A 7 series aluminum alloy plate and preparation method thereof

Abstract

The present invention provides a preparation method of a 7 series aluminum alloy plate, which relates to the technical field of aluminum alloys, and comprises the following steps: step 1) homogenizing heat treatment of the 7 series aluminum alloy ingot, preheating after cooling, and then performing multiple rolling processes to obtain a rolled plate; wherein the preheating temperature is higher than the recrystallization temperature of the 7 series aluminum alloy ingot and lower than the solution temperature of the 7 series aluminum alloy ingot; the pressing amount of each rolling process is 30%-40%; step 2) solution treatment of the rolled plate, and then double-stage aging treatment to obtain a 7 series aluminum alloy plate. By adopting a large reduction rolling process in the temperature range above recrystallization, the plane rheology of the rolling process is induced to change to a three-dimensional shear rheology, the plane rheology ratio along the rolling direction is reduced, the transverse plasticity of the plate is improved, and the anisotropy of the plate is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloys, and in particular relates to a 7 series aluminum alloy plate and a preparation method thereof. Background Art

[0002] 7 series aluminum alloy (Al-Zn-Mg-Cu alloy) has the characteristics of low density, high strength and good toughness, and is widely used in aerospace, national defense, military industry, transportation and other fields. The 7 series aluminum alloy sheet prepared by rolling processing will have obvious directional flow along the rolling direction during deformation, which will cause the anisotropy of the sheet. The plasticity and strength level perpendicular to the rolling direction (transverse direction) are usually lower than those along the rolling direction.

[0003] Existing technology has proposed a preparation method for reducing the anisotropy of aluminum alloy plates, which uses multiple cross-rolling passes, that is, the rolling direction of each pass is rotated 70 to 90 degrees around the normal direction of the rolling surface with respect to the previous pass, which can reduce the texture density in the plate. Although this reduces the anisotropy of the plate, the texture strengthening effect is reduced, which is not conducive to the improvement of the final plate strength. There is also a method for improving the anisotropy of Al-Zn-Mg-Cu alloy plates. The rolled plate is subjected to a long-term annealing treatment to induce sufficient recrystallization of the plate, which can reduce the anisotropy of the plate. However, during the long-term annealing process, obvious grain growth occurs, and the size of individual grains reaches hundreds of microns, which greatly reduces the plastic toughness of the material, and the elongation of the material is generally reduced to below 10%.

[0004] In view of this, it is necessary to provide a method for preparing a 7 series aluminum alloy sheet, which can improve the anisotropy of the 7 series aluminum alloy sheet while enhancing its strength and plasticity. Summary of the invention

[0005] Therefore, the present invention provides a 7 series aluminum alloy plate and a preparation method thereof, the purpose of which is to improve the anisotropy of the 7 series aluminum alloy plate while enhancing its strength and plasticity.

[0006] In order to solve the above problems, the present invention provides a method for preparing a 7 series aluminum alloy plate, comprising the following steps:

[0007] Step 1) homogenizing heat treatment of the 7 series aluminum alloy ingot, preheating after cooling, and then performing multiple rolling processes to obtain a rolled plate;

[0008] The preheating temperature is higher than the recrystallization temperature of the 7 series aluminum alloy ingot and lower than the solution temperature of the 7 series aluminum alloy ingot; the pressing amount of each rolling process is 30%-40%;

[0009] Step 2) The rolled plate is subjected to a solution treatment and then subjected to a double-stage aging treatment to obtain a 7 series aluminum alloy plate.

[0010] Furthermore, in the step 1), the temperature of the homogenization heat treatment is 400-468° C.; and / or

[0011] The holding time of homogenous heat treatment is 10-24h.

[0012] Furthermore, in the step 1), the cooling method is air cooling, and the air cooling time is 3-6 hours.

[0013] Furthermore, in step 1), the preheating temperature is 410-440° C.; and / or

[0014] The preheating time is 1-5h.

