Welding method of metal joint

Abstract

The invention relates to the technical field of metal processing and welding, in particular to a welding method of a metal joint. The niobium foil is used as a middle layer of the stainless steel plate and the titanium alloy plate, then the CMT welding technology is used for welding, and the mechanical property of the stainless steel and titanium alloy joint welding seam can be improved at the same time in the modes of improving the mechanical property of the welding seam, reducing the welding heat cycle influence area in base metal and the like; and the generation possibility of brittle metal IMC at the stainless steel and titanium alloy welding joint is reduced.

Description

Technical Field

[0001] This application relates to the field of metal processing and welding technology, and specifically to a welding method for metal joints. Background Technology

[0002] With increasingly stringent requirements for structures in terms of corrosion resistance, high strength, electrical conductivity, thermal conductivity, wear resistance, high-temperature strength, and low cost, single metals or alloys are insufficient to meet diverse performance needs. Therefore, reliable connections between dissimilar metals are necessary to achieve comprehensive performance. Titanium alloys, due to their low density and high strength, have become ideal materials for lightweighting rail transit equipment. Furthermore, welded joints between titanium and stainless steel are not only used in rail vehicle repair processes but also have wide applications in the nuclear, chemical, and aerospace industries, making their reliable connections of significant practical importance.

[0003] Currently, the main methods for joining titanium and stainless steel include fusion welding, diffusion joining, explosive welding, brazing, and hot rolling joining. These methods are used to combine the two materials to meet the application needs of relevant industrial fields.

[0004] Due to the strong reaction between Ti and Fe, the aforementioned joining methods are prone to forming hard and brittle intermetallic compounds at high temperatures during implementation. The formation of this brittle phase significantly reduces the bonding strength of the titanium alloy-stainless steel welded joint, and may even cause cracking, severely affecting the mechanical properties and service life of the joint. The significant metallurgical incompatibility and physical property differences between titanium and stainless steel further exacerbate this problem. Summary of the Invention

[0005] In order to solve the technical problems involved in the background art, this application provides a welding method for metal joints. The welding method includes the following steps: providing at least one titanium alloy plate, at least one stainless steel plate, and at least one niobium foil, and sequentially performing a first grinding and a first cleaning on the titanium alloy plate and the stainless steel plate.

[0006] The stainless steel plate and titanium alloy plate are overlapped and fixed to the fixture along the first vertical direction. Niobium foil is sandwiched between the stainless steel plate and the titanium alloy plate. Then, the first cold metal transition welding is performed. When the arc is started, the welding torch is biased to one side of the stainless steel plate. When the arc is ended, the welding torch is moved at a constant speed in the width direction of the stainless steel plate. After welding, a metal joint is obtained.

[0007] According to one embodiment of this application, the thickness of the titanium alloy plate and the stainless steel plate is ≥2mm, and the overlap length between the projection of the titanium alloy plate along the first vertical direction and the surface portion of the stainless steel plate is 8-12mm.

[0008] According to one embodiment provided in this application, the welding parameters for the first cold metal transition welding are: welding current of 125-135A, welding speed of 7-9mm / s, and wire feed speed of 6.5-7.5mm / min.

[0009] According to one embodiment of this application, the protective gas includes argon gas, and the argon gas flow rate is 18-20 L / min.

[0010] According to one embodiment of this application, the welding wire for the first cold metal transition welding includes a silicon bronze alloy welding wire.

[0011] According to one embodiment provided in this application, when the arc is started, the welding torch is offset from the stainless steel plate weld by 0.5mm-1.5mm, and when the arc is terminated, the center of the weld termination is 1.5mm-2mm away from the center of the weld ignition.

[0012] According to one embodiment of this application, the overlap length between the arc-starting weld and the arc-ending weld is 15mm-20mm.

[0013] According to one embodiment of this application, the welding torch is at a 90° angle to the overlapping portion, and the welding torch is at a 60°-90° angle to the horizontal surface of the titanium alloy plate.

[0014] According to one embodiment provided in this application, the niobium foil portion of the structure is exposed on the outside of the stainless steel plate, and the niobium foil thickness is 10-200 μm.

[0015] According to one embodiment provided in this application, the stainless steel plate includes 304 stainless steel, and the titanium alloy plate includes TC4 titanium alloy.

