Method for orderly construction of ultrafine grain network structure by composite friction stir processing in additive manufacturing

Abstract

The application provides a method for additive manufacturing composite friction stir processing ordered construction of ultra-fine grain network structure, which is characterized by the following steps: through synchronous friction stir processing in electric arc wire additive manufacturing, strong plastic deformation of the friction stir processing is utilized to cause mechanical crushing of the deposited state organization, and a cross friction stir processing mode is combined to obtain an ultra-fine grain network structure; a repeated deposition process causes the organization which has been subjected to strong plastic deformation to undergo recovery recrystallization and grain growth, different span friction stir processing is utilized to cause ordered construction of the deposited state organization grain gradient, and finally, the construction of the component material of the ultra-fine grain three-dimensional network structure is realized.

Description

Technical Field

[0001] The present invention relates to the field of 3D printing additive technology, and in particular to a method for orderly constructing an ultrafine grain network structure by composite stir friction processing in additive manufacturing. Background Art

[0002] Wire arc additive manufacturing (WAAM) has become a key option for large-scale structural fabrication due to its advantages, including high deposition efficiency, high material yield, short manufacturing cycles, and low costs. Furthermore, compared to other heat sources, it is less sensitive to alloy type, making it suitable for materials with high laser reflectivity, particularly aluminum alloys widely used in aerospace applications. Despite this, high-strength aluminum alloys (such as the 2000 and 7000 series) that rely on deformation and precipitation strengthening for toughness still face numerous metallurgical bottlenecks, such as coarse microstructure, disruption of the strengthening phase type and ordered precipitation, porosity, and significant hot cracking tendency. These factors result in inferior performance compared to forgings, creating a mismatch between efficiency and performance, making it difficult to meet the engineering requirements of large, load-bearing structural components. Therefore, improving the strength and toughness of WAAM aluminum alloys is crucial for promoting their engineering applications. The formation of microstructure and metallurgical defects in WAAM aluminum alloys is closely related to insufficient compositional supercooling caused by cyclic remelting, heat accumulation, and temperature gradients during the deposition process. Furthermore, the inherent characteristics of deformed high-strength aluminum alloys, such as low melting point, wide liquid-solid eutectic range, element volatility, and a high concentration of highly crack-sensitive elements, exacerbate the formation of these defects.

[0003] Finding the optimal structure-manufacturing-organization-performance-efficiency fit based on the characteristics of additive manufacturing is essential for promoting technological development and fully leveraging its advantages. In recent years, domestic and international researchers have developed a variety of toughening methods based on organizational structure design, including gradient nanostructured materials and particle network-reinforced composites based on Hashin and Shtrikman HS theory, which have played a significant role in improving the overall performance of materials.

[0004] Academician Lu Ke and Professor Lu Lei of the Institute of Metal Research have published more than ten academic papers in journals such as Nature and Science, demonstrating the application of nanoscale gradient structures in materials as diverse as copper and aluminum alloys. Chen et al. fabricated nanocrystals in a NiTi alloy with a gradient transition from the center to the surface, significantly improving their elastic and plastic properties.

[0005] Kei Ameyama's research team used hot pressing and sintering to mix ultrafine powder with coarse powder to prepare an alloy with a laminated structure and a spatial network distribution structure. The overall structural strength can be increased from 600 MPa to 1400 MPa. Compared with the laminated structure, the spatial network has better performance.

[0006] Geng Lin, Huang Lujun and others from Harbin Institute of Technology used powder metallurgy and in-situ self-generation to prepare TiBw / Ti primary spatial network structure and (TiBw+TiCp) and (TiBw+Ti5Si3) secondary network structures, achieving performance improvement.

[0007] In the above theory, without changing the material composition, constructing a nano-gradient or realizing an ultrafine-grained network structure design can, to a certain extent, construct a local network structure and improve its strength and elongation, but its construction is restricted, it cannot be freely designed, and its performance improvement is limited. Summary of the Invention

[0008] The purpose of the present invention is to address the deficiencies of the existing technology and provide a method for orderly constructing an ultrafine-grained network structure by additive manufacturing and composite stir friction processing. The method combines additive manufacturing, especially arc fuse additive manufacturing, and stir friction processing. Through the optimization design of stirring and deposition paths, a continuous gradient, localized, and structured spatially orderly distribution of ultrafine grains is constructed, and localized structure enhancement is achieved by utilizing ultrafine grains, thus breaking through the bottleneck of matching additive efficiency with comprehensive performance.

[0009] According to a first aspect of the present invention, a method for orderly constructing an ultrafine-grained network structure by additive manufacturing composite friction stir processing is provided, comprising the following steps:

[0010] According to the 3D structural model of the component to be processed, the additive manufacturing process is planned, and the material is deposited layer by layer on the substrate in an upward growth manner starting from the first layer according to the process procedure until the Nth layer is deposited to obtain the required component;

[0011] In the process of depositing the first layer to the Nth layer, each time a deposition layer is printed, the layer is subjected to a stir friction treatment, wherein the stir friction treatment is performed in an orthogonal manner of transverse stir friction and longitudinal stir friction, so that each deposition layer forms a network structure with the ultrafine crystal region as the intersection point, and the final component forms a three-dimensional network structure with the ultrafine crystal region as the intersection point; wherein the ultrafine crystal region is the overlapping area of ​​the stirring needle during the transverse stir friction and the longitudinal stir friction.

[0012] As an optional embodiment, during the melt deposition process, through the heat transfer of melt deposition, the previous deposited layer tends to gradually decrease from top to bottom due to heat, so that the stir friction treated part of the previous deposited layer presents a grain gradient with gradually increasing grain size along the deposition direction.

[0013] As an optional embodiment, the grain gradient presented by the ultrafine grain region includes an ultrafine grain region, a fine grain region, an equiaxed grain region and a columnar grain region sequentially superimposed along the deposition direction.

[0014] As an optional implementation manner, the grain size of the ultrafine grain region is 0.5 μm to 2 μm.

[0015] As an optional embodiment, the grain size of the fine grain zone is 2 μm to 10 μm.

[0016] As an optional implementation, the grain size of the equiaxed crystal region is 5 μm to 20 μm.

[0017] As an optional embodiment, the grain size of the columnar crystal region is greater than 20 μm.

[0018] As an optional embodiment, during the friction stir treatment process, the depth of the stirring needle inserted into the deposition layer, the diameter of the stirring needle, and the distance and overlap rate between single passes during transverse friction stir / longitudinal friction stir are planned and / or adjusted according to the grid characteristics of the three-dimensional network structure of densely distributed ultrafine crystal regions and the characteristics of a single ultrafine crystal region.

[0019] As an optional embodiment, the diameter of the stirring needle is increased to obtain a wider ultrafine grain region.

[0020] As an optional embodiment, the depth of the stirring needle inserted into the deposition layer is increased to obtain a deeper ultrafine grain region.

[0021] As an optional embodiment, during the transverse friction stir / longitudinal friction stir treatment, the overlap rate between adjacent single passes is controlled to be 0-70%.

[0022] As an optional implementation, the overlap ratio between adjacent single passes during the transverse friction stir and the longitudinal friction stir is reduced to reduce the spacing between adjacent ultrafine grain regions.

[0023] As an optional embodiment, for the component to be processed, during the transverse friction stir / longitudinal friction stir treatment, the single passes are parallel to each other.

