A method for pre-setting high-entropy alloy powder to enhance the performance of dissimilar metal friction stir welding seams

Abstract

The application discloses a method for enhancing the performance of a dissimilar metal friction stir welding joint by using a pre-set high-entropy alloy powder, belongs to the field of friction stir welding, and aims at solving the problem of low mechanical performance of a joint during dissimilar metal friction stir welding. Before dissimilar metal welding, high-entropy alloy powder particles are filled into a soft base metal by using friction stir welding, so that the powder particles are prevented from overflowing outwards during welding, the initial homogenization distribution of the powder particles in the base metal is realized, and the performance inconsistency between the dissimilar base metals is weakened, the homogenization plastic flow of the materials at the welding interface is promoted, and good welding joint formation is obtained. During dissimilar metal welding, the high-entropy effect of the high-entropy alloy particles is utilized to inhibit the formation of harmful intermetallic compounds in the dissimilar welding joint, the welding joint microstructure mainly in the form of a solid solution is obtained, and the bonding strength of the dissimilar metal welding interface is improved. The process flow of the application is simple and easy to operate, can be modularly designed, and is suitable for wide-range and large-scale popularization and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of friction stir welding, and particularly relates to a method for improving the performance of a dissimilar metal friction stir welded joint. BACKGROUND

[0002] With the increasing demand for complex parts in the field of engineering technology, the performance of single metal materials has gradually failed to meet the demand. Composite parts composed of different materials can maximize the advantages of each material, and the preparation of dissimilar alloy structural parts cannot be separated from the application of welding technology, so it is undoubtedly necessary to obtain a dissimilar metal welded joint with good performance.

[0003] Due to the great differences in physical, chemical and mechanical properties of dissimilar metal materials, it has been a research hotspot and difficulty in the field of welding to obtain a high-performance dissimilar metal welded joint. At present, the methods used for dissimilar metal welding include fusion welding, brazing, pressure welding, etc. Due to the characteristics of these processes and the particularity of dissimilar metal welding, these methods still have some technical limitations. For example, fusion welding has high heat input, which can easily lead to a large number of intermetallic compounds and high residual stress in the weld, seriously affecting the joint performance; although brazing has small joint deformation and fewer intermetallic compounds, it is easy to produce defects such as inclusions and pores, and the joint strength is low and easy to fail. Explosion welding and diffusion welding in pressure welding also have problems such as high welding environment requirements and low welding efficiency. Compared with the above methods, friction stir welding has significant technical advantages in dissimilar metal welding. First, as a solid-phase welding method, it can avoid various welding defects commonly found in fusion welding and brazing; second, it has high automation and high welding efficiency; third, it can be applied to various welding materials and structures, has little influence on the welding environment, and has high process applicability.

[0004] The basic principle of using friction stir welding technology to weld dissimilar metals is that a high-speed rotating tool penetrates into the interface to be welded and travels along the welding path to apply friction heat and mechanical stirring to the dissimilar materials, and the heat-plasticity-deformed dissimilar metals flow around the tool and form a solid-phase welded joint under the forging action of the tool. Currently, the factors affecting the mechanical properties of dissimilar metal friction stir welded joints mainly include two aspects: first, under the action of heat, the interface may still react to form brittle intermetallic compounds, leading to a decrease in joint performance; second, the differences in physical and mechanical properties of dissimilar metals can lead to inconsistency in plastic flow behavior when they rotate around the tool, causing groove, hole, micro-crack and other weld defects.

[0005] In order to inhibit the formation of intermetallic compounds in the friction stir welded joint of dissimilar metals and improve the plastic flow behavior of the welded joint material, the commonly used method is to apply an auxiliary energy field to the welding process or add an intermediate layer material at the welding interface. In the application of welding auxiliary energy field, previous studies have shown that by applying auxiliary heat field, auxiliary ultrasonic energy field and auxiliary cooling medium, etc. methods can optimize the plastic flow of the welded joint material to a certain extent, inhibit the formation of harmful intermetallic compounds and improve the joint performance. However, overall, the application of auxiliary energy field is easy to increase the manufacturing cost of welding device and the complexity of welding process control, and the applicability is limited to a certain extent.

