Aluminum alloy plate and preparation method thereof

Abstract

The invention provides an aluminum alloy plate and a preparation method thereof. The preparation method comprises the steps that smelting, casting, soaking and heating integrated treatment, hot rolling and cold rolling are sequentially conducted after ingredients of an aluminum alloy plate are prepared, and a cold-rolled coiled material is obtained; the aluminum alloy plate comprises the following components in percentage by mass: 0.6-1.3% of Si element, less than or equal to 0.5% of Fe element, 0.5-1.1% of Cu element, less than or equal to 1.0% of Mn element, 0.6-1.2% of Mg element, less than or equal to 0.25% of Cr element, less than or equal to 0.7% of Zn element, less than or equal to 0.2% of Ti element, less than or equal to 0.2% of Zr element and the balance of Al element. The cold-rolled coiled material is sequentially subjected to solid solution treatment, quenching (multi-stage cooling), straightening and pre-aging, and a first finished coiled material is obtained; and the first finished coiled material is subjected to differential temperature heating artificial aging treatment, and the aluminum alloy plate is obtained. The production efficiency of the preparation method is high, and the comprehensive performance of the obtained aluminum alloy plate is good.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, and more specifically, to an aluminum alloy sheet and its preparation method. Background Technology

[0002] Aluminum alloy sheets are considered ideal materials for automotive lightweighting due to their advantages such as light weight, high specific strength, excellent overall performance, and ease of recycling. However, for aluminum alloy parts to replace steel parts, the strength of aluminum alloy materials still needs further improvement.

[0003] High-strength alloys typically incorporate alloying elements to improve their mechanical properties, but these elements may reduce the material's corrosion resistance. Simply pursuing high strength can compromise corrosion resistance, thus requiring a balance between the two. Furthermore, in a vehicle collision, the material needs to absorb energy through bending and plastic deformation to reduce the impact on occupants. This necessitates that aluminum alloys maintain strength while possessing good formability.

[0004] Therefore, there is an urgent need to develop a corrosion-resistant aluminum alloy sheet and its preparation method that can take into account strength, corrosion resistance and formability, so as to meet the requirements of lightweighting and ensure the durability and safety of vehicles. Summary of the Invention

[0005] The main objective of this invention is to provide an aluminum alloy sheet and its preparation method, so as to solve the problems of low production efficiency of aluminum alloys in the prior art and the difficulty in achieving strength, corrosion resistance and formability of the prepared automotive aluminum alloys.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for preparing an aluminum alloy sheet is provided, the method comprising: step S1, after feeding the aluminum alloy sheet according to its composition, sequentially performing melting, casting, integrated homogenization heating treatment, hot rolling, and cold rolling to obtain a cold-rolled coil; wherein, by mass percentage, the composition of the aluminum alloy sheet comprises: 0.6~1.3% Si; Fe ≤0.5%; 0.5~1.1% Cu; Mn ≤1.0%; 0.6~1.2% Mg; Cr ≤0.25%; Zn ≤0.7%; Ti ≤0.2%; Zr ≤0.2%; and the total content of unavoidable impurities ≤0.15%. The content of a single type of impurity is ≤0.05%, with the balance being Al element; Step S2, the cold-rolled coil is subjected to solution treatment, quenching, straightening and pre-aging treatment in sequence to obtain the first finished coil; Step S3, the first finished coil is subjected to differential temperature heating artificial aging treatment to obtain aluminum alloy sheet; wherein, the quenching method is multi-stage cooling, which includes a first stage cooling, a second stage cooling and a third stage cooling in sequence, and the cooling rate in the temperature range of 300~400℃ during the second stage cooling is 100~300℃ / s; the differential temperature heating artificial aging treatment includes a first artificial aging treatment and a second artificial aging treatment in sequence, and the temperature of the first artificial aging treatment is 30~50℃ higher than the temperature of the second artificial aging treatment.

[0007] Further, in step S3 above, a trolley-type heating furnace is used for differential temperature heating artificial aging treatment. The trolley-type heating furnace includes a first heating zone, a second heating zone, a third heating zone, a fourth heating zone, a fifth heating zone, and a sixth heating zone connected in sequence. The first artificial aging treatment is performed in the first heating zone and the second heating zone, and the second artificial aging treatment is performed in the third heating zone, the fourth heating zone, the fifth heating zone, and the sixth heating zone. The heating rate of the first artificial aging treatment is 30~100℃ / h; the time of the first artificial aging treatment is 1.4~5.6h; the temperature of the second artificial aging treatment is 165~195℃, and the time of the second artificial aging treatment is 4~20h.

[0008] Further, in step S1 above, the integrated homogenization and heating process includes a homogenization heat treatment and a heating treatment performed sequentially; wherein, the heating rate of the homogenization heat treatment is 20~100℃ / h, the temperature of the homogenization heat treatment is 540~570℃, and the time of the homogenization heat treatment is 4~30h; the temperature of the heating treatment is 535~560℃, and the time of the heating treatment is 1~18h.

[0009] Furthermore, in step S1 above, the initial rolling temperature of hot rolling is 535~560℃, the final rolling temperature of hot rolling is 240~360℃, and the thickness of the hot-rolled coil is 2~8mm; and / or, the cold rolling rate of cold rolling is 50~90%, and the thickness of the cold-rolled coil is 0.6~3.0mm.

[0010] Furthermore, step S1 above also includes: intermediate annealing during the multi-pass cold rolling process; wherein the intermediate annealing temperature is 410~520℃ and the intermediate annealing time is 10~60s.

[0011] Furthermore, in step S2 above, the solution temperature is 535~570℃, the solution time is 10~150s; and / or, the straightening amount is 0.2~1.0%.

[0012] Furthermore, in step S2 above, the pre-aging treatment is either isothermal pre-aging treatment or cooling pre-aging treatment; wherein, the temperature of the isothermal pre-aging treatment is 70~100℃, and the time of the isothermal pre-aging treatment is 4~10h; the starting temperature of the cooling pre-aging treatment is 90~110℃, and the cooling rate of the cooling pre-aging treatment is 1~3℃ / h.