[0024] As an optional implementation, the intervals between adjacent single passes are equal, and the interval distance is 2-8 mm.

[0025] As an optional embodiment, when the depth of the stirring needle inserted into a certain deposition layer is equal to the thickness of the deposition layer, during the stir friction treatment, the stirring needle reaches the bottom of the deposition layer after being inserted into the deposition layer, so that the depth of the ultrafine crystal region reaches the entire deposition layer, and a grain gradient of ultrafine crystal region, fine crystal region, equiaxed crystal region and columnar crystal region can be formed in sequence along the deposition direction.

[0026] As an optional embodiment, when the depth of the stirring needle inserted into a certain deposition layer is less than the thickness of the deposition layer, the depth of the ultrafine crystal region is the depth of the stirring needle inserted, and a grain gradient of the original columnar crystal region, ultrafine crystal region, fine crystal region, equiaxed crystal region and columnar crystal region is formed in the deposition layer through stirring friction treatment, which appears in sequence along the deposition direction.

[0027] As an optional embodiment, for the component to be processed, the depth of the stirring needle inserted into the deposited layer remains consistent during the transverse friction stir / longitudinal friction stir treatment.

[0028] As an optional embodiment, the friction stir treatment process includes:

[0029] The diameter of the stirring needle is 1~4mm;

[0030] The rotation speed of the stirring head is 400-1800r / min;

[0031] Down force is 10000-50000N;

[0032] The stirring head feed speed is 150-600 mm / min; and

[0033] The length of the stirring needle is 1-5 mm.

[0034] As an optional embodiment, the additive manufacturing process is a metal wire feeding additive manufacturing process or a metal powder feeding additive manufacturing process.

[0035] As an optional embodiment, the method is applicable to the preparation of workpieces made of aluminum-lithium alloy, aluminum alloy, titanium alloy, magnesium alloy and high entropy alloy materials.

[0036] According to the second aspect of the present invention, there is provided an alloy component prepared by the above-mentioned additive manufacturing composite stir friction treatment method of orderly constructing an ultrafine-grained network structure, especially a large-sized aluminum alloy component or aluminum-magnesium alloy component such as that used in vehicles, aerospace and other fields.

[0037] Based on the above technical solution of the present invention, the method of the additive manufacturing composite stir friction treatment to orderly construct an ultrafine grain network structure proposed by the present invention realizes the ultrafine grain construction gradient and spatial distribution toughening by means of stir friction treatment, and prepares alloy components with a laminated structure and a spatial network distribution structure.

[0038] Among them, an ultrafine crystal grid is formed by network stirring, and a three-dimensional network of spatial ultrafine crystals is prepared by cyclic deposition; through nano-gradient hierarchical construction, a continuous gradient transition between nano-conventional coarse crystals is achieved, overcoming the shortcomings of nano-crystals themselves. Compared with nano-crystals or mixed grains of nano- and coarse crystals, the material of the ultrafine crystal regional grid structure prepared by the present invention has better strength-plastic matching, crack propagation resistance and fatigue performance. The strength of the alloy with gradient and spatial distribution structure is improved to a higher level compared with the lamination, achieving continuous gradient and local distribution enhancement and toughening of high-strength aluminum alloy ultrafine crystals, and the resulting alloy components have better performance.

[0039] It should be understood that the method of the additive manufacturing composite stir friction treatment for orderly constructing an ultrafine grain network structure proposed in the present invention, in which the composite of the additive manufacturing process and the stir friction process is adopted, is not only applicable to metal wire feeding additive manufacturing processes, such as arc fuse additive manufacturing (WAAM), electron beam fuse additive manufacturing (EBAM), laser fuse deposition additive manufacturing (LAM), etc., but also applicable to metal powder feeding additive manufacturing processes, such as selective laser melting deposition additive manufacturing (SLM), etc. In the printing process of each layer of additive manufacturing, by further performing orthogonal stir friction treatment on the deposition layer in the horizontal and vertical directions, the final printed component forms a three-dimensional grid structure with a grid distribution of ultrafine grains at the intersection of the orthogonal stir friction, thereby improving the performance of the component. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a process flow chart of the method of the present invention for orderly constructing an ultrafine grain network structure through composite stir friction processing in additive manufacturing.

[0041] Figure 2 It is a schematic diagram of the precise control method of the ultrafine grain region of the present invention.

[0042] Figure 3 Schematic diagram of the friction stir treatment process of the present invention.

[0043] Figure 4 It is a schematic diagram of the unit structure of the network structure with the ultrafine crystal region as the intersection point of the present invention.

[0044] Figure 5 It is a processing schematic diagram of the arc fuse additive manufacturing of the present invention.

[0045] Figure 6 It is a schematic diagram of the process of forming an ultrafine-grained spatial three-dimensional network structure through cross-stir friction processing in the present invention.

[0046] Figure 7 This is a schematic diagram of the ultrafine grain network structure gradient organization of the present invention.

[0047] Figure 8It is a schematic diagram of the gradient structure of a single-pass friction stir treatment part of the present invention.

[0048] Figure 9 It is a schematic diagram of the organization of a component with an ultrafine-grained continuous gradient three-dimensional network structure prepared by the method of the present invention. DETAILED DESCRIPTION

[0049] In order to better understand the technical content of the present invention, specific embodiments are given and described below with reference to the accompanying drawings.

[0050] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to be comprehensive. It should be understood that the various concepts and embodiments described above, as well as those described in more detail below, can be implemented in any of a number of ways.

[0051] High-strength deformable aluminum alloys are the most widely used lightweight materials for load-bearing aerospace structures. With the growing demand for high-load carrying and high-mobility weaponry, design concepts such as structural integration, topological configurations, and functional-structural integration are being explored in depth. High-efficiency, high-performance manufacturing of new high-strength aluminum alloy structures is key to their development. Additive manufacturing, which deposits complex structures layer by layer, is driving new material development, structural design, gradient functionalization, and high-efficiency manufacturing, and is attracting widespread attention and exploration.

[0052] WAAM offers significant advantages, including high efficiency and flexibility in manufacturing dimensions. However, the manufacturing efficiency of high-strength aluminum alloy WAAM is not well matched with its formability. Defects such as columnar grains and uneven microstructure, precipitation phase damage, and macro- and micro-cracks result in insufficient strength and toughness, limiting its engineering applications. Therefore, finding and unlocking the synergistic control of manufacturing efficiency, quality, and performance is becoming increasingly urgent.

[0053] The key to achieving the performance of traditional aluminum alloys lies in cyclic strong plastic deformation refinement and promoting the precipitation of precipitated phases, which provides new direction guidance for improving additive manufacturing organization, but how to improve the current online plastic deformation strength is the key.

[0054] Therefore, in the following embodiments, the present invention proposes a method for orderly constructing an ultrafine-grained network structure through composite stir friction treatment in additive manufacturing. By simultaneously performing stir friction treatment in arc fuse additive manufacturing, the strong plastic deformation of the stir friction treatment is utilized to promote mechanical crushing of grains in the deposited tissue, and the cross-stir friction treatment method is combined to obtain an ultrafine-grained grid tissue structure; the repeated deposition process causes the tissue that originally underwent strong plastic deformation to recover and recrystallize and grow grains, and the stir friction treatment of different spans is utilized to orderly construct the grain gradient of the deposited tissue, ultimately realizing a component with a three-dimensional network structure constructed in the ultrafine-grained region, thereby improving the performance of the component.

