Heat treatment method of Al-Zn-Mg-Cu alloy

Abstract

The invention relates to a heat treatment method of an Al-Zn-Mg-Cu alloy, and relates to the technical field of aluminum alloys and aluminum alloy heat treatment. According to the main technical scheme, the heat treatment method of the Al-Zn-Mg-Cu alloy comprises the following steps that the Al-Zn-Mg-Cu alloy is subjected to solution treatment, and the Al-Zn-Mg-Cu alloy subjected to solution treatment is obtained; under an external stress field and a thermal field, stress aging treatment is conducted on the Al-Zn-Mg-Cu alloy subjected to solution treatment, and the Al-Zn-Mg-Cu alloy subjected to stress aging treatment is obtained; and the Al-Zn-Mg-Cu alloy subjected to stress aging treatment is subjected to artificial aging treatment, and the Al-Zn-Mg-Cu alloy subjected to heat treatment is obtained. According to the heat treatment technology disclosed by the invention, the synergistic improvement of the strong plasticity and the corrosion resistance of the Al-Zn-Mg-Cu alloy can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys and aluminum alloy heat treatment, and particularly to a heat treatment method for Al-Zn-Mg-Cu alloys. Background Art

[0002] With the continuous development of high-end equipment for national defense, aerospace, and transportation, there is an urgent need for lightweight and high-performance components. Due to their high mechanical properties, Al-Zn-Mg-Cu alloy components are increasingly widely used in the above fields. Especially for Al-Zn-Mg-Cu alloy materials with a high Zn content, their tensile strength has gradually increased to over 700 MPa. Increasing the Zn content to obtain ultra-high strength has become the mainstream development direction of this series of aluminum alloys. However, as the equipment is expanding towards diverse service environments, requirements for the corrosion resistance of components are put forward under conditions such as high humidity and warm temperature.

[0003] For Al-Zn-Mg-Cu alloys with a Zn content greater than 8 wt%, after T6 heat treatment of their components, a large number of fine and dispersed MgZn2 are precipitated inside the grains, effectively improving the tensile strength and yield strength of the matrix. However, a large amount of Zn elements will also lead to the formation of coarse and continuous intergranular phases and form a precipitate-free zone around the grain boundaries. This composite microstructure morphology composed of large-sized intergranular phases - precipitate-free zones - matrix shows large differences in electrochemical properties, resulting in poor corrosion resistance of the material. At the same time, the uneven grain boundary - intragranular microstructure affects the further improvement of the matrix strength and plasticity. Eventually, the effect of composition optimization is not fully reflected in the mechanical property values.

[0004] Therefore, how to optimize the heat treatment process and effectively control the precipitation phase characteristics inside and at the grain boundaries of high-Zn aluminum alloys is the key to achieving the simultaneous improvement of the strength, plasticity, and corrosion resistance of such components. In response to this problem, relevant researchers have proposed the T77 process of pre-aging - over-aging - re-aging. Among them, using the T77 process can achieve corrosion resistance optimization, but the effect of eliminating the precipitate-free zone by this process is poor, and the improvement effect of the matrix strength and plasticity is limited; at the same time, in mass production, it is difficult to accurately control parameters such as the heating rate and time from low-temperature pre-aging to high-temperature over-aging, and its popularization and application are limited.

[0005] In summary, there is an urgent need for a new heat treatment technology to achieve the simultaneous improvement of the strength, plasticity, and corrosion resistance of Al-Zn-Mg-Cu alloys. Summary of the Invention

[0006] In view of this, the present invention provides a heat treatment method for Al-Zn-Mg-Cu alloys, with the main purpose of improving the strength, plasticity, and corrosion resistance of Al-Zn-Mg-Cu alloys.

[0007] To achieve the above object, the present invention mainly provides the following technical solutions:

[0008] On the one hand, an embodiment of the present invention provides a heat treatment method for an Al-Zn-Mg-Cu alloy, which includes the following steps:

[0009] Solution treatment: Perform solution treatment on the Al-Zn-Mg-Cu alloy to obtain the solution-treated Al-Zn-Mg-Cu alloy;

[0010] Stress aging treatment: Under an external stress field and a thermal field, perform stress aging treatment on the solution-treated Al-Zn-Mg-Cu alloy to obtain the stress-aged Al-Zn-Mg-Cu alloy;

[0011] Artificial aging treatment: Perform artificial aging treatment on the stress-aged Al-Zn-Mg-Cu alloy to obtain the heat-treated Al-Zn-Mg-Cu alloy.