[0013] Furthermore, in step S2 above, the yield strength of the first finished roll material is 145~200MPa, the tensile strength of the first finished roll material is ≥275MPa, the elongation at break of the first finished roll material is ≥20%, and the work hardening index n of the first finished roll material is... (5-15) ≥0.26, the Lankford coefficient r of the first finished roll material 10 ≥0.6; After sequential 2% pre-stretching and baking at 185℃ for 20 min, the yield strength of the first finished roll is ≥290MPa, the tensile strength of the first finished roll is ≥350MPa, the maximum depth of intergranular corrosion of the first finished roll is ≤250μm, and the average depth of intergranular corrosion of the first finished roll is ≤150μm.

[0014] According to another aspect of the present invention, an aluminum alloy sheet is provided, which is prepared by the above-described preparation method.

[0015] Furthermore, the aluminum alloy sheet has a yield strength ≥340MPa, a tensile strength ≥390MPa, and a fracture elongation ≥12%; the maximum depth of intergranular corrosion of the aluminum alloy sheet is ≤250μm, and the average depth of intergranular corrosion of the aluminum alloy sheet is ≤150μm.

[0016] The aluminum alloy sheet obtained by the preparation method of this application using the technical solution of this invention has high strength, good corrosion resistance, and formability, which can meet the requirements of lightweight aluminum alloys for automobiles while ensuring the durability and safety of vehicles. Specifically, 1) the aluminum alloy composition of this application constructs a novel Al-Mg-Si-Cu quaternary strengthening alloy system with Cu element mass content within the above-mentioned range. Increasing the Cu element mass content can reduce the nucleation barrier of precipitation strengthening phases, promote the formation of precipitation strengthening phases, thereby accelerating the aging hardening rate and improving the strength performance of the aluminum alloy sheet. This achieves a synergistic improvement in strength performance under various service conditions while maintaining good formability. Simultaneously, it accelerates aging kinetics, shortens heat treatment time, and thus improves production efficiency. By adding microalloying elements Mn, Cr, Ti, and Zr, the synergistic effect between the main alloying elements and microalloying elements can be improved, fully utilizing precipitation strengthening and grain refinement effects, thereby further synergistically improving the strength, formability, and corrosion resistance of the aluminum alloy sheet. Therefore, the aluminum alloy sheet of this application solves the core problems of insufficient strength and slow baking response of traditional Al-Mg-Si automotive sheets, and has high industrial application value. 2) Based on JMatPro thermodynamic calculations and TTT curve analysis, and combined with the characteristics of the on-site cooling equipment of the continuous annealing line, this application innovatively develops a multi-stage cooling process for solution quenching. In particular, by controlling the cooling rate of the second stage of quenching within the above-mentioned range, high-speed cooling can be achieved, thereby effectively suppressing the continuous network precipitation of the Q' phase (AlCuMgSi phase) at the grain boundaries, changing its morphology from a continuous distribution to a discontinuous distribution. The optimized and controlled microstructure of the grain boundaries can improve the intergranular corrosion resistance of the aluminum alloy sheet on the one hand, and enhance its formability on the other hand, thereby achieving a balance of comprehensive properties such as strength, formability and corrosion resistance. 3) Compared to traditional isothermal artificial aging treatment, the differential temperature heating artificial aging treatment in this application controls the temperature of the first artificial aging treatment to be 30-50°C higher than that of the second artificial aging treatment. This accelerates the heating rate of the heating stage (first artificial aging treatment) and reduces the time required for the heating stage, thereby significantly improving production efficiency. 4) The dwell time between solution quenching and artificial aging has a certain impact on the performance of the alloy in the T6 state. Traditional processes require strict control of consistent dwell time to ensure batch-to-batch performance stability. However, in actual production scheduling, this requirement is often difficult to achieve due to factors such as equipment scheduling and process integration. The pre-aging process introduced in this application can improve the stability of aluminum alloy sheets, reduce the sensitivity of aluminum alloy performance to the dwell time after solution treatment, and ensure the consistency of material performance across batches with different dwell times. This improves the flexibility of production scheduling and provides convenience for actual production management. Typically, Al-Mg-Si system aluminum alloys exhibit natural aging after solution treatment, which reduces the stability of the aluminum alloy material.This application incorporates a pre-aging process after solution treatment. On one hand, it actively utilizes supersaturated vacancies to form fine and uniform solute atom clusters or transition phases, reducing free vacancy concentration and hindering the formation of unfavorable coarse clusters during natural aging, thereby improving the stability of the aluminum alloy material. On the other hand, the fine clusters formed during pre-aging can serve as nucleation sites for the strengthening phase during subsequent differential temperature heating (DHT) artificial aging, promoting denser and more uniform precipitation, thus enhancing the response efficiency of DHT artificial aging and further improving the final strength of the aluminum alloy sheet. 5) The preparation method of this application eliminates the need for intermediate annealing between multiple cold rolling passes, thereby shortening the production cycle, improving production efficiency, and reducing production costs. Simultaneously, the absence of intermediate annealing significantly increases the cold rolling rate, further refining the grain structure and improving the overall performance of the aluminum alloy sheet. In summary, the preparation method of this application has high production efficiency, low energy consumption, and can reduce carbon emissions. Moreover, the aluminum alloy sheet prepared has good comprehensive performance and quality stability, thus making it better suited for application in fields such as automotive lightweighting, rail transportation, aerospace, and shipbuilding and marine engineering. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0018] As analyzed in the background section of this application, the production efficiency of aluminum alloys in the prior art is low, and the aluminum alloys prepared for automobiles have problems in balancing strength, corrosion resistance and formability. In order to solve the above problems, this application provides an aluminum alloy sheet and a method for preparing the same.

