Niobium interlayer assisted titanium-aluminum dissimilar metal ultrasonic-laser composite additive manufacturing method

Abstract

The invention belongs to the technical field of dissimilar metal additive manufacturing, and particularly relates to a niobium interlayer assisted titanium-aluminum dissimilar metal ultrasonic-laser composite additive manufacturing method. The method comprises the following steps: polishing the surfaces of an aluminum plate and niobium foil to remove an oxidation film; the niobium foil is placed on the surface of the aluminum plate and fixed, and the niobium foil is solidified through an ultrasonic additive manufacturing method; and melting a titanium alloy welding wire on the surface of the niobium foil by using a laser fuse additive method, and carrying out additive layer by layer in the same direction to finally realize effective connection of the titanium alloy wall body and the aluminum alloy substrate. According to the method, the niobium middle layer is prepared through ultrasonic additive manufacturing, and the titanium alloy is added in combination with laser fuse, so that aluminum-titanium dissimilar metal additive manufacturing is achieved, and the formed multi-channel multi-layer additive has good mechanical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of dissimilar metal additive manufacturing, and specifically relates to a niobium intermediate layer assisted titanium-aluminum dissimilar metal ultrasonic-laser composite additive manufacturing method. Background Art

[0002] Laser additive manufacturing has attracted wide attention in the fields of aerospace, military, automobile, etc. due to its advantages of high production efficiency, unlimited size, and low heat input. With the rapid development of industry, the demand for thin-walled structures of heterogeneous materials has gradually increased. Laser additive manufacturing technology, with its convenience and ability to achieve near-net shape, provides a new method for this.

[0003] Aluminum alloys are now widely used in the automotive, aerospace and other fields for lightweighting due to their low density and easy processing. However, the large-scale use of aluminum alloys can easily lead to strength problems. Titanium alloys have low density and high strength, and are considered to be a good material for local strengthening. Titanium / aluminum dissimilar metal additive manufacturing can achieve local strengthening and functional zoning. While retaining the lightweight characteristics, titanium alloys are used to enhance the strength, wear resistance and corrosion resistance in the local load-bearing area, combining the advantages of titanium and aluminum to achieve the unity of lightweight and high strength. Therefore, research on titanium / aluminum dissimilar metal additive manufacturing has received widespread attention. However, due to the large difference in thermophysical properties between aluminum alloys and titanium alloys, and the easy formation of brittle Ti-Al intermetallic compounds (IMCs), it is difficult to achieve effective connection.

[0004] Because the melting point of aluminum alloy is much lower than that of titanium alloy, in order to reduce interface reaction, researchers generally adopt the method of melting aluminum on a titanium substrate to realize aluminum / titanium dissimilar metal additive manufacturing. However, due to the influence of cost and production efficiency, it is more necessary to melt titanium on an aluminum substrate to realize aluminum / titanium dissimilar metal additive manufacturing in actual industrial production. At present, there are few studies on titanium / aluminum dissimilar additives with aluminum as the substrate. In addition, due to the large difference in the melting points of aluminum and titanium, the cladding of titanium alloy on the aluminum substrate will cause a large amount of aluminum to melt, thereby generating a large amount of brittle IMCs at the interface, resulting in very low interface strength. Therefore, a new method is needed to realize aluminum-titanium dissimilar additives with aluminum as the substrate while achieving a certain interface bonding strength. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing a niobium intermediate layer by ultrasonic additive manufacturing and combining it with laser fuse additive manufacturing of titanium alloy, thereby realizing aluminum-titanium dissimilar metal additive manufacturing and achieving good interface bonding strength.

[0006] To achieve the above object, the present invention provides the following technical solution: a niobium intermediate layer assisted titanium aluminum dissimilar metal ultrasonic-laser composite additive manufacturing method, comprising the following steps: (1) Grinding the surface of the aluminum plate and niobium foil to remove the oxide film; (2) placing the niobium foil on the surface of the aluminum plate and fixing it, and consolidating the niobium foil using an ultrasonic additive manufacturing method; (3) The titanium alloy welding wire is melted on the surface of the niobium foil using the laser fuse additive method, and additive processing is performed layer by layer in the same direction, ultimately achieving an effective connection between the titanium alloy wall and the aluminum alloy substrate.

[0007] Preferably, the niobium foil used in step (1) is pure niobium with a purity of not less than 99.9%, and the thickness of the niobium foil is 0.2 mm.

[0008] Preferably, the width of the ultrasonic additive manufacturing platform sonotrode used in step (2) needs to be greater than the width of the niobium foil used.

