Preparation method of aviation 7075 aluminum alloy coated thin plate with high forming performance

Abstract

The invention discloses a preparation method of a 7075 aluminum alloy coated thin plate for aviation with high forming performance, which comprises the following steps: (1) preparing a 7075 aluminum alloy large-size slab ingot through smelting and casting, and homogenizing; (2) sawing and milling the homogenized 7075 aluminum alloy slab ingot to obtain a slab ingot with a smooth surface as a core material; (3) determining the size specification of the coating material 7072 aluminum alloy, and brushing and grinding the coating surface of the coating material 7072 aluminum alloy; (4) attaching the cladding material and the core material, and fixing the cladding material and the core material by adopting a spot welding and riveting combined method to obtain a composite slab ingot; and (5) the composite slab ingot is subjected to hot rolling, cold rolling and annealing, and the 7075 aluminum-clad sheet is obtained. According to the method, the cast ingot with the uniform structure is obtained through two-stage homogenization, the cladding material and the core material are fixed in a spot welding and riveting combined mode, meanwhile, the roughness of the cladding surface of the cladding material is controlled, and the 7075 aluminum-clad sheet with the high forming performance is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy thin plate preparation, and in particular to a method for preparing a 7075 aluminum alloy clad thin plate for aviation with high formability. Background Art

[0002] The 7xxx series aluminum alloys belong to the Al-Zn-Mg-Cu family and are heat-treatable, high-strength aluminum alloys. Due to their high specific strength, high-temperature stability, and excellent weldability, they are often used as fuselage skin materials in the aerospace industry. 7075 aluminum alloy is particularly widely used. To further enhance the performance of 7075 aluminum alloy in the harsh environments of aviation and aerospace, a high-purity 7072 aluminum alloy can be applied to the surface of the alloy to improve its corrosion resistance. This not only physically protects the alloy matrix but also acts as an anode due to its inherent high electrode potential, providing anodic protection. However, the development of 7075 aluminum alloy clad sheet materials in China still faces some technical difficulties, particularly in terms of formability. The annealed 7075 clad material is prone to cracking in the cladding layer when bent under the aviation ASTM E290 standard. This is primarily due to the uneven thickness of the cladding layer, the high number of secondary phases in the transition zone of the cladding layer, and the large size of the sheet. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a method for preparing a 7075 aluminum alloy clad sheet for aviation with high formability.

[0004] The technical solution adopted in the present invention is:

[0005] A method for preparing a 7075 aluminum alloy clad sheet for aviation with high formability comprises the following steps:

[0006] (1) Prepare raw materials according to the composition and proportion of 7075 aluminum alloy, obtain large-sized flat ingots through smelting and casting, and place the flat ingots in a homogenizing furnace for homogenization treatment;

[0007] (2) sawing and milling the homogenized 7075 aluminum alloy flat ingot to obtain a flat ingot with a smooth surface as the core material;

[0008] (3) Determine the size specifications of the 7072 aluminum alloy cladding material according to the size of the core material 7075 aluminum alloy slab, brush and grind the cladding surface of the cladding material, and then clean and dry the cladding surface of the cladding material;

[0009] (4) laminating the cladding material obtained in step (3) to the core material, and fixing the cladding material and the core material by combining spot welding and riveting to obtain a composite flat ingot fixed as one;

[0010] (5) The composite ingot obtained in step (4) is hot-rolled, cold-rolled, and annealed to obtain 7075 clad aluminum sheets.

[0011] Further, the alloy composition of the 7075 aluminum alloy in step (1) is as follows: by mass percentage, Si ≤ 0.40%, Fe ≤ 0.50%, Cu: 1.2 - 2.0%, Mn ≤ 0.30%, Mg: 2.1 - 2.9%, Cr: 0.18 - 0.28%, Zn: 5.1 - 6.1%, Ti ≤ 0.20%, for other impurity elements, each does not exceed 0.05%, and the total does not exceed 0.15%, with the balance being aluminum.

[0012] Further, the homogenization process of the ingot in step (1) adopts two-stage homogenization. Among them, the first-stage homogenization temperature is 465 ± 3 °C, and the first-stage homogenization time is 8 - 10 h; the second-stage homogenization temperature is 475 ± 3 °C, and the second-stage homogenization time is 25 - 30 h. After the homogenization heat treatment is completed, it is cooled to room temperature at a cooling rate of not less than 60 - 100 °C / h.