[0015] Furthermore, in the step 1), the total pressing amount of the multiple rolling processes is 60%-90%; and / or

[0016] The rolling speed is 1.4-1.6m / s.

[0017] Furthermore, in the step 1), the starting rolling temperature of the multi-pass rolling process is 400°C-430°C, and the final rolling temperature is 380°C-410°C.

[0018] Furthermore, in step 2), the temperature of the solution treatment is 460-490° C.; and / or

[0019] The solution treatment time is 1-5h.

[0020] Furthermore, in the step 2), the two-stage aging treatment includes low-temperature pre-aging and high-temperature aging;

[0021] Among them, the temperature of low temperature pre-aging is 60-80℃, and the time is 24-72h;

[0022] The temperature of high temperature aging is 110-165℃ and the time is 6-24h.

[0023] On the other hand, the present invention further provides a 7 series aluminum alloy plate, wherein the texture of the 7 series aluminum alloy plate comprises (110) and (111) textures, and the maximum pole density values ​​of the two textures differ by no more than 5%; the microstructure of the 7 series aluminum alloy plate comprises an intragranular precipitation phase and a needle-shaped grain boundary precipitation phase;

[0024] The size of the intracrystalline precipitated phase is 5-10 nm, and the narrow side size of the needle-shaped grain boundary precipitated phase is 10-20 nm.

[0025] Furthermore, the 7 series aluminum alloy sheet is obtained by any of the preparation methods described above.

[0026] The preparation method of a 7 series aluminum alloy plate provided by the present invention has the following beneficial effects:

[0027] 1. The present invention preheats the alloy ingot and then performs rolling processing, that is, rolling deformation is performed above the recrystallization temperature, which induces a more sufficient dynamic recrystallization inside the material, can reduce the dislocation density, and prevent deformation damage caused by dislocation accumulation, thereby effectively reducing the risk of defect initiation. Compared with rolling deformation below the recrystallization temperature, the rolling reduction of each pass is allowed to increase without causing rolling defects, thereby improving the production efficiency of aluminum alloy plates; through step-by-step rolling deformation with a large reduction, the longitudinal and transverse shear rheology of the plate can be increased, inducing more deformation textures that are conducive to the activation of the transverse slip system of the plate, improving the transverse plasticity of the plate, and improving the anisotropy of the plate.

[0028] 2. The residual dislocation content in the crystal is high due to large reduction deformation. Conventional aging treatment will cause heterogeneous nucleation at the dislocation and rapid growth, thereby reducing the strength. The present invention adopts double-stage aging, in which the first-stage aging (low-temperature pre-aging) has a low temperature, which will promote the uniform distribution of atomic clusters, and then the secondary aging treatment (high-temperature aging) at a higher temperature will cause the precipitated phase to grow with the atomic cluster as the core, which can reduce the adverse effects of heterogeneous nucleation at the dislocation, which is beneficial to improving the strength.

[0029] 3. Furthermore, the 7 series aluminum alloy sheet prepared by the method of the present application can reduce the plane rheological ratio due to the strong three-dimensional shear deformation, and the texture formed is equivalent to the maximum pole density of the (110) and (111) pole figures. Compared with the texture type dominated by the (110) pole figure shown by conventional rolling, the plane directional rheological trend is weakened, which is conducive to improving anisotropy. At the same time, the double-stage aging treatment adopted can make the precipitation phases in the grain and the grain boundary small and dense. The precipitation phases at the grain boundary mostly exist in the form of needles, and their narrow side size is about 10nm. Compared with the conventional single-pole aging treatment, the precipitation phase size is smaller and the distribution is more dense, which is conducive to improving strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0031] Figure 1 This is the positive electrode diagram measured along the normal direction of the plate in Example 1;

[0032] Figure 2 The morphology of the precipitated phase of Example 1: (a) is a low-magnification image, and (b) is a high-magnification image;

[0033] Figure 3 This is the positive electrode diagram measured along the normal direction of the plate in Comparative Example 1;

