High-magnesium 5xxx series h32 aluminum alloy sheet and preparation method therefor

Abstract

The present disclosure relates to a high-magnesium 5XXX series H32 aluminum alloy sheet and a preparation method therefor. The aluminum alloy sheet comprises the following chemical components in percentage by weight: Si: 0-0.15%, Fe: 0.20-0.30%, Cu: 0-0.05%, Mn: 0.41-0.49%, Mg: 4.0-4.9%, Cr: 0.06-0.14%, Zn: 0-0.05%, Ti: 0.01-0.03%, and the balance being Al and inevitable impurities; wherein the content of each of the inevitable impurities in percentage by weight is greater than or equal to 0 and less than or equal to 0.05%, and the total content in percentages by weight of the inevitable impurities is greater than or equal to 0 and less than or equal to 0.15%; and the following formula is satisfied: (Si+Fe) / Mn ≤ 1, wherein element symbols in the formula respectively represent the numerical values preceding the % symbol of the weight percentage content of corresponding elements. The aluminum alloy sheet according to the present disclosure has a yield strength of ≥ 260MPa, an elongation rate of ≥ 12%, and a minimum bend radius at 90° of ≤ 1.0 × sheet thickness. Furthermore, the production process is greatly shortened, the production efficiency is improved, and the performance consistency between batches of sheets is better.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of aluminum alloy processing, and particularly relates to a high-magnesium 5XXX series H32 aluminum alloy sheet and a preparation method therefor.BACKGROUND

[0002] High-magnesium 5XXX series aluminum alloy is a type of aluminum alloy system that cannot be strengthened by heat treatment, and Mg is its main alloying element. When used in a fully annealed state, the high-magnesium 5XXX series aluminum alloy exhibits excellent bending performance but relatively low strength. However, in applications where high strength is required, it is usually necessary to retain varying degrees of work hardening effect, resulting in an increased strength and a reduced bending performance. The high-magnesium 5XXX series aluminum alloy sheet with H32 temper provides a balance between high strength and good bending performance, and is widely used in products such as battery trays of new energy vehicles.

[0003] Chinese Patent 1 (ZL 202210670223.3) discloses a production method for 5052-H32 aluminum alloy sheets used in automotive structural components. The 5052 alloy is sequentially subjected to melting and casting, homogenization, hot rolling, cold rolling, cleaning, annealing, and tension leveling straightening to obtain sheets with a 5052-H32 temper. The 5052 alloy described in the patent has a Mg content ranging from 2.2% to 2.8% and is classified as a medium-magnesium 5XXX series alloy. The H32 temper is obtained by controlling the reduction rate of cold rolling and performing low-temperature annealing treatment in an air-cushion furnace. The resulting alloy exhibits typical mechanical properties including a yield strength of 175 MPa, a tensile strength of 220 MPa, and an elongation rate of 14.1%. However, for high-magnesium 5XXX series alloy sheets with a Mg content ranging from 4.0% to 5.0%, this method suffers from a narrow process window and is difficult to control.

[0004] Chinese Patent 2 (ZL 201210581522.6) discloses a production method for 5754-H32 aluminum alloy plate strip, comprising sequential steps of melting and casting, sawing, milling, heating, hot rolling, cold rolling, and stabilization annealing and finishing. In this patent, the thickness of the hot-rolled coil is reserved with a 20-35% cold rolling amount based on the finished thickness. The coil is cold rolled to the final thickness in a single pass, followed by stabilization annealing at 140-200°C for 1-5 hours, thereby obtaining 5754-H32 plates exhibiting a yield strength of 216 MPa, a tensile strength of 268 MPa, and elongation rate of 12%. However, stabilization annealing in a box furnace for 1-5 hours inevitably leads to differences in the microstructure and properties between the outer and inner rings of the plates, and the heating phase is relatively time-consuming. Chinese application 3 (Application No. 202211623184.8) discloses a method for controlling Lüders bands during stamping of 5XXX series automotive panel materials, in particular 5XXX series alloys with a high magnesium content. The aluminum alloy ingot is subjected to heating, rough rolling, hot finish rolling, first cold rolling, intermediate annealing, second cold rolling, texturing, finished product annealing, surface treatment and stamping. By controlling the composition and process, a plate product free of Lüders bands is obtained, with properties including: a yield strength of 125 MPa, a tensile strength of 274.5 MPa, and an elongation rate of 28%. This patent is applied to the production of high-magnesium O-state plates, which exhibit good formability but relatively low strength.

