A thermomechanical treatment method for improving the comprehensive performance of 6xxx aluminum alloy coil containing Cu element and aluminum alloy coil

Abstract

The present invention discloses a thermomechanical treatment method for improving the comprehensive performance of a 6xxx aluminum alloy coil containing Cu, and the aluminum alloy coil. The present invention belongs to the technical field of aluminum alloy manufacturing. The method comprises the following steps: melting and casting, homogenizing heat treatment, gradient cooling rolling, solution quenching, low-temperature rolling, and aging treatment. The method optimizes the production process, regulates the distribution and size of precipitated phases, improves the microstructure and mechanical properties of the aluminum alloy, maintains excellent mechanical properties while adding a relatively high content of copper, improves the mechanical strength and elongation of the product, reduces material anisotropy, shortens the process steps, eliminates the need for annealing and secondary cold rolling, reduces energy consumption, and improves production efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy manufacturing, and in particular to a thermomechanical treatment method for improving the comprehensive performance of a 6xxx aluminum alloy coil containing Cu elements and the aluminum alloy coil. Background Art

[0002] Lightweighting battery packs can increase energy density and is an effective way to extend the range of new energy vehicles. Battery pack baseplates require materials with high strength and excellent stamping formability, adaptability to bending, SPR, and other processing techniques, and excellent corrosion resistance to meet automotive safety and durability design requirements. The development and application of new high-strength aluminum alloy products play a vital role in promoting the development of new energy vehicles.

[0003] 6xxx aluminum alloy has become the preferred material for battery pack bottom plates due to its excellent extrusion performance. The copper content of 6xxx aluminum alloy is generally below 0.3%. While maintaining the good weldability, corrosion resistance and formability of 6xxx aluminum alloy, the strength and hardness of the alloy are significantly improved by adding copper elements, making it suitable for applications with high performance requirements. However, the copper-containing 6xxx aluminum alloy in traditional processes has certain limitations: in order to ensure mechanical strength and certain corrosion resistance and electrical and thermal conductivity, the process flow is often complicated, the production cycle is long, the efficiency is low, and the energy consumption is high. The preparation method of a 6xxx aluminum alloy coil with homogenization and heating separation, application number CN202210878837.0, cannot meet the preparation requirements of 6xxx high-strength aluminum alloy with a higher copper content, and requires two cold rollings and intermediate annealing, which has a long process cycle and high energy consumption. This method mainly considers the optimization of mechanical properties before baking, and its application in the high-strength state after baking is limited.

[0004] Based on this, we hope to explore a deformation heat treatment method to improve the comprehensive performance of 6xxx aluminum alloy coils containing Cu elements, which can improve the microstructure and mechanical properties, maintain excellent mechanical properties while adding a higher content of copper elements, reduce material anisotropy, and at the same time reduce energy consumption and improve production efficiency. Summary of the Invention

[0005] To address the above shortcomings, the present invention provides a thermomechanical treatment method and aluminum alloy coil containing Cu to improve the comprehensive performance of the aluminum alloy coil, which can achieve excellent mechanical properties. The obtained product has a tensile strength of ≥400 MPa, a yield strength of ≥350 MPa, an elongation of ≥12%, and does not crack when bent at a 90° radius with a 1.5T bending radius in the horizontal and vertical directions. At the same time, it reduces energy consumption and improves production efficiency. The specific technical solution is as follows:

[0006] A thermomechanical treatment method for improving the comprehensive performance of a 6xxx aluminum alloy coil containing Cu comprises the following steps:

[0007] S1. Melting and casting: Melting and casting the aluminum alloy raw material to obtain an ingot;

[0008] S2, homogenization heat treatment: the ingot obtained in step S1 is cut and milled, and then subjected to homogenization heat treatment to obtain an ingot after homogenization heat treatment;