[0034] Figure 4 The morphology of the precipitated phase of Comparative Example 2: (a) is a low-magnification image, and (b) is a high-magnification image. DETAILED DESCRIPTION

[0035] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0036] The present invention adopts large reduction rolling processing in the temperature range above recrystallization, inducing the plane rheology of the rolling process to transform into three-dimensional shear rheology, reducing the plane rheology ratio along the rolling direction. Then, in the subsequent heat treatment process, a two-stage aging treatment of low temperature first and high temperature is adopted. The low temperature pre-aging can promote homogeneous nucleation in the crystal, and combined with the subsequent high temperature aging, a high-density fine precipitate phase can be formed in the crystal, which reduces the probability of heterogeneous nucleation of the precipitate phase, and can effectively improve the short board of insufficient transverse strength of the plate.

[0037] The specific plan is as follows:

[0038] The present invention provides a method for preparing a 7 series aluminum alloy plate, comprising the following steps:

[0039] Step 1) homogenizing heat treatment of the 7 series aluminum alloy ingot, preheating after cooling, and then performing multiple rolling processes to obtain a rolled plate;

[0040] The preheating temperature is higher than the recrystallization temperature of the 7 series aluminum alloy ingot (about 400°C) and lower than the solution temperature of the 7 series aluminum alloy ingot (about 470°C); the pressing amount of each rolling process is 30%-40%;

[0041] Step 2) The rolled plate is subjected to a solution treatment and then subjected to a double-stage aging treatment to obtain a 7 series aluminum alloy plate.

[0042] Based on the above method, the elements of the ingot are made more uniform through homogenization heat treatment, and then the ingot is preheated to above the recrystallization temperature before rolling deformation. The preheating induces a more sufficient dynamic recrystallization inside the material, which can reduce the dislocation density and prevent deformation damage caused by dislocation accumulation, thereby effectively reducing the risk of defect initiation. Compared with rolling deformation below the recrystallization temperature, the rolling reduction of each pass is allowed to increase without causing rolling defects; and multiple passes of step-by-step large reduction rolling deformation can increase the longitudinal and transverse shear rheology of the plate, induce more deformation textures that are conducive to the activation of the transverse slip system of the plate, enhance the transverse plasticity of the plate, and improve the anisotropy of the plate.

[0043] The crystallographic orientation after plane rheology is relatively simple, and its texture type is dominated by directional rolling texture, which will result in different properties along the rolling direction and perpendicular to the rolling direction, and the elongation perpendicular to the rolling direction will be much lower than that along the rolling direction. After reducing the directional flow ratio (i.e. increasing the longitudinal and transverse shear rheology of the plate), the crystallographic orientation of the material in the plate becomes diverse, and the shear texture ratio increases, which will increase the plasticity perpendicular to the rolling direction.

[0044] In some embodiments, in step 1), the temperature of the homogenization heat treatment is 400-468° C.; and / or

[0045] The holding time of homogenous heat treatment is 10-24h.

[0046] In some embodiments, in step 1), the cooling method is air cooling, and the air cooling time is 3-6 hours.

[0047] In some embodiments, in step 1), the preheating temperature is 410-440° C.; and / or

[0048] The preheating time is 1-5h.

[0049] In some embodiments, in step 1), the total pressing amount of the multiple rolling processes is 60%-90%; and / or

[0050] The rolling speed is 1.4-1.6m / s. The plate needs to be reheated to the rolling temperature between two adjacent rolling passes and kept warm for 30-120min. Since a large number of dislocations will be generated during the rolling process, the greater the deformation, the higher the dislocation density. High-density dislocation entanglement will aggravate the deformation damage such as cracks in the material. It is necessary to keep warm in the middle to eliminate the dislocation density by heat to prevent the dislocation density accumulated in a single pass from being too high.

[0051] In some embodiments, in step 1), the starting rolling temperature of the multi-pass rolling process is 400°C-430°C, and the final rolling temperature is 380°C-410°C.

