Aluminum alloy plate strip for subway vehicle body and preparation method of aluminum alloy plate strip

Abstract

The invention relates to the technical field of aluminum alloy processing and manufacturing, in particular to an aluminum alloy plate strip for a subway vehicle body and a preparation method thereof. The aluminum alloy plate strip comprises the following components in percentage by weight: less than or equal to 0.1% of Si; the Fe content is less than or equal to 0.2%; the Cu content is less than or equal to 0.02%; the content of Mn is 0.2 to 0.4 percent; the content of Mg is 2.8 to 3.2 percent; the content of Cr is smaller than or equal to 0.15%; the content of Zn is less than or equal to 0.02%; the content of Ti is 0.02 to 0.04 percent; the single impurity content is less than or equal to 0.03%; the total content of other impurity elements is less than or equal to 0.1%; and the balance of Al. The aluminum alloy plate strip for the metro car body is uniform in performance, excellent in corrosion resistance and welding performance and suitable for production and processing of the metro car body, and the preparation method of the aluminum alloy plate strip for the metro car body improves the corrosion resistance of the aluminum alloy plate strip and reduces energy consumption and production cost.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy processing and manufacturing, and in particular to an aluminum alloy plate and strip material for a subway car body and a preparation method thereof. Background Art

[0002] With the rapid development of my country's rail transit industry, the lightweighting of rail transit vehicles has become a research focus of the rail transit industry. Aluminum alloys have been gradually used in the manufacture of rail trains, such as high-speed rail, subway, urban rail, light rail, and cloud rail, because of their low density (about one-third of the density of steel), high specific strength, easy processing, good corrosion resistance, and weldability. It plays a very important role in the lightweighting of rail transit vehicles.

[0003] 5754 aluminum alloy belongs to the A1-Mg alloy series and is an aluminum alloy that cannot be strengthened by heat treatment. It has medium strength, low density, good corrosion resistance, excellent processing performance, etc. In recent years, 5754-H22 has been used in the processing and manufacturing of subway car body panels. Most subway main engine factories and parts processing plants use bending processing and fusion welding (TIG / MIG) processing, which not only has strict uniformity and bending requirements for aluminum alloy materials before processing, but also the materials must have good welding performance and post-weld strength, and good post-weld processing performance. However, in practical applications, the following problems exist: 1. The poor uniformity of aluminum alloy materials and improper control of mechanical properties (mainly strength) cannot meet the bending processing requirements that are far higher than the standard; 2. The welding process is poor, and the tensile strength after welding (165-185MPa) is unqualified, which is lower than the requirements of ISO 15614-2 Specification and qualification of welding procedures for metallic materials-Welding procedure test-Part 2: Arc welding of aluminium and its alloys (tensile strength ≥ 190MPa); 3. After aluminum welding, the back bending test is prone to cracking, and it does not meet the welding process specifications and qualification assessment standards. After analyzing the fracture, it was found that the slag content was relatively high. Due to the high production technology barriers, there are only a handful of domestic companies that can produce this material. Therefore, the development of aluminum alloy plates and strips suitable for subway car bodies has become an important issue for aluminum processing manufacturers.

[0004] In summary, it is urgent to solve the problems of poor uniformity of aluminum alloy plates and strips suitable for subway car bodies in the prior art, improper control of mechanical properties, low mechanical properties after welding, and bending cracking. Summary of the invention

[0005] The invention aims to solve the problems of poor uniformity, improper control of mechanical properties, low mechanical properties after welding and cracking due to bending of aluminum alloy plates and strips suitable for subway car bodies.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides an aluminum alloy sheet and strip for a subway car body, wherein the components and their weight percentages in the aluminum alloy sheet and strip are:

[0007] Si content ≤ 0.1%;

[0008] Fe content ≤ 0.2%;

[0009] Cu content ≤ 0.02%;

[0010] Mn content is 0.2-0.4%;

[0011] Mg content is 2.8-3.2%;

[0012] Cr content ≤ 0.15%;

[0013] Zn content ≤ 0.02%;

[0014] Ti content is 0.02-0.04%;

[0015] Single impurity content ≤ 0.03%;

[0016] The total content of other impurity elements is ≤0.1%;

[0017] The balance is Al.

