A friction welding method for aluminum and steel based on the interlocking and regulation of additive and subtractive micro-textures

Abstract

The present invention provides a friction welding method for aluminum-steel based on the interlocking and regulation of additive and subtractive micro-textures. A surface subtractive micro-texture is constructed in the welding area of the aluminum plate to obtain the aluminum plate to be welded. An additive micro-texture matching the surface subtractive micro-texture is constructed in the welding area of the steel plate by using alloy powder to obtain the steel plate to be welded. Then, after the surface subtractive micro-texture on the aluminum plate to be welded and the additive micro-texture are matched to form an interlocking structure, welding is carried out through a friction welding process. During the friction welding process, the tool head of the friction welding acts on the top surface of the steel plate. The present invention can, without changing the physical form of the micro-texture of the base material, avoid the out-of-hole of the welding material and improve the strength of the joint by virtue of the continuous layered distribution of the brittle phase at the discrete interface of the micro-texture of the high-entropy alloy compared with the traditional friction stir welding.

Description

Technical Field

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

[0002] In recent years, due to the necessity of reducing 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 in the welding of large aluminum alloy tanks of launch vehicles. As a type of friction stir welding, friction welding can effectively avoid defects such as porosity and cracks that are prone to occur during the melting and solidification of the base material and the formation of holes in the welding material. Since friction welding is a solid-phase welding process, the types and thicknesses of intermetallic compounds (IMCs) formed at the aluminum-steel joint interface are often important factors determining the successful welding of aluminum-steel dissimilar joints and their mechanical properties. Some studies have shown that when no metal compounds are formed at the aluminum-steel joint interface, 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 rapidly decreases. Therefore, regulating the intermetallic compounds at the aluminum-steel dissimilar joints can effectively improve the mechanical properties of the aluminum-steel dissimilar joints.

[0003] In the existing solutions, the metallurgical regulation method for rotary friction welding of dissimilar materials disclosed in Document CN116900468A involves drilling holes in the end face of the metal with lower strength and adding alloy bars, so that the alloy bars and the material with lower strength undergo plastic deformation and flow synchronously during the friction welding process, thereby regulating the interfacial reaction of the welded joint. For the rotary friction welded joint of dissimilar materials with a limited solubility system, through metallurgical regulation, the types, distribution, and thickness of the intermetallic compounds formed at the friction interface are changed to promote the formation of high-strength and high-toughness intermetallic compounds, and at the same time, the phenomenon of uneven distribution of intermetallic compounds caused by the non-uniformity of the thermo-mechanical coupling during friction welding at the interface is improved, thereby further enhancing the mechanical properties of the welded joint. However, this solution requires drilling holes in the end face of the metal with lower strength and adding alloy bars, and in essence, it has damaged the physical structure at the joint of the materials to be welded during the welding process.

[0004] In addition, the existing literature CN107160109A discloses a method for aluminum-steel dissimilar metal riveted welding composite connection. This method first pre-drills at the lap joint of the aluminum plate and the steel plate to be connected to obtain pre-drilled holes, then inserts the rivets into the pre-drilled holes so that the end face of the rivet head 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 uses a rotating stirring head to perform the 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, continue to perform the second downward pressure so that the rivet forms a countersunk rivet head in the steel plate. However, the following technical defects exist in this prior art: The method of using aluminum-steel dissimilar metal riveted welding composite connection increases the weight of aluminum-steel structural parts and cannot meet the lightweight use requirements in the fields of automobiles and aerospace; the cooperation between the rivet and the hole results in a reduction in the quality of aluminum-steel dissimilar joints. When the rivet size is small, the assembly gap is large. As the stirring head presses down, it cannot meet the requirement that the pressing position of the stirring head is completely concentric with the rivet, resulting in uneven distribution of the post-welding compressive stress, large differences in the strength of joints of the same batch, and affecting the actual service life of the components; when the rivet size is large, the assembly gap is small. As the stirring head presses down, the rivet and the plate extrude each other, and cracks appear at the connection between the rivet and the plate, reducing the mechanical strength of the joint. Moreover, with different welding parameters, the degree of extrusion is different, and the size of the rivet needs to be adjusted according to the parameters. The size of the rivet is closely related to the joint strength, affecting the welding standardization of aluminum-steel dissimilar metal riveted welding composite connection. Therefore, on the basis of the existing technical route, in order to overcome the above technical defects, further improvement is needed. Summary of the Invention

