Stirring head and method for preparing functional matching composite structure through critical configuration

Abstract

The invention provides a stirring head and a method for preparing a functional matching composite structure through critical configuration, and particularly relates to the field of additive manufacturing of multi-layer composite structures. The stirring head sequentially comprises a sleeve and a dumbbell-shaped stirring needle, and the dumbbell-shaped stirring needle comprises a shaft shoulder, a dumbbell body small end, a dumbbell body conical rod and a dumbbell body large end which are sequentially and coaxially connected. According to the method, when the composite material is added, various parameters of a composite structure are designed according to needed functions and the performance of a plate, then a critical state is defined, the material adding sequence and the material adding process are formulated, a proper stirring head is selected according to the critical state, the process parameters of the stirring head are determined, and finally material adding treatment is conducted according to the requirements. According to the dumbbell-shaped stirring needle, an annular strong flow area is formed by a metal material during material adding, impact deformation occurs on interfaces on the premise that mutual mixing does not occur, the form complexity of the bonding interfaces is increased, the bonding strength of the bonding interfaces is effectively improved, and the connection strength is further improved.

Description

Technical Field

[0001] The present invention relates to the field of additive manufacturing of multi-layer composite structures, and particularly to a stirring head and a method for preparing a function-matched composite structure with a critical configuration. Background Art

[0002] With the continuous improvement of the requirements for manufacturing structures, a single alloy often cannot meet multiple requirements such as high strength, high toughness, strong corrosion resistance, and extreme working environments simultaneously. Taking aluminum alloys as an example, different types of alloys often have different advantages and disadvantages. The 7xxx series aluminum alloys have relatively high strength but poor toughness; the 2xxx series aluminum alloys have excellent strength and toughness but poor corrosion resistance; while the 1xxx and 4xxx series aluminum alloys have good corrosion resistance but low strength. Therefore, through matching design, combining the advantages of different alloys to obtain a multi-layer composite structure alloy component with controllable functions is one of the methods to improve the applicability of manufacturing structures.

[0003] The preparation of multi-layer composite structures is one of the methods for preparing multi-functional materials. Currently, many scholars prepare multi-layer composite structures through methods such as hot or cold rolling forming of multi-layer plates, explosive welding, etc. Rolling forming can obtain a composite structure with a clear interface, and each layer of material can maintain its own performance characteristics. However, the interfacial connection strength of rolling forming is relatively low, and delamination failure is likely to occur during use, making it difficult to ensure the structural strength during use. For multi-layer composite structures prepared by melting welding methods such as explosive welding, the materials between layers melt and mix, easily generating defects such as pores and cracks in the connection area. The mixing between different layers of materials will cause the original functionality of the materials to be disordered, which is not conducive to restoring the functional design requirements.

[0004] Friction stir additive manufacturing of multi-layer composite structures is a process in which a rapidly rotating stirring tool causes intense plastic flow of the material, and metallurgical connection of the interfacial materials occurs under the combined action of heat and stirring. Since this method is a solid-phase processing manufacturing technology, its heat input is relatively low, and it will not produce defects such as pores and cracks generated by fusion welding, showing good development prospects in the field of multi-layer composite structure preparation.

[0005] The patent with the application number CN202411000117.X discloses a friction stir additive manufacturing method. By adding additive raw materials to the device, the additive raw materials are plasticized, and then the device is driven to move in the first direction to form the first deposition layer. Finally, the device is driven to move in the second direction to tightly combine with the first deposition layer to form the second deposition layer. However, when forming the second deposition layer, the stirring pin penetrates into the first deposition layer to form the second deposition layer in the first deposition layer, which directly causes the mixing of materials between the first deposition layer and the second deposition layer, resulting in changes in the performance of the additive raw materials themselves and the overall performance of the component, and reducing the restoration degree of the designed performance of the component.

[0006] The patent with the application number CN202410886274.9 discloses a method for preparing a laminated metal composite component based on friction stir additive manufacturing. By using a specific friction stir additive device, the stirring pin is inserted into the material to be added. After the metal wire inside the stirring head reaches the thermoplastic state, the additive raw material is deposited layer by layer on the surface of the substrate under the action of the top force, avoiding the generation of defects such as voids and cracks caused by inconsistent solidification shrinkage of dissimilar materials. However, during the additive process, the insertion of the stirring pin into the substrate causes material mixing, changing the properties of the component and making it impossible to restore the designed properties.