[0052] In some embodiments, in step 2), the temperature of the solution treatment is 460-490° C.; and / or

[0053] The solution treatment time is 1-5h.

[0054] In some embodiments, in step 2), the double-stage aging treatment includes low-temperature pre-aging and high-temperature aging;

[0055] Among them, the temperature of low temperature pre-aging is 60-80℃, and the time is 24-72h;

[0056] The temperature of high temperature aging is 110-165℃, and the time is 6-24h. The aging process of low temperature first and high temperature later is adopted. Through low temperature pre-aging, the homogeneous nucleation of precipitation phase is induced, which can effectively improve the phenomenon of dislocation and grain boundary segregation of solid solution atoms. The precipitation phase of the material prepared by step-by-step large reduction rolling combined with double-stage aging is evenly and densely distributed, and the strength and plasticity of the material are improved synchronously compared with the ordinary 7 series aluminum alloy plate.

[0057] On the other hand, the present invention further provides a 7 series aluminum alloy plate, wherein the texture of the plate comprises (110) and (111) textures, and the maximum pole density values ​​of the two textures differ by no more than 5%; the microstructure of the 7 series aluminum alloy plate comprises an intragranular precipitation phase and a needle-shaped grain boundary precipitation phase;

[0058] The size of the intracrystalline precipitated phase is 5-10 nm, and the narrow side size of the needle-shaped grain boundary precipitated phase is 10-20 nm.

[0059] Furthermore, the above-mentioned 7 series aluminum alloy sheet is obtained by using any of the above-mentioned preparation methods.

[0060] The present invention is further described below in conjunction with specific embodiments.

[0061] Example 1

[0062] This embodiment provides a method for preparing a 7 series aluminum alloy plate, comprising the following steps:

[0063] Step 1) subjecting a 20 mm thick 7050 aluminum alloy ingot to homogenization heat treatment in a homogenization furnace, the homogenization heat treatment temperature is 450° C., and the time is 12 h; immediately after the homogenization heat treatment, the ingot is transferred to a cooling chamber for air cooling for 6 h; the cooled aluminum alloy ingot is preheated, the preheating temperature is 420° C., and the preheating time is 2 h; the preheated ingot is rolled, the starting rolling temperature is 410° C., the final rolling temperature is 400° C., 3 passes are adopted, the pressing amount of each pass is 6 mm, 5 mm, and 3 mm, the total deformation is 70%, and the rolling speed is (1.5±0.1) m / s, to obtain a rolled plate, the thickness of the rolled plate is 6 mm;

[0064] Step 2) The hot rolled plate is subjected to a solution treatment in a heat treatment furnace, the solution treatment temperature is 480°C, the solution treatment time is 1 hour, and then a water quenching treatment is performed. The plate after the solution treatment is removed from the solution furnace in less than 15 seconds, and the plate is removed after being water cooled to room temperature; then the plate after the solution treatment is subjected to a double-stage artificial aging, the aging process is first kept at 70°C for 24 hours, and then kept at 115°C for 12 hours, to obtain a high-strength and ductile 7 series aluminum alloy plate.

[0065] See also Figure 1 The texture formed by the 7 series aluminum alloy plate prepared in this embodiment has the same maximum pole density at the (110) and (111) pole figures, which are 4.61 and 4.70 respectively. The plane directional rheological trend is reduced under the action of shear deformation, which is beneficial to improve the anisotropy of the material; see Figure 2 The intragranular precipitation phase of the material is very dense, and the grain boundary precipitation phase is only slightly coarsened compared with the intragranular precipitation phase. Performance tests show that its yield strength along the rolling direction is 545MPa, the elongation is 15%, and the transverse yield strength is 522MPa, and the elongation is 14%.

