Aluminum alloy sheet having high stability and high baking hardening performance, preparation method therefor and use thereof

Abstract

Disclosed in the present invention are an aluminum alloy sheet having high stability and high baking hardening performance, a preparation method therefor and a use thereof. The aluminum alloy sheet comprises the following components in percentage by mass: 0.20-1.50% of Si, less than or equal to 0.40% of Fe, 0.06-0.30% of Cu, 0.05-0.2% of Mn, 0.20-0.80% of Mg, less than or equal to 0.10% of Cr, 0.01-0.05% of Ti, and 0.005-0.045% of Sn, with the balance being Al. The composition of the aluminum alloy sheet and the preparation process according to the present invention are greatly different from those in the prior art. According to the sheet prepared in the present invention, vacancy, cluster, and precipitated phase states are effectively regulated, thereby greatly improving the stability of storage of the sheet at room temperature and the paint-baking hardenability of the sheet. The sheet also has low yield strength in a T4P state, high stability of storage at room temperature, and high paint-baking performance in a T8X state after baking, and can be widely used in industries such as automobiles.

Description

High-stability aluminum alloy sheet with high bake-hardening properties, its preparation method and application Technical Field

[0001] This invention relates to the field of aluminum alloy manufacturing technology, specifically to an aluminum alloy sheet with high stability and high bake hardening performance, its preparation method, and its application. Background Technology

[0002] Gasoline vehicle emissions are a major source of global air pollution. Lightweighting of automobiles is an important means of energy conservation, emission reduction, and pollution reduction. Aluminum alloy sheets are considered ideal materials for automotive lightweighting due to their light weight, high specific strength, and excellent overall performance. Currently, 5xxx and 6xxx aluminum alloys are mainly used to manufacture automotive sheet metal. Among them, 6xxx alloys are the most widely used and have a trend of further expanding their application range and replacing 5xxx aluminum alloys, and are also more conducive to recycling.

[0003] In recent years, some universities and research institutes in China have conducted research on 6xxx aluminum alloy automotive steel sheets, but most have only focused on some performance indicators, with few reports on Sn and Cu composite microalloying. For example:

[0004] Patent CN 117305670 B improves paint baking performance by controlling the cooling rate. However, it does not involve the addition of Sn and Cu composite microalloys.

[0005] Patent CN 107699755 B adds trace elements such as Sn and In, as well as a large amount of Zn, to improve the performance of the paint, but increases the cost and difficulty of industrial production.

[0006] Japanese patents JP6301175B2 and JP6190308B2 also use Sn to improve the material's room temperature stability and baking performance, but they do not add Cu to further enhance the baking effect. In addition, they use lower homogenization and solution temperatures. Summary of the Invention

[0007] The present invention aims to provide an aluminum alloy sheet with high stability and high bake hardening performance, its preparation method and application. The aluminum alloy sheet has both low yield strength and high room temperature storage stability in the T4P state and high paint performance in the T8X state after baking.

[0008] To achieve the above objectives, according to one aspect of the present invention, an aluminum alloy sheet with high stability and high bake-hardening performance is provided. The aluminum alloy sheet comprises the following components by mass percentage: Si: 0.20%–1.50%; Fe: ≤0.40%; Cu: 0.06–0.30%; Mn: 0.05%–0.2%; Mg: 0.20%–0.80%; Cr: ≤0.10%; Ti: 0.01–0.05%; Sn: 0.005–0.045%, and the balance Al.

[0009] Further, aluminum alloy sheets are prepared by the following preparation method: (1) casting aluminum alloy melt into ingots; (2) homogenizing the ingots; (3) hot rolling and cold rolling the homogenized ingots in sequence to prepare cold-rolled coils; (4) solution treatment and quenching treatment of the cold-rolled coils to obtain coils; (5) pre-aging treatment of the quenched coils to obtain T4P state coils; (7) uncoiling, straightening and slicing the pre-aged T4P state coils to obtain aluminum alloy sheets.

[0010] Further, the homogenization process in step (2) involves heating to 480-520℃ at a rate of 40-70℃ / h and holding for 4-10h, and then heating to 560-580℃ at a rate of 20-40℃ / h and holding for 6-10h.

[0011] Furthermore, in step (3), the hot rolling temperature is 560-580℃, and the thickness of the hot-rolled plate is 4-8mm.

