Al-mg alloy sheet and strip and method of making

Abstract

The application discloses an Al-Mg alloy plate strip and a preparation method thereof. The composition comprises 0 < Si < 0.1%, 0 < Fe < 0.18%, Mn: 0.2-0.28%, Mg: 4.5-4.85%, Ti: 0.01-0.02%, Cu < 0.1%, the balance comprising Al and other inevitable impurities, and simultaneously satisfying Fe / Si >= 1 and 4.75% <= Mn+Mg+Cu <= 5.1%. The thickness of the obtained alloy plate strip reaches 1.8-3 mm, the structure of the plate strip is regulated, and the plate strip has high strength and good forming performance. The Al-Mg alloy plate strip has the following properties: in the 0° direction, the yield strength is 260-280 MPa, the tensile strength is 345-375 MPa, the elongation is 9-14%, and the plate strip does not crack after 90° bending; in the 90° direction, the yield strength is 250-270 MPa, the tensile strength is 341-372 MPa, the elongation is 10-15%, and the plate strip does not crack after 90° bending.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy preparation technology, specifically relating to an Al-Mg alloy plate and strip and its preparation method. Background Technology

[0002] 5xxx series aluminum alloy sheets possess suitable strength, excellent elongation, formability, and corrosion resistance, and are widely used in the manufacture of automotive interior panels, automotive internal components, and bus skins. 5xxx alloys are heat-treatable non-strengthable aluminum alloys; the main strengthening methods are solution strengthening and work hardening. Fully annealed (O temper) 5xxx alloys have excellent formability and bending properties, but relatively low strength. In applications requiring higher strength, incompletely annealed states are generally used, such as H22, H24, H32, and H34 tempers. Among these, 5182 aluminum alloy is one of the representative alloys and enjoys widespread application.

[0003] Chinese patent CN201811245798.0 discloses a 5182-H36 aluminum alloy sheet for luggage compartment door panels of new energy buses and its preparation method. The alloy contains: 0.05-0.1% Si, 0.1-0.2% Fe, 0.01-0.1% Cu, 0.4-0.8% Mn, 4.6-5.2% Mg, 0.07-0.12% Cr, 0.01-0.2% Zn, 0.01-0.05% Ti, with the balance being Al and other unavoidable impurities. The process steps are as follows: after homogenization of the ingot, hot rolling is performed at a final rolling temperature of 320-360℃ to a final rolling thickness of 2.2-2.8mm; cold rolling is performed with a total cold rolling rate of 45-65% at a final rolling temperature above 130℃; after cold rolling, stabilization annealing is performed at room temperature for no more than 1 hour (holding at 150-180℃ for 1-3 hours). The prepared 1.2mm material has a tensile strength of 360-390MPa, a yield strength of 290-320MPa, an elongation of 10-13%, and good performance when bent at 90° (bending radius of 0.5mm). This patent only allows for an alloy thickness of 1.2mm; whether the bending performance of thicker alloys meets the requirements has not been investigated.

[0004] Chinese patent CN201511014410.2 discloses a 5182 aluminum alloy strip and its production method. The alloy contains: 0.1% Si, 0.12-0.22% Fe, 0.05-0.5% Cu, 0.34-0.4% Mn, 4.5-4.9% Mg, 0.03-0.06% Cr, with the balance being Al and other unavoidable impurities. The process steps are as follows: the ingot is hot-rolled after two-stage homogenization (holding at 430-460℃ for 3-6 hours + holding at 490-530℃ for 4-8 hours), then cold-rolled to 2-2.5 mm, annealed at 240-280℃ for 4-8 hours, cold-rolled again to 0.2-0.8 mm, and then subjected to low-temperature annealing (holding at 190-240℃ for 4-8 hours). The prepared material has a tensile strength of 380-420 MPa and does not crack when bent at 90°. The alloy thickness in this patent is only 0.8mm, and no research has been conducted on whether the bending performance of thicker alloys meets the requirements.