[0006] In terms of adding an intermediate layer, non-metallic materials such as graphene nanosheets and SiC nanoparticles have been applied in the friction stir welding of aluminum-copper dissimilar materials, and have played a positive role in regulating the microstructure of the welded joint and strengthening the welded joint. However, overall, the flowability of non-metallic intermediate layer materials is quite different from that of the metal matrix, and agglomeration is likely to occur in the welded joint during welding, which is not conducive to the improvement of joint performance. Low-melting-point metal intermediate layers such as zinc foil and tin foil can improve the interface microstructure of the friction stir welded joint of dissimilar metals through a process similar to brazing, but this method is mainly suitable for thin plate welding, at which time the tool is more likely to generate sufficient heat input at the welding interface. As a new type of multi-principal-element alloy with excellent performance, high-entropy alloys can better inhibit the formation of harmful intermetallic compounds due to their strong lattice distortion effect and slow element diffusion effect, so they have been widely used as intermediate layer materials in the field of friction stir welding of dissimilar metals. For example, patents CN111575698A, CN114571189A, CN111575699A, CN110724949A and CN111069761A use high-entropy alloy powder to reinforce metal matrix composites by friction stir welding. Patents CN113828907A and CN113118613A use high-entropy alloy powder as an intermediate layer material to realize the friction stir welding of aluminum-magnesium and aluminum-copper dissimilar metals, respectively, which not only reduces the content of intermetallic compounds in the welded joint, but also improves the mechanical properties of the joint.

[0007] The existing method of pre-placing the intermediate layer material before welding often involves first placing the powder in the grooves or holes processed on the surface of the workpiece to be welded, and then using a needleless tool to weld it. This method is easy to cause the intermediate layer powder to overflow outward during pre-placing or formal welding, reducing the filling efficiency and strengthening effect of the powder. In addition, the powder material is also prone to agglomeration during formal welding, which often requires multiple repeated welding to achieve uniform distribution of the intermediate layer particles in the matrix, which not only increases the welding heat input, but also reduces the welding efficiency. SUMMARY

[0008] This invention addresses the problem that dissimilar metals with significantly different physical and mechanical properties are prone to fluidity defects and hard, brittle intermetallic compounds in the weld during friction stir welding, leading to low joint mechanical properties. It proposes a method for enhancing the performance of dissimilar metal friction stir welds by pre-applying high-entropy alloy powder. The specific principle is as follows:

[0009] Before dissimilar metal welding, high-entropy alloy powder particles are first filled into the soft base metal using friction stir welding, thus preparing a high-entropy alloy particle-reinforced composite material for the soft base metal. This achieves high-efficiency pre-filling of the intermediate layer powder particles, completely preventing them from flowing outwards during the actual friction stir welding. At the same time, the strong lattice distortion effect of the high-entropy alloy particles is used to initially strengthen the soft base metal, thereby reducing the performance inconsistencies between the dissimilar base metals during friction stir welding, promoting the homogeneous plastic flow of materials at the welding interface and obtaining good weld formation. In addition, the high-entropy effect of the high-entropy alloy particles can also suppress the formation of brittle intermetallic compounds in the dissimilar weld, obtaining a weld microstructure dominated by solid solution, and improving the bonding strength of the dissimilar metal welding interface.

[0010] A method for enhancing the performance of dissimilar metal friction stir welds using pre-placed high-entropy alloy powder, the specific technical solution of which includes the following steps:

[0011] Step 1: Preliminary Preparations

[0012] A groove is machined on the first surface of the first base material to be welded, the groove being along the welding trajectory line and having the width symmetry center thereon; the surfaces of the first base material to be welded, the cover plate, and the second base material to be welded are cleaned to remove all oxide film, oil, and impurities from the surfaces of the plates;

[0013] The welding trajectory line is the trajectory formed from the starting point to the ending point of the preset welding position;

[0014] Step 2: Pre-placed particle friction stir welding

[0015] The groove processed in step 1 is filled with high-entropy alloy powder particles and compacted; the cover plate is stacked on the first base material to be welded, and directly contacts the first surface to be welded of the first base material to be welded, forming the first lap structure, and is mounted and positioned on the welding machine worktable, and moves along the preset welding trajectory line to perform the first welding; after welding is completed, the upper cover plate is removed to obtain a high-entropy alloy particle reinforced metal matrix composite material.

