A 6000 series aluminum alloy material for automobile body panels and a high-efficiency and low-carbon preparation method thereof

Abstract

The invention discloses a 6000 series aluminum alloy material for automobile body panels and a high-efficiency and low-carbon preparation method thereof. The aluminum alloy is composed of the following components: Ho 0.05-0.12wt.%, Mg 0.45-0.65wt.%, Si 0.85-1.10wt.%, Cu 0.05-0.20wt.%, the remainder being Al and unavoidable impurities, and the Mg / Si content ratio is 0.4-0.7. The preparation method of the aluminum alloy thin plate comprises the following steps: (1) according to the aluminum alloy component ratio, the aluminum alloy raw material is smelted and cast to obtain a cast alloy ingot; (2) the ingot is directly hot-rolled and deformed without cooling after homogenization heat treatment, and then immediately coiled to obtain a hot-rolled strip coil, which is then cooled to room temperature and subjected to self-annealing treatment; (3) the hot-rolled strip coil is directly cold-rolled and deformed to obtain a cold-rolled plate strip without intermediate annealing treatment; (4) the plate strip is subjected to solid solution quenching and pre-aging treatment to obtain a T4P thin plate. The present invention forms a second phase with a suitable size and refines the grains through reasonable preparation method optimization, which significantly improves the forming performance of the thin plate and greatly shortens the preparation and processing steps.

Description

Technical Field

[0001] The invention relates to a 6000 series (Al-Mg-Si series) aluminum alloy material for automobile body covering parts with high formability and an efficient and low-carbon preparation method thereof, belonging to the technical field of aluminum alloy material preparation and processing. Background Art

[0002] In order to save energy, reduce emissions and increase driving range, fuel vehicles and new energy vehicles have an increasingly urgent need for lightweight vehicles. In the overall structure of a car, the car body accounts for about 30% of the total weight of the car. The use of lightweight materials to replace traditional car body steel plates has a significant weight reduction effect. Among all lightweight materials, aluminum alloy has become one of the ideal materials for car bodies due to its excellent comprehensive properties. Among all aluminum alloy materials, 6000 series aluminum alloy has the characteristics of medium strength, excellent corrosion resistance, weldability, easy surface coloring and recyclability. The most important thing is that it matches the existing automobile production system and can be hardened during the painting and baking process. Therefore, 6000 series aluminum alloy has become one of the most promising lightweight materials for automobile bodies.

[0003] Compared with mature automotive steel plates, the stamping performance of aluminum alloys is still its shortcoming. Therefore, researchers have improved the microstructure by adjusting the alloy composition, preparation and processing process, etc., in order to achieve the purpose of improving the stamping performance. The second phase, grains and texture in the microstructure of aluminum alloys are closely related to the alloy composition and preparation and processing process. The preparation and processing process of 6000 series aluminum alloy sheets are: smelting and casting → homogenization heat treatment → heating treatment → hot rolling deformation → intermediate annealing heat treatment → cold rolling deformation → intermediate annealing heat treatment → cold rolling deformation → solution treatment → pre-aging treatment → T4P state sheet. Its preparation process is relatively long, and the control requirements for each process are very high. Therefore, the 6000 series aluminum alloy sheet for automobile body is also the most difficult to manufacture among all sheets. In the preparation and processing of the above-mentioned 6000 series aluminum alloy thin plates, heating treatment is a necessary step before hot rolling. Its main function is to soften the ingot and reduce the deformation resistance to facilitate deformation. In addition, by adjusting its temperature, the microstructure can be adjusted; the intermediate annealing treatment mainly reduces or eliminates the energy stored in the deformation process to prevent this part of energy from coarsening the grains and precipitating phases; another function is to form a completely recrystallized structure or a randomly distributed grain orientation to improve the forming performance of the thin plate. If the existing preparation and processing process is adopted, the process is long, time-consuming, energy-intensive, and has high manufacturing costs. In addition, due to the large number of processes, it is difficult to control the process. If you want to obtain an ideal microstructure, it is difficult to control and the cost is high. Summary of the invention

[0004] The purpose of the present invention is to provide a 6000 series aluminum alloy for automobile body panels with high formability. According to the characteristics of the 6000 series aluminum alloy, elements that improve the grain structure are added to the alloy, and then the existing hot rolling and intermediate annealing processes are designed and optimized to achieve the purpose of regulating the microstructure and improving the formability.