[0007] The patent with the application number CN202410936752.2 discloses a method for preparing and applying an aluminum-steel composite plate. After overlapping the decontaminated steel plate and aluminum alloy plate, they are connected by friction stir additive to obtain the plate. The stirring pin does not penetrate into the lower steel plate and is 0.15 - 0.3 mm away from the lower steel plate, obtaining a flat bonding interface with a relatively thin compound. However, the interface bonding completely relies on the brittle and hard intermetallic compound, the bonding strength is low, and the bonding strength is sensitive to the morphology of the compound. Moreover, aging heat treatment is required after additive manufacturing, and the process is relatively complex.

[0008] Currently, the core key of the friction stir additive manufacturing method for preparing multi-layer composite structures is how to obtain a multi-layer composite structure with both high bonding strength and high functional design reduction. In order to obtain a multi-layer composite structure without defects, excellent overall structural performance, and high performance reduction, the present invention proposes a stirring head suitable for friction stir additive manufacturing in a supercritical configuration state, and a method for preparing a multi-functional matching composite structure using the stirring head, which can effectively design and prepare functional multi-layer structures, realize the control of component properties, and is of great significance for the manufacturing of functional alloys. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a stirring head and a method for preparing a function-matching composite structure in a critical configuration aiming at the deficiencies of the above-mentioned prior art.

[0010] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0011] A stirring head, the stirring head includes a sleeve and a dumbbell-shaped stirring needle. The dumbbell-shaped stirring needle is fixedly connected to the corresponding device through the sleeve. The dumbbell-shaped stirring needle includes a shoulder, a small end of the dumbbell body, a tapered rod of the dumbbell body, and a large end of the dumbbell body that are coaxially connected in sequence. The lower surface of the shoulder is fixedly connected to the upper surface of the small end of the dumbbell body. The side surface of the small end of the dumbbell body is a convex arc surface. The lower surface of the small end of the dumbbell body is fixedly connected to the upper surface of the tapered rod of the dumbbell body. An annular thread groove is machined on the side surface of the tapered rod of the dumbbell body. The lower surface of the tapered rod of the dumbbell body is fixedly connected to one surface of the large end of the dumbbell body. The large end of the dumbbell body is in the shape of a flying saucer with the largest diameter in the middle. A plurality of annular trapezoidal grooves are machined on the lower surface of the large end of the dumbbell body.

[0012] The diameter of the shoulder is greater than the diameter of the upper surface of the small end of the dumbbell body. The diameter of the lower surface of the small end of the dumbbell body is greater than the diameter of the upper surface of the tapered rod of the dumbbell body. And the difference between the diameter of the lower surface of the small end of the dumbbell body and the diameter of the lower surface of the tapered rod of the dumbbell body is 1 mm - 2 mm. Three times the diameter of the upper surface of the tapered rod of the dumbbell body is less than the diameter of the upper surface of the small end of the dumbbell body. The maximum diameter of the large end of the dumbbell body is greater than the diameter of the lower surface of the small end of the dumbbell body and less than the diameter of the shoulder.

[0013] The included angle α between the tangent plane at any point of the intersection line of the arc surface of the small end of the dumbbell body and the shoulder and the lower surface of the shoulder is 10° - 15°.

[0014] The number of annular thread grooves on the side surface of the tapered rod of the dumbbell body is 1 - 6.

[0015] The diameter of the annular trapezoidal groove on the lower surface of the large end of the dumbbell body is 0.1 mm - 1 mm, the depth is 0.05 mm - 0.1 mm, and the inner edge slope is 0° - 3°.

[0016] The length of the tapered rod of the dumbbell body is set according to different plate thicknesses, and the setting range is 0.5 mm - 5 mm.

[0017] The included angle γ between the edges of the upper and lower surfaces of the large end of the dumbbell body where they meet is 10° - 30°.