[0019] In a typical embodiment of this application, a method for preparing an aluminum alloy sheet is provided. The method includes: step S1, where the aluminum alloy sheet is prepared according to its composition and then sequentially subjected to melting, casting, integrated homogenization heating treatment, hot rolling, and cold rolling to obtain a cold-rolled coil. The aluminum alloy sheet, by mass percentage, comprises: 0.6-1.3% Si, ≤0.5% Fe, 0.5-1.1% Cu, ≤1.0% Mn, 0.6-1.2% Mg, ≤0.25% Cr, ≤0.7% Zn, ≤0.2% Ti, ≤0.2% Zr, and a total unavoidable impurity content ≤0.15%, with unavoidable single-type impurities... The content is ≤0.05%, and the balance is Al element; Step S2, the cold-rolled coil is subjected to solution treatment, quenching, straightening and pre-aging treatment in sequence to obtain the first finished coil; Step S3, the first finished coil is subjected to differential temperature heating artificial aging treatment to obtain aluminum alloy sheet; wherein, the quenching method is multi-stage cooling, which includes a first stage cooling, a second stage cooling and a third stage cooling in sequence. During the second stage cooling, the cooling rate in the temperature range of 300~400℃ is 100~300℃ / s, preferably 100~200℃ / s; the differential temperature heating artificial aging treatment includes a first artificial aging treatment and a second artificial aging treatment in sequence. The temperature of the first artificial aging treatment is 30~50℃ higher than the temperature of the second artificial aging treatment.

[0020] The aluminum alloy sheet prepared by the method described in this application exhibits high strength, good corrosion resistance, and formability, meeting the lightweight requirements of automotive aluminum alloys while ensuring vehicle durability and safety. Specifically, 1) the aluminum alloy composition of this application constructs a novel Al-Mg-Si-Cu quaternary strengthening alloy system with Cu content within the aforementioned range. Increasing the Cu content lowers the nucleation barrier of the precipitation strengthening phase, promoting its formation and accelerating the aging hardening rate, thereby improving the strength properties of the aluminum alloy sheet. This achieves a synergistic improvement in strength properties under various service conditions while maintaining good formability. Simultaneously, it accelerates aging kinetics, shortening heat treatment time and improving production efficiency. The addition of microalloying elements Mn, Cr, Ti, and Zr enhances the synergistic effect between the main alloying elements and microalloying elements, fully leveraging precipitation strengthening and grain refinement to further synergistically improve the strength, formability, and corrosion resistance of the aluminum alloy sheet. Therefore, the aluminum alloy sheet of this application solves the core problems of insufficient strength and slow baking response in traditional Al-Mg-Si automotive sheets, possessing high industrial application value. 2) Based on JMatPro thermodynamic calculations and TTT curve analysis, and combined with the characteristics of the on-site cooling equipment in the continuous annealing line, this application innovatively develops a multi-stage cooling process for solution quenching. In particular, by controlling the cooling rate of the second stage of quenching within the aforementioned range, high-speed cooling can be achieved, thereby effectively suppressing the continuous network precipitation of the Q' phase (AlCuMgSi phase) at the grain boundaries, changing its morphology from a continuous distribution to a discontinuous distribution. The optimized and controlled grain boundary microstructure can improve the intergranular corrosion resistance of aluminum alloy sheets on the one hand, and enhance their formability on the other hand, thus achieving a balance between comprehensive properties such as strength, formability, and corrosion resistance. 3) Compared with traditional isothermal artificial aging treatment, the differential temperature heating artificial aging treatment in this application controls the temperature of the first artificial aging treatment to be 30~50℃ higher than that of the second artificial aging treatment, which can accelerate the heating rate of the heating stage (first artificial aging treatment) and reduce the time required for the heating stage, thereby significantly improving production efficiency. 4) The dwell time between solution quenching and artificial aging has a certain impact on the properties of the alloy in the T6 state. Traditional processes require strict control of consistent dwell time to ensure batch-to-batch performance stability. However, in actual production scheduling, this requirement is often difficult to achieve due to factors such as equipment scheduling and process integration. This application introduces a pre-aging process, which can improve the stability of aluminum alloy sheets, reduce the sensitivity of aluminum alloy properties to the dwell time after solution treatment, and ensure the consistency of material properties in batches with different dwell times. This improves the flexibility of production scheduling and provides convenience for actual production management. Typically, Al-Mg-Si system aluminum alloys undergo natural aging after solution treatment, which reduces the stability of the aluminum alloy material.This application incorporates a pre-aging process after solution treatment. On one hand, it actively utilizes supersaturated vacancies to form fine and uniform solute atom clusters or transition phases, reducing free vacancy concentration and hindering the formation of unfavorable coarse clusters during natural aging, thereby improving the stability of the aluminum alloy material. On the other hand, the fine clusters formed during pre-aging can serve as nucleation sites for the strengthening phase during subsequent differential temperature heating (DHT) artificial aging, promoting denser and more uniform precipitation, thus enhancing the response efficiency of DHT artificial aging and further improving the final strength of the aluminum alloy sheet. 5) The preparation method of this application eliminates the need for intermediate annealing between multiple cold rolling passes, thereby shortening the production cycle, improving production efficiency, and reducing production costs. Simultaneously, the absence of intermediate annealing significantly increases the cold rolling rate, further refining the grain structure and improving the overall performance of the aluminum alloy sheet. In summary, the preparation method of this application has high production efficiency, low energy consumption, and can reduce carbon emissions. Moreover, the aluminum alloy sheet prepared has good comprehensive performance and quality stability, thus making it better suited for application in fields such as automotive lightweighting, rail transportation, aerospace, and shipbuilding and marine engineering.

[0021] Furthermore, no special requirements are placed on the first and third stages of cooling during quenching. According to the TTT curve analysis of precipitation kinetics, the nose temperature of the Q' phase (AlCuMgSi phase) in the alloy is 300~400℃, that is, the temperature range of the second stage of cooling is 300~400℃, the temperature range of the first stage is 400~570℃, and the temperature range of the third stage is room temperature~300℃. The precipitation kinetics of the Q' phase (AlCuMgSi phase) are relatively small. Therefore, no special requirements are placed on the cooling rate.

[0022] Preferably, the aluminum alloy sheet comprises, by mass percentage, the following elements: 0.65-0.95% Si, 0-0.3% Fe, 0.6-0.9% Cu, 0-0.3% Mn, 0.7-1.0% Mg, 0-0.3% Cr, 0-0.5% Zn, 0-0.1% Ti, and 0-0.1% Zr, with the total content of unavoidable impurities ≤0.15%, the content of any unavoidable single type of impurity ≤0.05%, and the balance being Al.

