Coupling distribution regulation and control method for double-gradient structure of high-formability aluminum alloy plate

Abstract

The invention discloses a double-gradient structure coupling distribution regulation and control method for a high-formability aluminum alloy plate, and belongs to the field of aluminum alloys. The method comprises the following steps: preparing an alloy, smelting the alloy in a non-vacuum medium-frequency induction furnace, and casting the alloy in a water-cooling steel mold for cooling; then short-time high-temperature heat treatment, large-deformation hot rolling deformation and two-stage high-temperature heat treatment are carried out; then, primary small-deformation cold rolling, low-temperature short-time annealing, secondary small-deformation cold rolling, low-temperature short-time annealing, third-time small-deformation cold rolling, low-temperature short-time annealing and fourth-time small-deformation cold rolling are sequentially conducted till the final thickness is achieved; then high-temperature short-time solid solution quenching and two-stage pre-aging regulation are carried out, so that the plate can form a double-gradient structure coupling distribution characteristic, and the plate has the characteristic of high formability; the method is very suitable for being applied to processing and production of aluminum alloy materials for automobile body structures and used by other aluminum alloy material production enterprises with specific requirements on the tissue characteristics, the stamping forming performance and the like of aluminum alloy plates.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloys, and is particularly aimed at the fact that the room temperature stamping forming performance of aluminum alloy sheets for vehicle body structural parts is still not high enough, and the application status of the automotive field for this performance requirement is constantly improving. A control method for improving the room temperature stamping forming performance of Al-Zn-Mg-Cu-Fe-Mn alloys that can be industrially applied is proposed. The control method can effectively control the coupled distribution characteristics of the primary iron-rich phase, the precipitated phase and the solute elements in the alloy, and form a dual-gradient tissue coupled distribution characteristic that has a significant promoting effect on the room temperature stamping forming performance of the alloy. Background Art

[0002] With the rapid development of automobile industrialization and the continuous improvement of people's living standards, the number of cars has increased significantly, and the resulting energy consumption and environmental pollution problems cannot be ignored. Lightweighting of automobiles is one of the effective ways to achieve energy conservation and emission reduction, and has gradually become an important trend in the development of the automobile industry. Aluminum alloys have become the key materials for lightweighting of automobiles due to their advantages such as light weight, corrosion resistance, high specific strength, easy processing and recyclability. At present, the aluminum alloys used in the inner and outer panels of automobile bodies mainly include 6xxx series that can be heat-treated and strengthened and 5xxx series aluminum alloys that cannot be heat-treated and strengthened. Among them, 5xxx series aluminum alloys have good formability and high corrosion resistance, but the surface quality after stamping is poor, and they are often used in the manufacture of automobile inner panels. 6xxx series aluminum alloys have excellent comprehensive properties, with medium and high strength, good formability and paint hardening ability, and are mainly used in the manufacture of body outer panels. 7xxx series aluminum alloys have both high strength and high toughness, and have been widely used in the aerospace field in the past. At this stage, steel is still the main material for automobile structural parts. In addition to the high density of steel, which leads to heavier body, another outstanding problem is that there are many problems in steel-aluminum dissimilar connections. For example, the Fe-Al brittle intermetallic compounds produced by metallurgical connection will seriously damage the strength and durability of the weld; there are also some problems in mechanical connection, mainly due to insufficient sealing and joint cracking caused by different mechanical properties of heterogeneous materials; in addition, there are problems of corrosion between heterogeneous metals, etc. Traditional 5xxx and 6xxx series aluminum alloys still have problems such as insufficient strength as body structural parts. Therefore, it is very necessary to solve the above problems by using higher strength Al-Zn-Mg-Cu series alloys to replace steel structural parts. However, the application of this series of alloys in automobiles is currently limited to the manufacture of some parts with low formability requirements. Studies have shown that the key problem affecting its widespread application in body structural parts is that the Al-Zn-Mg-Cu alloy sheet has poor formability and corrosion resistance, and the production cost is high. It can be seen that how to make Al-Zn-Mg-Cu alloy sheet have both high strength, high formability, good corrosion resistance and low production cost is the key to its application in the automotive field. Recently, a large number of studies have shown that hot forming or warm forming can promote the forming performance of this series of aluminum alloy sheets, but the forming process is complicated and the production cost is high. In addition, warm and hot forming can easily lead to coarsening of the precipitation phase, thereby reducing the strength of the alloy sheet, which is very unfavorable for the widespread application of this series of alloys in body structural parts. It can be seen that in order to better meet the actual application needs, it is urgent to improve the room temperature stamping forming performance of this series of alloy sheets through composition design and process control, which is of great significance for the rapid advancement of the lightweight process of automobiles and the widespread application of high-strength 7xxx series aluminum alloy materials in body structural parts. Summary of the invention

[0003] In order to better meet the urgent demand for high-performance aluminum alloy plates for lightweight automobiles, the present invention proposes a dual-gradient organization coupling distribution control method for effectively improving the room temperature stamping forming performance of low-cost Al-Zn-Mg-Cu-Fe-Mn alloy plates in view of the poor stamping forming performance of traditional Al-Zn-Mg-Cu alloy plates. The present invention makes full use of the fact that recycled aluminum or ordinary aluminum generally contains a high content of solute element Fe, and by controlling the melting and casting process, not only a certain amount of solute elements Zn, Mg, Fe and Cu elements can be dissolved in the alloy matrix, but also the gradient distribution characteristics of solute elements Zn, Mg, Cu, Fe and Mn can be formed inside the grains, that is, the concentration of solute elements gradually decreases from the grain boundary to the grain, showing a gradient characteristic. Subsequently, the distribution characteristics of the solute elements can be further precisely controlled through the regulation of the thermal processing process. For example, short-term low-temperature heat treatment regulation can appropriately optimize the cast structure, and then it is subjected to high-temperature hot rolling deformation, and the original solute element gradient distribution characteristics can be further inherited to the hot-rolled state; at this time, if it is subjected to double-stage heat treatment regulation, that is, the first stage makes the gradient solute elements precipitate into precipitation phases of different scales (including iron-rich phase and Mg-Zn-Cu precipitation phase, etc.), and then the second stage high-temperature heat treatment is used, not only the dissolution and diffusion of the Mg-Zn-Cu precipitation phase can be precisely controlled, because the precipitation phases of different scales formed can undergo different degrees of dissolution and diffusion. Dispersion, thereby constructing different coupled distribution characteristics of soft micro-regions and hard micro-regions, and at the same time, the second-level high-temperature heat treatment regulation can further precipitate fine iron-rich phase particles; subsequent cold rolling and intermediate annealing can further optimize and regulate its distribution; on this basis, subsequent high-temperature solid solution and pre-aging regulation can form precipitation phases with different gradient distribution characteristics (including iron-rich phase and Mg-Zn-Cu precipitation phase) in the micro-region; once the alloy matrix is ​​able to construct such a gradient organizational feature, due to the simultaneous existence of soft micro-regions and hard micro-regions in the micro-region, the alloy can exhibit excellent coordinated deformation ability during deformation, thereby significantly improving the room temperature stamping forming performance of the alloy sheet. In addition, if the cold rolling and intermediate annealing processes after the double-stage high-temperature heat treatment are also optimized, that is, repeated small deformation cold rolling deformation + low-temperature short-time annealing treatment, then the alloy plate will only generate a large amount of strain energy storage on the surface due to the small deformation amount, so a certain amount of nano-precipitation phase (including iron-rich phase and precipitation phase) can be precipitated on the surface during the low-temperature short-time annealing process. After repeated small deformation cold rolling deformation + low-temperature short-time annealing treatment, the precipitation phase (including iron-rich phase and precipitation phase) from the surface to the core of the alloy can show a gradient distribution characteristic, and its size is relatively small.Then this kind of gradient distribution feature can cooperate with the coarse iron-rich phase to effectively affect the recrystallization process in the subsequent high-temperature solid solution process, that is, the coarse iron-rich phase effectively stimulates the recrystallization nucleation, and the gradient fine precipitation phase can effectively hinder the rapid growth of recrystallized grains, which can further effectively regulate the microstructure of the alloy sheet and promote the improvement of the room temperature stamping forming performance of the alloy sheet. It can be seen that the coupling regulation of the gradient organization from the surface to the core of the sheet and the gradient organization distribution of the precipitation phase in the micro-region will inevitably greatly improve the room temperature stamping forming performance of the Al-Zn-Mg-Cu-Fe-Mn alloy sheet.

