High-magnesium 5xxx series H32 state aluminum alloy sheet and preparation method thereof

Abstract

The invention discloses a high-magnesium 5xxx series H32 state aluminum alloy sheet and a preparation method thereof. The high-magnesium 5xxx series H32 state aluminum alloy sheet comprises the following components in percentage by weight: 0 to 0.15 percent of Si, 0.20 to 0.30 percent of Fe, 0 to 0.05 percent of Cu, 0.41 to 0.49 percent of Mn, 4.0 to 4.9 percent of Mg, 0.06 to 0.14 percent of Cr, 0 to 0.05 percent of Zn, 0.01 to 0.03 percent of Ti and the balance of Al and inevitable impurities. The single impurity is less than or equal to 0.05%, and the total impurity is less than And (Si + Fe) / Mn is less than or equal to 1. According to the aluminum alloy thin plate, the yield strength is larger than or equal to 260 MPa, the elongation is larger than or equal to 12%, the limit bending radius of 90-degree bending performance is smaller than or equal to 1.0 * plate thickness, the production process is greatly shortened, the production efficiency is improved, and the performance consistency between plate batches is better.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy processing, and particularly relates to a high-magnesium 5xxx series H32 state aluminum alloy thin plate and a preparation method thereof. Background Art

[0002] 5xxx series aluminum alloys are 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, 5xxx series aluminum alloys have excellent bending properties, but low strength; in application scenarios with higher strength requirements, it is usually necessary to retain different degrees of work hardening effects. At this time, the strength increases, accompanied by a decrease in bending performance. 5xxx series aluminum alloy sheets in the H32 state balance higher strength and better bending performance, and are widely used in products such as new energy vehicle battery trays.

[0003] Chinese patent 202210670223.3 discloses a method for producing 5052-H32 aluminum alloy sheets for automotive structural parts, wherein the 5052 alloy is sequentially subjected to melting, homogenization, hot rolling, cold rolling, cleaning, annealing, and bending and straightening to obtain a sheet in the 5052-H32 state. The Mg content of the 5052 alloy described in the patent is 2.2-2.8%, which belongs to the medium-magnesium 5xxx alloy. By controlling the cold rolling reduction rate and coordinating with a lower temperature annealing treatment in an air cushion furnace, the performance of the H32 state is finally obtained, and its typical performance is: yield strength 175MPa, tensile strength 220MPa, and elongation 14.1%. However, for high-magnesium 5xxx alloy sheets with a Mg content of 4.0-5.0%, the process window of this method is narrow and the control difficulty is large.

[0004] Chinese patent 201210581522.6 discloses a production method of 5754-H32 aluminum alloy plate and strip, which is sequentially subjected to the processes of melting, sawing, milling, heating, hot rolling, cold rolling, and stabilization annealing and finishing. In the patent, the thickness of the hot-rolled coil reserves 20-35% of the cold rolling amount according to the thickness of the finished product, and the cold rolling is processed to the finished product thickness through one pass, and then stabilization annealing at 140-200℃ / 1-5h is performed to finally obtain 5754-H32 plate, whose properties are: yield strength 216MPa, tensile strength 268MPa, and elongation 12%. The stabilization annealing treatment for 1-5h in a box furnace will inevitably bring about differences in the microstructure and performance of the outer and inner ring plates, and the heating stage takes a long time.

[0005] Chinese patent 202211623184.8 discloses a control method for stamping Luders bands of 5-series automobile cover materials, which is mainly aimed at 5xxx series alloys with high magnesium content. The aluminum alloy ingot is heated, rough rolled, hot finished rolled, cold rolled once, intermediate annealed, cold rolled twice, roughened, finished annealed, surface treated, and stamped. The plate product without Luders band is obtained by controlling the composition and process. Its performance is: yield strength 125MPa, tensile strength 274.5MPa, elongation 28%. This patent is applied to the production of high-magnesium O-state plates, which have good forming properties but low strength.