[0005] Chinese Patent 4 (ZL 201410815173) discloses a 5083 aluminum alloy plate for high-speed rail and a production method therefor. The 5083 aluminum alloy plate for high-speed rail is made from a raw material has the following composition in weight percent: Si: 0.20-0.30%, Fe: 0.20-0.30%, Cu: 0.03-0.07%, Mn: 0.45-0.60%, Mg: 5.0-5.3%, Cr: 0.10-0.20%, Ti: 0.015-0.03%, Zn: 0-0.10%, and the balance being Al. The production method includes: raw material preparation, melting, casting, sawing and surface milling, homogenization, hot rough rolling, hot finish rolling, cold rolling, stretch leveling, annealing, and cutting and packaging. The plate produced by this method has a yield strength of 125-200MPa, a tensile strength of 275-350MPa, and an elongation rate of 20-26%. Although the elongation rate is relatively high, the strength is relatively low, which cannot meet the high-strength service environments.SUMMARY

[0006] The objective of the present disclosure is to provide a high-magnesium 5XXX series H32 aluminum alloy sheet and a preparation method therefor. The aluminum alloy sheet has a yield strength of ≥ 260 MPa, an elongation rate of ≥ 12%, and a minimum bend radius at 90° of ≤ 1.0 × sheet thickness (with the sheet thickness expressed in mm). Its overall performance is superior to that of existing products. Furthermore, compared with conventional H32 production methods, the present method significantly shortens the production process, improves production efficiency, and provides improved batch-to-batch consistency in properties.

[0007] The first aspect of the present disclosure provides an aluminum alloy sheet, comprising the following chemical components in percentage by weight: Si: 0-0.15%, Fe: 0.20-0.30%, Cu: 0-0.05%, preferably 0.01-0.05%, Mn: 0.41-0.49%, Mg: 4.0-4.9%, Cr: 0.06-0.14%, Zn: 0-0.05%, preferably 0.01-0.05%, Ti: 0.01-0.03%, and the balance being Al and inevitable impurities; wherein the content of each of the inevitable impurities in percentage by weight is greater than or equal to 0 and less than or equal to 0.05%, and the total content in percentages by weight of the inevitable impurities is greater than or equal to 0 and less than or equal to 0.15%; and the following formula is satisfied: (Si+Fe) / Mn ≤ 1, wherein element symbols in the formula respectively represent the numerical values preceding the % symbol of the weight percentage content of corresponding elements.

[0008] Preferably, the balance are Al and inevitable impurities.

[0009] The inevitable impurities of the present disclosure refer to those that are inevitably introduced during the manufacturing process of aluminum alloy sheets due to the purity of raw materials and production techniques, for example including but not limited to one or more of V, Ca, Li, etc. Preferably, Si: 0-0.12%; and / or, Fe: 0.20-0.25%; and / or, Mn: 0.43-0.47%.

[0010] Preferably, the microstructure of the aluminum alloy sheet comprises an iron-rich phase with a volume fraction of ≤ 3%, and the iron-rich phase has a maximum grain size of ≤ 5 µm. Preferably, the aluminum alloy sheet has a grain morphology of equiaxed grain with an average grain size of ≤ 20 µm, more preferably ≤ 15 µm.

[0011] Preferably, the aluminum alloy sheet has a yield strength of ≥ 260 MPa.

[0012] Preferably, the aluminum alloy sheet has an elongation rate of ≥ 12%.

[0013] Preferably, the aluminum alloy sheet has a minimum bend radius at 90° of ≤ 1.0 × sheet thickness, where the sheet thickness is expressed in mm.

[0014] Preferably, the aluminum alloy sheet has a tensile strength of ≥ 318 MPa.

[0015] The present disclosure optimizes the chemical composition of aluminum alloy sheets, particularly by limiting the contents of Si, Fe, and Mn, as well as the mass ratio of Si+Fe to Mn. Si, Fe and Mn elements can form a eutectic iron-rich phase during solidification. The eutectic iron-rich phase is a hard particle phase and has two effects: on the one hand, it promotes recrystallization through the PSN mechanism during deformation processing, facilitating the formation of fine recrystallized grains; on the other hand, it can easily become a crack initiation site for microcracks during sheet bending process, thereby reducing the bending performance of the sheet. Furthermore, Si and Fe elements are impurity elements in Al alloys and cannot be completely eliminated. By controlling the Si content to 0-0.15%, the Fe content to 0.20-0.30%, adding 0.41-0.49% of Mn, and maintaining the mass ratio of Si+Fe to Mn ≤ 1, the volume fraction of the iron-rich phase in the ingot can be limited to ≤ 3%. This weakens the segregation effect of the iron-rich phase on the matrix (α solid solution), reduces the tendency for microcrack initiation, and thereby enhances the bending performance of the sheet.