[0012] Furthermore, in step (3), the thickness of the sheet material after hot rolling and cold rolling is 0.5-3.0 mm.

[0013] Furthermore, the solution treatment in step (4) is completed in a continuous annealing furnace with an air cushion, where the temperature is raised to 565-585°C at a rate of 5°C / s or higher, held for 0.5-5 minutes, and then cooled to room temperature with water at a rate of 30°C / s or higher.

[0014] Furthermore, the pre-aging treatment in step (5) is carried out in a box furnace at 60-90℃ for 4-10 hours.

[0015] Furthermore, for aluminum alloy sheets: the yield strength of T4P state sheets is less than 100MPa after 7 days, and the yield strength increment from 7 days to 180 days is less than 25MPa. T4P state sheets are pre-stretched by 2% and baked at 185℃ for 20 minutes to obtain T8X state sheets, with a yield strength greater than 200MPa and a paint increment greater than 130MPa.

[0016] According to another aspect of the present invention, an application of any of the above-mentioned high-stability, high-bake-hardening-performance aluminum alloy sheets in automobile manufacturing is provided.

[0017] According to another aspect of the present invention, a method for preparing an aluminum alloy sheet with high stability and high bake-hardening performance is provided. The preparation method includes: (1) casting an aluminum alloy melt ingot; (2) homogenizing the ingot; (3) hot rolling and cold rolling the homogenized ingot sequentially to prepare a cold-rolled coil; (4) solution treatment and quenching of the cold-rolled coil to obtain a coil material; (5) pre-aging treatment of the quenched coil material to obtain a T4P state coil material; (7) uncoiling, straightening and slicing the pre-aged T4P state coil material to obtain an aluminum alloy sheet; wherein the aluminum alloy sheet material includes the following components by mass percentage: Si: 0.20%~1.50%; Fe: ≤0.40%; Cu: 0.06-0.30%; Mn: 0.05%~0.2%; Mg: 0.20%~0.80%; Cr: ≤0.10%; Ti: 0.01-0.05; Sn: 0.005-0.045%, and the balance Al;

[0018] Preferably, the homogenization process in step (2) involves heating to 480-520℃ at a rate of 40-70℃ / h and holding for 4-10h, followed by heating to 560-580℃ at a rate of 20-40℃ / h and holding for 6-10h.

[0019] Preferably, the hot rolling temperature in step (3) is 560-580℃, and the thickness of the hot-rolled plate is 4-8mm;

[0020] Preferably, the thickness of the sheet material after hot rolling and cold rolling in step (3) is 0.5-3.0 mm;

[0021] Preferably, the solution treatment in step (4) is completed in a continuous annealing furnace with an air cushion, where the temperature is raised to 565-585°C at a rate of 5°C / s or higher, held for 0.5-5 minutes, and then cooled to room temperature with water at a rate of 30°C / s or higher.

[0022] Preferably, the pre-aging treatment in step (5) is performed by holding the material in a box furnace at 50-90°C for 4-10 hours.

[0023] Preferably, the aluminum alloy sheet has a yield strength of less than 100 MPa after 7 days in the T4P state and a yield strength increment of less than 25 MPa from 7 days to 180 days. The T4P state sheet is pre-stretched by 2% and baked at 185℃ for 20 minutes to obtain the T8X state sheet, which has a yield strength greater than 200 MPa and a paint increment greater than 130 MPa.

[0024] The aluminum alloy sheet composition and preparation process of this invention differ significantly from existing technologies. The sheet prepared by this invention effectively controls the state of vacancies, clusters and precipitates, thereby greatly improving the room temperature storage stability and paint curing properties of the sheet. It combines the low yield strength and high room temperature storage stability of the T4P state with the high paint curing performance of the T8X state after baking, and can be widely used in the automotive and other industries.

[0025] Specifically, the main difference between this invention and the prior art is that:

[0026] (1) This invention incorporates trace amounts of Sn and Cu elements, effectively utilizing Sn's ability to bind vacancies and inhibit natural aging, while also combining Cu's ability to enhance paint baking performance. Compared to adding a single alloying element, this further optimizes the sheet material's performance. By adding trace amounts of Sn, compared to the main alloying elements Mg and Si in 6xxx alloys, Sn has a stronger vacancy-binding ability, thus binding vacancies and inhibiting the diffusion of Mg and Si elements, significantly improving the sheet material's stability at room temperature. Simultaneously, Sn releases vacancies during high-temperature baking, thereby enhancing paint baking performance. By adding trace amounts of Cu, its ability to enhance paint baking strengthening during high-temperature baking is utilized, further improving paint baking performance.