[0016] The first welding step is as follows: the welding tool is installed on the main shaft of the friction stir welding machine, the welding machine is started and moved to the first welding start position, and then the welding tool is inserted into the first lap structure, the welding tool shoulder is pressed into the upper surface of the cover plate, and the welding tool stirring needle is inserted into the first surface to be welded of the first base material; then the main shaft of the friction stir welding machine is moved so that the welding tool moves along the preset welding trajectory line.

[0017] Step 3: Dissimilar metal friction stir welding

[0018] The high-entropy alloy particle-reinforced metal matrix composite material obtained in step 2 is stacked and assembled with the second base material to be welded. The first surface to be welded of the high-entropy alloy particle-reinforced metal matrix composite material is in close contact with the second base material to be welded, forming a second lap structure, which is then clamped and positioned. The second lap structure is then clamped and positioned on the welding machine worktable and moved along the preset welding trajectory line to perform the second welding, resulting in a dissimilar metal friction stir welded joint.

[0019] The second welding step is as follows: the welding tool is installed on the main shaft of the friction stir welding machine, the welding machine is started and moved to the second welding start position, and then it is inserted into the second lap structure. The shoulder of the welding tool is inserted into the upper surface of the base material to be welded in the upper layer, and the stirring needle passes through the lap welding interface. Then the main shaft of the friction stir welding machine is moved so that the welding tool moves along the above welding trajectory line.

[0020] In step 1 above, both the first and second base materials are metal sheets, selected from magnesium and magnesium alloys, aluminum and aluminum alloys, copper and copper alloys, iron and iron alloys, and titanium and titanium alloys, respectively. The first and second base materials are made of different materials, and the first base material is a softer metal compared to the second base material. The thickness of both the first and second base materials is in the range of 0.5mm-10mm, and their thicknesses may be the same or different.

[0021] In step 1 above, the groove processed on the first base material to be welded is a groove-shaped structure with a uniform cross-section. The cross-section of the groove is rectangular, polygonal, or arc-shaped. The ratio of the maximum groove width to the thickness of the first base material to be welded is in the range of 0.05-1.5. The maximum groove depth does not exceed 0.5 times the thickness of the first base material to be welded. The surface roughness of the groove is not lower than the initial surface roughness of the first base material to be welded.

[0022] In step 1 above, a thin plate of the same type as the first base material to be welded is selected as the cover plate. The length and width of the cover plate must not only completely cover the processed groove, but also meet the requirements of welding clamping. The thickness of the cover plate is not greater than the thickness of the first base material to be welded.

[0023] In step 2 above, the high-entropy alloy powder particles used are multi-component structures with equal or non-equal atomic ratios, selected from one or more of the following high-entropy alloys: AlxCoxCrFeNix, AlxCoCrCuFe, TiAlNiCo, TiAlNiFe, AlCoCrFeNiTix, FexCoxNixAlxSix, AlCrCuFeNix, AlCoCrCuFeNi, TiAlNiCoFe, NbxMoxTaxWx, CoFeMnNiAl, CoFeNiTaAl, and AlNbTiZr. The particle size range of the high-entropy alloy powder particles is 0.1μm-30μm.

[0024] In step 2 above, the diameter of the welding tool shoulder is 2.5-4 times the sum of the thickness of the cover plate and the first base material to be welded, and the diameter of the welding tool stirring pin is greater than the maximum width of the processed groove and does not exceed 1.5 times the sum of the thickness of the cover plate and the first base material to be welded.

[0025] In step 2 above, the rotational speed at which the welding tool penetrates the first lap structure is 500-5000 r / min; the depth to which the shoulder of the welding tool presses into the upper surface of the cover plate is 0-0.3 mm; the depth to which the stirring pin of the welding tool penetrates the first surface to be welded of the first base material is greater than the depth of the processed groove but less than the thickness of the first base material; the traveling speed of the welding tool along the preset welding trajectory line is 20-1000 mm / min; and the removal of the upper cover plate makes the thickness of the welding area of ​​the first base material deviate from its original thickness by 0 mm.

[0026] In step 3 above, the first base material to be welded in the second lap structure can be located in the upper layer or the lower layer; the rotation speed of the welding tool when it enters the second lap structure is 500-5000 r / min; the depth to which the shoulder of the welding tool enters the upper surface of the base material to be welded in the upper layer is 0-0.3 mm; the minimum depth of the stirring pin through the lap welding interface is 0 mm, and the maximum depth does not exceed the thickness of the lower base material to be welded; the traveling speed of the welding tool when performing the second welding is 20-1000 mm / min.

