A method and system for preparing a multi-grain size heterogeneous metal sheet

Abstract

The present invention relates to a method and system for preparing a multi-grain scale heterogeneous metal sheet. The method comprises the following steps: (1) performing homogenization annealing on the metal sheet after pre-treatment; (2) performing surface rolling deformation by using a rolling device having a plurality of spherical rolling heads, with the adjacent rolling heads being spaced apart, and different rolling heads having different working temperatures to obtain a sheet with unequal thickness; the strain rate in the rolling deformation region is 10<supgt;2< / supgt> to 10<supgt;3< / supgt> s<supgt;~1< / supgt>; (3) performing rolling deformation on the sheet with unequal thickness obtained in step (2) to cause non-uniform plastic deformation of the sheet with unequal thickness in the thickness direction, and the strain rate of rolling is below 10 s<supgt;~1< / supgt> to obtain a rolled sheet with uniform thickness and flat surface. By changing the vibration frequency, amplitude and working temperature of the rolling heads, the present invention changes the microstructure of the rolling region, and further increases the microstructure difference between regions by performing non-uniform rolling deformation on the sheet with unequal thickness, so as to obtain a multi-grain scale heterogeneous sheet.

Description

Technical Field

[0001] The present invention belongs to the field of material preparation, and in particular relates to a preparation method and system for a multi-grain-scale heterogeneous metal plate. Background Art

[0002] Aluminum alloy has low density, high plasticity and good ductility. Therefore, various aluminum alloy parts and crafts can be obtained through extrusion, casting and other processes. They are widely used in aerospace, automotive industry and food packaging. The strength and toughness of metals are the two most important mechanical properties when used as structural materials. Generally, there is a mutually restrictive relationship between the strength and toughness of materials, that is, materials with high strength have poor toughness, and materials with good toughness have low strength. This inverted relationship has become an important bottleneck problem in the development of materials. In order to meet the needs of structural weight reduction, safety design and resource conservation, it is particularly important to obtain high-strength and tough aluminum alloy materials through appropriate processing methods. Recent studies have shown that heterogeneous metal materials are usually composed of two or more components with significant differences in microstructure and mechanical properties. During the deformation process, the components coordinate and cooperate with each other to improve the work hardening ability of the material, so that it has high strength and good plasticity.

[0003] After searching the prior art, it was found that Li et al. published an academic paper titled "Soft / hard copper / bronze laminates with superior mechanical properties" in Mater. Sci. Eng. A, reporting a method of combining dissimilar copper alloys together by diffusion welding, and then obtaining a laminated heterogeneous material with alternating soft / hard layers through subsequent rolling and annealing treatment. The characteristics of this technology are: (1) It is suitable for preparing large pieces of heterogeneous plates; (2) The diffusion welding interface bonding is relatively good. However, this technology also has the following disadvantages: (1) Diffusion welding has relatively high requirements for equipment; (2) The preparation process is complicated and the production efficiency is low.

[0004] Further searching revealed that patent CN10800006A "A method for preparing multi-scale precipitation heterogeneous aluminum alloy rods" introduces a method of using rotary forging technology to achieve metallurgical bonding between pure aluminum and 7075 aluminum alloy rods, and then controlling the precipitation of the second phase through aging treatment to obtain heterogeneous aluminum alloy rods. The characteristics of this technology are: (1) the use of inert gas to protect the material to prevent oxidation at the interface; (2) the process flow is simple and the production efficiency is high. However, this technology also has the following disadvantages: (1) this method is only applicable to materials with different precipitation behaviors and has limitations; (2) it is impossible to prepare heterogeneous aluminum alloy plates.

[0005] Further searching of the prior art revealed that patent CN111346939A "A method for preparing multi-grain size heterogeneous aluminum alloy plates by composite rolling" introduces a method for preparing multi-grain size heterogeneous aluminum alloy plates by surface rolling deformation, homogenization annealing, non-uniform rolling deformation and recrystallization annealing. The characteristics of this technology are: (1) the local thickness of the plate can be controlled by controlling the rolling depth of the pressure head to obtain aluminum alloy plates of unequal thickness; (2) multi-grain size heterogeneous aluminum alloy plates are obtained by non-uniform rolling and recrystallization annealing. However, this technology also has the following disadvantages: (1) multiple annealing treatments are required, and the process is relatively cumbersome; (2) there is only one pressure head for rolling, and the microstructure of the deformation area is relatively simple, and the processing efficiency is low. Summary of the invention

[0006] The object of the present invention is to provide a method and system for preparing a multi-grain-scale heterogeneous metal sheet.

