Aluminum steel friction welding method based on additive and subtractive microstructure interlocking and regulation

Abstract

The invention provides an aluminum steel friction welding method based on additive and subtractive microtexture interlocking and regulation, which comprises the following steps: constructing a surface subtractive microtexture in a to-be-welded area of an aluminum plate to obtain a to-be-welded aluminum plate, constructing an additive microtexture matched with the surface subtractive microtexture in a to-be-welded area of a steel plate by using alloy powder to obtain a to-be-welded steel plate, and welding the to-be-welded steel plate with the additive microtexture. Then, after the surface subtractive microstructure on the to-be-welded aluminum plate and the additive microstructure are matched to form an interlocking structure, welding is conducted through a friction welding technology; in the friction welding process, a friction welding tool head acts on the top face of the steel plate. Compared with traditional friction stir welding, the friction stir welding method has the advantages that under the condition that the physical form of the microstructure of the base metal is not changed, by means of continuous layered distribution of the brittle phase of the microstructure discrete interface of the high-entropy alloy, hole outlet of a welding material is avoided, and the strength of a joint is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum-steel friction welding, and specifically relates to an aluminum-steel friction welding method based on interlocking and regulation of additive and subtractive material micro-textures. Background Art

[0002] In recent years, in order to reduce the weight of components in the automotive industry and aerospace applications, the research on high-quality connection of aluminum and steel has been on the rise. Friction stir welding (FSW) is widely used in the connection of aluminum and steel, especially the welding of large tanks of launch vehicles involving aluminum alloys. As a type of friction stir welding, friction welding can effectively avoid the holes in the welding material, and the defects such as pores and cracks are easily generated when the base material melts and solidifies. Since friction welding is a solid phase welding, the type of intermetallic compounds (IMCs) formed on the interface of aluminum and steel joints and the thickness of IMCs are often important factors that determine whether the aluminum-steel dissimilar joint can be successfully welded and the quality of mechanical properties. Studies have shown that when there is no formation of metal compounds at the interface of aluminum-steel joints, the aluminum-steel dissimilar joints cannot be successfully welded, and when the generated Fe-Al IMCs reach a certain thickness, the failure load of the aluminum-steel dissimilar joints decreases rapidly. Therefore, regulating the intermetallic compounds of aluminum-steel dissimilar joints can effectively improve the mechanical properties of aluminum-steel dissimilar joints.

[0003] In the existing scheme, the metallurgical control method of rotary friction welding of heterogeneous materials disclosed in document CN116900468A, by drilling holes in the metal end face with lower strength and adding alloy rods, the alloy rods and the material with lower strength undergo plastic deformation and flow simultaneously during the friction welding process, thereby regulating the interface reaction of the welded joint. For the rotary friction welding joint of heterogeneous materials in a limited miscible system, the type, distribution and thickness of the intermetallic compounds generated at the friction interface are changed through metallurgical control, the generation of high-strength and high-toughness intermetallic compounds is promoted, and the phenomenon of uneven distribution of intermetallic compounds caused by the non-uniformity of thermal coupling of friction welding at the interface is improved, thereby further improving the mechanical properties of the welded joint. However, this scheme requires drilling holes in the metal end face with lower strength and adding alloy rods, and the physical structure of the joint of the materials to be welded has essentially been destroyed during the welding process.

[0004] In addition, the existing document CN107160109A discloses a method for riveting and welding composite connection of aluminum and steel dissimilar metals. The method first pre-drills at the overlap of the aluminum plate and the steel plate to be connected to obtain a pre-drilled hole, and then inserts the rivet into the pre-drilled hole so that the end face of the rivet cap is flush with the surface of the aluminum plate, and the other end of the rivet is higher than the surface of the steel plate; then, a rotating stirring head is used to perform a first downward pressure on the rivet higher than the surface of the steel plate so that the end face of the stirring head contacts the surface of the steel plate; finally, a second downward pressure is performed so that the rivet forms a countersunk rivet head in the steel plate. However, the prior art has the following technical defects: the method of using aluminum-steel dissimilar metal riveting and welding composite connection increases the weight of aluminum-steel structural parts, which cannot meet the lightweight use requirements in the automotive and aerospace fields; the coordination of rivets and holes leads to a decrease in the quality of aluminum-steel dissimilar joints. When the rivet size is small, the assembly gap is large. As the stirring head is pressed down, the stirring head pressing position cannot be completely concentric with the rivet, resulting in uneven distribution of compressive stress after welding, and large differences in joint strength in the same batch, which affects the actual service life of the component; when the rivet size is large, the assembly gap is small. As the stirring head is pressed down, the rivet and the plate are squeezed against each other, and cracks appear at the connection between the rivet and the plate, reducing the mechanical strength of the joint. And with different welding parameters, the degree of extrusion is different, and the size of the rivet needs to be adjusted according to the parameters, and the size of the rivet is closely related to the joint strength, which affects the welding standardization of aluminum-steel dissimilar metal riveting and welding composite connection. Therefore, on the basis of the existing technical route, in order to overcome the above technical defects, further improvements are needed. Summary of the invention