[0055] The primary columnar grain zone or the primary columnar grain state defined in the present application refers to the grain state of the alloy structure processed by the arc welding additive manufacturing but without the friction stir processing. The grain size of the primary columnar grain is greater than the grain size of the columnar grain zone.

[0056] In combination Figure 1 As shown in the examples, taking the metal arc welding additive manufacturing (WAAM) as an example, the method for additive manufacturing composite friction stir processing ordered construction of ultra-fine grain network structure is exemplarily described, which comprises the following steps:

[0057] According to the structure parameters of the component to be processed (taking the aluminum alloy as an example), a corresponding three-dimensional structure model is established. For the established three-dimensional structure model, the arc welding additive manufacturing process is adopted to deposit layer by layer in the upward growth manner from the first layer on the substrate according to the preset program until the deposition of the Nth layer is completed, and the required component is obtained.

[0058] In the process of depositing the first layer to the Nth layer, the friction stir processing is performed on each layer. The friction stir processing adopts the cross mode of transverse friction stir and longitudinal friction stir, so that each deposition layer presents a grid structure with the ultra-fine grain zone as the intersection point, and the final component forms a three-dimensional network structure with the ultra-fine grain zone as the intersection point. The ultra-fine grain zone is the overlapping area of the transverse friction stir and the longitudinal friction stir.

[0059] In the process of continuing melting and deposition, through the heat transfer of melting and deposition, the previous deposition layer presents a gradually decreasing trend from top to bottom due to heating, so that the friction stir processing part of the previous deposition layer presents a grain size gradually increasing grain gradient along the deposition direction.

[0060] It should be understood that in the actual production process, whether to perform friction on each deposition layer can be adjusted according to the actual situation. When the thickness of the deposition layer is relatively thin, in order to facilitate production and reduce cost, multiple deposition layers can be deposited and then subjected to friction stir processing. However, it is necessary to ensure that the thickness of the deposition layer matches the stirring depth of the stirring pin. For example, the thickness of one deposition layer is 2 mm, three layers can be deposited to obtain a 6 mm thick deposition layer, and then subjected to friction stir processing. At this time, the stirring depth is 6 mm. Of course, according to the performance needs, the complete friction stir processing can not be performed, that is, the stirring depth can be less than 6 mm.

[0061] In the optional embodiment, the grain gradient of the ultra-fine grain zone includes the ultra-fine grain zone, the fine grain zone, the equiaxed grain zone and the columnar grain zone which are sequentially superimposed along the deposition direction.

[0062] In the optional embodiment, the grain size of the ultra-fine grain is 0.5 μm to 2 μm.

[0063] In an optional embodiment, the fine-grained zone has a grain size of 2 μm to 10 μm.

[0064] In an optional embodiment, the equiaxed zone has a grain size of 5 μm to 20 μm.

[0065] In an optional embodiment, the columnar zone has a grain size of more than 20 μm.

[0066] As shown in FIG. 1, in an optional embodiment, the depth h at which the pin is inserted into the deposited layer, the diameter Φ of the pin, and the distance between each single pass during the transverse and longitudinal friction stirring are set according to the density requirement of the desired ultra-fine-grained network structure. Figure 2 In one preferred embodiment, when a wider (width b) ultra-fine-grained zone is required, the requirement is achieved by increasing the diameter of the pin.

[0067] In one preferred embodiment, when a deeper (depth h) ultra-fine-grained zone is required, the requirement is achieved by increasing the depth at which the pin is inserted into the deposited layer.

[0068] For example, when the depth at which the pin is inserted into the deposited layer is equal to the thickness of the deposited layer, i.e. the pin reaches the bottom of the deposited layer after being inserted into the deposited layer, the depth of the ultra-fine-grained zone can reach the entire deposited layer, and a grain gradient of the ultra-fine-grained zone, fine-grained zone, equiaxed zone and columnar zone sequentially presented along the deposition direction can be formed.

[0069] When the depth at which the pin is inserted into the deposited layer is less than the thickness of the deposited layer, the depth of the ultra-fine-grained zone is equal to the depth at which the pin is inserted, and a grain gradient of the original columnar zone, ultra-fine-grained zone, fine-grained zone, equiaxed zone and columnar zone sequentially presented along the deposition direction can be formed.

[0070] As shown in FIG. 2, in one preferred embodiment, during the transverse and longitudinal friction stirring, each single pass is parallel to each other.

[0071] Figure 3 In particular, the interval distance between adjacent single passes is set to be equal, and the interval distance can be controlled to be 2 to 8 mm.

[0072] In an optional embodiment, during the transverse and longitudinal friction stirring, the overlap rate between each single pass is controlled to be 0 to 70%.

[0073] In an optional embodiment, when a smaller distance between adjacent ultra-fine-grained zones is required, the overlap rate between each single pass during the transverse and longitudinal friction stirring can be reduced to achieve the requirement.

[0074] In an optional embodiment, when a smaller distance between adjacent ultra-fine-grained zones is required, the overlap rate between each single pass during the transverse and longitudinal friction stirring can be reduced to achieve the requirement.

[0075] ​During the friction stirring process, a temperature field is formed on the depositing layer being processed, so that the grains of the depositing layer in the core area of the processing site are more refined. The core area of the processing site is the area passed by the pin, so that after transverse friction stirring and longitudinal friction stirring, the grains in the overlapping area passed by the pin are refined into ultra-fine grains, so that the structure of the depositing layer forms a chessboard network structure with the ultra-fine grain area as the intersection point.

[0076] For example, in the friction stirring processing mode in which there is an equal interval between adjacent single passes, the unit structure after processing is as shown in Figure 4 The dashed part is the processing area, and the solid line part is the pin, i.e., the core area. The grains in the overlapping area of the pin are refined into ultra-fine grains (as shown in area a in Figure 4 ), which are processed by friction stirring, but in the area outside the overlapping area of the pin, the grains are refined into fine grain areas, and the un-stirred and un-frictioned part is the original columnar grain area (as shown in area b in Figure 4 ).

[0077] When the friction stirring processing mode with a lap rate of 0-70% between each single pass is used, the structure of the depositing layer does not have an original columnar grain area, and the ultra-fine grain network structure becomes more and more dense with the increase of the lap rate between single passes.

[0078] During the continuous melting and deposition process, through the heat transfer of the melting and deposition, the grain gradient finally presented by the fine grain area includes the grain gradient of the fine grain area, the equiaxed grain area and the columnar grain area stacked in turn along the deposition direction.

[0079] The grains of the original columnar grain area do not change in gradient with the continuous melting and deposition.

[0080] By controlling the length of the pin, the diameter of the pin, the insertion depth of the pin, the distance between single passes and the lap rate during transverse friction stirring and longitudinal friction stirring, the size of the ultra-fine grain local deformation area with different structural forms is prepared, the size of the grid structure is controlled, the free design of the spatial local configuration of the structure is realized, the ultra-fine grain spatial local configuration meeting the requirements is constructed, and the limitation of the current design on the performance improvement is broken through.