[0006] Chinese patent CN201410815173 discloses a 5083 aluminum alloy sheet for high-speed rail and its production method. Expressed in weight percentage, the 5083 aluminum alloy sheet for high-speed rail is made of raw materials 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 is Al. The production method includes: raw material preparation, smelting, casting, saw head washing, soaking, hot rough rolling, hot finish rolling, cold rolling, bending correction, annealing and slicing packaging. The plate produced by the method of the present invention has a yield strength of 125-200 MPa, a tensile strength of 275-350 MPa, and an elongation of 20-26%. The elongation is relatively high, but the strength value is relatively low, and cannot meet the service environment requiring high strength. Summary of the invention

[0007] The object of the present invention is to provide a high-magnesium 5xxx series H32 state aluminum alloy thin plate and a preparation method thereof, wherein the aluminum alloy thin plate has a yield strength ≥260MPa, an elongation ≥12%, a limiting bending radius of 90° bending performance ≤1.0*plate thickness, and comprehensive performance is better than existing products; moreover, compared with the conventional H32 state production method, the present invention greatly shortens the production process, improves production efficiency, and has better performance consistency between plate batches.

[0008] To achieve the above object, the technical solution of the present invention is:

[0009] A high-magnesium 5xxx series H32 state aluminum alloy thin plate, the components of which are as follows 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%, the balance includes Al and unavoidable impurities; a single impurity is ≤0.05%, and the total impurities are ≤0.15%; and at the same time, the following is satisfied: (Si+Fe) / Mn≤1.

[0010] Further, the balance is Al and other inevitable impurities.

[0011] Preferably, Si: 0-0.12%, and / or Fe: 0.20-0.25%, and / or Mn: 0.43-0.47%.

[0012] The volume fraction of the iron-rich phase in the microstructure of the aluminum alloy sheet of the present invention is ≤3%, the maximum size of the iron-rich phase is ≤5μm, the grain morphology is equiaxed crystal, and the average grain size is ≤20μm.

[0013] The aluminum alloy thin plate of the present invention has a yield strength of ≥260 MPa, an elongation of ≥12%, a limiting bending radius of 90° bending performance of ≤1.0×plate thickness, and the plate thickness is measured in mm.

[0014] The present invention optimizes the alloy composition, especially limits the content of Si, Fe, and Mn elements, as well as the mass ratio of Si+Fe to Mn. Si, Fe, and Mn elements will form eutectic iron-rich phases during solidification. These phases belong to hard particle phases, which have two effects: first, they will promote recrystallization through the PSN mechanism during deformation processing, which is conducive to obtaining fine recrystallized grains; but on the other hand, they are easy to become the crack source for the initiation of microcracks during the bending process of the plate, reducing the bending performance of the plate. Si and Fe elements are impurity elements in Al alloys and cannot be completely avoided. By controlling the Si content to 0-0.15%, the Fe content to 0.20-0.30%, adding 0.41-0.49% of Mn elements, and controlling the mass ratio of Si+Fe to Mn to ≤1. Through the above-mentioned component restrictions, the volume fraction of the iron-rich phase in the ingot can be controlled to ≤3%, weakening the splitting effect of the iron-rich phase on the matrix (α solid solution), reducing the tendency of microcrack initiation, and thus improving the bending performance of the plate.

[0015] The high-magnesium 5xxx series H32 state aluminum alloy sheet product and the preparation method thereof of the present invention comprise the following steps:

[0016] 1) Smelting and casting

[0017] Smelting and casting into billets according to the above ingredients;

[0018] 2) Homogenization heat treatment

[0019] Heating temperature 500-540℃, holding time 6-10h;

[0020] 3) Hot rolling

[0021] The hot rough rolling intermediate rolling stage pass reduction rate is ≥15%, and the hot finishing rolling pass reduction rate is ≥30%; the finishing rolling coiling temperature is 300-350℃, and the hot rolled billet thickness is determined based on the finished product thickness and cold rolling deformation;

[0022] 4) One-step cold rolling

[0023] The total reduction rate of the first cold rolling should be controlled above 40%;

[0024] 5) Intermediate annealing

[0025] Use air cushion furnace for intermediate annealing treatment, the target temperature of the plate is 450-550℃, keep warm for 0-20s, and air cool to room temperature after leaving the furnace;

[0026] 6) Secondary cold rolling

[0027] The secondary cold rolling reduction rate is controlled at 5-15%.

[0028] Preferably, in step 2), the heating temperature is 530-540° C. and the insulation time is 8-10 h.

[0029] Preferably, in step 3), the reduction rate of the intermediate rolling stage of hot rough rolling is ≥20%, the reduction rate of the hot finishing rolling pass is ≥35%, the hot finishing rolling coiling temperature is 310-330°C, and the thickness of the hot rolled billet is 3-4 times the thickness of the finished plate.