[0018] The thickness of the large end of the dumbbell body in the straight direction is 0.5 mm - 3 mm.

[0019] The number of annular trapezoidal grooves on the lower surface of the large end of the dumbbell body is 0 - 5.

[0020] A method for preparing a function-matched composite structure by critical configuration using the above-mentioned stirring head, the specific process is as follows:

[0021] Step 1: Determine the sheet materials that require a multi-layer composite structure. Design the composite structure based on the required functions and the properties of the sheet materials themselves, including: "strength + anti-corrosion" matching or "conductivity + anti-corrosion" matching; determine the number of layers, thickness, length, types, and matching order of the composite structure.

[0022] Step 2: Define the critical state. Define that the upper layer at the interface junction of adjacent sheets ≤ 0.1 mm is the upper critical, and the upper critical is applicable to the additive manufacturing between dissimilar materials; define that the lower layer at the interface junction of adjacent sheets ≤ 0.1 mm is the lower critical, and the lower critical is applicable to the additive manufacturing between the same materials.

[0023] Step 3: Determine the additive manufacturing sequence and additive manufacturing process according to principles such as the characteristics of the composite sheet and structural symmetry, including: formulating a suitable process sequence, selecting the critical state of the sheet according to the properties and dimensions of the sheet, selecting a suitable stirring head according to the critical state, ensuring that while meeting the downward pressure, the bottom surface of the stirring head is within the critical state, and determining the traveling speed, depth, number of passes, rotation direction, and traveling direction of the stirring head.

[0024] Step 4: Carry out the additive manufacturing of the multi-layer composite structure. Axially connect the sleeve of the stirring head to the main shaft of the friction stir additive manufacturing equipment, and perform the additive manufacturing treatment on the multi-layer composite structure according to Step 1, Step 2, and Step 3.

[0025] The beneficial effects produced by adopting the above technical solutions are as follows:

[0026] The present invention aims at the design and preparation of a multi-layer composite structure of the same or different alloys, and uses the supercritical friction stir additive manufacturing technology to manufacture a gradient composite structure. The critical configuration state enables the interface materials to undergo high-speed impact and form good metallurgical bonding while the multi-layer materials do not mix. The interface deforms under the high-speed flow and impact of the upper-layer material, forming a mechanical interlock at the interface and increasing the interface bonding length. The present invention combines "metallurgical bonding + mechanical interlock", enabling the multi-layer composite structure to have high overall performance. At the same time, it ensures a high reduction degree of the designed functions of the multi-layer composite structure and high manufacturability, reduces the loss of the performance of the composite structure during the manufacturing process, and improves the reduction degree of the composite structure design.

[0027] The present invention uses a dumbbell-shaped stirring pin with a brand-new design. The design of the large end of the dumbbell body promotes the high-speed flow of materials near the interface at the lower end of the large end of the dumbbell body along the dumbbell shape. The interface undergoes impact deformation without mutual mixing, increasing the complexity of the combined interface morphology and effectively improving the bonding strength of the combined interface. The shape of the large end of the dumbbell body can promote the flow of metal materials to both sides, flowing upward along the arc surface of the large end of the dumbbell body towards the upper part of the dumbbell-shaped stirring pin. At the same time, the upper plate flows downward under the combined action of the small end of the dumbbell body and the threaded tapered rod of the dumbbell body, forming a circular strong flow area of metal materials and further improving the connection strength. In addition, the large contact area of the large end of the dumbbell body can obtain the temperature required for additive interface bonding in a short time, increase the interface connection area, improve the single additive area, and effectively improve the additive manufacturing efficiency of the multi-layer composite structure.

