Preparation method of high-conductivity 6-series aluminum alloy plate for new energy vehicles

Abstract

This invention relates to a method for preparing a high-conductivity 6-series aluminum alloy sheet for new energy vehicles. The chemical composition of the aluminum alloy sheet, by mass fraction, is: Si: 0.30-0.48%, Fe: 0.06-0.16%, Cu≤0.02%, Mn≤0.03%, Mg: 0.40-0.56%, Cr≤0.01%, Zn≤0.05%, Ti≤0.02%, with the balance being aluminum and unavoidable impurities. Through high-speed hot rolling with high reduction, the second phases such as AlFeSi and Mg2Si are fully broken down and uniformly distributed in the matrix, fully utilizing the PSN-induced recrystallization nucleation effect. Simultaneously, coupled with a high hot rolling finishing temperature, the residual heat from hot rolling is used for annealing to fully recrystallize the hot-rolled structure, thereby obtaining a recrystallized structure with a relatively uniform grain structure. Subsequently, a high-temperature short-time solution treatment was performed to avoid grain growth and coarsening. The uniform second phase and fully recrystallized structure reduced the adverse effects on the electrical conductivity of the aluminum alloy. After artificial aging treatment, aluminum alloy sheet and strip with electrical conductivity ≥58.5%IACS, tensile strength ≥185MPa, yield strength ≥150MPa, elongation ≥16.5%, average grain size 100-140μm, and dispersed second phase with a second phase size ≤10μm was obtained.

Description

Technical Field

[0001] This invention relates to a method for preparing a high-conductivity 6-series aluminum alloy sheet for new energy vehicles, belonging to the field of aluminum alloy processing technology. Background Technology

[0002] With the rapid development of new energy vehicles and high-voltage power transmission in my country, higher requirements are being placed on the comprehensive performance of highly conductive metals such as aluminum and copper, as well as their alloys. These materials must possess excellent conductivity and formability while also maintaining high mechanical strength. Highly conductive aluminum alloys, represented by the 1-series and 6-series, have demonstrated significant advantages in achieving lightweighting and energy efficiency. Against this backdrop, "replacing copper with aluminum" has gradually become an inevitable trend driven by strategic resource allocation, technological innovation, and growing market demand.

[0003] Patent application number 202311231310.X discloses a method for preparing medium-strength, high-conductivity aluminum alloy plates. Using 6101 aluminum alloy as the matrix and adding a certain amount of Al-Cu master alloy, a conductive aluminum material with tensile strength higher than 187MPa, hardness greater than 75Hv, and electrical conductivity greater than 53%IACS was prepared by homogenization at 540℃-hot rolling-cold rolling-solution at 545℃ / 0.75h-water quenching-aging at 170℃ / 8h. The prepared conductive aluminum material has a low electrical conductivity.

[0004] Reducing impurity elements can effectively reduce scattering caused by the migration of free electrons. Based on this, patent application number 202011392715.8 discloses a process method to improve the boron absorption rate of aluminum alloy melt. By adding an aluminum-boron alloy to the melt and refining it after stirring, the actual boron absorption rate is improved, increasing the conductivity of 6101 alloy to 62.1% IACS and the conductivity of 1050 alloy to 62.8% IACS, but the microstructure is not disclosed.

[0005] Boration, the addition of an aluminum-boron master alloy during smelting, causes transition metal impurities such as vanadium (V), titanium (Ti), chromium (Cr), and zirconium (Zr), which severely reduce electrical conductivity, to form stable borides and precipitate out, thus purifying the molten aluminum and significantly improving the conductivity of the final product. However, these elements have a grain-refining effect in the melt, and after boration, they tend to form coarse, non-uniform columnar or equiaxed crystal structures. This not only degrades the mechanical properties of the material but may also adversely affect the uniformity of conductivity. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a method for preparing a high conductivity 6-series aluminum alloy sheet for new energy vehicles.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for preparing high-conductivity 6-series aluminum alloy sheet for new energy vehicles, using aluminum ingots, aluminum master alloy ingots, and electrolytic aluminum molten material, through melting, semi-continuous casting, sawing, milling, homogenization heat treatment, hot rolling, solution quenching, pre-stretching, and artificial aging to obtain a 6-series aluminum alloy sheet and strip with uniform structure and high electrical conductivity. The specific preparation method includes the following steps: (1) According to the alloy composition ratio, aluminum ingots, aluminum master alloy ingots and electrolytic aluminum raw materials are melted, refined, slag removed and degassed and then semi-continuously cast into aluminum alloy flat ingots. (2) After the aluminum alloy flat ingot is sawn and milled, it is put into the vertical pusher furnace for homogenization heat treatment. It is held at 540~580℃ for 6-10 hours, and then cooled to 480~520℃ and held for 1-2 hours. (3) Hot-rolled coils with a thickness of 2.5-6 mm after exiting the furnace; (4) The hot-rolled coil obtained in step (3) is subjected to short-time high-temperature solution treatment, quenching and pre-stretching in a continuous air cushion furnace; (5) The supersaturated solution-treated roll obtained in step (4) is subjected to artificial aging treatment at 185℃~215℃ for 8~14h; (6) The roll obtained in step (5) is rewound or cut into the required specifications by a rewinding machine, and finally a 6-series aluminum alloy material with uniform structure and high electrical conductivity is obtained.