[0009] Preferably, in step (2), the niobium foil consolidation process is an ultrasonic frequency of 20 kHz, an amplitude of 20-25 μm, a speed of 5 mm / s, and a pressure of 0.35 MPa.

[0010] Preferably, in the step (3), the laser fuse additive process has a laser power of 1.8-3 kW, a wire feeding speed of 30-50 mm / s, a defocusing amount of +2-+12 mm, a welding speed of 0.3-1.2 m / min, and a laser deflection angle of 3-10°.

[0011] The ultrasonic-laser composite additive manufacturing method adopted by the present invention uses ultrasonic additive manufacturing technology to consolidate niobium foil as an intermediate layer on an aluminum substrate, and adds titanium alloy by laser fusing. Since the melting point of niobium is significantly higher than that of titanium, when the titanium alloy welding wire is deposited and contacts the surface of the niobium foil under the action of laser energy, only the niobium in the center is melted, and the unmelted niobium on both sides has a significant hindering effect on the mass transfer behavior of the titanium molten pool into the aluminum, thereby reducing the area of ​​the reaction zone, and the titanium that passes through the niobium foil and is transferred to the aluminum is strongly heat-dissipated by the aluminum, and the aluminum is melted by the heat transfer of the titanium molten pool. Therefore, the titanium molten pool flows to both sides after passing through the niobium foil, and finally forms a rivet-like structure, which strengthens the interface. At the same time, the niobium melted in the center enters the molten pool and is doped in the titanium-aluminum brittle IMCs. It can effectively improve the plasticity and toughness of the joint. In addition, with the increase of the number of titanium alloy additive layers, the residual stress caused by the huge difference in thermal expansion coefficients between aluminum and titanium will gradually increase. Niobium as an intermediate layer has good plasticity and toughness, which can have a good buffering effect on the interface residual stress. The niobium foil consolidated by ultrasonic additive technology and the aluminum matrix form an effective connection through atomic diffusion and mechanical interlocking. Under the multi-layer additive thermal cycle, the atomic diffusion at the aluminum / niobium interface under the unmelted niobium foil intensifies. As the number of additive layers increases, a micron-level aluminum-niobium reaction layer is gradually formed, which has good mechanical properties. In addition, multiple layers of additives will form multiple rivet-like structures and form interlocking. During tensile or shear tests, this multi-pass interlocking rivet-like structure can bear loads synergistically, thereby achieving good mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A schematic diagram of a method for consolidating a niobium intermediate layer on an aluminum substrate by ultrasonic additive provided by the present invention; Figure 2 A schematic diagram of the method for laser fusing titanium alloy provided by the present invention; Figure 3 The SEM image and EDS surface scan result of the interface structure in Example 1 of the present invention; Figure 4 is the interface structure light microscope image in Example 1 of the present invention; Figure 5 This is a SEM image of the Al-Nb interface in Example 1 of the present invention; Figure 1-2 Middle: 1 is 6061 aluminum substrate, 2 is niobium foil, 3 is sonotrode pressure head, 4 is ultrasonic generator, 5 is cylinder, 6 is sonotrode vibration direction, 7 is additive base, 8 is fiber laser, 9 is laser head, 10 is laser beam, 11 is protective gas chamber, and 12 is TC4 welding wire. DETAILED DESCRIPTION

[0013] The technical scheme of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0014] Example 1 A niobium intermediate layer assisted titanium aluminum dissimilar metal ultrasonic-laser composite additive manufacturing method, such as Figure 1 and Figure 2 As shown, the specific steps are: (1) Use a drilling machine to machine two through holes with a diameter of 10 mm along the central axis of the aluminum substrate, and use sandpaper to polish the surface of the aluminum substrate and the niobium foil to remove the oxide film. The aluminum substrate material used is 6061-T6 aluminum alloy with a size of 120 mm × 80 mm × 10 mm. The niobium foil material used is pure niobium with a size of 150 mm × 16 mm × 0.2 mm. (2) The niobium foil was placed on the surface of the aluminum substrate and fixed, and the niobium foil was consolidated using an ultrasonic additive manufacturing platform. The consolidation parameters used were an ultrasonic frequency of 20 kHz, an amplitude of 20-25 μm, a speed of 5 mm / s, and a pressure of 0.35 MPa; (3) Place the aluminum substrate with niobium foil in the protection cabin of the laser fuse additive platform, adjust the laser beam position and angle, make the laser deflection angle 3°, the angle between the welding wire and the substrate 45°, set the laser parameters to laser power 2 kW, wire feeding speed 40 mm / s, defocusing amount +8 mm, welding speed 1 m / min, and set the additive path; (4) Open the valve of the argon gas bottle and introduce pure argon gas into the protective cabin for 10 minutes at a gas flow rate of 20 L / min to ensure that the aluminum substrate and welding wire are in an oxygen-free environment during the additive process; (5) After the protective gas is turned on, multiple additive processes are carried out, and the cooling time between passes is 10 minutes; (6) After the first layer of titanium alloy deposition is completed, the additive process parameters are adjusted to laser power 2 kW, wire feeding speed 30 mm / s, defocusing amount +8 mm, welding speed 0.3 m / min, and the additive path is set; (7) Continue to perform subsequent multi-pass multi-layer additive manufacturing, and keep the process parameters the same as in step (6). After the additive manufacturing is completed, let it stand for a period of time, and take it out after the workpiece is completely cooled. After the above steps, the niobium foil is partially melted, and a semi-metallurgical-semi-solid composite interface will be formed.