[0005] The present invention provides an aluminum-steel friction welding method based on interlocking and regulation of additive and subtractive material microtextures, which can at least effectively discretize the continuous layered distribution of the interface brittle phase without changing the physical morphology of the microtexture in the welding area, and improve the performance of the welded joint.

[0006] A method for friction welding of aluminum and steel based on interlocking and regulation of additive and subtractive microtextures, the steps comprising: constructing a surface subtractive microtexture in the area to be welded of the aluminum plate to obtain the aluminum plate to be welded, constructing an additive microtexture matching the surface subtractive microtexture in the area to be welded of the steel plate using alloy powder to obtain the steel plate to be welded, and then matching the surface subtractive microtexture on the aluminum plate to be welded with the additive microtexture to form an interlocking structure, and then welding by a friction welding process; during the friction welding process, the friction welding tool head acts on the top surface of the steel plate, and without changing the physical morphology of the microtexture, at least the continuous layered distribution of the interfacial brittle phase is discretized by the additive microtexture corresponding to the alloy powder. In the present invention, not changing the physical morphology of the microtexture means that the physical structure of the microtexture is still retained after welding; subtractive microtexture refers to the microtexture obtained after processing by a subtractive process, and additive microtexture refers to the microtexture obtained after processing by an additive process.

[0007] The above scheme not only enables the surface structures on both sides of the aluminum and steel to be welded to play a mechanical interlocking pre-tightening role before welding, which is beneficial to improving the mechanical properties of the welded components, but also does not require an additional rivet structure, does not increase the weight of the connection, has a strong tensile load at the weld joint, and meets the lightweight requirements. It can also make use of the continuous layered distribution of the discrete interface brittle phase of the additive microtexture of the high entropy alloy without changing the physical morphology of the microtexture.

[0008] Furthermore, the alloy powder is a high entropy alloy powder, and the high entropy alloy powder includes Fe, Co, Ni, Cr and Mn. When Fe, Co, Ni, Cr and Mn are mixed in a mass ratio of 1:1:1:1:1 to obtain the high entropy alloy powder, the tensile strength of the welded joint can be further improved.

[0009] Preferably, the rotation speed of the friction welding tool head is 1000-3000 rpm, the pressing rate is 10-15 mm / min, the pressing amount is 0.2-0.6 mm, and the dwell time is 30-90 s.

[0010] In the present invention, the surface subtractive micro-texture includes a plurality of long strip grooves distributed along a first direction and a plurality of long strip grooves distributed along a second direction, and the first direction and the second direction intersect so that the surface subtractive micro-texture is in a grid shape. Generally speaking, for the convenience of processing, the first direction and the second direction are perpendicular to each other. Preferably, the spacing between adjacent long strip grooves is 100-200 μm, the width of the long strip groove is 50-100 μm, and the depth is 300-500 μm. Preferably, the surface subtractive micro-texture includes a plurality of circular grooves arranged in a rectangular and / or circular array. More preferably, the spacing between the centers of adjacent circular grooves is 1-3 mm, the diameter of the circular groove is 1-3 mm, and the depth is 0.2-1 mm. More preferably, the surface subtractive micro-texture includes a plurality of long strip V-shaped grooves arranged closely in sequence, and the width of the opening of the long strip V-shaped groove is 0.2-1 mm and the depth is 0.1-0.5 mm. There is no special requirement for the angle of the long V-shaped groove, and 90° is generally used. Preferably, an ultrafast laser system is used to construct the surface subtractive microtexture, the ultrafast laser system has a laser pulse width of 300fs-8ps, a repetition frequency of 25kHz-5MHz, a wavelength of 1030nm, a laser power of 1-40W, a spot diameter of 20μm-100μm, and a scanning speed of 10mm / s-500mm / s.