[0005] Chinese patent CN201410010639.8 discloses a 5182 aluminum alloy strip for automotive heat shields and its manufacturing method. The alloy contains: 0.05-0.2% Si, 0.05-0.15% Fe, 0.01-0.15% Cu, 0.2-0.45% Mn, 4.5-5% Mg, 0.01-0.1% Cr, 0.01-0.25% Zn, 0.01-0.05% Ti, with the balance being Al and other unavoidable impurities. The process steps are as follows: the ingot is heated at 450-520℃ for 1-8 hours and hot-rolled to 2-7 mm, with a final rolling temperature of 260-340℃; after cold rolling, it is annealed at 320-360℃ for 1-2 hours, followed by cold rolling and tension leveling for finished product annealing (held at 300-380℃ for 1-8 hours). The prepared material is in the O-state, with a tensile strength of 260-300 MPa and a yield strength of 110-150 MPa. Chinese patents CN201610374422.4, CN201910344946.2, CN202010390301.5, CN202210369902.7, and CN202310783615.5 also only disclose methods for preparing 5182-O-state aluminum alloy sheets. The 5182 alloy prepared using these techniques has good formability but relatively low strength.

[0006] Chinese patent CN202210670223.3 discloses a method for producing 5052-H32 aluminum alloy sheet for automotive structural parts. The preparation process is as follows: after the ingot is heated to 480±10℃ for 6 hours for homogenization, it is hot rough rolled to a thickness of 42-44mm. Then, it is hot finished rolled in four consecutive rolling mills at a final rolling temperature of 335-355℃ to a thickness of 2.5-8mm. It is then cold rolled to 1-3mm with a deformation rate of 25-65%. After cleaning, it is annealed in a continuous annealing furnace at a temperature of 323-327℃ and a speed of 25-35m / min, and air-cooled to 10-30℃. Finally, it is tension-straightened (elongation of 0.5-0.8%). The alloy thickness prepared by this patent is 2.5-8mm, but it does not address the bending properties of the material.

[0007] Chinese patent CN202311057189.3 discloses a method for producing aluminum alloy strip for 5754-H22 automotive sealing strips. The preparation process is as follows: the ingot is heated at 460-490℃ for 2-3 hours and then hot-rolled to a final thickness of 2.5-3 mm at a final rolling temperature of 325-345℃; during cold rolling, the initial hot rolling temperature is 50-60℃, the pass rate is ≥45%, and the final rolling temperature is 120-150℃; the material is cleaned with an alkaline solution containing 6-9 g / L of mixed fluoride at a temperature of 65-80℃ for 10-15 minutes; then annealed (held at 170-240℃ for 2-3 hours), and finally leveled (elongation 0.1-0.2%). This patent does not mention the bending properties of the material.

[0008] Currently, the disclosed preparation methods for 5182 aluminum alloy mainly focus on the O-state process. The disclosed patent technologies regarding the preparation methods of H2X and H3X state materials are applied to products with relatively thin thicknesses. Thickness has a significant impact on the formability of the material; under the same bending radius, increasing the material thickness leads to a deterioration in bending performance. Therefore, increasing the material thickness increases the requirements for the material's formability, and the corresponding preparation process also needs to be adjusted.

[0009] In summary, for alloys with a thickness of 1.8mm or more, the current challenge lies in balancing strength and formability. Existing technologies and products cannot yet meet users' demands for high strength and high formability. Summary of the Invention

[0010] The purpose of this invention is to provide an Al-Mg alloy sheet / strip and its preparation method. For alloy sheets with a thickness of 1.8-3 mm, the microstructure of the sheet is controlled to achieve both high strength and good formability. The Al-Mg alloy sheet / strip exhibits the following characteristics in the 0° direction: yield strength 260-280 MPa, tensile strength 345-375 MPa, elongation 9-14%, and no cracking after 90° bending; in the 90° direction: yield strength 250-270 MPa, tensile strength 341-372 MPa, elongation 10-15%, and no cracking after 90° bending.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows:

[0012] An Al-Mg alloy sheet / strip, the composition of which by weight percentage includes: 0 < Si ≤ 0.1%, 0 < Fe ≤ 0.18%, Mn: 0.2-0.28%, Mg: 4.5-4.85%, Ti: 0.01-0.02%, Cu ≤ 0.1%, with the balance including Al and other unavoidable impurities, and also needs to simultaneously satisfy: Fe / Si ≥ 1; 4.75% ≤ Mn + Mg + Cu ≤ 5.1%.

[0013] Furthermore, it contains one or both of Cr and V, and satisfies Cr+V≤0.05%.

[0014] Preferably, the balance is Al and other unavoidable impurities.

[0015] Preferably, in the microstructure of the Al-Mg alloy sheet / strip, the number of compounds with a major axis dimension greater than 7 μm accounts for ≤5% of the total number of compounds, and the number of compounds with a major axis dimension greater than 10 μm is ≤50 per mm. 2 .

