阅读说明：本技术 一种航空用7系铝合包覆薄板的焊合方法 (Welding method of 7-series aluminum alloy clad thin plate for aviation ) 是由 顾华锋 于芳 晁代义 李红萍 徐志远 吕学科 郝建鹏 黄同瑊 孙有政 张华� 于 2021-08-19 设计创作，主要内容包括：一种航空用7系铝合包覆薄板的焊合方法,包括如下步骤：步骤一：将包覆材与铸锭贴合后,包覆材四周距离铸锭边部20-30mm,长度方向每隔1000-1500mm采用螺栓紧固的方式进行固定焊合,焊合用材料为7075-F态铝合金；步骤二：步骤一所得复合铸锭加热热轧；步骤三：将热轧7.0-8.0厚度板材经过3道冷轧至1.6-3.25mm。本发明采用点焊焊合的方式,在转运过程中必须进行钢带打包以免出现脱落风险,但是该方案在铸锭均热过程中,由于温度较高,钢带容易在表面留下痕迹,也由于在剪钢带过程中导致复合铸锭温度降低,两种因素都有可能导致在后续轧制过程引起轧辊黏铝,进而形成轧制黑线问题,导致表面质量不合格,降低产品的成品率。(A welding method of 7 series aluminum alloy clad thin plates for aviation comprises the following steps: the method comprises the following steps: after the coating material is attached to the ingot, the periphery of the coating material is 20-30mm away from the edge of the ingot, the coating material is fixedly welded in a bolt fastening mode every 1000-1500mm in the length direction, and the welding material is 7075-F state aluminum alloy; step two: heating and hot rolling the composite ingot; step three: the hot rolled plate with the thickness of 7.0-8.0 is cold rolled to 1.6-3.25mm by 3 times. According to the invention, a spot welding and welding mode is adopted, steel strips are required to be packed in a transfer process so as to avoid falling off risks, but in the ingot casting soaking process, due to the fact that the temperature is high, the steel strips are easy to leave traces on the surfaces, and due to the fact that the temperature of the composite ingot casting is reduced in the steel strip shearing process, the two factors can cause the aluminum adhesion of the rollers in the subsequent rolling process, the problem of rolling black lines is further formed, the surface quality is unqualified, and the yield of products is reduced.)

1. A welding method of 7 series aluminum alloy clad thin plates for aviation is characterized by comprising the following steps: the method comprises the following steps:

the method comprises the following steps: after the coating material is attached to the ingot, the periphery of the coating material is 20-30mm away from the edge of the ingot, the coating material is fixedly welded in a bolt fastening mode every 1000-1500mm in the length direction, and the welding material is 7075-F state aluminum alloy;

step two: heating the composite ingot obtained in the step one to 450-. The reduction amount of each pass is controlled to be less than or equal to 30mm, the rolling speed is controlled to be less than or equal to 2.0m/s, the roller surface is cleaned by using a brush roller in the rolling gap, the final rolling temperature is controlled to be 300-;

step three: the hot rolled plate with the thickness of 7.0-8.0 is cold rolled to 1.6-3.25mm by 3 times.

2. The welding method of the 7-series aluminum alloy clad sheet for aviation according to claim 1, wherein: the composition of the ingot casting alloy in the first step is as follows: the steel is characterized by comprising the following components, by weight, less than 0.08% of Si, less than 0.15% of Fe, 5.6% -5.9% of Zn, 1.3% -1.6% of Cu, 2.4% -2.7% of Mg, less than 0.1% of Mn, 0.18% -0.21% of Cr, less than 0.1% of Ti, no more than 0.05% of other impurity elements, no more than 0.15% of the total, and the balance of aluminum.

3. The welding method of the 7-series aluminum alloy clad sheet for aviation according to claim 1, wherein: the preparation method of the cast ingot in the first step comprises the following steps: putting raw materials into smelting, adding a remelting aluminum ingot and waste materials of the same alloy, smelting at 740 ℃, adding a covering agent after the melting is started, starting electromagnetic stirring after 60-70% of the aluminum alloy raw materials are melted, adjusting components after the aluminum alloy raw materials are completely melted, adding an intermediate alloy or an additive to adjust the components, then skimming, sampling and detecting chemical components, transferring the melt to a heat preservation furnace after the components are proper for temporary storage, putting the ingot into a homogenizing furnace for homogenization heat treatment, adopting a two-stage homogenizing process of 460 heat-storage type/465 ℃/6-10h +473 heat-storage type/476 ℃/20-30h, taking out of the furnace, and pushing into a cooling type for rapid cooling.

