A composite forming method of a coarse-grain and fine-grain layered distribution structure aluminum alloy

Abstract

The application discloses a kind of coarse-grained-fine-grained layered distribution structure aluminum alloy composite forming method, belong to additive manufacturing technical field.The application is under the assistance of friction stir fine-grained processing, using ultrasonic additive manufacturing technology, under room temperature or low temperature condition, the high-quality rapid solidification forming of fine-grained aluminum foil and coarse-grained aluminum foil is completed, obtains by fine-grained aluminum layer and coarse-grained aluminum layer staggered accumulation and is the heterogeneous aluminum alloy of the upper and lower surfaces being fine-grained aluminum layer, overcome the grain coarsening of high temperature, high heat effect brought by diffusion connection and explosion composite preparation layered composite material, and the insufficient of high process difficulty, high energy consumption, high cost, the coarse-grained layer-fine-grained layer of the application preparation alternately distributes structure organization dense, residual stress is small, coarse-fine-grained layer proportion can be quantitatively controlled, interface is combined closely between layers, can effectively coordinate the strength and plasticity of alloy material, improve its comprehensive mechanical properties, and the technology is simple, energy saving and environmental protection, and the yield rate is high.

Description

Technical Field

[0001] This invention relates to a method for preparing a high-strength and high-toughness heterogeneous aluminum alloy, belonging to the field of additive manufacturing technology for aluminum alloys. Background Technology

[0002] Aluminum alloys possess excellent properties such as low density, high specific strength, and corrosion resistance. Used in aerospace and rail transportation equipment, they can effectively reduce the weight of structural components, increase travel speed, and reduce energy consumption, demonstrating enormous application potential. Grain refinement is one of the main methods to improve the strength of aluminum alloys. By refining the grains, the grain boundary density of the aluminum alloy can be increased, thereby effectively hindering dislocation movement and improving its strength. However, while grain refinement strengthens aluminum alloys, it can also easily lead to a significant reduction in plasticity. To address this strength-plasticity inversion problem, one of the most effective solutions currently is to introduce a certain amount of coarse grains into fine-grained materials, constructing a multi-layered structure with alternating coarse and fine grains. The principle is that fine grains provide high strength, while coarse grains provide high plasticity. Simultaneously, the interface between the coarse and fine grain regions causes plastic incompatibility during loading, which can produce a back stress strengthening effect, thus simultaneously improving the material's strength, plasticity, and toughness.

[0003] Traditional methods for deforming metallic materials, such as extrusion, rolling, and large surface plastic deformation, can achieve a mixed coarse-fine grain structure in aluminum alloys. However, because these techniques control the material microstructure holistically, it is difficult to precisely control the volume fraction, grain size, and distribution of coarse and fine grains. Therefore, achieving high-precision forming and optimized design of a coarse-fine grain layered structure in heterogeneous aluminum alloys remains a bottleneck for these traditional processes.

[0004] In recent years, additive manufacturing technology has been widely developed due to its advantages such as strong designability. These technologies can also achieve rapid prototyping of multilayer metal structures. However, due to the effects of high-energy beams such as lasers and electric arcs, metal crystallization processes occur during the additive manufacturing of alloy materials, which easily leads to defects such as segregation, coarse grains, non-dense microstructure, and excessive residual stress, making it difficult to achieve high-quality forming of alternating coarse and fine grain structures in aluminum alloys.

[0005] From the perspective of the preparation process of layered metal composite materials, layered heterogeneous grain structure aluminum alloys can be prepared by diffusion composite method, explosive composite method, etc., based on the pre-prepared coarse-grained and fine-grained aluminum alloy plates or foils. However, these processes are often accompanied by high temperature and high heat, which can easily cause coarsening of small-sized grains. It is still very difficult to obtain a microstructure with alternating layers of hard fine grains and soft coarse grains. Moreover, most of the above preparation methods have problems such as high production energy consumption and complex process flow. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a composite forming method for aluminum alloys with a coarse-grained to fine-grained layered distribution structure.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A composite forming method for a coarse-grained to fine-grained layered aluminum alloy, employing friction stir assisted ultrasonic additive manufacturing, includes the following steps:

[0009] Step 1: Following a specific path, the cleaned rolled aluminum sheet is subjected to friction stirring processing to obtain a fine-grained aluminum sheet based on the grain-refining effect of friction stirring processing.