[0016] The second aspect of the present disclosure provides a preparation method for the aforementioned aluminum alloy sheet, which comprises the following steps performed in sequence: (1) smelting and casting: smelting and casting according to the aforementioned composition of the aluminum alloy sheet to obtain a slab; (2) performing homogenization heat treatment of the slab at a heating temperature of 500-540 °C for a holding time of 6-10 h; (3) hot rolling to obtain a hot-rolled billet: the intermediate stage of hot rough rolling is performed with a pass reduction rate of ≥ 15%, hot finish rolling is performed with a pass reduction rate of ≥ 30% and a coiling temperature of 300-350°C, and the thickness of the obtained hot-rolled billet is determined based on the thickness of the finished aluminum alloy sheet product and the cold rolling deformation amount; (4) first cold rolling to obtain a cold-rolled coil: the total reduction rate of the first cold rolling is 40% or more; (5) intermediate annealing of the cold-rolled coil: the intermediate annealing is carried out in an air-cushion furnace, with a target sheet temperature of 450-550 °C, preferably 480-530 °C, and a holding time of 0-20 s, and the sheet is air-cooled to room temperature after discharged from the furnace; (6) second cold rolling: a reduction rate of the second cold rolling is 5-15%.

[0017] Preferably, in step (2), the homogenization heat treatment is performed at a heating temperature of 530-540°C with a holding time of 8-10 h.

[0018] Preferably, in step (3), the intermediate stage of the hot roughing rolling is performed with a pass reduction rate of ≥ 20%, the hot finish rolling is performed with a pass reduction rate of ≥ 35% and a coiling temperature of 310-330°C, and the thickness of the obtained hot-rolled billet is 3-4 times that of the finished aluminum alloy sheet product.

[0019] Preferably, in step (4), the total reduction rate of the first cold rolling is 60-80%.

[0020] Preferably, in step (5), the target sheet temperature is 480-530°C.

[0021] Preferably, in step (6), the reduction rate of the second cold rolling is 8-10%.

[0022] In the preparation method of the high-magnesium 5XXX series H32 aluminum alloy sheet according to the present disclosure: In the present disclosure, the homogenization heat treatment is integrated with hot rolling. The heating temperature of homogenization heat treatment is control to 500-540°C for a holding time of 6-10 h. After the holding period, the slab is discharged from the furnace and subjected to hot rolling. This homogenization heat treatment process can eliminate intragranular segregation formed during the semi-continuous casting process. Soluble crystalline phases, such as β-Al 3 Mg 2 , are fully dissolved, and the insoluble iron-rich phases are fully transformed, which is beneficial for improving the bending performance of the finished sheet.

[0023] Hot rolling: In the intermediate rolling stage of hot rough rolling, the pass reduction rate is ≥ 15%. In the hot finish rolling, the pass reduction rate is ≥ 30%. A large reduction rate in the hot rolling facilitates sufficient deformation of the sheet from the surface layer to the middle layer, achieving a more uniform microstructure in the thickness of the sheet. At the same time, a large reduction is beneficial for the fragmentation and dispersed distribution of iron-rich phases, so that the maximum size of the iron-rich phase in the finished sheet is ≤ 5µm, thereby improving the bending performance of the finished sheet. The coiling temperature of finish rolling is 300-350°C. Within this temperature range, the dispersed phases precipitate finely and uniformly during cooling process after hot rolling coiling, which is conducive to inhibiting the growth of recrystallized grains during the intermediate annealing process. The thickness of the obtained hot-rolled billet needs to be calculated and determined based on the required thickness of the finished aluminum alloy sheet and the cold rolling deformation amount, ensuring that the total reduction rate of the cold rolling meets the requirements.

[0024] First cold rolling: The total reduction rate of cold rolling before intermediate annealing should be controlled to 40% or more to ensure that the sheet has sufficient deformation energy storage to provide an adequate driving force for recrystallization during intermediate annealing process. Fine recrystallized grains are critical for sheets to achieve high bending performance. If the total reduction rate of cold rolling is too low, recrystallized grains will be coarse or even abnormally grow, which is extremely detrimental to the bending performance of the finished sheet. Intermediate annealing: Intermediate annealing treatment is carried out in an air cushion furnace, with a target sheet temperature of 450-550 °C and a holding time of 0-20 s, and the sheet is air-cooled to room temperature after discharged from the furnace. Using an air cushion furnace for intermediate annealing enables the sheet to be heated to the target temperature in a very short time, thereby inhibiting recovery of the sheet during the heating process. Combined with a cold rolling reduction rate of ≥ 40% before intermediate annealing, a fine and uniform equiaxed grain structure with an average grain size of ≤ 20 µm and low intragranular dislocation density can be obtained. This is the basis for obtaining excellent overall properties in the finished sheet.

[0025] Second cold rolling: The reduction rate of cold rolling is controlled between 5% and 15%, ensuring the sheet obtain a certain degree of work hardening and enhancing the yield strength of the finished sheet.