[0023] The mass content of Mg, Si and Cu elements has a significant impact on the performance of the alloy. The mass content of Mg is X%, the mass content of Si is Y%, the mass content of Cu is Z%, and (X+Y)×Z is 0.87~1.76, which helps to balance the strength, formability and corrosion resistance of aluminum alloy sheets and comprehensively improve the performance of aluminum alloys.

[0024] In one embodiment of this application, in step S3 above, a trolley-type heating furnace is used for differential temperature heating artificial aging treatment. The trolley-type heating furnace includes a first heating zone, a second heating zone, a third heating zone, a fourth heating zone, a fifth heating zone, and a sixth heating zone connected in sequence. A first artificial aging treatment is performed in the first heating zone and the second heating zone, and a second artificial aging treatment is performed in the third heating zone, the fourth heating zone, the fifth heating zone, and the sixth heating zone. The heating rate of the first artificial aging treatment is 30~100℃ / h; the time of the first artificial aging treatment is 1.4~5.6 h; the temperature of the second artificial aging treatment is 165~195℃, and the time of the second artificial aging treatment is 4~20 h.

[0025] A bogie-type heating furnace is preferred for differential temperature heating artificial aging treatment. The furnace chamber is divided into six zones (first heating zone, second heating zone, third heating zone, fourth heating zone, fifth heating zone, and sixth heating zone), each with independently controllable temperature. This allows for precise control of the differential temperature heating process, better optimizing the distribution and size of precipitated phases, and achieving superior aging results. Preferably, the temperatures of the first two zones are higher than those of the latter four zones, which helps accelerate the aging process in different areas of the aluminum alloy and improves production efficiency. Controlling the heating rate, the time of the first artificial aging treatment, and the temperature and time of the second artificial aging treatment within the aforementioned ranges helps to orderly aggregate solute atoms in the aluminum alloy to form stable precipitated phases, thereby improving the overall performance of the aluminum alloy sheet.

[0026] The bogie speed of the bogie-type heating furnace is determined by the furnace length / (heating time + holding time), which helps to achieve rapid heating and continuous automated production in the artificial aging process. One end of the bogie-type heating furnace is the inlet and the other end is the outlet. Compared with traditional heating furnaces where the inlet and outlet are at the same end, or isothermal heating artificial aging processes (with consistent furnace temperature), the production efficiency of this application is increased by 30-40%.

[0027] Differential heating followed by artificial aging treatment and natural cooling helps to alleviate internal stress concentration caused by rapid cooling, thereby maintaining the stability and consistency of aluminum alloy materials.

[0028] In one embodiment of this application, step S1 above, the integrated heat homogenization and heating process includes a homogenization heat treatment and a heating treatment performed sequentially; wherein, the heating rate of the homogenization heat treatment is 20~100℃ / h, the temperature of the homogenization heat treatment is 540~570℃, and the time of the homogenization heat treatment is 4~30h; the temperature of the heating treatment is 535~560℃, and the time of the heating treatment is 1~18h.

[0029] The heating process directly transitions from the homogenization heat treatment process, which is an integrated homogenization heating process. This direct transition avoids the cooling and reheating processes after traditional heat treatment, reducing energy consumption, improving efficiency, and also avoiding performance degradation caused by phase changes that may occur during the cooling process.

[0030] Preferably controlling the heating rate, temperature, and time of the homogenization heat treatment within the aforementioned ranges facilitates the full diffusion of solute atoms within the aluminum alloy, reduces component segregation, and dissolves and destroys the hard phases formed during casting, thereby resulting in a more homogeneous microstructure of the aluminum alloy. Particularly in the Al-Mg-Si system, this facilitates the effective re-dissolution of the Mg2Si and Q' phases, thus promoting the subsequent formation of uniform, fine precipitates, thereby improving the strength and formability of the aluminum alloy sheet. Preferably controlling the temperature and time of the heat treatment within the aforementioned ranges also helps maintain the thermal stability of the aluminum alloy, reduces cracks and other defects during hot rolling, and simultaneously provides the aluminum alloy sheet with plasticity for hot rolling.

[0031] In one embodiment of this application, in step S1 above, the initial rolling temperature of hot rolling is 535~560℃, the final rolling temperature of hot rolling is 240~360℃, and the thickness of the hot-rolled coil is 2~8mm; and / or, the cold rolling rate of cold rolling is 50~90%, preferably 60~80%, and the thickness of the cold-rolled coil is 0.6~3.0mm.

[0032] Hot rolling helps optimize the microstructure of aluminum alloys, thereby improving the mechanical properties of aluminum alloy sheets. Preferably controlling the initial rolling temperature within the aforementioned range helps reduce the deformation resistance of the aluminum alloy sheet, ensuring good fluidity in the early stages of hot rolling, which facilitates thickness control and subsequent processing. Preferably controlling the final rolling temperature within the aforementioned range helps suppress recrystallization, maintaining the metastable structure of the aluminum alloy sheet at the end of hot rolling. This structure is rich in dislocations, providing greater plastic deformation space for subsequent cold rolling and solution treatment, thus contributing to finer grains and a more uniform precipitate distribution. Furthermore, it helps reduce oxidation and surface damage during hot rolling, thereby improving the surface quality and corrosion resistance of the finished product.

[0033] Preferably controlling the cold rolling ratio within the above range helps to increase the dislocation density of the cold-rolled sheet, causing the original grains to break and elongate, while accumulating a large amount of deformation energy. This high energy storage state helps to promote the formation of a large number of recrystallization nuclei during annealing, ultimately resulting in a fine and uniform grain structure. This optimization of the microstructure helps to simultaneously improve multiple properties of aluminum alloy sheets: the fine grain strengthening effect helps to improve the strength of the material; the uniform and fine grain structure helps to improve deformation coordination, thereby enhancing the formability of the material; in addition, the fine grain structure can also hinder the propagation of grain boundary corrosion, thereby improving the material's resistance to intergranular corrosion. This method of controlling grain size through cold rolling ratio provides an effective way to comprehensively improve the strength, formability, and corrosion resistance of aluminum alloy sheets.