4. The welding method of the 7-series aluminum alloy clad sheet for aviation according to claim 1, wherein: in the first step, the clad material is a low-alloy 7-series aluminum plate with higher corrosion resistance, the thickness of the clad plate is 13-15mm, the minimum cladding rate of the finished product of the clad aluminum sheet with the thickness of 1.6-3.25 is 2%, the nominal cladding rate is 3%, the thickness of the clad plate used by the clad aluminum sheet is 13-15mm, the width of the clad plate is equal to the width of an effective rolling surface of the core ingot- (25 +/-15 mm) × 2, and the length of the clad plate is equal to the length of the core ingot- (200 +/-10 mm) × 2.

5. The welding method of the 7-series aluminum alloy clad sheet for aviation according to claim 1, wherein: in the first step, the cladding material is brushed on one side before use, the brushing quality needs to be ensured, the brushing layer is uniform and has no omission, and the brushing surface is strictly forbidden to have dust, oil stain, aluminum chips and other foreign matters, so that the surface oxide layer is removed.

6. The welding method of the 7-series aluminum alloy clad sheet for aviation according to claim 1, wherein: and in the first step, before welding, the surface of the ingot is wiped by using a towel dipped with a butanone or acetone cleaning agent, the surface of the ingot is wiped by using a clean dry towel, and the air is used for blowing and removing the butanone or acetone remained on the surface, so that the surface is wiped by using white paper after wiping and is prevented from blackening, and interlayer slag inclusion is avoided.

Technical Field

The invention belongs to the field of aviation aluminum alloy clad sheets, and particularly relates to a welding method of an aviation 7-series aluminum alloy clad sheet.

Background

The 7-series aluminum alloy clad sheet material is used as an aircraft skin sheet material due to the advantages of excellent corrosion resistance, high strength, low specific gravity and the like. The main skin material of the aviation aircraft mainly comes from foreign import. The development of the prior clad sheet material has some technical difficulties, such as uneven cladding, and the problem that the risk of cladding falling caused by welding spot open welding is easy to occur due to the non-optimized cladding welding mode, and the like, can not be solved in time. At present, no mature technology is available at home for preparing related clad sheet materials. The Nanshan aluminum industry develops the aluminum alloy sheet material for civil aircrafts by means of the construction project of the related production line of the national new material application demonstration platform (aviation material), overcomes the blockade of foreign technologies, and lays a foundation for the localization of the aviation aluminum alloy skin sheet for the domestic large aircrafts.

The skin sheet for the airplane is exposed in the environment for a long time, the requirements on the corrosion resistance and the strength of the material are high, the 7075 aluminum alloy belongs to an Al-Zn-Mg-Cu system and is a high-strength aluminum alloy, and the aluminum-clad sheet gives higher corrosion resistance to the alloy and can sufficiently meet the design and use requirements of high safety and long service life of the airplane. The 7075 aluminum alloy clad sheet has the problems of insecure cast ingot welding, poor surface quality, difficult control of cladding thickness uniformity and the like in the development process, so that the comprehensive performance of the 7075 aluminum alloy clad sheet cannot meet the technical design requirements and cannot meet the domestic substitution of large aircraft skin materials.

The 7075 aluminum alloy belongs to an Al-Zn-Mg-Cu system, is a heat-treatable reinforced aluminum alloy, has the advantages of high strength, low specific gravity, high fatigue performance and the like, is applied to aviation airplanes as a structural member and a skin plate, but the alloy has poor corrosion resistance, so that a pure aluminum plate with high corrosion resistance needs to be coated on the surface of the alloy, the strength of the 7075 aluminum alloy is maintained, the corrosion resistance is improved, and the 7075 aluminum alloy is favored as a skin plate material in the world aviation industry.