[0004] According to a first aspect of the present invention, a method for regulating the dual-gradient organization coupling distribution of a high-formability aluminum alloy plate is provided, wherein the aluminum alloy is an Al-Zn-Mg-Cu-Fe-Mn alloy, and the chemical composition and its mass percentage content are: Zn: 5.0-7.0wt%, Mg: 1.0-2.0wt%, Cu: 1.5-2.5wt%, Fe: 0.1-0.5wt%, Mn: 0.05-0.3wt%, Ni: 0.02-0.07wt%, Ti: 0.02-0.3wt%, Cr: 0.01-0.04wt%, Si: 0.01-0.05wt%, and the balance is Al;

[0005] It is characterized by adopting the following technical route:

[0006] (1) Using recycled aluminum or ordinary aluminum to prepare a high-formability Al-Zn-Mg-Cu-Fe-Mn alloy, then using medium-frequency induction melting in non-vacuum conditions, and casting it in a water-cooled steel mold, the cooling rate is controlled to be greater than 30°C / min so that the alloy grain size, solute element segregation and primary phase distribution meet the subsequent regulation requirements;

[0007] (2) According to the as-cast structure, the ingot is subjected to a short-term high-temperature heat treatment at a temperature of 400-440°C, a heating rate of 22-35°C / min, and a treatment time of 0.5-3h; then the ingot subjected to the high-temperature heat treatment is directly subjected to a large deformation hot rolling deformation treatment, with a hot rolling deformation of 80-98%;

[0008] (3) The hot-rolled plate is then subjected to a secondary double-stage high-temperature heat treatment to control the distribution characteristics of the alloy's iron-rich phase, precipitation phase, and solute elements. The first stage heat treatment temperature is 390-430°C, the heating rate is 22-35°C / min, and the treatment time is 1-30h. The second stage temperature is 430-500°C, the heating rate is 22-35°C / min, and the treatment time is 0.5-30h.

[0009] (4) Subsequently, the alloy plate subjected to the secondary double-stage high-temperature heat treatment is subjected to four small deformation cold rolling deformation treatments and three low-temperature short-time annealing treatments in sequence, wherein the four small deformations are all 15-40%, and the annealing temperatures of the three low-temperature short-time annealing treatments are all 380-440° C., and the annealing time is all 10 min-240 min;

[0010] (5) The alloy plate subjected to the fourth small deformation cold rolling deformation treatment was then subjected to a high-temperature short-time solution treatment: the solution temperature was 470-500°C, and then the alloy sample after the solution treatment was quenched and cooled from the solution treatment temperature to room temperature. The quenched sample was transferred to an aging furnace within 1 min for a two-stage isothermal pre-aging treatment, with the first stage temperature being 60-120°C and the second stage temperature being 20-60°C. The alloy plate exhibited excellent stamping forming properties at room temperature.

[0011] Based on the above-mentioned dual-gradient tissue coupling distribution regulation, it can be ensured that the developed alloy sheet has excellent room temperature stamping forming performance.

[0012] Furthermore, in step (1), the alloy melting process using medium frequency induction under non-vacuum conditions is as follows: first, all the recycled aluminum or ordinary aluminum is added to a crucible and melted, and the temperature is controlled at 780-880°C, and then Al-20wt% Fe, Al-10wt% Mn, Al-10wt% Ti, Al-5wt% Cr, and Al-20wt% Si master alloys are added respectively, and after melting, Al-50wt% Cu master alloy is added, and then the melt is stirred at high power for 10 minutes, and then the required content of pure Ni is added to the melt and the melt is stirred at high power for 10 minutes, and then the temperature of the alloy melt is controlled to be above 720°C, and pure Zn and pure Mg are added respectively. When adding pure Mg, a graphite bell is used to press it into the bottom of the melt, and the bell is taken out after it is completely dissolved, and the power of the medium frequency induction furnace is adjusted to stabilize the temperature of the alloy melt at 740°C, then slag is removed, and a refining agent is added for degassing and refining; then when the melt temperature drops to 720°C, A is added. l-5wt% Ti-1wt% B grain refiner and properly stirred, and finally, after keeping the temperature at 720℃ for 10min, the melt is cast into a steel mold with water cooling on all sides, and the cooling rate is controlled to be greater than 30℃ / min.

[0013] Furthermore, in step (2), the ingot is subjected to a short-time high-temperature heat treatment at a temperature of 400-435°C, a heating rate of 22-35°C / min, and a time of 0.5-2.5h; and then the ingot subjected to the high-temperature heat treatment is directly subjected to a large deformation hot rolling deformation treatment, with a hot rolling deformation of 80-98%, a pass deformation of 5-20%, a final rolling temperature greater than 280°C, and unidirectional rolling.

[0014] Furthermore, in step (3), the hot-rolled plate is subjected to a secondary two-stage high-temperature heat treatment to regulate the distribution characteristics of the alloy's iron-rich phase, precipitation phase and solute elements. The first stage heat treatment temperature is 390-430°C, the heating rate is 22-35°C / min, the treatment time is 1-30h, the second stage temperature is 430-500°C, the heating rate is 22-35°C / min, the treatment time is 0.5-30h, and the cooling rate is greater than 100°C / min.

[0015] Furthermore, in step (4), the alloy plate subjected to the secondary double-stage high-temperature heat treatment is sequentially subjected to four small deformation cold rolling deformation treatments and three low-temperature short-time annealing treatments, the deformation amount is 15-40%, the deformation amount per pass is 2-7%, and all are unidirectional rolling; the heating rates of the three low-temperature short-time annealing treatments are all greater than 100°C / min, the heating temperatures are all 390-440°C, the annealing times are all 10min-240min, and then the temperature is cooled to room temperature at a cooling rate greater than 50°C / s.

[0016] Furthermore, in step (5), the alloy plate after the fourth small deformation cold rolling deformation treatment is subjected to high temperature short-time solution treatment: the solution temperature is 470-500°C, the heating rate is greater than 150°C / min, and then the alloy sample after the solution treatment is quenched and cooled from the solution treatment temperature to room temperature, the quenching cooling rate after solution treatment is greater than 100°C / s, and the quenched sample is transferred to an aging furnace within 1 minute for two-stage isothermal pre-aging treatment, the first stage temperature is 70-120°C / 1-12h, and the second stage temperature is 20-60°C / 5-100h. The alloy plate can exhibit excellent stamping forming performance at room temperature.

[0017] The high-formability Al-Zn-Mg-Cu-Fe-Mn alloy sheet developed by the present invention is very suitable for use in the production of automotive parts, especially for the manufacture of complex-shaped parts with high requirements on room temperature stamping forming performance.

[0018] Beneficial effects of the present invention:

[0019] By adopting the above-mentioned technical scheme, the present invention has the following advantages: the present invention can not only make the new Al-Zn-Mg-Cu alloy sheet have a lower production cost, but also form a suitable dual-gradient tissue coupling distribution feature after coordinated regulation of multiple processes of hot processing, so that the alloy sheet has excellent room temperature stamping forming performance. The dual-gradient tissue coupling distribution regulation method of the present invention can significantly improve the room temperature stamping forming performance of the alloy sheet, which has an important driving effect on the further widespread application of this series of aluminum alloy sheets. The present invention is very suitable for the processing and production of aluminum alloy materials for automobile body structures, as well as for other aluminum alloy material manufacturers that have specific requirements for the organizational characteristics and stamping forming performance of aluminum alloy sheets. Of course, it is also suitable for other technical industries that have high requirements for the organization and comprehensive performance of other series of aluminum alloy materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A flow chart of a method for controlling the dual-gradient structure coupling distribution of high-formability aluminum alloy plates;

[0021] Figure 2 TEM characterization results of the gradient distribution of fine dispersed particles of 1# alloy after the second low temperature short time annealing in Example 1;

[0022] Figure 3 TEM characterization results of the gradient distribution of fine dispersed particles of alloy 1# in Example 1 after the third low-temperature short-time annealing;

[0023] Figure 4 SEM characterization results of multi-scale dispersed particles of 1# alloy after the fourth small deformation cold rolling in Example 1;

[0024] Figure 5 SEM characterization results of the gradient distribution of fine dispersed particles of 1# alloy after the fourth small deformation cold rolling in Example 1;

[0025] Figure 6 EBSD characterization results of the microstructure of alloy 1 after double-stage pre-aging in Example 1;

[0026] Figure 7 The hardness matrix characterization results of the coupled distribution of soft and hard micro-regions of 1# alloy under double-stage pre-aging control in Example 1. DETAILED DESCRIPTION

[0027] The present invention is further supplemented and illustrated below in conjunction with specific implementation schemes.