[0026] The present disclosure controls the volume fraction of iron-rich phase in the ingot to ≤ 3% by controlling the contents of alloy elements and the mass ratio of Si+Fe to Mn. By adjusting the homogenization temperature and holding time of the ingot, soluble crystalline phases such as Al 3 Mg 2 in the ingot are fully dissolved, and the morphology of the insoluble iron-rich phase is transformed. Hot rough rolling and hot finish rolling processes with large reduction rates are adopted so that the sheet is fully deformed and the iron-rich phase is fragmentated and dispersed, which is conducive to achieving a maximum iron-rich phase size of ≤ 5 µm in the finished sheet, and a more uniform microstructure in the thickness direction of the sheet. By controlling the hot rolling coiling temperature, the dispersed phase is fine and uniformly distributed. The reduction rate of cold rolling before intermediate annealing is controlled to reserve sufficient deformation energy in the sheet, facilitating the transformation of deformed grains into recrystallized grains during intermediate annealing. Intermediate annealing is performed in an air cushion furnace at a temperature of 450-550°C. Rapid temperature rise can obtain fine and equiaxed recrystallized grain structures with an average grain size of ≤ 20 µm. Finally, cold rolling with a small reduction rate is employed to enhance the yield strength of the sheet.

[0027] Through the aforementioned integrated process control of the entire process, a high-performance aluminum alloy sheet product with an iron-rich phase volume fraction of ≤ 3%, an iron-rich phase maximum grain size ≤ 5µm, an morphology of equiaxed grain, an average grain size of ≤ 20 µm, a yield strength of ≥ 260 MPa, an elongation rate of ≥ 12%, and a minimum bend radius at 90° bending performance ≤ 1.0 × sheet thickness (thickness unit: mm) is ultimately obtained.

[0028] Compared to existing technologies, the present disclosure has the advantages of: 1) The composition of the aluminum alloy sheet is strictly limited in the present disclosure, and a specific requirement must be satisfied: (Si+Fe) / Mn ≤ 1; by controlling the ratio of Si, Fe and Mn, the proportion of iron-rich phase in the alloy can be controlled to be a volume fraction of ≤ 3%, thereby enhancing the bending performance of the sheet. 2) By synergistic control of homogenization heat treatment, hot rolling process, cold rolling process before intermediate annealing (i.e., first cold rolling g), intermediate annealing process, and cold rolling after intermediate annealing (i.e., second cold rolling) reduction rate, the present disclosure eliminates the finished annealing process in the conventional production process of steel sheets., saves heat treatment time of 10-20 hours , greatly shortening the production process, improving production efficiency. Moreover, the cold rolling process is the final process, the process control accuracy is higher, and the performance consistency between product batches is better. 3) the high-magnesium 5XXX series H32 aluminum alloy sheet products with a yield strength of ≥ 260 MPa, an elongation rate of ≥ 12%, and abend radius at 90° of ≤ 1.0 × sheet thickness can be obtained by the present disclosure, its overall performance is superior toc existing products. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a microstructure photograph of the aluminum alloy sheet prepared in Example 1 of the present disclosure. Figure 2 is a microstructure photograph of the aluminum alloy sheet prepared in Comparative Example 5. Figure 3 is a typical grain structure photograph of the aluminum alloy sheet prepared in Example 1 of the present disclosure (scale bar: 50 µm). DETAILED DESCRIPTION

[0030] To better understand the above-mentioned technical solutions of the present disclosure, the technical solutions of the present disclosure will be further explained below in conjunction with specific embodiments.

[0031] In the present disclosure, the aluminum alloy sheet has the following chemical composition (in weight percent): Si: 0-0.15%, Fe: 0.20-0.30%, Cu: 0-0.05%, preferably 0.01-0.05%, Mn: 0.41-0.49%, Mg: 4.0-4.9%, Cr: 0.06-0.14%, Zn: 0-0.05%, preferably 0.01-0.05%, Ti: 0.01-0.03%, and the balance being Al and inevitable impurities; wherein the content of each of the inevitable impurities in percentage by weight is greater than or equal to 0 and less than or equal to 0.05%, and the total content in percentages by weight of the inevitable impurities is greater than or equal to 0 and less than or equal to 0.15%; and the following formula is satisfied: (Si+Fe) / Mn ≤ 1, wherein element symbols in the formula respectively represent the numerical values preceding the % symbol of the weight percentage content of corresponding elements.

[0032] In the aluminum alloy sheet of the present disclosure, the design principles of each chemical element are as follows. In the present text, unless otherwise explicitly stated, all element contents are expressed in weight percent.

[0033] Cu: Cu mainly exists in the alloy in the form of solid solution, exerting a solid solution strengthening effect. However, it should be noted that the content of Cu should not be too high. When the Cu content is too high, it will affect the corrosion resistance of aluminum alloy sheets. Based on this, the content of Cu is controlled to be 0-0.05%, preferably 0.01-0.05%.

[0034] Mn: Mn plays a role in solid solution strengthening in the alloy, helps balance the adverse effects of Fe, and refines recrystallized grains. However, it should be noted the Mn content should not be too high. When the Mn content is too high, it can lead to the formation of blocky Al-Mn phases, which are detrimental to strength and formability. Based on this, the Mn content is controlled to be 0.41-0.49%.