Because the technology has no related patent application at home, the welding is carried out by adopting a spot welding mode by taking the experience and self search at foreign countries as reference. However, steel strips must be packed in the transfer process so as to avoid the risk of falling off, but in the ingot soaking process, due to the fact that the temperature is high, the steel strips are prone to leaving marks on the surfaces, and due to the fact that the temperature of the composite ingot is reduced in the steel strip shearing process, the two factors can cause the problem that the rollers are adhered with aluminum in the subsequent rolling process, rolling black lines are formed, the surface quality is unqualified, and the yield of products is reduced.

Disclosure of Invention

The invention provides a welding method of a 7-series aluminum alloy clad thin plate for aviation, which is used for overcoming the defects in the prior art.

The invention is realized by the following technical scheme:

a welding method of 7 series aluminum alloy clad thin plates for aviation comprises the following steps:

the method comprises the following steps: after the coating material is attached to the ingot, the periphery of the coating material is 20-30mm away from the edge of the ingot, the coating material is fixedly welded in a bolt fastening mode every 1000-1500mm in the length direction, and the welding material is 7075-F state aluminum alloy;

step two: heating the composite ingot obtained in the step one to 450-. The reduction amount of each pass is controlled to be less than or equal to 30mm, the rolling speed is controlled to be less than or equal to 2.0m/s, the roller surface is cleaned by using a brush roller in the rolling gap, the final rolling temperature is controlled to be 300-;

step three: the hot rolled plate with the thickness of 7.0-8.0 is cold rolled to 1.6-3.25mm by 3 times.

The welding method of the 7-series aluminum alloy clad thin plate for aviation comprises the following steps: the steel is characterized by comprising the following components, by weight, less than 0.08% of Si, less than 0.15% of Fe, 5.6% -5.9% of Zn, 1.3% -1.6% of Cu, 2.4% -2.7% of Mg, less than 0.1% of Mn, 0.18% -0.21% of Cr, less than 0.1% of Ti, no more than 0.05% of other impurity elements, no more than 0.15% of the total, and the balance of aluminum.

The welding method of the 7-series aluminum alloy clad thin plate for aviation comprises the following steps: putting raw materials into smelting, adding a remelting aluminum ingot and waste materials of the same alloy, smelting at 740 ℃, adding a covering agent after the melting is started, starting electromagnetic stirring after 60-70% of the aluminum alloy raw materials are melted, adjusting components after the aluminum alloy raw materials are completely melted, adding an intermediate alloy or an additive to adjust the components, then skimming, sampling and detecting chemical components, transferring the melt to a heat preservation furnace after the components are proper for temporary storage, putting the ingot into a homogenizing furnace for homogenization heat treatment, adopting a two-stage homogenizing process of 460 heat-storage type/465 ℃/6-10h +473 heat-storage type/476 ℃/20-30h, taking out of the furnace, and pushing into a cooling type for rapid cooling.

According to the welding method of the 7-series aluminum alloy clad thin plate for aviation, in the first step, the clad material is a low-alloy 7-series aluminum plate with higher corrosion resistance, the thickness of the clad plate is 13-15mm, the minimum cladding rate is 2% and the nominal cladding rate is 3% for the finished product of the clad aluminum thin plate with the thickness of 1.6-3.25, the thickness of the clad plate used for the clad aluminum thin plate is 13-15mm, the width of the clad plate is equal to the width of an effective rolling surface of a core ingot, which is- (25 +/-15 mm) × 2, and the length of the clad plate is equal to the length of the core ingot, which is- (200 +/-10 mm) × 2.

According to the welding method of the 7-series aluminum alloy clad thin plate for aviation, in the first step, the clad material is brushed on one side before use, the brushing quality needs to be ensured, the brushing layer is uniform and has no omission, and the brushing surface is strictly forbidden to have foreign matters such as dust, oil stain and aluminum scraps, so that the surface oxide layer is removed.

According to the welding method of the 7-series aluminum alloy clad thin plate for aviation, in the first step, before welding, an aluminum ingot is wiped on the surface of an ingot by using a towel dipped with a butanone or acetone cleaning agent, then the surface of the ingot is wiped by using a clean dry towel, and the residual butanone or acetone on the surface is removed by air purging, so that the wiping surface with white paper after wiping is prevented from blackening, and interlayer slag inclusion is avoided.