[0016] Compared with the prior art, the significant technical advancement of this application lies in the fact that the present invention uses niobium foil as an intermediate layer between stainless steel plate and titanium alloy plate, and then uses CMT welding technology for welding. By improving the mechanical properties of the weld and reducing the area of ​​the base material affected by the welding thermal cycle, the mechanical properties of the weld of stainless steel and titanium alloy joint can be improved at the same time, and the possibility of brittle metal IMC formation at the stainless steel and titanium alloy weld joint can be reduced. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1A schematic diagram of the welding method provided in the embodiments of this application;

[0019] Figure 2 The load-strain curve diagram of Embodiment 1 provided in this application;

[0020] Figure 3 The load-strain curve diagram of Embodiment 2 provided in this application;

[0021] Figure 4 A metallographic schematic diagram of Embodiment 1 provided in this application;

[0022] Figure 5 This is a metallographic schematic diagram of Embodiment 2 provided in this application.

[0023] Explanation of reference numerals in the attached figures:

[0024] 100 - Stainless steel plate; 200 - Titanium alloy plate; 300 - Niobium foil.

[0025] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] First, those skilled in the art should understand that these embodiments are merely for explaining the technical principles of this application and are not intended to limit the scope of protection of this application. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0028] Secondly, it should be noted that in the description of this application, the terms "front", "rear", "left", "right", "up", "down", "inner", "outer", etc., which indicate the direction or positional relationship, are based on the direction or positional relationship shown in the accompanying drawings. This is only for the convenience of description and does not indicate or imply that the device or component must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this application.

[0029] Furthermore, it should be noted that, in the description of this application, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0030] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0031] With increasingly stringent requirements for structures in terms of corrosion resistance, high strength, electrical conductivity, thermal conductivity, wear resistance, high-temperature strength, and low cost, single metals or alloys are insufficient to meet diverse performance needs. Therefore, reliable connections between dissimilar metals are necessary to achieve comprehensive performance. Titanium alloys, due to their low density and high strength, have become ideal materials for lightweighting rail transit equipment. Furthermore, welded joints between titanium and stainless steel are not only used in rail vehicle repair processes but also have wide applications in the nuclear, chemical, and aerospace industries, making their reliable connections of significant practical importance.

[0032] Currently, the main methods for joining titanium and stainless steel include fusion welding, diffusion joining, explosive welding, brazing, and hot rolling joining. These methods are used to combine the two materials to meet the application needs of relevant industrial fields.

[0033] Due to the strong reaction between Ti and Fe, the aforementioned joining methods are prone to forming hard and brittle intermetallic compounds at high temperatures during implementation. The formation of this brittle phase significantly reduces the bonding strength of the titanium alloy-stainless steel welded joint, and may even cause cracking, severely affecting the mechanical properties and service life of the joint. The significant metallurgical incompatibility and physical property differences between titanium and stainless steel further exacerbate this problem.

[0034] Figure 1 A schematic diagram of the welding method provided in the embodiments of this application; Figure 2 The load-strain curve diagram of Embodiment 1 provided in this application; Figure 3 The load-strain curve diagram of Embodiment 2 provided in this application; Figure 4 A metallographic schematic diagram of Embodiment 1 provided in this application; Figure 5 This is a metallographic schematic diagram of Embodiment 2 provided in this application.

[0035] To address the technical problems mentioned in the background section, this application provides a welding method for metal joints, as detailed in the attached diagram. Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 The welding method includes the following steps: providing at least one titanium alloy plate 200, at least one stainless steel plate 100, and at least one niobium foil 300, and sequentially performing a first grinding and a first cleaning on the titanium alloy plate 200 and the stainless steel plate 100.

[0036] Partial structures of stainless steel plate 100 and titanium alloy plate 200 are sequentially overlapped along the first vertical direction and fixed on a fixture. Niobium foil 300 is clamped between stainless steel plate 100 and titanium alloy plate 200. Then, the first cold metal transition welding is performed. When the arc is started, the welding torch is biased to one side of stainless steel plate 100. When the arc is ended, the welding torch moves at a constant speed in the width direction of stainless steel plate 100. After welding, a metal joint is obtained.