[0030] Preferably, in step 4), the total cold rolling reduction ratio before intermediate annealing needs to be controlled at 60-80%.

[0031] Preferably, in step 5), the target temperature of the plate is between 480 and 530°C.

[0032] Preferably, in step 6), the secondary cold rolling reduction rate is controlled at 8-10%.

[0033] In the method for preparing the high-magnesium 5xxx series H32 state aluminum alloy sheet of the present invention:

[0034] The present invention combines homogenization heat treatment with hot rolling heating, with a heating temperature of 500-540°C and a holding time of 6-10 hours. After the holding is completed, the steel is taken out of the furnace and rolled. The homogenization heat treatment process can eliminate the intracrystalline segregation in the semi-continuous casting process, completely dissolve the soluble crystalline phases such as β-Al3Mg2, and fully transform the insoluble iron-rich phase, which is conducive to improving the bending performance of the finished plate.

[0035] Hot rolling: The pass reduction rate of the hot rough rolling intermediate rolling stage is ≥15%, and the hot finishing rolling pass reduction rate is ≥30%. A large hot rolling reduction rate is conducive to the full deformation of the plate from the surface to the middle layer, and a more uniform microstructure is obtained in the thickness direction of the plate. At the same time, a large reduction is conducive to the crushing and discrete distribution of the iron-rich phase, so that the maximum iron-rich phase size in the finished plate is ≤5μm, improving the bending performance of the finished plate. The finishing rolling coiling temperature is 300-350℃. In this temperature range, the dispersed phase precipitates finely and uniformly during the cooling process after hot rolling coiling, which is conducive to inhibiting the growth of recrystallized grains in the intermediate annealing process. The thickness of the hot-rolled billet needs to be calculated and determined based on the finished product thickness and the cold rolling deformation to ensure that the total cold rolling reduction rate meets the requirements.

[0036] One cold rolling: The total cold rolling reduction before intermediate annealing needs to be controlled at more than 40% to ensure that the plate has sufficient deformation energy storage and provide sufficient recrystallization driving force for the intermediate annealing process. Fine recrystallized grains are an important factor affecting the high bending performance of the plate. If the total cold rolling reduction is too small, the recrystallized grains will be coarse, and even abnormal grain growth will occur, which is extremely unfavorable to the bending performance of the finished plate.

[0037] Intermediate annealing: Use an air cushion furnace for intermediate annealing, the target temperature of the plate is 450-550℃, keep warm for 0-20s, and air cool to room temperature after leaving the furnace. Using an air cushion furnace for intermediate annealing can make the plate heat up to the target temperature in a very short time, inhibit the recovery of the plate during the heating process, and with the cold rolling reduction rate of the plate ≥40% before the intermediate annealing, a fine and uniform equiaxed grain structure with an average grain size of ≤20μm can be obtained, and the dislocation density within the grain is low. This is the basis for the finished plate to obtain excellent comprehensive performance.

[0038] Secondary cold rolling: The cold rolling reduction rate is controlled between 5% and 15%, so that the plate can obtain a certain degree of work hardening and improve the yield strength of the finished plate.

[0039] The present invention controls the volume fraction of the iron-rich phase in the ingot to be ≤3% by controlling the content of alloy elements and the mass ratio of Si+Fe and Mn elements; regulates the homogenization temperature and holding time of the ingot to fully dissolve the soluble crystalline phases such as Al3Mg2 in the ingot and transform the morphology of the insoluble iron-rich phase; adopts hot rough rolling and hot finishing rolling processes with large reduction rates to fully deform the plate, break and disperse the iron-rich phase, which is beneficial to the maximum iron-rich phase size in the finished plate being ≤5μm and the microstructure in the thickness direction of the plate being more uniform; controls the hot rolling coiling temperature to make the dispersed phase fine and evenly distributed; controls the cold rolling reduction rate before intermediate annealing to reserve sufficient deformation energy for the plate and promote the transformation of deformed grains into recrystallized grains during the intermediate annealing; adopts an air cushion furnace at a temperature of 450-550°C for intermediate annealing, and rapidly heats up to obtain a fine equiaxed recrystallized grain structure with an average grain size of ≤20μm; and finally matches cold rolling with a small reduction rate to improve the yield strength of the plate.