The invention has the advantages that:

1. according to the invention, a spot welding and welding mode is adopted, steel strips are required to be packed in a transfer process so as to avoid falling off risks, but in the ingot casting soaking process, due to the fact that the temperature is high, the steel strips are easy to leave traces on the surfaces, and due to the fact that the temperature of the composite ingot casting is reduced in the steel strip shearing process, the two factors can cause the aluminum adhesion of the rollers in the subsequent rolling process, the problem of rolling black lines is further formed, the surface quality is unqualified, and the yield of products is reduced.

2. The core ingot and the base plate are fastened in a riveting mode, so that the bonding property and the fastening property of the core ingot and the base plate are firmer, the unfavorable application caused by packing a steel strip in the heat treatment process is avoided, meanwhile, the rapid continuity from soaking to entering a hot rolling process is solved, the temperature drop problem is avoided, the structure and the performance in the subsequent rolling process are effectively controlled, a sheet with higher surface quality and high performance can be obtained, and the production and preparation method of the high-performance cladding composite welding for aviation is further obtained.

3. The coating process of the invention is designed as follows: according to the requirement of the thickness of the coating layer, the thickness of the coating layer is designed by taking the final coating layer thickness higher than the required 50% allowance as a standard for the thickness of the original slab ingot, the rolling process parameters and the like. According to the invention, through the research of a large-size ingot casting homogenization process, the optimal homogenization process is determined, so that the content of the homogenized crystalline phase is lower than 2.0%; the method for producing the 7-series aluminum alloy clad skin sheet for aviation, which has high quality surface and better coating uniformity, is matched by adopting a hot rolling and cold rolling process.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a technical protocol of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1:

1. controlling chemical components: the invention adopts a semi-continuous casting mode to produce the flat ingot with the ingot size (400 + 620mm (thickness) × 1200 + 2200mm (width) × 2000 + 8000mm (length)) and controls the alloy components to be within the ranges of Si content being lower than 0.08%, Fe content being lower than 0.15%, Zn content being 5.6% -5.9%, Cu content being 1.3% -1.6%, Mg content being 2.4% -2.7%, Mn content being lower than 0.1%, Cr content being 0.18% -0.21%, Ti content being lower than 0.1%, other impurity elements, the single element is not more than 0.05%, and the total is not more than 0.15%.

2. The preparation method of the slab ingot alloy comprises the following steps: preparing raw materials according to the components and mass percent of the aluminum alloy sheet. Putting the raw materials into a smelting furnace, adding a remelting aluminum ingot and waste materials of the same alloy, smelting at 740 ℃, adding a covering agent after the melting is started, starting electromagnetic stirring after 60-70% of the aluminum alloy raw materials are melted, adjusting components after the aluminum alloy raw materials are completely melted, adding an intermediate alloy or an additive to adjust the components, then slagging off, sampling and detecting chemical components, and transferring the melt to a holding furnace after the components are proper. Refining by adopting mixed gas at the furnace side for 30-50min, standing for 40min when the temperature of the melt reaches 710-740 ℃, and casting into an aluminum alloy ingot through on-line (SNIF degassing, adding a refiner (Al5Ti1B point input amount is 1.5-2.0kg/t) and CCF two-stage filtration). The process control hydrogen content is less than 0.12mL/100g.Al, the Na content is within 2ppm, and the Ca content is within 3 ppm. The removal rate of the slag with the size of more than 20 mu m is more than 95 percent. Ensuring that the content of hydrogen and slag in the melt meets the requirement of aviation aluminum alloy.

3. And (3) homogenization process: the ingot is put into a homogenizing furnace for homogenizing heat treatment, a two-stage homogenizing process of 460-. After the ingot casting is finished, obtaining a high-quality soaking ingot with the volume fraction of the residual second phase less than 2.0% through an optimized homogenization process.

4. Coating design: the clad aluminum plate is a low-alloying 7-series aluminum plate with higher corrosion resistance, and the thickness of the clad plate is 13-15 mm. For the clad aluminum sheet with the finished thickness of 1.6-3.25, the minimum cladding rate is 2%, the nominal cladding rate is 3%, the thickness of the clad plate thickness T used for the clad aluminum sheet is 13-15mm, the width of the clad plate is equal to the effective rolling surface width of the core ingot- (25 +/-15 mm) × 2, and the length of the clad plate is equal to the length of the core ingot- (200 +/-10 mm) × 2.