[0027] (2) This invention employs a two-stage homogenization process. On the one hand, this ensures the effective re-dissolution of Sn, and on the other hand, it fully considers the practicalities of industrial production. The use of slow heating takes into account the limitations of equipment capacity in industrial production, which prevents rapid heating. The purpose of the first-stage homogenization is to promote the re-dissolution of the low-melting-point phase, thereby increasing its melting point and thus raising the temperature of the second-stage homogenization. The second-stage homogenization temperature needs to reach above 560℃ to ensure more complete dissolution of Sn, solving the problem of low Sn solubility in aluminum, while also preventing the material from overheating and becoming unusable due to excessively high temperatures.

[0028] (3) The present invention uses a high temperature solution temperature to ensure that Sn element is dissolved more fully, thereby effectively utilizing the characteristics of Sn element, while avoiding the material being overburned and scrapped due to excessive temperature.

[0029] (4) The present invention can significantly improve stability and paint performance by adding only a very small amount of Sn and Cu elements, without the need to add a large amount of Zn and Cu or expensive Sc and Zr elements as in the prior art, and the cost is controllable.

[0030] (5) This invention does not require additional processes or equipment and can meet the requirements for industrial-scale preparation.

[0031] The technological advancements of this invention are mainly reflected in:

[0032] (1) By adding trace amounts of Sn and Cu elements, the present invention can achieve a low yield strength and stable performance in the T4P state of the sheet material, which greatly improves its stamping performance and can meet the forming requirements of more complex parts.

[0033] (2) By adding trace amounts of Sn and Cu elements, this invention can achieve higher paint performance after the board is baked, thereby achieving material thinning under the same strength, reducing material usage, and further improving the lightweight effect.

[0034] (3) This invention fully considers the problems that Sn cannot exert its beneficial effects when it is too little, and that it cannot be fully dissolved back into the matrix when it is too much, leading to performance deterioration. Therefore, the Sn content is strictly controlled. In addition, this invention fully considers the problems that Cu cannot exert its beneficial effects when it is too little, and that Cu will lead to increased strength and decreased stamping performance of T4P state plates when it is too much, as well as decreased corrosion performance of plates. Therefore, the Cu content is strictly limited.

[0035] (4) The present invention uses a process without intermediate annealing to prepare 6xxx alloy plates, which has a short process and is conducive to industrial production; in addition, it has low carbon emissions, which is more environmentally friendly; and it has low cost, which is conducive to market promotion. Detailed Implementation

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0037] Terminology Explanation:

[0038] Weight percentage: The percentage of a certain alloy component by mass (weight) out of the total mass.

[0039] Yield strength: The yield limit of an aluminum alloy when it undergoes yielding. It is defined as the stress value at which 0.2% residual deformation occurs. The stress-strain curve is obtained through a uniaxial tensile test, and the yield strength data is derived from the curve.

[0040] T4P yield strength: The yield strength of the finished sheet material obtained after melting and casting, homogenization, hot rolling, cold rolling, solution treatment, pre-aging, and slicing. After the finished sheet material is left to stand at room temperature for 7 days, its mechanical properties are tested by uniaxial tensile testing to obtain the yield strength.

[0041] T8X yield strength: After the finished sheet material was left to stand at room temperature for 7 days, it was pre-stretched by 2% using a uniaxial tensile tester, and then held in an oil bath oven at 185℃ for 20 minutes to simulate the baking process in the actual production process of the OEM. The yield strength under the baked condition was tested by uniaxial tensile test.

[0042] Paint yield: The difference between the yield strength after baking and the initial yield strength.

[0043] In the application, high stability refers to: the yield strength of T4P state sheet material is less than 100MPa after 7 days, and the yield strength increment from 7 days to 180 days is less than 25MPa.

[0044] High bake hardening performance: T4P state sheet is pre-stretched by 2% and then baked at 185℃ for 20 min to obtain T8X state sheet, with yield strength greater than 200MPa and paint addition greater than 130MPa.