[0016] Preferably, in the microstructure of the Al-Mg alloy sheet / strip, more than 90% of the grains have an aspect ratio of 3.2-7, and the number of grains with an aspect ratio > 7 is < 5%.

[0017] Preferably, the Al-Mg alloy sheet / strip has a thickness of 1.8-3 mm, and in the 0° direction: yield strength 260-280 MPa, tensile strength 345-375 MPa, elongation 9-14%, and no cracking after 90° bending; in the 90° direction: yield strength 250-270 MPa, tensile strength 341-372 MPa, elongation 10-15%, and no cracking after 90° bending.

[0018] The composition design of the Al-Mg alloy sheet and strip of this invention:

[0019] 1) Si and Fe: These are the main impurity elements in the alloy and are elements that are inevitably introduced into the raw materials of aluminum ingots during the smelting process. The thickness of the strip and sheet material involved in this invention is 1.8-3mm. Under the condition of a small bending radius, the increase in the number of coarse compounds will cause bending cracks. It is necessary to more strictly control the upper limit of Si and Fe element content. This invention controls 0 < Si ≤ 0.1%, 0 < Fe ≤ 0.18%, and Fe / Si ≥ 1, so that the quantity and size of the second phase (AlFeMn, α-AlFeMnSi, etc.) formed by Si and Fe during the casting process are controlled within a certain range, avoiding the formation of more large-sized Fe and Si compounds due to high Fe and Si content, preventing them from becoming crack sources and reducing the forming performance.

[0020] 2) Mg: The main element of the alloy. This invention controls the Mg content to be between 4.5-4.85 wt% to ensure the necessary strength. Low content leads to insufficient alloy strength; high content, while increasing strength, also negatively impacts forming and bending performance. This is especially true for the sheet and strip materials involved in this invention, which are 1.8-3 mm thick and have higher requirements for bending performance. Increased strength can make the sheet prone to bending defects. Therefore, strict control of the Mg content range is necessary to simultaneously ensure both strength and bending performance.

[0021] 3) Mn: This invention controls the Mn content to be between 0.2-0.28 wt%, which can regulate the type of Fe phase from AlFe and AlFeSi to AlFeMn and AlFeMnSi, reduce the electrochemical potential difference between the compound and the aluminum matrix, inhibit pitting corrosion, and improve the morphology of the iron-rich phase from coarse or flake-like to small block or granular, reducing the adverse effects of the compound on the forming performance; at the same time, Mn has a solid solution strengthening effect, but too high a Mn content is detrimental to bending performance.

[0022] 4) Cu: The present invention controls the Cu content to ≤0.1wt%, which can supplement the strengthening and inhibit pitting corrosion; if the Cu content is too high, it will increase the strength of the alloy while reducing the bending performance, and will also lead to a decrease in the corrosion resistance of the alloy.

[0023] 5) Mn+Mg+Cu: This invention controls the content of Mn+Mg+Cu to be 4.75% ≤ 5.1%, which ensures that these three elements play their respective roles while reducing the adverse effects on forming performance caused by high strength due to high content of these three elements, or avoiding insufficient strength due to low content of these elements. When the content of Mn+Mg+Cu is too high, the high solid solution content of these elements will inhibit recrystallization during hot rolling, affecting the grain size distribution and making it easier for more grains with an aspect ratio > 7 to appear, which will affect the performance of the material and be unfavorable for bending. In particular, the thickness of the strip and sheet material involved in this invention is 1.8-3mm, which has high requirements for bending performance and strength. It is necessary to strictly control the content range of Mn+Mg+Cu in order to ensure both strength and bending performance.

[0024] 6) Furthermore, Cr and V can be added: forming dispersed Cr or V-containing compounds is beneficial to further improve strength, and controlling Cr+V≤0.05wt% can avoid the formation of coarse Cr or V-containing compounds, without reducing formability, and ensuring good formability of the alloy.

[0025] This invention controls the elements Si, Fe, Mn, and Cr+V, and ensures that Fe / Si ≥ 1, to prevent the formation of coarse compounds. This guarantees that the final alloy microstructure contains ≤5% of compounds with a long axis dimension greater than 7 μm, and ≤50 compounds with a long axis dimension greater than 10 μm per mm. 2 Controlling the number of compounds with a size greater than 7 μm in the alloy microstructure is beneficial for improving the elongation of the material and avoiding forming cracks. This is a key technical point for ensuring good formability and bending performance of the 1.8-3 mm thick sheet and strip involved in this invention.