[0005] Another object of the present invention is to provide a high-efficiency and low-carbon preparation method for 6000 series aluminum alloy thin plates. Through the reasonable design and optimization of the preparation process of 6000 series aluminum alloy thin plates, not only the optimal microstructure is obtained, but also the heating treatment before hot rolling and two intermediate annealing treatments are saved, thereby reducing the energy consumption and carbon emissions in the preparation process.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A 6000 series aluminum alloy for automobile body panels is composed of the following components by mass percentage: Ho 0.05-0.12wt.%, Mg 0.45-0.65wt.%, Si 0.85-1.10wt.%, Cu 0.05-0.20wt.%, Fe<0.15wt.%, and the balance is Al and unavoidable impurities, wherein the Mg / Si content ratio is 0.4-0.7.

[0008] The present invention improves the alloy structure by adjusting the Mg / Si mass ratio and adding the microalloying element Ho, and then combining the reasonable design and optimization of the preparation process; wherein the Ho element can refine the primary solidification phase and grains of the as-cast structure, and can also form dispersed particles Al in the homogenization process. x Ho, inhibits recrystallization and improves the uniformity of the organization. At the same time, the dispersed particles are also conducive to the random distribution of grain orientation, ultimately improving the forming performance.

[0009] Preferably, the aluminum alloy consists of the following components: Ho 0.08~0.10wt.%, Mg 0.45~0.65wt.%, Si0.85~1.10wt.%, Cu 0.05~0.20wt.%, Fe<0.15wt.%, and the remainder is Al and inevitable impurities, wherein the Mg / Si content ratio is 0.45~0.65.

[0010] A high-efficiency and low-carbon preparation method for a 6000 series aluminum alloy sheet comprises the following steps:

[0011] (1) melting and casting the aluminum alloy raw material according to the composition ratio of the aluminum alloy to obtain a cast alloy ingot;

[0012] (2) After the ingot is subjected to homogenization heat treatment, it is directly hot-rolled without cooling. The hot rolling start temperature is 530-575°C, the hot rolling finish temperature is 430-520°C, and then it is immediately coiled to obtain a hot-rolled coil. The coil is cooled to 250°C at a rate of 50°C / h-140°C / h, and then cooled to room temperature for self-annealing treatment.

[0013] (3) The hot-rolled coil is no longer subjected to intermediate annealing treatment, but is directly cold-rolled to obtain the cold-rolled sheet;

[0014] (4) The plate and strip are subjected to solution quenching and pre-aging treatment to obtain T4P state thin plate.

[0015] Preferably, in step (2), the hot rolling start temperature is 540-560°C, the hot rolling finish temperature is 440-490°C, and the coil is cooled to 250°C at a rate of 55°C / h-120°C / h.

[0016] Preferably, in step (2), the hot-rolled coil is cooled from 250° C. to room temperature by wind cooling, air cooling, mist cooling or a combination of these.

[0017] Preferably, in step (4), the area fraction of the second phase in the T4P state sheet is not higher than 1.30%, the maximum size of the second phase is not greater than 2.5 μm, the average grain size is 33 ± 5 μm, and the average plane plastic strain ratio r ave. Not less than 0.55.

[0018] Preferably, the second phase present in the T4P state thin plate is an Fe-rich phase.

[0019] In the present invention, the ingot is directly hot-rolled after homogenization heat treatment without cold rolling, which not only saves the cooling process of the ingot after homogenization heat treatment and the heating process before hot rolling, but also regulates the Mg2Si phase and inhibits the precipitation of coarse and harmful Mg2Si phase. In addition, hot rolling deformation within the temperature range will eventually form a randomly distributed texture in the TP state, which is beneficial to the forming performance. After hot rolling, the strip coil is temperature-controlled and cooled to regulate the submicron second phase in the structure, forming a randomly distributed texture, achieving the same effect as intermediate annealing, and also saving the separate intermediate annealing process. At the same time, the optimal T4P state microstructure is obtained, and efficient and low-carbon preparation of thin plates is achieved.