[0045] After undergoing solution treatment and pre-aging at the aluminum processing plant, 6xxx aluminum alloy sheets are prepared into T4P condition sheets and then sent to the stamping plant for further stamping. In the T4P condition, the sheets require a lower yield strength to meet the stamping requirements. Furthermore, due to the natural aging characteristic of 6xxx aluminum alloys, the sheet strength increases with prolonged storage time, leading to deterioration in formability. Therefore, it is necessary to suppress natural aging to ensure stable sheet performance and meet forming requirements. After stamping, the sheets are coated. 6xxx aluminum alloy sheets have heat-treatable strengthening properties; during the high-temperature drying process of the paint, the sheet strength can be significantly increased, thus meeting the strength performance requirements.

[0046] At room temperature, Sn exhibits a stronger vacancy-binding ability compared to Mg and Si, the main alloying elements in 6xxx alloys. Therefore, it can more effectively bind vacancies and inhibit the diffusion of Mg and Si, significantly improving the stability of the sheet material at room temperature. During high-temperature baking, the vacancies are released again, thereby enhancing the paint coating performance. Cu further improves the paint coating performance during the baking process.

[0047] Based on this, the present invention proposes the following technical solutions.

[0048] According to a typical embodiment of the present invention, an aluminum alloy sheet with high stability and high bake-hardening performance is provided. The aluminum alloy sheet comprises the following components by mass percentage: Si: 0.20%–1.50%; Fe: ≤0.40%; Cu: 0.06–0.30%; Mn: 0.05%–0.2%; Mg: 0.20%–0.80%; Cr: ≤0.10%; Ti: 0.01–0.05%; Sn: 0.005–0.045%, and the balance Al.

[0049] This invention combines trace amounts of Sn and Cu elements, effectively utilizing Sn's ability to bind vacancies and inhibit natural aging, while also incorporating Cu's ability to enhance paint coating performance. Compared to adding a single alloying element, this further optimizes the sheet material's properties. By adding trace amounts of Sn, compared to the main alloying elements Mg and Si in 6xxx alloys, Sn has a stronger vacancy-binding ability, thus binding vacancies and inhibiting the diffusion of Mg and Si elements, significantly improving the sheet material's stability at room temperature. Furthermore, it utilizes the ability to release vacancies during high-temperature baking, thereby enhancing paint coating performance. The addition of trace amounts of Cu further enhances paint coating performance by utilizing Cu's ability to strengthen the coating during high-temperature baking.

[0050] Furthermore, this invention only requires the addition of a very small amount of Sn and Cu elements to significantly improve stability and paint performance, without the need to add large amounts of Zn and Cu or expensive elements such as Sc and Zr as described in other patents, thus keeping costs under control.

[0051] According to a typical embodiment of the present invention, aluminum alloy sheet is prepared by the following preparation method: (1) casting aluminum alloy melt ingot; (2) homogenizing the ingot; (3) hot rolling and cold rolling the homogenized ingot in sequence to prepare a cold rolled coil; (4) solution treatment and quenching treatment of the cold rolled coil to obtain a coil material; (5) pre-aging treatment of the quenched coil material to obtain a T4P state coil material; (7) uncoiling, straightening and slicing the pre-aged T4P state coil material to obtain an aluminum alloy sheet.

[0052] This invention does not require additional processes or equipment and can meet the requirements for industrial-scale production.

[0053] Preferably, the homogenization process in step (2) involves heating to 480-520℃ at a rate of 40-70℃ / h and holding for 4-10 hours, followed by heating to 560-580℃ at a rate of 20-40℃ / h and holding for 6-10 hours. In other words, this invention employs a two-stage homogenization process. This is to ensure effective re-dissolution of Sn while also taking into full account the realities of industrial production. The use of slow heating takes into account the limitations of equipment capacity during industrial production, which prevent rapid heating. The purpose of the first-stage homogenization is to promote the re-dissolution of the low-melting-point phase, thereby increasing its melting point and thus raising the temperature of the second-stage homogenization. The second-stage homogenization temperature needs to reach above 560℃ to ensure more complete dissolution of Sn and solve the problem of low Sn solubility in aluminum. However, excessively high temperatures can lead to overheating and material failure, so the temperature is controlled within the aforementioned range.