[0026] The method for preparing the Al-Mg alloy plate and strip of the present invention includes the following steps:

[0027] 1) Smelting and casting

[0028] The above-mentioned components are melted, and after degassing and slag removal, they are cast into ingots.

[0029] 2) Homogenization

[0030] Heat the ingot to 400-460℃ and hold for 2-6 hours, then heat to 500-520℃ and hold for 4-6 hours.

[0031] 3) Hot rolling

[0032] Hot rolling produces hot-rolled coils;

[0033] 4) Cold rolling

[0034] The total deformation of cold rolling is 57-67%, and the thickness of cold-rolled finished products is 1.8-3mm;

[0035] 5) Annealing

[0036] Annealing temperature: 130-170℃.

[0037] Preferably, in step 1), the total inclusion content of the alloy melt obtained from smelting is ≤0.02mm after slag removal treatment. 2 / kg.

[0038] Preferably, in step 2), the ingot is first heated to 350-400℃, then heated to 400-460℃ at 40-70℃ / h and held for 2-6 hours, and then heated to 500-520℃ at 20-40℃ / h and held for 4-6 hours.

[0039] Preferably, in step 3), a hot-rolled coil is obtained by hot finishing rolling and hot roughing rolling, with the hot roughing rolling starting temperature at 490-510℃, the hot finishing rolling starting temperature at 380-420℃, and the coiling temperature at 300-330℃.

[0040] Preferably, in step 4), the total cold rolling deformation is 60-65%.

[0041] Preferably, in step 5), the temperature is increased to 130-160℃ at a heating rate of 30-60℃ / h for annealing and holding for 2-5 hours. After the holding period, the furnace is removed and air-cooled.

[0042] In the preparation method of Al-Mg alloy sheet and strip described in this invention:

[0043] 1) Homogenization: First, set the full power heating to heat the saw-milled ingot to 350-400℃, then heat it to 400-460℃ at 40-70℃ / h and hold it for 2-6 hours, then heat it to 500-520℃ at 20-40℃ / h and hold it for 4-6 hours.

[0044] Rapid heating at full power to 350-400℃ helps improve production efficiency without adversely affecting the ingot microstructure. Heating at 40-70℃ / h to 400-460℃ and holding for 2-6 hours helps the β-AlMg phase to fully dissolve and prevents overheating of the β-AlMg phase due to excessively rapid heating. Heating at 20-40℃ / h to 500-520℃ and holding for 4-6 hours helps the transformation and spheroidization of the Fe-containing phase and prevents the harmful effects of residual coarse Fe-containing phases on performance.

[0045] 2) Hot rolling: After the ingot is kept warm, hot rough rolling is carried out at a temperature of 490-510℃; then hot finish rolling is carried out at a temperature of 380-420℃, and finally the coiling temperature is 300-330℃ to obtain hot rolled coil.

[0046] After the ingot is kept warm, hot rough rolling is carried out. The starting temperature of hot rough rolling is 490-510℃, which can eliminate the waiting time of conventional ingot cooling and then rolling, without affecting the performance of the alloy and improving production efficiency.

[0047] A hot finishing rolling temperature of 380-420℃ and a coiling temperature of 300-330℃ can obtain a recrystallized grain structure with relatively uniform size and suitable dimensions, which helps to achieve good subsequent forming properties. Hot rolling coiling temperatures below 300℃ will lead to insufficient recrystallization and uneven grain size, which is detrimental to the forming properties of the finished sheet. Coiling temperatures above 330℃ will cause adhesion defects on the coil surface, reducing the surface quality of the material; and will also cause some recrystallized grains to grow, resulting in grain size inhomogeneity and affecting the forming properties of the finished sheet.

[0048] 3) Cold rolling: Cold-rolled thickness 1.8-3mm, controlling the total cold-rolling deformation to 57-67% to obtain suitable initial strength to meet the subsequent finished product performance requirements, and controlling the degree of grain deformation: more than 90% of the grains have an aspect ratio of 3.2-7, and the number of grains with an aspect ratio >7 is <5%, ensuring subsequent forming performance. If the total cold-rolling deformation is too small, the strength will be too low, and the strength requirements of the finished sheet cannot be guaranteed. If the total cold-rolling deformation is too large, the energy stored around the second phase particles is easily higher than that of the matrix. During the finished product annealing process, recrystallization is likely to occur in this area, resulting in non-uniform grain size in the finished product and an increase in shear bands, reducing the bending performance of the material.