[0012] Preferably, in terms of weight percentage, the chemical composition of the Al-Zn-Mg-Cu alloy includes: Zn 9.5-10.5 wt%, Mg 2.5-3.5 wt%, Cu 1.5-2.5 wt%, Zr 0.05-0.15 wt%, Ti 0-0.01 wt%, and the balance is Al.

[0013] Preferably, the chemical composition of the Al-Zn-Mg-Cu alloy further includes the Fe element; wherein, the content of the Fe element is less than or equal to 0.01 wt%.

[0014] Preferably, the chemical composition of the Al-Zn-Mg-Cu alloy further includes the Si element; wherein, the content of the Si element is less than or equal to 0.01 wt%.

[0015] Preferably, the Al-Zn-Mg-Cu alloy is an Al-Zn-Mg-Cu alloy profile;

[0016] Preferably, before the solution treatment step, it further includes:

[0017] Preparation step of the Al-Zn-Mg-Cu alloy profile: Perform hot extrusion treatment on the Al-Zn-Mg-Cu alloy bar; wherein, the temperature of the extrusion treatment is 455-465 °C, the speed of the extrusion treatment is ≤10 m / min, and the extrusion ratio is 15-17.

[0018] Preferably, in the solution treatment step:

[0019] The Al-Zn-Mg-Cu alloy is solution-treated at a temperature of 465-475 °C for 3-4 h, and after cooling, the solution-treated Al-Zn-Mg-Cu alloy is obtained;

[0020] Preferably, the cooling method is selected as water quenching.

[0021] Preferably, in the step of stress aging treatment: the applied tensile stress value is 135-450 MPa, the stress aging treatment temperature is 100-130 °C, and the stress aging treatment time is 12-24 h.

[0022] Preferably, in the microstructure of the Al-Zn-Mg-Cu alloy after stress aging treatment:

[0023] The grain boundary precipitates show a discontinuous distribution, the size of the grain boundary precipitates is 20-35 nm, and the grain boundary precipitates include long rod-shaped MgZn2 phases; the size of the intragranular precipitates is 5-10 nm, and the intragranular precipitates include short rod-shaped MgZn2 phases; there is no precipitation-free zone at the grain boundary (that is, the two sides of the grain boundary are covered with precipitates).

[0024] Preferably, in the step of artificial aging treatment: the artificial aging treatment temperature is 140-160 °C, and the artificial aging treatment time is 5-10 h.

[0025] On the other hand, an embodiment of the present invention provides a heat-treated Al-Zn-Mg-Cu alloy, which is characterized in that the heat-treated Al-Zn-Mg-Cu alloy is obtained by heat-treating an Al-Zn-Mg-Cu alloy by using the heat treatment method of the Al-Zn-Mg-Cu alloy described in any one of the above.

[0026] Preferably, in the microstructure of the heat-treated Al-Zn-Mg-Cu alloy: the precipitates at the grain boundary show a discontinuous distribution, the size of the intergranular precipitates is 20-35 nm, the grain boundary precipitates include long rod-shaped MgZn2 phases, the size of the intragranular precipitates does not exceed 10 nm, and the intragranular precipitates include short rod-shaped MgZn2 phases; there is no precipitation-free zone at the grain boundary; a precipitate twin interface morphology is formed in the matrix.