[0008] Preferably, in step (3), the hot roughing is continuously rolled in 3 or more passes with a reduction rate of 35%~42%, the rolling speed is ≥3.5m / s, and the total deformation of hot roughing / hot roughing passes is ≥42mm; the reduction of each pass of hot finishing is ≥40%, the final stand reduction is ≥50%, and the final rolling temperature is 330~380℃.

[0009] Preferably, the solution temperature in step (4) is 495-535℃ and the solution time is 8-15s.

[0010] Preferably, the chemical composition of the aluminum alloy sheet, by mass fraction, is: Si: 0.30-0.48%, Fe: 0.06-0.16%, Cu≤0.02%, Mn≤0.03%, Mg: 0.40-0.56%, Cr≤0.01%, Zn≤0.05%, Ti≤0.02%, with the balance being aluminum and unavoidable impurities.

[0011] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention applies a large reduction and high-speed rolling deformation to the ingot and intermediate billet during the hot rolling stage. Through plastic deformation, the undissolved second phase (mainly AlFeSi and Mg2Si) in the homogenization stage is broken down, reducing the size of the second phase and achieving uniform dispersion in the matrix. The dislocation density is increased as much as possible through rolling deformation, and recrystallization is carried out under the drive of high temperature in the rolling gap and high final rolling temperature. The fine second phase plays a role in inducing recrystallization nucleation and pinning and restricting grain growth during the recovery-recrystallization process, thereby obtaining a relatively uniform recrystallized hot-rolled structure.

[0012] (2) The strip is annealed with residual heat at a high final rolling temperature to obtain an incomplete recrystallized structure, followed by a high-temperature short-time solution treatment to obtain an equiaxed fully recrystallized structure. After high-temperature solution treatment, the grain structure that is elongated during the hot rolling stage is transformed into equiaxed grains. In order to avoid excessive grain growth and obtain a uniform fully recrystallized structure, the solution treatment time in the high-temperature solution stage is shortened to 8-15s as much as possible while ensuring that the element re-dissolution does not affect the subsequent precipitation. The aluminum alloy for conductive components produced by this process has a uniform structure, an average grain size of 100-140μm, a reduced grain boundary ratio, and a dispersed second phase distribution in the finished product. The second phase size is refined to ≤10μm, which can reduce the scattering of electrons when passing through the grain boundaries and improve the conductivity of the actual material. The obtained material has high conductivity and good formability, and can fully meet the requirements of 90° bending.

[0013] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0014] Figure 1 A hot-rolled grain structure diagram of Embodiment 1 of the present invention is shown; Figure 2 The diagram shows the grain structure of the finished roll material according to Embodiment 1 of the present invention; Figure 3 The image shows a microscopic morphology of the second phase of the hot-rolled coil according to Embodiment 1 of the present invention; Figure 4 The image shows a microscopic morphology of the second phase of the finished roll material according to Embodiment 1 of the present invention; Figure 5 The grain structure diagram of the hot-rolled coil in Comparative Example 1 is shown; Figure 6 A grain structure diagram of the finished roll material of Comparative Example 1 is shown. Detailed Implementation

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0016] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0017] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0018] like Figures 1-6 As shown, this embodiment provides a method for preparing a high-conductivity 6-series aluminum alloy sheet for new energy vehicles. The aluminum alloy sheet and strip prepared using the alloy composition and production process achieves the following properties: conductivity ≥58.5% IACS, tensile strength ≥185MPa, yield strength ≥150MPa, and elongation ≥16.5%. It can be used for internal conductive components in new energy vehicles and new energy charging piles.