[0054] Preferably, the hot rolling temperature in step (3) is 560-580℃, and the thickness of the hot-rolled plate is 4-8mm. Under these conditions, the homogenization temperature and hot rolling temperature of the alloy are higher than those of conventional 6xxx alloys, which can fully utilize the role of Sn. Preferably, the thickness of the plate after hot rolling and cold rolling in step (3) is 0.5-3.0mm;

[0055] In a preferred embodiment of this application, the solution treatment in step (4) is completed in an air-cushion continuous annealing furnace, where the temperature is raised to 565-585°C at a rate of 5°C / s or higher, held for 0.5-5 minutes, and then water-cooled to room temperature at a rate of 30°C / s or higher. The high solution temperature used in this invention is to ensure more complete dissolution of the Sn element, thereby effectively utilizing the properties of Sn. However, excessively high temperatures can lead to overheating and spoilage of the material, so the temperature is controlled within the aforementioned range.

[0056] Preferably, the pre-aging treatment in step (5) is carried out in a box furnace at 60-90℃ for 4-10 hours. During the pre-aging process, a certain number of clusters will precipitate, the purpose of which is: 1) to consume solutes and vacancies, thereby inhibiting natural aging and improving the stability of room temperature storage; 2) the precipitated clusters can be directly converted into the strengthening phase during the baking process, thereby improving the baking strength.

[0057] Preferably, the aluminum alloy sheet has a yield strength of less than 100 MPa after 7 days in the T4P state and a yield strength increment of less than 25 MPa from 7 days to 180 days. The T4P state sheet is pre-stretched by 2% and baked at 185℃ for 20 minutes to obtain the T8X state sheet, which has a yield strength greater than 200 MPa and a paint increment greater than 130 MPa.

[0058] The present invention will be further supplemented and explained below with reference to specific implementation schemes. Obviously, the described embodiments are only some embodiments of the present invention, and not all of them.

[0059] Example

[0060] First, pure aluminum and various intermediate alloys are melted according to the composition ratio shown in Table 1. After refining, the melt is cast into ingots using a semi-continuous casting equipment. The ingots are then cut and milled before being placed in a heat treatment furnace for homogenization. After homogenization, the ingots are directly taken out of the furnace for hot rolling. After hot rolling, the resulting hot-rolled plates are cold-rolled. The cold-rolled plates are then solution-treated, quenched, and pre-aged before being uncoiled, straightened, and sliced ​​to obtain finished plates in the T4P state. The specific experimental parameters in the examples are shown in Table 2. In addition, unless otherwise specified in the following examples, the hot rolling temperature in step (3) is 570℃, the thickness of the hot-rolled plate is 6mm, and the thickness of the cold-rolled plate after hot rolling in step (3) is 2.0mm. The pre-aging treatment in step (5) is performed in a box furnace at 80℃ for 6 hours.

[0061] Table 1. Composition of aluminum alloy sheets with high stability and high bake-hardening properties

[0062] Table 2. Preparation process of aluminum alloy sheets with high stability and high bake hardening performance

[0063] Finished T4P condition sheets were tested for mechanical properties after being left at room temperature for 7 days and 180 days. Baking performance was assessed using the evaluation standards of most OEMs, which involved pre-stretching the finished sheet by 2%, then holding it in an oil bath furnace at 185℃ for 20 minutes, followed by water quenching to room temperature before testing mechanical properties. Mechanical properties were tested according to GB / T 13239-2006, "Metallic Materials - Low Temperature Tensile Testing".

[0064] Table 3 Mechanical properties (MPa) of high-baking 6xxx aluminum alloy sheets

[0065] Examples 1-2 and Comparative Examples 1-2: according to 1 in Table 1 # The aluminum alloy composition preparation examples 1-2, corresponding to alloy numbers 1-1 and 1-2, and comparative examples 1-2, corresponding to alloy numbers 1-3 and 1-4, are shown in Table 2. The mechanical properties of the final finished plates are shown in Table 3. The mechanical properties of the finished plates obtained in Examples 1-2 are qualified. The mechanical properties of the plates obtained in Comparative Examples 1-2 are unqualified. In Comparative Example 1, the homogenization temperature was too low, and the Sn element was not completely dissolved, failing to play its due role, resulting in poor room temperature stability of the T4P state plate and insufficient paint strength of the T8X state plate; in Comparative Example 2, the pre-aging temperature was too high, resulting in excessively high strength of the T4P state plate, which is not conducive to stamping.