[0007] The technical solution to achieve the purpose of the present invention is: a method for preparing a multi-grain size heterogeneous metal sheet, comprising the following steps:

[0008] Step (1): pre-treating the metal sheet and then performing homogenization annealing;

[0009] Step (2): a rolling device with multiple spherical rolling heads is used to roll and deform the surface of the metal plate, with adjacent rolling heads spaced apart and different rolling heads having different working temperatures to obtain plates of different thicknesses; the strain rate in the rolling deformation area is 10 2 ~10 3 s ～1 ;

[0010] Step (3): rolling deformation, rolling deformation of the unequal thickness plates obtained in step (2) to cause non-uniform plastic deformation of the unequal thickness plates in the thickness direction, the rolling strain rate is 10s ～1 Next, a rolled plate with uniform thickness and smooth surface is obtained.

[0011] Furthermore, the dimensions of the metal plate in step (1) are as follows: length 10-300 mm, width 10-300 mm, thickness 5-20 mm.

[0012] Furthermore, the pretreatment in step (1) is: cleaning impurities and oxides on the surface of the metal plate by degreasing and pickling, and then grinding the surface of the metal plate with a grinding wheel.

[0013] Furthermore, the homogenization annealing in step (1) is specifically as follows: annealing the pretreated plate at an annealing temperature of 390 to 490°C, introducing an inert protective atmosphere during the annealing heating process, keeping warm for 1 to 2 hours and then cooling at a cooling rate of less than 30°C / h, cooling to below 260°C and then taking the plate out of the furnace for air cooling to obtain a near-equilibrium structure.

[0014] Furthermore, in step (2), the diameter of the rolling head is 5 to 10 mm, the amount of pressure reduction in the rolling area of ​​the rolling head is 0.5 to 3 mm, the working temperature of the rolling head is 25 to 500° C., and the distance between adjacent rolling heads is 5 to 10 mm.

[0015] Furthermore, there are two rolling heads, the vibration frequency of the rolling heads is 50-150 Hz, the stepping speed is 3-10 mm / s, the working temperature of one rolling head is 25-100°C, and the working temperature of the other rolling head is 350-450°C.

[0016] Furthermore, the cumulative rolling deformation of the rolling deformation in step (3) is 20% to 80%, and the rolling temperature is 25 to 400°C.

[0017] Furthermore, the rolling device used in step (2) includes a piezoelectric control system, a heating system, a pressing head system and a three-axis CNC milling machine;

[0018] The indenter system is installed on a three-axis CNC milling machine and runs on the sample surface along a specified trajectory according to the CNC program. The indenters of the indenter system are connected to a piezoelectric control system and a heating system. The vibration frequency and amplitude of the indenter can be adjusted by changing the parameters of the piezoelectric control system, and the working temperature of the indenter can be adjusted by changing the parameters of the heating system.

[0019] A pressing head of the pressing head system includes an impact head, a transmission head and a piezoelectric transducer;

[0020] The rolling deformation in step (3) is performed using a cylindrical flat roll.

[0021] Furthermore, the metal plate is an aluminum alloy plate.

[0022] A multi-grain-scale heterogeneous metal plate with a smooth surface. The plate includes a fine-grained zone with the highest degree of refinement formed by a cold-pressed zone with a high strain rate, a sub-fine-grained zone composed of recrystallized grains formed by a hot-pressed zone, and a coarse-grained zone with a larger grain size formed after rolling in an undeformed annealed zone.

[0023] Compared with the prior art, the present invention has the following significant advantages:

[0024] 1. The present invention adopts two special pressing heads in conjunction with a three-axis CNC milling machine to perform rolling deformation. This method has low equipment requirements, low production cost, high production efficiency, and can be produced and processed in large quantities.

[0025] 2. The present invention uses numerical control software to accurately compile the rolling tool path. The programming technology of the numerical control milling machine can perform surface treatment of aluminum alloy plates in different paths with high manufacturing accuracy. The microstructure distribution of heterogeneous materials can also be flexibly designed through programming.

[0026] 3. The piezoelectric vibration used in the present invention has a high natural frequency and a fast speed, and can effectively drive the indenter to cause the material to undergo plastic deformation at a high strain rate, resulting in significant grain refinement.

[0027] 4. The present invention can adjust the microstructure of the rolling area by changing processing parameters such as the working temperature, vibration frequency, and pressure reduction of the pressure head, thereby flexibly regulating the grain size distribution after rolling. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the rolling cutter head.