[0018] The second aspect of the present invention provides a method for preparing the aluminum alloy sheet and strip for subway car body, wherein the preparation method includes batching, smelting, refining, casting, sawing, milling, heating, hot rolling, cold rolling, oil cleaning, annealing, rewinding or unwinding, and packaging;

[0019] The heating conditions include a metal heating temperature of 460°C-520°C and a heating time of 1-4h;

[0020] The hot rolling conditions include: the hot rough rolling pass is 17-19, the intermediate billet thickness is 33-37 mm, the intermediate billet temperature is 420-450° C., the frame down pressure is 39-55%, and the coiling temperature is 320-340° C.;

[0021] Self-annealing is performed between hot and cold rolling processes;

[0022] The cold rolling conditions include cold rolling to a finished product thickness of 3-6 mm in one pass and a processing rate of 10-25%;

[0023] Oil cleaning is performed after the cold rolling;

[0024] The annealing conditions are as follows: the annealing temperature is 100-140° C. and the annealing time is 2-6 hours.

[0025] The beneficial effects of the present invention are:

[0026] (1) The present invention reduces the content of impurity elements such as Si, Fe, Cu, Cr, and Zn, and optimizes the ratio of Mn and Mg alloy elements. The aluminum alloy plate and strip for subway car body provided by the present invention has uniform performance, excellent corrosion resistance and welding performance, and is suitable for the production and processing of subway car body.

[0027] (2) The present invention uses the temperature of hot rolling coiling to perform self-annealing until complete recrystallization to obtain a billet with stable mechanical properties and uniform structure. The present invention adopts a low-temperature annealing process, does not need to use high-purity nitrogen protection annealing, and reduces the annealing time by more than 25%, which is conducive to improving production efficiency. The obtained aluminum alloy plate and strip for subway car body has uniform performance, excellent corrosion resistance and welding performance;

[0028] (3) The present invention reduces the cold rolling processing rate and cold-rolls to the finished product thickness in one pass, thereby reducing energy consumption and production costs;

[0029] (4) The present invention uses oil cleaning to remove surface rolling oil, aluminum ash, etc., with excellent surface quality. The oil after cleaning is filtered and recycled without generating waste liquid. DETAILED DESCRIPTION

[0030] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0031] The cold rolling processing rate of the existing technology for preparing aluminum alloy plates and strips for subway car bodies is too large. If production cannot be achieved in one pass, not only will the number of cold rolling passes need to be increased, but the energy consumption of the rolling mill will also be greatly increased. More importantly, in order to obtain a lower strength that meets the standards to obtain bending performance, the annealing temperature needs to be above 230°C, which obviously increases the energy consumption of the annealing process. Moreover, the aluminum alloy plates and strips are very sensitive to changes in the turning point of performance, and the annealing process is not easy to control, which can easily produce defective products.

[0032] In the present invention, the inventors found that if the annealing temperature is lowered and combined with other optimization methods and specific alloy ratios, aluminum alloy plates and strips for subway car bodies with uniform performance, excellent corrosion resistance and welding performance can be produced.

[0033] To this end, the first aspect of the present invention provides an aluminum alloy sheet and strip for a subway car body, wherein the components and their weight percentages in the aluminum alloy sheet and strip are:

[0034] Si content ≤ 0.1%;

[0035] Fe content ≤ 0.2%;

[0036] Cu content ≤ 0.02%;

[0037] Mn content is 0.2-0.4%;

[0038] Mg content is 2.8-3.2%;

[0039] Cr content ≤ 0.15%;

[0040] Zn content ≤ 0.02%;

[0041] Ti content is 0.02-0.04%;

[0042] Single impurity content ≤ 0.03%;

[0043] The total content of other impurity elements is ≤0.1%;

[0044] The balance is Al.