[0013] In the above technical solution, the present invention obtains an ingot with uniform grain structure and reduces the volume fraction of the second phase by performing two-stage homogenization treatment on the ingot and controlling the cooling rate.

[0014] Further, when the ingot is sawed in step (2), 1.5 - 2.0% is sawed at the gate end and 4.0 - 5.0% is sawed at the expanded end; when the ingot is milled, 10.0 - 14.0% of milling is performed on both the upper and lower surfaces of the ingot.

[0015] In the above technical solution, the present invention removes the segregation layer of the ingot by controlling the milling amount, ensures that the grain structure of the transition zone where the cladding material is welded to the core material is uniform, and improves the welding effect. Due to element diffusion problems, the precipitated phases in the coarse grain layer or segregation layer are severely coarsened, and there are many impurity elements, many coarse primary phases, and many coarse second phases at this place, which are prone to microcracks or pores during the welding process, affecting the welding quality and further affecting the formability of the 7075 aluminum alloy clad sheet material.

[0016] Further, the surface roughness of the cladding surface of the cladding material after brushing and grinding in step (3) is 2.5 - 3.5 μm.

[0017] In the above technical solution, the present invention brushes and grinds the coating surface of the clad material, not only removing the surface oxide layer of the coating surface, but also controlling its surface roughness within a certain range, which can increase the contact area between the clad material and the core material and improve the bonding performance between the clad material and the core material during hot rolling; however, the roughness of the coating surface should not be too large, otherwise, it is difficult to completely remove cleaning agents on the coating surface, resulting in defects such as poor bonding between the clad material and the core material; in addition, if the roughness of the coating surface is too large, it may also affect the flow performance of the clad material during hot rolling, resulting in uneven coating layers, and even affecting the coating area, causing the coating layer to not completely cover the core material.

[0018] Further, in step (3), for the 7075 aluminum-clad sheet with a finished product thickness of 1.60 - 4.75 mm, the nominal cladding rate is set to 3.0%, and the minimum cladding rate is not less than 2.5%; and the thickness of the clad material is 15 - 25 mm, the width of the clad material is (the width of the effective rolling surface of the core material - (20 ± 15 mm) × 2), and the length is (the length of the core material - (200 ± 10 mm) × 2).

[0019] Further, when the clad material and the core material are fixed in step (4), the materials of the welding wires and rivets used at the spot welding positions and riveting positions are the same as that of the core material, and the spot welding positions and riveting positions are arranged on both side edges of the clad material. The spot welding positions and riveting positions on each side are alternately and evenly distributed, and the spot welding position or riveting position at the outermost end is 20 - 50 mm away from the end edge of the clad material, and the distance between the spot welding positions and the riveting positions is 200 mm - 600 mm.

[0020] Further, the specific process of step (5) for hot rolling is as follows: putting the composite ingot into a heating furnace and heating it to 415 - 430 °C, keeping it warm for 2 - 4 h and then performing hot rolling. The number of hot rolling passes is 20 - 25 passes; among them, the reduction of the first two passes is 1 - 4 mm, the rolling speed is 0.35 - 0.5 m / s for the bonding rolling of the composite flat ingot; emulsion spraying is started in the third pass, with the upper surface spraying amount of 15 - 25% and the lower surface spraying amount of 40 - 55%. The emulsion spraying amount is increased to 35 - 45% on the upper surface and 70 - 80% on the lower surface at the 10th pass or 13th pass. Starting from the 4th pass, the reduction per pass is controlled to be ≤ 30 mm, the rolling speed is ≤ 2.0 m / s, the final rolling temperature is controlled at 300 - 330 °C, and the thickness of the hot-rolled finished product is 5.0 - 8.0 mm.

[0021] Further, the specific process of step (5) for cold rolling is as follows: cold rolling the hot-rolled finished product blank through 2 - 4 passes to the target thickness, ensuring that the cold rolling deformation rate is 50 - 80%, and the rolling speed is controlled at 0.35 - 0.5 m / s, finally obtaining a 7075 aluminum-clad sheet with a thickness of 1.60 - 4.75 mm.