[0035] Mg: Mg is a primary strengthening element that exerts a solid solution strengthening effect. However, it should be noted the Mg content should not be too high. When the Mg content is too high, it may negatively affect the formability and corrosion resistance of the aluminum alloy sheet. Based on this, the Mg content is controlled to be 4.0-4.9%.

[0036] Cr: Cr is a microalloying element with an effect similarly to Mn, facilitating the refinement of recrystallized grains and resulting in a fine and uniform grain structure. However, it should be noted that the Cr content should not be too high. When the Cr content is too high, it can have a negative impact on the alloy plasticity. Based on this, the Cr content is controlled to be 0.06-0.14%. Zn: Zn has a certain strengthening effect. However, it should be noted that the content of Zn should not be too high. When the content of Zn is too high, it will have an adverse effect on the corrosion resistance of the sheet. Based on this, the content of Zn is controlled to be 0-0.05%.

[0037] Ti: Ti is a primary grain-refinement element that exhibits a significant grain refinement effect on as-cast grains. However, it should be noted that the Ti content should not be too high. When the Ti content is too high, it can be detrimental to the formability of the sheet material. Based on this, the Ti content is controlled to be between 0.01% and 0.03%.

[0038] In alternative embodiments, the thickness of the aluminum alloy sheet of the present disclosure can be adjusted as needed, generally not exceeding 3 mm, preferably ranging from 0.5 to 2 mm, and more preferably ranging from 1.33 - 1.79 mm.

[0039] Performance testing standards / regulations: The microstructure of the aluminum alloy sheet in the present disclosure is examined according to the method specified in GB / T 3246.

[0040] The test specimens and methods for tensile mechanical properties of the aluminum alloy sheets in the present disclosure comply with the regulations of GB / T 16865 and GB / T 228.1.

[0041] The test for the bending performance of the aluminum alloy sheets in the present disclosure is conducted in accordance with the regulations of GB / T 232.

[0042] In the present disclosure, the volume fraction of iron-rich phases in the microstructure of the aluminum alloy sheets is determined by calculating the area proportion of iron-rich phases within a unit field of view by using image processing software.

[0043] The following provides further explanation and illustration of the aluminum alloy sheet and its preparation method according to the present disclosure with reference to specific embodiments. It should be noted that the following examples are intended solely to describe specific implementations of the present disclosure and do not constitute any limitation on the scope of protection of the present disclosure.Example 1

[0044] A slab was obtained by smelting and casting, followed by homogenization at 500°C for 6 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 7 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 16%, and that of hot finish rolling was 40%). The coiling temperature of hot finish rolling was 300°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 1.4 mm (cold rolling reduction rate: 80%). Then annealing was carried out by using an air cushion furnace at 550°C for 0 seconds (the sheet was immediately discharged from furnace and cooled after reaching 500°C). Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.33 mm (cold rolling reduction rate: 5%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Example 2

[0045] A slab was obtained by smelting and casting, followed by homogenization at 506°C for 6.5 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 6.5 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 17%, and that of hot finish rolling was 38%). The coiling temperature of hot finish rolling was 305°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 1.63 mm (cold rolling reduction rate: 75%). Then annealing was carried out by using an air cushion furnace at 530°C for 3 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.51 mm (cold rolling reduction rate: 7%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Example 3

[0046] A slab was obtained by smelting and casting, followed by homogenization at 512°C for 7 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 6 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 16%, and that of hot finish rolling was 40%). The coiling temperature of hot finish rolling was 310°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 1.8 mm (cold rolling reduction rate: 70%). Then annealing was carried out by using an air cushion furnace at 520°C for 5 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.64 mm (cold rolling reduction rate: 9%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Example 4

[0047] A slab was obtained by smelting and casting, followed by homogenization at 518°C for 7.5 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 5.5 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 18%, and that of hot finish rolling was 35%). The coiling temperature of hot rolling was 315°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 1.93 mm (cold rolling reduction rate: 65%). Then annealing was carried out by using an air cushion furnace at 510°C for 8 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.71 mm (cold rolling reduction rate: 11%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Example 5

[0048] A slab was obtained by smelting and casting, followed by homogenization at 524°C for 8 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 5 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 20%, and that of hot finish rolling was 33%). The coiling temperature of hot rolling was 320°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 2 mm (cold rolling reduction rate: 60%). Then annealing was carried out by using an air cushion furnace at 500°C for 10 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.76 mm (cold rolling reduction rate: 12%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Example 6

[0049] A slab was obtained by smelting and casting, followed by homogenization at 530°C for 8.5 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 4.5 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 17%, and that of hot finish rolling was 34%). The coiling temperature of hot rolling was 330°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 2.03 mm (cold rolling reduction rate: 55%). Then annealing was carried out by using an air cushion furnace at 480°C for 13 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.76 mm (cold rolling reduction rate: 13%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Example 7