[0020] The advantages of the present invention are:

[0021] The present invention optimizes the composition of 6000 series aluminum alloy for automobile body covering parts and rationally designs and optimizes the thin plate preparation and processing process, thereby eliminating the heating treatment before hot rolling and two intermediate annealing treatments, and ultimately obtaining the optimal microstructure pattern and improving the forming performance of the thin plate. In addition, by eliminating the preparation and processing steps, the production time is saved, the production cost is reduced, and the carbon emission is reduced, thereby truly realizing efficient and low-carbon preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the grain morphology of the alloy T4P state thin plate in the present invention.

[0023] Figure 2 This is a TEM bright field image of the alloy T4P state thin plate in the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope of the present invention and its application.

[0025] The preparation process of the aluminum alloy thin plate in the present invention is: smelting and casting → homogenization heat treatment → hot rolling deformation → temperature-controlled cooling self-annealing → cold rolling deformation → solution treatment → pre-aging treatment → T4P state thin plate.

[0026] In the present invention, the ingot is directly hot-rolled without cooling after homogenization heat treatment, the hot rolling start temperature is 530-575°C, the hot rolling finish temperature is 430-520°C, and then the hot-rolled coil is immediately coiled to obtain the hot-rolled coil, the coil is cooled to 250°C at a rate of 50°C / h-140°C / h, and then cooled to room temperature for self-annealing. Preferably, the hot rolling start temperature is 540-560°C, the hot rolling finish temperature is 440-490°C, the coil is cooled to 250°C at a rate of 55°C / h-120°C / h, and then cooled to room temperature for self-annealing.

[0027] Example 1

[0028] The aluminum alloy composition of this embodiment is: Al-0.55Mg-0.95Si-0.15Cu-0.08Ho-0.12Fe (wt.%). The preparation process of the aluminum alloy sheet is as follows: the alloy raw material is melted and cast into an ingot at 700°C, and then hot rolled without cooling after homogenization heat treatment, and then directly rolled after hot rough rolling and hot finish rolling to a finished product thickness of 6mm to obtain a hot-rolled strip coil, and then the temperature is controlled and cooled to 250°C for self-annealing treatment, and after cooling to room temperature, cold rolled to obtain a cold-rolled strip coil with a thickness of 1.0mm, which is subjected to solid solution and pre-aging treatment to obtain a T4P state thin plate. The specific technical parameters are shown in Table 1.

[0029] Processes 1-1 to 1-4 in Table 1 are not the technical solutions of the present invention, and the process flow adopted is: the alloy ingot is homogenized and then cooled to room temperature, and then the ingot is heated to 480°C, 500°C, 450°C and 520°C respectively, which is the hot rolling start temperature, and the hot-rolled coil is obtained after hot finishing rolling and hot rough rolling, and the final rolling temperatures are 230°C, 250°C, 200°C and 270°C respectively. After the coil is cooled to room temperature, it is subjected to intermediate annealing treatment at a temperature of 400°C / 2h (heating time of 8-12h), and then cold rolling deformation is carried out, and intermediate annealing treatment is carried out again between cold rolling passes at a temperature of 400°C / 2h (heating time of 8-12h), and then cold rolling is carried out to a finished product thickness of 1.0mm. Processes 1-5 to 1-14 are technical solutions of the present invention. Compared with processes 1-1 to 1-4, the technical solution of the present invention obtains a hot-rolled coil by direct hot rolling deformation after homogenization, and realizes self-annealing by regulating the hot rolling start temperature and the cooling process of the hot-rolled coil to 250°C, thereby avoiding the precipitation of coarse and harmful Mg2Si phase during the homogenization cooling process, and regulating the submicron and nanoscale phases (Mg2Si phase, AlCuMgSi phase, Al(Fe,Mn)Si phase) in the structure during the self-annealing process, forming a randomly distributed texture, improving the forming performance, and at the same time saving the process, reducing the manufacturing cost and reducing carbon emissions.