[0022] Further, the annealing process in the step (5) is as follows: the annealing temperature is 475 ± 2 °C, and the annealing time is 2 - 3 h.

[0023] The beneficial effects of the present invention are as follows:

[0024] The present invention provides a preparation method of a 7075 aluminum alloy clad sheet for aviation with high formability. By adopting a two-stage homogenization process to control the cooling rate, the structure of the ingot is made uniform, and the volume fraction of the second phase is reduced; and a combination of spot welding and riveting is used to fix the clad material and the core material. At the same time, the roughness of the clad surface of the clad material is controlled, so that the contact area between the clad material and the core material is large and the contact is firm, ensuring the hot rolling welding effect and the uniform thickness of the clad layer during the rolling process; solving the problems such as the shedding of the clad layer or uneven mechanical properties caused by the large number and size of the second phases in the structure of the clad transition region, the uneven welding effect of the clad welding interface, and the uneven thickness of the clad layer, making the prepared 7075 aluminum-clad sheet have good formability. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is the metallographic photo of the homogenized ingot in Embodiment 2 of the present invention;

[0027] Figure 2 It is the SEM photo of the clad layer and the transition region of the clad sheet prepared in Embodiment 2 of the present invention;

[0028] Figure 3 It is the bending property test photo of the clad sheet prepared in Embodiment 2 of the present invention;

[0029] Figure 4 It is the metallographic photo of the homogenized ingot in Comparative Example 5 of the present invention. Detailed Embodiments

[0030] The present invention provides a preparation method of a 7075 aluminum alloy clad sheet for aviation with high formability. To make the purpose, technical solutions and effects of the present invention clearer and more definite, the following further details the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] Embodiment 1

[0032] In this embodiment, a clad sheet of 7075 aluminum alloy for aviation is prepared, and the steps are as follows:

[0033] (1) The 7075 aluminum alloy flat ingot is a large-sized flat ingot with specifications of 480 mm (thickness) × 2000 mm (width) × 6000 mm (length), produced by semi-continuous casting. The alloy composition is (mass fraction / wt.%) Si: 0.19, Fe: 0.16, Cu: 1.45, Mn: 0.08, Mg: 2.33, Cr: 0.21, Zn: 5.63, Ti: 0.03. After casting, the flat ingot is put into a homogenizing furnace for two-stage homogenization treatment at 468 °C × 10 h + 478 °C × 28 h. After the homogenization heat treatment is completed, it is cooled to room temperature at a cooling rate of 70 °C / h.

[0034] (2) Saw off 150 mm of waste ingot from the gate end and 300 mm of waste ingot from the expansion end of the homogenized 7075 aluminum alloy flat ingot. Milling 25 mm of segregation layer from each of the upper and lower surfaces of the flat ingot, and milling 5 mm of segregation layer from each side of the flat ingot to obtain a surface-smooth flat ingot with specifications of 430 mm (thickness) × 1990 mm (width) × 5550 mm (length) as the core material.

[0035] (3) Determine the size specifications of the 7072 aluminum alloy clad material according to the size of the 7075 aluminum alloy flat ingot core material. Design the cladding rate to be 3.0%. Determine that the thickness of the 7072 aluminum alloy clad material is 23 mm, the width is 1930 mm, and the length is 5130 mm. Brush and grind the cladding surface of the clad material to remove the surface oxide layer, and at the same time control its surface roughness to be 3.0 μm to increase the contact area. After brushing and grinding, clean and dry the cladding surface to ensure that the brushing and grinding are uniform without omission and there are no foreign matters such as dust, oil stains, and aluminum chips.

[0036] (4) Use the brushed 7072 aluminum alloy to clad the core material. Fit the clad material with the core material, and use a method combining spot welding and riveting to fix the clad material and the core material to obtain a composite flat ingot fixed as a whole. Specifically, the welding wire and rivets used for spot welding and riveting are both 7075 aluminum alloy. The spot welding positions and riveting positions are set on both side edges of the clad material, and the spot welding positions and riveting positions on each side are alternately and evenly distributed. The spot welding position or riveting position at the outermost end of each side is 15 mm away from the end edge of the clad material, and the distance between adjacent two spot welding positions and riveting positions is 300 mm.