[0028] Aiming at the research and application status that the room temperature stamping forming performance of high-strength Al-Zn-Mg-Cu alloy sheets for automobile body structural parts still needs to be further improved and the production cost urgently needs to be significantly reduced, the present invention proposes a dual-gradient organization coupling control method, that is, by optimizing the contents of Zn, Mg, Cu, Fe and Mn and their matching relationship, and then controlling the melting and casting process, not only a certain amount of solute elements Zn, Mg, Fe and Cu can be dissolved in the alloy matrix, but also a gradient distribution feature of the solute elements Zn, Mg, Cu, Fe and Mn can be formed inside the grains, that is, a distribution feature in which the concentration of the solute elements gradually decreases from the grain boundary to the grain. Subsequently, the distribution characteristics of the solute elements can be further optimized and regulated through multiple processes of thermal processing. For example, short-term low-temperature heat treatment can appropriately optimize and regulate the cast structure, and then it is subjected to high-temperature hot rolling deformation, and the original solute element gradient distribution characteristics can be further inherited to the hot-rolled state; at this time, if it is subjected to double-stage heat treatment regulation, that is, the first stage makes the gradient solute elements precipitate into precipitation phases of different scales (including iron-rich phase and Mg-Zn-Cu precipitation phase, etc.), and then the second stage high-temperature heat treatment is used to accurately regulate the dissolution and diffusion of the Mg-Zn-Cu precipitation phase, then the precipitation phases of different scales formed can be developed. Different degrees of dissolution and diffusion occur, thereby constructing different coupled distribution characteristics of soft micro-regions and hard micro-regions; subsequent cold rolling and intermediate annealing can further optimize and regulate its distribution; on this basis, precipitation phases with different gradient distribution characteristics (including iron-rich phase and Mg-Zn-Cu precipitation phase) can be formed in the micro-region through subsequent high-temperature solid solution and pre-aging regulation; once the alloy matrix is ​​able to construct such gradient organizational characteristics, due to the simultaneous existence of soft micro-regions and hard micro-regions in the micro-region, the alloy can exhibit excellent coordinated deformation ability during deformation, thereby significantly improving the room temperature stamping forming performance of the alloy sheet. In addition, if the cold rolling and intermediate annealing process after the double-stage high-temperature heat treatment is also effectively regulated, that is, repeated small deformation cold rolling deformation + low-temperature short-time annealing treatment is adopted, then due to the small deformation, the alloy sheet only generates a large amount of strain energy storage on the surface, and a certain amount of nano-precipitation phase (including iron-rich phase and precipitation phase) can be precipitated on the surface of the sheet during the low-temperature short-time annealing process. After repeated small deformation cold rolling deformation + low-temperature short-time annealing treatment, the precipitation phase (including iron-rich phase and precipitation phase) from the surface to the core of the alloy can present a gradient distribution feature, and its size is relatively small. Then this gradient organizational distribution feature can cooperate with the coarse iron-rich phase in the subsequent high-temperature solid solution process to effectively affect the recrystallization process, that is, the coarse iron-rich phase effectively stimulates the recrystallization nucleation, and the gradient fine precipitation phase can effectively hinder the rapid growth of recrystallized grains, thereby effectively regulating the microstructure of the alloy sheet, which is beneficial to the improvement of the room temperature stamping forming performance of the alloy sheet.Finally, based on the coupled distribution control of the gradient structure from the surface to the core of the sheet and the precipitated phase gradient structure in the micro-region, the room temperature stamping forming performance of the alloy sheet can be greatly improved. The method of the present invention is very suitable for the manufacture of new aluminum alloy sheets for automobiles, especially for the manufacture of complex-shaped parts with high requirements for room temperature stamping forming performance.

[0029] According to a method for controlling the dual gradient organization coupling distribution of a high-formability aluminum alloy plate of the present invention, the aluminum alloy is an Al-Zn-Mg-Cu-Fe-Mn alloy, and the raw materials are recycled aluminum or ordinary aluminum, industrial pure Mg, industrial pure Zn, industrial pure Ni, intermediate alloys such as Al-20wt%Si, Al-50wt%Cu, Al-20wt%Fe, Al-10wt%Mn, Al-5wt%Cr, and Al-10wt%Ti. Figure 1 As shown, the following technical route is adopted:

[0030] Step 101: preparing a high-formability Al-Zn-Mg-Cu-Fe-Mn alloy using recycled aluminum or ordinary aluminum, then melting the alloy using medium-frequency induction in a non-vacuum environment, and casting the alloy in a water-cooled steel mold, controlling the cooling rate to be greater than 30°C / min so that the alloy grain size, solute element segregation, and primary phase distribution meet subsequent control requirements;

[0031] Step 102: According to the as-cast structure, the ingot is subjected to a short-term high-temperature heat treatment at a temperature of 400-440° C., a heating rate of 22-35° C. / min, and a treatment time of 0.5-3 h; and the ingot subjected to the high-temperature heat treatment is directly subjected to a large deformation hot rolling deformation treatment, with a hot rolling deformation of 80-98%;

[0032] Step 103: Subsequently, the hot-rolled plate is subjected to a secondary double-stage high-temperature heat treatment to adjust the distribution characteristics of the alloy iron-rich phase, precipitation phase and solute elements, the first stage heat treatment temperature is 390-430°C, the heating rate is 22-35°C / min, the treatment time is 1-30h, the second stage temperature is 430-500°C, the heating rate is 22-35°C / min, and the treatment time is 0.5-30h;

[0033] Step 104: Subsequently, the alloy sheet subjected to the secondary double-stage high-temperature heat treatment is subjected to a small deformation amount cold rolling deformation treatment (deformation amount 15-40%) and a low-temperature short-time annealing treatment (380-440°C, 10min-240min); the alloy sheet subjected to the primary low-temperature short-time annealing is subjected to a secondary small deformation amount cold rolling deformation treatment (deformation amount 15-40%) and a secondary low-temperature short-time annealing treatment (380-440°C, 10min-240min); the alloy sheet subjected to the primary low-temperature short-time annealing is subjected to a third small deformation amount cold rolling deformation treatment (deformation amount 15-40%) and a third low-temperature short-time annealing treatment (380-440°C, 10min-240min); and finally, the alloy sheet subjected to the third low-temperature annealing is subjected to a fourth small deformation amount cold rolling deformation treatment (deformation amount 15-40%).

[0034] Step 105: Then, the alloy plate subjected to the fourth small deformation cold rolling deformation treatment is subjected to a high-temperature short-time solution treatment: the solution temperature is 470-500°C, and then the alloy sample after the solution treatment is quenched and cooled from the solution treatment temperature to room temperature, and the quenched sample is transferred to an aging furnace within 1 minute for a two-stage isothermal pre-aging treatment, with the first stage temperature being 60-120°C and the second stage temperature being 20-60°C. The alloy plate can exhibit excellent stamping forming performance at room temperature.

[0035] Based on the above-mentioned dual-gradient microstructure coupling regulation, it can be ensured that the developed alloy sheet has excellent room temperature stamping forming performance.