[0037] It should be noted that the combination of mechanical sanding and alcohol cleaning can thoroughly remove oxide films and oil stains from the surfaces of 304 stainless steel and TC4 titanium alloy. Oxide films can hinder the metallurgical bonding between the base material and the niobium foil and filler wire, while oil stains decompose at the high welding temperatures, generating gases that lead to weld porosity defects. A clean surface provides a clean interface environment free of impurities for close contact between the niobium foil and the base materials on both sides, as well as for subsequent fusion, ensuring that the niobium foil can fully exert its physical barrier function and reducing joint brittleness caused by interface contamination from the source.

[0038] According to an embodiment of this application, in this step, the two plates are mechanically sanded with sandpaper and cleaned with alcohol to remove the oxide film and oil stains from the plate surfaces. According to an embodiment of this application, the plate materials can be stainless steel and titanium alloy plate 200. More specifically, the stainless steel plate 100 can include 304 stainless steel, and the titanium alloy plate 200 can include TC4 titanium alloy. The thickness of the plates used in this application can be 2 mm. Therefore, using this method to weld 304 stainless steel and TC4 titanium alloy of the aforementioned thickness can significantly improve the mechanical properties and service life of the welded joint.

[0039] Furthermore, the corrosion resistance of 304 stainless steel combined with the high strength and low density of TC4 titanium alloy, along with the corrosion resistance and plasticity of niobium foil, gives the joint both the environmental adaptability of stainless steel and the lightweight advantages of titanium alloy. Meanwhile, the 2mm plate thickness is common in applications such as rail transportation. This method, through precise control of the welding process, ensures that the joint is less prone to failure under repeated loads during service, significantly extending its service life and meeting the dual requirements of mechanical performance and reliability for industrial applications.

[0040] According to one embodiment of this application, the overlap length between the projection of the titanium alloy plate 200 along the first vertical direction and the surface portion of the stainless steel plate 100 is 8-12 mm.

[0041] It should be noted that, in the embodiments of this application, the stainless steel plate 100 overlaps with the titanium alloy plate 200 and the niobium foil 300 along the first vertical direction shown in the figure, with the stainless steel plate 100 positioned above the titanium alloy plate 200. The three plates are sequentially placed and clamped on a tool table fixture to ensure close contact between their surfaces. The length of the overlapping portion of the stainless steel plate 100 and the titanium alloy plate 200 can be 8-12 mm, such as 8 mm, 9 mm, 10 mm, 11 mm, or 12 mm. This ensures that the electric arc and welding wire can act evenly on the overlapping area during welding, allowing the niobium foil 300 to fully fuse with the 304 stainless steel and TC4 titanium alloy, reducing defects such as incomplete fusion and slag inclusions. Simultaneously, this range facilitates assembly and positioning, stably ensuring close contact between the three surfaces, providing conditions for forming a continuous and uniform weld transition layer, and improving the overall consistency of the joint.

[0042] According to one embodiment of this application, the welding parameters for the first cold metal transition welding are as follows: welding current of 125-135A, such as 125A, 130A, or 135A; welding speed of 7-9mm / s, such as 7mm / s, 8mm / s, or 9mm / s; and wire feed speed of 6.5-7.5mm / min, such as 6.5mm / min, 7mm / min, or 7.5mm / min. The welding current of 125-135A and the welding speed of 7-9mm / s form a suitable line energy density. This range ensures that the CuSi3 copper-silicon alloy welding wire melts sufficiently to form a continuous filler layer, while avoiding localized overheating caused by excessive current or slow speed. This combination limits the heat-affected zone to a smaller area, reducing the internal stress caused by thermal deformation of the 304 stainless steel and TC4 titanium alloy base materials. The wire feed speed allows the CuSi3 welding wire to uniformly fill the interface between the stainless steel, niobium foil 300, and titanium alloy, forming a dense transition layer.

[0043] It should be further explained that niobium has a melting point as high as 2470℃, which is much higher than the melting temperature of titanium alloys and stainless steel. This energy range allows only a slight melting of the surface layer of the niobium foil, ensuring a strong metallurgical bond between it and the base materials on both sides and the CuSi3 welding wire, while maintaining the integrity of the middle part. This allows it to continue to play its core role in preventing the interdiffusion of Ti with Fe and Cr, avoiding the loss of diffusion prevention function due to excessive melting of the niobium foil caused by excessive current, or poor bonding between the niobium foil and the base material due to insufficient current and excessive speed. This fundamentally reduces the formation of brittle intermetallic compounds (IMCs).