[0050] A slab was obtained by smelting and casting, followed by homogenization at 536°C for 9 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 4 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 19%, and that of hot finish rolling was 33%). The coiling temperature of hot rolling was 340°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 2 mm (cold rolling reduction rate: 50%). Then annealing was carried out by using an air cushion furnace at 460°C for 16 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.72 mm (cold rolling reduction rate: 14%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Example 8

[0051] A slab was obtained by smelting and casting, followed by homogenization at 540°C for 10 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 3.5 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 16%, and that of hot finish rolling was 40%). The coiling temperature of hot rolling was 350°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 2.1 mm (cold rolling reduction rate: 40%). Then annealing was carried out by using an air cushion furnace at 450°C for 20 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.79 mm (cold rolling reduction rate: 15%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Comparative Example 1

[0052] A slab was homogenized at 480°C for 2 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 7 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 15%, and that of hot finish rolling was 38%). The coiling temperature of hot rolling was 300°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 1.4 mm (cold rolling reduction rate: 80%). Then annealing was carried out by using an air cushion furnace at 550°C for 0 seconds (the sheet was immediately discharged from furnace and cooled after reaching 500°C). Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.33 mm (cold rolling reduction rate: 5%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Comparative Example 2

[0053] A slab was homogenized at 506°C for 6.5 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 6.5 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 19%, and that of hot finish rolling was 36%). The coiling temperature of hot rolling was 360°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 1.63 mm (cold rolling reduction rate: 75%). Then annealing was carried out by using an air cushion furnace at 530°C for 3 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.51 mm (cold rolling reduction rate: 7%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Comparative Example 3

[0054] A slab was homogenized at 512°C for 7 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 3.5 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 18%, and that of hot finish rolling was 35%). The coiling temperature of hot rolling was 310°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 2.5 mm (cold rolling reduction rate: 28.6%). Then annealing was carried out by using an air cushion furnace at 520°C for 5 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 2.28 mm (cold rolling reduction rate: 9%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Comparative Example 4

[0055] A slab was homogenized at 518°C for 7.5 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 5.5 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 19%, and that of hot finish rolling was 32%). The coiling temperature of hot rolling was 315°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 1.93 mm (cold rolling reduction rate: 65%). Then annealing was carried out by using an air cushion furnace at 350°C for 8 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.71 mm (cold rolling reduction rate: 11%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.Comparative Example 5

[0056] A slab was homogenized at 524°C for 8 hours, and then discharged from the furnace and hot-rolled into a hot-rolled billet with a thickness of 5 mm (the pass reduction rate in the intermediate stage of hot rough rolling was 17%, and that of hot finish rolling was 37%). The coiling temperature of hot rolling was 320°C. The hot-rolled billet was then cold-rolled in a rolling mill to a thickness of 2 mm (cold rolling reduction rate: 60%). Then annealing was carried out by using an air cushion furnace at 500°C for 10 seconds. Finally, the annealed coil was cold-rolled into a finished aluminum alloy sheet with a thickness of 1.76 mm (cold rolling reduction rate: 20%). The tensile mechanical properties and bending performance of the finished aluminum alloy sheet were tested.

[0057] Table 1 shows the chemical compositions of the aluminum alloy sheets of Examples and Comparative Examples. Table 1 (Unit: percentage by weight)SiFeCuMnMgCrZnTiAlExample 10.080.200.010.414.00.060.010.01balanceExample 20.090.210.0150.424.20.070.0150.013balanceExample 30.100.220.020.434.30.080.020.016balanceExample 40.110.240.0250.444.40.090.0250.02balanceExample 50.120.260.030.454.50.100.030.023balanceExample 60.130.270.0350.464.60.110.0350.026balanceExample 70.140.280.040.474.70.120.040.028balanceExample 80.150.300.050.494.90.140.050.03balanceComparative Example 10.080.500.010.414.00.060.010.01balanceComparative Example 20.400.210.0150.424.20.070.0150.013balanceComparative Example 30.100.220.020.804.30.080.020.016balanceComparative Example 40.300.400.0250.444.40.090.0250.02balanceComparative Example 50.120.400.030.604.50.100.030.023balance

[0058] Table 2 shows the process parameters of the aluminum alloy sheets of Examples and Comparative Examples Table 2Heating temperature / °CHoldin g time / hCoiling temperature of hot finishing / °CThickness of hot-rolled billet / mmThickness of cold-rolled intermediate sheet / mmFirst cold deformation amount / %Intermediate annealing temperature / °CIntermediate annealing time / sSecond cold rolling deformation amount / %Example 1500630071.48055005Example 25066.53056.51.637553037Example 3512731061.87052059Example 45187.53155.51.9365510811Example 5524832052.0605001012Example 65308.53304.52.03554801313Example 7536934042.0504601614Example 8540103503.52.1404502015Comparative Example 1480230071.48055005Comparative Example 25066.53606.51.637553037Comparative Example 351273103.52.528.652059Comparative Example 45187.53155.51.9365350811Comparative Example 5524832052.0605001020