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

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

[0007] Adopting the above solution not only enables the surface structures to be welded on both sides of aluminum and steel to play a pre-tightening role of mechanical interlocking before welding, which is beneficial to improving the mechanical properties of welded components, but also does not require additional rivet structures, will not increase the weight at the connection, has a strong tensile load at the welding head, meets the lightweight requirements, and can also, without changing the physical form of the microtexture, rely on the continuous layered distribution of brittle phases at the discrete interface of the additive microtexture of the high-entropy alloy.

[0008] Furthermore, 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. When the high-entropy alloy powder is obtained by mixing Fe, Co, Ni, Cr, and Mn in a mass ratio of 1:1:1:1:1, the tensile strength at the welded joint can be further improved.

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

[0010] In the present invention, the surface subtractive microtexture includes a plurality of elongated grooves distributed along a first direction and a plurality of elongated grooves distributed along a second direction, and the first direction and the second direction intersect so that the surface subtractive microtexture is in a grid shape. Generally, for the convenience of processing, the first direction and the second direction are perpendicular to each other. Preferably, the distance between adjacent elongated grooves is 100 - 200 μm, the width of the elongated groove is 50 - 100 μm, and its depth is 300 - 500 μm. Preferably, the surface subtractive microtexture includes a plurality of circular grooves arranged in a rectangular and / or circular array. More preferably, the distance 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 microtexture includes a plurality of sequentially and closely arranged elongated V-shaped grooves, the width of the opening of the elongated 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 elongated V-shaped groove, and generally 90° is adopted.

[0011] Preferably, an ultrafast laser system is used to construct the surface subtractive microtexture. The laser pulse width of the ultrafast laser system is 300 fs - 8 ps, the repetition frequency is 25 kHz - 5 MHz, the wavelength is 1030 nm, the laser power is 1 - 40 W, the spot diameter is 20 μm - 100 μm, and the scanning speed is 10 mm / s - 500 mm / s.

[0012] The surface subtractive micro-texture of the present invention is a millimeter-scale or micron-scale 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 is carried out in combination with high-entropy alloy powder, which can greatly improve the tensile load at the welded joint.

[0013] Preferably, a 3D printing system is used to construct an additive micro-texture that matches the surface subtractive micro-texture. The layer thickness of the 3D printing system is 20μm - 80μm, the laser power is 1 - 400W, the scanning speed is 10mm / s - 7000mm / s, the spot diameter is 50μm - 200μm, and the forming accuracy is 50μm - 200μm.

[0014] Furthermore, the welding method further includes: before constructing the surface subtractive micro-texture and the additive micro-texture that matches the surface subtractive micro-texture, removing the oxide films on the surfaces of the aluminum plate and the steel plate and performing a first cleaning; the welding method further includes: performing a second cleaning on the aluminum plate to be welded and the steel plate to be welded, and then performing the welding.

[0015] Preferably, the process of removing the oxide films on the surfaces of the aluminum plate and the steel plate is: using 400 - 800 - mesh sandpaper to polish the surfaces of the aluminum plate and the steel plate to be welded. Preferably, the cleaning liquid used for the first cleaning is acetone. Preferably, the cleaning liquid used for the second cleaning is acetone, and ultrasonic treatment is supplemented during the second cleaning.

[0016] Preferably, during the friction welding process, the aluminum plate is located below the steel plate.

