: First homogenization treatment: The alloy plate is homogenized at 280℃ for 1h; Second homogenization treatment: The alloy plate is homogenized at 400℃ for 3h; Third homogenization + rapid cooling treatment: The alloy plate is homogenized at 480℃ for 12h, and then rapidly cooled at a rate of 300℃ / s. (2) The alloy after three homogenization and rapid cooling treatments is preheated; (3) The preheated alloy is hot-rolled; (4) The hot-rolled alloy is subjected to multi-stage solution treatment, quenching treatment, pre-deformation, pre-aging treatment and over-aging treatment in sequence; The 7xxx series aluminum alloys comprise the following components by mass percentage: 5.0~6.2% Zn, 2.2~2.7% Mg, 1.2~1.6% Cu, 0.02~0.05% Cr, with the balance being Al and unavoidable impurities; The average strain rate of the hot rolling process is 2.1~5.1 s. -1 The deformation per rolling cycle is 65%. The preheating temperature is 380~440℃, and the time is 30 minutes. The multi-stage solution treatment specifically involves holding at 450°C for 40 minutes, then holding at 490°C for 30 minutes, and finally holding at 550°C for 20 minutes. The pre-aging treatment is performed at 125°C for 20 minutes, followed by heat treatment for 1 hour. The over-aging treatment is performed at a temperature of 190℃~230℃ for 4 hours.

2. The preparation method for improving the strength properties of 7xxx series aluminum alloys as described in claim 1, characterized in that, The quenching process uses CL-1 organic quenching agent as the quenching medium.

3. The preparation method for improving the strength properties of 7xxx series aluminum alloys as described in claim 1, characterized in that, The deformation amount of the pre-deformation is 3%.

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