[0045] In the present invention, the contents of Si, Fe, Cu, Cr, Zn and impurity elements are reduced, the ratio of Mn and Mg alloy elements is optimized, and the produced aluminum alloy plate and strip for subway car body has uniform performance, excellent corrosion resistance and welding performance.

[0046] According to the present invention, the thickness of the aluminum alloy plate and strip for subway car body is 3-6 mm.

[0047] Furthermore, when used for the production of subway car body side walls, the alloy state is 5754-H22.

[0048] The second aspect of the present invention provides a method for preparing the aluminum alloy sheet and strip for subway car body, wherein the preparation method includes batching, smelting, refining, casting, sawing, milling, heating, hot rolling, cold rolling, oil cleaning, annealing, rewinding or unwinding, and packaging;

[0049] The heating conditions include a metal heating temperature of 460°C-520°C and a heating time of 1-4h;

[0050] The hot rolling conditions include: the hot rough rolling pass is 17-19, the intermediate billet thickness is 33-37 mm, the intermediate billet temperature is 420-450° C., the frame down pressure is 39-55%, and the coiling temperature is 320-340° C.;

[0051] Self-annealing is performed between hot and cold rolling processes;

[0052] The cold rolling conditions include cold rolling to a finished product thickness of 3-6 mm in one pass and a processing rate of 10-25%;

[0053] Oil cleaning is performed after the cold rolling;

[0054] The annealing conditions are as follows: the annealing temperature is 100-140° C. and the annealing time is 2-6 hours.

[0055] In the present invention, it is well known in the art that too high coiling temperature can easily cause interlayer adhesion. In order to ensure both annealing to complete recrystallization and the surface quality of the strip, the inventor accidentally discovered that by changing the process method: the rough rolling is 17-19 passes, the thickness of the intermediate billet is controlled to 33-37mm and the downward pressure of the frame is 40-55%, the coiling temperature of the hot rolling can be controlled to 320-340°C, thereby ensuring a suitable coiling temperature.

[0056] The inventors analyzed that the reason is that large deformation at high temperature after leaving the furnace can reduce heat loss, and the plate is in dynamic recovery and recrystallization, so high-quality intermediate billet can be obtained; the thickness of the intermediate billet is controlled at 33-37mm, and the temperature is controlled at 420-450℃, providing high temperature conditions for hot rolling and coiling; the reduction amount of each frame is controlled, and a large reduction amount not only maintains the dynamic recrystallization state, but also the deformation resistance of the aluminum material itself generates heat, reducing excessive heat loss and ensuring a suitable coiling temperature.

[0057] In the present invention, the intermediate billet is processed by a 4-row hot finishing rolling mill.

[0058] In the present invention, a low-temperature annealing process is adopted, which can inhibit the precipitation of Al2Mg3 phase along the grain boundary to form a continuous grain boundary network film, thereby improving the corrosion resistance of the aluminum material.

[0059] The cold rolling processing rate of the existing technology is above 25%. The higher the cold rolling processing rate, the higher the bending requirements, the more uniform the organization and the lower the mechanical properties. If the cold rolling processing rate is too high, if one pass cannot be produced, not only the number of cold rolling passes needs to be increased, but also the energy consumption of the rolling mill is greatly increased. More importantly, in order to obtain a lower strength that meets the standard, the annealing temperature must be above 230°C to obtain a lower strength, which increases the energy consumption of the annealing process. In addition, 5754-H22 is very sensitive to the turning point of performance changes, and the annealing process is not easy to control, which is prone to produce defective products.

[0060] In addition, considering the actual production application, the cold rolling processing rate is too high. In order to achieve excellent surface quality and avoid oil spot surface defects during annealing, a negative pressure degreasing process of 200-240°C is usually used to remove the residual rolling oil on the surface of the aluminum sheet and strip. In addition, the entire annealing process requires the introduction of high-purity nitrogen (≥99.5%) as a protective gas, which greatly increases the production cost.

