A titanium-steel dissimilar metal and its processing method

Abstract

This invention discloses a titanium-steel dissimilar metal and its processing method. The materials are placed in an overlapping manner from top to bottom in the order of stainless steel, copper foil, vanadium foil, and titanium alloy. The overlapping areas are welded to fuse the materials. During the welding process, the V foil does not completely melt, which effectively hinders the diffusion of elements from the base materials on both sides and avoids the formation of Ti-Fe binary brittle phase in the joint. At the same time, it prevents Cu elements from diffusing downward and combining with Ti elements to form Cu-Ti binary brittle phase, thereby greatly improving the mechanical properties of the joint.

Description

Technical Field

[0001] This invention belongs to the field of dissimilar material welding (connection), and particularly relates to a titanium-steel dissimilar metal and its processing method. It has applications in the fields of new energy vehicles, aerospace, and nuclear power industries. Background Technology

[0002] Heterogeneous composite structures made of titanium alloys and steel through welding combine the advantages of titanium alloys (good corrosion resistance and high specific strength) and steel (superior overall performance, ease of processing, and low cost). Therefore, they have broad application prospects in new energy vehicles, medical equipment, aerospace, and nuclear power industries. However, welded joints made of titanium / steel dissimilar metals are prone to forming brittle Ti-Fe intermetallic compounds. Furthermore, due to significant differences in their physicochemical properties, the welded joint exhibits high residual stress, resulting in poor mechanical properties.

[0003] In the process of realizing this invention, the inventors discovered that the prior art has at least the following problems:

[0004] Existing technologies that add single interlayer materials such as Cu, Ni, and V can reduce the content of brittle Ti-Fe intermetallic compounds in titanium / steel laser-welded joints to some extent, thus improving the joint's mechanical properties. However, the addition of a single interlayer material cannot prevent the interdiffusion of Ti and Fe elements in the base metal during welding, resulting in the formation of a certain amount of brittle Ti-Fe phase in the joint. Therefore, the improvement in mechanical properties of joints prepared by laser welding of dissimilar metals like titanium / steel using current techniques with the addition of a single interlayer material is limited.

[0005] CN104028914A, "Welding Wire for Welding the Near-Steel Layer of Titanium-Pipeline Steel Composite Plate and its Preparation Method," discloses a welding wire for welding the near-steel layer of titanium-pipeline steel composite plates, composed of the following components by mass percentage: Si 2.7–3.3%, Mn 1.2–1.8%, C ≤ 0.04%, P ≤ 0.007%, S ≤ 0.035%, with the balance being Cu, and the sum of the mass percentages of all components being 100%. However, this method also fails to solve the aforementioned technical problems. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a titanium / steel dissimilar metal and its processing method. Addressing the issue of a large amount of Ti-Fe binary brittle phase in titanium / steel dissimilar metal joints, this invention uses a laser beam as the welding heat source, and stacks Cu and V foils of unequal thickness as a composite intermediate layer material. The welding structure adopts an lap joint form. By adjusting and optimizing the laser process parameters, a stainless steel-copper-vanadium (incompletely melted)-titanium alloy welded joint is obtained. Because the V foil does not completely melt during the welding process, it effectively hinders the diffusion of elements from the base materials on both sides, avoiding the formation of Ti-Fe binary brittle phases in the joint. Simultaneously, it prevents Cu elements from diffusing downwards and combining with Ti elements to form Cu-Ti binary brittle phases, thereby significantly improving the mechanical properties of the joint.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a titanium-steel dissimilar metal, wherein the materials are placed in an overlapping manner from top to bottom in the order of stainless steel, copper foil, vanadium foil and titanium alloy, and the overlapping areas are welded to fuse the materials.

[0008] After the materials are placed, use clamps to hold them in place, so that the materials are kept in pressure.

[0009] The fixture has a base plate on which stainless steel, copper foil, vanadium foil, and titanium alloy are placed in sequence. Pressure plates are provided on both sides of the base plate, and the pressure plates are connected to the base plate by fastening nuts. The pressure plates can clamp the materials.

[0010] The vanadium foil is 0.05 mm thick, and the copper foil is 0.03 mm thick.

