7xxx series aluminum alloy and its heat treatment method

Abstract

The present invention provides a 7xxx series aluminum alloy and a heat treatment method therefor. The heat treatment method includes: holding the cold drawn material of the 7xxx series aluminum alloy at 300-470 °C for 1-10 h to obtain a first heat-treated material, and performing a second heat treatment in a first manner or a second manner. The first manner includes cooling the first heat-treated material to 150-250 °C and holding for 2-10 h; the second manner includes cooling the first heat-treated material to 25-30 °C, then heating it to 150-250 °C and holding for 2-10 h; after obtaining the second heat-treated material, performing cooling and other treatments to obtain the 7xxx series aluminum alloy. In the preparation process of the 7xxx series aluminum alloy, the present invention adopts a two-stage intermediate annealing heat treatment process of short-time high temperature - short-time low temperature, which can well control the morphological characteristics of intragranular and grain boundary precipitation phases, achieving the effects of slowing down the increase in natural aging strength during the parking process and improving the intergranular corrosion resistance of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys, and in particular, to a 7xxx series aluminum alloy and a heat treatment method thereof. Background Art

[0002] Aviation flight equipment serves in the harsh environment of coastal areas for a long time, and has high requirements for the strength and corrosion resistance of materials. During the material selection process of aluminum alloys used in existing aviation aircraft equipment, in order to ensure light weight and high strength, 7xxx series aluminum alloys are usually selected as the structural materials.

[0003] Materials such as 7xxx series aluminum alloy profiles, plates, wire rods, etc. mainly go through processes such as melting and casting, homogenization, hot rolling, cold rolling, intermediate annealing, cold drawing forming, solution quenching, aging, etc. During the preparation process, due to the high strength of 7xxx series alloys, intermediate annealing is required before each cold drawing to soften the material and improve the forming performance. In addition, due to the long inventory storage time intervals during intermediate annealing, cold drawing, and subsequent forming processes, the stability of various properties of the material is particularly important. In the industrial material preparation process, there are often problems such as the increase in natural aging strength and intergranular corrosion after intermediate annealing or cold drawing of the material, resulting in deterioration of the surface quality, an increase in the scrap rate, inability to meet the requirements of subsequent forming operations, greatly reducing the material production efficiency, and increasing the production cost. Summary of the Invention

[0004] The main object of the present invention is to provide a 7xxx series aluminum alloy and a heat treatment method thereof to solve the problems of poor strength stability and corrosion resistance of 7xxx series aluminum alloys during long-term natural storage in the prior art.

[0005] To achieve the above object, according to one aspect of the present invention, there is provided a heat treatment method for a 7xxx series aluminum alloy, including the following steps: Step S1, melting and casting, homogenizing, hot rolling, cold rolling, and cold drawing the raw materials of the 7xxx series aluminum alloy to obtain cold-drawn state materials; Step S2, performing a first heat treatment on the cold-drawn state materials, the holding temperature of the first heat treatment being 300 - 470°C, and the holding time being 1 - 10 h, to obtain first heat-treated materials; Step S3, performing a second heat treatment on the first heat-treated materials in manner one or manner two to obtain second heat-treated materials; where manner one includes: cooling the first heat-treated materials to 150 - 250°C and holding for 2 - 10 h; manner two includes: first cooling the first heat-treated materials to 25 - 30°C, then heating to 150 - 250°C and holding for 2 - 10 h; Step S4, cooling the second heat-treated materials, then performing cold deformation, solution quenching, and aging treatment to obtain a 7xxx series aluminum alloy.

[0006] Further, by weight percentage, the 7xxx series aluminum alloy comprises 5.80 - 7.10% of Zn, 1.90 - 2.60% of Cu, 1.80 - 2.70% of Mg, 0.05 - 0.18% of Cr, 0.08 - 0.15% of Zr, 0.01 - 0.15% of Fe, 0 - 0.10% of Mn, 0.05 - 0.20% of Ti, 0.01 - 0.15% of Si, with the balance being Al and unavoidable impurities, each unavoidable impurity < 0.05%, and the total impurities < 0.15%.

[0007] Further, in step S2, the heating rate of the first heat treatment is 30 - 150 °C / h.

[0008] Further, in step S2, the heating rate of the first heat treatment is 105 - 150 °C / h, the holding temperature is 400 - 470 °C, and the holding time is 1 - 2 h.

[0009] Further, in step S3, the cooling rate of method one is 30 - 200 °C / h.