[0010] Step 2: Use wire electrical discharge machining (EDM) to process the fine-grained aluminum plate obtained in Step 1 into fine-grained aluminum foil of the required size;

[0011] Step 3: Using coarse-grained aluminum foil and fine-grained aluminum foil obtained in Step 2 as raw materials, after cleaning, stack them with fine-grained aluminum foil at the bottom and coarse-grained aluminum foil at the top to form a solidification unit. Fix the unit to the worktable of the metal ultrasonic solidification equipment and preheat it to a certain temperature. Then perform ultrasonic solidification to weld the different layers of the unit together.

[0012] Step 4: Repeat Step 3, and continue to stack and weld the second, third, ... nth solidification unit on the coarse-fine grain composite foil that has been solidified. Finally, weld fine grain aluminum foil on the surface of the nth solidification unit to obtain a layered heterogeneous aluminum alloy material with fine and coarse grains stacked alternately and fine grain structure on both the upper and lower surfaces.

[0013] In a preferred embodiment of the present invention, in step one, the shoulder diameter of the stirring head is 18-22 mm, the stirring needle on the stirring head is frustum-shaped, the needle length is 2-5.5 mm, the root diameter is 6-8 mm, the tip diameter is 5-6 mm, and the stirring friction processing parameters are: the stirring head has no tilt angle, the rotation speed is 400-1200 rpm, the processing speed is 15-180 mm / min, the downward pressure is 0.05-0.25 mm, and the distance between the axes of the stirring heads of adjacent processing paths is the tip diameter of the stirring needle.

[0014] Even better, the use of a cooling circulating water system during the friction stirring process can further refine the grains, resulting in ultrafine or even nanocrystals; the use of an argon protective atmosphere can prevent oxidation of the foil surface.

[0015] In a preferred embodiment of the present invention, the cleaning process mentioned in steps one and three refers to wiping the surface of the board / foil with anhydrous ethanol and then letting it dry.

[0016] In a preferred embodiment of the present invention, the fine-grained aluminum plate obtained in step one is processed into fine-grained aluminum foil of the required size using wire electrical discharge machining (EDM). The length and width are adjustable, and the thickness is generally 0.1 to 0.5 mm.

[0017] In a preferred embodiment of the present invention, in step three, the coarse-grained aluminum foil refers to a rolled aluminum sheet of a certain size, wherein the length and width are adjustable, and the thickness is generally 0.1 to 0.5 mm.

[0018] In a preferred embodiment of the present invention, in step three, the power of the metal ultrasonic consolidation equipment is 9kW, the positive pressure during consolidation is 1300-2000N, the ultrasonic amplitude is 25-28μm, the consolidation speed is 20-25mm / s, the preheating temperature is room temperature to 190℃, and the ultrasonic welding head travels in the same direction from one end of the unit body to the other end each time until all areas of the entire unit body have completed one consolidation.

[0019] In a preferred embodiment of the present invention, in step four, the obtained layered heterogeneous aluminum alloy material has at least one coarse-grained aluminum layer and at least two fine-grained aluminum layers.

[0020] This invention discloses a composite forming method for friction stir-assisted ultrasonic additive manufacturing of heterogeneous aluminum alloys containing a coarse-fine grain layered structure. Compared with the prior art, its advantages are as follows:

[0021] (1) The composite forming method of coarse-fine grain layered distribution structure aluminum alloy proposed in this invention achieves grain refinement of the original coarse-grained aluminum material under the dual action of stirring and friction. It can obtain ultrafine grain and even nano-grain structure with controllable grain size and uniform distribution in aluminum and its alloys at room temperature, providing fine grain components for heterogeneous aluminum alloys. The process is simple, energy-saving and environmentally friendly, with a wide range of raw materials and high yield.