[0027] Compared with the prior art, the heat treatment method of an Al-Zn-Mg-Cu alloy of the present invention has at least the following beneficial effects:

[0028] An embodiment of the present invention provides a heat treatment method for an Al-Zn-Mg-Cu alloy, comprising the following steps: performing solution treatment on the Al-Zn-Mg-Cu alloy to obtain the solution-treated Al-Zn-Mg-Cu alloy; performing stress aging treatment on the solution-treated Al-Zn-Mg-Cu alloy under an external stress field and a thermal field to obtain the stress-aged Al-Zn-Mg-Cu alloy; performing artificial aging treatment on the stress-aged Al-Zn-Mg-Cu alloy to obtain the heat-treated Al-Zn-Mg-Cu alloy. It should be noted regarding the above solution: In the stress aging treatment stage, the external stress field and the thermal field act together on the supersaturated solid solution. The lattice distortion introduced by the stress field increases the binding force of matrix vacancies, making the migration rate thereof slow down within the crystal and at the grain boundary. At the same time, the lattice distortion and dislocation defects increase the nucleation sites of solute atoms, reduce the precipitation ability barrier, promote the dispersion distribution of intragranular precipitation phases, and simultaneously inhibit the precipitation-free zone between grains. A large number of supersaturated solute atoms precipitate within the crystal, effectively controlling the size and quantity of the grain boundary precipitation phases, and ultimately realizing the coordinated regulation of intragranular and grain boundary precipitation phases. During the subsequent artificial aging treatment, the fine precipitation phases originally formed at the grain boundary further grow and spheroidize, effectively improving the corrosion resistance of the matrix. More importantly, when performing artificial aging treatment at a temperature higher than the stress aging temperature, the intragranular precipitation phases grow. Due to the phase orientation relationship characteristics of the precipitation phases, they intersect during the growth process, forming a twin morphology at the precipitation phase interface, effectively blocking dislocations during the plastic deformation process, and at the same time achieving the purpose of coordinating dislocation movement by means of its own deformation, ultimately realizing the improvement of the strength and plasticity of the matrix.

[0029] Compared with traditional processes such as T77, the heat treatment technology of the present invention further improves the strength and plasticity, and simultaneously optimizes the corrosion resistance. In addition, the process of the present invention is simple, the feasible range of process parameters is wide, and it is convenient for industrial production.

[0030] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly and implement it in accordance with the content of the specification, the following describes in detail with reference to the preferred embodiments of the present invention and the accompanying drawings. Description of the Drawings

[0031] Figure 1 is a transmission microstructure diagram of the heat-treated Al-Zn-Mg-Cu alloy; wherein, Figure 1 Figure (a) in is a transmission microstructure diagram of the Al-Zn-Mg-Cu alloy after T77 aging treatment in Comparative Example 1;

[0032] Figure 1 Figure (b) in is a transmission microstructure diagram of the Al-Zn-Mg-Cu alloy after completing stress aging treatment in Comparative Example 3; Figure 1Figure (c1) therein is the distribution morphology diagram of grain boundary precipitation phases of the heat-treated Al-Zn-Mg-Cu alloy in Example 5. Figure 1 Figure (c2) therein is the morphological characterization diagram of the precipitation phase interface twin microstructure of the heat-treated Al-Zn-Mg-Cu alloy in Example 5.

[0033] Figure 2 is the intergranular corrosion depth diagram of the heat-treated Al-Zn-Mg-Cu alloy; wherein, Figure 2 Figure (a) therein is the intergranular corrosion depth diagram of the heat-treated Al-Zn-Mg-Cu alloy in Example 5. Figure 2 Figure (b) therein is the intergranular corrosion depth diagram of the Al-Zn-Mg-Cu alloy after T77 aging treatment in Comparative Example 1. Specific Embodiments

[0034] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following combines the accompanying drawings and preferred embodiments to detail the specific embodiments, structures, features, and their effects of the application according to the present invention. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0035] The present invention provides a heat treatment method for an Al-Zn-Mg-Cu alloy. After solution treatment of the Al-Zn-Mg-Cu alloy profile, a supersaturated solid solution is obtained. First, stress aging treatment is carried out under an external stress field and a thermal field, and then artificial aging treatment is carried out. The principle of the present invention is explained as follows:

[0036] In the stress aging stage, the external stress field and the thermal field act together on the supersaturated solid solution. The lattice distortion introduced by the stress field increases the matrix vacancy binding force, making the migration rate of vacancies in the grains and grain boundaries slow down. At the same time, the lattice distortion and dislocation defects increase the nucleation sites of solute atoms, reduce the precipitation ability barrier, promote the dispersion distribution of intragranular precipitation phases, and simultaneously inhibit the precipitation-free zone between grains. A large number of supersaturated solute atoms precipitate in the grains, effectively controlling the size and quantity of grain boundary precipitation phases, and finally realizing the coordinated regulation of intragranular and grain boundary precipitation phases.