[0011] The above-mentioned titanium steel dissimilar metal processing method adopts a welding process, and the welding is performed using a high-efficiency ytterbium-doped fiber laser.

[0012] During welding, the laser emission angle is adjusted to weld the overlapping areas, resulting in a stainless steel-copper foil weld. The copper foil interlayer continues to conduct heat downwards, forming a copper foil-vanadium foil weld and a vanadium foil-titanium alloy weld.

[0013] To prevent Fe and Ti elements in the stainless steel and titanium alloy base materials from diffusing into each other, the welding speed and laser power were adjusted to ensure that the vanadium foil interlayer did not completely melt. After welding, a joint was obtained consisting of a weld formed by the melting of stainless steel and copper, a weld formed by copper and vanadium, a weld formed by the incomplete melting of vanadium foil and a weld formed by the thermal conduction of vanadium and titanium alloy.

[0014] The high-efficiency ytterbium-doped fiber laser has a laser power of 2800W-3000W and a defocusing amount of 0.

[0015] The laser emission angle is 9°-12° with the material surface.

[0016] The laser welding speed is 30 mm / s. Through welding, welded joints are formed by the melting of stainless steel and copper, and by the thermal conduction of copper-vanadium and vanadium-titanium alloys.

[0017] One of the above technical solutions has the following advantages or beneficial effects: Addressing the problem of a large amount of Ti-Fe binary brittle phase in titanium / steel dissimilar joints, a laser beam is used as the welding heat source, and Cu foil and V foil of unequal thickness are stacked as a composite intermediate layer material. The welding structure adopts an lap joint form. By adjusting and optimizing the laser process parameters, a stainless steel-copper-vanadium (incompletely melted)-titanium alloy welded joint is obtained. Because the V foil is not completely melted during the welding process, it effectively hinders the diffusion of elements from the base materials on both sides, avoiding the formation of Ti-Fe binary brittle phases in the joint. Simultaneously, it prevents Cu elements from diffusing downwards and combining with Ti elements to form Cu-Ti binary brittle phases, thereby significantly improving the mechanical properties of the joint. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the welding structure and welding process of titanium steel dissimilar metal and its processing method provided in the embodiments of the present invention;

[0019] Figure 2 Microstructure morphology of the titanium alloy-stainless steel joint of the present invention: (a) low magnification photograph of the cross-section of the stainless steel-copper-vanadium-titanium alloy weld, (b) high magnification photograph of the central area near the stainless steel side of the cross-section of the stainless steel-copper-vanadium-titanium alloy weld, (c) high magnification photograph of the central area near the titanium alloy side of the cross-section of the stainless steel-copper-vanadium-titanium alloy weld.

[0020] Figure 3 This is a schematic diagram of the preparation process of the titanium alloy-stainless steel welded joint of the present invention.

[0021] The markings in the above figures are: 1. Positioning base plate, 2. Pressure plate, 3. Fastening adjusting nut, 4. Stainless steel plate, 5. Titanium alloy plate, 6. Cu and V foil composite intermediate layer. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1

[0024] See Figures 1-3This invention relates to a titanium-steel dissimilar metal composite material. The materials are arranged in a top-to-bottom sequence: stainless steel 4, copper foil, vanadium foil, and titanium alloy 5, overlapping each other. The overlapping areas are then welded to fuse the materials. After placement, a clamp is used to maintain pressure between the base material and the intermediate layers at each contact surface. This overlapping welded structure (stainless steel 4-copper-vanadium-titanium alloy 5) requires only one welding operation, and the welded joint is achieved through heat conduction.

[0025] The fixture has a base plate 1, on which stainless steel 4, copper foil, vanadium foil, and titanium alloy 5 are placed in sequence. Pressure plates 2 are provided on both sides of the base plate 1, and are connected to the base plate 1 by fastening nuts 3. The pressure plates 2 can clamp the materials. After the materials are placed, the fixture is used to hold them, maintaining a certain clamping force between the contact surfaces of the welding base material and the intermediate layer material.