[0027] In step 3 above, the diameter of the welding tool shoulder is 2.5-4 times the sum of the thicknesses of the first and second base materials to be welded, and the diameter of the welding tool stirring pin is greater than the maximum width of the processed groove and does not exceed 1.5 times the sum of the thicknesses of the first and second base materials to be welded.

[0028] In steps 2 and 3 above, the starting and ending positions of the first weld should both be within the length of the groove, and the starting and ending positions of the second weld should both be within the length of the weld formed by the first weld.

[0029] In step 3 above, the friction stir welded joint is one of the following: friction stir butt joint, friction stir corner joint, friction stir multilayer additive structure, and friction stir lap joint with straight and curved welding trajectory.

[0030] The method for enhancing the performance of dissimilar metal friction stir welds with pre-placed high-entropy alloy powder, as described in this invention, has the following advantages compared to existing technologies:

[0031] 1. By introducing a cover plate and friction stir welding, the particle reinforcement phase is pre-placed in the base material to be welded, which can improve the filling efficiency of powder particles, avoid the powder overflowing during pre-filling welding and formal welding, and improve the utilization rate of powder and its strengthening effect.

[0032] 2. Pre-powder welding is equivalent to performing a homogenization treatment of high-entropy alloy powder particles in the metal matrix in advance. During the actual dissimilar metal friction stir welding, the number of welding passes used for particle homogenization can be reduced, which not only improves welding efficiency, but also helps to improve joint performance due to the reduction of welding heat input.

[0033] 3. Pre-place high-entropy alloy powder particles in soft metals improves the consistency of mechanical properties of metals on both sides of the weld, which helps to promote uniform material flow at the welding interface during dissimilar metal welding and obtain good weld formation.

[0034] 4. Pre-placed particle friction stir welding is essentially a process for preparing high-entropy alloy particles-reinforced metal matrix composites. This process is simple to operate, can be carried out independently, and is conducive to large-scale and batch production applications.

[0035] 5. This invention is applicable to various welding structure forms. In addition to the lap joint structure described in this invention, based on the basic principles of this invention, this method can also be extended to high-quality welding of butt joints, corner joints, and other structures, and can also be used in friction stir additive manufacturing. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the groove processed on the first base material to be welded according to the present invention, wherein: 1-first base material to be welded, 2-groove, 3-center line of the first welding trajectory, 4-first surface to be welded;

[0037] Figure 2 This is a schematic diagram of powder particle filling according to the present invention, wherein: 1-first base material to be welded, 4-first surface to be welded, and 5-high entropy alloy powder particles;

[0038] Figure 3 This is a schematic diagram of the first lap joint structure of the present invention, wherein: 1-first base material to be welded, 5-high entropy alloy powder particles, 6-cover plate;

[0039] Figure 4 This is a schematic diagram of pre-placed particle friction stir welding according to the present invention, wherein: 1-first base material to be welded, 6-cover plate, 7-welding tool;

[0040] Figure 5 This is a schematic diagram of the first base material to be welded using the pre-placed high-entropy alloy powder of the present invention, wherein: 1-first base material to be welded, 3-center line of the first welding trajectory, 4-first surface to be welded, and 8-first welding area;

[0041] Figure 6 This is a schematic diagram of the second lap joint structure of the present invention, wherein: 1-first base material to be welded, 8-first welding area, 9-second base material to be welded;

[0042] Figure 7 This is a schematic diagram of friction stir welding of dissimilar metals according to the present invention, wherein: 1-first base material to be welded, 7-welding tool, 8-first welding area, 9-second base material to be welded;

[0043] Figure 8 This is a schematic diagram of the stirring head of the present invention, wherein: 7-welding tool, 71-shoulder, 72-stirring needle;

[0044] Figure 9 The images show cross-sectional photographs of the welds, where: a is a conventional dissimilar weld, and b is a high-entropy alloy particle-reinforced dissimilar weld obtained in Example 1 of this invention;

[0045] Figure 10 This is the load-displacement curve of the joint tensile-shear test in Embodiment 1 of the present invention. Detailed Implementation

[0046] The following describes specific embodiments and appendices. Figures 1-8 The present invention will be further described below. The embodiments are only used to better illustrate the present invention and are not intended to limit the scope of application of the present invention.