[0010] Further, in step S3, the cooling rate of method one is 30 - 90 °C / h, the holding temperature is 200 - 250 °C, and the holding time is 2 - 3 h.

[0011] Further, in step S3, the cooling rate of method two is 100 - 200 °C / s, and the heating rate is 30 - 150 °C / h.

[0012] Further, in step S4, the cooling method is one or more of water cooling, furnace cooling, and air cooling.

[0013] According to another aspect of the present invention, there is provided a 7xxx series aluminum alloy obtained by the above heat treatment method of the present invention.

[0014] Further, for the 7xxx series aluminum alloy, the increase in tensile strength after being parked for 270 days ≤ 5 MPa, and the intergranular corrosion depth ≤ 25 μm.

[0015] Applying the technical solution of the present invention, between the cold drawing passes in the preparation process of 7xxx series aluminum alloy, a two-stage intermediate annealing heat treatment process of short-time high temperature - short-time low temperature can be adopted to well control the morphological characteristics of the precipitates in the grains and at the grain boundaries, achieving the effects of slowing down the increase in natural aging strength during the parking process and improving the intergranular corrosion resistance of the material. Among them, the first heat treatment adopts high-temperature heat treatment, which can play a recovery or recrystallization effect, reduce the previous work hardening strength, and is beneficial to subsequent re-forming; the second heat treatment adopts low-temperature heat preservation treatment, which can achieve the purpose of promoting the full precipitation of the second phase in the grains and at the grain boundaries. On the one hand, the full precipitation of the second phase in the grains fully consumes the solute elements in the aluminum alloy, and GP zones and strengthening phases cannot be precipitated again during the natural parking process, thereby reducing the increase in tensile strength caused by the natural aging parking effect of the material; on the other hand, the low-temperature heat preservation process can also promote the precipitation, growth and discontinuous morphology of the second phase at the grain boundaries, hindering the continuous occurrence of intergranular corrosion along the grain boundary phase, thereby significantly improving the intergranular corrosion resistance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0017] Figure 1 Shows the morphology diagram of intragranular precipitates of aluminum alloy according to Embodiment 3 of the present invention;

[0018] Figure 2 Shows the morphology diagram of intragranular precipitates of aluminum alloy according to Comparative Example 3 of the present invention;

[0019] Figure 3 Shows the intergranular corrosion morphology diagram of aluminum alloy according to Embodiment 3 of the present invention;

[0020] Figure 4 Shows the intergranular corrosion morphology diagram of aluminum alloy according to Comparative Example 3 of the present invention; and

[0021] Figure 5 Shows the parking stability trend diagram of aluminum alloy according to Embodiment 3 and Comparative Example 3 of the present invention, where 3a is Embodiment 3 and 3b is Comparative Example 3. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0023] As described in the background art of the present invention, there are problems in the prior art that the strength stability and corrosion resistance of 7xxx series aluminum alloys are not good during long-term natural storage. To solve the above problems, in a typical embodiment of the present invention, a heat treatment method for 7xxx series aluminum alloys is provided, including the following steps: Step S1, melting, homogenizing, hot rolling, cold rolling, and cold drawing the raw materials of the 7xxx series aluminum alloy to obtain a cold-drawn material; Step S2, performing a first heat treatment on the cold-drawn material, the holding temperature of the first heat treatment is 300-470 °C, and the holding time is 1-10 h, to obtain a first heat-treated material; Step S3, performing a second heat treatment on the first heat-treated material in manner one or manner two to obtain a second heat-treated material; Manner one includes: cooling the first heat-treated material to 150-250 °C and holding for 2-10 h; Manner two includes: first cooling the first heat-treated material to 25-30 °C, then heating it to 150-250 °C and holding for 2-10 h; Step S4, cooling the second heat-treated material, and then performing cold deformation, solution quenching, and aging treatment to obtain a 7xxx series aluminum alloy.