[0049] 4) Stabilization Annealing: Anneal at a furnace temperature of 30-60℃ / h from room temperature to 130-160℃, holding for 2-5 hours. After annealing, remove from the furnace and air cool. If the annealing temperature is too low, the material's recovery is limited; if the strength is too high, it is detrimental to formability and prone to cracking during bending. If the annealing temperature is too high, it can cause partial or complete recrystallization, resulting in a significant decrease in strength that fails to meet requirements. A heating rate that is too slow is detrimental to production efficiency. A heating rate that is too fast can leave rolling oil residue on the aluminum surface, affecting surface quality.

[0050] This invention targets materials with a thickness of 1.8-3mm. By optimizing the combination of homogenization, hot rolling, cold rolling, and annealing parameters, the grain size of the finished product is controlled. More than 90% of the grains have an aspect ratio of 3.2-7, and the number of grains with an aspect ratio >7 is <5%. This ensures that the alloy has high strength while also having good formability, especially bending performance.

[0051] To achieve the above objectives, the technical solution of the present invention is as follows:

[0052] In the existing technology, 5182 aluminum alloy products can achieve good bending performance when the thickness is relatively thin, but it is difficult to meet the requirement of not cracking when bending aluminum alloys with a thickness of more than 1.8mm.

[0053] This invention targets thick sheet and strip materials with alloy thicknesses of 1.8-3 mm, balancing strength and formability requirements. Based on the conventional Al-Mg alloy composition, it preferentially selects the ranges of Mg, Mn, and Cu elements, controlling the content to 4.75% ≤ Mg + Mn + Cu ≤ 5.1%. Through solid solution strengthening, the alloy achieves the required high strength and controls grain size uniformity, avoiding the formation of grains with aspect ratios > 7, thus improving the material's formability. Simultaneously, it preferentially controls Fe, Si, and Cr+V, controlling Fe / Si ≥ 1 and Cr+V ≤ 0.05%, preventing the formation of coarse compounds. This ensures that in the final 1.8-3 mm thick microstructure, the proportion of compounds with a long axis dimension greater than 7 μm is ≤ 5% of the total compounds, and the number of compounds with a long axis dimension greater than 10 μm is ≤ 50 per mm. 2 While achieving high strength in the strip, it also ensures the strip's elongation and formability, and guarantees that it will not crack when bent.

[0054] Based on the composition design, this invention controls the total deformation of cold rolling within the range of 57-67% by optimizing the combination of homogenization, hot rolling, and cold rolling, thereby regulating the grain size and forming a uniform grain structure. This ensures that more than 90% of the grains in the 1.8-3mm thick alloy sheet have an aspect ratio of 3.2-7, and the number of grains with an aspect ratio >7 is <5%. This can effectively improve the elongation and formability of the material, especially meeting the bending requirements of 1.8-3mm thick materials.

[0055] The Al-Mg alloy finished sheet and strip obtained by this invention, especially the sheet and strip with a thickness of 1.8-3mm, has both high strength and good formability. In the 0° direction: yield strength 260-280MPa, tensile strength 345-375MPa, elongation 9-14%, no cracking after 90° bending; in the 90° direction: yield strength 250-270MPa, tensile strength 341-372MPa, elongation 10-15%, no cracking after 90° bending. Attached Figure Description

[0056] Figure 1 This is an image of the grain structure of the strip obtained in Example 1 of the present invention.

[0057] Figure 2 This is an image of the strip grain structure obtained in Comparative Example 1.

[0058] Figure 3 This is a photograph of the strip after bending, obtained in Embodiment 1 of the present invention.

[0059] Figure 4 This is a photo of the strip after bending, obtained from Comparative Example 1. Detailed Implementation

[0060] The present invention will be further described below with reference to the embodiments and accompanying drawings. However, this is not a limitation of the present invention. Those skilled in the art can make modifications or improvements based on the basic idea of ​​the invention, but as long as they do not depart from the basic idea of ​​the present invention, they are all within the scope of the present invention.