[0081] In the preferred embodiment, the process parameters of the friction stirring processing are as follows:

[0082] The diameter of the pin is 1-4 mm, the rotation speed of the pin is 400-1800 r / min, the downward pressure is 10000-50000 N, the feeding speed of the pin is 150-600 mm / min, and the length of the pin is 1-5 mm.

[0083] The present invention proposes a method for orderly constructing an ultrafine-grained network structure through composite stir friction treatment in additive manufacturing, in which the composite additive manufacturing process and stir friction process are used. The method is not only applicable to metal wire feeding additive manufacturing processes, such as arc fuse additive manufacturing (WAAM), electron beam fuse additive manufacturing (EBAM), laser fuse deposition additive manufacturing (LAM), etc., but also applicable to metal powder feeding additive manufacturing processes, such as selective laser melting deposition additive manufacturing (SLM), etc. In the printing process of each layer of additive manufacturing, the deposition layer is further subjected to orthogonal stir friction treatment in the horizontal and vertical directions, so that the final printed component forms a three-dimensional grid structure with a grid distribution of ultrafine grains at the intersection of the orthogonal stir friction, thereby improving the performance of the component.

[0084] Below, we take arc fuse additive manufacturing printing as an example to describe in more detail the implementation process of the method of orderly constructing an ultrafine-grained network structure using the aforementioned additive manufacturing composite stir friction processing.

[0085] (1) Establish the corresponding three-dimensional structural model based on the structural parameters of the component to be processed.

[0086] It should be understood that the method of additive manufacturing composite stir friction treatment to orderly construct an ultrafine-grained network structure proposed in the present invention is not only applicable to aluminum-lithium alloys, but also to other aluminum alloys and aluminum-lithium alloys such as Al-Cu-Mg, 2024, 2219, 6061, 7050, 7075, as well as titanium alloys, magnesium alloys and other high-entropy alloys.

[0087] In the following embodiments of the present invention, aluminum-lithium alloy (2195) is taken as an example for description.

[0088] (2) For the established three-dimensional structural model, additive manufacturing is performed along its height direction.

[0089] The conventional arc fuse additive manufacturing process in this field is used for processing. The heat source can be a metal inert gas (MIG) arc, a tungsten inert gas (TIG) arc, a CO2 gas shielded arc, a plasma arc, etc. By melting the metal wire, under the control of the program, a metal solid component is gradually formed from a line-surface-body according to the three-dimensional digital model.

[0090] In one exemplary embodiment, Figure 5 As shown, a zigzag printing path is adopted, the wire is fed through the wire feeding mechanism 1, the welding gun 2 performs arc melting and deposition on the alloy wire to obtain a deposition layer, and at the same time, gas protection is performed through the shielding gas nozzle 3.

[0091] In a more specific embodiment, the welding gun 2 is moved by the actuator to a certain position on the substrate as the starting point, the welding gun is turned on, and a high-temperature arc is obtained after the arc is struck. A high-temperature liquid molten pool is formed locally on the substrate under the action of the arc heat. At the same time, the alloy wire is fed into the molten pool through the wire feeding mechanism 1, and is melted into a liquid by the combined heating of the arc and the molten pool.

[0092] High-purity argon gas is passed through the welding gun, forming a local protective atmosphere above the molten pool to prevent oxidation. The welding gun 2 moves step by step along the preset trajectory with the execution structure, and the high-temperature molten pool begins to cool and solidify to form solid metal, which is gradually accumulated and stacked to complete the near-net additive forming of the target part.

[0093] Among them, the wire feeding mechanism adopts the front wire feeding method, and the heat source type of the welding gun is AC tungsten inert gas arc welding.

[0094] The AC frequency of the welding gun is ≥100Hz; the average current of the welding gun is 65-125A; the average voltage of the welding gun is 13-15V; Ar-CO2 mixed gas is used for protection, wherein CO2 is 18-30vol%, and the protective gas flow rate is 15-35L / min.

[0095] The diameter of the alloy wire in the wire feeding mechanism is 1 to 3 mm; the wire feeding speed of the wire feeding mechanism is 1 to 9 m / min, the heat source moving speed of the welding gun is 1 to 3 m / min, the stacked layer thickness is ≥1.5 mm, and the track overlap amount is 10% to 50%.

[0096] (3) After each layer is deposited, the current deposited layer is subjected to friction stir treatment.

[0097] like Figure 3 As shown, taking the first deposition layer as an example, the first single pass 4 of the stir friction treatment is performed first (this can be defined as a transverse stir friction treatment). After the first stir friction is completed, the second single pass 5 of the stir friction treatment is performed at a certain interval until the transverse stir friction is completed.

[0098] After the transverse friction stir treatment is completed, the forward direction of the stirring head is changed by 90 degrees to perform longitudinal friction stir treatment, forming cross friction stir, and the same interval distance as the transverse stirring is formed between each pass until the longitudinal friction stir is completed.

[0099] like Figure 6 As shown, the friction stirring action between the stirring head and the deposited layer causes the grains of the current deposited layer to be mechanically broken to obtain fine grains ( Figure 6 In the region a of part A of the treatment, the core area of ​​the treatment part has finer grains, and ultrafine grains are formed in the overlapping area after horizontal and vertical treatment ( Figure 6 The region b in part B) causes the organization of the single-layer deposited layer to form an orthogonal network structure with the ultrafine crystal region as the intersection point, as shown in FIG. Figure 6As shown in Part B.

[0100] (4) If Figure 6 As shown in FIG, the wire continues to melt and deposit on the surface of the treated deposited layer. Due to the heat transfer of melting and deposition, the grains in the remelting zone of the treated deposited layer grow, so that the stir friction treated part of the previous deposited layer presents a grain gradient with gradually increasing grain size along the deposition direction, as shown in FIG. Figure 6 Area c of part C.

[0101] like Figure 7 As shown in the figure, taking the first deposited layer after the stir friction treatment as an example, in the process of continuing the arc fuse additive manufacturing, through the heat transfer of melting deposition, the top layer of the first deposited layer is heated more, and the ultrafine grains grow into a columnar crystal state after recovery recrystallization; as the heat decreases, the middle grains recrystallize into equiaxed crystals, and as the heat decreases, the lower grains continue to recover and recrystallize and grow into a fine crystal state; while the bottom is heated less and cannot reach the recovery recrystallization temperature, so that the bottom grains retain the ultrafine grain state, thereby prompting the first deposited layer to have a grain gradient of ultrafine crystal zone, fine crystal zone, equiaxed crystal zone and columnar crystal zone along the deposition direction.

[0102] like Figure 8 As shown in the figure, after friction stir treatment, but in the fine-grained area outside the overlapping area of ​​the stirring needle, as the heat transfer of melt deposition occurs, the structure along the deposition direction shows a grain gradient of fine-grained area, equiaxed crystal area and columnar crystal area.

[0103] The grains in the area where friction stir was not performed showed the original columnar crystal state.

[0104] (5) Repeat the process of arc fuse deposition and stir friction until the component is formed to form a component with an ultrafine grain three-dimensional network structure.

[0105] Combine Figure 6 As shown in Figure 1, a network structure with ultrafine crystal regions as intersections is formed by forming printing growth deposition and each stirring friction treatment in the vertical and horizontal orthogonal directions, as shown in Figure 1. Figure 6 As shown in part D.