[0015] The interface of the sample after additive manufacturing in Example 1 was characterized. The specific method was as follows: a cross section of the additive sample was cut using an electric spark wire cutting machine, and the cross section should cover the width of multiple layers of the sample and part of the parent material. The cross section was metallographically prepared, and polished with 400 mesh, 800 mesh, 1500 mesh, and 2500 mesh metallographic sandpaper in sequence, and then polished with 5 μm diamond polishing liquid and 0.04 μm alumina polishing liquid respectively, and the microstructure was observed using an optical digital microscope (OM) and a scanning electron microscope (SEM); tensile and shear specimens were cut using an electric spark wire cutting machine, and tensile and shear tests were performed using a universal mechanical testing machine to evaluate the tensile and shear strengths of the additive joint.

[0016] The results are as follows Figure 3-Figure 5 As shown, Figure 3 The SEM image and EDS surface scan results of the interface structure of Example 1 are shown below. Figure 4 is the interface structure light microscope image in Example 1. Figure 3It can be seen that only the center of the niobium foil melts under the heat transfer of the TC4 titanium alloy droplet, and the unmelted niobium foil on both sides hinders the flow of the titanium molten pool into the aluminum matrix, thereby reducing the area of ​​reaction with aluminum. The titanium that passes through the niobium foil and is transferred to the aluminum is strongly dissipated by the aluminum, and the aluminum is melted by the heat transfer of the titanium molten pool. Therefore, the titanium molten pool flows to both sides after passing the niobium foil, and finally forms a rivet-like structure, which strengthens the interface. At the same time, the niobium melted in the center enters the molten pool and is doped in the titanium-aluminum brittle IMCs, which can effectively improve the plastic toughness of the joint. At the same time, since the niobium foil is consolidated to the surface of the aluminum matrix by ultrasonic action, the severe deformation and mechanical interlocking characteristics between the unmelted niobium and aluminum caused by ultrasonic action are retained, so the residual stress caused by the increase in the number of titanium additive layers can be effectively overcome to avoid deformation.

[0017] Depend on Figure 4 It can be seen that when multiple layers of material are added, multiple rivet structures will be formed and interlocked, resulting in Figure 4 The serrated interface shown is composed of partial metallurgical bonding and partial solid phase connection. During tensile or shear tests, this multi-pass interlocking rivet structure can bear the load synergistically, thereby achieving good mechanical properties.

[0018] Depend on Figure 5 It can be seen that during multiple additions, atomic diffusion can occur at the interface between unmelted niobium and aluminum under the action of heat transfer. As the number of additive layers increases, the amount of atomic diffusion gradually accumulates and eventually forms Figure 5 The compound layer distributed along the niobium layer is shown in Table 1. According to the EDS point scanning results, the compound layer is an aluminum-niobium compound, which further enhances the interface strength. The final tensile strength is 127 MPa and the shear strength is 81 MPa.

[0019] Table 1 Figure 5 Elemental composition and possible phases at different positions in Location Mg Al Si Ti V Nb Possible phase 1 0.41 1.34 0.33 0.28 0.04 97.61 Nb 2 1.79 95.23 1.05 1.93 0 0 Al 3 0.91 78.33 0.78 2.41 0 17.56 <![CDATA[Al+Al 3 Nb]]> 4 0.71 86.19 0.62 8.44 0.02 4.01 <![CDATA[Al+Al 3 If]]> 5 1.08 85.53 0.57 3.58 0.03 9.20 <![CDATA[Al+Al 3 Nb <!-- 3 -->]]> 6 0.79 80.60 0.56 3.03 0.02 14.99 <![CDATA[Al+Al 3 Nb]]> 7 0.29 77.14 0.41 15.86 0.14 6.17 (Al, Ti, Nb) .