[0044] According to one embodiment of this application, the protective gas includes argon and a mixed gas, wherein the flow rate of the argon or mixed gas is 18-20 L / min, such as 18 L / min, 19 L / min, or 20 L / min. A flow rate of 18-20 L / min can form a stable and dense gas protective layer in the welding area, effectively isolating air from contact with the high-temperature molten pool and the heat-affected zone. Titanium alloys and stainless steel readily react with oxygen at high temperatures to form oxide films. These oxide films can damage the metallurgical bond of the molten pool, leading to defects such as porosity and slag inclusions in the weld. Furthermore, if the niobium foil 300 interlayer is oxidized, it will form brittle niobium oxide, weakening its ability to prevent the interdiffusion of titanium with iron and chromium. This flow rate range ensures that the gas continuously covers the welding area, avoiding the aforementioned oxidation reactions.

[0045] According to one embodiment provided in this application, when the arc is started, the welding torch is offset from the stainless steel plate 100 weld by 0.5mm-1.5mm, and when the arc is terminated, the center of the weld termination is 1.5mm-2mm away from the center of the weld ignition.

[0046] The inventors discovered that, under the aforementioned conditions, cold metal transfer welding, by offsetting the welding torch 0.5mm-1.5mm away from the stainless steel plate weld seam during arc initiation, allows more of the initial arc energy to be applied to the stainless steel side and the interface between the niobium foil 300 and the stainless steel. Since stainless steel has better heat resistance than titanium alloys, this offset prevents the titanium alloy side from overheating due to concentrated heat input at the moment of arc initiation, thereby reducing the direct diffusion reaction between titanium and stainless steel. Furthermore, titanium and iron readily form brittle intermetallic compounds (IMCs), and this offset can further suppress IMC formation by limiting overheating of the titanium alloy side. Simultaneously, sufficient heating of the stainless steel side ensures good fusion between the niobium foil 300 and the stainless steel, providing a stable metallurgical bonding foundation for the joint.

[0047] On the other hand, the distance between the arc termination center and the arc initiation center is 1.5mm-2mm. This avoids overheating due to overlap between the arc initiation and termination areas, and ensures effective connection between the weld end and the starting end, preventing defects such as incomplete fusion or arc crater. This ensures that the filler metal wire at the arc termination point evenly covers the joint end, guaranteeing continuous bonding between the niobium foil 300 and the base materials on both sides, and avoiding stress concentration caused by weld interruption.

[0048] According to one embodiment of this application, the overlap length between the arc-starting weld and the arc-ending weld is 15mm-20mm.

[0049] It should be noted that the lap length of this weld can be 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm. Titanium and stainless steel are prone to forming brittle intermetallic compounds (IMCs) at high temperatures, and niobium foil 300 needs to maintain its integrity to prevent interdiffusion. If the lap length is too short, the heat input at the beginning and end of the joint will be concentrated, which may lead to local overheating failure of the niobium foil 300; if it is too long, the double heat input will accumulate, which may easily destroy the barrier effect of the niobium foil 300. Therefore, it needs to be limited to 15-20mm to balance the heat effect. This lap section can ensure that the weld metal of the arc initiation and arc termination stages is fully fused, avoiding defects such as incomplete fusion and arc craters caused by insufficient connection at the beginning and end. In CMT welding, the arc energy gradually stabilizes during arc initiation and gradually decays during arc termination. The 15-20mm lap area can cover the transition zone between these two stages, so that the filler metal wire forms a continuous and dense weld at the beginning and end of the joint, eliminating weak points in the joint.