[0017] The beneficial effects of the present invention compared with the prior art include:

[0018] (1) It is possible to utilize the continuous layered distribution of brittle phases at the discrete interfaces of the micro-texture of the high-entropy alloy without changing the physical form of the micro-texture of the base material;

[0019] (2) Compared with traditional friction stir welding, the formation of holes in the welding material is avoided; the ultrafast laser surface subtractive micro-texture and 3D printing microstructure provide a pre-tightening force for the aluminum plate and the steel plate before welding, increasing the mechanical interlocking ability between the plates and improving the strength of the joint;

[0020] (3) The welding process is simple, easy to control, and has good stability during the welding process. Description of the Drawings

[0021] Figure 1 is a schematic diagram of the lap joint of the aluminum plate and the steel plate in the embodiment;

[0022] Figure 2 is a schematic diagram of etching in the welding area of the aluminum plate by the ultrafast laser system in the embodiment (the first style of the surface subtractive micro-texture);

[0023] Figure 3 It is a schematic diagram of the additive micro-texture constructed by the 3D printing system in the to-be-welded area of the steel plate to match the surface subtractive micro-texture in the embodiment;

[0024] Figure 4 It is a schematic diagram of friction welding in the embodiment;

[0025] Figure 5 It is a schematic diagram of another style of the surface subtractive micro-texture in the embodiment;

[0026] Figure 6 It is a schematic diagram of the surface subtractive micro-texture style in Embodiment 2. Detailed implementation manners

[0027] The following will describe the detailed implementation manners of the present invention with reference to the accompanying drawings. It should be understood that the detailed implementation manners 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, and 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 thus cannot be understood as a limitation to the present application. The terms "first", "second", etc. are used to distinguish similar objects, rather than to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are usually of the same type, and the number of objects is not limited. For example, the first object can be one or multiple. 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 can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0028] Embodiment 1

[0029] S1: First, use 600-mesh sandpaper to polish a 304 stainless steel plate with a thickness of 2 mm and a size of 100 mm × 20 mm and a T6-state 6061 aluminum alloy plate with a thickness of 4 mm and a size of 100 mm × 20 mm, and use acetone to clean the grinding debris on the surfaces of the aluminum plate and the steel plate. The specific sizes of the stainless steel plate and the aluminum alloy plate are as Figure 1 shown.

[0030] S2: Place the polished and cleaned aluminum alloy sheet on the processing platform of the ultrafast laser system (this system is a prior art and will not be elaborated here), and fix it with a fixture. Set the size of 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 microtexture in the area to be welded. This surface subtractive microtexture has multiple strip-shaped grooves distributed along the first direction and multiple strip-shaped grooves distributed along the second direction. The first direction and the second direction are perpendicular to each other, so that the surface subtractive microtexture is in a grid shape. Among them, the width of the strip-shaped groove is 50 μm, the depth is 300 μm, and the spacing between adjacent strip-shaped grooves is 150 μm. Start the ultrafast laser processing system to etch on the surface of the aluminum alloy sheet. The structural schematic diagram and scanning path of the ultrafast laser system are as Figure 2 shown to obtain the aluminum alloy sheet to be welded.

[0031] S3: Model in Materialise Magics 21.0 (3D printing system). The height of the mesh model is 300μm, the width is 50 μm, and the spacing is 150 μm (i.e., matching the surface subtractive microtexture), as shown in Figure 3 below. Then import the mesh model into the M2 using machine in CLS format. Then place the stainless steel sheet after sandblasting for 30 s on the processing platform of M2 using, and fix it with a fixture.

[0032] Set the printing parameters 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, printing layer thickness 50 μm. Use 99.99% argon as the shielding gas, control the oxygen content below 50 ppm, preheat the substrate, the preheating temperature is 150°, and the time is 30 min. Start the system to perform 3D printing in the area to be welded of the stainless steel sheet. The schematic diagram of 3D printing processing is as Figure 3 shown. The material used for 3D printing is high-entropy alloy powder, which is formed by mixing Fe element, Co element, Ni element, Cr element, and Mn element in a mass ratio of 1:1:1:1:1 to obtain the steel sheet to be welded.