[0037] (5) Place the composite ingot in a heating furnace for preheating before hot rolling at 420 °C for 2.5 h. After heating, perform hot rolling. Set the number of hot rolling passes to 25. Among them, the reduction in the first and second passes is 3 mm, and the rolling speed is 0.40 m / s; in the third pass, emulsion spraying is started, with the spraying amount on the upper surface being 20% and the spraying amount on the lower surface being 40%; after the fourth pass, control the reduction per pass ≤ 30 mm and the rolling speed ≤ 2.0 m / s; and increase the emulsion spraying amount to 40% on the upper surface and 70% on the lower surface in the tenth pass; control the final rolling temperature at 330 °C, and the thickness of the hot-rolled finished product is 7.5 mm; then roll the hot-rolled finished product blank through 2 passes of cold rolling to the target thickness of 4.6 mm, where the reduction in the first pass is 1.80 mm and the reduction in the second pass is 1.10 mm, and control the rolling speed at 0.40 m / s to finally obtain a cold-rolled finished product with a thickness of 4.6 mm; then perform continuous annealing treatment on the cold-rolled finished product in a cushion-type continuous annealing furnace at 475 °C for 2 h to obtain a 7075 aluminum-clad thin sheet in a fully recrystallized annealed state.

[0038] The cladding layer of the annealed 7075 aluminum-clad thin sheet prepared in this example has a uniform thickness and good cladding effect; its tensile strength is 199 MPa, yield strength is 100 MPa, and elongation is 25%, meeting the usage standards of 7075 aviation aluminum materials; under the condition that the bending punch radius is 9.5 mm, according to the ASTM E290-14 standard test, there are no cracks after bending 180°.

[0039] Example 2

[0040] In this example, an aviation-use 7075 aluminum alloy clad thin sheet is prepared, and the steps are as follows:

[0041] (1) The 7075 aluminum alloy ingot uses a large-sized ingot with specifications of 480 mm (thickness) × 2000 mm (width) × 6000 mm (length), and is produced by a semi-continuous casting method. The alloy composition is (mass fraction / wt.%) Si: 0.22, Fe: 0.18, Cu: 1.85, Mn: 0.05, Mg: 2.83, Cr: 0.22, Zn: 5.96, Ti: 0.03; after casting, place the ingot in a homogenizing furnace for two-stage homogenization treatment at 465 °C for 9 h + 474 °C for 25 h, and after the homogenization heat treatment is completed, cool it to room temperature at a cooling rate of 90 °C / h.

[0042] (2) Saw off 200 mm of waste ingot from the gate end of the homogenized 7075 aluminum alloy ingot and 380 mm of waste ingot from the expansion end. Milling 30 mm of segregation layer from each of the upper and lower surfaces of the ingot and 8 mm of segregation layer from each side of the ingot to obtain a surface-smooth ingot with specifications of 420 mm (thickness) × 1984 mm (width) × 5420 mm (length) as the core material.

[0043] (3) Determine the size specifications of the cladding material 7072 aluminum alloy according to the size of the core material 7075 aluminum alloy flat ingot. Design the cladding rate to be 3.0%, and determine that the thickness of the 7072 aluminum alloy cladding material is 25 mm, the width is 1930 mm, and the length is 5130 mm. Brush and grind the cladding surface of the cladding material to remove the surface oxide layer, and at the same time control its surface roughness to be 2.8 μm to increase the contact area. After brushing and grinding, clean and dry the cladding surface to ensure that the brushing and grinding are uniform without omission and there are no foreign matters such as dust, oil, and aluminum chips;

[0044] (4) Use the brushed 7072 aluminum alloy to perform cladding treatment on the core material. Fit the cladding material and the core material, and use a method combining spot welding and riveting to fix the cladding material and the core material to obtain a composite flat ingot fixed as a whole. Specifically, the welding wire and rivets used for spot welding and riveting are both 7075 aluminum alloy. The spot welding positions and riveting positions are set on both side edges of the cladding material, and the spot welding positions and riveting positions on each side are alternately and evenly distributed. The distance from the spot welding position or riveting position at the outermost end of each side to the end edge of the cladding material is 15 mm, and the distance between adjacent two spot welding positions and riveting positions is 510 mm;