[0066] Examples 3-4, Comparative Example 3: according to 2 in Table 1 # Examples 3-4 (alloy numbers 2-1 and 2-2) and Comparative Example 3 (alloy number 2-3) were prepared using aluminum alloys. Their preparation processes are shown in Table 2, and the mechanical properties of the final finished sheets are shown in Table 3. The finished sheets obtained in Examples 3-4 have satisfactory mechanical properties. The finished sheet obtained in Comparative Example 3 has unsatisfactory mechanical properties. The homogenization temperature in Comparative Example 3 was too high, leading to overheating and material scrap.

[0067] Examples 5-6, Comparative Example 4: according to 3 in Table 1 #Examples 5 and 6, corresponding to alloy numbers 3-1 and 3-2, and Comparative Example 4, corresponding to alloy number 3-3, were prepared using aluminum alloys. Their preparation processes are shown in Table 2, and the mechanical properties of the final finished sheets are shown in Table 3. The finished sheets obtained in Examples 5 and 6 have satisfactory mechanical properties. The finished sheets obtained in Comparative Example 4 have unsatisfactory mechanical properties. The solution temperature in Comparative Example 4 was too low, and the Sn element failed to completely dissolve, thus failing to play its proper role. This resulted in poor room temperature stability of the T4P state sheet and insufficient paint strength in the T8X state sheet.

[0068] Examples 7-8, Comparative Example 5: according to 4 in Table 1 # Examples 7 and 8, corresponding to alloy numbers 4-1 and 4-2, and Comparative Example 5, corresponding to alloy number 4-3, were prepared using aluminum alloys. Their preparation processes are shown in Table 2, and the mechanical properties of the final finished plates are shown in Table 3. The finished plates obtained in Examples 3 and 4 have satisfactory mechanical properties. The finished plate obtained in Comparative Example 5 has unsatisfactory mechanical properties. The solution treatment temperature in Comparative Example 5 was too high, leading to overheating and material scrap.

[0069] Comparative Example 6: According to 5 in Table 1 # Comparative Example 6, corresponding to alloy number 5-1, was prepared using aluminum alloys. Its preparation process is shown in Table 2, and the mechanical properties of the final finished sheet are shown in Table 3. The mechanical properties of the finished sheet obtained in Comparative Example 6 were unqualified. Insufficient Sn and Cu elements were added in Comparative Example 6, resulting in insufficient room temperature stability in the T4P state and insufficient paint strength in the T8X state.

[0070] Comparative Example 7: According to 6 in Table 1 # Comparative Example 7, corresponding to alloy number 6-1, was prepared using the process shown in Table 2, and the mechanical properties of the final finished sheet are shown in Table 3. The mechanical properties of the finished sheet obtained in Comparative Example 7 were unqualified. The excessively high content of Cu and Sn elements in Comparative Example 7 resulted in an excessively high yield strength in the T4P state sheet.

[0071] Comparative Example 8: According to 7 in Table 1 # Comparative Example 8, corresponding to alloy number 7-1, was prepared using the process shown in Table 2. The mechanical properties of the final finished sheet are shown in Table 3. The mechanical properties of the finished sheet obtained in Comparative Example 7 were substandard. The Cu element content in Comparative Example 7 was too low, resulting in insufficient paint addition.

[0072] Comparative Example 9: According to 8 in Table 1 # Comparative Example 9, corresponding to alloy number 8-1, was prepared using aluminum alloys. Its preparation process is shown in Table 2, and the mechanical properties of the final finished sheet are shown in Table 3. The finished sheet obtained in Comparative Example 7 failed to meet mechanical property standards. The Sn element content in Comparative Example 7 was too low, resulting in insufficient room temperature stability and insufficient paint yield.

[0073] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0074] (1) By adding trace amounts of Sn and Cu elements, this invention can achieve a low yield strength and stable performance in the T4P state of the sheet metal, which greatly improves its stamping performance and can meet the forming requirements of more complex parts.

[0075] (2) By adding trace amounts of Sn and Cu elements, this invention can achieve higher paint performance after the board is baked, thereby achieving material thinning under the same strength, reducing material usage, and further improving the lightweight effect;

[0076] (3) This invention fully considers the problems that Sn cannot play its beneficial role when it is too little, and that it cannot be fully dissolved back into the matrix when it is too much, leading to performance deterioration. Therefore, the Sn content is strictly controlled. In addition, this invention fully considers the problems that Cu cannot play its beneficial role when it is too little, and that Cu will lead to increased strength and decreased stamping performance of T4P state plates when it is too much, as well as decreased corrosion performance of plates. Therefore, the Cu content is strictly limited.