[0022] (2) The composite forming method of coarse-fine grain layered aluminum alloy proposed in this invention, with the assistance of friction stirring fine graining treatment technology, utilizes ultrasonic additive manufacturing to complete the high-quality and rapid solidification forming of fine-grained aluminum foil and coarse-grained aluminum foil at room temperature or low temperature. It overcomes the shortcomings of grain coarsening and high process difficulty, high energy consumption and high cost caused by the high temperature and high heat effect of preparing layered composite materials by diffusion bonding and explosive composite. This technology is simple to operate, energy-saving and environmentally friendly, and has a high yield.

[0023] (3) The composite forming method of coarse-fine grain layered aluminum alloy proposed in this invention can easily achieve the controllable preparation of heterogeneous aluminum alloy materials with different specifications and properties by changing parameters such as the composition, layer thickness, number of stacked layers and stacking order of the original aluminum material.

[0024] (4) The composite forming method of the coarse-fine grain layered aluminum alloy proposed in this invention produces a dense structure with alternating coarse-fine grain layers, low residual stress, quantitatively controllable coarse-fine grain layer ratio, and tight interlayer interface bonding, which can effectively coordinate the strength and plasticity of the material and improve its comprehensive mechanical properties. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of an aluminum alloy with a coarse-fine grain layered distribution.

[0026] Figure 2 Flowchart for ultrasonic additive manufacturing assisted by friction stir processing for coarse-fine grain layered aluminum alloys.

[0027] Figure 3 The image shows the multilayer structure (a) and microstructure (b) of the coarse-fine grain region of the heterogeneous aluminum alloy in Example 1.

[0028] Figure 4 The images show the microstructure of the fine-grained layer (a) and coarse-grained layer (b) of the heterogeneous aluminum alloy in Example 2. Detailed Implementation

[0029] The technical solution of the present invention will be described in detail below through specific embodiments. It should be understood that the embodiments are used to illustrate the present invention, not to limit the present invention. Simple improvements made to the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0030] A schematic diagram of the coarse-fine grain layered aluminum alloy material of the present invention is shown below. Figure 1 As shown, it is a heterogeneous aluminum alloy composed of alternating layers of fine-grained and coarse-grained aluminum, with both the upper and lower surfaces being composed of fine-grained aluminum layers.

[0031] Combination Figure 2 The following embodiments provide a composite forming method for aluminum alloys with a coarse-fine grain layered distribution structure.

[0032] Example 1

[0033] ① Clean the surface of a 150mm×25mm×6mm (length×width×thickness) rolled 6061 aluminum alloy sheet with an alcohol swab, and then air dry it.

[0034] ② Fix the cleaned 6061 aluminum alloy sheet onto the worktable of the friction stir welding machine. To prevent the aluminum sheet from welding together with the worktable, place a 6061 aluminum alloy pad of the same size between them.

[0035] ③ Install a stirring head with a shoulder diameter of 22mm and a stirring pin length of 4.8mm on a friction stir welding machine. Set the process parameters as follows: the stirring head rotates clockwise at 1000rpm, the processing speed is 80mm / min, the downward pressure is 0.2mm, and the stirring head has no tilt angle. Then, use the friction stir welding equipment to process the aluminum plate in multiple passes to obtain 6061 aluminum alloy plate with refined grains.

[0036] ④ The grain-refined 6061 aluminum alloy sheet after the above-mentioned friction stir treatment is processed using an electric discharge wire cutting machine to obtain a fine-grained 6061 aluminum alloy foil with dimensions of 150mm×25mm×0.3mm (length×width×thickness).

[0037] ⑤ Stack the above-mentioned fine-grained 6061 aluminum alloy foil and the original rolled 1100 pure aluminum foil, i.e., coarse-grained 1100 pure aluminum foil (length × width × thickness: 600mm × 25mm × 0.2mm) on the worktable of the ultrasonic consolidation equipment, with the fine-grained 6061 aluminum alloy foil at the bottom and a 6061 aluminum alloy pad between it and the worktable, and the coarse-grained 1100 Al foil at the top, with its two ends clamped and fixed. Then preheat the worktable to 160°C.