[0047] Example 1

[0048] A method for enhancing the performance of dissimilar metal friction stir welds using pre-placed high-entropy alloy powder, such as... Figures 1-8 As shown, it includes the following steps:

[0049] Step 1: Preliminary Preparations

[0050] A 6061-O aluminum alloy plate with dimensions of 200mm × 100mm × 3mm was selected as the soft first weld base material 1. A 6061-O aluminum alloy plate with dimensions of 200mm × 100mm × 1mm was selected as the cover plate 6. A T3 copper plate with dimensions of 200mm × 100mm × 3mm was selected as the hard second weld base material 9. The surfaces of the soft first weld base material 1, the cover plate 6, and the hard second weld base material 9 were cleaned to remove all oxide film, oil, and impurities from the surfaces of the plates.

[0051] A groove 2 is machined along the preset first welding area 8 on the first surface 4 of the first base material 1 to be welded. The groove 2 is a uniform rectangular cross-section groove structure, and its width is symmetrically distributed relative to the center line 3 of the first welding trajectory. The size of the groove 2 is 180mm×1mm×0.5mm, and the surface roughness of the groove 2 is not lower than the initial surface roughness value of the first base material 1 to be welded.

[0052] Step 2: Pre-placed particle friction stir welding

[0053] The groove 2 is filled with high-entropy alloy powder particles 5 and compacted. The powder is AlCoCrFeNi high-entropy alloy particles with a particle size range of 0.5μm-24μm prepared by vacuum atomization process.

[0054] The cover plate 6 is stacked on top of the first base material 1 to be welded, and directly contacts the first surface 4 to be welded of the first base material 1 to form a first lap structure. The first lap structure is then clamped and positioned on the welding machine worktable using a clamp. The welding tool 7 is installed on the spindle of the friction stir welding machine, wherein the diameter of the shoulder 71 of the welding tool 7 is 12mm and the length of the stirring needle 72 is 2.85mm. Start the welding machine, move the welding tool 7 stirring pin 72 to a position 2mm away from its starting point inside the groove 2, and then insert the welding tool 7 into the first lap structure at a rotation speed of 800r / min. The shoulder 71 of the welding tool 7 is pressed into the upper surface of the cover plate 6 to a depth of 0.15mm. At this time, the stirring pin 72 of the welding tool 7 is inserted into the first surface 4 to be welded of the first base material 1 located in the lower layer to a depth of 2mm. Then move the main shaft of the friction stir welding machine so that the welding tool 7 moves along the center line 3 of the first welding trajectory at a travel speed of 50mm / min to perform the first welding. When the stirring pin 72 of the welding tool 7 moves to the end point of the groove 2 with a distance of 2mm remaining, the welding tool 7 is pulled out to obtain the first welding area 8.

[0055] Then, the upper cover plate 6 is removed by machining to ensure that the thickness of the first welding area 8 of the first base material 1 deviates from the original thickness of the first base material 1 by 0 mm.

[0056] Step 3: Dissimilar metal friction stir welding

[0057] The first base material 1 and the second base material 9, which are filled with high-entropy alloy powder particles 5, are stacked and assembled together. The first surface 4 to be welded of the first base material 1 is in close contact with the second base material 9, forming a second lap structure. The first base material 1 is located on the upper layer. The second lap structure is clamped and positioned using tooling fixtures.

[0058] The welding tool 7 is mounted on the spindle of the friction stir welding machine. The machine is started, and the stirring pin 72 of the welding tool 7 is moved to a position 2 mm away from its starting point inside the first welding zone 8. Then, the welding tool 7 is driven into the second lap structure at a rotation speed of 1000 r / min. The shoulder 71 of the welding tool 7 is driven into the upper surface of the first base material 1 located on the upper layer to a depth of 0.15 mm. At this time, the stirring pin 72 of the welding tool 7 is driven into the first surface 4 to be welded of the first base material 1 located on the lower layer to a depth of 0 mm. Then, the spindle of the friction stir welding machine is moved so that the welding tool 7 travels along the center line 3 of the first welding trajectory at a travel speed of 25 mm / min to perform the second welding.