[0019] To achieve the above objectives, the present invention adopts the following technical solution: The chemical composition of the aluminum alloy sheet, by mass fraction, is as follows: Si: 0.30-0.48%, Fe: 0.06-0.16%, Cu≤0.02%, Mn≤0.03%, Mg: 0.40-0.56%, Cr≤0.01%, Zn≤0.05%, Ti≤0.02%, with the balance being aluminum and unavoidable impurities.

[0020] In this embodiment of the invention, aluminum ingots, aluminum master alloy ingots, and electrolytic aluminum molten material are used to produce 6-series aluminum alloy sheet and strip with uniform structure and high electrical conductivity through smelting, semi-continuous casting, sawing, milling, homogenization heat treatment, hot rolling, solution quenching, pre-stretching, and artificial aging.

[0021] In this embodiment of the invention, the specific preparation method includes the following steps: (1) According to the alloy composition ratio, pure aluminum ingots, aluminum intermediate alloy ingots and electrolytic aluminum raw materials are melted, refined, slag removed and degassed and then semi-continuously cast into aluminum alloy flat ingots. (2) The aluminum alloy flat ingots are sawed and milled to remove defects at the head and tail, as well as surface segregation and coarse grain layer. Then the aluminum alloy flat ingots are placed in a vertical pusher furnace for homogenization heat treatment. (3) After homogenization, the aluminum alloy flat ingot is subjected to high-speed hot rough rolling with large reduction. The billet thickness is rolled to 22-30mm and then rolled to 2.5-6mm in the hot finishing mill. The final rolling temperature is 330-380℃ when it comes off the mill. After natural cooling or air cooling, a hot rolled coil with recrystallization structure is obtained. (4) The hot-rolled coil obtained in step (3) is subjected to short-time high-temperature solution treatment, quenching and pre-stretching through an air cushion continuous annealing line (continuous air cushion furnace) to obtain a coil in a supersaturated solution state. (5) Place the coil obtained in step (4) in a supersaturated solution state in an aging furnace and keep it at a temperature of 185-215℃ for 8-14 hours to obtain a finished aluminum coil that meets the performance requirements. (6) The roll obtained in step (5) is rewound or cut into the required specifications by a rewinding machine, and finally a 6-series aluminum alloy material with uniform structure and high electrical conductivity is obtained.

[0022] In this embodiment of the invention, in step (2), the homogenization heat treatment temperature is 540-580℃, the holding time is 6-10h, and after homogenization is completed, the furnace cooling fan is turned on to cool down the temperature at a rate of 20-50℃ / h. The thermocouple detection on the surface of the ingot shows that the ingot has cooled down to 480-520℃ and is held for 1-2 hours before it can be taken out of the furnace for rolling.

[0023] In this embodiment of the invention, in step (3), the rolling speed of the hot roughing passes, except for the first 1-2 passes of billet opening, is controlled at 1.5-3.8 m / s, and the total deformation of hot roughing / hot roughing passes is ≥42 mm, the reduction rate of hot roughing for 3 or more consecutive passes is 35%~42%, and the rolling speed is ≥3.5 m / s; In step (3), the reduction of each hot finishing rolling pass is ≥40%, the final stand reduction is ≥50%, and the final rolling temperature is 330~380℃.

[0024] In this embodiment of the invention, the solution temperature in step (4) is 495-535℃, the solution time is 8-15s, the quenching is water quenching or air cooling, the cooling rate is ≥15℃ / s, and the strip pre-stretching elongation is 1-2%.

[0025] Specific implementation steps: The present invention will be further described in detail below with reference to the embodiments.

[0026] Example 1 A high-conductivity 6-series aluminum alloy sheet, the mass percentage of each chemical component is as follows: Si 0.35%, Fe 0.077%, Cu 0.001%, Mn 0.004%, Mg 0.45%, Cr 0.001%, Zn 0.016%, Ti 0.01%, with the balance being aluminum and unavoidable impurities.

[0027] The method for producing the high conductivity 6-series aluminum alloy sheet includes the following steps: (1) According to the alloy ratio, pure aluminum ingots and aluminum intermediate alloy ingots are added to the melting furnace and heated and melted. After refining, slag removal and degassing, flat ingots are made by semi-continuous casting.