[0034] In one embodiment of this application, step S1 further includes: performing intermediate annealing during the multi-pass cold rolling process; wherein the intermediate annealing temperature is 410~520℃ and the intermediate annealing time is 10~60s.

[0035] Depending on actual production needs, intermediate annealing can be set between multiple cold rolling passes. Controlling the temperature and time of intermediate annealing within the above range helps to restore the plasticity of aluminum alloy sheets, reduce cold work hardening, and reduce the generation of cracks.

[0036] In one embodiment of this application, in step S2 above, the solution temperature is 535~570℃, the solution time is 10~150s; and / or, the straightening amount is 0.2~1.0%.

[0037] Preferably controlling the solution temperature and time within the aforementioned range not only helps promote the dissolution of elements such as Cu and Mg, forming a supersaturated state, which in turn facilitates the rapid precipitation of fine strengthening phases during subsequent aging treatment, thereby improving the strength of the aluminum alloy sheet, but also helps to make the microstructure more uniform, thus improving the plasticity and formability of the aluminum alloy sheet. Preferably controlling the straightening amount within the aforementioned range helps to reduce residual stress within the aluminum alloy sheet, reducing warping during storage and transportation, while maintaining the material's strength and plasticity.

[0038] In one embodiment of this application, in step S2 above, the pre-aging treatment is either isothermal pre-aging treatment or cooling pre-aging treatment; wherein, the temperature of the isothermal pre-aging treatment is 70~100℃, and the time of the isothermal pre-aging treatment is 4~10h; the starting temperature of the cooling pre-aging treatment is 90~110℃, and the cooling rate of the cooling pre-aging treatment is 1~3℃ / h.

[0039] Preferably controlling the temperature and time of the isothermal pre-aging treatment within the aforementioned range not only helps stabilize the microstructure of the material and reduce strength changes caused by natural aging, thereby improving the stability of the material during subsequent processing and use, but also helps promote the formation of atomic clusters or transition phases, which serve as nucleation centers for precipitates during differential heating artificial aging, promoting the uniform distribution of precipitates and thus improving the final strength of the aluminum alloy sheet. Preferably controlling the starting temperature of the cooling pre-aging treatment within the aforementioned range helps promote the formation of atomic clusters or transition phases, while controlling the cooling rate within the aforementioned range helps promote the uniform distribution and stable growth of clusters, thereby balancing the strength and plasticity of the aluminum alloy sheet.

[0040] In one embodiment of this application, in step S2 above, the yield strength of the first finished roll material is 145~200MPa, the tensile strength of the first finished roll material is ≥275MPa, the elongation at break of the first finished roll material is ≥20%, and the work hardening index n of the first finished roll material is... (5-15) ≥0.26, the Lankford coefficient r of the first finished roll material 10 ≥0.6; After sequential 2% pre-stretching and baking at 185℃ for 20 min, the yield strength of the first finished roll is ≥290MPa, the tensile strength of the first finished roll is ≥350MPa, the maximum depth of intergranular corrosion of the first finished roll is ≤250μm, and the average depth of intergranular corrosion of the first finished roll is ≤150μm.

[0041] This application optimizes the alloy composition and process of the Al-Mg-Si-Cu quaternary strengthening system, resulting in excellent strength performance of the plate in various states.

[0042] Preferably, the yield strength of the first finished roll is 145~200MPa, the tensile strength of the first finished roll is ≥285MPa, the elongation at break of the first finished roll is ≥25%, and the work hardening index n of the first finished roll is... (5-15) The Lankford coefficient r of the first finished roll material is ≥0.27. 10 The yield strength of the first finished roll material is ≥0.65; after sequential 2% pre-stretching and baking at 185℃ for 20 min, the yield strength of the first finished roll material is ≥295MPa, the tensile strength of the first finished roll material is ≥355MPa, the maximum depth of intergranular corrosion of the first finished roll material is ≤150μm, and the average depth of intergranular corrosion of the first finished roll material is ≤100μm.

[0043] In another typical embodiment of this application, an aluminum alloy sheet is provided, which is prepared by the above-described preparation method.

[0044] The aluminum alloy sheet obtained by the above preparation method of this application has high strength, good corrosion resistance and formability, which can not only meet the requirements of lightweight aluminum alloy for automobiles, but also ensure the durability and safety of vehicles, and can also be used in rail transportation, aerospace, shipbuilding and marine engineering and other fields.

[0045] In one embodiment of this application, the aluminum alloy sheet has a yield strength ≥340MPa, a tensile strength ≥390MPa, and a fracture elongation ≥12%; the maximum depth of intergranular corrosion of the aluminum alloy sheet is ≤250μm, and the average depth of intergranular corrosion of the aluminum alloy sheet is ≤150μm.

[0046] Compared to the 6451 alloy, which currently boasts the highest strength in the Al-Mg-Si automotive sheet system, the aluminum alloy sheet of this application exhibits mechanical properties improved by over 20%, making it a high-strength automotive sheet material in both the Al-Mg-Si and Al-Mg-Si-Cu systems.

[0047] Preferably, the aluminum alloy sheet has a yield strength of ≥345MPa, a tensile strength of ≥400MPa, and a fracture elongation of ≥14%; the maximum depth of intergranular corrosion of the aluminum alloy sheet is ≤200μm, and the average depth of intergranular corrosion of the aluminum alloy sheet is ≤140μm.

[0048] It should be noted that, due to the special nature of the alloy field and the limitations of existing testing and characterization methods, it is difficult to conduct a comprehensive quantitative characterization of the microstructure of the aluminum alloy sheet obtained above. However, experiments show that the aluminum alloy sheet obtained in this application has higher comprehensive mechanical properties and corrosion resistance.