[0026] The vanadium foil is 0.05 mm thick, and the copper foil is 0.03 mm thick. The thickness of the copper and vanadium foils in the composite intermediate layer is controlled to ensure that the vanadium foil does not completely melt, thereby hindering the mutual diffusion of Ti and Fe elements in the base material, and to form an effective weld joint.

[0027] The processing method employs welding technology, using a high-efficiency ytterbium-doped fiber laser. By optimizing process parameters, the joint performance is improved to achieve the optimal weld morphology, avoiding defects such as porosity, spatter, and cracking. The welded joint obtained through laser welding exhibits good surface morphology, uniform weld, and is free from defects such as porosity, spatter, cracks, and incomplete penetration, demonstrating excellent welding process performance.

[0028] During welding, the laser emission angle is adjusted to weld the overlapping areas, resulting in a stainless steel 4-copper foil weld. The copper foil intermediate layer continues to conduct heat downwards, forming a copper foil-vanadium foil weld and a vanadium foil-titanium alloy 5 weld.

[0029] To prevent Fe and Ti elements in the stainless steel 4 and titanium alloy 5 base materials from diffusing into each other, the welding speed and laser power were adjusted so that the vanadium foil intermediate layer did not melt completely. After welding, a joint was obtained consisting of a weld formed by the melting of stainless steel 4 and copper, copper-vanadium, incompletely melted vanadium foil, and a weld formed by the thermal conduction of vanadium-titanium alloy 5.

[0030] Because copper foil has excellent ductility and plasticity, it relieves stress in the joint during welding and cooling, thereby improving the joint's mechanical properties. Composite welded joints consisting of welds formed by the melting of stainless steel 4 and copper, and welds formed by the thermal conduction of copper-vanadium and vanadium-titanium alloys 5, achieve tensile strengths of 380-410 MPa.

[0031] The high-efficiency ytterbium-doped fiber laser has a power of 2800W-3000W and a defocusing amount of 0. The laser emission angle is 9°-12° to the material surface. The laser welding speed is 30mm / s. Through welding, welded joints are formed by the melting of stainless steel 4-copper and the formation of welds between copper-vanadium and vanadium-titanium alloys 5 through thermal conduction. By precisely adjusting parameters such as laser power, intermediate layer thickness, and welding speed, the formation of the Ti-Fe binary brittle phase in the stainless steel 4-vanadium-copper-titanium alloy 5 welded joint is controlled. Maintaining the composite interlayer thickness at 0.05mm vanadium foil and 0.03mm copper foil, a welding speed of 30mm / s, and a defocusing amount of 0, at a laser power of 2800W, no Ti-Fe phase was found in the weld zone. Near the stainless steel side (4), the molten vanadium foil formed a large amount of (Fe, V) and (Cr, V) solid solutions with the two base materials, along with a small amount of brittle CuTi2 phase. Near the titanium alloy side (5), a (β-Ti, V) solid solution was formed, indicating a relatively brittle joint. At a laser power of 3000W, the welding power was high, and the heat input... Excessive laser power leads to joint cracking and propagation, rendering it unusable. At a laser power of 2900W, no Ti-Fe phase was observed in the weld zone. Near the stainless steel side (4), the molten vanadium foil formed a large amount of (Fe, V) and (Cr, V) solid solutions with the two base materials. Near the titanium alloy side (5), a large amount of (β-Ti, V) solid solutions and a small amount of Cu-Al ductile phase were formed. This reduced joint brittleness. Furthermore, due to the excellent ductility and plasticity of the copper foil, stress was relieved during welding and cooling, resulting in a significant improvement in mechanical properties.

[0032] The incompletely melted vanadium interlayer effectively prevents the diffusion and bonding of Ti, Fe, and Cu, Ti elements, thus avoiding the formation of Ti-Fe and Cu-Ti binary brittle phases in the joint. Simultaneously, strict control of laser power and welding speed ensures the formation of (Fe, V), (Cr, V), and (β-Ti, V) solid solutions in the joint. Furthermore, the excellent ductility and plasticity of the copper foil alleviate stress during welding and cooling, thereby improving the joint's mechanical properties.