[0106] It should be understood that for a part to be processed, the N-layer deposition printing path and printing parameters of the processing object, such as wire feed rate, layer height, and printing path, can be obtained by processing with slicing software. Existing slicing software can be used to convert the three-dimensional part model into two-dimensional layers, divide the deposition layers, and thus drive the printing device to perform layer-by-layer deposition until the final layer, i.e., the Nth layer, is completed.

[0107] During the deposition of each deposition layer, printing can be paused after deposition is completed, and the deposition layer can be subjected to stir friction treatment according to the intervals of 60s, 120s, 180s, etc. after the arc fuse and complete cooling. The deposited part can also be subjected to stir friction during the deposition process.

[0108] In an optional embodiment, taking WAAM arc fused wire additive manufacturing as an example, the stirring head can be set to maintain a distance of 15-20 cm from the arc welding gun, and stir friction treatment can be performed on the deposited part simultaneously during deposition.

[0109] In another exemplary embodiment of the present invention, there is also provided an aluminum alloy component produced by the aforementioned method of arc fuse additive manufacturing combined with friction stir processing to orderly construct an ultrafine grain network structure.

[0110] The present invention constructs an ultrafine grain continuous gradient and realizes its localized orderly distribution through arc additive-friction stir processing, realizes the synergistic composite strengthening of WAAM high-strength aluminum alloy ultrafine grain, continuous gradient and fine grain structure configuration, constructs the spatial uneven distribution of additive tissue into a local ordered and network structured distribution of ultrafine grain, forms ultrafine grain confined enhancement on the macro structure, not only proposes a new theory and method for WAAM enhancement and toughening, but also fully integrates the concept of free design and free self-manufacturing layer by layer of additive manufacturing, proposes a new concept for shape-property collaborative manufacturing, and promotes the development and innovation of additive manufacturing.

[0111] For better understanding, the present invention is further described below with reference to several specific examples, but the processing technology is not limited thereto, and the content of the present invention is not limited thereto.

[0112] The following embodiments and comparative examples use 2195 aluminum-lithium alloy welding wire to print workpieces with dimensions of 40 mm*40 mm*40 mm in length, width and height.

[0113] The stirring head is made of tungsten-rhenium alloy, and the length and diameter of the stirring needle can be selected according to needs.

[0114] The thickness of the aluminum-lithium alloy substrate is 1 to 20 mm; the diameter of the aluminum-lithium alloy welding wire is 1 to 2 mm.

[0115] The typical composition of 2195 aluminum-lithium alloy wire is shown in Table 1.

[0116] Table 1

[0117]

[0118] Example 1

[0119] Step 1: Prepare the required micron-grade 2195 aluminum-lithium alloy into a wire with a diameter of 1.2 mm.

[0120] The process parameters of the WAAM wire-feed additive manufacturing equipment are set as follows: based on an AC tungsten inert gas welding power supply, an AC frequency of 200 Hz, an average current of 75 Hz, a voltage of 13-15 V, an Ar-CO2 mixed gas shield with a CO2 content of 28 vol%, a shielding gas flow rate of 25 L / min, a wire feeding speed of 8 m / min, a moving speed of 0.9 m / min, and a track overlap of 30%.

[0121] Step 2: The wire material in step 1 is used for arc fuse additive manufacturing. The wire is fed in a zigzag path using a wire feeding mechanism according to the preset parameters in step 1 and 3D printing is performed. After printing one layer, the printing is paused to obtain an alloy deposition layer with a thickness of 2 mm.

[0122] Step 3: Use the CNC system to stir friction treatment on the deposited layer formed in step 2. The stirring head stirs friction treatment in a zigzag path. First, construct transverse localized ultrafine crystals. At the starting point, the stirring needle is completely pressed into the deposited layer. After completing the first transverse single-pass stir friction treatment, the stirring needle is pulled out and moved to the starting point of the second transverse single-pass according to the established path. The stirring needle is again completely pressed into the deposited layer to complete the second transverse single-pass stir friction treatment. This is done until all transverse stir friction is completed. After the transverse stir friction is completed, the forward direction of the stirring head is changed by 90° and longitudinal stirring is performed to construct longitudinal localized ultrafine crystals in the same way.

[0123] The parameters of the friction stir treatment are as follows: stirring head feed speed of 320 mm / min, stirring depth of 2 mm, stirring needle diameter of 2 mm, stirring head rotation speed of 1300 r / min, down force of 35000 N, and interval between passes of 2 mm.

[0124] Step 4: Perform 3D printing using the process in step 1, and continue printing a new deposition layer on the surface of the deposition layer processed in step 3. After printing one layer, pause printing to obtain a new alloy deposition layer.

[0125] Step 5: Use the numerical control system in step 3 to perform cross stir friction treatment on the deposited layer formed in step 4.

[0126] Step 6: Repeat steps 2, 3, 4, and 5 for printing and friction stir processing (friction stir processing is a layer-by-layer process) until the component is fully formed.

[0127] Step 7: After printing is completed, wait for the molded parts to completely cool down (1-2 hours) and then open the hatch to take out the 2195 aluminum-lithium alloy ultrafine grain three-dimensional network structure parts.

[0128] Example 2

[0129] Step 1: Prepare the required micron-grade 2195 aluminum-lithium alloy into a wire with a diameter of 1.2 mm.

[0130] The process parameters of the WAAM wire-feed additive manufacturing equipment are set as follows: based on an AC tungsten inert gas welding power supply, an AC frequency of 200 Hz, an average current of 75 Hz, a voltage of 13-15 V, an Ar-CO2 mixed gas shield with a CO2 content of 28 vol%, a shielding gas flow rate of 25 L / min, a wire feeding speed of 8 m / min, a moving speed of 0.9 m / min, and a track overlap of 30%.

[0131] Step 2: The wire material in step 1 is used for arc fuse additive manufacturing. The wire is fed in a zigzag path using a wire feeding mechanism according to the preset parameters in step 1 for 3D printing. After printing one layer, the printing is paused to obtain an alloy deposition layer with a thickness of 2 mm.

[0132] Step 3: Use the CNC system to stir friction treatment on the deposited layer formed in step 2. The stirring head stirs friction treatment in a zigzag path. First, construct transverse localized ultrafine crystals. At the starting point, the stirring needle is completely pressed into the deposited layer. After completing the first transverse single-pass stir friction treatment, the stirring needle is pulled out and moved to the starting point of the second transverse single-pass according to the established path. The stirring needle is again completely pressed into the deposited layer to complete the second transverse single-pass stir friction treatment. This is done until all transverse stir friction is completed. After the transverse stir friction is completed, the forward direction of the stirring head is changed by 90° and longitudinal stirring is performed to construct longitudinal localized ultrafine crystals in the same way.

[0133] The parameters of the friction stir treatment are as follows: stirring head feed speed of 320 mm / min, stirring depth of 1 mm, stirring needle diameter of 3.5 mm, stirring head rotation speed of 1300 r / min, down force of 35000 N, and interval between passes of 2 mm.

[0134] Step 4: Perform 3D printing using the process in step 1, and continue printing a new deposition layer on the surface of the deposition layer processed in step 3. After printing one layer, pause printing to obtain a new alloy deposition layer.

[0135] Step 5: Use the numerical control system in step 3 to perform cross stir friction treatment on the deposited layer formed in step 4.

[0136] Step 6: Repeat steps 2, 3, 4, and 5 for printing and friction stir processing (friction stir processing is a layer-by-layer process) until the component is fully formed.