[0028] When the present invention is used for riveting and welding connections, the structural edge of the large end of the dumbbell body can form a mechanical interlock between dissimilar materials, greatly improving the bonding strength between difficult-to-connect dissimilar metals. At the same time, multiple annular trapezoidal grooves are designed on the lower end surface of the large end of the dumbbell body. When the stirring head rotates at high speed and presses down and contacts the lower plate, this can promote the upward deformation and curling of the large end of the dumbbell body, thereby forming a better mechanical interlock, further improving the strength of the mechanical interlock and forming a high-quality riveted and welded joint. Description of the Drawings

[0029] Figure 1 It is the front view of the sleeve of the present invention;

[0030] Figure 2 It is the main cross-sectional view of the sleeve of the present invention;

[0031] Figure 3 It is the bottom view of the sleeve of the present invention;

[0032] Figure 4 It is the front view of the dumbbell-shaped stirring pin of the present invention;

[0033] Figure 5 It is the vertical view of the dumbbell-shaped stirring pin of the present invention;

[0034] Figure 6 It is the bottom view of the dumbbell-shaped stirring pin of the present invention;

[0035] Figure 7 It is the main cross-sectional view of the dumbbell-shaped stirring pin of the present invention;

[0036] Figure 8 It is the schematic diagram of supercritical lap joint of the present invention;

[0037] Figure 9 It is the schematic diagram of the cross-section and fracture interface of the composite structure in Example 1 of the present invention;

[0038] Figure 10Schematic diagram of the fracture cross-section of the composite structure in Embodiment 2 of the present invention;

[0039] Figure 11 Schematic diagram of the friction stir riveting welding process in Embodiment 3 of the present invention;

[0040] Figure 12 Schematic diagram of the cross-section of the composite structure in Embodiment 3 of the present invention;

[0041] 1 - Sleeve; 2 - Dumbbell-shaped stirring pin; 21 - Shoulder; 22 - Small end of the dumbbell body; 23 - Tapered rod of the dumbbell body; 24 - Large end of the dumbbell body; d z - Diameter of the shoulder; d s1 - Diameter of the upper surface of the small end of the dumbbell body; d s2 - Diameter of the lower surface of the small end of the dumbbell body; d m1 - Diameter of the upper surface of the tapered rod of the dumbbell body; d m2 - Diameter of the lower surface of the tapered rod of the dumbbell body; d b - Maximum diameter of the large end of the dumbbell body; α - Angle between the tangent plane at any point on the intersection line of the arc surface of the small end of the dumbbell body and the shoulder and the lower surface of the shoulder; γ - Angle at the junction of the upper and lower surface edges of the large end of the dumbbell body. Detailed implementation manners

[0042] The following combines the accompanying drawings and embodiments to further describe in detail the specific implementation manners of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0043] As Figures 1-12 shown, the present invention provides a stirring head, the stirring head is a split dumbbell-shaped stirring head, and at the same time provides a method for preparing a function-matched composite structure by using the critical configuration of the stirring head, and prepares a multi-function-matched composite structure under the conditions of supercritical configuration friction stir additive manufacturing.

[0044] Embodiment 1

[0045] A stirring head provided in this embodiment includes a sleeve 1 and a dumbbell-shaped stirring needle 2, wherein the dumbbell-shaped stirring needle 2 includes a shoulder 21, a dumbbell body small end 22, a dumbbell body tapered rod 23 and a dumbbell body large end 24 which are coaxially connected in sequence, and the shoulder 21 of the dumbbell-shaped stirring needle 2 is fixedly connected to the main shaft of the stirring friction device through the sleeve 1, and the sleeve 1 is sleeved outside the shoulder 21 and fastened from the side by bolts. The upper surface of the dumbbell body small end 22 is fixedly connected to the lower surface of the shoulder 21, wherein the side surface of the dumbbell body small end 22 is an outwardly convex arc surface, and the angle α between the section of any point of the intersection of the arc surface and the shoulder 21 and the lower surface of the shoulder 21 is 10°. The lower surface of the dumbbell body small end 22 is fixedly connected to the upper surface of the dumbbell body tapered rod 23, and the dumbbell body tapered rod 23 is a cone with a thick upper part and a thin lower part, and an annular thread groove is processed on the side surface of the dumbbell body tapered rod 23. The dumbbell body big end 24 is fixedly connected to the lower surface of the dumbbell body conical rod 23 away from the dumbbell body small end 22. An annular trapezoidal groove is processed on the lower surface of the dumbbell body big end 24. The dumbbell body big end 24 is in the shape of a flying saucer, with the largest diameter in the middle. The angle γ where the upper and lower surface edges of the dumbbell body big end 24 meet is 20°; the thickness of the dumbbell body big end 24 in the straight direction is 1mm. The stirring head proposed by the present invention can be critically configured to prepare a functional matching composite structure. This embodiment uses the above-mentioned stirring head to prepare a 5083-2024-5083 aluminum alloy functional composite material. The specific critical configuration method for preparing a functional matching composite structure is:

[0046] Step 1: Determine the composite sheet that needs to be added, and design the composite structure based on the required functions and the performance of the sheet itself, including: "strength + anti-corrosion" matching or "conductivity + anti-corrosion" matching, etc., and determine the number of layers, thickness, length, type, matching order, etc. of the composite structure.