[0066] Example 2

[0067] This embodiment provides a method for preparing a 7 series aluminum alloy plate, comprising the following steps:

[0068] Step 1) subjecting a 30 mm thick 7075 aluminum alloy ingot to homogenization heat treatment in a homogenization furnace, the homogenization heat treatment temperature is 420° C., and the time is 12 h; immediately after the homogenization heat treatment, the ingot is transferred to a cooling chamber for air cooling for 6 h; the cooled aluminum alloy ingot is preheated, the preheating temperature is 420° C., and the preheating time is 2 h; the preheated ingot is rolled, the starting rolling temperature is 410° C., the final rolling temperature is 400° C., 3 rolling passes are adopted, the pressing amount of each pass is 9 mm, 7.5 mm, and 4.5 mm, respectively, the total deformation is 70%, and the rolling speed is (1.5±0.1) m / s, to obtain a rolled plate, the thickness of the rolled plate is 9 mm;

[0069] Step 2) The hot rolled rolled plate is solution treated in a heat treatment furnace at a temperature of 470°C for 1.5 hours, followed by water quenching. The plate after solution treatment is removed from the solution furnace for less than 15 seconds, and the plate is removed after being water cooled to room temperature. The plate after solution treatment is then subjected to double-stage artificial aging, and the aging process is first kept at 70°C for 24 hours and then kept at 115°C for 12 hours to obtain a high-strength and ductile 7 series aluminum alloy plate.

[0070] The 7 series aluminum alloy plate prepared in this embodiment has a yield strength of 538 MPa and an elongation of 17% along the rolling direction, and a transverse yield strength of 516 MPa and an elongation of 15%.

[0071] Example 3

[0072] This embodiment provides a method for preparing a 7 series aluminum alloy plate, comprising the following steps:

[0073] Step 1) subjecting a 40 mm thick 7065 aluminum alloy ingot to homogenization heat treatment in a homogenization furnace, the homogenization heat treatment temperature is 420° C., and the time is 12 h; immediately after the homogenization heat treatment, the ingot is transferred to a cooling chamber for air cooling for 6 h; the cooled aluminum alloy ingot is preheated, the preheating temperature is 420° C., and the preheating time is 2 h; the preheated ingot is rolled, the starting rolling temperature is 410° C., the final rolling temperature is 400° C., 3 rolling passes are adopted, the pressing amount of each pass is 12 mm, 10 mm, and 6 mm, respectively, the total deformation is 70%, and the rolling speed is (1.5±0.1) m / s, to obtain a rolled plate, the thickness of the rolled plate is 12 mm;

[0074] Step 2) The hot rolled rolled plate is solution treated in a heat treatment furnace at a temperature of 470°C for 1.5 hours, followed by water quenching. The plate after solution treatment is removed from the solution furnace for less than 15 seconds, and the plate is removed after being water cooled to room temperature. The plate after solution treatment is then subjected to double-stage artificial aging, with the aging process being first kept at 70°C for 24 hours and then kept at 110°C for 24 hours to obtain a high-strength and ductile 7 series aluminum alloy plate.

[0075] The 7 series aluminum alloy plate prepared in this embodiment has a yield strength of 565 MPa and an elongation of 12% in the rolling direction, and a transverse yield strength of 531 MPa and an elongation of 11%.

[0076] Comparative Example 1

[0077] This comparative example provides a method for preparing a 7 series aluminum alloy plate, comprising the following steps:

[0078] Step 1) subjecting a 20 mm thick 7050 aluminum alloy ingot to homogenization heat treatment in a homogenization furnace, the homogenization heat treatment temperature is 450° C., and the time is 12 h; immediately after the homogenization heat treatment, the ingot is transferred to a cooling chamber for air cooling for 6 h; the cooled aluminum alloy ingot is preheated, the preheating temperature is 420° C., and the preheating time is 2 h; the preheated ingot is rolled, the starting rolling temperature is 410° C., the final rolling temperature is 400° C., 7 rolling passes are adopted, the pressing amount of each pass is 3.5 mm, 2.5 mm, 2.5 mm, 1.5 mm, 1.5 mm, 1.5 mm, 1 mm, the total deformation is 70%, the rolling speed is (1.5±0.1) m / s, and a rolled plate is obtained, and the thickness of the rolled plate is 6 mm;