[0009] S3, gradient cooling rolling: directly subjecting the ingot after homogenization heat treatment obtained in step S2 to gradient cooling rolling, controlling the cooling rate after each rolling pass to be 20-50°C / min, the final rolling temperature to be less than 200°C, the total rolling processing rate to be greater than 90%, and the number of rolling passes to be less than 20, to obtain a gradient cooling rolled coil;

[0010] S4, solution quenching: subjecting the gradient cooling rolled coil obtained in step S3 to solution quenching to obtain a solution quenched coil;

[0011] S5, low temperature rolling: subjecting the solution quenched coil obtained in step S4 to low temperature rolling to obtain a low temperature rolled coil;

[0012] S6, aging treatment: performing aging treatment on the low-temperature rolled coil obtained in step S5 to obtain a finished aluminum alloy coil;

[0013] The mass percentages of the chemical components of the aluminum alloy are: Si=0.6-1.5%, Fe≤0.3%, Cu=0.4-1.2%, Mn=0.4-0.8%, Mg=0.6-1.5%, Cr≤0.25%, Zn≤0.3%, Ti≤0.1%, and the balance is Al and unavoidable impurity elements.

[0014] Preferably, the holding temperature of the homogenization heat treatment is 530-560° C., and the holding time is 6-12 hours.

[0015] Preferably, the solution quenching holding temperature is 540-570° C., and the holding time is 0.2-1 h.

[0016] Preferably, the low-temperature rolling temperature is 0-20° C., the pass processing rate is 2-20%, and the number of rolling passes is greater than 2.

[0017] Preferably, the aging treatment temperature is 190-230° C., and the holding time is 3-10 hours.

[0018] Preferably, in the solution quenching step, the cooling rate is greater than 50°C / s.

[0019] The present invention also provides a 6xxx aluminum alloy coil containing Cu element prepared by the above method.

[0020] The properties of the Cu-containing 6xxx aluminum alloy coil of the present invention meet the following requirements:

[0021] Tensile strength ≥400MPa, yield strength ≥350MPa, elongation ≥12%, 1.5T bending radius in horizontal and vertical directions and 90° bending without cracking.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention provides a thermomechanical treatment method for improving the comprehensive properties of Cu-containing 6xxx aluminum alloy coils, comprising the following steps: melting and casting, homogenization heat treatment, gradient cooling rolling, solution quenching, low-temperature rolling, and aging treatment. This method optimizes the production process, regulating the average size of dispersed phases such as Al2Cu2Mn3 to less than 1μm, and the average size of precipitated phases such as β(Mg2Si), S(Al2CuMg), Q(Al5Cu2Mg8Si6), and θ(Al2Cu) to less than 500nm. The secondary phases are uniformly distributed within the grains and at grain boundaries. This method improves the microstructure and mechanical properties of the aluminum alloy, maintaining excellent mechanical properties while adding a high copper content, enhancing the product's mechanical strength and elongation, and reducing material anisotropy. The method also shortens the process steps, eliminating the need for annealing or secondary cold rolling, reducing energy consumption, and improving production efficiency.

[0024] 2. The present invention combines homogenization treatment with gradient cooling rolling to effectively dissolve the low-melting-point elements in the primary phase, control the atomic solubility and avoid the growth of the dispersed phase. The gradient cooling rolling process effectively breaks up the second phase and promotes dissolution, so that the precipitated phase is more evenly distributed in the subsequent solution quenching and aging process of the alloy. After the gradient cooling rolling, the solution quenching step is entered without annealing. After the solution quenching, low-temperature rolling is implemented, which effectively increases the matrix energy storage and increases lattice defects such as dislocations, which is conducive to uniform and rapid nucleation during the low-temperature short-time aging process, and grows to obtain a certain number and size of precipitated phases.