[0047] In this embodiment, the raw materials of 5083 aluminum alloy and 2024 aluminum alloy are first evaluated and screened to obtain the basic properties of the materials. Based on the measured properties, it can be seen that 2024 aluminum alloy has higher strength, and 5083 aluminum alloy has better corrosion resistance and toughness. Therefore, the composite structure of this embodiment is determined to be a "hard inside and soft outside" gradient matching combined with an outer layer of anti-corrosion aluminum alloy multilayer structure design, and the size of the aluminum alloy plate is selected to be 200mm×100mm×2mm.

[0048] Step 2, define the critical state: define the upper layer of the interface bonding ≤0.1mm as the upper critical state, which is the diffusion connection of stir friction, define the lower layer of the interface bonding ≤0.1mm as the lower critical state, which is the micro-mixing connection of stir friction. The upper critical state is more suitable for additives between dissimilar materials, which can ensure that the materials are not mixed. The lower critical state is more suitable for additives between the same materials and additives that need to meet the high strength of composite plates, because the micro-mixing of materials has less effect on performance and the interface bonding is better.

[0049] In this embodiment, according to the different properties of 5083 aluminum alloy and 2024 aluminum alloy, the upper critical state is determined. Since the critical state is the basis for fabricating the composite plate, it can ensure that the function of the fabricated composite plate is consistent with that of the initially designed composite plate.

[0050] Step 3: Determine the additive manufacturing sequence and additive manufacturing process according to principles such as the characteristics of the composite plate material and structural symmetry, including: formulating a suitable process sequence, selecting the critical state of the plate according to the performance and size of the plate, selecting a suitable dumbbell-shaped stirring head according to the critical state, ensuring that while meeting the downward pressure amount, the bottom surface of the stirring head is within the critical state, and determining process parameters such as the traveling speed, depth, number of passes, rotation direction, and traveling direction of the dumbbell-shaped stirring head.

[0051] In this embodiment, the material of the dumbbell-shaped stirring pin 2 is H13 tool steel. The dimensions of the dumbbell-shaped stirring pin 2 selected according to the upper critical state are: the diameter d of the shoulder 21 z is 15 mm; the diameter d of the upper surface of the small end 22 of the dumbbell body s1 is 6 mm, the diameter d of the lower surface of the small end 22 of the dumbbell body s2 is 4 mm, and the thickness of the small end 22 of the dumbbell body is 1 mm; the length of the tapered rod 23 of the dumbbell body is 2.7 mm, the diameter d of the upper surface of the tapered rod 23 of the dumbbell body m1 is 3 mm, the diameter d of the lower surface of the tapered rod 23 of the dumbbell body m2 is 2 mm; the maximum diameter d of the large end 24 of the dumbbell body b is 8 mm, the diameter of the annular trapezoidal groove on the bottom surface is 1 mm, the depth is 0.1 mm, and the inner slope is 2°. The overall length of the dumbbell-shaped stirring pin 2 is 4 mm.

[0052] The process parameters of the dumbbell-shaped stirring head are: the rotation direction of the stirring head is selected as counterclockwise rotation, the rotation speed is 1000 rpm / min, the traveling speed is 50 mm / min, the downward pressure amount of the shoulder 21 is selected as 0.2 mm, and the residence time is 10 s. The composite structure is formed by two-pass friction stir additive manufacturing, and the additive manufacturing direction is from the middle to both sides.