[0040] Through the integrated process control of the above-mentioned whole process, a high-performance aluminum alloy thin plate product is finally obtained with an iron-rich phase volume fraction of ≤3%, a maximum iron-rich phase size of ≤5μm; equiaxed grain morphology, an average grain size of ≤20μm; yield strength ≥260MPa, elongation ≥12%, and a limiting bending radius of 90° bending performance ≤1.0*plate thickness.

[0041] Compared with the prior art, the advantages of the present invention are:

[0042] 1) The present invention strictly limits the alloy composition, and particularly requires that: (Si+Fe) / Mn≤1; by controlling the ratio of Si, Fe, and Mn, the proportion of the iron-rich phase in the alloy can be controlled to be ≤3% by volume, thereby improving the bending performance of the plate.

[0043] 2) The present invention eliminates the finished product annealing process in the conventional production process of plates through coordinated regulation of homogenization and hot rolling processes, cold rolling processes before intermediate annealing, intermediate annealing processes, and cold rolling reduction rate after intermediate annealing, thereby saving 10 to 20 hours of heat treatment time, greatly shortening the production process, and improving production efficiency; moreover, using the cold rolling process as the final process has higher process control accuracy and better performance consistency between product batches.

[0044] 3) The present invention can obtain a high-magnesium 5xxx series H32 aluminum alloy thin plate product with a yield strength of ≥260MPa, an elongation of ≥12%, and a 90° bending radius of ≤1.0*plate thickness, and its comprehensive performance is better than that of existing products. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a microstructure photo of the plate of Example 1 of the present invention;

[0046] Figure 2This is a microstructure photograph of the plate of comparative example 5. DETAILED DESCRIPTION

[0047] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0048] The chemical composition of the alloys in the embodiments and comparative examples of the present invention is shown in Table 1, the key process parameters of the embodiments and comparative examples are shown in Table 2, and Table 3 shows the tensile properties and bending properties of the embodiments and comparative examples under different preparation process conditions.

[0049] Example 1

[0050] The slab obtained by smelting and casting is homogenized at 500℃ / 6h and then rolled out of the furnace. It is hot rolled into 7mm thick hot rolled slab, the hot rolling coiling temperature is 300℃, and it is rolled into 1.4mm thick cold rolled coil (cold rolling reduction rate is 80%) in a cold rolling mill; then it is annealed at 550℃ / 0s in an air cushion furnace (the plate is cooled after being heated to 500℃), and finally the annealed coil is cold rolled into a 1.33mm finished product (cold rolling reduction rate is 5%). The tensile mechanical properties and bending properties of the finished product are tested.

[0051] Example 2

[0052] The slab obtained by smelting and casting was homogenized at 506℃ / 6.5h and then rolled out of the furnace. It was hot-rolled into 6.5mm thick hot-rolled slab, the hot rolling coiling temperature was 305℃, and it was rolled into 1.63mm thick cold-rolled coil (cold rolling reduction rate 75%) on a cold rolling mill. Then, it was annealed at 530℃ / 3s in an air cushion furnace. Finally, the annealed coil was cold-rolled into a 1.51mm finished product (cold rolling reduction rate 7%), and the tensile mechanical properties and bending properties of the finished product were tested.

[0053] Example 3

[0054] The slab obtained by smelting and casting was homogenized at 512℃ / 7h and then rolled out of the furnace. It was hot rolled into 6mm thick hot-rolled slab with a hot rolling coiling temperature of 310℃ and rolled into 1.8mm thick cold-rolled coil (cold rolling reduction rate of 70%) on a cold rolling mill. Then, it was annealed at 520℃ / 5s in an air cushion furnace. Finally, the annealed coil was cold rolled into a 1.64mm finished product (cold rolling reduction rate of 9%), and the tensile mechanical properties and bending properties of the finished product were tested.

[0055] Example 4

[0056] The slab obtained by smelting and casting was homogenized at 518℃ / 7.5h and then rolled out of the furnace. It was hot-rolled into 5.5mm thick hot-rolled slab, the hot rolling coiling temperature was 315℃, and it was rolled into 1.93mm thick cold-rolled coil (cold rolling reduction rate 65%) on a cold rolling mill. Then, it was annealed at 510℃ / 8s in an air cushion furnace. Finally, the annealed coil was cold-rolled into a 1.71mm finished product (cold rolling reduction rate 11%), and the tensile mechanical properties and bending properties of the finished product were tested.