[0049] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0050] Example 1

[0051] After the aluminum alloy sheet is prepared according to its composition, it is melted and cast sequentially at 750℃ to obtain an ingot. The ingot is then subjected to an integrated homogenization heat treatment, which consists of sequential homogenization heat treatment and heating treatment. The homogenization heat treatment has a heating rate of 30℃ / h, a temperature of 560℃, and a time of 8h; the heating treatment has a temperature of 540℃ and a time of 2h. Subsequently, it is hot-rolled to obtain a hot-rolled coil. The initial rolling temperature is 540℃, the final rolling temperature is 270℃, and the thickness of the hot-rolled coil is 7mm. The hot-rolled coil is then subjected to multiple cold rolling passes to obtain a cold-rolled coil with a cold rolling rate of 79% and a thickness of 1.5mm. The cold-rolled coil is then subjected to sequential solution treatment, quenching, straightening, and pre-aging treatment to obtain the first finished coil. The solution treatment temperature is 555℃, and the time is 30s. The quenching process employs a multi-stage cooling method, involving sequential first, second, and third-stage cooling. During the second-stage cooling, the cooling rate is 100℃ / s within the 300-400℃ temperature range. The straightening amount is 0.5%. Pre-aging treatment is a cooling pre-aging process with an initial temperature of 100℃ and a cooling rate of 2℃ / h. The first finished coil is then subjected to differential heating artificial aging in a bogie-type heating furnace, followed by slicing to obtain aluminum alloy sheets. The differential heating artificial aging process involves sequential first and second artificial aging treatments. The bogie-type heating furnace comprises sequentially connected first, second, third, fourth, fifth, and sixth heating zones. The first artificial aging treatment is performed in the first and second heating zones, and the second artificial aging treatment is performed in the third, fourth, fifth, and sixth heating zones. The temperatures of the first and second heating zones are set to 220℃, and the temperatures of the third, fourth, fifth, and sixth heating zones are set to 180℃. The heating rate of the first artificial aging treatment is 60℃ / h, the temperature of the first artificial aging treatment is 220℃, and the time is 3.3h; the temperature of the second artificial aging treatment is 180℃, and the time of the second artificial aging treatment is 8h.

[0052] The specific composition of the aluminum alloy sheet is shown in Table 1, and the parameters of the preparation method are shown in Tables 2 and 3.

[0053] Examples 2 to 6

[0054] The difference from Example 1 is that the elemental composition of the aluminum alloy sheet is different, as shown in Table 1.

[0055] Examples 7 to 15

[0056] The difference from Example 1 is that the parameters of the preparation method of the aluminum alloy sheet are different, as shown in Tables 2 and 3.

[0057] The intermediate annealing in Examples 9 and 14 was carried out in a multi-pass cold rolling process.

[0058] Example 16

[0059] The difference from Example 1 is that the cooling rate during the second stage of quenching in the temperature range of 300~400℃ is 200℃ / s, and the final product is an aluminum alloy sheet.

[0060] Example 17

[0061] The difference from Example 1 is that the heating rate of the first artificial aging treatment is 100℃ / h, the temperature of the first artificial aging treatment is 215℃, and the time is 19h; the temperature of the second artificial aging treatment is 165℃, and the time of the second artificial aging treatment is 20h, finally obtaining an aluminum alloy sheet.

[0062] Example 18

[0063] The difference from Example 1 is that the heating rate of the first artificial aging treatment is 30℃ / h, the temperature of the first artificial aging treatment is 225℃, and the time is 5h; the temperature of the second artificial aging treatment is 195℃, and the time of the second artificial aging treatment is 4h, finally obtaining an aluminum alloy sheet.

[0064] Example 19

[0065] The difference from Example 1 is that the mass content of Mg is 1.0 (X)%, the mass content of Si is 0.95 (Y)%, the mass content of Cu is 0.9 (Z)%, and (X+Y)×Z is 1.76, resulting in an aluminum alloy sheet.

[0066] Example 20

[0067] The difference from Example 1 is that the mass content of Mg is 0.6 (X)%, the mass content of Si is 0.6 (Y)%, the mass content of Cu is 0.5 (Z)%, and (X+Y)×Z is 0.6, finally obtaining an aluminum alloy sheet.

[0068] Comparative Examples 1 to 5

[0069] The difference from Example 1 is that the elemental composition of the aluminum alloy sheet is different, as shown in Table 1.

[0070] Comparative ratios 6 to 8

[0071] The difference from Example 1 is that the parameters of the preparation method of the aluminum alloy sheet are different, as shown in Tables 2 and 3.

[0072] Test method:

[0073] The mechanical properties, baking performance, and intergranular corrosion performance of the first finished sheet and aluminum alloy sheet were evaluated after being left at room temperature (25°C) for 7 days.

[0074] Yield strength, tensile strength, and elongation at break: Refer to GB / T 228-2010 Metallic materials, tensile test, room temperature test method.

[0075] Work hardening index n ((5-15) Tested according to GB / T 5028-2008 Determination of tensile strain hardening index (n value) of thin plates and strips of metallic materials.

[0076] Lankford coefficient r 10 Tested according to GB / T 5027-2016 Determination of Plastic Strain Ratio (r value) of Thin Plates and Strips of Metallic Materials.

[0077] Baking performance: Tested according to GB / T 33227-2016 Aluminum and aluminum alloy sheets and strips for automobiles.

[0078] Intergranular corrosion:

[0079] According to the test of "BMW Group AA0255-2017-02 Testing the Sensitivity of 6xxxAluminum Alloys for Integranular Corrosion".

[0080] The test results are shown in Tables 4 and 5.

[0081] Table 1

[0082]

[0083] Table 2

[0084]

[0085] Table 3

[0086]

[0087] Table 4

[0088]

[0089] Table 5

[0090]

[0091] As can be seen from the above, the high Cu content in Comparative Example 1 leads to increased element segregation and continuous distribution of Cu-containing precipitates at grain boundaries. Although the strength of the aluminum alloy sheet is improved, the elongation decreases and the corrosion resistance is significantly reduced.

[0092] The low Cu content in Comparative Example 2 resulted in reduced strength performance of the aluminum alloy sheet.

[0093] The high Si content in Comparative Example 3 negatively impacts the formability and corrosion resistance of the aluminum alloy sheet, leading to decreased elongation and corrosion resistance.