5. Preparing before composite welding: the coating material is brushed on one side before use to ensure the brushing quality, the brushing layer is uniform and has no omission, and the brushing surface is strictly forbidden to have dust, oil stain, aluminum scraps and other foreign matters, so as to remove the surface oxide layer. Cleaning the surface of the cast ingot by dipping in a butanone or acetone cleaning agent, cleaning the surface of the cast ingot by using a clean dry towel, and removing residual butanone or acetone on the surface by air blowing, so that the surface is polished by using white paper after cleaning, and interlayer slag is prevented from being formed, thereby avoiding the risk of 'bag penetration' of the cladding plate in the subsequent use process.

6. And (3) welding process: after the coating material is attached to the cast ingot, the periphery of the coating material is 20-30mm away from the edge, the coating material is fixedly welded in a bolt fastening mode every 1000-1500mm in the length direction, and the welding material is 7075-F aluminum alloy, so that the fixing strength of the coating material is ensured, and the coating material has high ductility.

7. The hot rolling process comprises the following steps: and (4) placing the composite ingot into a preheating furnace, heating to the temperature of 450-470 ℃, preserving heat for 2-5h, and carrying out hot rough rolling. Setting hot rough rolling for 20-25 times, welding and rolling for the first two times, controlling the rolling reduction by 1-3mm and the rolling speed to be 0.35-0.5 m/s. The latter pass adopts conventional rolling mode to provide sufficient lubrication, and the spraying amount of the emulsion is 20-40% and 50-80%. The rolling reduction of each pass is controlled to be less than or equal to 30mm, the rolling speed is controlled to be less than or equal to 2.0m/s, the roller surface is cleaned by using a brush roller in the rolling gap, the final rolling temperature is controlled to be 300-330 ℃, and the thickness of the hot rolled finished product is 7.0-8.0 mm. After rolling, the surface has no obvious black strips, the oxidation grade is more than grade B, and the surface has no bulge phenomenon.

8. The cold rolling process comprises the following steps: for a thin plate with the thickness of 1.6-3.25mm, a hot-rolled plate with the thickness of 7.0-8.0 is subjected to 3 cold rolling to be 1.6-3.25 mm.

The obtained product has good surface quality, does not have the defects of scratch, black stripes and the like, and simultaneously better solves the problem of uneven thickness of the coating layer.

Example 2

1. Controlling chemical components: the invention adopts a semi-continuous casting mode to produce the flat ingot with the ingot size (400 + 620mm (thickness) × 1200 + 2200mm (width) × 2000 + 8000mm (length)) and controls the alloy components to be within the ranges of Si content being lower than 0.08%, Fe content being lower than 0.15%, Zn content being 5.6% -5.9%, Cu content being 1.3% -1.6%, Mg content being 2.4% -2.7%, Mn content being lower than 0.1%, Cr content being 0.18% -0.21%, Ti content being lower than 0.1%, other impurity elements, the single element is not more than 0.05%, and the total is not more than 0.15%.

2. The preparation method of the slab ingot alloy comprises the following steps: preparing raw materials according to the components and mass percent of the aluminum alloy sheet. Putting the raw materials into a smelting furnace, adding a remelting aluminum ingot and waste materials of the same alloy, smelting at 740 ℃, adding a covering agent after the melting is started, starting electromagnetic stirring after 60-70% of the aluminum alloy raw materials are melted, adjusting components after the aluminum alloy raw materials are completely melted, adding an intermediate alloy or an additive to adjust the components, then slagging off, sampling and detecting chemical components, and transferring the melt to a holding furnace after the components are proper. Refining by adopting mixed gas at the furnace side for 30-50min, standing for 40min when the temperature of the melt reaches 710-740 ℃, and casting into an aluminum alloy ingot through on-line (SNIF degassing, adding a refiner (Al5Ti1B point input amount is 1.5-2.0kg/t) and CCF two-stage filtration). The process control hydrogen content is less than 0.12mL/100g.Al, the Na content is within 2ppm, and the Ca content is within 3 ppm. The removal rate of the slag with the size of more than 20 mu m is more than 95 percent. Ensuring that the content of hydrogen and slag in the melt meets the requirement of aviation aluminum alloy.