[0011] The surface subtractive micro-texture of the present invention is a millimeter-level or micrometer-level structure. The constructed micro-texture causes very little damage to the plate and basically does not affect the strength of the plate itself. At the same time, welding with high-entropy alloy powder can greatly increase the tensile load at the welding joint.

[0012] Preferably, a 3D printing system is used to construct an additive microtexture that matches the surface subtractive microtexture, and the 3D printing system has a layer thickness of 20μm-80μm, a laser power of 1-400W, a scanning speed of 10mm / s-7000mm / s, a spot diameter of 50μm-200μm, and a molding accuracy of 50μm-200μm.

[0013] Furthermore, the welding method also includes: before constructing the surface subtractive micro-texture and the additive micro-texture matching the surface subtractive micro-texture, removing the oxide film on the surface of the aluminum plate and the steel plate, and performing a first cleaning; the welding method also includes: performing a second cleaning on the aluminum plate to be welded and the steel plate to be welded, and then performing the welding.

[0014] Preferably, the process of removing the oxide film on the surface of the aluminum plate and the steel plate is: grinding the surfaces of the aluminum plate and the steel plate to be welded with 400-800 mesh sandpaper. Preferably, the cleaning liquid used in the first cleaning is acetone. Preferably, the cleaning liquid used in the second cleaning is acetone, and the second cleaning is assisted by ultrasonic treatment.

[0015] Preferably, during the friction welding process, the aluminum plate is located below the steel plate.

[0016] The beneficial effects of the present invention compared with the prior art include: (1) It can achieve continuous layered distribution of discrete interface brittle phases of the microtexture of high entropy alloy without changing the physical morphology of the microtexture of the parent material; (2) Compared with traditional friction stir welding, it avoids the hole formation of welding materials; through ultrafast laser surface subtractive micro-texturing and 3D printing micro-structure, the pre-welding preload is provided to the aluminum plate and the steel plate to increase the mechanical interlocking ability between the plates and improve the strength of the joint; (3) The welding process is simple and easy to control, and the stability during the welding process is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the overlap of the aluminum plate and the steel plate in the embodiment; Figure 2 Schematic diagram of etching the area to be welded on the aluminum plate by the ultrafast laser system in the embodiment (the first style of surface subtractive micro-texturing); Figure 3is a schematic diagram of a 3D printing system in an embodiment constructing an additive micro-texture matching a surface subtractive micro-texture in a to-be-welded area of ​​a steel plate; Figure 4 Schematic diagram of friction welding in the embodiment; Figure 5 is another schematic diagram of a surface subtractive micro-texture in an embodiment; Figure 6 It is a schematic diagram of the surface subtractive micro-texture pattern in Example 2. DETAILED DESCRIPTION

[0018] The specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention. In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "vertical", "horizontal", "top", "bottom", etc. is based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present application. The terms "first", "second", etc. are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are usually a class, and the number of objects is not limited. For example, the first object can be one or more. In addition, the term "and / or" in the specification and claims is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0019] Example 1 S1: First, use 600-grit sandpaper to grind 2 mm thick 304 stainless steel plates with a size of 100 mm × 20 mm and 4 mm thick T6 6061 aluminum alloy plates with a size of 100 mm × 20 mm. Use acetone to clean the grinding debris on the surface of the aluminum plate and steel plate. The specific dimensions of the stainless steel plate and aluminum alloy plate are as follows: Figure 1 shown.

[0020] S2: Place the aluminum alloy plate after grinding and cleaning on the processing platform of the ultrafast laser system (this system is prior art and will not be described here), and fix it with a clamp. Set the scanning processing area (i.e., the area to be welded) to 20 mm×20 mm, the laser power to 30 W, the scanning speed to 100 mm / s, the frequency to 200 kHz, and the spot size to 50 μm. Construct a surface subtractive micro-texture in the area to be welded. The surface subtractive micro-texture has a plurality of long strip grooves distributed along a first direction and a plurality of long strip grooves distributed along a second direction. The first direction and the second direction are perpendicular to each other so that the surface subtractive micro-texture is in a grid shape, wherein the width of the long strip groove is 50 μm, the depth is 300 μm, and the spacing between adjacent long strip grooves is 150 μm. Start the ultrafast laser processing system to start etching on the surface of the aluminum alloy plate. The structural schematic diagram and scanning path of the ultrafast laser system are shown in the figure. Figure 2 As shown, the aluminum plates to be welded are obtained.