[0025] 3. Through the implementation of this plan, the obtained product has a tensile strength of ≥400MPa, a yield strength of ≥350MPa, an elongation of ≥12%, and will not crack when bent at a 90° bending radius in the horizontal and vertical directions of 1.5T. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0027] Figure 1 It is a process flow diagram of the present invention;

[0028] Figure 2 Schematic diagram of the microstructure of the finished aluminum alloy coil of Example 1 of the present invention;

[0029] Figure 3 Schematic diagram of the tensile fracture of the finished aluminum alloy coil of Example 1 of the present invention; wherein, dimple fracture exists in the cleavage fracture. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Unless otherwise defined, all technical terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be prepared by existing methods.

[0031] Reference Figure 1 The process flow of the embodiment of the present invention includes: subjecting the ingot formed by molten aluminum alloy raw material to a homogenization heat treatment at 530-560°C for 6-12 hours, then directly performing gradient cooling rolling, then heating to 540-570°C for solution quenching for 0.2-1 hour, cooling after the solution quenching, and performing low-temperature rolling. After the low-temperature rolling is completed, the temperature is raised to 190-230°C for 3-10 hours for aging treatment.

[0032] Example 1

[0033] The mass percentages of the chemical composition of the aluminum alloy in this embodiment are: Si=1.4%, Fe=0.2%, Cu=1.2%, Mn=0.6%, Mg=0.9%, Cr=0.20%, Zn=0.2%, Ti=0.05%, and the balance is Al and unavoidable impurity elements.

[0034] A thermomechanical treatment method for improving the comprehensive performance of a Cu-containing 6xxx aluminum alloy coil according to this embodiment includes the following steps:

[0035] S1. Melting and casting: Melting and casting the aluminum alloy raw material to obtain an ingot;

[0036] S2, homogenization heat treatment: the ingot obtained in step S1 is cut and milled, and then subjected to homogenization heat treatment at a holding temperature of 545° C. for 9 hours to obtain an ingot after homogenization heat treatment;

[0037] S3, gradient cooling rolling: directly subjecting the ingot obtained in step S2 after homogenization heat treatment to gradient cooling rolling, controlling the cooling rate after each rolling pass to 20-25°C / min, the final rolling temperature to 130°C, the total rolling processing rate to 93%, and the number of rolling passes to 19, to obtain a gradient cooling rolled coil;

[0038] S4, solution quenching: The gradient cooling rolled coil obtained in step S3 is solution quenched at a holding temperature of 550° C. for 0.6 h to obtain a solution quenched coil;

[0039] S5, low temperature rolling: the solution quenched coil obtained in step S4 is subjected to low temperature rolling, with a rolling temperature of 0-10°C, a pass processing rate of 10%, and 3 rolling passes to obtain a low temperature rolled coil;

[0040] S6, aging treatment: the low-temperature rolled coil obtained in step S5 is subjected to aging treatment at a temperature of 210° C. for a holding time of 6 h, and then cooled to obtain a finished aluminum alloy coil.

[0041] Figure 2 Schematic diagram of the microstructure of the finished aluminum alloy coil obtained by Example 1 of the present invention. It can be seen that there are a large number of dislocation entanglements and dislocation cells inside the grains, most of which are located near larger dispersed phases, and new dispersed phases are precipitated near the dislocations. These characteristics all indicate that the mechanical properties of the coil have been enhanced. Figure 3 This is a schematic diagram of the tensile fracture of the finished aluminum alloy coil obtained by Example 1 of the present invention. It can be seen that the fracture mode is mainly cleavage fracture, and there are dimples of varying sizes. Cleavage fracture indicates that the material has brittle fracture during the tensile process, while dimple fracture indicates that the material has ductile fracture during the tensile process. The simultaneous occurrence of these two types of fractures indicates that the material exhibits dual characteristics of brittleness and toughness during the fracture process, and the bending ability is improved.

[0042] Example 2

[0043] The mass percentages of the chemical composition of the aluminum alloy of this embodiment are: Si=0.8%, Fe=0.2%, Cu=0.5%, Mn=0.5%, Mg=0.7%, Cr=0.23%, Zn=0.2%, Ti=0.06%, and the remainder is Al and unavoidable impurity elements.