[0036] Specifically, the treatment process comprises the following steps: firstly, all the recycled aluminum or ordinary aluminum is added into a crucible and melted, and the temperature is controlled at 780-880°C, then Al-20wt%Fe, Al-10wt%Mn, Al-10wt%Ti, Al-5wt%Cr, Al-20wt%Si master alloys are added respectively, and Al-50wt%Cu master alloy is added after melting, and then the melt is stirred at high power for 10 minutes, and then the required content of pure Ni is added into the melt and the melt is stirred at high power for 10 minutes, and then the temperature of the alloy melt is controlled to be above 720°C, and pure Zn and pure Mg are added respectively, when adding pure Mg, a graphite bell is used to press it into the bottom of the melt, and the bell is taken out after it is completely melted, and the power of the medium frequency induction furnace is adjusted to stabilize the temperature of the alloy melt at 740°C, and then slag is removed and a refining agent is added to perform degassing and refining; then when the melt temperature drops to 720°C, Al-5wt%Ti is added. i-1wt% B grain refiner and properly stirred, and finally, after keeping the temperature at 720℃ for 10min, the melt was cast into a steel mold with water cooling on all sides, and the cooling rate was controlled to be greater than 30℃ / min. The specific chemical composition of the alloy of the invention is shown in Table 1:

[0037] Table 1 Chemical composition of alloys according to the present invention (mass percentage, wt%)

[0038]

[0039]

[0040] In order to construct the expected dual-gradient microstructure coupling distribution characteristics, the ingot is subjected to the following multi-process coordinated control treatment: (1) the ingot is subjected to a short-term high-temperature heat treatment at a temperature of 400-435°C, a heating rate of 22-35°C / min, and a time of 0.5-2.5h; then the ingot subjected to high-temperature heat treatment is directly subjected to a large deformation unidirectional hot rolling deformation treatment, with a hot rolling deformation of 80-98%, a pass deformation of 5-20%, and a final rolling temperature greater than 280°C; (2) the hot-rolled plate is subjected to a secondary two-stage high-temperature heat treatment to control the distribution characteristics of the alloy's iron-rich phase, precipitation phase, and solute elements. The first stage heat treatment temperature is 390-430°C, the heating rate is 22-35°C / min, and the treatment time is 1-3 0h, the second stage temperature is 430-500℃, the heating rate is 22-35℃ / min, the processing time is 0.5-30h, and the cooling rate is greater than 100℃ / min; (3) the alloy plate subjected to the secondary double-stage high-temperature heat treatment is subjected to a small deformation cold rolling deformation treatment (deformation 15-40%, pass deformation 2-7%, unidirectional rolling) and a low-temperature short-time annealing treatment (heating to 390-440℃ at a heating rate greater than 100℃ / min for 10min-240min annealing, and then cooling to room temperature at a cooling rate greater than 50℃ / s); the alloy plate subjected to the primary low-temperature short-time annealing is subjected to a secondary small deformation cold rolling deformation (deformation 15- 40%, deformation per pass 2-7%, unidirectional rolling) and two low-temperature short-time annealing treatments (heating to 390-440℃ at a heating rate greater than 100℃ / min for 10min-240min annealing, followed by cooling to room temperature at a cooling rate greater than 50℃ / s); three small deformation cold rolling (deformation 15-40%, deformation per pass 2-7%, unidirectional rolling) and three low-temperature short-time annealing treatments (heating to 390-440℃ at a heating rate greater than 100℃ / min for 10min-240min annealing, followed by cooling to room temperature at a cooling rate greater than 50℃ / s); finally, the three low-temperature annealing alloy sheets are subjected to a fourth small Deformation cold rolling deformation treatment (deformation 15-40%, pass deformation 2-7%, unidirectional rolling); (4) high temperature short time solution treatment of the alloy plate subjected to the fourth small deformation cold rolling deformation treatment: solution temperature 470-500℃, heating rate greater than 150℃ / min, then quenching and cooling the alloy sample after solution treatment from the solution treatment temperature to room temperature, quenching cooling rate after solution treatment greater than 100℃ / s, transferring the quenched sample to an aging furnace within 1min for two-stage isothermal pre-aging treatment, the first stage temperature 70-120℃ / 1-12h, the second stage temperature 20-60℃ / 5-100h, the alloy plate can show excellent room temperature stamping forming performance. The specific implementation method is as follows:

[0041] Example 1

[0042] Implementation of the Invention Alloy 1# alloy is melted and cast by medium frequency induction as follows. The alloy melting process using medium frequency induction under non-vacuum is as follows: first, all the recycled aluminum or ordinary aluminum is added to the crucible and melted, and the temperature is controlled at 780-880°C. Then, Al-20wt%Fe, Al-10wt%Mn, Al-10wt%Ti, Al-5wt%Cr, Al-20wt%Si master alloys are added respectively, and Al-50wt%Cu master alloy is added after melting. Then, the melt is stirred at high power for 10 minutes, and then the required content of pure N is added. i into the melt and stir the melt at high power for 10 minutes, then control the temperature of the alloy melt to above 720°C, add pure Zn and pure Mg respectively, use a graphite bell to press it into the bottom of the melt when adding pure Mg, remove the bell after it is completely dissolved, adjust the power of the medium frequency induction furnace to stabilize the temperature of the alloy melt at 740°C, then remove the slag, add a refining agent for degassing and refining; then add Al-5wt% T when the melt temperature drops to 720°C i-1wt% B grain refiner and stir appropriately, finally, after keeping the temperature at 720℃ for 10min, cast the melt into a water-cooled steel mold on all sides, and control the cooling rate to be greater than 30℃ / min; then the ingot is subjected to short-term high-temperature heat treatment, the temperature is 400-435℃, the heating rate is 22-35℃ / min, and the time is 0.5-2.5h; then the ingot subjected to high-temperature heat treatment is directly subjected to large deformation unidirectional hot rolling deformation treatment, the hot rolling deformation is 80-98%, the pass deformation is 5-20%, and the final rolling temperature is greater than 280℃; then the hot-rolled plate is subjected to secondary two-stage high-temperature heat treatment to regulate the distribution characteristics of the alloy's iron-rich phase, precipitation phase and solute elements, the first stage heat treatment temperature is 390-430℃, the heating rate is 22-35℃ / min, the treatment time is 1-10h, the second stage temperature is 430-500℃, the heating rate is 22-35℃ / min, the treatment time is 0.5-5h, cooling rate greater than 100℃ / min; a small deformation cold rolling deformation treatment (deformation 15-40%, pass deformation 2-7%, unidirectional rolling) and a low temperature short time annealing treatment (heating at a heating rate greater than 100℃ / min to 390-440℃ for 10min-240min annealing, and then cooling to room temperature at a cooling rate greater than 50℃ / s) are performed on the alloy plate regulated by the secondary double-stage high temperature heat treatment; the alloy plate subjected to the primary low temperature short time annealing is subjected to secondary small deformation in sequence The steel sheet is subjected to cold rolling with a small amount of deformation (15-40% deformation, 2-7% deformation per pass, unidirectional rolling) and a secondary low-temperature short-time annealing treatment (heating to 390-440°C at a heating rate greater than 100°C / min for 10min-240min annealing, followed by cooling to room temperature at a cooling rate greater than 50°C / s); the steel sheet is subjected to cold rolling with a small amount of deformation (15-40% deformation, 2-7% deformation per pass, unidirectional rolling) and a secondary low-temperature short-time annealing treatment (heating to 390-4 The alloy plates subjected to the three low-temperature annealing treatments were subjected to a fourth cold rolling deformation treatment with a small deformation amount (deformation amount 15-40%, pass deformation amount 2-7%, unidirectional rolling); the alloy plates subjected to the fourth cold rolling deformation treatment with a small deformation amount were subjected to a high-temperature short-time solution treatment: the solution temperature was 470-500°C, the heating rate was greater than 150°C / min, and the alloy samples after the solution treatment were then heated from the solution treatment temperature to the temperature of 470-500°C. After quenching and cooling to room temperature, the cooling rate of quenching after solution treatment is greater than 100℃ / s. The quenched sample is transferred to the aging furnace within 1min for double-stage isothermal pre-aging treatment, with the first stage temperature of 70-120℃ / 1-12h and the second stage temperature of 20-60℃ / 5-100h. Finally, the mechanical properties of the 1# alloy plate treated with double-stage isothermal pre-aging are measured, and the corresponding mechanical properties are shown in Table 2. The TEM structure of the fine dispersed particles after the second and third low-temperature short-time annealing treatments during the hot working process of the 1# alloy is shown in Table 2. Figure 2 and 3 As shown in the figure, the SEM characterization results of the gradient distribution characteristics of multi-scale dispersed particles and fine dispersed particles from the surface to the core after the fourth small deformation cold rolling are as follows Figure 4 and 5 As shown, the EBSD structure of alloy 1# after double-stage pre-aging control is as follows Figure 6 As shown in the figure, the hardness matrix representation of the coupled distribution of soft micro-regions and hard micro-regions after double-stage pre-aging control is as follows Figure 7 shown.