[0059] Table 3 shows the tensile properties and bending performance of the aluminum alloy sheets of Examples and Comparative Examples. Table 3Final product thickness / mmTensile propertiesBending performanceRp0.2 / MPaRm / MPaA50 / %Minimum bend radius at 90° (t represents sheet thickness)Example 11.3326131813.60.7tExample 21.5126731913.10.8tExample 31.6427132012.90.8tExample 41.7127232512.50.8tExample 51.7627332412.90.9tExample 61.7627733113.20.9tExample 71.7228233812.91.0tExample 81.7928734212.31.0tComparative Example 11.3326331011.21.1tComparative Example 21.5126131412.61.1tComparative Example 32.2826430910.41.2tComparative Example 41.7127731911.31.2tComparative Example 51.602863378.31.5t

[0060] As can be seen from Table 3, Examples 1-8 prepared according to the process of the present disclosure all achieved a yield strength of ≥ 260MPa, an elongation rate of ≥ 12%, a minimum bend radius at 90° of ≤ 1.0 × sheet thickness, and a tensile strength Rm of 318 MPa or more.

[0061] The performance requirements for 5083-H32 as specified in the GB / T 3880 standard are as follows: Thickness / mmTensile strength / MPaYield strength / MPaElongation rate after fracture / % A 50 Bending radius at 90°> 0.50-1.50305-38021561.5t> 1.50-3.072.0t> 3.00-6.082.5t

[0062] Obviously, the yield strength and bending performance of the high-magnesium 5XXX series H32 aluminum alloy sheet according to the present disclosure are significantly higher than the standard requirements for 5083-H32 aluminum alloy sheet specified in the GB / T 3880 standard.

[0063] In Comparative Example 1, the Fe content exceeded the upper limit specified in the present disclosure, the ratio of Si+Fe to Mn exceeded the upper limit specified in the present disclosure, and the homogenization temperature and holding time were below the lower limit specified in the present disclosure. As a result, the dissolution of soluble crystalline phases was insufficient, a large number of iron-rich phases remained and failed to undergo sufficient transformation. Consequently, the elongation rate was only 11.2%, and the minimum bend radius at 90° was 1.1 × sheet thickness.

[0064] In Comparative Example 2, the Si content exceeded the upper limit specified in the present disclosure, the ratio of Si+Fe to Mn also exceeded the upper limit specified in the present disclosure, leading to the easy precipitation of elemental Si. Moreover, the hot-rolling coiling temperature exceeded the upper limit specified in the present disclosure, causing the dispersed phase to precipitate and grow during cooling of the hot rolling coil. As a result, the minimum bend radius at 90° was 1.1 × sheet thickness.

[0065] In Comparative Example 3, the Mn content exceeded the upper limit specified in the present disclosure, and the thickness of the hot-rolled coil did not meet the requirements of the present disclosure. This resulted in a total reduction rate of cold rolling before intermediate annealing that was lower than the specified lower limit, leading to an elongation rate of only 10.4% and a minimum bend radius at 90° of 1.2 × sheet thickness.

[0066] In Comparative Example 4, both the Si and Fe contents exceeded the upper limit specified in the present disclosure, the ratio of Si+Fe to Mn exceeded the upper limit specified in the present disclosure, and the intermediate annealing temperature was lower than the lower limit specified in the present disclosure, resulting in a minimum bend radius at 90° of 1.2 × sheet thickness.

[0067] In Comparative Example 5, both the Fe and Mn contents exceeded the upper limits specified in the present disclosure, and the reduction rate of second cold rolling after intermediate annealing exceeded the upper limit specified in the present disclosure, resulting in excessive work hardening. The elongation rate was only 8.3%, and the minimum bend radius at 90° was 1.5 × sheet thickness. Figures 1 and 2 show the microstructure photographs of the sheets from Example 1 and Comparative Example 5, respectively. Figure 3 shows a typical grain structure photograph of Example 1, with an average grain size of 13µm.

[0068] As can be seen from the photo of Figure 1, in Example 1 where the contents of Si, Fe, and Mn is within the specified ranges of the present disclosure, the volume fraction of the iron-rich phase is 1.3%, and the particles are fine (maximum size of the iron-rich phase ≤ 5µm). The tendency for crack initiation at the iron-rich phases during deformation of the sheet is low, thereby providing good plasticity and bending performance for the sheet.

[0069] As can be seen from the photo of Figure 2, in Comparative Example 5, where the contents of Fe and Mn exceed the upper limit specified in the present disclosure, the microstructure photo of the sheet shows a large number and large size of iron-rich phases. The iron-rich phases have a volume fraction of 4.8%, and a maximum grain size of 20 µm, which has a significant fracturing effect on the sheet matrix, a high tendency for crack initiation during deformation, deteriorating the shaping and bending performance of the sheet, and adversely affecting the mechanical properties of the sheet.