[0061] In the present invention, the temperature is automatically controlled by adopting a heating program, so as to prevent Mg2Al3 from being overburned.

[0062] In the present invention, the purpose of oil cleaning after cold rolling is to remove residual rolling oil and aluminum ash on the surface of the aluminum alloy plate and strip.

[0063] According to the present invention, the hot-rolled strip is placed in an elevated intelligent warehouse, and self-annealing is performed using the coiling temperature of the hot-rolled strip, so that a billet with stable mechanical properties and uniform structure can be obtained.

[0064] According to the present invention, the refining is followed by furnace refining, online degassing and online filtration.

[0065] According to the present invention, the sawing and milling process comprises cutting the aluminum alloy ingot after cooling and removing the solidified shell layer on the surface of the ingot by a milling machine.

[0066] According to the present invention, after the refining, the hydrogen content of the melt is ≤0.15 mL / 100 g Al.

[0067] Furthermore, the refining is performed by covering with flux, and stirring is started after the materials in the furnace are melted after feeding. After refining, slag removal and obtaining qualified chemical composition, a mixed gas of Ar gas and Cl2 gas is used to bring hydrogen and fine impurities in the aluminum liquid to the surface of the melt.

[0068] According to the present invention, the online filtration is a two-stage filtration.

[0069] In the present invention, there is no limitation on the double-stage filtration method, as long as the slag content of the melt can be reduced and the purity of the melt can be ensured, CFF+CFF filtration, CFF+deep bed filtration or CFF+tubular filtration can be used.

[0070] According to the present invention, the preparation method further comprises online refinement, and the grain refiner is Al-5Ti-B.

[0071] Test Method

[0072] The tensile mechanical properties (tensile strength, specified non-proportional elongation strength, elongation after fracture) are measured according to GB / T 16865.

[0073] The bending properties are measured according to GB / T232.

[0074] The exfoliation corrosion performance is measured according to GB / T22639.

[0075] Welding properties (weld strength, positive bend, back bend) were measured according to ISO 15614.

[0076] The technical scheme of the present invention is further described in detail below in conjunction with the embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. Based on the embodiments in the present invention, all other embodiments implemented by ordinary technicians in the field without making creative improvements belong to the protection scope of the present invention.

[0077] The alloy compositions of each embodiment are shown in Table 1 below

[0078] Example 1

[0079] The preparation steps are as follows:

[0080] A. According to the predetermined mass percentage, the ingredients of each chemical element of the aluminum alloy are placed in a smelting furnace for smelting, furnace refining, online degassing, and online filtering, and the aluminum liquid with qualified composition is cast into an aluminum alloy ingot;

[0081] B. After the aluminum alloy ingot is cooled, the head and tail are cut off, and then the solidified shell layer on the surface of the ingot is milled off with a milling machine;

[0082] C. Place the sawn and milled ingot into a pusher heating furnace with a metal temperature of 480°C for 2 hours;

[0083] D. After heating, the strip is directly taken out of the furnace and rolled. The hot rolling is performed for 19 passes. The intermediate billet thickness is 33 mm. A 4-row hot finishing mill is used. The reduction of each stand is controlled at 39-46%. The coiling temperature of the hot rolled strip is controlled at 328°C.

[0084] E. Place the hot-rolled strip in an elevated intelligent warehouse and use the coiling temperature of the hot-rolled strip for self-annealing to obtain a billet with uniform structure;

[0085] F. After cooling naturally to room temperature, cold rolling is carried out, and the finished product thickness is 4.0mm through one pass, and the processing rate is: 15%;

[0086] G. Use oil cleaning after cold rolling to remove residual rolling oil and aluminum ash on the surface of aluminum alloy plates and strips;

[0087] H. After cleaning, transfer the strip to a box-type annealing furnace for annealing at a metal temperature of 100°C for 6 hours.

[0088] I. After annealing, take the product out of the furnace and cool it naturally to room temperature. Then take samples for testing. After passing the test, rewind the product and pack it for storage, or unwrap it and pack it in sheets for storage.