[0030] Table 2 shows the corresponding forming properties and characteristic microstructure of 6000 series aluminum alloy sheets after pre-aging treatment (T4P) using different technical solutions in Table 1, where the average plane plastic strain ratio r ave. According to GB / T 16865 test, ave. =(r 0° +2×r 45° +r 90° ) / 4, the average grain size is calculated according to GB / T 3246.1, the second phase area fraction and the maximum second phase size are calculated according to YS / T 1624. Figure 1 The figure shows the grain morphology of the T4P thin plate obtained after using processes 1-5 in Table 1. It can be seen from the figure that the grains are small and uniform, and the grain size is 38μm according to statistics; Figure 2 This is a TEM bright field image of a T4P state sheet obtained after using processes 1-5 in Table 1. It can be seen from the figure that the phase present in the organization is an Fe-rich phase, and the length dimension of the phase is 2.5 μm. It can be seen from the table that after adopting the technical solution of the present invention, the average grain size of the 6000 series aluminum alloy sheet is significantly reduced. It can also be seen from the morphology diagram that the grains are small and uniform, and the maximum second phase size is significantly reduced, which reduces the risk of cracking caused by coarse, uneven and coarse grains during the stamping process. In addition, the grain orientation is randomly distributed, and the average plane plastic strain ratio is significantly improved, which significantly improves the forming performance of the sheet.

[0031] Table 1

[0032]

[0033] Table 2

[0034]

[0035] Example 2

[0036] The aluminum alloy composition of this embodiment is: Al-0.65Mg-1.05Si-0.15Cu-0.10Ho-0.13Fe (wt.%). The preparation process of the aluminum alloy sheet is as follows: the alloy raw material is melted and cast into a flat ingot at 700°C, and then directly hot rolled after homogenization heat treatment, and then directly rolled after hot rough rolling and hot finish rolling to a finished product thickness of 6mm to obtain a hot rolled strip coil, and then the temperature is controlled and cooled to 250°C for self-annealing treatment, and after cooling to room temperature, cold rolled to obtain a cold rolled strip coil with a thickness of 1.0mm, which is subjected to solid solution and pre-aging treatment to obtain a T4P state thin plate. The specific technical parameters are shown in Table 3.

[0037] Processes 2-1 to 2-4 in Table 3 are not the technical solutions of the present invention. The process flow adopted is: cooling to room temperature after homogenization, and then heating the ingot to 480°C, 500°C, 450°C and 520°C respectively, which is the hot rolling start temperature. After hot finishing rolling and hot rough rolling, the hot-rolled coils are obtained, and the final rolling temperatures are 230°C, 250°C, 200°C and 270°C respectively. After the coils are cooled to room temperature, they are subjected to intermediate annealing treatment at a rate of 400°C / 2h (heating time of 8 to 12h), and then cold rolling deformation is carried out. Between cold rolling passes, intermediate annealing treatment is carried out again at a rate of 400°C / 2h (heating time of 8 to 12h), and then cold rolling is carried out to a finished product thickness of 1.0mm. Processes 2-5 to 2-14 are the technical solutions of the present invention. Compared with processes 2-1 to 2-4, the technical solutions of the present invention obtain hot-rolled coils by direct hot rolling deformation after homogenization, and realize self-annealing by regulating the hot rolling start temperature and the cooling process of the hot-rolled coils to 250°C, thereby avoiding the formation of coarse and harmful Mg2Si phases by precipitation during the cooling process of the ingot after homogenization, regulating the submicron and nanoscale phases during the self-annealing process, and forming a randomly distributed texture, thereby improving the forming performance, while saving steps, reducing manufacturing costs, and reducing carbon emissions.