[0094] In Comparative Example 4, the Mg content was too high, indicating an excess Mg system. This resulted in a greater driving force from Mg2Si in each process, leaving residual Mg2Si phase in the finished plate. The density of the effectively dispersed strengthening phase was low, leading to a reduction in the strength properties of the aluminum alloy plate.

[0095] The high Zn content in Comparative Example 5 resulted in reduced corrosion resistance of the aluminum alloy sheet.

[0096] In Comparative Example 6, the cooling rate of the second stage of quenching was relatively low, resulting in the continuous network precipitation of the Q' phase (AlCuMgSi) at the grain boundaries, which significantly reduced the corrosion resistance of the aluminum alloy sheet.

[0097] In Comparative Example 7, the temperature of the first artificial aging treatment was 20°C higher than that of the second artificial aging treatment, a relatively small difference, resulting in reduced production efficiency. Meanwhile, the lower temperature of the second artificial aging treatment left the aluminum alloy sheet in an under-aged state, leading to a decrease in its mechanical properties.

[0098] In Comparative Example 8, the first and second artificial efficiency treatments were performed at the same temperature, which is an isothermal artificial efficiency treatment, resulting in a significant decrease in production efficiency. The second artificial efficiency treatment was performed at a higher temperature, causing the aluminum alloy sheet to be in an over-aged state, leading to poor elongation of the aluminum alloy sheet.

[0099] In Example 12, the homogenization temperature was too low, resulting in poor uniformity of the as-cast microstructure. The soluble phases Mg2Si and Q' (AlCuMgSi) were not completely dissolved, and the discontinuity of the insoluble phase AlFeMnSi was not high, leaving the initial phase in the finished plate. The hot rolling temperature was too low, causing Mg2Si to precipitate. The solid solution process could not completely dissolve the Mg2Si phase, leaving the Mg2Si phase in the finished plate. All of these factors combined led to a reduction in the various properties of the aluminum alloy sheet.

[0100] In Example 13, the final rolling temperature of hot rolling was too high, which caused a large amount of Mg2Si to precipitate after hot rolling and coiling, which had an adverse effect on subsequent processing and heat treatment. The solution process could not completely dissolve the Mg2Si phase, leaving residual Mg2Si phase in the finished plate. At the same time, the recrystallized grains grew after hot rolling and coiling, and the genetic effect caused the finished plate to have coarse grains, which together led to a reduction in various properties of the aluminum alloy plate.

[0101] In Example 14, the intermediate annealing temperature was too low, resulting in a lower degree of recrystallization during the intermediate annealing process. At the same time, the precipitation and growth of Mg2Si in this alloy system had an adverse effect on subsequent processing and heat treatment, leading to a reduction in various properties of the aluminum alloy sheet.

[0102] In Example 15, the solution temperature was too low, the recrystallization degree of the cold-rolled sheet was low, and the degree of Mg2Si re-dissolution was poor, which together led to a reduction in the strength and corrosion resistance of the alloy sheet.

[0103] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0104] The aluminum alloy sheet prepared by the method described in this application exhibits high strength, good corrosion resistance, and formability, meeting the lightweight requirements of automotive aluminum alloys while ensuring vehicle durability and safety. Specifically, 1) the aluminum alloy composition of this application constructs a novel Al-Mg-Si-Cu quaternary strengthening alloy system with Cu content within the aforementioned range. Increasing the Cu content lowers the nucleation barrier of the precipitation strengthening phase, promoting its formation and accelerating the aging hardening rate, thereby improving the strength properties of the aluminum alloy sheet. This achieves a synergistic improvement in strength properties under various service conditions while maintaining good formability. Simultaneously, it accelerates aging kinetics, shortening heat treatment time and improving production efficiency. The addition of microalloying elements Mn, Cr, Ti, and Zr enhances the synergistic effect between the main alloying elements and microalloying elements, fully leveraging precipitation strengthening and grain refinement to further synergistically improve the strength, formability, and corrosion resistance of the aluminum alloy sheet. Therefore, the aluminum alloy sheet of this application solves the core problems of insufficient strength and slow baking response in traditional Al-Mg-Si automotive sheets, possessing high industrial application value. 2) Based on JMatPro thermodynamic calculations and TTT curve analysis, and combined with the characteristics of the on-site cooling equipment in the continuous annealing line, this application innovatively develops a multi-stage cooling process for solution quenching. In particular, by controlling the cooling rate of the second stage of quenching within the aforementioned range, high-speed cooling can be achieved, thereby effectively suppressing the continuous network precipitation of the Q' phase (AlCuMgSi phase) at the grain boundaries, changing its morphology from a continuous distribution to a discontinuous distribution. The optimized and controlled grain boundary microstructure can improve the intergranular corrosion resistance of aluminum alloy sheets on the one hand, and enhance their formability on the other hand, thus achieving a balance between comprehensive properties such as strength, formability, and corrosion resistance. 3) Compared with traditional isothermal artificial aging treatment, the differential temperature heating artificial aging treatment in this application controls the temperature of the first artificial aging treatment to be 30~50℃ higher than that of the second artificial aging treatment, which can accelerate the heating rate of the heating stage (first artificial aging treatment) and reduce the time required for the heating stage, thereby significantly improving production efficiency. 4) The dwell time between solution quenching and artificial aging has a certain impact on the properties of the alloy in the T6 state. Traditional processes require strict control of consistent dwell time to ensure batch-to-batch performance stability. However, in actual production scheduling, this requirement is often difficult to achieve due to factors such as equipment scheduling and process integration. This application introduces a pre-aging process, which can improve the stability of aluminum alloy sheets, reduce the sensitivity of aluminum alloy properties to the dwell time after solution treatment, and ensure the consistency of material properties in batches with different dwell times. This improves the flexibility of production scheduling and provides convenience for actual production management. Typically, Al-Mg-Si system aluminum alloys undergo natural aging after solution treatment, which reduces the stability of the aluminum alloy material.This application incorporates a pre-aging process after solution treatment. On one hand, it actively utilizes supersaturated vacancies to form fine and uniform solute atom clusters or transition phases, reducing free vacancy concentration and hindering the formation of unfavorable coarse clusters during natural aging, thereby improving the stability of the aluminum alloy material. On the other hand, the fine clusters formed during pre-aging can serve as nucleation sites for the strengthening phase during subsequent differential temperature heating (DHT) artificial aging, promoting denser and more uniform precipitation, thus enhancing the response efficiency of DHT artificial aging and further improving the final strength of the aluminum alloy sheet. 5) The preparation method of this application eliminates the need for intermediate annealing between multiple cold rolling passes, thereby shortening the production cycle, improving production efficiency, and reducing production costs. Simultaneously, the absence of intermediate annealing significantly increases the cold rolling rate, further refining the grain structure and improving the overall performance of the aluminum alloy sheet. In summary, the preparation method of this application has high production efficiency, low energy consumption, and can reduce carbon emissions. Moreover, the aluminum alloy sheet prepared has good comprehensive performance and quality stability, thus making it better suited for application in fields such as automotive lightweighting, rail transportation, aerospace, and shipbuilding and marine engineering.