[0043] Example 2

[0044] Implementation of the Invention Alloy 2# alloy is carried out by medium frequency induction melting and casting as follows. The alloy melting process using medium frequency induction under non-vacuum is as follows: first, all the recycled aluminum or ordinary aluminum is added to the crucible and melted, and the temperature is controlled at 780-880°C, and then A l-20wt%Fe, A l-10wt%Mn, A l-10wt%Ti, A l-5wt%Cr, A l-20wt%Si master alloys are added respectively, and then A l-50wt%Cu master alloy is added after melting, and then the melt is stirred at high power for 10 minutes, and then the required content of pure N is added. i into the melt and stir the melt at high power for 10 minutes, then control the temperature of the alloy melt to above 720°C, add pure Zn and pure Mg respectively, use a graphite bell to press it into the bottom of the melt when adding pure Mg, remove the bell after it is completely dissolved, adjust the power of the medium frequency induction furnace to stabilize the temperature of the alloy melt at 740°C, then remove the slag, add a refining agent for degassing and refining; then add Al-5wt% T when the melt temperature drops to 720°C i-1wt% B grain refiner and stir appropriately, finally, after keeping the temperature at 720℃ for 10min, cast the melt into a water-cooled steel mold on all sides, and control the cooling rate to be greater than 30℃ / min; then the ingot is subjected to short-term high-temperature heat treatment, the temperature is 400-435℃, the heating rate is 22-35℃ / min, and the time is 0.5-2.5h; then the ingot subjected to high-temperature heat treatment is directly subjected to large deformation unidirectional hot rolling deformation treatment, the hot rolling deformation is 80-98%, the pass deformation is 5-20%, and the final rolling temperature is greater than 280℃; then the hot-rolled plate is subjected to secondary two-stage high-temperature heat treatment to regulate the distribution characteristics of the alloy's iron-rich phase, precipitation phase and solute elements, the first stage heat treatment temperature is 390-430℃, the heating rate is 22-35℃ / min, the treatment time is 3-15h, the second stage temperature is 430-500℃, the heating rate is 22-35℃ / min, the treatment time is 0.5-4h, cooling rate greater than 100℃ / min; a small deformation amount cold rolling deformation treatment (deformation amount 15-40%, pass deformation amount 2-7%, unidirectional rolling) and a low temperature short time annealing treatment (heating to 390-440℃ at a heating rate greater than 100℃ / min for 10min-240min annealing, and then cooling to room temperature at a cooling rate greater than 50℃ / s) are performed on the alloy plate regulated by the secondary double-stage high temperature heat treatment; the low temperature short time annealing alloy plate is subjected to a first cold rolling deformation treatment (deformation amount 15-40%, pass deformation amount 2-7%, unidirectional rolling) and a low temperature short time annealing treatment (heating to 390-440℃ at a heating rate greater than 100℃ / min for 10min-240min annealing, and then cooling to room temperature at a cooling rate greater than 50℃ / s); The gold plate is subjected to secondary small deformation cold rolling deformation (deformation 15-40%, deformation 2-7% per pass, unidirectional rolling) and secondary low-temperature short-time annealing treatment (heating to 390-440°C at a heating rate greater than 100°C / min for 10min-240min annealing, and then cooling to room temperature at a cooling rate greater than 50°C / s); thrice small deformation cold rolling (deformation 15-40%, deformation 2-7% per pass, unidirectional rolling) and thrice low-temperature short-time annealing treatment (heating to 390-440°C at a heating rate greater than 100°C / min for 10min-240min annealing, and then cooling to room temperature at a cooling rate greater than 50°C / s); The alloy sheet subjected to the three low-temperature annealing treatments is subjected to a fourth cold rolling deformation treatment with a small deformation amount (deformation amount 15-40%, pass deformation amount 2-7%, unidirectional rolling); the alloy sheet subjected to the fourth cold rolling deformation treatment with a small deformation amount is subjected to a high-temperature short-time solution treatment: the solution temperature is 470-500℃, the heating rate is higher than 100℃ / min, and the temperature is then cooled to room temperature at a cooling rate higher than 50℃ / s. The rate is greater than 150℃ / min, and then the alloy sample after solution treatment is quenched and cooled from the solution treatment temperature to room temperature. The quenching cooling rate after solution treatment is greater than 100℃ / s. The quenched sample is transferred to the aging furnace within 1min for double-stage isothermal pre-aging treatment. The first stage temperature is 70-120℃ / 1-12h, and the second stage temperature is 20-60℃ / 5-100h. Finally, the mechanical properties of the 2# alloy plate treated with double-stage isothermal pre-aging are measured, and the corresponding properties are shown in Table 2.

[0045] Example 3

[0046] Implementation of the Invention Alloy 2# alloy is carried out by medium frequency induction melting and casting as follows. The alloy melting process using medium frequency induction under non-vacuum is as follows: first, all the recycled aluminum or ordinary aluminum is added to the crucible and melted, and the temperature is controlled at 780-880°C, and then A l-20wt%Fe, A l-10wt%Mn, A l-10wt%Ti, A l-5wt%Cr, A l-20wt%Si master alloys are added respectively, and then A l-50wt%Cu master alloy is added after melting, and then the melt is stirred at high power for 10 minutes, and then the required content of pure N is added. i into the melt and stir the melt with high power for 10 minutes, then control the temperature of the alloy melt to above 720°C, add pure Zn and pure Mg respectively, use a graphite bell to press pure Mg into the bottom of the melt when adding it, take out the bell after it is completely dissolved, adjust the power of the medium frequency induction furnace to stabilize the temperature of the alloy melt at 740°C, then remove the slag, add a refining agent for degassing and refining; then add Al-5wt% Ti-1wt% B grain refiner when the melt temperature drops to 720°C and stir appropriately, finally, after keeping the temperature at 720°C for 10 minutes, cast the melt into a steel mold with water cooling on all sides, and control the cooling rate to be greater than 30°C / min; then perform a short-time high-temperature heat treatment on the ingot, the temperature is 400-435°C, the heating rate is 22-35°C / min, and the time is 0.5-2.5h; then the ingot subjected to high temperature heat treatment is directly subjected to large deformation unidirectional hot rolling deformation treatment, the hot rolling deformation is 80-98%, the pass deformation is 5-20%, and the final rolling temperature is greater than 280°C; then the hot rolled plate is subjected to secondary double-stage high temperature heat treatment to regulate the distribution characteristics of the alloy iron-rich phase, precipitation phase and solute elements, the first stage heat treatment temperature is 390-430°C, the heating rate is 22-35°C / min, the treatment time is 5-20h, the second stage temperature is 430-500°C, the heating rate is 22-35°C / min, the treatment time is 2-20h, and the cooling rate is greater than 100°C / min; the alloy plate regulated by the secondary double-stage high temperature heat treatment is subjected to A small deformation cold rolling deformation treatment (deformation 15-40%, pass deformation 2-7%, unidirectional rolling) and a low temperature short time annealing treatment (heating to 390-440°C at a heating rate greater than 100°C / min for 10min-240min annealing, and then cooling to room temperature at a cooling rate greater than 50°C / s); the alloy plate subjected to the first low temperature short time annealing is sequentially subjected to a second small deformation cold rolling deformation (deformation 15-40%, pass deformation 2-7%, unidirectional rolling) and a second low temperature short time annealing treatment (heating to 390-440°C at a heating rate greater than 100°C / min for 10min-240m in annealing treatment, followed by cooling to room temperature at a cooling rate greater than 50°C / s); three small deformation cold rolling (deformation 15-40%, pass deformation 2-7%, unidirectional rolling) and three low-temperature short-time annealing treatments (heating to 390-440°C at a heating rate greater than 100°C / min for 10min-240min annealing treatment, followed by cooling to room temperature at a cooling rate greater than 50°C / s); finally, the three low-temperature annealing alloy sheets are subjected to a fourth small deformation cold rolling deformation treatment (deformation 15-40%, pass deformation 2-7%, unidirectional rolling); the fourth small deformation cold rolling deformation alloy sheet is subjected to a high Short-time solution treatment at high temperature: solution temperature 470-500℃, heating rate greater than 150℃ / min, then quench the alloy sample after solution treatment from solution treatment temperature to room temperature, quenching cooling rate greater than 100℃ / s after solution treatment, transfer the quenched sample to the aging furnace within 1min for double-stage isothermal pre-aging treatment, the first stage temperature 70-120℃ / 1-12h, the second stage temperature 20-60℃ / 5-100h; finally, the mechanical properties of the 1# alloy plate treated with double-stage isothermal pre-aging were measured, and finally, the mechanical properties of the 2# alloy plate treated with double-stage isothermal pre-aging were measured, and the corresponding properties are shown in Table 2.