[0029] Figure 2 Schematic diagram of the rolling deformation process.

[0030] Figure 3 Schematic diagram of rolling deformation.

[0031] Figure 4 This is a microscopic schematic diagram of the plate cross section before and after rolling.

[0032] Description of Reference Numerals

[0033] 1~impact head, 2~transmission head, 3~piezoelectric transducer, 4~piezoelectric control system, 5~heating system, 6~rolling head I, 7~rolling head II, 8~aluminum alloy plate in fully annealed state, 9~aluminum alloy plate with unequal thickness treatment, 9~1~hot rolling fine grain zone, 9~2~complete annealing zone, 9~3~cold rolling hardening zone, 10~roller, 11~aluminum alloy plate after rolling, 11~1~hot pressing zone after rolling, 11~2~complete annealing zone after rolling, 11~3~cold pressing hardening zone after rolling. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0035] The present invention discloses a device and method for preparing multi-grain size heterogeneous aluminum alloy plates by piezoelectric vibration rolling. The device comprises a piezoelectric control system, a heating system, a pressure head system and a three-axis CNC milling machine. The pressure head system is equipped with a piezoelectric transducer and a vibration transmission device. Under the action of alternating voltage, the vibration can be transmitted to the spherical pressure head at the bottom, continuously hitting various positions of the workpiece surface to be processed at high frequency, and a high strain rate (10 2 ~10 3 s ～1) dynamic plastic deformation, usually the higher the deformation rate, the better the grain refinement effect under the same deformation amount. The punch system can be installed on a three-axis CNC milling machine and run on the sample surface according to the specified trajectory according to the CNC program. Both punches are connected to the piezoelectric control system and the heating system. The vibration frequency and vibration amplitude of the punch can be adjusted by changing the parameters of the piezoelectric control system, thereby changing the deformation degree of the sample at the position of the punch; the working temperature of the punch can be adjusted by changing the parameters of the heating system, thereby affecting the microstructure of the deformed sample. By reasonably selecting the punch rolling trajectory and rolling parameters, aluminum alloy plates of unequal thickness can be obtained, and there are obvious differences in the microstructure between the regions. Among them, high strain rate plastic deformation occurs in the low temperature rolling area, resulting in structural changes such as work hardening, dislocation entanglement, grain elongation, and increased hardness. Compared with conventional low strain rate plastic deformation, this high strain rate dynamic plastic deformation can produce more significant grain refinement effect; recrystallization occurs in the high temperature rolling area, the dislocation density in the grains is reduced, and the hardness is reduced. In summary, by adjusting the vibration frequency, rolling depth, and temperature of the punch during processing, the strain rate, deformation amount, and deformation temperature of the punch processing area are controlled to obtain different microstructures. Finally, an aluminum alloy rolled plate with uniform thickness and smooth surface is obtained by rolling deformation at a low strain rate. Although the cumulative deformation thickness of each region is almost the same in the end, the initial structure before rolling deformation is regulated by controlling the punch processing parameters. After rolling deformation, the grain refinement degree of the cold-pressed area with a high strain rate is the highest, and the hot-pressed area is a refined recrystallized grain. After rolling in the undeformed annealed area, a dislocation cell structure with a high dislocation density is formed, and the grain size is large, and finally a multi-grain scale heterogeneous aluminum alloy plate with a smooth surface is obtained.

[0036] like Figures 1 to 4 As shown, the present invention takes aluminum alloy sheet as an example to provide a detailed implementation method and specific operation. The following embodiments involve four steps including: surface treatment, homogenization annealing, surface rolling deformation, and non-uniform rolling deformation.

[0037] Example 1

[0038] The first step is surface treatment: take a piece of aluminum alloy plate with a length of 50mm, a width of 50mm and a thickness of 10mm, use a grinding wheel to grind the surface of the metal plate, and clean the surface impurities and oxides.

[0039] The second step is homogenization annealing: the surface treated aluminum alloy sheet is fully annealed at 470°C for 1.5 hours at a cooling rate of 25°C / h. When the temperature drops below 260°C, the sheet is air-cooled to obtain a nearly balanced structure.