[0038] ⑥ Set the ultrasonic consolidation process parameters as follows: positive pressure 2000N, ultrasonic amplitude 28μm, consolidation speed 20mm / s, and then solidify the coarse-fine crystalline foil material into shape.

[0039] ⑦ Using the same process, weld fine-grained 6061 aluminum alloy foil onto the solidified coarse-fine grain composite foil to complete the forming and preparation of a coarse-fine grain layered distribution structure composite aluminum material containing two layers of fine-grained 6061 aluminum alloy and one layer of coarse-grained 1100 pure aluminum (both the upper and lower surfaces are fine-grained 6061 aluminum alloy layers).

[0040] The typical microstructure of the heterogeneous aluminum alloy obtained in this embodiment is as follows: Figure 3 As shown, the coarse-fine grain interface is well bonded, and the fine grain structure does not become coarse due to the ultrasonic consolidation process.

[0041] Example 2

[0042] ① Clean the surface of a 150mm×150mm×6mm (length×width×thickness) rolled 1100 pure aluminum sheet (1100Al) with an alcohol swab, and then air dry it.

[0043] ② Fix the cleaned 1100Al plate onto the worktable of the friction stir welding machine. To prevent the aluminum plate from welding together with the worktable, place a 6061 aluminum alloy pad of the same size between them.

[0044] ③ Install a stirring tool head with a shoulder diameter of 22mm and a stirring pin length of 5.5mm on a friction stir welding machine. Set the process parameters as follows: the stirring head rotates clockwise at a speed of 600rpm, the processing speed is 100mm / min, the downward pressure is 0.15mm, and the stirring head has no tilt angle. Then, use the friction stir welding equipment to process the aluminum plate in multiple passes to obtain 1100Al plate with refined grains.

[0045] ④ The grain-refined 1100Al plate after the above-mentioned friction stir treatment was processed using an electric discharge wire cutting machine to obtain a fine-grained 1100Al foil with dimensions of 150mm×25mm×0.3mm (length×width×thickness).

[0046] ⑤ Stack the above-mentioned fine-grained 1100Al foil and the original rolled 1100Al foil, i.e., coarse-grained 1100Al foil (length × width × thickness: 600mm × 25mm × 0.2mm) on the worktable of the ultrasonic consolidation equipment, with the fine-grained 1100Al foil at the bottom and a 6061 aluminum alloy pad between it and the worktable, and the coarse-grained 1100Al foil at the top, with its two ends clamped and fixed.

[0047] ⑥ Set the ultrasonic consolidation process parameters as follows: positive pressure 1500N, ultrasonic amplitude 28μm, consolidation speed 25mm / s. Then connect and form the coarse-fine crystalline foil. During welding, the ultrasonic welding head travels in a straight line from one end of the stacking unit to the other end along the length of the foil to complete the consolidation of the first group of layered coarse-fine crystalline composite foil.

[0048] ⑦ Repeat step ⑥, successively stacking and welding the second and third groups of coarse-fine crystalline composite foils on the first group of layered coarse-fine crystalline composite foils that have been consolidated. Finally, stack fine crystalline aluminum foil on the surface (top layer) and weld it to complete the additive manufacturing of heterogeneous 1100Al material containing 4 fine crystalline layers and 3 coarse crystalline layers with fine crystalline layers on both the top and bottom surfaces.