[0059] When the stirring pin 72 of the welding tool 7 moves to the end point of the first welding zone 8 with a distance of less than 2mm, the welding tool 7 is pulled out to obtain a high-entropy alloy particle-reinforced aluminum-copper dissimilar metal friction stir welded joint.

[0060] from Figure 9 As shown in Figure a, in conventional aluminum-copper dissimilar metal friction stir welds without the addition of high-entropy alloy powder particles, the significant differences in the physical and mechanical properties of aluminum and copper make it difficult for the copper metal at the bottom to deform. Therefore, the mixing and flow between aluminum and copper at the interface is weak, and the tensile-shear strength of the lap joint is only 251 N / mm. However, by using the method of this invention to pre-place high-entropy alloy powder particles into the aluminum-copper dissimilar metal friction stir weld, as shown in Figure a... Figure 9 b. High-entropy alloy particles are relatively uniformly distributed at the welding interface, and the hard base copper metal at the bottom undergoes significant plastic deformation. This is because the high-entropy alloy powder particles pre-placed in the soft aluminum base strengthen the aluminum matrix at the welding interface, thereby reducing the difference in mechanical properties between aluminum and copper materials at the welding interface and promoting uniform flow and thorough mixing of the two during welding. Figure 10 As shown, the tensile shear strength of the welded joint prepared by the method of the present invention is increased to 391 N / mm.

[0061] It should be noted that the above embodiments are only used to better explain the present invention, and the scope of protection of the present invention is not limited to these embodiments. Within the technical scope covered by the present invention, any other similar technical solutions or improvements that are obviously derived from the ideas described in the present invention are within the scope of protection of the present invention.

Claims

1. A method for enhancing the performance of dissimilar metal friction stir welds using pre-placed high-entropy alloy powder, characterized in that, It includes the following steps: Step 1: Preliminary Preparations A groove is machined on the first surface of the first base material to be welded, the groove being along the welding trajectory line and having the width symmetry center thereon; the surfaces of the first base material to be welded, the cover plate, and the second base material to be welded are cleaned to remove all oxide film, oil, and impurities from the surfaces of the plates; Both the first and second base materials to be welded are metal plates. The materials of the first and second base materials to be welded are different, and the first base material to be welded is a softer metal compared to the second base material to be welded. Step 2: Pre-placed particle friction stir welding The groove processed in step 1 is filled with high-entropy alloy powder particles and compacted; the cover plate is stacked on the first base material to be welded, and directly contacts the first surface to be welded of the first base material to be welded, forming the first lap structure, and is mounted and positioned on the welding machine worktable, and moves along the preset welding trajectory line to perform the first welding; after welding is completed, the upper cover plate is removed to obtain a high-entropy alloy particle reinforced metal matrix composite material. The first welding steps are as follows: the welding tool is installed on the main shaft of the friction stir welding machine, the welding machine is started and moved to the first welding start position, and then the welding tool is inserted into the first lap structure, the welding tool shoulder is pressed into the upper surface of the cover plate, and the welding tool stirring needle is inserted into the first surface to be welded of the first base material; then the main shaft of the friction stir welding machine is moved so that the welding tool moves along the preset welding trajectory line. Step 3: Dissimilar metal friction stir welding The high-entropy alloy particle-reinforced metal matrix composite material obtained in step 2 is stacked and assembled with the second base material to be welded. The first surface to be welded of the high-entropy alloy particle-reinforced metal matrix composite material is in close contact with the second base material to be welded, forming a second lap structure, which is then clamped and positioned. The second lap structure is then clamped and positioned on the welding machine worktable and moved along the preset welding trajectory line to perform the second welding, resulting in a dissimilar metal friction stir welded joint. The second welding steps are as follows: the welding tool is installed on the main shaft of the friction stir welding machine, the welding machine is started and moved to the second welding start position, and then it is inserted into the second lap structure. The shoulder of the welding tool is inserted into the upper surface of the base material to be welded on the upper layer, and the stirring needle passes through the lap welding interface. Then the main shaft of the friction stir welding machine is moved so that the welding tool moves along the above welding trajectory line.

2. The method for enhancing the performance of dissimilar metal friction stir welds with pre-placed high-entropy alloy powder according to claim 1, characterized in that, In step 1, the thickness of both the first and second base materials to be welded is within the range of 0.5-10mm. The thicknesses of the two materials can be the same or different.