[0033] A superior titanium / steel dissimilar metal lap-joint laser heat-conducting welding process has been achieved by innovatively employing a lap structure with an unequal-thickness copper-vanadium composite interlayer. This process optimizes the microstructure of the titanium / steel dissimilar metal weld joint, improves its weldability, and enhances the mechanical properties of the joint. This lap-joint laser heat-conducting welding process with an unequal-thickness copper-vanadium composite interlayer is original in the field of dissimilar material welding (joining).

[0034] Example 2

[0035] This invention relates to a laser welding process for dissimilar titanium / steel metals, employing a composite interlayer of Cu and V foils of unequal thickness. Addressing the issue of abundant Ti-Fe binary brittle phases in titanium / steel dissimilar joints, this method uses a laser beam as the welding heat source and stacks Cu and V foils of unequal thickness as the composite interlayer material. The welding structure utilizes an lap joint. By adjusting and optimizing laser process parameters, the formation of Ti-Fe binary brittle phases in the joint is effectively avoided, thereby significantly improving the mechanical properties of the joint. Laser thermal conductivity welding is used to obtain high-quality welded joints composed of welds formed by the melting of stainless steel and copper, incompletely melted vanadium foil, and welds formed by thermal conduction between copper-vanadium and copper-titanium alloys. The process steps are as follows: materials are stacked according to the designed welding structure → the contact surfaces of the materials are locked with locking nuts → the laser performs welding by irradiating the stainless steel surface in a single pass, thus achieving the connection of dissimilar materials such as titanium alloy and stainless steel. Specific steps are as follows:

[0036] (1) Welding structure: The base material and intermediate layer material are overlapped from top to bottom in the order of stainless steel, copper foil, vanadium foil and titanium alloy. After placement, clamps are used to hold them so that a certain pressure is maintained between the contact surfaces of the base material and the intermediate layer material.

[0037] (2) Welding process: Welding is carried out using a high-efficiency ytterbium-doped fiber laser. The laser emission angle is 9°-12° to the material surface, the laser power is 2800W-3000W, the welding speed is 30mm / s, and the defocusing amount is 0. Welding improves the joint performance and aims to obtain the optimal weld morphology, avoiding defects such as porosity, spatter, and cracking.

[0038] (3) When welding, adjust the laser emission angle and weld the overlapping area to obtain a stainless steel-copper foil weld. The copper foil middle layer will continue to conduct heat downward to form a copper foil-vanadium foil weld and a vanadium foil-titanium alloy weld.

[0039] (4) The vanadium foil intermediate layer in the welded joint does not melt completely, which allows the Fe, Ti and Cu, Ti elements in the stainless steel and titanium alloy base material to diffuse and combine, thereby avoiding the formation of Ti-Fe and Cu-Ti binary brittle phases in the joint.

[0040] By precisely adjusting parameters such as laser power, interlayer thickness, and welding speed, the formation of the Ti-Fe binary brittle phase in the stainless steel-vanadium-copper-titanium alloy weld joint can be controlled. Maintaining a composite interlayer thickness of 0.05mm vanadium foil and 0.03mm copper foil, a welding speed of 30mm / s, and zero defocusing, at a laser power of 2800W, no Ti-Fe phase was observed in the weld zone. Near the stainless steel side, the molten vanadium foil formed a large amount of (Fe, V) and (Cr, V) solid solutions with the two base materials, along with a small amount of CuTi2 brittle phase. Near the titanium alloy side, a (β-Ti, V) solid solution was formed, resulting in a relatively brittle joint. At a laser power of 3000W, the welding power was high, and the heat input... If the laser power is too high, cracks will form and propagate in the joint, rendering it useless. When the laser power is 2900W, no Ti-Fe phase was found in the weld zone. On the side near the stainless steel, the molten vanadium foil formed a large amount of (Fe, V) and (Cr, V) solid solutions with the two base materials. On the side near the titanium alloy, a large amount of (β-Ti, V) solid solutions and a small amount of Cu-Al ductile phase were formed. The brittleness of the joint was reduced. At the same time, due to the excellent ductility and plasticity of the copper foil, the stress of the joint was relieved during welding and cooling, thereby significantly improving the mechanical properties.