[0044] A thermomechanical treatment method for improving the comprehensive performance of a Cu-containing 6xxx aluminum alloy coil according to this embodiment includes the following steps:

[0045] S1. Melting and casting: Melting and casting the aluminum alloy raw material to obtain an ingot;

[0046] S2, homogenization heat treatment: the ingot obtained in step S1 is cut and milled, and then subjected to homogenization heat treatment at a holding temperature of 530° C. for 12 h to obtain an ingot after homogenization heat treatment;

[0047] S3, gradient cooling rolling: directly subjecting the ingot obtained in step S2 after homogenization heat treatment to gradient cooling rolling, controlling the cooling rate after each rolling pass to 30-45°C / min, the final rolling temperature to 100°C, the total rolling processing rate to 91%, and the number of rolling passes to 14, to obtain a gradient cooling rolled coil;

[0048] S4, solution quenching: The gradient cooling rolled coil obtained in step S3 is solution quenched at a holding temperature of 540° C. for 1 h to obtain a solution quenched coil;

[0049] S5, low temperature rolling: the solution quenched coil obtained in step S4 is subjected to low temperature rolling, with a rolling temperature of 0-10°C, a pass processing rate of 20%, and 4 rolling passes to obtain a low temperature rolled coil;

[0050] S6, aging treatment: the low-temperature rolled coil obtained in step S5 is subjected to aging treatment at a temperature of 190° C. for 10 h, and then cooled to obtain a finished aluminum alloy coil.

[0051] Example 3

[0052] The mass percentages of the chemical composition of the aluminum alloy in this embodiment are: Si=1.2%, Fe=0.3%, Cu=1.0%, Mn=0.8%, Mg=1.5%, Cr=0.10%, Zn=0.1%, Ti=0.09%, and the remainder is Al and unavoidable impurity elements.

[0053] A thermomechanical treatment method for improving the comprehensive performance of a Cu-containing 6xxx aluminum alloy coil according to this embodiment includes the following steps:

[0054] S1. Melting and casting: Melting and casting the aluminum alloy raw material to obtain an ingot;

[0055] S2, homogenization heat treatment: the ingot obtained in step S1 is cut and milled, and then subjected to homogenization heat treatment at a holding temperature of 560° C. for 6 hours to obtain an ingot after homogenization heat treatment;

[0056] S3, gradient cooling rolling: directly subjecting the ingot after homogenization heat treatment obtained in step S2 to gradient cooling rolling, controlling the cooling rate after each rolling pass to 25-45°C / min, the final rolling temperature to 150°C, the total rolling processing rate to 95%, and the number of rolling passes to 15, to obtain a gradient cooling rolled coil;

[0057] S4, solution quenching: The gradient cooling rolled coil obtained in step S3 is solution quenched at a holding temperature of 570° C. for 0.2 h to obtain a solution quenched coil;

[0058] S5, low temperature rolling: the solution quenched coil obtained in step S4 is subjected to low temperature rolling, with a rolling temperature of 5-15°C, a pass processing rate of 20%, and 3 rolling passes to obtain a low temperature rolled coil;

[0059] S6, aging treatment: the low-temperature rolled coil obtained in step S5 is subjected to aging treatment at a temperature of 230° C. for a holding time of 3 h, and then cooled to obtain a finished aluminum alloy coil.

[0060] Comparative Example 1

[0061] The hot rolling finishing temperature of this comparative example is 250° C. The rest of the process is the same as that of Example 1.

[0062] Comparative Example 2

[0063] The mass percentages of the chemical components of the aluminum alloy of this comparative example are: Si=1.4%, Fe=0.2%, Cu=1.2%, Mn=0.6%, Mg=0.9%, Cr=0.20%, Zn=0.2%, and Ti=0.05%.