[0089] The properties of the aluminum alloy sheet and strip A1 for subway car body prepared in Example 1 are shown in Table 2 below.

[0090] Example 2

[0091] The preparation steps are as follows:

[0092] A. According to the predetermined mass percentage, the ingredients of each chemical element of the aluminum alloy are placed in a smelting furnace for smelting, furnace refining, online degassing, and online filtering, and the aluminum liquid with qualified composition is cast into an aluminum alloy ingot;

[0093] B. After the aluminum alloy ingot is cooled, the head and tail are cut off, and then the solidified shell layer on the surface of the ingot is milled off with a milling machine;

[0094] C. Place the sawn and milled ingot into a pusher heating furnace with a metal temperature of 480°C for 2 hours;

[0095] D. After heating, the strip is directly taken out of the furnace and rolled. The hot rolling is performed for 19 passes. The intermediate billet thickness is 35 mm. A 4-row hot finishing mill is used. The reduction of each stand is controlled at 43-51%. The coiling temperature of the hot rolled strip is controlled at 331°C.

[0096] E. Place the hot-rolled strip in an elevated intelligent warehouse and use the coiling temperature of the hot-rolled strip for self-annealing to obtain a billet with uniform structure;

[0097] F. After cooling naturally to room temperature, cold rolling is carried out, and the finished product thickness is 4.0mm through one pass, and the processing rate is: 18%;

[0098] G. Use oil cleaning after cold rolling to remove residual rolling oil and aluminum ash on the surface of aluminum alloy plates and strips;

[0099] H. After cleaning, transfer the strip to a box-type annealing furnace for annealing at a metal temperature of 120°C for 4 hours.

[0100] I. After annealing, take the product out of the furnace and cool it naturally to room temperature. Then take samples for testing. After passing the test, rewind the product and pack it for storage, or unwrap it and pack it in sheets for storage.

[0101] The properties of the aluminum alloy sheet and strip A2 for subway car body prepared in Example 2 are shown in Table 2 below.

[0102] Example 3

[0103] The preparation steps are as follows:

[0104] A. According to the predetermined mass percentage, the ingredients of each chemical element of the aluminum alloy are placed in a smelting furnace for smelting, furnace refining, online degassing, and online filtering, and the aluminum liquid with qualified composition is cast into an aluminum alloy ingot;

[0105] B. After the aluminum alloy ingot is cooled, the head and tail are cut off, and then the solidified shell layer on the surface of the ingot is milled off with a milling machine;

[0106] C. Place the sawn and milled ingot into a pusher heating furnace with a metal temperature of 480°C for 2 hours;

[0107] D. After heating, the strip is directly taken out of the furnace and rolled. The hot rolling is performed for 19 passes. The intermediate billet thickness is 37 mm. A 4-row hot finishing mill is used. The reduction of each stand is controlled at 46-55%. The coiling temperature of the hot rolled strip is controlled at 335°C.

[0108] E. Place the hot-rolled strip in an elevated intelligent warehouse and use the coiling temperature of the hot-rolled strip for self-annealing to obtain a billet with uniform structure;

[0109] F. After cooling naturally to room temperature, cold rolling is carried out, and the finished product thickness is 4.0mm through one pass, and the processing rate is: 21%;

[0110] G. Use oil cleaning after cold rolling to remove residual rolling oil and aluminum ash on the surface of aluminum alloy plates and strips;

[0111] H. After cleaning, the strip is transferred to a box-type annealing furnace for annealing at a metal temperature of 140°C for 4 hours.

[0112] I. After annealing, take the product out of the furnace and cool it naturally to room temperature. Then take samples for testing. After passing the test, rewind the product and pack it for storage, or unwrap it and pack it in sheets for storage.

[0113] The properties of the aluminum alloy sheet and strip A3 for subway car body prepared in Example 3 are shown in Table 2 below.