[0021] S3: Modeling was performed in Materialise Magics 21.0 (3D printing system), with a mesh model height of 300 μm, a width of 50 μm, and a spacing of 150 μm (i.e., matching the surface subtractive microtexture), as shown in Figure 3. The mesh model was then imported into the M2 using machine in CLS format. The stainless steel sheet, which had been sandblasted for 30 s, was then placed on the processing platform of the M2 using and fixed with a fixture.

[0022] The printing parameters were set as follows: spot diameter 50 μm, laser power 100 W, scanning speed 300 mm / s, rotation angle between each layer 67°, hatch spacing 30 μm, and printing layer thickness 50 μm. 99.99% argon was used as the protective gas, and the oxygen content was controlled below 50 ppm. The substrate was preheated at 150° for 30 min, and the system was started to perform 3D printing on the welded area of ​​the stainless steel plate. The 3D printing process diagram is shown in Figure 1. Figure 3 As shown, the material used for 3D printing is high entropy alloy powder, which is formed by mixing Fe, Co, Ni, Cr and Mn elements in a mass ratio of 1:1:1:1:1 to obtain a steel plate to be welded.

[0023] The aluminum plate to be welded and the steel plate to be welded are placed in an ultrasonic cleaning device with propanol added thereto and vibrated and cleaned at room temperature for 60 seconds to remove machining debris on the machining surface.

[0024] The cleaned and dried aluminum plate and steel plate to be welded are assembled with the steel on top and the aluminum on the bottom, and fixed with a fixture.

[0025] The tool head is set to press down at a speed of 10 mm / min and a rotation speed of 2000 rpm. After the tool head contacts the upper aluminum plate to be welded, it continues to press down for 0.6 mm and then stops pressing down. After staying for 60 s, the tool head retreats. The schematic diagram of aluminum-steel friction welding is shown in Figure 4 As shown, welding is completed after cooling for 1 minute.

[0026] In the scheme of Example 1, during the friction welding process, the subtractive microtexture of the aluminum plate surface and the additive microtexture of the steel plate mainly undergo structural interlocking and atomic diffusion, achieving the continuous layered distribution of the interfacial brittle phase mainly by means of the additive high entropy alloy microtexture without changing the physical morphology of the parent material microtexture, and on the other hand, suppressing the formation and growth of the interfacial brittle IMC through the high entropy effect and hysteresis diffusion effect. Example 2, referring to Example 1, differs from Example 1 in that the long strip grooves are parallel to each other, and the cross-section of the surface subtractive microtexture is toothed (such as Figure 6 As shown), the spacing between adjacent long strip grooves is 120 μm, the width of the long strip grooves is 80 μm, and the depth is 400 μm. In the solution of this embodiment 2, the subtractive micro-texture on the surface of the aluminum plate and the additive micro-texture on the steel plate are mainly structural interlocking and atomic diffusion, which achieves that the generation of Fe-Al brittle hard phase intermetallic compounds is mainly hindered by the additive micro-texture without changing the physical morphology of the parent material micro-texture, and reacts with the texture layer to generate a simple disordered solid solution structure.

[0027] Comparative Example 1: The method of Example 1 is referred to, except that: the surface subtractive micro-texture is not constructed on the aluminum alloy plate, and the additive micro-texture matching the surface texture is not constructed on the stainless steel plate using high entropy alloy powder. In this scheme, the bonding interface of the obtained welded joint is a whole layer of hard and brittle Fe-Al IMC layer distributed on the entire bonding interface.

[0028] Comparative Example 2: The method of Example 1 is referred to, except that the tool head speed of the friction welding is 5000 rpm and the dwell time is 150 s. In this scheme, the bonding interface of the obtained weld joint has multiple large-plate hard and brittle Fe-Al IMC layers and other simple FCC or BCC phases, and the morphology of the microtexture is severely squeezed and deformed, that is, the physical structure of the microtexture is changed.

[0029] The welded joints obtained in the embodiments and comparative examples were subjected to tensile mechanical property tests, and the tests were conducted three times. The three tensile loads of the welded joint in embodiment 1 were 3912.04 N, 3981.40 N, and 4018.28 N, respectively, and the average tensile load reached 3970.57 N; while the three tensile loads of the welded joint in comparative example 1 were 1285.63 N, 1201.23 N, and 1227.62 N, respectively, and the average tensile load was 1238.16 N. Compared with comparative example 1, the average tensile load of the welded joint increased by 220.68%. The three tensile loads of the welded joint in embodiment 2 were 3768.94 N, 3037.16 N, and 3470.09 N, respectively, and the average tensile load reached 3425.40 N. The three tensile loads of the welded joint of Comparative Example 2 were 1339.42 N, 1388.71 N, and 1479.33 N, respectively, and the average tensile load reached 1402.49 N. Compared with Comparative Example 2, the average tensile load of the welded joint increased by 144.24%.