[0047] Example 4

[0048] Implementation of the Invention Alloy 5# alloy is carried out by medium frequency induction melting and casting as follows. The alloy melting process using medium frequency induction under non-vacuum is as follows: first, all the recycled aluminum or ordinary aluminum is added to the crucible and melted, and the temperature is controlled at 780-880°C, and then A l-20wt%Fe, A l-10wt%Mn, A l-10wt%Ti, A l-5wt%Cr, A l-20wt%Si master alloys are added respectively, and then A l-50wt%Cu master alloy is added after melting, and then the melt is stirred at high power for 10 minutes, and then the required content of pure N is added. i into the melt and stir the melt with high power for 10 minutes, then control the temperature of the alloy melt to above 720°C, add pure Zn and pure Mg respectively, press the pure Mg into the bottom of the melt with a graphite bell, take out the bell after it is completely dissolved, adjust the power of the medium frequency induction furnace to stabilize the temperature of the alloy melt at 740°C, then remove the slag, add a refining agent for degassing and refining; then add Al-5wt% Ti-1wt% B grain refiner when the melt temperature drops to 720°C and stir appropriately, finally, after keeping the temperature at 720°C for 10 minutes, cast the melt into a steel mold with water cooling on all sides, and control the cooling rate to be greater than 30°C / min; then perform short-term high-temperature heat treatment on the ingot, the temperature is 400-435°C, the heating rate is 22-35°C / min, the time is 0.5-2h; then the ingot subjected to high temperature heat treatment is directly subjected to large deformation unidirectional hot rolling deformation treatment, the hot rolling deformation is 80-98%, the pass deformation is 5-20%, and the final rolling temperature is greater than 280°C; then the hot rolled plate is subjected to secondary double-stage high temperature heat treatment to adjust the distribution characteristics of the alloy iron-rich phase, precipitation phase and solute elements, the first stage heat treatment temperature is 390-430°C, the heating rate is 22-35°C / min, the treatment time is 3-20h, the second stage temperature is 430-500°C, the heating rate is 22-35°C / min, the treatment time is 2-8h, and the cooling rate is greater than 100°C / min; the secondary double-stage high temperature heat treatment is adjusted The alloy plate subjected to the control is subjected to a first small deformation cold rolling deformation treatment (deformation 15-40%, deformation 2-7% per pass, unidirectional rolling) and a low temperature short time annealing treatment (heating to 390-440°C at a heating rate greater than 100°C / min for 10min-240min annealing, and then cooling to room temperature at a cooling rate greater than 50°C / s); the alloy plate subjected to the first low temperature short time annealing is subjected to a second small deformation cold rolling deformation treatment (deformation 15-40%, deformation 2-7% per pass, unidirectional rolling) and a second low temperature short time annealing treatment (heating to 390-440°C at a heating rate greater than 100°C / min for 10min-240min annealing) in sequence. 0℃ for 10min-240min annealing, then cooling to room temperature at a cooling rate greater than 50℃ / s); three small deformation cold rolling (deformation 15-40%, pass deformation 2-7%, unidirectional rolling) and three low temperature short time annealing (heating to 390-440℃ at a heating rate greater than 100℃ / min for 10min-240min annealing, then cooling to room temperature at a cooling rate greater than 50℃ / s); finally, the alloy sheet subjected to the three low temperature annealing treatments is subjected to a fourth small deformation cold rolling deformation treatment (deformation 15-40%, pass deformation 2-7%, unidirectional rolling); The alloy plates subjected to the fourth small deformation cold rolling deformation treatment were subjected to high temperature short-time solution treatment: solution temperature 470-500℃, heating rate greater than 150℃ / min, then the alloy samples after solution treatment were quenched and cooled from solution treatment temperature to room temperature, the quenching cooling rate after solution treatment was greater than 100℃ / s, the quenched samples were transferred to the aging furnace within 1min for double-stage isothermal pre-aging treatment, the first stage temperature was 70-120℃ / 1-12h, the second stage temperature was 20-60℃ / 5-100h; finally, the mechanical properties of the 5# alloy plates subjected to double-stage isothermal pre-aging treatment were measured, and the corresponding mechanical properties are shown in Table 2.

[0049] Example 5

[0050] Implementation of the Invention Alloy 5# alloy is carried out by medium frequency induction melting and casting as follows. The alloy melting process using medium frequency induction under non-vacuum is as follows: first, all the recycled aluminum or ordinary aluminum is added to the crucible and melted, and the temperature is controlled at 780-880°C, and then A l-20wt%Fe, A l-10wt%Mn, A l-10wt%Ti, A l-5wt%Cr, A l-20wt%Si master alloys are added respectively, and then A l-50wt%Cu master alloy is added after melting, and then the melt is stirred at high power for 10 minutes, and then the required content of pure N is added. i into the melt and stir the melt with high power for 10 minutes, then control the temperature of the alloy melt to above 720°C, add pure Zn and pure Mg respectively, press the pure Mg into the bottom of the melt with a graphite bell, take out the bell after it is completely dissolved, adjust the power of the medium frequency induction furnace to stabilize the temperature of the alloy melt at 740°C, then remove the slag, add a refining agent for degassing and refining; then add Al-5wt% Ti-1wt% B grain refiner when the melt temperature drops to 720°C and stir appropriately, finally, after keeping the temperature at 720°C for 10 minutes, cast the melt into a steel mold with water cooling on all sides, and control the cooling rate to be greater than 30°C / min; then perform short-term high-temperature heat treatment on the ingot, the temperature is 400-435°C, the heating rate is 22-35°C / min, the time is 0.5-2h; then the ingot subjected to high temperature heat treatment is directly subjected to large deformation unidirectional hot rolling deformation treatment, the hot rolling deformation is 80-98%, the pass deformation is 5-20%, and the final rolling temperature is greater than 280°C; then the hot rolled plate is subjected to secondary double-stage high temperature heat treatment to adjust the distribution characteristics of the alloy iron-rich phase, precipitation phase and solute elements, the first stage heat treatment temperature is 390-430°C, the heating rate is 22-35°C / min, the treatment time is 4-30h, the second stage temperature is 430-500°C, the heating rate is 22-35°C / min, the treatment time is 6-30h, and the cooling rate is greater than 100°C / min; the secondary double-stage high temperature heat treatment The regulated alloy plate is subjected to a small deformation cold rolling deformation treatment (deformation 15-40%, pass deformation 2-7%, unidirectional rolling) and a low temperature short time annealing treatment (heating to 390-440°C at a heating rate greater than 100°C / min for 10min-240min annealing, and then cooling to room temperature at a cooling rate greater than 50°C / s); the alloy plate subjected to the first low temperature short time annealing is subjected to a second small deformation cold rolling deformation (deformation 15-40%, pass deformation 2-7%, unidirectional rolling) and a second low temperature short time annealing treatment (heating to 390-4 40℃ for 10min-240min annealing, then cooling to room temperature at a cooling rate greater than 50℃ / s); three small deformation cold rolling (deformation 15-40%, pass deformation 2-7%, unidirectional rolling) and three low temperature short time annealing (heating to 390-440℃ at a heating rate greater than 100℃ / min for 10min-240min annealing, then cooling to room temperature at a cooling rate greater than 50℃ / s); finally, the three low temperature annealing alloy plates are subjected to a fourth small deformation cold rolling deformation treatment (deformation 15-40%, pass deformation 2-7%, unidirectional rolling); The alloy plates subjected to the fourth small deformation cold rolling deformation treatment were subjected to high temperature short-time solution treatment: solution temperature 470-500℃, heating rate greater than 150℃ / min, then the alloy samples after solution treatment were quenched and cooled from solution treatment temperature to room temperature, the quenching cooling rate after solution treatment was greater than 100℃ / s, the quenched samples were transferred to the aging furnace within 1min for double-stage isothermal pre-aging treatment, the first stage temperature was 70-120℃ / 1-12h, the second stage temperature was 20-60℃ / 5-100h; finally, the mechanical properties of the 5# alloy plates subjected to double-stage isothermal pre-aging treatment were measured, and the corresponding mechanical properties are shown in Table 2.