[0114] Comparative Example 1

[0115] The aluminum alloy sheet and strip for subway car body is prepared according to the preparation method of Example 1, except that the hot rolling pass is 21, the intermediate billet thickness is 38 mm, the intermediate billet temperature is 400°C, the frame downward pressure is 35%, and the coiling temperature is 350°C. The properties of the aluminum alloy sheet and strip DA1 for subway car body are shown in Table 2 below.

[0116] Comparative Example 2

[0117] The aluminum alloy sheet and strip for subway car body is prepared according to the preparation method of Example 1, except that the annealing temperature is 150° C. The properties of the prepared aluminum alloy sheet and strip DA2 for subway car body are shown in Table 2 below.

[0118] Comparative Example 3

[0119] The aluminum alloy sheet and strip for subway car body is prepared according to the preparation method of Example 1, except that the alloy composition is different. The properties of the prepared aluminum alloy sheet and strip for subway car body DA3 are shown in Table 2 below.

[0120] Table 1

[0121]

[0122] Table 2

[0123]

[0124]

[0125] By comparing the embodiments with the comparative examples, it can be seen that the aluminum alloy plates and strips for subway car bodies in embodiments 1-3 have good mechanical properties and bending properties, excellent exfoliation corrosion resistance, and reach the highest N level; comprehensive evaluation of mechanical properties and bending properties after welding all meet the requirements specified in the standards and can be applied to the side walls of subway cars.

[0126] The present invention obtains aluminum alloy plates and strips for subway car bodies with uniform performance, excellent corrosion resistance and welding performance by regulating the alloy composition and the preparation method, wherein the process improvements include hot rolling passes, intermediate billet thickness, intermediate billet temperature, rack downward pressure, coiling temperature and annealing temperature and time, and the above improvements work together to improve the performance of the strip.

[0127] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An aluminum alloy plate and strip for subway car body, characterized in that: The components and their weight percentages in the aluminum alloy strip are: Si content ≤ 0.1%; Fe content ≤ 0.2%; Cu content ≤ 0.02%; Mn content is 0.2-0.4%; Mg content is 2.8-3.2%; Cr content ≤ 0.15%; Zn content ≤ 0.02%; Ti content is 0.02-0.04%; Single impurity content ≤ 0.03%; The total content of other impurity elements is ≤0.1%; The balance is Al.

2. The aluminum alloy sheet and strip for subway car body according to claim 1, characterized in that: The thickness of the aluminum alloy plate and strip for subway car body is 3-6 mm.

3. A method for preparing the aluminum alloy sheet and strip for subway car body according to claim 1 or 2, characterized in that: The preparation method includes batching, smelting, refining, casting, sawing, milling, heating, hot rolling, cold rolling, oil cleaning, annealing, rewinding or unwinding, and packaging; The heating conditions include a metal heating temperature of 460°C-520°C and a heating time of 1-4h; The hot rolling conditions include: the hot rough rolling pass is 17-19, the intermediate billet thickness is 33-37 mm, the intermediate billet temperature is 420-450° C., the frame down pressure is 39-55%, and the coiling temperature is 320-340° C.; Self-annealing is performed between hot and cold rolling processes; The cold rolling conditions include cold rolling to a finished product thickness of 3-6 mm in one pass and a processing rate of 10-25%; Oil cleaning is performed after the cold rolling; The annealing conditions are as follows: the annealing temperature is 100-140° C. and the annealing time is 2-6 hours.

4. The preparation method according to claim 3, characterized in that: After the refining, furnace refining, online degassing and online filtration are performed.

5. The preparation method according to claim 3, characterized in that: The sawing and milling process includes cutting the aluminum alloy ingot after it is cooled and removing the solidified shell layer on the surface of the ingot by milling with a milling machine.

6. The preparation method according to claim 3, characterized in that: After the refining, the hydrogen content of the melt is ≤0.15 mL / 100 g Al.

7. The preparation method according to claim 3, characterized in that: The online filtration is a double-stage filtration.

8. The preparation method according to claim 3, characterized in that: The preparation method also includes online refinement, and the grain refiner is Al-5Ti-B.

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