[0028] (2) The flat ingots are sawn and milled to remove defects at the head and tail, as well as surface segregation and coarse grain layer. Then the flat ingots are placed in a vertical pusher furnace for homogenization heat treatment at 550℃ / 10h. After homogenization, the temperature is lowered to 490℃ and held for 2h before being taken out of the furnace.

[0029] (3) The 630mm flat ingot is rolled to 30mm through 13 passes of hot roughing rolling. The billet thickness and speed for each pass are shown in the table below: (4) After being rolled to 5mm on a hot finishing mill, the hot finishing thickness varies from 30.32 to 17.31 to 9.88 to 5.03mm. The actual measured final rolling temperature when it comes off the mill is 352~361℃. After natural cooling, hot-rolled coils are obtained.

[0030] (5) The hot-rolled coil is solution-treated at 535°C for 10s through an air-cushion continuous annealing line, then cooled by water quenching and pre-stretched with a deformation rate of 1% to obtain a coil in a supersaturated solution-treated state.

[0031] (6) The solution-treated coil is placed in an aging furnace and kept at 185°C for 13 hours to obtain a finished aluminum coil that meets the performance requirements.

[0032] Tests showed that this 6-series high-conductivity aluminum alloy has an electrical conductivity of 58.5% IACS, a tensile strength of 191 MPa, a yield strength of 157 MPa, an elongation of 16.8%, an average grain size of 124.49 μm, and a maximum second phase size of 8.89 μm within the field of view.

[0033] Example 2 A high-conductivity 6-series aluminum alloy sheet, the mass percentage of each chemical component is as follows: Si 0.33%, Fe 0.095%, Cu 0.002%, Mn 0.002%, Mg 0.47%, Cr 0.001%, Zn 0.01%, Ti 0.005%, with the balance being aluminum and unavoidable impurities.

[0034] The method for producing the high conductivity 6-series aluminum alloy sheet includes the following steps: (1) According to the alloy ratio, pure aluminum ingots and aluminum intermediate alloy ingots are added to the melting furnace and heated and melted. After refining, slag removal and degassing, flat ingots are made by semi-continuous casting.

[0035] (2) The flat ingots are sawn and milled to remove defects at the head and tail, as well as surface segregation and coarse grain layer. Then the flat ingots are placed in a vertical pusher furnace for homogenization heat treatment at 560℃ / 9h. After homogenization, the temperature is lowered to 480℃ and held for 2h before being taken out of the furnace.

[0036] (3) The 626mm flat ingot after milling is rolled to 30mm through 13 passes of hot rough rolling. The billet reduction ratio of each pass is set in the same way as in Example 1. The rolling speed of 3.8m / s is used for passes 9-13.

[0037] (4) After being rolled to 5mm on a hot finishing mill, the hot finishing thickness varies from 30.33 to 17.29 to 9.87 to 5.02mm. The actual measured final rolling temperature when it comes off the mill is 365~369℃. After natural cooling, hot-rolled coils are obtained.

[0038] (5) The hot-rolled coil is solution-treated at 530°C for 10s through an air-cushion continuous annealing line, then cooled by water quenching and pre-stretched with a deformation rate of 1% to obtain a coil in a supersaturated solution-treated state.

[0039] (6) The solution-treated coil is placed in an aging furnace and kept at 190°C for 12.5 hours to obtain a finished aluminum coil that meets the performance requirements.

[0040] Tests showed that this 6-series high-conductivity aluminum alloy has an electrical conductivity of 58.7% IACS, a tensile strength of 185 MPa, a yield strength of 152 MPa, an elongation of 17.4%, an average grain size of 136.51 μm, and a maximum second phase size of 9.49 μm within the field of view.

[0041] Comparative Example 1 The production and preparation methods of Comparative Example 1 and Example 1 are roughly the same, except that the mass percentage of each chemical component in the alloy is as follows: Si 0.32%, Fe 0.086%, Cu 0.0005%, Mn 0.0017%, Mg 0.45%, Cr 0.0005%, Zn 0.0092%, Ti 0.0095%, with the balance being aluminum and unavoidable impurities.

[0042] The hot roughing rolling process involves 17 passes, with a flat billet thickness of 616 mm and an intermediate billet thickness of 30 mm. The total deformation per hot roughing rolling pass is 34.47 mm. Except for the two initial rolling passes, the hot roughing rolling process uses a rolling speed of 2.0-2.5 m / s. The final rolling temperature is set at 360℃, and the final rolling temperature after exiting the mill is 354-364℃. The hot rolled thickness is 5 mm.