[0051] Table 2 Summary of tensile properties of pre-aged alloy plates after different heat treatment processes

[0052]

[0053]

[0054] In recent years, with the acceleration of the lightweight process of automobiles, the amount of aluminum used in the outer and inner panels of the body has gradually increased. However, if the body structure still uses steel structural parts, it will inevitably cause problems such as difficulty in connecting steel and aluminum and corrosion of heterogeneous metals, which is very unfavorable for the rapid development of aluminum alloys for lightweight automobiles. Therefore, it is urgent to develop high-strength and tough new 7xxx series aluminum alloy sheets and preparation methods for body structural parts. However, the aluminum alloy sheets of this series prepared by traditional processes generally have problems such as low room temperature stamping forming performance and high production cost. In order to further reduce the production cost of this series of alloy sheets, it is necessary to make full use of recycled aluminum to melt and cast this series of alloys. However, recycled aluminum generally contains impurity elements Fe, which is very easy to produce dendritic, rod-shaped or coarse granular iron-rich phases in the cast alloy after the presence of this element. Although these phases can be broken during the subsequent hot working process, it is inevitable that coarse iron-rich phase particles that are not completely broken will be distributed in the final alloy matrix, and microcracks will remain inside it, as well as uneven distribution, which will affect the plasticity, forming properties and corrosion resistance of the alloy. Therefore, it is necessary to optimize the composition design and coordinately control the size, morphology and distribution of the alloy sheet through subsequent hot working multi-process, so that the stamping forming performance of the alloy sheet can be significantly improved. The present invention makes full use of the solute element Fe, which is generally contained in a high content of recycled aluminum or ordinary aluminum. By optimizing the content of Zn, Mg, Fe, Cu and Mn elements, it can not only be dissolved in the alloy matrix, but also form a concentration gradient distribution feature in the cast state. The distribution characteristics of the solute elements can be further precisely controlled through the hot working process control. For example, short-term low-temperature heat treatment control can appropriately optimize the cast structure, and then it is subjected to high-temperature hot rolling deformation, and the original solute element gradient distribution characteristics can be further inherited to the hot rolled state; at this time, if it is subjected to two-stage heat treatment control, that is, the first stage causes the gradient solute elements to precipitate different scales of precipitation phases (including iron-rich phases and Mg-Zn-Cu precipitation phases, etc.), and then the second stage is used to control the solute elements. High-temperature heat treatment can not only precisely regulate the dissolution and diffusion of the Mg-Zn-Cu precipitate phase, thereby constructing different coupled distribution characteristics of soft micro-regions and hard micro-regions; at the same time, the second-level high-temperature heat treatment regulation can further precipitate fine iron-rich phase particles; subsequent cold rolling and intermediate annealing can further optimize and regulate its distribution; on this basis, subsequent high-temperature solid solution and pre-aging regulation can form precipitate phases with different gradient distribution characteristics (including iron-rich phase and Mg-Zn-Cu precipitate phase) in the micro-region; once the alloy matrix is ​​able to construct such a gradient organizational feature, due to the simultaneous existence of soft micro-regions and hard micro-regions in the micro-region, the alloy can exhibit excellent coordinated deformation ability during deformation, thereby significantly improving the room temperature stamping forming performance of the alloy sheet.In addition, if the cold rolling and intermediate annealing process after the double-stage high-temperature heat treatment is also optimized, that is, repeated small deformation cold rolling deformation + low-temperature short-time annealing treatment, then the alloy sheet will only generate a large amount of strain energy storage on the surface due to the small deformation amount, so a certain amount of nano-precipitation phase (including iron-rich phase and precipitation phase) can be precipitated on the surface during the low-temperature short-time annealing process. After repeated small deformation cold rolling deformation + low-temperature short-time annealing treatment, the precipitation phase (including iron-rich phase and precipitation phase) from the surface to the core of the alloy can present a gradient distribution feature, and its size is relatively small. Then this gradient distribution feature can cooperate with the coarse iron-rich phase in the subsequent high-temperature solid solution process to effectively affect the recrystallization process, that is, the coarse iron-rich phase effectively stimulates the recrystallization nucleation, and the gradient fine precipitation phase can effectively hinder the rapid growth of recrystallized grains, so that the microstructure of the alloy sheet can be further effectively regulated, and the room temperature stamping forming performance of the alloy sheet can be improved. It can be seen from this that the room temperature stamping performance of Al-Zn-Mg-Cu-Fe-Mn alloy sheets can be greatly improved based on the coupled regulation of the gradient structure from the surface to the core of the sheet and the gradient structure distribution of the precipitated phase in the micro-region.

[0055] According to the TEM microstructures of the second and third intermediate annealing states of the 1# alloy prepared in Example 1, it can be seen that an obvious gradient microstructure distribution feature is formed in the alloy matrix. The fine precipitate phase has a gradient distribution feature due to the concentration of solute elements. When the precipitate phase precipitates during the intermediate annealing process, a gradient distribution feature will also appear (such as Figure 2 and 3 In addition, the coarse iron-rich phase formed in the melting and casting process can be effectively crushed by coupling the multi-process of hot processing, and a multi-scale uniform dispersion distribution characteristic is formed in the final state of cold rolling (as shown in FIG. Figure 4 As shown), this is beneficial to further optimize and control the alloy recrystallization structure. In addition, with the introduction of small deformation cold rolling process and low temperature short time intermediate annealing process, the surface strain energy storage of alloy plate is large during cold rolling. During the annealing process, a large number of fine dispersed particles will inevitably be rapidly precipitated on the surface, including iron-rich phase and Al-Mg-Zn-Cu precipitation phase. Finally, in the cold-rolled final alloy plate, there will be a gradient distribution feature of fine dispersed particles from the surface to the core (as shown in Figure 2). Figure 5 ). It can be seen that after the above-mentioned hot processing multi-process coupling regulation, a dual-gradient coupled distribution organizational feature is formed in the alloy cold-rolled final plate, that is, the micro-region gradient organization in which the high-concentration precipitate phase and the low-concentration precipitate phase coexist in the micro-region, and the gradient distribution characteristics of fine dispersed particles from the surface to the core of the alloy plate. The formation of this dual-gradient coupled distribution organizational feature will not only synergistically affect the alloy recrystallization process, optimize the alloy recrystallization organization, and then form the fine-grained and coarse-grained coupled distribution characteristics (such as Figure 6As shown in Figure 2, and because of the coexistence of high-concentration solute micro-regions and low-concentration solute micro-regions in the alloy plate micro-regions, the alloy will show typical soft micro-region and hard micro-region coupling distribution characteristics after double-stage pre-aging regulation (as shown in Figure 2). Figure 7 At the same time, due to the gradient distribution of fine dispersed particles from the surface to the core of the alloy plate, the surface hardness is significantly higher than the core hardness (as shown in Figure 7 As shown in Table 2, it is precisely because of the formation of this dual-gradient coupling distribution feature in the alloy sheet that the alloy sheet exhibits excellent room temperature stamping forming performance (as shown in Table 2), and the average plastic strain ratio r value can reach 0.7171, which is much higher than the level that can be achieved by the previous 7xxx series aluminum alloys.