[0057] Example 5

[0058] The slab obtained by smelting and casting was homogenized at 524℃ / 8h and then rolled out of the furnace. It was hot rolled into 5mm thick hot-rolled slab with a hot rolling coiling temperature of 320℃ and rolled into 2mm thick cold-rolled coil (cold rolling reduction rate of 60%) on a cold rolling mill. Then, it was annealed at 500℃ / 10s in an air cushion furnace. Finally, the annealed coil was cold rolled into a 1.76mm finished product (cold rolling reduction rate of 12%), and the tensile mechanical properties and bending properties of the finished product were tested.

[0059] Example 6

[0060] The slab obtained by smelting and casting was homogenized at 530℃ / 8.5h and then rolled out of the furnace. It was hot-rolled into 4.5mm thick hot-rolled slab, the hot rolling coiling temperature was 330℃, and it was rolled into 2.03mm thick cold-rolled coil (cold rolling reduction rate 55%) on a cold rolling mill. Then, it was annealed at 480℃ / 13s in an air cushion furnace. Finally, the annealed coil was cold-rolled into a 1.76mm finished product (cold rolling reduction rate 13%), and the tensile mechanical properties and bending properties of the finished product were tested.

[0061] Example 7

[0062] The slab obtained by smelting and casting was homogenized at 536℃ / 9h and then rolled out of the furnace. It was hot rolled into 4mm thick hot-rolled slab, the hot rolling coiling temperature was 340℃, and it was rolled into 2mm thick cold-rolled coil (cold rolling reduction rate 50%) on a cold rolling mill. Then, it was annealed at 460℃ / 16s in an air cushion furnace. Finally, the annealed coil was cold rolled into a 1.72mm finished product (cold rolling reduction rate 14%), and the tensile mechanical properties and bending properties of the finished product were tested.

[0063] Example 8

[0064] The slab obtained by smelting and casting was homogenized at 540℃ / 10h and then rolled into 3.5mm thick hot-rolled slab. The hot rolling coiling temperature was 350℃ and rolled into 2.1mm thick cold-rolled coil (cold rolling reduction rate 40%) on a cold rolling mill. Then, it was annealed at 450℃ / 20s in an air cushion furnace. Finally, the annealed coil was cold rolled into 1.79mm finished product (cold rolling reduction rate 15%), and the tensile mechanical properties and bending properties of the finished product were tested.

[0065] Comparative Example 1

[0066] The homogenization process is 480℃ / 2h and then rolled out of the furnace. The hot-rolled billet is hot-rolled into 7mm thick hot-rolled billet. The hot-rolling coiling temperature is 300℃, and it is rolled into 1.4mm thick cold-rolled coil (cold rolling reduction rate is 80%) on a cold rolling mill. Then, it is annealed at 550℃ / 0s in an air cushion furnace (the plate is heated to 500℃ and then cooled out of the furnace). Finally, the annealed coil is cold-rolled into a 1.33mm finished product (cold rolling reduction rate is 5%), and the tensile mechanical properties and bending properties of the finished product are tested.

[0067] Comparative Example 2

[0068] The homogenization process is 506℃ / 6.5h and the steel is rolled out of the furnace. The steel is hot-rolled into 6.5mm thick hot-rolled billet. The hot rolling coiling temperature is 360℃ and the steel is rolled into 1.63mm thick cold-rolled coil (cold rolling reduction rate is 75%) on a cold rolling mill. Then, the steel is annealed at 530℃ / 3s in an air cushion furnace. Finally, the annealed coil is cold-rolled into a 1.51mm finished product (cold rolling reduction rate is 7%), and the tensile mechanical properties and bending properties of the finished product are tested.

[0069] Comparative Example 3

[0070] The homogenization process is 512℃ / 7h and the steel is rolled out of the furnace to form 3.5mm thick hot-rolled billets. The hot rolling coiling temperature is 310℃ and the steel is rolled into 2.5mm thick cold-rolled coils (cold rolling reduction rate is 28.6%) on a cold rolling mill. Then, the steel is annealed at 520℃ / 5s in an air cushion furnace. Finally, the annealed coils are cold rolled into 2.28mm finished products (cold rolling reduction rate is 9%), and the tensile mechanical properties and bending properties of the finished products are tested.