[0037] The inventors of the present invention found that the stress field couples with the thermal field, comprehensively solving the control of intragranular precipitate dispersion and precipitation-free zones at grain boundaries, which is of great benefit to improving the strength and plasticity of the material. At the same time, the stress-aged material is subjected to artificial aging treatment, and the fine precipitates originally formed at the grain boundaries further grow and spheroidize, effectively improving the corrosion resistance of the matrix. More importantly, when the artificial aging treatment is carried out at a temperature higher than the stress aging temperature, the intragranular precipitates grow. Due to the characteristics of the precipitate orientation relationship, they intersect during the growth process, and the orientation of the intersection plane is Taking this interface as the axis, the precipitates show a symmetric relationship on both sides, forming a twin interface. The key factors are as follows: During the stress aging process, due to the introduction of lattice defects, the precipitation energy barrier of the η' phase is reduced, the precipitation rate is increased, and at the same time, the lattice defects provide more nucleation sites for the precipitates, increasing the precipitate density. Under the combined action, the docking probability of the precipitates is promoted, thereby changing the precipitate morphology and promoting the formation of the twin microstructure at the precipitate interface. Further research found that during the room-temperature tensile process, the twin structure at the precipitate interface increased from 109.5° to 112.7° (the force axis is parallel to the twin interface) and 121.5° (the force axis is perpendicular to the twin interface) respectively. Compared with the conventional η' / η phase with the dislocation bypass mechanism as the main deformation mode, the change in the structure of the precipitate twin interface itself improves its ability to constrain and trap dislocations. Therefore, this precipitate interface twin microstructure can effectively trap dislocations during the plastic deformation process, and at the same time, by means of its own deformation, achieve the purpose of coordinating dislocation movement, and ultimately achieve the improvement of the strength and plasticity of the matrix.

[0038] The specific solution of the present invention is as follows:

[0039] The embodiment of the present invention provides a heat treatment method for an Al-Zn-Mg-Cu alloy, which includes the following steps:

[0040] Solution treatment: The Al-Zn-Mg-Cu alloy (i.e., the Al-Zn-Mg-Cu alloy profile) is subjected to solution treatment to obtain the solution-treated Al-Zn-Mg-Cu alloy.

[0041] Among them, in terms of weight percentage, the chemical composition of the Al-Zn-Mg-Cu alloy includes: Zn 9.5-10.5 wt%, Mg 2.5-3.5 wt%, Cu 1.5-2.5 wt%, Zr 0.05-0.15 wt%, Ti 0-0.01 wt%, and the balance is Al.

[0042] Preferably, the chemical composition of the Al-Zn-Mg-Cu alloy further includes the Fe element; among them, the content of the Fe element is less than or equal to 0.01 wt%. Preferably, the chemical composition of the Al-Zn-Mg-Cu alloy further includes the Si element; among them, the content of the Si element is less than or equal to 0.01 wt%.

[0043] Preferably, the Al-Zn-Mg-Cu alloy is solution-treated at a temperature of 465-475°C for 3-4 h, and after cooling, the solution-treated Al-Zn-Mg-Cu alloy is obtained; preferably, the cooling method is water quenching.

[0044] In addition, it should be noted that the preparation steps of the Al-Zn-Mg-Cu alloy profile include: hot extrusion of the Al-Zn-Mg-Cu alloy bar; wherein, the extrusion temperature is 455-465°C, the extrusion speed ≤ 10 m / min, and the extrusion ratio is 15-17.

[0045] Stress aging treatment: Under an external stress field and a thermal field, the solution-treated Al-Zn-Mg-Cu alloy is subjected to stress aging treatment to obtain the stress-aged Al-Zn-Mg-Cu alloy.

[0046] In this step, the externally applied tensile stress value is 135-450 MPa, the stress aging treatment temperature is 100-130°C, and the stress aging treatment time is 12-24 h.