[0045] (5) Put the composite flat ingot into a heating furnace for preheating before hot rolling at 430 °C for 2 h. After heating, perform hot rolling. Set the number of hot rolling passes to 21 passes. Among them, the reduction of the first and second passes is 4 mm, and the rolling speed is 0.40 m / s; the emulsion spray is started in the third pass, with the upper surface spray amount of 25% and the lower surface spray amount of 50%; after the fourth pass, control the reduction of each pass ≤ 30 mm and the rolling speed ≤ 2.0 m / s; and increase the emulsion spray amount to 45% on the upper surface and 75% on the lower surface in the tenth pass; control the final rolling temperature at 320 °C, and the thickness of the hot-rolled finished product is 6.5 mm; then roll the hot-rolled finished product blank through 3 passes of cold rolling to the target thickness of 3.25 mm. Among them, the reduction of the first pass is 1.25 mm, the reduction of the second pass is 0.90 mm, and the reduction of the third pass is 1.10 mm. The rolling speed is controlled at 0.35 m / s, and finally obtain a cold-rolled finished product with a thickness of 3.25 mm; then perform continuous annealing treatment on the cold-rolled finished product in a cushion-type continuous annealing furnace at 477 °C for 2 h to obtain a 7075 aluminum-clad thin sheet in a fully recrystallized annealing state.

[0046] Take samples of the homogenized flat ingot in step (1) of this embodiment for metallographic inspection, as Figure 1 shown. It can be seen from Figure 1 that after double-stage homogenization, the ingot structure is uniform and there are no coarse second phases, etc.

[0047] Perform SEM inspection on the annealed 7075 aluminum-clad thin sheet prepared in this embodiment, as Figure 2 shown. It can be seen fromFigure 2 It can be seen that: the cladding layer of the 7075 aluminum-clad thin plate prepared in this embodiment has a uniform thickness, the transition region between the cladding layer and the core material is well welded, there is no aggregation of coarse second phases, and there are no defects such as cracks, slag inclusions, and pores.

[0048] The mechanical properties of the annealed 7075 aluminum-clad thin plate prepared in this embodiment were tested. Its tensile strength is 187.5 MPa, yield strength is 92.4 MPa, and elongation is 22.5%, meeting the usage standards of 7075 aviation aluminum materials, and the cladding effect of the formed cladding layer is uniform; the bending performance of the annealed 7075 aluminum-clad thin plate prepared in this embodiment was tested, and the bending test photos are as Figure 3 shown. As can be seen from Figure 3 it: the 7075 aluminum-clad thin plate prepared in this embodiment has no cracks when bent 180° under the condition that the bending indenter radius is 6.5 mm according to the ASTM E290-14 standard test.

[0049] Comparative Example 1

[0050] A 7075 aluminum alloy clad thin plate for aviation was prepared in this Comparative Example 1. The difference from Example 2 is that: in this comparative example, the cladding surface of the cladding material was brushed and ground, and the surface roughness after brushing and grinding is 6.0 μm.

[0051] The 7075 aluminum-clad thin plate prepared in this comparative example had cracks when bent 180° under the condition that the bending indenter radius is 6.5 mm according to the ASTM E290-14 standard test. This is because in the comparative example, due to the high roughness, the friction resistance prevented full rolling or the rolling deformation was uneven under the normal reduction rolling force, resulting in an uneven cladding layer thickness, and the cladding layer could not be fully covered in some width directions.

[0052] Comparative Example 2

[0053] A 7075 aluminum alloy clad thin plate for aviation was prepared in this Comparative Example 2. The difference from Example 2 is that: in this comparative example, the cladding surface of the cladding material was brushed and ground, and the surface roughness after brushing and grinding is 1.0 μm.

[0054] The 7075 aluminum-clad thin plate prepared in this comparative example had cracks when bent 180° under the condition that the bending indenter radius is 6.5 mm according to the ASTM E290-14 standard test. This is because in this comparative example, during the rolling process, due to the low roughness of the contact surface between the cladding material and the core material, the metal flow of the cladding layer was relatively fast under the normal reduction rolling force, and the density of the bonding interface between the cladding layer and the core material was low.

[0055] Comparative Example 3

[0056] Comparative Example 3 prepared an aviation - used 7075 aluminum alloy clad sheet, and the difference from Example 2 is that in this comparative example, the clad material and the core material were fixed by a method combining spot welding and riveting. The spot - welding positions were evenly distributed on one side edge of the clad material, and the riveting positions were evenly distributed on the other side edge of the clad material.