[0024] In the present invention, the raw materials of the 7xxx series aluminum alloy are first melted, homogenized, hot rolled, cold rolled, and cold drawn to obtain a cold-drawn material; then the cold-drawn material is subjected to a short-term high-temperature first heat treatment at 300-470 °C for 1-10 h to obtain a first heat-treated material. The high-temperature heat treatment can achieve a recovery or recrystallization effect, reduce the strength of the previous work hardening, and is beneficial to subsequent re-forming; then the first heat-treated material is cooled to 150-250 °C and held for 2-10 h, or the first heat-treated material is first cooled to 25-30 °C and then heated to 150-250 °C and held for 2-10 h to perform a short-term low-temperature second heat treatment. The low-temperature holding treatment can achieve the purpose of promoting the full precipitation of the second phase in the crystal and at the grain boundary. On the one hand, the full precipitation of the second phase in the crystal fully consumes the solute elements (such as Mg, Zn, etc.) in the aluminum alloy. During the subsequent natural storage process, the GP zones that can promote the increase in the strength of the material will not precipitate again, ensuring the stability of the strength, and thus can slow down the increase in the tensile strength caused by the natural aging storage effect of the material.

[0025] On the other hand, the low-temperature heat preservation process can also promote the precipitation and growth of the second phase at grain boundaries, manifested as discontinuous and coarse precipitation of the grain boundary phase, which hinders the continuous occurrence of intergranular corrosion along the grain boundary phase, thereby significantly improving the intergranular corrosion resistance of the material; finally, the second heat-treated material is cooled, and then cold-deformed, solution quenched, and aged to obtain the 7xxx series aluminum alloy. Among them, melting and casting, homogenization, hot rolling, cold rolling, cold drawing, solution quenching, aging treatment, etc. can use conventional methods in the art, and the established purpose can be achieved in combination with the specific heat treatment process of the present invention. The corresponding process parameters or process sequences can be adjusted as needed. The specific heat treatment process of the present invention can be carried out once or multiple times during the preparation process of the aluminum alloy, which is easy to understand for those skilled in the art and will not be elaborated here.

[0026] The present invention fully considers the influence of the corrosion resistance and strength stability of the 7xxx aluminum alloy material after cold drawing on subsequent re-forming. Between cold drawing and cold deformation in the preparation process of the 7xxx series aluminum alloy, by optimizing and adjusting the intermediate annealing heat treatment system, a two-stage intermediate annealing heat treatment process of short-time high temperature - short-time low temperature can, on the basis of softening the material, enable the second phase to fully precipitate, and well control the morphological characteristics of the precipitates in the grains and at the grain boundaries, achieving the effects of slowing down the natural aging strength increase during the parking process and improving the intergranular corrosion resistance of the material.

[0027] The specific composition of the 7xxx series aluminum alloy can use the conventional composition in the art. For the purpose of further improving the adaptability of the aluminum alloy composition and the preparation process, and further taking into account the parking strength stability and intergranular corrosion performance of the aluminum alloy, in a preferred embodiment, by weight percentage, the 7xxx series aluminum alloy includes 5.80 - 7.10% of Zn, 1.90 - 2.60% of Cu, 1.80 - 2.70% of Mg, 0.05 - 0.18% of Cr, 0.08 - 0.15% of Zr, 0.01 - 0.15% of Fe, 0 - 0.10% of Mn, 0.05 - 0.20% of Ti, 0.01 - 0.15% of Si, and the balance is Al and inevitable impurities, each inevitable impurity < 0.05%, and the total impurities < 0.15%.

[0028] In a preferred embodiment, in step S2, the heating rate of the first heat treatment is 30 - 150 °C / h. The above heating rate can enable the core of large-sized materials such as aluminum alloy profiles, plates, bars, and wires to uniformly reach the set temperature, which is more suitable for the application of industrial large-sized materials.

[0029] In order to further improve the recovery or recrystallization effect of the first heat treatment, and thus better reduce the pre - processing hardening strength of the aluminum alloy, in a preferred embodiment, in step S2, the heating rate of the first heat treatment is 105 - 150 °C / h, the holding temperature is 400 - 470 °C, and the holding time is 1 - 2 h.

[0030] In a preferred embodiment, in step S3, for method one, the cooling rate is 30 - 200 °C / h, and the cooling method is preferably furnace cooling or air cooling. The above - mentioned cooling rate can enable the overall material to be cooled more uniformly.

[0031] For the purpose of better promoting the full precipitation of the second phase in the grains and at the grain boundaries of the aluminum alloy, and thus further improving the strength stability and intergranular corrosion resistance of the aluminum alloy, in a preferred embodiment, in step S3, for method one, the cooling rate is 30 - 90 °C / h, the holding temperature is 200 - 250 °C, and the holding time is 2 - 3 h.

[0032] For similar reasons, in a preferred embodiment, in step S3, for method two, the cooling rate is 100 - 200 °C / s, the cooling method is preferably water cooling, and the heating rate is 30 - 150 °C / h.