[0071] Comparative Example 4

[0072] The homogenization process is 518℃ / 7.5h and the steel is rolled out of the furnace. The steel is hot-rolled into 5.5mm thick hot-rolled billet. The hot rolling coiling temperature is 315℃ and the steel is rolled into 1.93mm thick cold-rolled coil (cold rolling reduction rate is 65%) on a cold rolling mill. Then, the steel is annealed at 350℃ / 8s in an air cushion furnace. Finally, the annealed coil is cold-rolled into a 1.71mm finished product (cold rolling reduction rate is 11%), and the tensile mechanical properties and bending properties of the finished product are tested.

[0073] Comparative Example 5

[0074] The homogenization process is 524℃ / 8h and then rolled out of the furnace. The hot rolled billet is 5mm thick. The hot rolling coiling temperature is 320℃ and rolled into 2mm thick cold rolled coil (cold rolling reduction rate is 60%) on a cold rolling mill. Then, it is annealed at 500℃ / 10s in an air cushion furnace. Finally, the annealed coil is cold rolled into a 1.76mm finished product (cold rolling reduction rate is 20%), and the tensile mechanical properties and bending properties of the finished product are tested.

[0075] It can be seen from Table 3 that the preparation process embodiments 1-8 of the present invention all achieve a yield strength ≥ 260 MPa, an elongation ≥ 12%, and a limiting bending radius of 90° bending performance ≤ 1.0*plate thickness.

[0076] The performance requirements of 5083-H32 in GB / T 3880 standard are as follows:

[0077]

[0078] Obviously, the yield strength and bending performance of the high-magnesium 5xxx series H32 state aluminum alloy sheet of the present invention are much higher than the H32 state standard requirements.

[0079] In Comparative Example 1, since the Fe element exceeds the upper limit required by the present invention, the ratio of Si+Fe to Mn exceeds the upper limit required by the present invention, the homogenization temperature and the holding time are lower than the lower limit required by the present invention, the soluble crystalline phase is not fully dissolved, the number of iron-rich phases is large, and they are not fully transformed, resulting in an elongation of only 11.2%, and the limiting bending radius of the 90° bending performance = 1.1*plate thickness.

[0080] In Comparative Example 2, since the Si element exceeds the upper limit required by the present invention, the ratio of Si+Fe to Mn exceeds the upper limit required by the present invention, single Si is easily precipitated, and the hot rolling coiling temperature exceeds the upper limit required by the present invention. During the cooling process of the hot rolled coil, the dispersed phase precipitates and grows, resulting in the limiting bending radius of the 90° bending performance = 1.1*plate thickness.

[0081] In Comparative Example 3, since the Mn element exceeds the upper limit required by the present invention and the hot rolled coiling thickness does not meet the requirements of the present invention, the total cold rolling reduction rate before intermediate annealing is lower than the lower limit required by the present invention, resulting in an elongation of only 10.4%, and the limiting bending radius of 90° bending performance = 1.2*plate thickness.

[0082] In Comparative Example 4, since the Si and Fe elements exceed the upper limit required by the present invention, the ratio of Si+Fe to Mn exceeds the upper limit required by the present invention, and the intermediate annealing temperature is lower than the lower limit required by the present invention, the limiting bending radius of the 90° bending performance is 1.2*plate thickness.

[0083] In Comparative Example 5, since the Fe and Mn elements exceed the upper limit required by the present invention, and the secondary cold rolling reduction rate after intermediate annealing exceeds the upper limit required by the present invention, the degree of work hardening is too high, the elongation is only 8.3%, and the limiting bending radius of 90° bending performance is 1.5*plate thickness.

[0084] Figure 1 , Figure 2 Shown are microstructure photographs of the plates of Example 1 and Comparative Example 5, respectively.

[0085] from Figure 1 It can be seen from the photos that the Si, Fe, and Mn elements in the composition of Example 1 are within the required range of the present invention, the volume proportion of the iron-rich phase is 1.3%, and the size is small. There is a small tendency for cracks to initiate from the iron-rich phase during the deformation of the plate, so that the plate has good plasticity and bending properties.

[0086] from Figure 2 It can be seen from the photos that the Fe and Mn elements in the ingredients of Comparative Example 5 exceed the upper limit required by the present invention. Figure 2 The microstructure photos of the plate show that the iron-rich phase is large in number and large in size. The volume of the iron-rich phase accounts for 4.8%, and the maximum size of the iron-rich phase is 20μm. It has a great effect on the matrix splitting, and has a high tendency to initiate cracks during deformation. The plate's shaping and bending properties are deteriorated, which is extremely unfavorable to the plate's mechanical properties.