[0064] A thermomechanical treatment method for improving the comprehensive performance of a 6xxx aluminum alloy coil containing Cu in this comparative example comprises the following steps:

[0065] S1. Melting and casting: Melting and casting the aluminum alloy raw material to obtain an ingot;

[0066] S2, homogenization heat treatment: the ingot obtained in step S1 is cut and milled, and then subjected to homogenization heat treatment at a holding temperature of 540° C. for 3 h to obtain an ingot after homogenization heat treatment;

[0067] S3, gradient cooling rolling: the ingot after homogenization heat treatment obtained in step S2 is directly subjected to gradient cooling rolling, with a final rolling temperature of 250° C. and a total rolling processing rate of 70%, to obtain a gradient cooling rolled coil;

[0068] S4, primary cold rolling: subjecting the gradient cooling rolled coil obtained in step S3 to a single cold rolling at room temperature, with a pass processing rate of 10%, to obtain a single cold rolled coil;

[0069] S5, annealing: annealing the cold-rolled coil obtained in step S4 at a holding temperature of 450° C. for a holding time of 0.2-1 h to obtain an annealed coil;

[0070] S6, secondary cold rolling: the annealed coil obtained in step S5 is subjected to secondary cold rolling at room temperature, with a pass processing rate of 10%, to obtain a secondary cold rolled coil;

[0071] S7, solution quenching: subjecting the secondary cold-rolled coil obtained in step S6 to solution quenching at a holding temperature of 550° C. for 0.6 h to obtain a solution quenched coil;

[0072] S8, aging treatment: The solution quenched coil obtained in step S7 is subjected to aging treatment at a temperature of 210° C. for a holding time of 6 h, and then cooled to obtain a finished aluminum alloy coil.

[0073] The rest of the process is the same as in Example 1.

[0074] Comparative Example 3

[0075] The mass percentages of the chemical components of the aluminum alloy of this comparative example are: Si=1.5%, Fe=0.2%, Cu=0.8%, Mn=0.5%, Mg=0.9%, Cr=0.18%, Zn=0.1%, and Ti=0.05%.

[0076] The preparation method of the aluminum alloy of this comparative example comprises the following steps:

[0077] S1. Melting and casting: Melting and casting the aluminum alloy raw material to obtain an ingot;

[0078] S2, homogenization heat treatment: the ingot obtained in step S1 is cut and milled, and then subjected to homogenization heat treatment at a holding temperature of 560° C. for 10 h to obtain an ingot after homogenization heat treatment;

[0079] S3, hot rolling: directly hot rolling the ingot after homogenization heat treatment obtained in step S2, with a final rolling temperature of 310° C. and a total rolling processing rate of 70%, to obtain a hot-rolled coil;

[0080] S4, cold rolling: cold rolling the hot rolled coil obtained in step S3, with a total rolling processing rate of 60%, to obtain a cold rolled coil;

[0081] S5, solution quenching: The annealed coil obtained in step S4 is solution quenched at a holding temperature of 560° C. for 0.6 h to obtain a solution quenched coil;

[0082] S8, aging treatment: The solution quenched coil obtained in step S7 is subjected to aging treatment at a temperature of 220° C. for a holding time of 3 h, and then cooled to obtain an aluminum alloy product.

[0083] The finished aluminum alloy coils of the examples and comparative examples were subjected to microstructure tests and performance tests.

[0084] The samples were electropolished using an HNO₃+CH₃OH solution, and the microstructure was observed using a Tecnai G2 F20 transmission electron microscope. The samples were subjected to room temperature tensile testing according to GB / T 228.1-2021. Bending tests were performed using the three-point bending method.

[0085] The results are shown in Table 1 below.