[0033] In a preferred embodiment, in step S4, the cooling method is one or more of water cooling, furnace cooling, and air cooling, which is simple to operate and has a better cooling effect.

[0034] In another typical embodiment of the present invention, a 7xxx series aluminum alloy is further provided, which is prepared by the above - mentioned heat treatment method of the present invention and can balance the strength stability and corrosion resistance.

[0035] Specifically, in a preferred embodiment, the increase in the tensile strength of the 7xxx series aluminum alloy after being parked for 270 days is ≤5 MPa, and the intergranular corrosion depth is ≤25 μm.

[0036] Typically but not limited to, in the first heat treatment of the present invention, the heating rate is 30°C / h, 40°C / h, 50°C / h, 60°C / h, 70°C / h, 80°C / h, 90°C / h, 100°C / h, 105°C / h, 110°C / h, 120°C / h, 130°C / h, 140°C / h, 150°C / h or a range value composed of any two of these values; the holding temperature is 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C or a range value composed of any two of these values; the holding time is 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or a range value composed of any two of these values.

[0037] Typically but not limited to, in the second heat treatment of the present invention, for Method 1, the cooling rate is 30°C / h, 40°C / h, 50°C / h, 60°C / h, 70°C / h, 80°C / h, 90°C / h, 100°C / h, 110°C / h, 120°C / h, 130°C / h, 140°C / h, 150°C / h, 160°C / h, 170°C / h, 180°C / h, 190°C / h, 200°C / h or a range value composed of any two of these values; the holding temperature is 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C or a range value composed of any two of these values; the holding time is 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or a range value composed of any two of these values.

[0038] Typically but not limited to, in the second heat treatment of the present invention, for Method 2, the cooling rate is 100°C / s, 110°C / s, 120°C / s, 130°C / s, 140°C / s, 150°C / s, 160°C / s, 170°C / s, 180°C / s, 190°C / s, 200°C / s or a range value composed of any two of these values; first cool to 25°C, 26°C, 27°C, 28°C, 29°C, 30°C or a range value composed of any two of these values.

[0039] Typically but not limitedly, in the second heat treatment of the present invention, the heating rate in the second method is 30°C / h, 40°C / h, 50°C / h, 60°C / h, 70°C / h, 80°C / h, 90°C / h, 100°C / h, 110°C / h, 120°C / h, 130°C / h, 140°C / h, 150°C / h or a range value composed of any two of these values; heated to 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C or a range value composed of any two of these values; the holding time is 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h or a range value composed of any two of these values.

[0040] Typically but not limited to, by weight percentage, the 7xxx series aluminum alloy of the present invention comprises Zn of 5.80%, 5.90%, 6.00%, 6.10%, 6.20%, 6.30%, 6.40%, 6.50%, 6.60%, 6.70%, 6.80%, 6.90%, 7.00%, 7.10% or a range value composed of any two of these values; Cu of 1.90%, 2.00%, 2.10%, 2.20%, 2.30%, 2.40%, 2.50%, 2.60% or a range value composed of any two of these values; Mg of 1.80%, 1.90%, 2.00%, 2.10%, 2.20%, 2.30%, 2.40%, 2.50%, 2.60%, 2.70% or a range value composed of any two of these values; Cr of 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18% or a range value composed of any two of these values; Zr of 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15% or a range value composed of any two of these values; Fe of 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15% or a range value composed of any two of these values; Mn of 0.00%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10% or a range value composed of any two of these values; Ti of 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20% or a range value composed of any two of these values; Si of 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15% or a range value composed of any two of these values; the balance being Al and unavoidable impurities.

[0041] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0042] Example 1

[0043] The components and weight percentages of the 7xxx aluminum alloy are as follows: Si 0.01%, Fe 0.03%, Cu 2.10%, Mg 1.80%, Mn 0.10%, Cr 0.05%, Zn 5.80%, Ti 0.05%, Zr 0.10%, and the balance is Al and unavoidable impurities. The heat treatment method is as follows:

[0044] Step S1: The raw materials of the above 7xxx series aluminum alloy are subjected to melting and casting, homogenization, hot rolling, cold rolling, and cold drawing to obtain a cold-drawn material;

[0045] Step S2: The cold-drawn material is heated to 300 °C at a rate of 30 °C / h and held for 10 h to obtain a first heat-treated material;

[0046] Step S3, the first second heat treatment method: The first heat-treated material is air-cooled to 200 °C at a rate of 30 °C / h and held for 3 h to obtain a second heat-treated material;

[0047] Step S4: The second heat-treated material is cooled in the furnace, and then subjected to cold deformation, solution quenching, and aging treatment to obtain a 7xxx series aluminum alloy.