[0050] According to one embodiment of this application, the welding torch is tilted at a 90° angle to the overlapping portion, and at a 60°-90° angle to the horizontal surface of the titanium alloy plate 200. This angle can be 60°, 70°, 80°, or 90°. In this embodiment, the 60°-90° tilt angle, combined with a shielding gas flow of 18-20 L / min, forms a stable gas curtain. If the angle is too small, excessive tilting of the welding torch may obstruct the flow of shielding gas to the molten pool, leading to air entrapment and oxidation. At a 90° tilt angle, the arc and shielding gas flow path ensure that the inert gas fully envelops the high-temperature molten pool and heat-affected zone, preventing oxidation of the titanium alloy and niobium foil 300.

[0051] At the same time, the appropriate angle can guide the CuSi3 welding wire to accurately fill the lap gap, so that the filler metal is evenly distributed on the interface, reducing defects such as incomplete fusion and slag inclusion. Combined with the low heat input characteristics of CMT technology, it forms a well-formed and high-strength lap joint.

[0052] According to one embodiment of this application, a portion of the niobium foil 300 structure is exposed on the outside of the stainless steel plate 100. The thickness of the niobium foil 300 is 10-200 μm, which can be 10 μm, 50 μm, 90 μm, 130 μm, 170 μm, or 200 μm. The 10-200 μm thickness of the niobium foil 300 provided in this application is a pure niobium sheet adapted to the low heat input characteristics of CMT welding. An excessively thin niobium foil 300 may completely melt during welding, losing its barrier function; an excessively thick niobium foil 300 requires a higher heat input to achieve surface fusion, easily leading to overheating of the base material and promoting IMC formation. This thickness range allows the niobium foil 300 to undergo only surface micro-melting during welding, achieving a tight bond with the base materials on both sides while preserving the integrity of the intermediate layer. Combined with the smooth droplet transfer of CMT technology, this reduces weld defects caused by uneven thickness.

[0053] In summary, this invention utilizes niobium foil 300 as an intermediate layer between stainless steel plate 100 and titanium alloy plate 200, and then uses CMT welding technology for welding. By improving the mechanical properties of the weld and reducing the area of ​​the base material affected by the welding thermal cycle, the mechanical properties of the welded joint can be significantly improved.

[0054] The present invention will be described below through specific embodiments. It should be noted that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product manual.

[0055] Example 1:

[0056] (1) Before welding, the surfaces of stainless steel and titanium alloy plates 200 were cleaned respectively. The experimental base material was mechanically polished with sandpaper and cleaned with alcohol to remove the oxide film and oil stains on the sample surface, and then dried.

[0057] (2) The stainless steel plate 100, the niobium intermediate layer, and the titanium alloy plate 200 are sequentially placed and clamped on the workbench fixture by overlapping, ensuring close surface contact. The width of the overlapping part of the stainless steel plate 100 and the titanium alloy plate 200 is 10mm. The welding process parameters are as follows: CuSi3 welding wire is used, the wire feed speed is 6.5~7.5m / min, the welding speed is 7~9mm / s, the welding current is 125~135A, and the gas shielding flow rate is 18~20L / min. The welding torch is offset from the steel by 0.5~1.5mm for the arc-starting weld. When the arc approaches the arc-starting point for the arc-ending weld, the welding torch is moved evenly to the outside of the steel side. The distance between the center of the arc-ending weld and the center line of the arc-starting weld is 1.5~2mm, and the overlap length between the arc-starting weld and the arc-ending weld is 15~20mm.

[0058] Example 2:

[0059] The welding process in this embodiment is the same as in embodiment 1, except that niobium foil 300 is not used as an intermediate layer in this embodiment.

[0060] test:

[0061] The performance evaluation test method for welded joints is based on GB / T228-2010 Metallic Materials - Tensile Testing at Room Temperature.