[0047] Artificial aging treatment: The stress-aged Al-Zn-Mg-Cu alloy is subjected to artificial aging treatment to obtain the heat-treated Al-Zn-Mg-Cu alloy.

[0048] In this step, the artificial aging treatment temperature is 140-160°C, and the artificial aging treatment time is 5-10 h.

[0049] The present invention will be further described below through specific examples:

[0050] Comparative Example 1

[0051] Comparative Example 1 heat-treats the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile, which mainly includes the following steps:

[0052] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile is solution-treated at a temperature of 470°C for 3 h, and then water quenched to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0053] T77 aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile is subjected to T77 aging treatment to obtain the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0054] Among them, the process parameters of T77 aging treatment are: 120°C / 24h + 180°C / 1h + 120°C / 24h. After completing the above aging process, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles were tested, and the results are shown in Table 1.

[0055] Example 1

[0056] In this example, the heat treatment of Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles mainly includes the following steps:

[0057] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles were solution-treated at a temperature of 470°C for 3h and then quenched in cold water to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles;

[0058] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles were stress-aged at an applied tensile stress value of 135 MPa and a temperature of 120°C for 24h to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles;

[0059] Artificial aging treatment: The stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles were artificially aged at a temperature of 150°C for 7h to obtain the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles.

[0060] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles in this example were tested, and the results are shown in Table 1.

[0061] Example 2

[0062] In this example, the heat treatment of Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles mainly includes the following steps:

[0063] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles were solution-treated at a temperature of 470°C for 3h and then quenched in cold water to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles;

[0064] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles were subjected to stress aging treatment at an applied tensile stress value of 270 MPa and a temperature of 120 °C for 24 h to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles.

[0065] Artificial aging treatment: The stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles were subjected to artificial aging treatment at 150 °C for 7 h to obtain the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles.

[0066] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles of this example were tested, and the results are shown in Table 1.

[0067] Example 3

[0068] In this example, the heat treatment of the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles mainly includes the following steps:

[0069] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles were solution-treated at a temperature of 470 °C for 3 h and then quenched in cold water to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles.

[0070] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles were subjected to stress aging treatment at an applied tensile stress value of 450 MPa and a temperature of 120 °C for 24 h to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles.

[0071] Artificial aging treatment: The stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles were subjected to artificial aging treatment at 150 °C for 7 h to obtain the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles.

[0072] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles of this example were tested, and the results are shown in Table 1.

[0073] Comparative Example 2

[0074] Comparative Example 2 Heat treatment was carried out on an Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile, mainly including the following steps:

[0075] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was solution-treated at a temperature of 470°C for 3 h and then water quenched to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0076] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was stress-aged at an applied tensile stress value of 135 MPa and a temperature of 120°C for 24 h to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0077] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile of Comparative Example 2 were tested, and the results are shown in Table 1.

[0078] Example 4

[0079] In this example, heat treatment was carried out on an Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile, mainly including the following steps:

[0080] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was solution-treated at a temperature of 470°C for 3 h and then water quenched to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0081] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was stress-aged at an applied tensile stress value of 135 MPa and a temperature of 120°C for 24 h to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0082] Artificial aging treatment: The stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was artificially aged at 160°C for 10 h to obtain the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0083] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile of this embodiment were tested, and the results are shown in Table 1.

[0084] Comparative Example 3

[0085] Comparative Example 3 carried out heat treatment on the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile, which mainly included the following steps:

[0086] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was solution-treated at a temperature of 470 °C for 3 h, and then water quenched to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0087] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was stress-aged at an applied tensile stress value of 270 MPa and a temperature of 120 °C for 24 h to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0088] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile of Comparative Example 3 were tested, and the results are shown in Table 1.

[0089] Example 5

[0090] This example carried out heat treatment on the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile, which mainly included the following steps:

[0091] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was solution-treated at a temperature of 470 °C for 3 h, and then water quenched to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0092] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was stress-aged at an applied tensile stress value of 270 MPa and a temperature of 120 °C for 24 h to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0093] Artificial aging treatment: The stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles are subjected to artificial aging treatment at 160 °C for 10 h to obtain the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles.

[0094] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles of this example are tested, and the results are shown in Table 1.