3. And (3) homogenization process: the ingot is put into a homogenizing furnace for homogenizing heat treatment, a two-stage homogenizing process of 460-. After the ingot casting is finished, obtaining a high-quality soaking ingot with the volume fraction of the residual second phase less than 2.0% through an optimized homogenization process.

4. Coating design: the clad aluminum plate is a low-alloying 7-series aluminum plate with higher corrosion resistance, and the thickness of the clad plate is 13-15 mm. For the clad aluminum sheet with the finished thickness of 1.6-3.25, the minimum cladding rate is 2%, the nominal cladding rate is 3%, the thickness of the clad plate thickness T used for the clad aluminum sheet is 13-15mm, the width of the clad plate is equal to the effective rolling surface width of the core ingot- (25 +/-15 mm) × 2, and the length of the clad plate is equal to the length of the core ingot- (200 +/-10 mm) × 2.

5. Preparing before composite welding: the coating material is brushed on one side before use to ensure the brushing quality, the brushing layer is uniform and has no omission, and the brushing surface is strictly forbidden to have dust, oil stain, aluminum scraps and other foreign matters, so as to remove the surface oxide layer. Cleaning the surface of the cast ingot by dipping in a butanone or acetone cleaning agent, cleaning the surface of the cast ingot by using a clean dry towel, and removing residual butanone or acetone on the surface by air blowing, so that the surface is polished by using white paper after cleaning, and interlayer slag is prevented from being formed, thereby avoiding the risk of 'bag penetration' of the cladding plate in the subsequent use process.

6. And (3) welding process: after the coating material is attached to the cast ingot, the periphery of the coating material is 20-30mm away from the edge, the coating material is fixedly welded in a bolt fastening mode every 1000-1500mm in the length direction, and the welding material is 1050/7075-T aluminum alloy.

7. The hot rolling process comprises the following steps: and (4) placing the composite ingot into a preheating furnace, heating to the temperature of 450-470 ℃, preserving heat for 2-5h, and carrying out hot rough rolling. Setting hot rough rolling for 20-25 times, welding and rolling for the first two times, controlling the rolling reduction by 1-3mm and the rolling speed to be 0.35-0.5 m/s. The latter pass adopts conventional rolling mode to provide sufficient lubrication, and the spraying amount of the emulsion is 20-40% and 50-80%. The rolling reduction of each pass is controlled to be less than or equal to 30mm, the rolling speed is controlled to be less than or equal to 2.0m/s, the roller surface is cleaned by using a brush roller in the rolling gap, the final rolling temperature is controlled to be 300-330 ℃, and the thickness of the hot rolled finished product is 7.0-8.0 mm.

8. The cold rolling process comprises the following steps: for a thin plate with the thickness of 1.6-3.25mm, a hot-rolled plate with the thickness of 7.0-8.0 is subjected to 3 cold rolling to be 1.6-3.25 mm.

After rolling, it is found that 1050 pure aluminum is adopted as a fastening material, and after rolling, a long pressing mark appears at a fastening position, mainly because the too soft deformation of the material is severe compared with that of a cladding material; the 7075-T6 aluminum alloy is adopted as a fastening material, cracks appear in a contact area, and the cracks are generated mainly because the aluminum alloy is harder than a cladding material and the deformation is inconsistent during rolling.

Example 3

1. Controlling chemical components: the invention adopts a semi-continuous casting mode to produce the flat ingot with the ingot size (400 + 620mm (thickness) × 1200 + 2200mm (width) × 2000 + 8000mm (length)) and controls the alloy components to be within the ranges of Si content being lower than 0.08%, Fe content being lower than 0.15%, Zn content being 5.6% -5.9%, Cu content being 1.3% -1.6%, Mg content being 2.4% -2.7%, Mn content being lower than 0.1%, Cr content being 0.18% -0.21%, Ti content being lower than 0.1%, other impurity elements, the single element is not more than 0.05%, and the total is not more than 0.15%.