[0049] The additive manufacturing heterogeneous 1100Al microstructure obtained in this embodiment is as follows: Figure 4 As shown, the average grain size of the fine-grained aluminum is less than 6 μm, while the average grain size of the coarse-grained aluminum is greater than 50 μm. The mechanical properties of the layered heterogeneous aluminum material obtained in this embodiment are as follows: at a strain rate of ~0.001 / s, the tensile strength parallel to the layer direction is ~167 MPa, and the failure strain is ~16%. Compared with rolled 1100Al pure aluminum (tensile strength ~155 MPa / elongation ~32%), it has higher strength, and compared with ultrafine-grained pure aluminum obtained by friction stir processing (tensile strength ~175 MPa / elongation ~9%), it has better ductility. This result is based on the synergistic effect of the coarse-fine grain layers and the back stress strengthening effect at the interlayer interface.

Claims

1. A method of composite forming of a coarse-fine layered distribution structure aluminum alloy, characterized by, The method comprises the following steps: Step one: according to a certain path, the rolled pure aluminum / aluminum alloy plate after cleaning treatment is subjected to friction stir processing, and fine-grained aluminum plate is obtained based on the fine-grain effect of the friction stir processing; Step two: the fine-grained aluminum plate obtained in step one is processed into a fine-grained aluminum foil of a required size by using wire electrical discharge machining technology; Step three: the coarse-grained aluminum foil and the fine-grained aluminum foil obtained in step two are used as raw materials, after cleaning treatment, the fine-grained aluminum foil is stacked below the coarse-grained aluminum foil to form a unit body, the unit body is fixed to the worktable of a metal ultrasonic consolidation device and preheated to a certain temperature, and then ultrasonic consolidation is performed to weld different layers of the unit body together; Step four: step three is repeated, and a second unit body, a third unit body, and an n-th unit body are successively welded on the coarse-fine-grained composite foil obtained in step three, and finally a fine-grained aluminum foil is welded on the surface of the n-th unit body to obtain a layered heterogeneous aluminum alloy material with fine-grained and coarse-grained aluminum foils stacked alternately and the upper and lower surfaces being fine-grained.

2. The method of claim 1, wherein, In step one, the shoulder diameter of the stir head used in the friction stir processing is 18-22 mm, the stirring needle on the stir head is in the shape of a circular truncated cone, the needle length is 2-5.5 mm, the root diameter is 6-8 mm, the top end diameter is 5-6 mm, and the friction stir processing parameters are as follows: the stir head has no inclination, the rotation speed is 400-1200 rpm, the processing speed is 15-180 mm / min, the pressing amount is 0.05-0.25 mm, and the center distance between the stir heads of adjacent processing paths is equal to the top end diameter of the stirring needle.

3. The method of claim 1, wherein, During the friction stir processing, a cooling circulating water system is used for cooling, and an argon protective atmosphere is used.

4. The method of claim 1, wherein, In steps one and three, the cleaning treatment refers to wiping the surface of the plate / foil with anhydrous ethanol and air-drying.

5. The method of claim 1, wherein, In step two, the fine-grained aluminum plate obtained in step one is processed into a fine-grained aluminum foil of a required size by using wire electrical discharge machining technology, and the thickness of the fine-grained aluminum foil is 0.1-0.5 mm.

6. The method of claim 1, wherein, In step three, the coarse-grained aluminum foil refers to a rolled aluminum plate of a certain size, and the thickness of the coarse-grained aluminum foil is 0.1-0.5 mm.

7. The method of claim 1, wherein, In step three, the power of the metal ultrasonic consolidation device is 9 kW, the normal pressure during consolidation is 1300-2000 N, the ultrasonic amplitude is 25-28 μm, the consolidation speed is 20-25 mm / s, the preheating temperature is room temperature-190 °C, the ultrasonic welding head travels linearly from one end of the unit body to the other end in the same direction each time until all areas of the unit body are consolidated once.

8. The method of claim 1, wherein, In step four, in the layered heterogeneous aluminum alloy material obtained, the number of coarse-grained aluminum layers is at least one, and the number of fine-grained aluminum layers is at least two.

9. The coarse-fine hierarchical distribution structure aluminum alloy prepared by the method according to any one of claims 1-8, wherein, In the aluminum alloy structure, the average grain size of the fine-grained aluminum foil is 0.1-10 μm, and the average grain size of the coarse-grained aluminum foil is 10-100 μm.

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