[0095] Comparative Example 4

[0096] Comparative Example 4 performs heat treatment on the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles, which mainly includes the following steps:

[0097] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles are solution-treated at a temperature of 470 °C for 3 h and then quenched in cold water to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles;

[0098] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles are stress-aged at an applied tensile stress value of 450 MPa and a temperature of 120 °C for 24 h to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles.

[0099] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles of Comparative Example 4 are tested, and the results are shown in Table 1.

[0100] Example 6

[0101] This example performs heat treatment on the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles, which mainly includes the following steps:

[0102] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles are solution-treated at a temperature of 470 °C for 3 h and then quenched in cold water to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profiles;

[0103] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile is subjected to stress aging treatment for 24 h under an applied tensile stress value of 450 MPa and at 120 °C to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0104] Artificial aging treatment: The stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile is subjected to artificial aging treatment for 10 h at 140 °C to obtain the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0105] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile of this example are tested, and the results are shown in Table 1.

[0106] Example 7

[0107] In this example, the heat treatment of the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile mainly includes the following steps:

[0108] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile is solution-treated at 470 °C for 3 h and then quenched in cold water to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0109] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile is subjected to stress aging treatment for 24 h under an applied tensile stress value of 450 MPa and at 100 °C to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0110] Artificial aging treatment: The stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile is subjected to artificial aging treatment for 10 h at 140 °C to obtain the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0111] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile of this example are tested, and the results are shown in Table 1.

[0112] Example 8

[0113] In this example, heat treatment is performed on an Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile. The difference from Example 6 is that the stress aging treatment time is 12 h.

[0114] Others are the same as in Example 6.

[0115] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile in this example are tested, and the results are shown in Table 1.

[0116] Comparative Example 5

[0117] Comparative Example 5 performs heat treatment on an Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile, which mainly includes the following steps:

[0118] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile is solution-treated at a temperature of 470 °C for 3 h and then quenched in cold water to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0119] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile is stress-aged at an applied tensile stress value of 85 MPa and a temperature of 90 °C for 24 h to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0120] Artificial aging treatment: The stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile is artificially aged at 150 °C for 7 h to obtain the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0121] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile in this comparative example are tested, and the results are shown in Table 1.

[0122] Comparative Example 6

[0123] Comparative Example 6 performs heat treatment on an Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile, which mainly includes the following steps:

[0124] Solution treatment: The Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was solution-treated at 470 °C for 3 h and then water-quenched to obtain the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0125] Stress aging treatment: The solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was stress-aged at an applied tensile stress value of 135 MPa and a temperature of 120 °C for 24 h to obtain the stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile;

[0126] Artificial aging treatment: The stress-aged Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile was artificially aged at 120 °C for 12 h to obtain the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile.

[0127] Among them, the tensile strength, yield strength, elongation, and intergranular corrosion of the heat-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy profile of this comparative example were tested, and the results are shown in Table 1.

[0128] Table 1

[0129]

[0130] It can be seen from Table 1 that: compared with the comparative example, the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy prepared in the embodiment of the present invention has excellent strength, plasticity, and corrosion resistance.

[0131] Figure 1 It is the transmission microstructure diagram of the heat-treated Al-Zn-Mg-Cu alloy; among them, Figure 1 Figure (a) in

[0132] Figure 1 is the transmission microstructure diagram of the Al-Zn-Mg-Cu alloy after T77 aging treatment in Comparative Example 1; Figure 1 Figure (b) in Figure 1 is the transmission microstructure diagram of the Al-Zn-Mg-Cu alloy after stress aging treatment in Comparative Example 3;

[0133] Among them, from Figure 1As can be seen from Figure (a) in [reference], in Comparative Example 1, after the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy was subjected to T77 treatment, the intergranular precipitates of the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy showed a discontinuous distribution, with a size of approximately 70 - 90 nm. The precipitate-free zone between grains was relatively wide, about 145 nm, and the intragranular precipitate size was about 15 - 25 nm. The precipitate-free zone, as a soft region, is prone to form stress concentration areas during uniaxial tension, leading to premature fracture of the material and restricting the further improvement of strength and plasticity. At the same time, the electrochemical properties of this region are different from those of the matrix and grain boundaries, and the improvement effect of its intergranular corrosion resistance is limited.