[0041] Laser thermal conductive welding is employed, with precise adjustment of welding process parameters. The laser irradiates the stainless steel surface, creating a high-quality welded joint in a single process. This joint comprises a weld seam formed by the melting of stainless steel and copper, an incompletely melted vanadium foil, and a weld seam formed by the thermal conduction of copper-vanadium and copper-titanium alloys. Because the vanadium foil interlayer is not completely melted, it effectively prevents the interdiffusion and bonding of Ti and Fe elements, avoiding the formation of the Ti-Fe binary brittle phase. Furthermore, the heat input is controlled by adjusting the laser power, and the amounts of vanadium and copper elements are controlled by adjusting the thickness of the vanadium and copper foils in the composite interlayer. The copper foil is also positioned on top to minimize the formation of the Cu-Ti binary brittle phase. Simultaneously, the excellent ductility and plasticity of the copper foil alleviate stress during welding and cooling, significantly improving the mechanical properties of the joint.

[0042] By adopting the above scheme, and addressing the issue of a large number of Ti-Fe binary brittle phases in titanium / steel dissimilar joints, a laser beam was used as the welding heat source. Cu foils and V foils of unequal thickness were stacked as composite intermediate layer materials, and the welding structure adopted an lap joint form. By adjusting and optimizing the laser process parameters, a stainless steel-copper-vanadium (incompletely melted)-titanium alloy welded joint was obtained. Because the V foil did not completely melt during the welding process, it effectively hindered the diffusion of elements from both base materials, preventing the formation of Ti-Fe binary brittle phases in the joint. Simultaneously, it prevented Cu elements from diffusing downwards and combining with Ti elements to form Cu-Ti binary brittle phases, thereby significantly improving the mechanical properties of the joint.

[0043] In the description of this invention, it should be understood that the terms "coaxial," "bottom," "one end," "top," "middle," "other end," "upper," "side," "top," "inner," "front," "center," "both ends," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0044] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "screw connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0045] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for processing titanium steel dissimilar metals, characterized in that, The materials are placed in the following order from top to bottom: stainless steel, copper foil, vanadium foil, and titanium alloy. The overlapping areas are then welded to fuse the materials together. The processing method employs welding technology, and welding is carried out using a ytterbium-doped fiber laser. During welding, the laser emission angle is adjusted to weld the overlapping areas to obtain a stainless steel-copper foil weld. The copper foil middle layer continues to conduct heat downwards to form a copper foil-vanadium foil weld and a vanadium foil-titanium alloy weld. To prevent Fe and Ti elements in the stainless steel and titanium alloy base materials from diffusing into each other, the welding speed and laser power were adjusted to ensure that the vanadium foil interlayer did not completely melt. After welding, a joint was obtained consisting of a weld formed by the melting of stainless steel and copper, a weld formed by copper and vanadium, a weld formed by the incomplete melting of vanadium foil and a weld formed by the thermal conduction of vanadium and titanium alloy.

2. The method for processing titanium steel dissimilar metals as described in claim 1, characterized in that, After the materials are placed, use clamps to hold them in place, so that the materials are kept in pressure.

3. The method for processing titanium steel dissimilar metals as described in claim 2, characterized in that, The fixture has a base plate on which stainless steel, copper foil, vanadium foil, and titanium alloy are placed in sequence. Pressure plates are provided on both sides of the base plate, and the pressure plates are connected to the base plate by fastening nuts. The pressure plates can clamp the materials.

4. The method for processing titanium steel dissimilar metals as described in claim 3, characterized in that, The vanadium foil is 0.05 mm thick, and the copper foil is 0.03 mm thick.

5. The method for processing titanium steel dissimilar metals as described in claim 4, characterized in that, The ytterbium-doped fiber laser has a laser power of 2800W-3000W and a defocusing amount of 0.

6. The method for processing titanium steel dissimilar metals as described in claim 5, characterized in that, The laser emission angle is 9°-12° with the material surface.

7. The method for processing titanium steel dissimilar metals as described in claim 6, characterized in that, The laser welding speed is 30 mm / s. Through welding, welded joints are formed by the melting of stainless steel and copper, and by the thermal conduction of copper-vanadium and vanadium-titanium alloys.

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