2. The preparation method of the slab ingot alloy comprises the following steps: preparing raw materials according to the components and mass percent of the aluminum alloy sheet. Putting the raw materials into a smelting furnace, adding a remelting aluminum ingot and waste materials of the same alloy, smelting at 740 ℃, adding a covering agent after the melting is started, starting electromagnetic stirring after 60-70% of the aluminum alloy raw materials are melted, adjusting components after the aluminum alloy raw materials are completely melted, adding an intermediate alloy or an additive to adjust the components, then slagging off, sampling and detecting chemical components, and transferring the melt to a holding furnace after the components are proper. Refining by adopting mixed gas at the furnace side for 30-50min, standing for 40min when the temperature of the melt reaches 710-740 ℃, and casting into an aluminum alloy ingot through on-line (SNIF degassing, adding a refiner (Al5Ti1B point input amount is 1.5-2.0kg/t) and CCF two-stage filtration). The process control hydrogen content is less than 0.12mL/100g.Al, the Na content is within 2ppm, and the Ca content is within 3 ppm. The removal rate of the slag with the size of more than 20 mu m is more than 95 percent. Ensuring that the content of hydrogen and slag in the melt meets the requirement of aviation aluminum alloy.

3. And (3) homogenization process: the ingot is put into a homogenizing furnace for homogenizing heat treatment, a two-stage homogenizing process of 460-. After the ingot casting is finished, obtaining a high-quality soaking ingot with the volume fraction of the residual second phase less than 2.0% through an optimized homogenization process.

4. Coating design: the clad aluminum plate is a low-alloying 7-series aluminum plate with higher corrosion resistance, and the thickness of the clad plate is 13-15 mm. For the clad aluminum sheet with the finished thickness of 1.6-3.25, the minimum cladding rate is 2%, the nominal cladding rate is 3%, the thickness of the clad plate thickness T used for the clad aluminum sheet is 13-15mm, the width of the clad plate is equal to the effective rolling surface width of the core ingot- (25 +/-15 mm) × 2, and the length of the clad plate is equal to the length of the core ingot- (200 +/-10 mm) × 2.

5. Preparing before composite welding: the coating material is brushed on one side before use to ensure the brushing quality, the brushing layer is uniform and has no omission, and the brushing surface is strictly forbidden to have dust, oil stain, aluminum scraps and other foreign matters, so as to remove the surface oxide layer. Cleaning the surface of the cast ingot by dipping in a butanone or acetone cleaning agent, cleaning the surface of the cast ingot by using a clean dry towel, and removing residual butanone or acetone on the surface by air blowing, so that the surface is polished by using white paper after cleaning, and interlayer slag is prevented from being formed, thereby avoiding the risk of 'bag penetration' of the cladding plate in the subsequent use process.

6. And (3) welding process: after the coating material is attached to the cast ingot, the periphery of the coating material is 20-30mm away from the edge, the coating material is fixedly welded in a bolt fastening mode every 2000mm or 500mm in the length direction, and the welding material is 7075-O state aluminum alloy.

7. The hot rolling process comprises the following steps: and (4) placing the composite ingot into a preheating furnace, heating to the temperature of 450-470 ℃, preserving heat for 2-5h, and carrying out hot rough rolling. Setting hot rough rolling for 20-25 times, welding and rolling for the first two times, controlling the rolling reduction by 1-3mm and the rolling speed to be 0.35-0.5 m/s. The latter pass adopts conventional rolling mode to provide sufficient lubrication, and the spraying amount of the emulsion is 20-40% and 50-80%. The rolling reduction of each pass is controlled to be less than or equal to 30mm, the rolling speed is controlled to be less than or equal to 2.0m/s, the roller surface is cleaned by using a brush roller in the rolling gap, the final rolling temperature is controlled to be 300-330 ℃, and the thickness of the hot rolled finished product is 7.0-8.0 mm.

8. The cold rolling process comprises the following steps: for a thin plate with the thickness of 1.6-3.25mm, a hot-rolled plate with the thickness of 7.0-8.0 is subjected to 3 cold rolling to be 1.6-3.25 mm.

The fastening distance of 2000mm is adopted, so that the package is easy to wear in the hoisting process, and the good fastening effect is not achieved mainly because the fastening distance is larger; the rolled surface is easy to wrinkle due to the fact that the distance between the clad plate and the base plate is small, the clad plate and the base plate are completely fastened, the core of the composite plate is difficult to extend outwards in the rolling process, deformation is easy to occur, and the phenomenon of wrinkling is easy to occur.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.