[0057] Under the condition that the bending punch radius of the 7075 aluminum - clad sheet prepared in this comparative example was 6.5 mm, according to the ASTM E290 - 14 standard test, when bent 180°, it fractured, and some welded materials showed cracking during the rolling process due to different bearing capacities on both sides during welding, and the crack source was likely to appear on the spot - welding side.

[0058] Comparative Example 4

[0059] Comparative Example 4 prepared an aviation - used 7075 aluminum alloy clad sheet, and the difference from Example 2 is that in this comparative example, only the riveting method was used to fix the clad material and the core material. The riveting positions were set on both side edges of the clad material and were evenly distributed on each side.

[0060] The clad layer thickness of the 7075 aluminum - clad sheet prepared in this comparative example was uniform, and the transition region between the clad layer and the core material was well - welded. And under the condition that the bending punch radius was 6.5 mm, according to the ASTM E290 - 14 standard test, when bent 180°, there were no cracks. However, riveting requires secondary processing of the core material and the clad material, the production process is cumbersome, and the production and manufacturing cost is high.

[0061] Comparative Example 5

[0062] Comparative Example 5 prepared an aviation - used 7075 aluminum alloy clad sheet, and the difference from Example 2 is that when homogenizing the slab in this comparative example, the homogenization process used was: 460 °C × 9 h, and after homogenization, it was furnace - cooled at a cooling rate of 40 °C / h.

[0063] The 7075 aluminum - clad sheet prepared in this comparative example cracked when bent 180° under the condition that the bending punch radius was 6.5 mm, according to the ASTM E290 - 14 standard test. The main reason was that: referring to Figure 4 , the homogenization effect of the homogenization process used in this comparative example was poor, and there were more residual second - phase and eutectic structures in the ingot, resulting in a large amount of coarse phases remaining during the subsequent welding and rolling process, and further causing the poor cladding effect of the formed clad layer and cracking during the bending process.

[0064] By analyzing the test results of the above embodiments and comparative examples: In Example 2 of the present invention, a two-stage homogenization process of controlling the cooling rate is adopted to make the structure of the ingot uniform and reduce the volume fraction of the second phase; and a combination of spot welding and riveting is used to fix the cladding material and the core material. At the same time, the roughness of the cladding surface of the cladding material is controlled, so that the fitting area between the cladding material and the core material is large and the fitting is firm, ensuring the hot rolling welding effect, and the thickness of the cladding layer is uniform during the rolling process, so that the prepared 7075 aluminum-clad thin sheet has good formability and prevents the thin sheet from cracking during bending. Moreover, the combination of spot welding and riveting fixing method in Example 2 of the present invention is combined with the roughness of the cladding surface, which can achieve the same effect as that of Comparative Example 4 fixed only by the riveting method. However, the method of Example 2 reduces the number of riveting positions, reduces the workload of secondary processing, and reduces the production cost.

[0065] It should be noted that the parts not described in the present invention can be realized by adopting or referring to the existing technologies.

[0066] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A preparation method of a 7075 aluminum alloy clad sheet for aviation with high formability, characterized in that, Including steps: (1) Prepare raw materials according to the composition and proportion of 7075 aluminum alloy, obtain large-sized flat ingots through smelting and casting, and place the flat ingots in a homogenizing furnace for homogenization treatment; (2) sawing and milling the homogenized 7075 aluminum alloy flat ingot to obtain a flat ingot with a smooth surface as the core material; (3) Determine the size specifications of the 7072 aluminum alloy cladding material according to the size of the core material 7075 aluminum alloy slab, brush and grind the cladding surface of the cladding material, and then clean and dry the cladding surface of the cladding material; (4) laminating the cladding material obtained in step (3) to the core material, and fixing the cladding material and the core material by combining spot welding and riveting to obtain a composite flat ingot fixed as one; (5) The composite flat ingot obtained in step (4) is subjected to hot rolling, cold rolling, and annealing to obtain 7075 aluminum-clad thin plates.