[0077] (4) The present invention uses a process without intermediate annealing to prepare 6xxx alloy plates, which has a short process and is conducive to industrial production; in addition, it has low carbon emissions, which is more environmentally friendly; and it has low cost, which is conducive to market promotion.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An aluminum alloy sheet with high stability and high bake-hardening performance, characterized in that, The aluminum alloy sheet comprises the following components by mass percentage: Si: 0.20%–1.50%; Fe: ≤0.40%; Cu: 0.06%–0.30%; Mn: 0.05%–0.2%; Mg: 0.20%~0.80%; Cr: ≤0.10%; Ti: 0.01-0.05; Sn: 0.005-0.045%, with the balance being Al.

2. The aluminum alloy sheet according to claim 1, characterized in that, The aluminum alloy sheet is prepared by the following method: (1) Cast the molten aluminum alloy into an ingot; (2) The ingot is homogenized; (3) The homogenized ingot is hot-rolled and cold-rolled sequentially to prepare a cold-rolled coil; (4) The cold-rolled coil is subjected to solution treatment and quenching to obtain a coil material; (5) The quenched coil is pre-aged to obtain a T4P state coil. (7) The T4P state coil after pre-aging treatment is unwound, straightened and sliced ​​to obtain the aluminum alloy sheet.

3. The aluminum alloy sheet according to claim 2, characterized in that, The homogenization process in step (2) involves heating the temperature to 480-520℃ at a rate of 40-70℃ / h and holding it at that temperature for 4-10h, and then heating the temperature to 560-580℃ at a rate of 20-40℃ / h and holding it at that temperature for 6-10h.

4. The aluminum alloy sheet according to claim 2, characterized in that, The hot rolling temperature in step (3) is 560-580℃, and the thickness of the hot-rolled plate is 4-8mm.

5. The aluminum alloy sheet according to claim 2, characterized in that, The thickness of the sheet material after hot rolling and cold rolling in step (3) is 0.5-3.0 mm.

6. The aluminum alloy sheet according to claim 2, characterized in that, The solution treatment in step (4) is completed in a continuous annealing furnace with an air cushion. The temperature is raised to 565-585°C at a rate of 5°C / s or higher, and held for 0.5-5 minutes. The temperature is then cooled to room temperature by water at a rate of 30°C / s or higher.

7. The aluminum alloy sheet according to claim 2, characterized in that, The pre-aging treatment in step (5) involves holding the material in a box furnace at 60-90℃ for 4-10 hours.

8. The aluminum alloy sheet according to any one of claims 1 to 7, characterized in that, The aluminum alloy sheet: the T4P state sheet has a yield strength of less than 100 MPa after 7 days and a yield strength increment of less than 25 MPa from 7 days to 180 days. The T4P state sheet is pre-stretched by 2% and baked at 185℃ for 20 minutes to obtain the T8X state sheet, which has a yield strength of more than 200 MPa and a paint increment of more than 130 MPa.

9. The application of the aluminum alloy sheet with high stability and high bake hardening performance as described in any one of claims 1 to 8 in automobile manufacturing.

10. A method for preparing an aluminum alloy sheet with high stability and high bake-hardening performance, characterized in that, include: (1) Cast the molten aluminum alloy into an ingot; (2) The ingot is homogenized; (3) The homogenized ingot is hot-rolled and cold-rolled sequentially to prepare a cold-rolled coil; (4) The cold-rolled coil is subjected to solution treatment and quenching to obtain a coil material; (5) The quenched coil is pre-aged to obtain a T4P state coil. (7) The T4P state coil after pre-aging treatment is unwound, straightened and sliced ​​to obtain the aluminum alloy sheet; The aluminum alloy sheet comprises the following components by mass percentage: Si: 0.20%–1.50%; Fe: ≤0.40%; Cu: 0.06–0.30%; Mn: 0.05%–0.2%; Mg: 0.20%–0.80%; Cr: ≤0.10%; Ti: 0.01–0.05%; Sn: 0.005–0.045%; and the balance Al.

Images