[0040] The third step is surface rolling deformation: Assemble the pressure head device to the three-axis CNC milling machine, the pressure head diameter is 10mm, the distance between the two pressure heads is 5mm, the frequency of the pressure head vibration is 100Hz, and the stepping speed is 5mm / s. Fix the plate on the fixture of the three-axis CNC milling machine, establish a three-axis coordinate system with the plate surface (X, Y) and the top (Z), and compile the pressure head stroke according to the needs. Before rolling, perform the tool setting operation to determine the processing starting point, and then turn on the power of the piezoelectric vibration system and the heating system. The temperatures of the two pressure heads are 25 and 400℃ respectively. According to the set program, the aluminum alloy plate is rolled and deformed, where the low-temperature rolling area is pressed down by 1.5mm, and the high-temperature rolling area is pressed down by 2mm, to obtain aluminum alloy plates of unequal thickness.

[0041] The fourth step is rolling deformation: rolling deformation is performed on the aluminum alloy plates of different thicknesses after rolling to make the plates of different thicknesses undergo non-uniform plastic deformation in the thickness direction, and obtain aluminum alloy rolled plates with uniform thickness and smooth surface. The rolling deformation temperature is 25°C, the single-pass rolling amount is 10%, the total rolling amount is 50%, and the plate thickness is 5mm. After rolling deformation, the microstructural differences between the regions are further increased, and multi-grain heterogeneous aluminum alloy plates are obtained. Among them, the grains of the cold-pressed fine-grained area are further refined after rolling, the grain size of the hot-pressed recrystallized area is reduced after rolling deformation, and the grains of the undeformed annealed area are larger after rolling deformation.

[0042] Example 2

[0043] The first step is surface treatment: take a piece of aluminum alloy plate with a length of 50mm, a width of 50mm and a thickness of 10mm, use a grinding wheel to grind the surface of the metal plate, and clean the surface impurities and oxides.

[0044] The second step is homogenization annealing: the surface treated aluminum alloy sheet is fully annealed at 470°C for 1.5 hours at a cooling rate of 25°C / h. When the temperature drops below 260°C, the sheet is air-cooled to obtain a nearly balanced structure.

[0045] The third step is surface rolling deformation: Assemble the pressure head device to the three-axis CNC milling machine, the pressure head diameter is 10mm, the distance between the two pressure heads is 5mm, the frequency of the pressure head vibration is 100Hz, and the stepping speed is 5mm / s. Fix the plate on the fixture of the three-axis CNC milling machine, establish a three-axis coordinate system with the surface (X, Y) and top (Z) of the plate, and compile the pressure head stroke according to the needs. Before rolling, perform the tool setting operation to determine the processing starting point, and then turn on the power of the piezoelectric vibration system and the heating system. The temperatures of the two pressure heads are 35 and 400℃ respectively. According to the set program, the aluminum alloy plate is rolled and deformed, where the low-temperature rolling area is pressed down by 1mm, and the high-temperature rolling area is pressed down by 1mm, to obtain aluminum alloy plates of unequal thickness.

[0046] The fourth step is rolling deformation: rolling deformation is performed on the aluminum alloy plates of different thicknesses after rolling to make the plates of different thicknesses undergo non-uniform plastic deformation in the thickness direction, and obtain aluminum alloy rolled plates with uniform thickness and smooth surface. The rolling deformation temperature is 25°C, the single-pass rolling amount is 10%, the total rolling amount is 50%, and the plate thickness is 5mm. After rolling deformation, the microstructural differences between the regions are further increased, and multi-grain heterogeneous aluminum alloy plates are obtained. Among them, the grains of the cold-pressed fine-grained area are further refined after rolling, the grain size of the hot-pressed recrystallized area is reduced after rolling deformation, and the grains of the undeformed annealed area are larger after rolling deformation.

[0047] Example 3

[0048] The first step is surface treatment: take a piece of aluminum alloy plate with a length of 50mm, a width of 50mm and a thickness of 10mm, use a grinding wheel to grind the surface of the metal plate, and clean the surface impurities and oxides.

[0049] The second step is homogenization annealing: the surface treated aluminum alloy sheet is fully annealed at 470°C for 1.5 hours at a cooling rate of 25°C / h. When the temperature drops below 260°C, the sheet is air-cooled to obtain a nearly balanced structure.