[0056] On this basis, the content and matching ratio of Mg, Zn, Cu, Fe and Mn elements in the alloy matrix are further designed and optimized, and the double gradient structure in the alloy sheet is further optimized and regulated through subsequent hot processing multiple processes. The new Al-Zn-Mg-Cu-Fe alloy two-stage pre-aged sheet can show more excellent room temperature stamping performance, and the average plastic strain ratio r value characterizing the stamping performance is above 0.8, and the highest can even reach 0.889. This is a level that many series of aluminum alloy sheets, including 5xxx series, 6xxx series and 7xxx series aluminum alloy sheets, have not been able to achieve. It can be seen that the room temperature stamping performance of high-strength 7xxx series aluminum alloy sheets can be greatly improved based on the coupling distribution regulation of the double gradient organization, which plays an important role in further promoting the rapid application of this series of aluminum alloy sheets in the automotive field.

[0057] In summary, the present invention can not only construct the coupled distribution characteristics of the dual gradient organization in the alloy matrix, but also make full use of the excellent coordinated deformation ability between the dual gradient organizations to greatly improve the room temperature stamping forming performance of the aluminum alloy sheet of the series by coordinating the multi-process hot processing of the new Al-Zn-Mg-Cu-Fe alloy ingot. At the same time, the regulation of the dual gradient organization of the aluminum alloy sheet of the series makes full use of the original iron-rich phase, which allows the alloy to be melted and cast using recycled aluminum and ordinary aluminum, which is very beneficial for effectively reducing the production cost of the alloy sheet. The substantial improvement in room temperature stamping forming performance and the effective reduction in production costs indicate that the new aluminum alloy material and its preparation method are very suitable for the manufacture of automotive body structural parts, and also play an important role in promoting the rapid development of aluminum alloys for lightweight automobiles. In addition, it also has certain guiding significance for the development, processing and application of high-formability and high-strength aluminum alloys in other fields, and it is worthy of automobile manufacturers and aluminum alloy processing enterprises to pay attention to this invention so that it can be promoted and applied in this field as soon as possible.

[0058] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for regulating the dual-gradient structure coupling distribution of a high-formability aluminum alloy sheet, characterized in that: The aluminum alloy is an Al-Zn-Mg-Cu-Fe-Mn alloy, and its chemical composition and mass percentage are as follows: Zn: 5.0-7.0wt%, Mg: 1.0-2.0wt%, Cu: 1.5-2.5wt%, Fe: 0.1-0.5wt%, Mn: 0.05-0.3wt%, Ni: 0.02-0.07wt%, Ti: 0.02-0.3wt%, Cr: 0.01-0.04wt%, Si: 0.01-0.05wt%, and the balance is Al; The specific preparation steps include: (1) Using recycled aluminum or ordinary aluminum to prepare a high-formability Al-Zn-Mg-Cu-Fe-Mn alloy, then using medium-frequency induction melting in non-vacuum conditions, and casting it in a water-cooled steel mold, the cooling rate is controlled to be greater than 30°C / min so that the alloy grain size, solute element segregation, and primary phase distribution meet the subsequent regulation requirements; (2) According to the as-cast structure, the ingot is subjected to a short-term high-temperature heat treatment at a temperature of 400-440°C, a heating rate of 22-35°C / min, and a treatment time of 0.5-3h; then the ingot subjected to the high-temperature heat treatment is directly subjected to a large deformation hot rolling deformation treatment, with a hot rolling deformation of 80-98%; (3) The hot-rolled plate is then subjected to a secondary double-stage high-temperature heat treatment to control the distribution characteristics of the alloy's iron-rich phase, precipitation phase, and solute elements. The first stage heat treatment temperature is 390-430°C, the heating rate is 22-35°C / min, and the treatment time is 1-30h. The second stage temperature is 430-500°C, the heating rate is 22-35°C / min, and the treatment time is 0.5-30h. (4) Subsequently, the alloy plate subjected to the secondary double-stage high-temperature heat treatment is subjected to four small deformation cold rolling deformation treatments and three low-temperature short-time annealing treatments in sequence, wherein the four small deformations are all 15-40%, and the annealing temperatures of the three low-temperature short-time annealing treatments are all 380-440° C., and the annealing time is all 10 min-240 min; (5) The alloy plate subjected to the fourth small deformation cold rolling deformation treatment was then subjected to a high-temperature short-time solution treatment: the solution temperature was 470-500°C, and then the alloy sample after the solution treatment was quenched and cooled from the solution treatment temperature to room temperature. The quenched sample was transferred to an aging furnace within 1 min for a two-stage isothermal pre-aging treatment, with the first stage temperature being 60-120°C and the second stage temperature being 20-60°C. The alloy plate exhibited excellent stamping forming properties at room temperature.

2. According to the method for controlling the dual gradient structure coupling distribution of a high formability aluminum alloy plate material as described in claim 1, in step (1) of the preparation method, the alloy melting process using medium frequency induction under non-vacuum is as follows: first, all the recycled aluminum or ordinary aluminum is added to the crucible and melted, and the temperature is controlled at 780-880°C, and then Al-20wt% Fe, Al-10wt% Mn, Al-10wt% Ti, Al-5wt% Cr, Al-20wt% Si master alloys are added respectively, and Al-50wt% Cu master alloy is added after melting, and then the melt is stirred at high power for 10 minutes, and then the required content of pure N is added. i into the melt and stir the melt with high power for 10 minutes, then control the temperature of the alloy melt to above 720°C, add pure Zn and pure Mg respectively, use a graphite bell to press it into the bottom of the melt when adding pure Mg, take out the bell after it is completely dissolved, adjust the power of the medium frequency induction furnace to stabilize the temperature of the alloy melt at 740°C again, then skim the slag, add a refining agent for degassing and refining; then add Al-5wt%Ti-1wt%B grain refiner when the melt temperature is reduced to 720°C and stir appropriately, finally, after keeping the temperature at 720°C for 10 minutes, cast the melt into a steel mold with water cooling on all sides, and control the cooling rate to be greater than 30°C / min.

3. According to the method for controlling the dual gradient microstructure coupling distribution of a high-formability aluminum alloy plate material as described in claim 1, in step (2) of the preparation method, the ingot is subjected to a short-term high-temperature heat treatment at a temperature of 400-435°C, a heating rate of 22-35°C / min, and a time of 0.5-2.5h; then the ingot subjected to the high-temperature heat treatment is directly subjected to a large deformation hot rolling deformation treatment, with a hot rolling deformation of 80-98%, a pass deformation of 5-20%, a final rolling temperature greater than 280°C, and unidirectional rolling.

4. According to the method for controlling the dual gradient structure coupling distribution of a high-formability aluminum alloy plate material as described in claim 1, in step (3) of the preparation method, the hot-rolled plate material is subjected to a secondary two-stage high-temperature heat treatment to control the distribution characteristics of the alloy's iron-rich phase, precipitation phase and solute elements, the first stage heat treatment temperature is 390-430°C, the heating rate is 22-35°C / min, the processing time is 1-30h, the second stage temperature is 430-500°C, the heating rate is 22-35°C / min, the processing time is 0.5-30h, and the cooling rate is greater than 100°C / min.

5. According to the method for controlling the dual gradient microstructure coupling distribution of a high formability aluminum alloy plate as described in claim 1, in step (4) of the preparation method, the alloy plate subjected to the secondary double-stage high temperature heat treatment is sequentially subjected to four small deformation cold rolling deformation treatments and three low temperature short time annealing treatments, the deformation amount is 15-40%, the deformation amount per pass is 2-7%, and all are unidirectional rolling; the heating rates of the three low temperature short time annealing treatments are all greater than 100°C / min, the heating temperatures are all 390-440°C, the annealing time is all 10min-240min, and then the temperature is cooled to room temperature at a cooling rate greater than 50°C / s.

6. According to the method for controlling the dual gradient microstructure coupling distribution of a high-formability aluminum alloy plate material as described in claim 1, in step (5) of the preparation method, the alloy plate material after the fourth small deformation cold rolling deformation treatment is subjected to a high-temperature short-time solution treatment: the solution temperature is 470-500°C, and the heating rate is greater than 150°C / min. The alloy sample after the solution treatment is then quenched and cooled from the solution treatment temperature to room temperature. The quenching cooling rate after solution treatment is greater than 100°C / s. The quenched sample is transferred to an aging furnace within 1 minute for a two-stage isothermal pre-aging treatment. The first stage temperature is 70-120°C / 1-12h, and the second stage temperature is 20-60°C / 5-100h. The alloy plate material can exhibit excellent stamping forming performance at room temperature.

Images