[0048] Examples 2 to 4

[0049] The differences between Examples 2 to 4 and Example 1 are that the aluminum alloy compositions and the process parameters of the heat treatment are different, as shown in Tables 1 to 2 for details.

[0050] Examples 5 to 6

[0051] The differences between Examples 5 to 6 and Example 1 are that the process parameters of the heat treatment are different, as shown in Table 2 for details.

[0052] Example 7

[0053] The components and weight percentages of the 7xxx aluminum alloy are as follows: Si 0.01%, Fe 0.03%, Cu 2.50%, Mg 2.10%, Cr 0.15%, Zn 6.20%, Ti 0.10%, Zr 0.15%, and the balance is Al and unavoidable impurities. The heat treatment method is as follows:

[0054] Step S1: The raw materials of the above 7xxx series aluminum alloy are subjected to melting and casting, homogenization, hot rolling, cold rolling, and cold drawing to obtain a cold-drawn material;

[0055] Step S2: The hot-rolled material is heated to 410 °C at a rate of 105 °C / h and held for 2 h to obtain a first heat-treated material;

[0056] Step S3, the second second heat treatment method: The first heat-treated material is water-cooled to 25 °C at a rate of 100 °C / s, and then heated to 150 °C at a rate of 30 °C / h and held for 10 h to obtain a second heat-treated material;

[0057] In step S4, the second heat treatment material is cooled in the furnace, and then undergoes cold deformation, solution quenching, and aging treatment to obtain a 7xxx series aluminum alloy.

[0058] Example 8

[0059] The difference between Example 8 and Example 7 lies in the different aluminum alloy compositions and heat treatment process parameters, as detailed in Tables 1 to 2.

[0060] Examples 9 to 10

[0061] The difference between Examples 9 to 10 and Example 7 lies in the different heat treatment process parameters, as detailed in Table 2.

[0062] Comparative Example 1

[0063] The difference between Comparative Example 1 and Example 2 is that in step S2, the temperature is raised to 350 °C at a rate of 110 °C / h and held for 5 h; in step S3, it is cooled to 25 °C at a rate of 60 °C / h.

[0064] Comparative Example 2

[0065] The difference between Comparative Example 2 and Example 3 is that in step S2, the temperature is raised to 400 °C at a rate of 75 °C / h and held for 3 h; in step S3, it is cooled to 28 °C at a rate of 30 °C / h.

[0066] Comparative Example 3

[0067] The difference between Comparative Example 3 and Example 3 is that in step S2, the temperature is raised to 430 °C at a rate of 110 °C / h and held for 1 h; in step S3, it is cooled to 30 °C at a rate of 100 °C / h.

[0068] Comparative Example 4

[0069] The difference between Comparative Example 4 and Example 3 is that the second heat treatment is not carried out.

[0070] The aluminum alloy compositions of the above examples are shown in Table 1, and the heat treatment process parameters of the above examples and comparative examples are shown in Table 2.

[0071] Table 1

[0072]

[0073] Table 2

[0074]

[0075]

[0076] The tensile strength at 0 day, the tensile strength after 270 days of storage, and the intergranular corrosion depth of the aluminum alloy materials prepared in the above examples and comparative examples were measured, and the results are shown in Table 3.

[0077] The morphology diagram of the intragranular precipitation phase of the aluminum alloy in Example 3 is shown in Figure 1 , and the morphology diagram of the intragranular precipitation phase of the aluminum alloy in Comparative Example 3 is shown in Figure 2 . It can be seen that compared with Comparative Example 3, the intragranular precipitation in Example 3 increased significantly.

[0078] The intergranular corrosion morphology diagram of the aluminum alloy in Example 3 is shown in Figure 3 , and the intergranular corrosion morphology diagram of the aluminum alloy in Comparative Example 3 is shown in Figure 4 . It can be seen that the partial corrosion of the grain boundary in Comparative Example 3 is obvious, the corrosion in Example 3 is less, and the intergranular corrosion resistance is significantly increased.