[0079] Step 2) The hot rolled plate is subjected to a solution treatment in a heat treatment furnace, the solution treatment temperature is 480°C, the solution treatment time is 1 hour, and then a water quenching treatment is performed. The plate after the solution treatment is removed from the solution furnace for less than 15 seconds, and the plate is removed after being water cooled to room temperature; then the plate after the solution treatment is subjected to double-stage artificial aging, the aging process is first kept at 70°C for 24 hours, and then kept at 110°C for 12 hours, to obtain a 7 series aluminum alloy plate.

[0080] See also Figure 3 The 7 series aluminum alloy plate prepared in this comparative example mainly has a (110) texture, and the maximum pole density of the (110) texture is 5.29; compared with Example 1, the (111) texture is significantly weakened, and the maximum pole density of the (111) texture is 4.31, indicating that the shear deformation inside the material is weak; the intragranular precipitation phase of the material obtained in the comparative example is very dense, and the grain boundary precipitation phase only shows a slight coarsening phenomenon compared with the intragranular precipitation phase. The performance test shows that its yield strength along the rolling direction is 542MPa, the elongation is 17%, and the transverse yield strength is 502MPa, and the elongation is 11%. Its strength and plasticity along the rolling direction are equivalent to those in Example 1. However, due to the use of 7 rolling deformation passes, the total rolling pressure is the same as in Example 1, but the rolling step amount is reduced, resulting in the material being mainly plane rheological during the rolling deformation process. The longitudinal and transverse shear deformations of each pass are insufficient, and cracking along the streamline section is likely to occur under transverse loading conditions, resulting in a significant reduction in its transverse strength and elongation compared with Example 1.

[0081] Comparative Example 2

[0082] This comparative example provides a method for preparing a 7 series aluminum alloy plate, comprising the following steps:

[0083] Step 1) subjecting a 20 mm thick 7050 aluminum alloy ingot to homogenization heat treatment in a homogenization furnace, the homogenization heat treatment temperature is 450° C., and the time is 12 h; immediately after the homogenization heat treatment, the ingot is transferred to a cooling chamber for air cooling for 6 h; the cooled aluminum alloy ingot is preheated, the preheating temperature is 420° C., and the preheating time is 2 h; the preheated ingot is rolled, the starting rolling temperature is 410° C., the final rolling temperature is 400° C., 3 passes are adopted, the pressing amount of each pass is 6 mm, 5 mm, and 3 mm, the total deformation is 70%, and the rolling speed is (1.5±0.1) m / s, to obtain a rolled plate, the thickness of the rolled plate is 6 mm;

[0084] Step 2) The hot rolled rolled plate is subjected to a solution treatment in a heat treatment furnace, the solution treatment temperature is 480°C, the solution treatment time is 1 hour, and then a water quenching treatment is performed. The plate after the solution treatment is removed from the solution furnace for less than 15 seconds, and the plate is removed after being water cooled to room temperature; then the plate after the solution treatment is subjected to a single-stage artificial aging, and the aging process is to keep warm at 115°C for 12 hours to obtain a 7 series aluminum alloy plate.

[0085] See also Figure 4 The densification degree of the 7-series aluminum alloy sheet prepared in this comparative example is lower than that in Example 1, and the grain boundary precipitate phase shows obvious coarsening phenomenon. This is because it has not undergone low-temperature pre-aging treatment. The high-density dislocations formed during the rolling deformation process will cause the precipitate phase to form heterogeneously and grow, especially the precipitate phase at the grain boundary is obviously coarsened, ellipsoidal, and the narrow side width is 30-50nm. The coarsening of the grain boundary precipitate phase will reduce the content of the precipitate phase in the crystal. The coarsening of the grain boundary precipitate phase will aggravate the cracking along the crystal, which is not conducive to the improvement of plasticity, and the reduction of the number density of the precipitate phase in the crystal will deteriorate the strength of the material. Performance tests show that its yield strength along the rolling direction is 527MPa, the elongation is 13%, and the transverse yield strength is 492MPa, and the elongation is 9%. Compared with Example 1, both the strength and elongation along the rolling direction and the transverse direction are reduced.