[0134] Among them, from Figure 1 As can be seen from Figure (b) in [reference], in Comparative Example 3, after the solution-treated Al-10Zn-3Mg-2.5Cu-0.15Zr alloy in Comparative Example 3 was subjected to stress aging treatment at 270 MPa - 120 °C / 24 h, the intergranular precipitates of the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy showed a discontinuous distribution, with a size of approximately 20 - 35 nm. There was no precipitate-free zone between grains, and the intragranular precipitate size was about 5 - 10 nm. This microstructure is beneficial to the coordinated improvement of matrix strength and corrosion resistance. However, based on the strength-plasticity constraint relationship, the matrix plasticity is relatively low.

[0135] Among them, from Figure 1 As can be seen from Figures (c1) and (c2) in [reference], after stress aging treatment at 270 MPa - 120 °C / 24 h and then completing artificial aging treatment at 160 °C / 10 h, the intergranular precipitates of the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy showed a discontinuous distribution, with a size of approximately 5 - 25 nm. There was no precipitate-free zone between grains, and the intragranular precipitate size did not exceed 10 nm. At the same time, a precipitate-twin interface microstructure was formed in the matrix. This new microstructure has a good dislocation storage effect during uniaxial tension and has a significant effect on improving the matrix plasticity.

[0136] Intergranular corrosion tests were carried out on the alloys after heat treatment in Example 5 and Comparative Example 1; among them, Figure 2 is the intergranular corrosion depth map of the heat-treated Al-Zn-Mg-Cu alloy; among them, Figure 2 Figure (a) in [reference] is the intergranular corrosion depth map of the heat-treated Al-Zn-Mg-Cu alloy in Example 5; Figure 2 Figure (b) in [reference] is the intergranular corrosion depth map of the Al-Zn-Mg-Cu alloy after T77 aging treatment in Comparative Example 1.

[0137] From Figure 2It can be seen from [reference] that for the Al-10Zn-3Mg-2.5Cu-0.15Zr alloy after solution treatment, after stress aging treatment at 270 MPa - 120 °C / 24 h, and then continuing with artificial aging at 160 °C / 10 h, the intergranular corrosion depth (as shown in Figure (a) of [reference 2]) is shallower and the intergranular corrosion width is smaller than that after T77 treatment (as shown in Figure (b) of [reference Figure 1 ). This indicates that by eliminating the precipitate-free zone at the grain boundaries, the precipitation difference between the grain interior and the grain boundaries is effectively reduced, the formation and expansion of the anodic corrosion channels are inhibited, and the corrosion resistance of the alloy is improved.

[0138] In addition, it can be seen from the comparison between the examples and Comparative Example 5 and Comparative Example 6 that the control of the parameters (applied tensile stress value, temperature) of stress aging and artificial aging is very important, otherwise it is difficult to achieve the synergistic improvement of strength and plasticity.

[0139] In summary, compared with the traditional regression re-aging (pre-aging - over-aging - re-aging), both the strength and plasticity of the alloy treated by the process of the present invention are improved, and at the same time, the corrosion resistance is also significantly improved. During the aging process of the present invention, a stress field is synchronously added, introducing lattice distortion and dislocation defects inside the grains, promoting the dispersion precipitation of the MgZn2 phase inside the grains. At the same time, the lattice distortion strengthens the binding force on the vacancies in the matrix, slows down the migration of solute atoms to the grain boundaries, and thus effectively inhibits the formation of the precipitate-free zone at the grain boundaries. The intergranular precipitate phases obtained are fine and discontinuous, enabling the simultaneous improvement of the strength, plasticity and corrosion resistance of the alloy. In addition, the process of the present invention has simple technological processes and a wide parameter range, which is convenient for industrial production.

[0140] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A heat treatment method for an Al-Zn-Mg-Cu alloy, characterized in that, It includes the following steps: Solution treatment: Perform solution treatment on the Al-Zn-Mg-Cu alloy to obtain the solution-treated Al-Zn-Mg-Cu alloy; Stress aging treatment: Under an external stress field and thermal field, perform stress aging treatment on the solution-treated Al-Zn-Mg-Cu alloy to obtain the stress-aged Al-Zn-Mg-Cu alloy; Artificial aging treatment: Perform artificial aging treatment on the stress-aged Al-Zn-Mg-Cu alloy to obtain the heat-treated Al-Zn-Mg-Cu alloy.