[0038] Table 4 shows the strength, formability and characteristic microstructure of 6016 aluminum alloy sheet samples after pre-aging treatment (T4P) using different technical schemes in Table 3, where the average plane plastic strain ratio r ave. According to GB / T16865 test,ave. =(r 0° +2×r 45° +r 90° ) / 4, the average grain size is calculated according to GB / T 3246.1, and the second phase area fraction and the maximum second phase size are calculated according to YS / T 1624. It can be seen from the table that after adopting the technical solution of the present invention, the average grain size of the 6000 series aluminum alloy sheet is significantly reduced, and the maximum second phase size in the organization is also significantly reduced, which reduces the risk of cracking caused by coarse and uneven grains and coarse phases during stamping. In addition, the grain orientation is randomly distributed, the average plane plastic strain ratio is significantly improved, and the forming performance of the sheet is significantly improved.

[0039] Table 3

[0040]

[0041] Table 4

[0042]

[0043] From the above examples, it can be seen that the present invention, by adding elements to improve the grain structure in the alloy and combining the high-efficiency and low-carbon preparation method, not only obtains the best T4P state microstructure, but also the area fraction of the second phase in the T4P state sheet is not higher than 1.30%, the maximum size of the second phase is not greater than 2.5 μm, the average grain size is 33 ± 5 μm and the average plane plastic strain ratio r ave. Not less than 0.55, which significantly improves the stamping performance of the thin plate; and through the integration of hot rolling and heating and self-annealing after hot rolling, the three processes of heating treatment before hot rolling and the subsequent two intermediate annealing treatments are saved, which saves production time, reduces production costs, and reduces carbon emissions, truly realizing the efficient and low-carbon preparation of 6000 series aluminum alloy sheets for automobile body coverings.

Claims

1. A method for preparing a 6000 series aluminum alloy sheet, characterized in that: The 6000 series aluminum alloy is composed of the following components by mass percentage: Ho 0.05-0.12wt.%, Mg 0.45-0.65wt.%, Si 0.85-1.10wt.%, Cu 0.05-0.20wt.%, Fe<0.15wt.%, and the balance is Al and unavoidable impurities, wherein the Mg / Si content ratio is 0.4-0.7, and the preparation method comprises the following steps: (1) According to the composition ratio of 6000 series aluminum alloy, the aluminum alloy raw material is melted and cast to obtain a cast alloy ingot; (2) After the ingot is subjected to homogenization heat treatment, it is directly hot-rolled without cooling. The hot rolling start temperature is 530-575°C, the hot rolling finish temperature is 430-520°C, and then it is immediately coiled to obtain a hot-rolled coil. The coil is cooled to 250°C at a rate of 50°C / h-140°C / h, and then cooled to room temperature for self-annealing treatment. (3) The hot-rolled coil is no longer subjected to intermediate annealing treatment, but is directly cold-rolled to obtain the cold-rolled sheet; (4) The plate and strip are subjected to solution quenching and pre-aging treatment to obtain T4P state thin plate.

2. The method for preparing a 6000 series aluminum alloy sheet according to claim 1, characterized in that: The 6000 series aluminum alloy is composed of the following components: Ho 0.08~0.10wt.%, Mg 0.45~0.65wt.%, Si 0.85~1.10wt.%, Cu 0.05~0.20wt.%, Fe<0.15wt.%, and the remainder is Al and inevitable impurities, wherein the Mg / Si content ratio is 0.45~0.

65.

3. The method for preparing a 6000 series aluminum alloy sheet according to claim 1, characterized in that: In the step (2), the hot rolling start temperature is 540-560°C, the hot rolling finish temperature is 440-490°C, and the coil is cooled to 250°C at a rate of 55°C / h-120°C / h.

4. The method for preparing a 6000 series aluminum alloy sheet according to claim 1, characterized in that: In the step (2), the hot rolled coil is cooled from 250° C. to room temperature by using one or a combination of wind cooling, air cooling, and mist cooling.

5. The method for preparing a 6000 series aluminum alloy sheet according to claim 1, characterized in that: In the step (4), the area fraction of the second phase in the T4P state thin plate is not higher than 1.30%, the maximum size of the second phase is not greater than 2.5 μm, the average grain size is 33±5 μm, and the average plane plastic strain ratio r ave. Not less than 0.

55.

6. The method for preparing a 6000 series aluminum alloy sheet according to claim 5, characterized in that: The second phase present in the T4P state thin plate is an Fe-rich phase.

Images