[0061] The chemical composition of the alloys in the embodiments and comparative examples of this invention is shown in Table 1, with the balance including Al and other unavoidable impurities. The process parameters for the embodiments and comparative examples of this invention are shown in Table 2, and the properties of the prepared alloys are shown in Table 3.

[0062] Figure 1 The strip grain structure image obtained in Example 1 of this invention shows that 90% of the grains have an aspect ratio in the range of 3.2-7, and 4.8% of the grains have an aspect ratio > 7. Figure 3 The strip obtained in Embodiment 1 of this invention has been bent without cracking, indicating that the bending is qualified.

[0063] As can be seen from the data in Table 3, the 1.8-3mm thick alloy sheet and strip obtained in the embodiments of the present invention have both high strength and good formability. In the 0° direction: yield strength 260-280MPa, tensile strength 345-375MPa, elongation 9-14%, no cracking after 90° bending; in the 90° direction: yield strength 250-270MPa, tensile strength 341-372MPa, elongation 10-15%, no cracking after 90° bending, which can meet the customer's requirements for alloy strength and formability.

[0064] Comparative Example 1 has a high Mn content in the alloy, and a high total Mg+Mn+Cu content, exceeding the requirements of this invention. Although the same process as this invention was used, the alloy strip has a high proportion of compounds with a long axis dimension greater than 7 μm, a low number of grains with an aspect ratio of 3.2-7, and a high number of grains with an aspect ratio greater than 7. The alloy strip has high yield strength and tensile strength in the 0° and 90° directions, but low elongation, cracking during bending, and poor formability. Figure 2 The image shows the grain structure of the strip obtained in Comparative Example 1. The grain structure characteristics of the strip can be seen from the image. 72% of the grains have an aspect ratio in the range of 3.2-7, and the grains with an aspect ratio >7 reach 13%. Figure 4 The photo shows the strip after bending obtained from Comparative Example 1. The bending was not up to standard and cracks appeared.

[0065] In Comparative Example 2, the content of Mg and Mg+Mn+Cu was relatively high, exceeding the requirements of this invention. Although the same process as this invention was used, the number of grains with an aspect ratio of 3.2-7 in the obtained alloy plate and strip structure was relatively small, while the number of grains with an aspect ratio >7 was relatively large. The alloy plate and strip had a high yield strength in the 0° direction and a low elongation. However, the aluminum material prepared had poor formability, and cracking occurred when bending in the 0° and 90° directions, indicating poor formability.

[0066] In Comparative Example 3, the Mg content was low, and the total Mg+Mn+Cu content was low, exceeding the requirements of this invention. Although the same process as this invention was used, the yield strength and tensile strength of the alloy plate and strip obtained were low in the 0° and 90° directions.

[0067] In Comparative Example 4, the Fe and Si contents and Fe / Si ratio exceeded the requirements of this invention. Although the same process as this invention was used, the number of compounds with a long axis dimension greater than 7 μm in the microstructure of the obtained alloy strip was relatively high, and the number of compounds with a long axis dimension greater than 10 μm per unit area was relatively large. The number of grains with an aspect ratio of 3.2-7 was also relatively large. The elongation of the obtained alloy strip in the 0° and 90° directions was low, and cracking occurred when bending, resulting in poor formability.

[0068] In Comparative Example 5, the Cr+V content was too high, exceeding the requirements of this invention. Although the same process as this invention was used, the number of compounds with a long axis dimension greater than 7 μm in the microstructure of the obtained alloy plate and strip accounted for a relatively high proportion of the total number of compounds, and the number of compounds with a long axis dimension greater than 10 μm per unit area was relatively large. The number of grains with an aspect ratio of 3.2-7 was relatively large, and the number of grains with an aspect ratio greater than 7 was relatively large. The elongation of the obtained alloy plate and strip in the 0° and 90° directions was low, and cracking occurred when bending, resulting in poor formability.

[0069] In Comparative Example 6, the Cu content was too high, exceeding the requirements of this invention. Although the same process as this invention was used, the obtained alloy strip cracked when bent in the 0° and 90° directions, resulting in poor formability.

[0070] Comparative Example 7 uses the same composition as Example 7 of the present invention, but the preparation process is different. Single-stage high-temperature homogenization is used. The resulting alloy strip has a high proportion of compounds with a long axis dimension greater than 7 μm in its microstructure, and a large number of compounds with a long axis dimension greater than 10 μm per unit area. The alloy strip has low tensile strength, cracks when bent at 0°, and poor formability.