[0137] Step 7: After printing is completed, wait for the molded parts to completely cool down (1-2 hours) and then open the hatch to take out the 2195 aluminum-lithium alloy ultrafine grain three-dimensional network structure parts. Example 3

[0138] Step 1: Prepare the required micron-grade 2195 aluminum-lithium alloy into a wire with a diameter of 1.2 mm.

[0139] The process parameters of the WAAM wire-feed additive manufacturing equipment are set as follows: based on an AC tungsten inert gas welding power supply, an AC frequency of 200 Hz, an average current of 75 Hz, a voltage of 13-15 V, an Ar-CO2 mixed gas shield with a CO2 content of 28 vol%, a shielding gas flow rate of 25 L / min, a wire feeding speed of 8 m / min, a moving speed of 0.9 m / min, and a track overlap of 30%.

[0140] Step 2: Use the wire material in step 1 for arc fuse additive manufacturing, and use a wire feeding mechanism to feed the wire in a zigzag path according to the preset parameters in step 1 for 3D printing. After printing one layer, pause printing to obtain an alloy deposition layer with a thickness of 2 mm. Print three deposition layers continuously.

[0141] Step 3: Use the CNC system to stir friction treatment on the deposited layer formed in step 2. The stirring head stirs friction treatment in a zigzag path. First, construct transverse localized ultrafine crystals. At the starting point, the stirring needle is completely pressed into the deposited layer. After completing the first transverse single-pass stir friction treatment, the stirring needle is pulled out and moved to the starting point of the second transverse single-pass according to the established path. The stirring needle is again completely pressed into the deposited layer to complete the second transverse single-pass stir friction treatment. This is done until all transverse stir friction is completed. After the transverse stir friction is completed, the forward direction of the stirring head is changed by 90° and longitudinal stirring is performed to construct longitudinal localized ultrafine crystals in the same way.

[0142] The parameters of the friction stir treatment are as follows: stirring head feed speed of 320 mm / min, stirring depth of 5 mm, stirring needle diameter of 4 mm, stirring head rotation speed of 1300 r / min, down force of 35000 N, and interval between passes of 4 mm.

[0143] Step 4: Perform 3D printing using the process in step 1, and continue printing a new deposition layer on the surface of the deposition layer processed in step 3. After printing one layer, pause printing to obtain a new alloy deposition layer.

[0144] Step 5: Use the numerical control system in step 3 to perform cross stir friction treatment on the deposited layer formed in step 4.

[0145] Step 6: Repeat steps 2, 3, 4, and 5 for printing and friction stir processing (friction stir processing is a layer-by-layer process) until the component is fully formed.

[0146] Step 7: After printing is completed, wait for the molded parts to completely cool down (1-2 hours) and then open the hatch to take out the 2195 aluminum-lithium alloy ultrafine grain three-dimensional network structure parts. Example 4

[0147] Step 1: Prepare the required micron-grade 2195 aluminum-lithium alloy into a wire with a diameter of 1.2 mm.

[0148] The process parameters of the WAAM wire-feed additive manufacturing equipment are set as follows: based on an AC tungsten inert gas welding power supply, an AC frequency of 200 Hz, an average current of 75 Hz, a voltage of 13-15 V, an Ar-CO2 mixed gas shield with a CO2 content of 28 vol%, a shielding gas flow rate of 25 L / min, a wire feeding speed of 8 m / min, a moving speed of 0.9 m / min, and a track overlap of 30%.

[0149] Step 2: The wire material in step 1 is used for arc fuse additive manufacturing. The wire is fed in a zigzag path using a wire feeding mechanism according to the preset parameters in step 1 and 3D printing is performed. After printing one layer, the printing is paused to obtain an alloy deposition layer with a thickness of 2 mm.

[0150] Step 3: Use the CNC system to stir friction treatment on the deposited layer formed in step 2. The stirring head stirs friction treatment in a zigzag path. First, construct transverse localized ultrafine crystals. At the starting point, the stirring needle is completely pressed into the deposited layer. After completing the first transverse single-pass stir friction treatment, the stirring needle is pulled out and moved to the starting point of the second transverse single-pass according to the established path. The stirring needle is again completely pressed into the deposited layer to complete the second transverse single-pass stir friction treatment. This is done until all transverse stir friction is completed. After the transverse stir friction is completed, the forward direction of the stirring head is changed by 90° and longitudinal stirring is performed to construct longitudinal localized ultrafine crystals in the same way.

[0151] The parameters of the friction stir treatment are as follows: stirring head feed speed of 320 mm / min, stirring depth of 1.5 mm, stirring needle diameter of 2 mm, stirring head rotation speed of 1300 r / min, down force of 35000 N, and interval between passes of 6 mm.

[0152] Step 4: Perform 3D printing using the process in step 1, and continue printing a new deposition layer on the surface of the deposition layer processed in step 3. After printing one layer, pause printing to obtain a new alloy deposition layer.

[0153] Step 5: Use the numerical control system in step 3 to perform cross stir friction treatment on the deposited layer formed in step 4.

[0154] Step 6: Repeat steps 2, 3, 4, and 5 for printing and friction stir processing (friction stir processing is a layer-by-layer process) until the component is fully formed.

[0155] Step seven: after printing is completed, open the door and take out the 2195 aluminum lithium alloy ultra-fine grain three-dimensional network structure part after the part is completely cooled (1-2h). Example 5

[0156] Step one: the required micron 2195 aluminum lithium alloy is made into a wire with a diameter of 1.2mm.

[0157] The process parameters of the WAAM wire feeding additive manufacturing equipment are set: based on an alternating current tungsten electrode argon arc welding power supply, alternating current frequency 200Hz, average current 75Hz, voltage 13-15V, Ar-CO2 mixed gas is used for protection, wherein CO2 is 28vol%, protection gas flow is 25L / min, wire feeding speed is 8m / min, moving speed is 0.9m / min, and track overlap is 30%.

[0158] Step two: the wire in step one is used for arc melting wire additive manufacturing, a zigzag path is adopted, the wire feeding mechanism feeds the wire according to the preset parameters in step one and performs 3D printing, after printing a layer, the printing is paused, a layer of alloy deposition layer is obtained, and the deposition layer thickness is 2mm.

[0159] Step three: the deposition layer formed in step two is subjected to friction stir processing by using a numerical control system, the friction stir head is subjected to friction stir processing in a zigzag path, first, transverse local ultra-fine grains are constructed, at the starting point, all the stirring pins are pressed into the deposition layer, after the first transverse single pass friction stir processing is completed, the stirring pins are pulled out, and then moved to the starting point of the second transverse single pass according to the predetermined path, the stirring pins are pressed into the deposition layer again, the second transverse single pass friction stir processing is completed, and so on, until the transverse friction stir is completed; after the transverse friction stir is completed, the friction stir head is advanced in the longitudinal direction after the direction is turned by 90°, and longitudinal local ultra-fine grains are constructed in the same way.

[0160] The parameters of the friction stir processing are as follows: the feed speed of the friction stir head is 320mm / min, the stirring depth is 2mm, the diameter of the stirring pin is 2mm, the rotation speed of the friction stir head is 1300r / min, the pressing force is 35000N, and the interval between passes is 8mm.