[0062] Tensile strain analysis was performed on the welded joints of Examples 1 and 2, respectively. The tensile strain curves are shown below. Figure 2 and Figure 3 As shown, Figure 2 The X-axis in the figure represents the nominal strain, which refers to the absolute deformation of the welded joint under stress. Figure 2 and Figure 3 This indicates that the welded joint of Example 2 has a significant difference in strain capacity compared to the welded joint of Example 1. From... Figure 2 Looking at the load-strain curve, the slope slows significantly at the nominal strain of 0.18 mm, and drops sharply at the nominal strain of 1.15 mm. This indicates that the maximum deformation of the joint is approximately 1.15 mm, and at this maximum deformation, the joint can withstand a load of approximately 5000 N. Figure 3 Looking at the load-strain curve, there are no abrupt changes in slope. However, when the nominal strain is 0.22 mm, the load-strain curve drops rapidly, indicating that the maximum deformation of the joint is approximately 0.22 mm. At this maximum deformation, the joint can withstand a load of approximately 2700 N. From... Figure 2 and Figure 3 Based on the data of maximum deformation and maximum load, it can be concluded that adding niobium foil 300 as an interlayer between titanium and steel can significantly improve the mechanical properties of the joint. On the other hand, the strain change with tensile distance at 0.18 mm in Example 1 slows down, that is, under the same load, the amount of change in deformation produced by Example 1 is much smaller than the amount of change in deformation produced by Example 2.

[0063] Metallographic analysis was performed on the welded joints of Examples 1 and 2, respectively. The metallographic results obtained in Examples 1 and 2 are as follows: Figure 3 and Figure 4 As shown, from Figure 3 As can be seen, by adding niobium foil 300 as an intermediate layer, the interdiffusion between titanium alloy and stainless steel was suppressed, and no obvious IMC formation was observed; see attached reference. Figure 4 As shown in the figure, the mutual diffusion between titanium alloy and stainless steel can be clearly seen, and there is obvious IMC formation at the intermediate layer interface.

[0064] As can be seen from the above tests, the method according to the embodiments of this application can simultaneously improve the mechanical properties of the weld seam of the stainless steel and titanium alloy joint and reduce the possibility of brittle metal IMC formation at the stainless steel and titanium alloy weld joint.

[0065] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0066] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A welding method for a metal joint, characterized in that, The welding method includes the following steps: providing at least one titanium alloy plate (200), at least one stainless steel plate (100), and at least one niobium foil (300), and sequentially performing a first grinding and a first cleaning on the titanium alloy plate (200) and the stainless steel plate (100); The stainless steel plate (100) and a portion of the titanium alloy plate (200) are sequentially overlapped and fixed to a fixture along a first vertical direction. The niobium foil (300) is sandwiched between the stainless steel plate (100) and the titanium alloy plate (200). Then, a first cold metal transition welding is performed. When the arc is started, the welding torch is biased to one side of the stainless steel plate. When the arc is ended, the welding torch moves at a constant speed in the width direction of the stainless steel plate (100). After welding, a metal joint is obtained.

2. The welding method for a metal joint according to claim 1, characterized in that, The thickness of the titanium alloy plate (200) and the stainless steel plate (100) is ≥2mm, and the overlap length between the projection of the titanium alloy plate (200) along the first vertical direction and the surface portion of the stainless steel plate (100) is 8-12mm.

3. The welding method for a metal joint according to claim 1, characterized in that, The welding parameters for the first cold metal transition welding are: welding current of 125-135A, welding speed of 7-9mm / s, and wire feeding speed of 6.5-7.5mm / min.

4. The welding method for a metal joint according to claim 1, characterized in that, The protective gas includes argon, and the flow rate of the argon is 18-20 L / min.

5. The welding method for a metal joint according to claim 3, characterized in that, The welding wire for the first cold metal transition welding includes silicon bronze alloy welding wire.

6. The welding method for a metal joint according to claim 1, characterized in that, When the arc is started, the welding torch is offset from the stainless steel plate (100) weld by 0.5mm-1.5mm. When the arc is terminated, the center of the weld termination is 1.5mm-2mm away from the center of the weld ignition.

7. The welding method for a metal joint according to claim 1, characterized in that, The overlap length between the arc-starting weld and the arc-ending weld is 15mm-20mm.

8. A welding method for a metal joint according to claim 5, characterized in that, The welding torch is at a 90° angle to the overlapping portion, and the welding torch is at a 60°-90° angle to the horizontal surface of the titanium alloy plate (200).

9. The welding method for a metal joint according to claim 1, characterized in that, The niobium foil (300) has a partial structure exposed outside the stainless steel plate (100), and the niobium foil (300) has a thickness of 10-200 μm.

10. A welding method for a metal joint according to any one of claims 1-9, characterized in that, The stainless steel plate (100) includes 304 stainless steel, and the titanium alloy plate (200) includes TC4 titanium alloy.

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