[0020] In summary, compared with the prior art, the present invention combines laser additive technology with ultrasonic additive technology to achieve additive manufacturing of aluminum-titanium dissimilar metals with aluminum as the substrate, regulates the interface to a semi-metallurgical and semi-solid form, and obtains good mechanical properties. The present invention uses ultrasonic additive manufacturing technology to consolidate niobium foil as an intermediate layer on an aluminum substrate, and adds titanium alloy by laser fusing. Since the melting point of niobium is significantly higher than that of titanium, only the niobium in the center melts when the titanium alloy welding wire is deposited and contacts the surface of the niobium foil under the action of laser energy. The unmelted niobium on both sides significantly hinders the mass transfer behavior of the titanium molten pool into the aluminum, thereby reducing the area of ​​the reaction zone. The titanium that crosses the niobium foil and is transferred to the aluminum is strongly dissipated by the aluminum, and the aluminum is melted by the heat transfer from the titanium molten pool. Therefore, the titanium molten pool flows to both sides after crossing the niobium foil, and finally forms a rivet-like structure, which strengthens the interface. At the same time, the niobium melted in the center enters the molten pool and is doped in the titanium-aluminum brittle IMCs, which can effectively improve the joint. In addition, as the number of titanium alloy additive layers increases, the residual stress caused by the huge difference in thermal expansion coefficients between aluminum and titanium will gradually increase. Niobium, as an intermediate layer, has good plasticity and toughness, which can have a good buffering effect on the interface residual stress. The niobium foil consolidated by ultrasonic additive technology and the aluminum matrix form an effective connection through atomic diffusion and mechanical interlocking. Under the multi-layer additive thermal cycle, the atomic diffusion at the aluminum-niobium interface below the unmelted niobium foil intensifies. As the number of additive layers increases, a micron-level aluminum-niobium reaction layer is gradually formed, which has good mechanical properties. In addition, when multiple layers are added, a multi-pass rivet structure will be formed and interlocked. This multi-pass interlocking rivet structure can cooperate to bear the load during tensile or shear tests, thereby achieving good mechanical properties. Finally, an aluminum-titanium dissimilar additive joint with a tensile strength of 127 MPa and a shear strength of 81 MPa was obtained.

[0021] The above is only a preferred embodiment of the present invention. For those skilled in the art, relevant improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A niobium intermediate layer-assisted titanium-aluminum dissimilar metal ultrasonic-laser composite additive manufacturing method, comprising the following steps: (1) Grinding the surface of the aluminum plate and niobium foil to remove the oxide film; (2) placing the niobium foil on the surface of the aluminum plate and fixing it, and consolidating the niobium foil using an ultrasonic additive manufacturing method; (3) The titanium alloy welding wire is melted on the surface of the niobium foil using the laser fuse additive method, and additive processing is performed layer by layer in the same direction, ultimately achieving an effective connection between the titanium alloy wall and the aluminum alloy substrate.

2. The niobium intermediate layer-assisted titanium-aluminum dissimilar metal ultrasonic-laser composite additive manufacturing method according to claim 1 is characterized in that: The niobium foil is pure niobium with a purity of not less than 99.9%, and the thickness of the niobium foil is 0.2 mm.

3. The niobium intermediate layer-assisted titanium-aluminum dissimilar metal ultrasonic-laser composite additive manufacturing method according to claim 1 is characterized in that: The width of the ultrasonic additive manufacturing platform sonotrode must be greater than the width of the niobium foil used.

4. The niobium intermediate layer assisted titanium aluminum dissimilar metal ultrasonic-laser composite additive manufacturing method according to claim 1, characterized in that: The niobium foil consolidation process is an ultrasonic frequency of 20 kHz, an amplitude of 20-25 μm, a speed of 5 mm / s, and a pressure of 0.35 MPa.

5. The niobium intermediate layer-assisted titanium-aluminum dissimilar metal ultrasonic-laser composite additive manufacturing method according to claim 1, characterized in that: The laser fuse additive process has a laser power of 1.8-3 kW, a wire feeding speed of 30-50 mm / s, a defocusing amount of +2-+12 mm, a welding speed of 0.3-1.2 m / min, and a laser deflection angle of 3-10°.

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