3. The method for enhancing the performance of dissimilar metal friction stir welds with pre-placed high-entropy alloy powder according to claim 1, characterized in that, In step 1, the groove processed on the first base material to be welded is a groove-shaped structure with a uniform cross-section. The cross-section of the groove is rectangular, polygonal, or arc-shaped. The ratio of the maximum groove width to the thickness of the first base material to be welded is in the range of 0.05-1.

5. The maximum groove depth does not exceed 0.5 times the thickness of the first base material to be welded. The surface roughness of the groove is not lower than the initial surface roughness of the first base material to be welded.

4. The method for enhancing the performance of dissimilar metal friction stir welds with pre-placed high-entropy alloy powder according to claim 1, characterized in that, In step 1, a thin plate of the same type as the first base material to be welded is selected as the cover plate. The length and width of the cover plate should be sufficient to completely cover the processed groove. The thickness of the cover plate should not be greater than the thickness of the first base material to be welded.

5. The method for enhancing the performance of dissimilar metal friction stir welds with pre-placed high-entropy alloy powder according to claim 1, characterized in that, In step 2, the high-entropy alloy powder particles have an equiatomic ratio or non-equiatomic ratio multi-component structure, selected from Al. x Co x CrFeNi x Al x CoCrCuFe, TiAlNiCo, TiAlNiFe, AlCoCrFeNiTi x Fe x Co x Ni x Al x Si x AlCrCuFeNi x , AlCoCrCuFeNi, TiAlNiCoFe, Nb x Mo x Ta x W x The high entropy alloy powder consists of one or more of the following: CoFeMnNiAl, CoFeNiTaAl, and AlNbTiZr, with a particle size range of 0.1-30 μm.

6. The method for enhancing the performance of dissimilar metal friction stir welds with pre-placed high-entropy alloy powder according to claim 1, characterized in that, In step 2, the diameter of the welding tool shoulder is 2.5-4 times the sum of the thickness of the cover plate and the first base material to be welded, and the diameter of the welding tool stirring pin is greater than the maximum width of the processed groove and does not exceed 1.5 times the sum of the thickness of the cover plate and the first base material to be welded.

7. The method for enhancing the performance of dissimilar metal friction stir welds with pre-placed high-entropy alloy powder according to claim 1, characterized in that, In step 2, the rotational speed of the welding tool when it penetrates the first lap structure is 500-5000 r / min; the depth of the welding tool shoulder pressing into the upper surface of the cover plate is 0-0.3 mm; the depth of the welding tool stirring pin penetrating into the first surface to be welded of the first base material is greater than the depth of the processed groove but less than the thickness of the first base material; the traveling speed of the welding tool along the preset welding trajectory line is 20-1000 mm / min; the removal of the upper cover plate makes the thickness of the welding area of ​​the first base material deviate from its original thickness by 0 mm.

8. The method for enhancing the performance of dissimilar metal friction stir welds with pre-placed high-entropy alloy powder according to claim 1, characterized in that, In step 3, the first base material to be welded in the second lap structure can be located in the upper layer or the lower layer; the rotation speed of the welding tool when it enters the second lap structure is 500-5000 r / min; the depth of the welding tool shoulder into the upper surface of the base material to be welded in the upper layer is 0-0.3 mm; the minimum depth of the stirring pin through the lap welding interface is 0 mm, and the maximum depth does not exceed the thickness of the lower base material to be welded; the traveling speed of the welding tool when performing the second welding is 20-1000 mm / min; the diameter of the welding tool shoulder is 2.5-4 times the sum of the thicknesses of the first and second base materials to be welded, and the diameter of the stirring pin of the welding tool is greater than the maximum width of the processed groove and does not exceed 1.5 times the sum of the thicknesses of the first and second base materials to be welded.

9. The method for enhancing the performance of dissimilar metal friction stir welds with pre-placed high-entropy alloy powder according to claim 1, characterized in that, In steps 2 and 3, the start and end positions of the first weld are both within the length of the groove, and the start and end positions of the second weld are both within the length of the weld formed by the first weld.

10. The method for enhancing the performance of dissimilar metal friction stir welds with pre-placed high-entropy alloy powder according to claim 1, characterized in that, In step 3, the friction stir welded joint is one of the following: friction stir butt joint, friction stir corner joint, friction stir multilayer additive structure, and friction stir lap joint with straight and curved welding trajectory.

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