[0033] Put the aluminum alloy sheet to be welded and the steel sheet to be welded into an ultrasonic cleaning device with propanol added and vibrate and clean at room temperature for 60 s to remove the processing debris on the processing surface.

[0034] Assemble the cleaned and dried aluminum alloy sheet to be welded and the steel sheet to be welded in the form of steel on top and aluminum below, and fix them well with a tooling fixture.

[0035] Set the downward pressure speed of the tool head to 10 mm / min and the rotation speed to 2000 rpm. After the tool head contacts the aluminum alloy plate to be welded above, continue to press down by 0.6 mm and then stop pressing. After staying for 60 s, the tool head retracts. The schematic diagram of aluminum-steel friction welding is as shown in Figure 4 After cooling for 1 min, the welding is completed.

[0036] In the solution of Example 1, during the friction welding process, the subtractive micro-texture on the surface of the aluminum alloy plate and the additive micro-texture on the steel plate mainly carried out structural interlocking and atomic diffusion, realizing that without changing the physical morphology of the base metal micro-texture, mainly by means of the additive high-entropy alloy micro-texture to effectively disperse the continuous layered distribution of the brittle phase at the interface. On the other hand, the formation and growth of the brittle IMC at the interface were inhibited through the high-entropy effect and the retarded diffusion effect. Example 2, referring to Example 1, the difference between it and Example 1 is that the long strip-shaped grooves are parallel to each other, and the cross-section of the subtractive micro-texture on the surface is tooth-shaped (as shown in Figure 6 ). The distance between adjacent long strip-shaped grooves is 120 μm, the width of the long strip-shaped grooves is 80 μm, and the depth is 400 μm. In the solution of this Example 2, the subtractive micro-texture on the surface of the aluminum alloy plate and the additive micro-texture on the steel plate mainly carried out structural interlocking and atomic diffusion, realizing that without changing the physical morphology of the base metal micro-texture, mainly by means of the additive micro-texture to hinder the formation of the brittle Fe-Al intermetallic compound phase and react with the texture layer to form a simple disordered solid solution structure.

[0037] Comparative Example 1: Carried out in the same way as Example 1, the difference is only that: no subtractive micro-texture was constructed on the aluminum alloy plate, and no additive micro-texture matching the surface texture was constructed on the stainless steel plate using high-entropy alloy powder. In this solution, the bonding interface of the obtained welded joint is a whole-layer hard and brittle Fe-Al IMC layer, distributed on the entire bonding interface.

[0038] Comparative Example 2: Carried out in the same way as Example 1, the difference is only that: the rotation speed of the tool head for friction welding is 5000 rpm, and the residence time is 150 s. In this solution, the bonding interface of the obtained welded joint has multiple large sheet-shaped hard and brittle Fe-Al IMC layers and other simple FCC or BCC phases, and the morphology of the micro-texture is severely compressed and deformed, that is, the physical structure of the micro-texture has changed.

[0039] The tensile mechanical properties of the welded joints obtained in the examples and comparative examples were tested three times respectively. The three tensile loads of the welded joint of Example 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 of 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 of Example 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%.

[0040] Example 3, referring to Example 1, the difference between it and Example 1 is that: the surface subtractive micro-texture uses cylindrical grooves, and the additive micro-texture uses cylindrical protrusions, 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 welded 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 the continuous layered distribution of the interface brittle phase is discretized by the additive micro-texture corresponding to the alloy powder; 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; and / or, The surface subtractive microtexture comprises a plurality of circular grooves arranged in a rectangular and / or circular array; and / or, The surface subtractive micro-texture comprises a plurality of closely arranged long strip V-shaped grooves, wherein the opening of the long strip V-shaped grooves has a width of 0.2-1 mm and a depth of 0.1-0.5 mm.

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 claim 3, characterized in that: The spacing between adjacent long strip-shaped grooves is 100-200 μm, the width of the long strip-shaped grooves is 50-100 μm, and the depth thereof is 300-500 μm; And / or, 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.

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 includes: 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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