[0053] Step 4: Carry out additive manufacturing of the multi-layer composite structure. Connect the sleeve 1 of the dumbbell-shaped stirring head in Step 3 to the shoulder 21, and then axially connect the sleeve 1 to the main shaft of the friction stir additive manufacturing equipment. Carry out additive manufacturing treatment on the multi-layer composite structure according to Step 1, Step 2, and Step 3. Before additive manufacturing, clean the surface of the aluminum alloy plate to prevent affecting the quality of the bonding interface between adjacent plates.

[0054] In this embodiment, under the condition that the pressing amount of the shaft shoulder 21 is 0.2 mm, the interface of the friction stir additive manufactured component of 5083-2024-5083 aluminum alloy has good bonding, no defects, and there is no material mixing between adjacent plates. The tensile test results show that the multi-layer composite structure fabricated this time fractures as a whole along 45°, indicating that the fabricated structure has good overall strength. The implementation effect diagram is as shown in Figure 9 shown. The results of the embodiment show that it is feasible to prepare a high-performance multi-functional matching gradient composite structure by friction stir additive manufacturing in a supercritical configuration state.

[0055] Embodiment 2

[0056] In this embodiment, a supercritical friction stir additive manufacturing technology is used to design and prepare an alloy structure of 2024Al / Zn / 316L stainless steel.

[0057] Step 1: Select a 2-mm-thick 2024 aluminum alloy plate and 1.5-mm-thick 316L stainless steel as the base materials, and the thickness of the middle Zn layer is 0.02 mm.

[0058] Step 2: Since the materials of the composite structure are different, the upper critical state is selected.

[0059] Step 3: Select a dumbbell-shaped stirring pin 2 made of H13 tool steel. According to the upper critical state, the dimensions of the dumbbell-shaped stirring pin 2 of the stirring head are as follows: the diameter d of the shaft shoulder 21 z is 13.5 mm, the upper surface diameter d of the small end 22 of the dumbbell body s1 is 4 mm, the diameter d of the lower surface of the small end 22 of the dumbbell body s2 is 3 mm, and the thickness of the small end 22 of the dumbbell body is 1 mm; the length of the conical rod 23 of the dumbbell body is 1.5 mm, and the diameter d of the upper surface of the conical rod 23 of the dumbbell body m1 is 2.5 mm, the diameter d of the lower surface of the conical rod 23 of the dumbbell body m2 is 1.5 mm; a right-handed annular thread groove is engraved on the side surface of the conical rod 23 of the dumbbell body, and the maximum diameter d of the large end 24 of the dumbbell body b is 6 mm, the number of annular trapezoidal grooves on the bottom surface is one, the diameter is 1 mm, the depth is 0.1 mm, and the inner slope is 2°. The overall length of the dumbbell-shaped stirring pin 2 is 1.7 mm.

[0060] Set the rotation direction of the stirring head to counterclockwise rotation, the rotation speed to 1600 rad / min, the traveling speed to 50 mm / min, the pressing depth of the dumbbell-shaped stirring pin 2 to 0.5 mm above the Zn foil, and the additive direction to be consistent with the rolling direction of the composite structure plate, and the additive direction is from top to bottom.

[0061] Step 4: Carry out additive manufacturing of the multi-layer composite structure. Connect the sleeve 1 of the stirring head in Step 3 to the shoulder 21, and then axially connect the sleeve 1 to the main shaft of the friction stir additive manufacturing equipment. Carry out additive manufacturing on the multi-layer composite structure according to Steps 1, 2, and 3. Before additive manufacturing, clean the surface of the aluminum alloy plate to prevent affecting the quality of the bonding interface between adjacent plates.

[0062] In this embodiment, the joint morphology was observed, and it was found that the interface between the 2024 aluminum alloy plate and the steel plate in the upper critical friction stir additive manufacturing was well bonded, and the overall joint showed tensile fracture. The implementation effect diagram is as Figure 10 shown, which indicates that it is feasible to prepare a multi-functional matching gradient composite structure by friction stir additive manufacturing under supercritical conditions.

[0063] Embodiment 3

[0064] In this embodiment, a designed dumbbell-shaped stirring head and supercritical (lower critical) configuration friction stir riveting technology were used to design and prepare a riveting structure of 2024Al / DP590 stainless steel. The specific process is as Figure 11 shown. The stirring head provided by the present invention can be used for high-strength friction stir riveting of alloys in the "soft + hard" configuration state.