2. The heat treatment method of the Al-Zn-Mg-Cu alloy according to claim 1, characterized in that, In terms of weight percentage, the chemical composition of the Al-Zn-Mg-Cu alloy includes: Zn 9.5 - 10.5wt%, Mg 2.5 - 3.5wt%, Cu 1.5 - 2.5wt%, Zr 0.05 - 0.15wt%, Ti 0 - 0.01wt%, and the balance is Al.

3. The heat treatment method of the Al-Zn-Mg-Cu alloy according to claim 2, characterized in that, The chemical composition of the Al-Zn-Mg-Cu alloy further includes the Fe element; wherein, the content of the Fe element is less than or equal to 0.01wt%; and / or The chemical composition of the Al-Zn-Mg-Cu alloy further includes the Si element; wherein, the content of the Si element is less than or equal to 0.01wt%.

4. The heat treatment method of the Al-Zn-Mg-Cu alloy according to any one of claims 1-3, characterized in that, The Al-Zn-Mg-Cu alloy is an Al-Zn-Mg-Cu alloy profile; Preferably, before the solution treatment step, it further includes: Preparation step of the Al-Zn-Mg-Cu alloy profile: Perform hot extrusion treatment on the Al-Zn-Mg-Cu alloy bar; wherein, the temperature of the extrusion treatment is 455 - 465°C, the speed of the extrusion treatment is ≤10m / min, and the extrusion ratio is 15 - 17.

5. The heat treatment method of the Al-Zn-Mg-Cu alloy according to any one of claims 1-4, characterized in that, In the solution treatment step: Heat the Al-Zn-Mg-Cu alloy at a temperature of 465 - 475°C for 3 - 4h for solution treatment, and after cooling, obtain the solution-treated Al-Zn-Mg-Cu alloy; Preferably, the cooling method uses water quenching.

6. The heat treatment method of the Al-Zn-Mg-Cu alloy according to any one of claims 1-5, characterized in that, In the stress aging treatment step: The externally applied tensile stress value is 135 - 450MPa, the temperature of the stress aging treatment is 100 - 130°C, and the time of the stress aging treatment is 12 - 24h.

7. The heat treatment method of the Al-Zn-Mg-Cu alloy according to any one of claims 1-6, characterized in that, In the microstructure of the stress-aged Al-Zn-Mg-Cu alloy: The grain boundary precipitation phases show discontinuous distribution, the size of the grain boundary precipitation phases is 20 - 35nm, and the grain boundary precipitation phases include rod-shaped MgZn2 phases; the size of the intragranular precipitation phases is 5 - 10nm, and the intragranular precipitation phases include short rod-shaped MgZn2 phases; there is no precipitate-free zone at the grain boundaries.

8. The heat treatment method of the Al-Zn-Mg-Cu alloy according to claim 1, characterized in that, In the artificial aging treatment step: The temperature of the artificial aging treatment is 140 - 160°C, and the time of the artificial aging treatment is 5 - 10h.

9. A heat-treated Al-Zn-Mg-Cu alloy, characterized in that, The heat-treated Al-Zn-Mg-Cu alloy is obtained by heat-treating the Al-Zn-Mg-Cu alloy using the heat treatment method of the Al-Zn-Mg-Cu alloy according to any one of claims 1 - 8.

10. The heat-treated Al-Zn-Mg-Cu alloy according to claim 9, characterized in that, In the microstructure of the heat-treated Al-Zn-Mg-Cu alloy: The precipitates at the grain boundaries show a discontinuous distribution. The size of the intergranular precipitates is 20 - 35 nm. The grain boundary precipitates include rod-shaped MgZn2 phases. The size of the intragranular precipitates does not exceed 10 nm. The intragranular precipitates include short rod-shaped MgZn2 phases. There is no precipitation-free zone between grains. A precipitate twin interface morphology is formed in the matrix.

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