[0070] In summary, the high-magnesium 5XXX series H32 aluminum alloy sheet according to the present disclosure exhibits yield strength and bending performance that are significantly higher than the standard requirements for the H32 temper, and has a performance that is notably superior to existing products. Additionally, the production process is significantly shortened, production efficiency is improved, and the consistency of product performance is enhanced. The sheet can be widely applied to products such as battery trays for new energy vehicles.

[0071] It should be noted that all technical features described in the present application can be freely combined or integrated in any manner, unless they contradict each other. The present disclosure can be variously modified and varied without departing from the scope of the present disclosure. This will be obvious to those skilled in the art. For instance, features shown or described as part of one embodiment can be utilized with another embodiment to generate yet another embodiment. Therefore, the present disclosure is intended to encompass these modifications and variations within the scope of the appended claims and their equivalents.

Claims

1. An aluminum alloy sheet, wherein the aluminum alloy sheet comprises the following chemical components in percentage by weight: Si: 0-0.15%, Fe: 0.20-0.30%, Cu: 0-0.05%, preferably 0.01-0.05%, Mn: 0.41-0.49%, Mg: 4.0-4.9%, Cr: 0.06-0.14%, Zn: 0-0.05%, preferably 0.01-0.05%, Ti: 0.01-0.03%, and the balance being Al and inevitable impurities; wherein the content of each of the inevitable impurities in percentage by weight is greater than or equal to 0 and less than or equal to 0.05%, and the total content in percentages by weight of the inevitable impurities is greater than or equal to 0 and less than or equal to 0.15%; and wherein the following formula is satisfied: (Si+Fe) / Mn ≤ 1, wherein element symbols in the formula respectively represent the numerical values preceding the % symbol of the weight percentage content of corresponding elements.

2. The aluminum alloy sheet according to claim 1, wherein the balance are Al and inevitable impurities.

3. The aluminum alloy sheet according to claim 1, wherein Si: 0-0.12%; and / or, Fe: 0.20-0.25%; and / or, Mn: 0.43-0.47%.

4. The aluminum alloy sheet according to any one of claims 1 to 3, wherein the microstructure of the aluminum alloy sheet comprises an iron-rich phase with a volume fraction of ≤ 3%, and the iron-rich phase has a maximum grain size of ≤ 5 µm; preferably, the aluminum alloy sheet has a grain morphology of equiaxed grain with an average grain size of ≤ 20 µm, preferably ≤ 15 µm.

5. The aluminum alloy sheet according to any one of claims 1 to 4, wherein the aluminum alloy sheet has a yield strength of ≥ 260 MPa, an elongation rate of ≥ 12%, a minimum bend radius at 90° of ≤ 1.0 × sheet thickness, where the sheet thickness is expressed in mm; preferably, the aluminum alloy sheet has a tensile strength of ≥ 318 MPa.

6. A preparation method for the aluminum alloy sheet according to any one of claims 1 to 5, including the following steps performed in sequence: (1) smelting and casting: smelting and casting according to the composition of the aluminum alloy sheet to obtain a slab; (2) performing homogenization heat treatment of the slab at a heating temperature of 500-540 °C for a holding time of 6-10 h; (3) hot rolling to obtain a hot-rolled billet: the intermediate stage of hot rough rolling is performed with a pass reduction rate of ≥ 15%, hot finish rolling is performed with a pass reduction rate of ≥ 30% and a coiling temperature of 300-350°C, and the thickness of the obtained hot-rolled billet is determined based on the thickness of the finished aluminum alloy sheet product and the cold rolling deformation amount; (4) first cold rolling to obtain a cold-rolled coil: the total reduction rate of the first cold rolling is 40% or more; (5) intermediate annealing of the cold-rolled coil: the intermediate annealing is carried out in an air-cushion furnace, with a target sheet temperature of 450-550 °C, preferably 480-530 °C, and a holding time of 0-20 s, and the sheet is air-cooled to room temperature after discharged from the furnace; (6) second cold rolling: a reduction rate of the second cold rolling is 5-15%.

7. The preparation method according to claim 6, wherein in step (2), the homogenization heat treatment is performed at a heating temperature of 530-540°C with a holding time of 8-10 h.

8. The preparation method according to claim 6, wherein in step (3), the intermediate stage of the hot roughing rolling is performed with a pass reduction rate of ≥ 20%, the hot finish rolling is performed with a pass reduction rate of ≥ 35% and a coiling temperature of 310-330°C, and the thickness of the obtained hot-rolled billet is 3-4 times that of the finished aluminum alloy sheet product.

9. The preparation method according to claim 6, wherein in step (4), the total reduction rate of the first cold rolling is 60-80%.

10. The preparation method according to claim 6, wherein in step (6), the reduction rate of the second cold rolling is 8-10%.

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