[0065] Step 1: Select a 2-mm-thick 2024 aluminum alloy plate and a 1.5-mm-thick DP590 stainless steel as the base materials.

[0066] Step 2: Select the lower critical state.

[0067] Step 3: Make a dumbbell-shaped stirring pin 2 from DP590 stainless steel, and use the dumbbell-shaped stirring pin 2 as a riveting rivet. According to the lower critical state, the dimensions of the dumbbell-shaped stirring pin 2 of the stirring head are determined as follows: the diameter d of the shoulder 21 z is 13.5 mm, the upper surface diameter d of the small end 22 of the dumbbell body s1 is 4 mm, the diameter d of the lower surface of the small end 22 of the dumbbell body s2 is 3 mm, and the thickness of the small end 22 of the dumbbell body is 1 mm; the length of the tapered rod 23 of the dumbbell body is 1.5 mm, and the upper surface diameter d of the tapered rod 23 of the dumbbell body m1 is 2.5 mm, the diameter d of the lower surface of the tapered rod 23 of the dumbbell body m2 is 1.5 mm; a right-handed annular thread groove is engraved on the side surface of the tapered rod 23 of the dumbbell body, and the maximum diameter d of the large end 24 of the dumbbell body b is 6 mm, the number of annular trapezoidal grooves on the bottom surface is one, the diameter is 1 mm, the depth is 0.1 mm, and the inner slope is 2°. The overall length of the dumbbell-shaped stirring pin 2 is 1.7 mm.

[0068] Set the rotation direction of the stirring head to counterclockwise rotation, the rotation speed to 1600 rad / min, and the dumbbell-shaped stirring pin 2 to plunge into the 2024 aluminum alloy at a plunge speed of 2 mm / min. Plunge to a position 0.08 mm from the upper and lower interfaces, rotate and stay for 30 s; then rotate and plunge down at 8 mm / min to 0.08 mm below the DP590 stainless steel, and stop rotating. When the rivet touches the lower-layer DP590 stainless steel, the large end 24 of the dumbbell body deforms and bends upward. At this time, stop rotating. While the rivet undergoes metallurgical bonding with the lower-layer DP590 stainless steel, the deformed area plunges into the upper-layer 2024 aluminum alloy and forms a mechanical interlock with the upper-layer 2024 aluminum alloy, forming a high-strength riveted welding joint with "metallurgical bonding + mechanical interlock". Finally, unlock the split sleeve 1 to complete the friction stir riveting of the functional matching composite structure under the critical configuration.

[0069] Step 4: Carry out riveting of the multi-layer composite structure. Connect the sleeve 1 of the stirring head in Step 3 to the shoulder 21, and then axially connect the sleeve 1 to the main shaft of the friction stir welding equipment. Carry out riveting treatment on the multi-layer composite structure according to Steps 1, 2, and 3. Before riveting, clean the surface of the aluminum alloy plate to prevent affecting the quality of the bonding interface between adjacent plates.

[0070] In this embodiment, the morphology of the joint was observed macroscopically, and it was found that the aluminum alloy plate and the steel plate had good bonding during the lower critical friction stir spot welding, and the stirring pin and the steel plate and the aluminum alloy formed a "metallurgical bonding + mechanical interlock" riveted welding joint. The implementation effect diagram is as Figure 12 shown. It shows that it is feasible to weld dissimilar alloy spot welding joints by friction stir riveting under the supercritical state.

[0071] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope defined by the claims of the present invention.