[0079] The trend diagram of the storage stability of the aluminum alloys in Example 3 and Comparative Example 3 is shown in Figure 5 , where 3a is Example 3 and 3b is Comparative Example 3. It can be seen that the tensile strength of Comparative Example 3 increased significantly by 33 MPa after 270 days of storage, while the tensile strength of Example 3 of the present invention only increased by 3 MPa after 270 days of storage, showing significantly improved storage stability.

[0080] Test method:

[0081] Tensile strength: GB / T 228.1-2021.

[0082] Intergranular corrosion depth: GB / T 7998-2005.

[0083] Table 3

[0084]

[0085]

[0086] As can be seen from the above, the increase in tensile strength after 270 days of storage in each comparative example is ≥33 MPa, and the intergranular corrosion depth is ≥65 μm; the increase in tensile strength after 270 days of storage in each example of the present invention is ≤16 MPa, and the intergranular corrosion depth is ≤59 μm. It can be seen that compared with the comparative examples, each example of the present invention adopts a two-stage intermediate annealing heat treatment process of short-time high temperature - short-time low temperature, which can well control the morphological characteristics of intragranular and intergranular precipitation phases, achieving the effects of slowing down the increase in natural aging strength during storage and improving the intergranular corrosion resistance of the material. In addition, it can be seen that when all the preparation process parameters are within the preferred range of the present invention, the storage strength stability and intergranular corrosion resistance of the 7xxx series aluminum alloy are better.

[0087] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A heat treatment method for 7xxx series aluminum alloy, characterized in that It includes the following steps: Step S1: The raw materials of the 7xxx series aluminum alloy are subjected to melting and casting, homogenization, hot rolling, cold rolling, and cold drawing to obtain a cold-drawn material; Step S2: The cold-drawn material is subjected to a first heat treatment, the holding temperature of the first heat treatment is 300 - 470 °C, and the holding time is 1 - 10 h to obtain a first heat-treated material; Step S3: The first heat-treated material is subjected to a second heat treatment in Method 1 or Method 2 to obtain a second heat-treated material; Among them, Method 1 includes: cooling the first heat-treated material to 150 - 230 °C and holding for 2 - 10 h; Method 2 includes: first cooling the first heat-treated material to 25 - 30 °C, then heating it to 150 - 230 °C and holding for 2 - 10 h; Step S4: The second heat-treated material is cooled, then subjected to cold deformation, solution quenching, and aging treatment to obtain the 7xxx series aluminum alloy.

2. The heat treatment method according to claim 1, characterized in that, By weight percentage, the 7xxx series aluminum alloy includes Zn 5.80 - 7.10%, Cu 1.90 - 2.60%, Mg 1.80 - 2.70%, Cr 0.05 - 0.18%, Zr 0.08 - 0.15%, Fe 0.01 - 0.15%, Mn 0 - 0.10%, Ti 0.05 - 0.20%, Si 0.01 - 0.15%, and the balance is Al and unavoidable impurities, each of the unavoidable impurities < 0.05%, and the total impurities < 0.15%.

3. The heat treatment method according to claim 1 or 2, characterized in that, In Step S2, the heating rate of the first heat treatment is 30 - 150 °C / h.

4. The heat treatment method according to claim 1 or 2, characterized in that, In Step S2, the heating rate of the first heat treatment is 105 - 150 °C / h, the holding temperature is 400 - 470 °C, and the holding time is 1 - 2 h.

5. The heat treatment method according to claim 1 or 2, characterized in that, In Step S3, the cooling rate of Method 1 is 30 - 200 °C / h.

6. The heat treatment method according to claim 1 or 2, characterized in that In Step S3, the cooling rate of Method 1 is 30 - 90 °C / h, the holding temperature is 200 - 250 °C, and the holding time is 2 - 3 h.

7. The heat treatment method according to claim 1 or 2, characterized in that In Step S3, the cooling rate of Method 2 is 100 - 200 °C / s, and the heating rate is 30 - 150 °C / h.

8. The heat treatment method according to claim 1 or 2, characterized in that In Step S4, the cooling method is one or more of water cooling, furnace cooling, and air cooling.

9. A 7xxx series aluminum alloy, characterized in that, Prepared by the heat treatment method according to any one of Claims 1 to 8.

10. The 7xxx series aluminum alloy according to claim 9, characterized in that, The increase in tensile strength of the 7xxx series aluminum alloy after being parked for 270 days ≤ 5 MPa, and the intergranular corrosion depth ≤ 25 μm.

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