[0086] Comparative Example 3

[0087] This comparative example provides a method for preparing a 7 series aluminum alloy plate, comprising the following steps:

[0088] A 20mm thick 7050 aluminum alloy ingot is subjected to homogenization heat treatment in a homogenization furnace at a temperature of 450°C for 12 hours; immediately after the homogenization heat treatment, it is transferred to a cooling chamber for air cooling for 6 hours; the cooled aluminum alloy ingot is preheated at a preheating temperature of 420°C for 2 hours; the preheated ingot is rolled at a starting rolling temperature of 410°C and a final rolling temperature of 400°C, with two rolling passes, each with a pressing amount of 8mm and 6mm respectively, a total deformation of 70%, a rolling speed of (1.5±0.1) m / s, to obtain a rolled plate with a thickness of 6mm.

[0089] The plate has severe surface cracking during the second rolling process and is considered scrapped material. This is because a large number of dislocations will be generated during the rolling process of the plate. The greater the deformation, the higher the dislocation density. If the deformation in a single pass is too large, the high-density dislocation entanglement formed inside the material will aggravate the crack damage of the material.

[0090] Comparative Example 4

[0091] This comparative example provides a method for preparing a 7 series aluminum alloy plate, comprising the following steps:

[0092] Step 1) a 30 mm thick 7075 aluminum alloy ingot is subjected to homogenization heat treatment in a homogenization furnace, the temperature of the homogenization heat treatment is 450° C., and the time is 12 h; after the homogenization heat treatment is completed, the ingot is immediately transferred to a cooling chamber for air cooling for 6 h; the cooled aluminum alloy ingot is preheated, the preheating temperature is 420° C., and the preheating time is 2 h; the preheated ingot is rolled, the starting rolling temperature is 410° C., the final rolling temperature is 400° C., 7 rolling passes are adopted, the pressing amount of each pass is 5 mm, 4 mm, 3 mm, 2.5 mm, 2.5 mm, 1.5 mm, 1.5 mm, 1 mm, the total deformation is 70%, the rolling speed is (1.5±0.1) m / s, and a rolled plate is obtained, and the thickness of the rolled plate is 9 mm;

[0093] Step 2) The hot rolled rolled plate is subjected to a solution treatment in a heat treatment furnace, the solution treatment temperature is 470°C, the solution treatment time is 1 hour, and then a water quenching treatment is performed. The plate after the solution treatment is removed from the solution furnace for less than 15 seconds, and the plate is removed after being water cooled to room temperature; then the plate after the solution treatment is subjected to a single-stage artificial aging, and the aging process is to keep warm at 115°C for 12 hours to obtain a 7 series aluminum alloy plate.

[0094] The 7 series aluminum alloy sheet prepared in this comparative example has a yield strength of 522MPa and an elongation of 17% in the rolling direction, a transverse yield strength of 501MPa and an elongation of 11%. Compared with Example 2, its strength and elongation in the rolling direction and transverse direction are reduced. This is because it has not undergone low-temperature pre-aging treatment. Even if it is rolled 7 times with a small amount of deformation per pass, dislocations will still occur in the matrix, resulting in heterogeneous nucleation and growth of precipitation phases. The coarsening of the precipitation phase at the grain boundary will aggravate cracking along the grain, which is not conducive to plasticity improvement, and the reduction in the number density of the precipitation phase within the grain will deteriorate the strength of the material.