[0030] Example 3, referring to Example 1, differs from Example 1 in that the surface subtractive micro-texture adopts cylindrical grooves, and the additive micro-texture adopts cylindrical protrusions, such as Figure 5 shown.

Claims

1. A friction welding method for aluminum steel based on interlocking and regulation of additive and subtractive micro-textures, characterized in that: The steps include: A surface subtractive micro-texture is constructed in the area to be welded of the aluminum plate to obtain the aluminum plate to be welded, and an additive micro-texture matching the surface subtractive micro-texture is constructed in the area to be welded of the steel plate using alloy powder to obtain the steel plate to be welded, and then the surface subtractive micro-texture and the additive micro-texture on the aluminum plate to be welded are matched to form an interlocking structure, and then welding is performed through a friction welding process; during the friction welding process, the friction welding tool head acts on the top surface of the steel plate, and the continuous layered distribution of the interface brittle phase is discretized through the additive micro-texture corresponding to the alloy powder.

2. The aluminum-steel friction welding method according to claim 1, characterized in that: The alloy powder is a high entropy alloy powder, and the high entropy alloy powder includes Fe element, Co element, Ni element, Cr element and Mn element.

3. The aluminum-steel friction welding method according to claim 1 or 2, characterized in that: The tool head rotation speed of the friction welding is 1000-3000rpm, the pressing rate is 10-15mm / min, the pressing amount is 0.2-0.6mm, and the dwell time is 30-90s.

4. The aluminum-steel friction welding method according to any one of claims 1 to 3, characterized in that: The surface subtractive micro-texture comprises a plurality of long strip grooves distributed along a first direction and a plurality of long strip grooves distributed along a second direction, wherein the first direction and the second direction intersect so that the surface subtractive micro-texture is in a grid shape; Preferably, the spacing between adjacent long strip-shaped grooves is 100-200 μm, the width of the long strip-shaped groove is 50-100 μm, and the depth thereof is 300-500 μm; and / or, the surface subtractive microtexture comprises a plurality of circular grooves arranged in a rectangular and / or circular array; Preferably, the spacing between the centers of adjacent circular grooves is 1-3 mm, the diameter of the circular groove is 1-3 mm, and the depth is 0.2-1 mm; And / or, the surface subtractive micro-texture comprises a plurality of closely arranged elongated V-shaped grooves, wherein the width of the opening of the elongated V-shaped grooves is 0.2-1 mm and the depth is 0.1-0.5 mm.

5. The aluminum-steel friction welding method according to claim 4, characterized in that: The surface subtractive microtexture is constructed using an ultrafast laser system, wherein the laser pulse width of the ultrafast laser system is 300fs-8ps, the repetition frequency is 25kHz-5MHz, the wavelength is 1030nm, the laser power is 1-40W, the spot diameter is 20μm-100μm, and the scanning speed is 10mm / s-500mm / s.

6. The aluminum-steel friction welding method according to claim 5, characterized in that: An additive microtexture matching the surface subtractive microtexture is constructed using a 3D printing system. The 3D printing system has a layer thickness of 20 μm-80 μm, a laser power of 1-400 W, a scanning speed of 10 mm / s-7000 mm / s, a spot diameter of 50 μm-200 μm, and a molding accuracy of 50 μm-200 μm.

7. The aluminum-steel friction welding method according to claim 1 or 2, characterized in that: The welding method further comprises: before constructing the surface subtractive micro-texture and the additive micro-texture, removing the oxide film on the surface of the aluminum plate and the steel plate, and performing a first cleaning; And / or, the welding method further includes: performing a second cleaning on the aluminum plate to be welded and the steel plate to be welded before performing the welding.

8. The aluminum-steel friction welding method according to claim 7, characterized in that: The process of removing the oxide film on the surface of the aluminum plate and the steel plate is as follows: grinding the surfaces of the aluminum plate and the steel plate to be welded using 400-800 mesh sandpaper; And / or, the cleaning liquid used in the first cleaning is acetone; And / or, the cleaning liquid used in the second cleaning is acetone, and the second cleaning is assisted by ultrasonic treatment.

9. The aluminum-steel friction welding method according to claim 1, characterized in that: During the friction welding process, the aluminum plate is located below the steel plate.

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