[0071] Comparative Example 8 uses the same composition as Example 7 of the present invention, but the preparation process is different. The total cold rolling processing rate is higher than that specified in the present invention. The resulting alloy strip has fewer grains with an aspect ratio of 3.2-7 and more grains with an aspect ratio >7. The alloy strip has higher yield strength in the 0° and 90° directions, lower elongation, and cracks when bent in the 0° and 90° directions, resulting in poor formability.

[0072]

[0073]

[0074]

[0075]

Claims

1. An Al-Mg alloy sheet / strip, the composition of which includes, by weight percentage: 0 < Si ≤ 0.1%, 0 < Fe ≤ 0.18%, Mn: 0.2-0.28%, Mg: 4.5-4.85%, Ti: 0.01-0.02%, Cu ≤ 0.1%, the balance includes Al and other unavoidable impurities, and must also meet the following requirements: Fe / Si ≥ 1; 4.75% ≤ Mn + Mg + Cu ≤ 5.1%.

2. The Al-Mg alloy sheet and strip as described in claim 1, characterized in that, It also contains one or both of Cr and V, and satisfies Cr+V≤0.05%.

3. The Al-Mg alloy sheet / strip as described in claim 1 or 2, characterized in that, The balance consists of Al and other unavoidable impurities.

4. The Al-Mg alloy sheet / strip as described in claim 1, 2, or 3, characterized in that, In the microstructure of the Al-Mg alloy sheet and strip, the number of compounds with a major axis dimension greater than 7 μm accounts for ≤5% of the total number of compounds.

5. The Al-Mg alloy sheet / strip as described in claim 1, 2, 3, or 4, characterized in that, The number of compounds with a major axis dimension greater than 10 μm in the microstructure of the Al-Mg alloy sheet / strip is ≤50 per mm. 2 .

6. The Al-Mg alloy sheet / strip as described in claim 1, 2, 3, 4, or 5, characterized in that, In the microstructure of the Al-Mg alloy sheet and strip, more than 90% of the grains have an aspect ratio of 3.2-7, and the number of grains with an aspect ratio > 7 is < 5%.

7. The Al-Mg alloy sheet / strip as described in claim 1, 2, 3, 4, 5, or 6, characterized in that, The Al-Mg alloy sheet / strip has a thickness of 1.8-3 mm, and in the 0° direction: yield strength 260-280 MPa, tensile strength 345-375 MPa, elongation 9-14%, and no cracking after 90° bending; in the 90° direction: yield strength 250-270 MPa, tensile strength 341-372 MPa, elongation 10-15%, and no cracking after 90° bending.

8. The method for preparing Al-Mg alloy sheet / strip as described in any one of claims 1 to 7, characterized in that, Includes the following steps: 1) Smelting and casting The components are smelted according to the composition described in claim 1, 2 or 3, and then degassed and deslag-removed to cast ingots. 2) Homogenization Heat the ingot to 400-460℃ and hold for 2-6 hours, then heat to 500-520℃ and hold for 4-6 hours. 3) Hot rolling Hot rolling produces hot-rolled coils; 4) Cold rolling The total deformation of cold rolling is 57-67%, and the thickness of cold-rolled finished products is 1.8-3mm; 5) Annealing Annealing temperature: 130-170℃.

9. The preparation method according to claim 8, characterized in that, In step 1), the total inclusion content of the alloy melt obtained from smelting is ≤0.02mm after slag removal treatment. 2 / kg.

10. The preparation method according to claim 8, characterized in that, In step 2), the ingot is first heated to 350-400℃, then heated to 400-460℃ at 40-70℃ / h and held for 2-6 hours, and then heated to 500-520℃ at 20-40℃ / h and held for 4-6 hours.

11. The preparation method according to claim 8, characterized in that, In step 3), hot-rolled coils are obtained through hot roughing and hot finishing rolling. The starting temperature of hot roughing rolling is 490-510℃, the starting temperature of hot finishing rolling is 380-420℃, and the coiling temperature is 300-330℃.

12. The preparation method according to claim 8, characterized in that, In step 4), the total deformation during cold rolling is 60-65%.

13. The preparation method according to claim 8, characterized in that, In step 5), the temperature is increased to 130-160℃ at a heating rate of 30-60℃ / h for annealing and holding for 2-5 hours. After holding, the furnace is removed and air-cooled.

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