[0095] Comparative Example 5

[0096] This comparative example provides a method for preparing a 7 series aluminum alloy plate, comprising the following steps:

[0097] A 20 mm thick 7050 aluminum alloy ingot is subjected to homogenization heat treatment in a homogenization furnace at a temperature of 450°C for 12 hours; after the homogenization heat treatment, it is immediately transferred to a cooling chamber for air cooling for 6 hours; the cooled aluminum alloy ingot is preheated at a temperature of 350°C for 2 hours; the preheated ingot is rolled at a starting rolling temperature of 340°C and a final rolling temperature of 300°C, with three rolling passes, each of which has a pressing amount of 6 mm, 5 mm, and 3 mm, respectively, a total deformation of 70%, and a rolling speed of (1.5±0.1) m / s to obtain a rolled plate having a thickness of 6 mm;

[0098] The plate had severe surface cracking during the third rolling, and was deemed scrapped. This was because the rolling temperature of the plate was below the recrystallization temperature of the aluminum alloy (about 400°C), and the rolling process could not form a sufficient recrystallization structure to reduce the dislocation density. The high-density dislocation entanglement formed inside the material would aggravate the crack damage of the material.

[0099] It is easy for those skilled in the art to understand that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present invention. These improvements and variations should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a 7 series aluminum alloy sheet, characterized in that: The following steps are involved: Step 1) homogenizing heat treatment of the 7 series aluminum alloy ingot, preheating after cooling, and then performing multiple rolling processes to obtain a rolled plate; The preheating temperature is higher than the recrystallization temperature of the 7 series aluminum alloy ingot and lower than the solution temperature of the 7 series aluminum alloy ingot; the pressing amount of each rolling process is 30%-40%; Step 2) performing a solution treatment on the rolled plate, and then performing a double-stage aging treatment to obtain a 7 series aluminum alloy plate; The two-stage aging treatment includes low-temperature pre-aging and high-temperature aging; Among them, the temperature of low temperature pre-aging is 60-80℃; The temperature for high temperature aging is 110-165℃.

2. The method for preparing the 7 series aluminum alloy sheet according to claim 1, characterized in that: In the step 1), the temperature of the homogenization heat treatment is 400-468° C.; and / or The holding time of homogenous heat treatment is 10-24h.

3. The method for preparing the 7 series aluminum alloy sheet according to claim 1, characterized in that: In the step 1), the cooling method is air cooling, and the air cooling time is 3-6 hours.

4. The method for preparing a 7 series aluminum alloy sheet according to claim 1, characterized in that: In the step 1), the preheating temperature is 410-440° C.; and / or The preheating time is 1-5h.

5. The method for preparing the 7 series aluminum alloy sheet according to claim 1, characterized in that: In step 1), the total pressing amount of the multi-pass rolling process is 60%-90%; and / or The rolling speed is 1.4-1.6m / s.

6. The method for preparing the 7 series aluminum alloy sheet according to claim 5, characterized in that: In the step 1), the starting rolling temperature of the multi-pass rolling process is 400°C-430°C, and the final rolling temperature is 380°C-410°C.

7. The method for preparing a 7 series aluminum alloy sheet according to claim 1, characterized in that: In the step 2), the temperature of the solution treatment is 460-490°C; and / or The solution treatment time is 1-5h.

8. The method for preparing a 7 series aluminum alloy sheet according to claim 1, characterized in that: In the step 2), the low temperature pre-aging time is 24-72h; The high temperature aging time is 6-24h.

9. A 7 series aluminum alloy sheet, characterized in that: The texture of the 7 series aluminum alloy plate includes (110) and (111) textures, and the maximum pole density values ​​of the two textures differ by no more than 5%; the microstructure of the 7 series aluminum alloy plate includes intragranular precipitation phases and needle-shaped grain boundary precipitation phases; The size of the intracrystalline precipitated phase is 5-10 nm, and the narrow side size of the needle-shaped grain boundary precipitated phase is 10-20 nm.

10. The 7 series aluminum alloy sheet according to claim 9, characterized in that: The 7 series aluminum alloy sheet is obtained by the preparation method described in any one of claims 1 to 8.

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