[0161] Step four: 3D printing is performed by using the process in step one, and new deposition layers are continuously printed on the surface of the deposition layer processed in step three, after printing a layer, the printing is paused, and a new layer of alloy deposition layer is obtained.

[0162] Step five: the deposition layer formed in step four is subjected to cross friction stir processing by using the numerical control system in step three.

[0163] Step six: steps two, three, four and five are repeated in sequence until the component is completely formed.

[0164] Step seven: after printing is completed, wait for the formed part to cool completely (1-2h), open the door and take out the 2195 aluminum lithium alloy ultra-fine grain three-dimensional network structure part. Example 6

[0165] Step one: the required micron-sized 2195 aluminum lithium alloy is made into a wire with a diameter of 1.2mm.

[0166] The process parameters of the WAAM wire feeding additive manufacturing equipment are set as follows: based on an alternating current tungsten electrode argon arc welding power supply, alternating current frequency 200Hz, average current 75Hz, voltage 13-15V, Ar-CO2 mixed gas is used for protection, wherein CO2 is 28vol%, protective gas flow is 25L / min, wire feeding speed is 8m / min, moving speed is 0.9m / min, and track overlap is 30%.

[0167] Step two: the wire in step one is used for arc wire melting additive manufacturing, a zigzag path is adopted, the wire feeding mechanism feeds the wire according to the preset parameters in step one and performs 3D printing, after printing a layer, the printing is paused, a layer of alloy deposition layer is obtained, and the deposition layer thickness is 2mm.

[0168] Step three: the deposition layer formed in step two is subjected to friction stir processing by using a numerical control system, the friction stir head is subjected to friction stir processing in a zigzag path, first, transverse local ultra-fine grains are constructed, at the starting point, all the stirring pins are pressed into the deposition layer, after completing the first transverse single pass friction stir processing, the stirring pins are pulled out, and then moved to the starting point of the second transverse single pass according to the predetermined path, the stirring pins are pressed into the deposition layer again, the second transverse single pass friction stir processing is completed, and so on, until all the transverse friction stir processing is completed; after the transverse friction stir processing is completed, the friction stir head is advanced in the longitudinal direction by 90°, and then subjected to longitudinal stirring, and the longitudinal local ultra-fine grains are constructed in the same way.

[0169] The parameters of the friction stir processing are as follows: the feed speed of the friction stir head is 320mm / min, the stirring depth is 2mm, the diameter of the stirring pin is 2mm, the rotation speed of the friction stir head is 1000r / min, the pressing force is 20000N, and the interval between passes is 0mm.

[0170] Step four: 3D printing is performed by using the process in step one, and new deposition layers are continuously printed on the surface of the deposition layer processed in step three, after printing a layer, the printing is paused, and a new layer of alloy deposition layer is obtained.

[0171] Step five: the deposition layer formed in step four is subjected to cross friction stir processing by using the numerical control system in step three.

[0172] Step 6: Repeat steps 2, 3, 4, and 5 for printing and friction stir processing (friction stir processing is a layer-by-layer process) until the component is fully formed.

[0173] Step 7: After printing is completed, wait for the molded parts to completely cool down (1-2 hours) and then open the hatch to take out the 2195 aluminum-lithium alloy ultrafine grain three-dimensional network structure parts. Example 7

[0174] Step 1: Prepare the required micron-grade 2195 aluminum-lithium alloy into a wire with a diameter of 1.2 mm.

[0175] The process parameters of the WAAM wire-feed additive manufacturing equipment are set as follows: based on an AC tungsten inert gas welding power supply, an AC frequency of 200 Hz, an average current of 75 Hz, a voltage of 13-15 V, an Ar-CO2 mixed gas shield with a CO2 content of 28 vol%, a shielding gas flow rate of 25 L / min, a wire feeding speed of 8 m / min, a moving speed of 0.9 m / min, and a track overlap of 30%.

[0176] Step 2: The wire material in step 1 is used for arc fuse additive manufacturing. The wire is fed in a zigzag path using a wire feeding mechanism according to the preset parameters in step 1 and 3D printing is performed. After printing one layer, the printing is paused to obtain an alloy deposition layer with a thickness of 2 mm.

[0177] Step 3: Use the CNC system to stir friction treatment on the deposited layer formed in step 2. The stirring head stirs friction treatment in a zigzag path. First, construct transverse localized ultrafine crystals. At the starting point, the stirring needle is completely pressed into the deposited layer. After completing the first transverse single-pass stir friction treatment, the stirring needle is pulled out and moved to the starting point of the second transverse single-pass according to the established path. The stirring needle is again completely pressed into the deposited layer to complete the second transverse single-pass stir friction treatment. This continues until all transverse stir friction is completed. After the transverse stir friction is completed, the forward direction of the stirring head is changed by 90° and longitudinal stirring is performed to construct longitudinal localized ultrafine crystals in the same way.

[0178] The parameters of the friction stir treatment are as follows: stirring head feed speed of 320 mm / min, stirring depth of 2 mm, stirring needle diameter of 2 mm, stirring head rotation speed of 800 r / min, down force of 10000 N, and overlap rate between passes of 70%.

[0179] Step 4: Perform 3D printing using the process in step 1, and continue printing a new deposition layer on the surface of the deposition layer processed in step 3. After printing one layer, pause printing to obtain a new alloy deposition layer.

[0180] Step 5: Use the numerical control system in step 3 to perform cross stir friction treatment on the deposited layer formed in step 4.

[0181] Step six: repeat steps two, three, four, five printing and friction stir processing (friction stir processing is a layer-by-layer process) in turn until the component is completely formed.

[0182] Step seven: printing is completed, wait for the formed part to cool completely (1-2h), open the cabin door and take out the 2195 aluminum lithium alloy ultra-fine crystal three-dimensional network structure part. Comparative example

[0183] Step one: the required micron-sized 2195 aluminum lithium alloy is made into a wire with a diameter of 1.2 mm.

[0184] The process parameters of the WAAM wire feeding additive manufacturing equipment are set as follows: based on an alternating current tungsten electrode argon arc welding power source, alternating current frequency 200 Hz, average current 75 Hz, voltage 13-15 V, Ar-CO2 mixed gas is used for protection, wherein CO2 is 28 vol%, protective gas flow rate is 25 L / min, wire feeding speed is 8 m / min, moving speed is 0.9 m / min, and track overlap is 30%.

[0185] Step two: the wire in step one is used for arc wire melting additive manufacturing, a "zigzag" path is adopted, the wire feeding mechanism is used to feed the wire according to the preset parameters in step one and 3D printing is carried out, printing is paused after one layer is printed, and an alloy deposition layer with a thickness of 2 mm is obtained.

[0186] Step three: the deposition layer formed in step two is subjected to friction stir processing by using a numerical control system, the stirring pin of the stirring head is subjected to friction stir processing in a "zigzag" path, the stirring pin is fully pressed into the deposition layer at the starting point, the stirring pin is pulled out after completing the first single pass of friction stir processing, and the stirring pin is moved to the starting point of the second single pass according to the predetermined path, the stirring pin is again fully pressed into the deposition layer, the second single pass of friction stir processing is completed, and so on, until the entire friction stir processing is completed.

[0187] The parameters of the friction stir processing are as follows: the feeding speed of the stirring head is 320 mm / min, the stirring depth is 2 mm, the diameter of the stirring pin is 2 mm, the rotation speed of the stirring head is 1300 r / min, the pressing force is 35000 N, and the interval between passes is 2 mm.