[0043] The 6-series high-conductivity aluminum alloy was tested and found to have an electrical conductivity of 57.1% IACS, a tensile strength of 186 MPa, a yield strength of 155 MPa, an elongation of 12.8%, an average grain size of 177.73 μm, localized coarse grains, a maximum grain diameter of 706.67 μm in the field of view, and a maximum second phase size of 13.21 μm in the field of view.

[0044] Comparative Example 2 The production and preparation methods of Comparative Example 2 are roughly the same as those in Example 1, except that the mass percentage of each chemical component in the alloy is as follows: Si 0.36%, Fe 0.071%, Cu 0.0008%, Mn 0.0001%, Mg 0.50%, Cr 0.0003%, Zn 0.0097%, Ti 0.0033%, with the balance being aluminum and unavoidable impurities.

[0045] The hot roughing rolling process involves 15 passes, with a flat billet thickness of 598 mm and an intermediate billet thickness of 30 mm. The total deformation per hot roughing rolling pass is 37.87 mm. Except for the two initial rolling passes, the hot roughing rolling process uses a rolling speed of 2.5 m / s. The final rolling temperature is set at 360℃, and the final rolling temperature after exiting the mill is 357-366℃. The hot rolled thickness is 5 mm.

[0046] Tests showed that the 6-series high-conductivity aluminum alloy had an electrical conductivity of 56.8% IACS, a tensile strength of 199 MPa, a yield strength of 169 MPa, an elongation of 14%, an average grain size of 162.07 μm, localized coarse grains with a maximum grain diameter of 629.86 μm, and a maximum second phase size of 12.94 μm within the field of view.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-conductivity 6-series aluminum alloy sheet for new energy vehicles, characterized by: Using aluminum ingots, aluminum master alloy ingots, and molten electrolytic aluminum as raw materials, 6-series aluminum alloy sheets and strips with uniform microstructure and high electrical conductivity are prepared through smelting, semi-continuous casting, sawing, milling, homogenization heat treatment, hot rolling, solution quenching, pre-stretching, and artificial aging. The specific preparation method includes the following steps: ​ (1) According to the alloy composition ratio, aluminum ingots, aluminum master alloy ingots and electrolytic aluminum raw materials are melted, refined, slag removed and degassed and then semi-continuously cast into aluminum alloy flat ingots. (2) After the aluminum alloy flat ingot is sawn and milled, it is put into a vertical pusher furnace for homogenization heat treatment. It is held at 540~580℃ for 6-10h, and then cooled to 480~520℃ for 1-2h. (3) Hot-rolled coils with a thickness of 2.5-6 mm after exiting the furnace; (4) The hot-rolled coil obtained in step (3) is subjected to short-time high-temperature solution treatment, quenching and pre-stretching in a continuous air cushion furnace; (5) The supersaturated solution-treated roll obtained in step (4) is subjected to artificial aging treatment at 185℃~215℃ for 8~14h; (6) The roll obtained in step (5) is rewound or cut into the required specifications by a rewinding machine, and finally a 6-series aluminum alloy material with uniform structure and high electrical conductivity is obtained. In step (3), the hot roughing rolling continuously uses 3 or more passes with a reduction rate of 35%~42%, the rolling speed is ≥3.5m / s, and the total deformation of hot roughing rolling / hot roughing rolling passes is ≥42; the reduction of each pass of hot finishing rolling is ≥40%, the final stand reduction is ≥50%, and the final rolling temperature is 330~380℃.

2. The method for preparing a high-conductivity 6-series aluminum alloy sheet for new energy vehicles according to claim 1, characterized in that: In step (4), the solution temperature is 495-535℃ and the solution time is 8-15s.

3. The method for preparing a high-conductivity 6-series aluminum alloy sheet for new energy vehicles according to claim 1, characterized in that: The chemical composition of the aluminum alloy sheet, by mass fraction, is as follows: Si: 0.30-0.48%, Fe: 0.06-0.16%, Cu≤0.02%, Mn≤0.03%, Mg: 0.40-0.56%, Cr≤0.01%, Zn≤0.05%, Ti≤0.02%, with the balance being aluminum and unavoidable impurities.

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