[0105] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an aluminum alloy sheet, characterized in that, The preparation method includes: Step S1: After the aluminum alloy sheet is prepared according to its composition, it is sequentially smelted, cast, homogenized heating integrated treatment, hot rolling, and cold rolling to obtain a cold-rolled coil. The aluminum alloy sheet, by mass percentage, comprises: 0.6~1.3% Si; ≤0.5% Fe; 0.5~1.1% Cu; ≤1.0% Mn; 0.6~1.2% Mg; ≤0.25% Cr; ≤0.7% Zn; ≤0.2% Ti; ≤0.2% Zr; total unavoidable impurities ≤0.15%; content of any unavoidable single type of impurity ≤0.05%; and the balance is Al. Step S2: The cold-rolled coil is subjected to solution treatment, quenching, straightening and pre-aging treatment in sequence to obtain the first finished coil. Step S3: Perform differential temperature heating and artificial aging treatment on the first finished coil to obtain the aluminum alloy sheet; The quenching method is multi-stage cooling, which includes a first stage of cooling, a second stage of cooling and a third stage of cooling performed sequentially. During the second stage of cooling, the cooling rate in the temperature range of 300~400℃ is 100~300℃ / s. The differential temperature heating artificial aging treatment includes a first artificial aging treatment and a second artificial aging treatment performed sequentially, wherein the temperature of the first artificial aging treatment is 30-50°C higher than the temperature of the second artificial aging treatment.

2. The preparation method according to claim 1, characterized in that, In step S3, a trolley-type heating furnace is used to perform the differential temperature heating artificial aging treatment. The trolley-type heating furnace includes a first heating zone, a second heating zone, a third heating zone, a fourth heating zone, a fifth heating zone, and a sixth heating zone connected in sequence. The first artificial aging treatment is performed in the first heating zone and the second heating zone, and the second artificial aging treatment is performed in the third heating zone, the fourth heating zone, the fifth heating zone, and the sixth heating zone. The heating rate of the first artificial aging treatment is 30~100℃ / h; the time of the first artificial aging treatment is 1.4~5.6h; the temperature of the second artificial aging treatment is 165~195℃; and the time of the second artificial aging treatment is 4~20h.

3. The preparation method according to claim 1 or 2, characterized in that, In step S1, the integrated homogenization and heating process includes a homogenization heat treatment and a heating treatment performed sequentially; wherein, the heating rate of the homogenization heat treatment is 20~100℃ / h, the temperature of the homogenization heat treatment is 540~570℃, and the time of the homogenization heat treatment is 4~30h; the temperature of the heating treatment is 535~560℃, and the time of the heating treatment is 1~18h.

4. The preparation method according to claim 1 or 2, characterized in that, In step S1, the initial rolling temperature of the hot rolling is 535~560℃, the final rolling temperature of the hot rolling is 240~360℃, and the thickness of the hot-rolled coil is 2~8mm. And / or, the cold rolling rate is 50-90%, and the thickness of the cold-rolled coil is 0.6-3.0 mm.

5. The preparation method according to claim 1 or 2, characterized in that, Step S1 further includes: performing intermediate annealing during the multi-pass cold rolling process; wherein the intermediate annealing temperature is 410~520℃ and the intermediate annealing time is 10~60s.

6. The preparation method according to claim 1 or 2, characterized in that, In step S2, the solution temperature is 535~570℃, the solution time is 10~150s; and / or, the straightening amount is 0.2~1.0%.

7. The preparation method according to claim 1 or 2, characterized in that, In step S2, the pre-aging treatment is either isothermal pre-aging treatment or cooling pre-aging treatment; wherein, the temperature of the isothermal pre-aging treatment is 70~100℃, and the time of the isothermal pre-aging treatment is 4~10h; the starting temperature of the cooling pre-aging treatment is 90~110℃, and the cooling rate of the cooling pre-aging treatment is 1~3℃ / h.

8. The preparation method according to claim 1 or 2, characterized in that, In step S2, the yield strength of the first finished roll material is 145~200MPa, the tensile strength of the first finished roll material is ≥275MPa, the elongation at break of the first finished roll material is ≥20%, and the work hardening index n of the first finished roll material is... (5-15) The Lankford coefficient r of the first finished roll material is ≥0.

26. 10 ≥0.6; After sequential 2% pre-stretching and baking at 185°C for 20 minutes, the yield strength of the first finished roll is ≥290MPa, the tensile strength of the first finished roll is ≥350MPa, the maximum depth of intergranular corrosion of the first finished roll is ≤250μm, and the average depth of intergranular corrosion of the first finished roll is ≤150μm.

9. An aluminum alloy sheet, characterized in that, The aluminum alloy sheet is prepared by the preparation method according to any one of claims 1 to 8.

10. The aluminum alloy sheet according to claim 9, characterized in that, The aluminum alloy sheet has a yield strength ≥340MPa, a tensile strength ≥390MPa, and a fracture elongation ≥12%; the maximum depth of intergranular corrosion of the aluminum alloy sheet is ≤250μm, and the average depth of intergranular corrosion of the aluminum alloy sheet is ≤150μm.

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