[0086] Table 1 Performance test results of finished aluminum alloy coils of Examples and Comparative Examples

[0087]

[0088] In summary, the present invention provides a thermomechanical treatment method and aluminum alloy coil for improving the comprehensive properties of Cu-containing 6xxx aluminum alloys. The method comprises the following steps: melting, homogenization heat treatment, gradient cooling rolling, solution quenching, low-temperature rolling, and aging treatment. This optimized production process allows the average size of dispersed phases such as Al2Cu2Mn3 to be controlled to less than 1 μm, and the average size of precipitated phases such as β(Mg2Si), S(Al2CuMg), Q(Al5Cu2Mg8Si6), and θ(Al2Cu) to be controlled to less than 500 nm. The secondary phases are uniformly distributed within the grains and at grain boundaries. This method improves the microstructure and mechanical properties of the aluminum alloy, maintains excellent mechanical properties, enhances the mechanical strength and elongation of the product, and reduces material anisotropy. Furthermore, the method shortens the process steps, eliminates the need for annealing or secondary cold rolling, reduces energy consumption, and improves production efficiency. The present invention combines homogenization treatment and gradient cooling rolling to effectively dissolve the low-melting-point elements in the primary phase, control the atomic solubility and avoid the growth of the dispersed phase. The gradient cooling rolling process effectively breaks up the second phase and promotes dissolution, making the precipitated phase more evenly distributed during the subsequent solution quenching and aging process. After the gradient cooling rolling, the solution quenching step is entered without annealing. After the solution quenching, low-temperature rolling is implemented, which effectively increases the matrix energy storage and increases lattice defects such as dislocations, which is conducive to uniform and rapid nucleation during the low-temperature short-time aging process, and grows to obtain a certain number and size of precipitated phases. Through the implementation of this solution, the obtained tensile strength is ≥400MPa, the yield strength is ≥350MPa, the elongation is ≥12%, and the bending radius of 1.5T in the horizontal and vertical directions does not crack when bent at a 90° radius.

[0089] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A thermomechanical treatment method for improving the comprehensive performance of a 6xxx aluminum alloy coil containing Cu, characterized in that: The steps include: S1. Melting and casting: Melting and casting the aluminum alloy raw material to obtain an ingot; S2, homogenization heat treatment: the ingot obtained in step S1 is cut and milled, and then subjected to homogenization heat treatment, wherein the holding temperature of the homogenization heat treatment is 530-560° C. and the holding time is 6-12 hours to obtain the ingot after homogenization heat treatment; S3, gradient cooling rolling: directly subjecting the ingot after homogenization heat treatment obtained in step S2 to gradient cooling rolling, controlling the cooling rate after each rolling pass to be 20-50°C / min, the final rolling temperature to be less than 200°C, the total rolling processing rate to be greater than 90%, and the number of rolling passes to be less than 20, to obtain a gradient cooling rolled coil; S4, solution quenching: The gradient cooling rolled coil obtained in step S3 is solution quenched, wherein the solution quenching holding temperature is 540-570° C. and the holding time is 0.2-1 h, to obtain a solution quenched coil; S5, low temperature rolling: subjecting the solution quenched coil obtained in step S4 to low temperature rolling, wherein the low temperature rolling temperature is 0-20°C, the pass processing rate is 2-20%, and the number of rolling passes is greater than 2, to obtain a low temperature rolled coil; S6, aging treatment: performing aging treatment on the low-temperature rolled coil obtained in step S5, wherein the aging treatment temperature is 190-230° C. and the holding time is 3-10 hours to obtain a finished aluminum alloy coil; The mass percentages of the chemical components of the aluminum alloy are: Si=0.6-1.5%, Fe≤0.3%, Cu=0.4-1.2%, Mn=0.4-0.8%, Mg=0.6-1.5%, Cr≤0.25%, Zn≤0.3%, Ti≤0.1%, and the balance is Al and unavoidable impurity elements.

2. The thermomechanical treatment method for improving the comprehensive performance of a 6xxx aluminum alloy coil containing Cu according to claim 1, characterized in that: In the solution quenching step, the cooling rate is greater than 50°C / s.

3. A 6xxx aluminum alloy coil containing Cu prepared by the method according to any one of claims 1 to 2.

4. The Cu-containing 6xxx aluminum alloy coil according to claim 3, wherein: Its performance meets: Tensile strength ≥400MPa, yield strength ≥350MPa, elongation ≥12%, 1.5T bending radius in horizontal and vertical directions and 90° bending without cracking.

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