Claims

1. A stirring head, characterized in that: The stirring head comprises a sleeve (1) and a dumbbell-shaped stirring needle (2), the dumbbell-shaped stirring needle (2) being fixedly connected to a corresponding device through the sleeve (1), the dumbbell-shaped stirring needle (2) comprising a shaft shoulder (21), a dumbbell body small end (22), a dumbbell body conical rod (23) and a dumbbell body large end (24) which are coaxially connected in sequence, the lower surface of the shaft shoulder (21) being fixedly connected to the upper surface of the dumbbell body small end (22), and the side surface of the dumbbell body small end (22) being fixedly connected to the upper surface of the dumbbell body small end (24). The dumbbell body has a convex arc surface, the lower surface of the dumbbell body small end (22) is fixedly connected to the upper surface of the dumbbell body tapered rod (23), the side surface of the dumbbell body tapered rod (23) is processed with an annular thread groove, the lower surface of the dumbbell body tapered rod (23) is fixedly connected to one side of the dumbbell body large end (24), the dumbbell body large end (24) is in the shape of a flying saucer, the middle part has the largest diameter, and the lower surface of the dumbbell body large end (24) is processed with a plurality of annular trapezoidal grooves.

2. A stirring head according to claim 1, characterized in that: The diameter of the shaft shoulder (21) is larger than the diameter of the upper surface of the dumbbell body small end (22), the diameter of the lower surface of the dumbbell body small end (22) is larger than the diameter of the upper surface of the dumbbell body tapered rod (23), and the difference between the diameter of the lower surface of the dumbbell body small end (22) and the diameter of the lower surface of the dumbbell body tapered rod (23) is 1 mm to 2 mm, three times the diameter of the upper surface of the dumbbell body tapered rod (23) is smaller than the diameter of the upper surface of the dumbbell body small end (22), and the maximum diameter of the dumbbell body large end (24) is larger than the diameter of the lower surface of the dumbbell body small end (22) and smaller than the diameter of the shaft shoulder (21).

3. A stirring head according to claim 1, characterized in that: The included angle α between a tangent plane at any point of the intersection line between the arc surface of the dumbbell body small end (22) and the shaft shoulder (21) and the lower surface of the shaft shoulder (21) is 10° to 15°.

4. A stirring head according to claim 1, characterized in that: The number of the annular thread grooves on the side surface of the dumbbell-shaped tapered rod (23) is 1 to 6.

5. A stirring head according to claim 1, characterized in that: The annular trapezoidal groove on the lower surface of the dumbbell body large end (24) has a diameter of 0.1 mm to 1 mm, a depth of 0.05 mm to 0.1 mm, and an inner edge slope of 0° to 3°.

6. A stirring head according to claim 1, characterized in that: The length of the dumbbell-shaped tapered rod (23) is set according to the thickness of the plate, and the setting range is 0.5 mm to 5 mm.

7. A stirring head according to claim 1, characterized in that: The angle γ where the upper and lower surface edges of the dumbbell body large end (24) meet is 10° to 30°.

8. A stirring head according to claim 1, characterized in that: The thickness of the dumbbell body large end (24) in the straight direction is 0.5 mm to 3 mm.

9. A stirring head according to claim 1, characterized in that: The number of annular trapezoidal grooves on the lower surface of the dumbbell body large end (24) is 0 to 5.

10. A method for preparing a functionally matched composite structure by critical configuration using the stirring head of claim 1, characterized in that: The specific process of the method is: Step 1: Determine the plate material that needs a multi-layer composite structure, and design the composite structure based on the required functions and the performance of the plate material itself, including: "strength + anti-corrosion" matching or "conductivity + anti-corrosion" matching; determine the number of layers, thickness, length, type, and matching order of the composite structure; Step 2, define the critical state, define the upper layer of the interface of adjacent plates ≤ 0.1mm as the upper critical state, and the upper critical state is applicable to the additive between different materials; define the lower layer of the interface of adjacent plates ≤ 0.1mm as the lower critical state, and the lower critical state is applicable to the additive between the same materials; Step 3: Formulate the additive sequence and additive process according to the principles of composite plate characteristics and structural symmetry, including: formulating a suitable process sequence; selecting the critical state of the plate according to the performance and size of the plate, selecting a suitable stirring head according to the critical state, ensuring that the stirring head meets the downward pressure and the bottom surface of the stirring head is located within the critical state, and determining the travel speed, depth, pass number, rotation direction and travel direction of the stirring head; Step 4: Carry out additive processing on the multi-layer composite structure, axially connect the sleeve of the stirring head to the main shaft of the friction stir additive equipment, and perform additive processing on the multi-layer composite structure according to steps 1, 2 and 3.

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