[0188] Step four: 3D printing is carried out by using the process in step one, new deposition layers are continuously printed on the surface of the deposition layer treated in step three, printing is paused after one layer is printed, and a new alloy deposition layer is obtained.

[0189] Step five: the deposition layer formed in step four is subjected to friction stir processing by using the numerical control system in step three.

[0190] Step 6: Repeat steps 2, 3, 4, and 5 for printing and friction stir processing (friction stir processing is a layer-by-layer process) until the component is fully formed.

[0191] Step 7: After printing is completed, wait for the molded parts to completely cool down (1-2 hours) and then open the hatch to take out the 2195 aluminum-lithium alloy ultrafine grain three-dimensional network structure parts.

[0192] The formed parts of Comparative Examples 1-5 and the comparative example were subjected to tensile tests, and the test results are shown in Table 2.

[0193] Table 2

[0194]

[0195] The results show that in Examples 1-5, through the arc fuse composite stir friction treatment, under the strong stirring action of the stirring head and the planning of the stirring path, the processed material undergoes severe plastic deformation, achieving the densification, homogenization and refinement of the microstructure, and the strong plastic deformation of the deposited organization. The combination of cross stirring and secondary deposition can obtain a continuous gradient organization structure of ultrafine grains-fine grains-equiaxed grains-columnar grains, and the network structure formed has higher strength-plastic matching, elongation and fatigue performance than the laminate. This is because when the crack propagates, the process of its expansion through the action of the fine grain grid can increase its crack propagation path, thereby achieving a strengthening and toughening effect, greatly improving the strengthening and toughening of its organization. When the grid metal structure is subjected to external impact, the crack deflects, extends, and bifurcates, effectively dispersing stress and avoiding stress concentration. Compared with a single alloy material, the comprehensive properties such as plasticity and toughness are improved, thereby also improving the fatigue life of the material. At the same time, the horizontal and vertical stir friction treatment further reduces defects such as inclusions, pores and cracks formed in the alloy during the additive manufacturing process, thereby improving the quality and performance of the material.

[0196] In the comparative experiment, fine crystals were obtained between single passes through friction stir and friction stir treatment, and the performance of the material was improved to a certain extent through the refinement effect. However, compared with the dense grid structure formed by the arc additive combined with vertical and horizontal cross stirring in the present invention, its performance improvement has a certain gap.

[0197] While the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Persons skilled in the art will readily appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for orderly constructing an ultrafine grain network structure by additive manufacturing composite friction stir processing, characterized in that: The following steps are involved: According to the 3D structural model of the component to be processed, the additive manufacturing process is planned, and the material is deposited layer by layer on the substrate in an upward growth manner starting from the first layer according to the process procedure until the Nth layer is deposited to obtain the required component; In the process of depositing the first to Nth layers, each time a deposited layer is printed, a friction stir treatment is performed on the layer, wherein the friction stir treatment is performed in an orthogonal manner by using transverse friction stir and longitudinal friction stir, so that each deposited layer forms a grid structure with an ultrafine crystal region as the intersection point, and the final component forms a three-dimensional network structure with the ultrafine crystal region as the intersection point; wherein the ultrafine crystal region is the overlapping area of ​​the stirring needles during the transverse friction stir and the longitudinal friction stir; During the melt deposition process, the heat transfer of the melt deposition causes the previous deposited layer to gradually decrease from top to bottom due to the heat, so that the stir friction treated portion of the previous deposited layer presents a grain gradient with gradually increasing grain size along the deposition direction; wherein the grain gradient presented by the ultrafine grain region includes an ultrafine grain region, a fine grain region, an equiaxed grain region, and a columnar grain region sequentially superimposed along the deposition direction; The strong plastic deformation of the stir friction treatment is used to induce mechanical crushing of the grains of the deposited tissue, and the cross stir friction treatment is combined to obtain an ultrafine-grained grid tissue structure. Through repeated deposition processes, the tissue that has undergone strong plastic deformation undergoes recovery recrystallization and grain growth. The stir friction treatment with different spans is used to orderly construct the grain gradient of the deposited tissue, and finally realize the three-dimensional network structure constructed in the ultrafine-grained region.

2. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: The grain size of the ultrafine grain region is 0.5 μm to 2 μm.

3. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: The grain size of the fine grain area is 2 μm to 10 μm.

4. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: The grain size of the equiaxed crystal region is 5 μm to 20 μm.

5. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: The grain size of the columnar crystal region is greater than 20 μm.

6. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: During the friction stir treatment process, the depth of the stirring needle inserted into the deposition layer, the diameter of the stirring needle, and the distance and overlap rate between single passes during transverse friction stir / longitudinal friction stir are planned and / or adjusted according to the grid characteristics of the three-dimensional network structure of densely distributed ultrafine crystal regions and the characteristics of a single ultrafine crystal region.

7. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: Increase the diameter of the stirring needle to obtain a wider ultrafine grain area.

8. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: The depth of the stirring needle inserted into the deposited layer was increased to obtain a deeper ultrafine grain region.

9. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: During the transverse friction stir / longitudinal friction stir treatment process, the overlap rate between adjacent single passes is controlled between 0 and 70%.

10. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: For the component to be processed, during the transverse friction stir treatment / longitudinal friction stir treatment, the single passes are parallel to each other.

11. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: The interval between adjacent single passes is equal, and the interval distance is 2~8mm.

12. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: When the depth of the stirring needle inserted into a certain sedimentary layer is equal to the thickness of the sedimentary layer, during the stir friction treatment, the stirring needle reaches the bottom of the sedimentary layer after being inserted into the sedimentary layer, so that the depth of the ultrafine crystal region reaches the entire sedimentary layer, and a grain gradient of ultrafine crystal region, fine crystal region, equiaxed crystal region and columnar crystal region can be formed in sequence along the deposition direction.

13. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: When the depth of the stirring needle inserted into a certain deposition layer is less than the thickness of the deposition layer, the depth of the ultrafine grain region is the depth of the stirring needle inserted. Then, through the stirring friction treatment, a grain gradient of the original columnar grain region, ultrafine grain region, fine grain region, equiaxed grain region and columnar grain region is formed in the deposition layer in sequence along the deposition direction.

14. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to any one of claims 6 to 13, characterized in that: For the component to be processed, the depth of the stirring needle inserted into the deposited layer remains consistent during the transverse stir friction / longitudinal stir friction treatment.

15. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: The friction stir treatment process includes: The diameter of the stirring needle is 1~15mm; The rotation speed of the stirring head is 400-1800r / min; Down force is 10000-50000N; The stirring head feed speed is 150-600 mm / min; and The length of the stirring needle is 1-10 mm.

16. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: The additive manufacturing process is a metal wire feeding additive manufacturing process or a metal powder feeding additive manufacturing process.

17. The method for orderly constructing an ultrafine grain network structure by composite friction stir processing in additive manufacturing according to claim 1, characterized in that: The method is suitable for preparing workpieces made of aluminum-lithium alloy, aluminum alloy, titanium alloy, magnesium alloy and high-entropy alloy materials.

18. A component manufactured by the method for orderly constructing an ultrafine grain network structure by additive manufacturing composite friction stir processing according to any one of claims 1 to 17.

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