[0050] The third step is surface rolling deformation: Assemble the pressure head device to the three-axis CNC milling machine, the pressure head diameter is 10mm, the distance between the two pressure heads is 5mm, the frequency of the pressure head vibration is 100Hz, and the stepping speed is 5mm / s. Fix the plate on the fixture of the three-axis CNC milling machine, establish a three-axis coordinate system with the surface (X, Y) and top (Z) of the plate, and compile the pressure head stroke according to the needs. Before rolling, perform the tool setting operation to determine the processing starting point, and then turn on the power of the piezoelectric vibration system and the heating system. The temperatures of the two pressure heads are 25 and 450℃ respectively. According to the set program, the aluminum alloy plate is rolled and deformed, where the reduction in the low-temperature rolling area is 2mm, and the reduction in the high-temperature rolling area is 2.5mm, to obtain aluminum alloy plates of unequal thickness.

[0051] The fourth step is rolling deformation: rolling deformation is performed on the aluminum alloy plates of different thicknesses after rolling to make the plates of different thicknesses undergo non-uniform plastic deformation in the thickness direction, and obtain aluminum alloy rolled plates with uniform thickness and smooth surface. The rolling deformation temperature is 25°C, the single-pass rolling amount is 10%, the total rolling amount is 50%, and the plate thickness is 5mm. After rolling deformation, the microstructural differences between the regions are further increased, and multi-grain heterogeneous aluminum alloy plates are obtained. Among them, the grains of the cold-pressed fine-grained area are further refined after rolling, the grain size of the hot-pressed recrystallized area is reduced after rolling deformation, and the grains of the undeformed annealed area are larger after rolling deformation.

Claims

1. A method for preparing a multi-grain size heterogeneous metal sheet, characterized in that: The metal sheet is an aluminum alloy sheet, and the steps include: Step (1): pre-treating the metal sheet and then performing homogenization annealing; Step (2): Use a rolling device with two spherical rolling heads to roll and deform the surface of the metal plate, with adjacent rolling heads spaced apart and different rolling heads having different working temperatures to obtain plates of different thicknesses; the strain rate in the rolling deformation area is 10 2 ~10 3 s -1 ; Step (3): rolling deformation, rolling deformation of the unequal thickness plates obtained in step (2) to make the unequal thickness plates undergo non-uniform plastic deformation in the thickness direction, and the rolling strain rate is 10 s -1 Next, a rolled plate with uniform thickness and smooth surface is obtained; The homogenization annealing in step (1) is specifically as follows: annealing the pretreated plate at an annealing temperature of 390-490°C, introducing an inert protective atmosphere during the annealing heating process, cooling after keeping warm for 1-2 hours at a cooling rate of less than 30°C / h, cooling to below 260°C, and then taking the plate out of the furnace for air cooling to obtain a near-equilibrium structure; In step (2), the diameter of the rolling head is 5-10 mm, the pressing amount of the rolling head in the rolling area is 0.5-3 mm, and the distance between adjacent rolling heads is 5-10 mm; There are two rolling heads, the vibration frequency of the rolling heads is 50~150 Hz, the stepping speed is 3~10 mm / s, the working temperature of one rolling head is 25~100℃, and the working temperature of the other rolling head is 350~450℃; The cumulative rolling deformation of the rolling deformation in step (3) is 20%~80%, and the rolling temperature is 25~400℃.

2. The method according to claim 1, characterized in that: The dimensions of the metal sheet in step (1) are as follows: length 10-300 mm, width 10-300 mm, thickness 5-20 mm.

3. The method according to claim 2, characterized in that The pretreatment in step (1) is to remove impurities and oxides from the surface of the metal sheet by degreasing and pickling, and then grind the surface of the metal sheet with a grinding wheel.

4. The method according to claim 3, characterized in that The rolling device used in step (2) includes a piezoelectric control system, a heating system, a pressing head system and a three-axis CNC milling machine; The indenter system is installed on a three-axis CNC milling machine and runs on the sample surface along a specified trajectory according to the CNC program. The rolling heads of the indenter system are connected to the piezoelectric control system and the heating system. The vibration frequency and amplitude of the rolling heads can be adjusted by changing the parameters of the piezoelectric control system, and the working temperature of the rolling heads can be adjusted by changing the parameters of the heating system. A rolling head of the pressing head system includes an impact head, a transmission head and a piezoelectric transducer; The rolling deformation in step (3) is performed using a cylindrical flat roll.

5. A multi-grain size heterogeneous metal sheet, characterized in that: The multi-grain size heterogeneous plate is prepared by the method described in any one of claims 1 to 4, and the surface of the plate is flat. The plate includes a fine-grained zone with the highest degree of refinement formed by a cold-pressed zone with a high strain rate, a sub-fine-grained zone composed of recrystallized grains formed by a hot-pressed zone, and a coarse-grained zone with a larger grain size formed after rolling in an undeformed annealed zone.

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