2. The preparation method of a 7075 aluminum alloy clad thin plate for aviation with high formability according to claim 1, characterized in that, The alloy composition of the 7075 aluminum alloy in step (1) is as follows: in percentage by mass, Si≤0.40%, Fe≤0.50%, Cu: 1.2-2.0%, Mn≤0.30%, Mg: 2.1-2.9%, Cr: 0.18-0.28%, Zn: 5.1-6.1%, Ti≤0.20%, and other impurity elements, each not exceeding 0.05% and the total not exceeding 0.15%, with the balance being aluminum.

3. The preparation method of a 7075 aluminum alloy clad sheet for aviation with high formability according to claim 1, characterized in that, In the step (1), the flat ingot is homogenized by a two-stage homogenization process, wherein the first-stage homogenization temperature is 465±3°C and the first-stage homogenization time is 8 to 10 hours; the second-stage homogenization temperature is 475±3°C and the second-stage homogenization time is 25 to 30 hours. After the homogenization heat treatment is completed, the ingot is cooled to room temperature at a cooling rate of not less than 60 to 100°C / h.

4. The preparation method of a 7075 aluminum alloy clad sheet for aviation with high formability according to claim 1, characterized in that, When sawing the slab in step (2), the gate end is sawed by 1.5-2.0% and the expansion end is sawed by 4.0-5.0%; when milling the slab, both the upper and lower surfaces of the slab are milled by 10.0-14.0%.

5. The preparation method of a 7075 aluminum alloy clad sheet for aviation with high formability according to claim 1, characterized in that, The roughness of the coating surface of the coating material after brushing in the step (3) is 2.5 to 3.5 μm.

6. The preparation method of a 7075 aluminum alloy clad sheet for aviation with high formability according to claim 1, characterized in that, In the step (3), for the finished product of 7075 aluminum-clad thin plate with a thickness of 1.60 to 4.75 mm, the nominal cladding rate is set to 3.0%, and the minimum cladding rate is not less than 2.5%; and the thickness of the cladding material is 15 to 25 mm, and the width of the cladding material is (core material effective rolling surface width - (20 ± 15 mm) × 2), and the length of the cladding material is (core material length - (200 ± 10 mm) × 2).

7. The preparation method of a 7075 aluminum alloy clad sheet for aviation with high formability according to claim 1, characterized in that, When the covering material and the core material are fixed in the step (4), the material of the welding wire and the rivet used at the spot welding position and the riveting position is the same as that of the core material, and the spot welding position and the riveting position are arranged on both side edges of the covering material, the spot welding position and the riveting position on each side are alternately and evenly distributed, and the spot welding position or the riveting position at the end is 10 to 30 mm away from the end edge of the covering material, and the distance between the spot welding position and the riveting position is 200 mm to 600 mm.

8. The preparation method of a 7075 aluminum alloy clad sheet for aviation with high formability according to claim 1, characterized in that, The hot rolling process in step (5) is specifically as follows: Put the composite ingot into a heating furnace and heat it to 415 - 430 °C. After holding for 2 - 4 h, carry out hot rolling with 20 - 25 passes; among them, the reduction in the first two passes is 1 - 4 mm, the rolling speed is 0.35 - 0.5 m / s for the welding rolling of the composite flat ingot; in the third pass, start the emulsion spraying, with the spraying amount on the upper surface being 15 - 25% and the spraying amount on the lower surface being 40 - 55%. Increase the emulsion spraying amount to 35 - 45% on the upper surface and 70 - 80% on the lower surface in the 10th or 13th pass. Starting from the 4th pass, control the reduction per pass ≤ 30 mm and the rolling speed ≤ 2.0 m / s, and control the final rolling temperature at 300 - 330 °C. The thickness of the hot-rolled finished product is 5.0 - 8.0 mm.

9. The preparation method of a 7075 aluminum alloy clad sheet for aviation with high formability according to claim 1, characterized in that, The cold rolling process in step (5) is specifically as follows: Cold roll the hot-rolled finished product blank through 2 - 4 passes to the target thickness, ensure that the cold rolling deformation rate is 50 - 80%, and control the rolling speed at 0.35 - 0.5 m / s to finally obtain a 7075 aluminum-clad thin sheet with a thickness of 1.60 - 4.75 mm.

10. The preparation method of a 7075 aluminum alloy clad thin plate for aviation with high formability according to claim 1, characterized in that, The annealing process in step (5) is: The annealing temperature is 475 ± 2 °C, and the annealing time is 2 - 3 h.

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