[0087] In summary, the high-magnesium 5xxx series H32 state aluminum alloy sheet described in the present invention has a yield strength and bending performance that are far higher than the H32 state standard requirements, and its comprehensive performance is significantly better than existing products. At the same time, it significantly shortens the production process, improves production efficiency and consistency of product performance, and can be widely used in products such as new energy vehicle battery trays.

[0088] It should be noted that the embodiments listed above are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments. Similar changes or modifications made therewith can be directly derived from the contents disclosed in the present invention or can be easily associated with by those skilled in the art, and should all fall within the protection scope of the present invention.

[0089]

[0090]

[0091]

Claims

1. A high-magnesium 5xxx series H32 state aluminum alloy sheet, whose components by weight percentage are: 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%, the balance includes Al and unavoidable impurities; a single impurity is ≤ 0.05%, and the total impurities are ≤ 0.15%; and at the same time meet the following requirements: (Si+Fe) / Mn≤1.

2. The high magnesium 5xxx series H32 state aluminum alloy sheet according to claim 1, characterized in that: The balance is Al and other inevitable impurities.

3. The high magnesium 5xxx series H32 state aluminum alloy sheet according to claim 1, characterized in that: Si: 0 to 0.12%, and / or Fe: 0.20 to 0.25%, and / or Mn: 0.43 to 0.47%.

4. The high magnesium 5xxx series H32 state aluminum alloy sheet according to claim 1, 2 or 3, characterized in that: The volume fraction of the iron-rich phase in the microstructure of the aluminum alloy sheet is ≤3%, and the maximum size of the iron-rich phase is ≤5 μm; the grain morphology is equiaxed grains, and the average grain size is ≤20 μm.

5. The high magnesium 5xxx series H32 state aluminum alloy sheet according to claim 1, 2, 3 or 4, characterized in that: The yield strength of the aluminum alloy sheet is ≥260 MPa, the elongation is ≥12%, and the limiting bending radius of the 90° bending performance is ≤1.0×sheet thickness, where the sheet thickness is measured in mm.

6. The method for preparing a high-magnesium 5xxx series H32 state aluminum alloy sheet according to any one of claims 1 to 5, characterized in that: The steps include: 1) Smelting and casting Smelting and casting into slabs according to the composition of claim 1, 2 or 3; 2) Homogenization heat treatment Heating temperature 500-540℃, holding time 6-10h; 3) Hot rolling The reduction rate of the intermediate rolling stage of hot rough rolling is ≥15%, and the reduction rate of the hot finishing rolling is ≥30%; the hot finishing rolling coiling temperature is 300-350℃, and the thickness of the hot rolled billet is determined by the finished product thickness and the cold rolling deformation; 4) One-step cold rolling The total reduction rate of the first cold rolling is controlled at more than 40%; 5) Intermediate annealing An air cushion furnace is used for intermediate annealing treatment, the target temperature of the plate is 450-550°C, the temperature is kept for 0-20s, and the plate is air-cooled to room temperature after being taken out of the furnace; preferably, the target temperature of the plate is 480-530°C; 6) Secondary cold rolling The secondary cold rolling reduction rate is controlled at 5-15%.

7. The method for preparing a high-magnesium 5xxx series H32 state aluminum alloy sheet as claimed in claim 6, characterized in that: In step 2), the heating temperature is 530-540° C. and the insulation time is 8-10 hours.

8. The method for preparing a high-magnesium 5xxx series H32 state aluminum alloy sheet as claimed in claim 6, characterized in that: In step 3), the reduction rate of the intermediate rolling stage of hot rough rolling is ≥20%, the reduction rate of the hot finishing rolling pass is ≥35%, the hot finishing rolling coiling temperature is 310-330°C, and the thickness of the hot rolled billet is 3-4 times the thickness of the finished plate.

9. The method for preparing a high-magnesium 5xxx series H32 state aluminum alloy sheet as claimed in claim 6, characterized in that: In step 4), the total cold rolling reduction ratio before intermediate annealing needs to be controlled at 60-80%.

10. The method for preparing a high-magnesium 5xxx series H32 state aluminum alloy sheet as claimed in claim 6, characterized in that: In step 6), the secondary cold rolling reduction rate is controlled at 8-10%.

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