Dissimilar metal transition connection structure and its welding method

Abstract

This invention provides a dissimilar metal transition connection structure and its welding method. The method includes: S1, machining a transition metal ring column into a conical ring with a certain angle, machining a corresponding conical surface on the upper metal column, and machining a corresponding conical surface and guide post on the lower metal column; S2, assembling the transition metal ring column with the upper and lower metal columns, placing the assembled whole between upper and lower cover plates, and placing limiting pads at equal intervals around it; S3, placing the whole in a vacuum diffusion welding device, evacuating, heating, and pressurizing, gradually increasing the pressure, and after the pressure head displacement reaches the limit and no longer changes, holding it at the temperature for a period of time, and then cooling it to room temperature in the furnace before removing the product; S4, removing the excess parts of the inner and outer layers by machining to obtain the dissimilar metal transition connection structure. This invention solves the problems of difficult removal of dissimilar metal oxide films and low weld strength caused by the generation of a large number of brittle intermetallic compounds during long-term diffusion processes, and significantly improves the weld strength and welding efficiency of the product.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically relating to a dissimilar metal transition connection structure and its welding method. Background Technology

[0002] Dissimilar metal transition joints are core components of power pipelines, transfer valves, and thermal control systems. Single alloys sometimes cannot meet strength requirements; composite structures such as copper / steel and aluminum / steel can fully leverage the performance advantages of both materials. While ensuring sufficiently high strength and other properties, they also reduce weight, match thermal expansion coefficients, and achieve efficient heat exchange, showing broad application prospects in aerospace, energy, and other fields. For example, aluminum / steel dissimilar metal transport pipelines for high-thrust liquid engines in aerospace and joints for efficient heat exchange in metal heat pipes are typical dissimilar metal tubular welded structures. However, the application and development of these composite structures face the technical challenges of high-strength, high-reliability welding of dissimilar metals.

[0003] Invention CN106312344A provides a method for preparing a titanium and aluminum dissimilar metal thick plate lap structure. First, a titanium alloy substrate and a thin aluminum alloy cladding plate are connected by explosive welding to obtain a composite plate. The thickness of the thin aluminum alloy cladding plate is 1.5-3 mm. Then, the composite plate and the thick aluminum alloy plate are connected by friction stir welding to obtain a titanium and aluminum dissimilar metal thick plate lap structure. The thick aluminum alloy plate is connected to the thin aluminum alloy cladding plate layer in the composite plate.

[0004] However, invention CN106312344A still has the following drawbacks: Differences in the microstructure and properties of dissimilar metals (such as melting point, coefficient of expansion, and alloy composition) increase the difficulty of overall welding, requiring suitable welding processes to achieve high-strength and reliable connections between dissimilar metals. During the fusion welding of dissimilar material joints, hot cracks and microcracks are easily generated. While diffusion bonding can avoid crack formation, the prolonged diffusion process produces a large amount of brittle and hard intermetallic compounds, making it difficult to obtain a high-quality joint. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a dissimilar metal transition connection structure and its welding method.

[0006] A welding method for a dissimilar metal transition joint structure provided by the present invention includes:

[0007] S1, the transition metal ring column is processed into a conical ring with a certain angle, the upper metal tube column is processed with the corresponding conical surface, and the lower metal tube column is processed with the corresponding conical surface and guide column;

[0008] S2, the transition metal ring column is assembled with the upper metal column and the lower metal column. The assembled whole is placed in the middle of the upper and lower cover plates, and the limiting pads are placed at equal distances around it.

[0009] S3. Place the whole unit in a vacuum diffusion welding equipment, evacuate, heat and pressurize, and remove the oxides on the metal surface by using inclined plane friction and extrusion deformation. Increase the pressure step by step. After the pressure head displacement reaches the limit and no longer changes, keep it at the temperature for a period of time, and then take out the product after cooling to room temperature in the furnace.

[0010] S4, by machining to remove the excess parts of the inner and outer layers, a dissimilar metal transition connection structure is obtained.

[0011] Preferably, the transition metal ring post is made of copper or aluminum alloy.

[0012] Preferably, the upper metal column and the lower metal column are made of stainless steel or high-temperature alloy.

[0013] Preferably, the angle between the inclined surface of the transition metal ring column, which is processed into a conical ring, and the vertical direction is 35° to 50°.

[0014] Preferably, the limiting pad is made of graphite and is lower than the height of the workpiece.

[0015] Preferably, after placing the limiting pads at equal intervals around the perimeter, it is ensured that the deformation of the softer metal reaches 2.5% to 10%.

[0016] Preferably, the specific process of diffusion welding includes: evacuating the furnace to a vacuum level of 1×10⁻⁶. -2 After Pa, heating begins. Once the temperature reaches 100℃~200℃ below the melting temperature of the lower-melting-point metal, pressure is applied at 1~5MPa. The pressure is gradually increased in 3~5 stages until the pressure head reaches its limit and no longer deforms. The product is then kept at this temperature for 10~20 minutes and then removed after cooling to room temperature in the furnace.

[0017] Preferably, the roughness of the surfaces to be welded after pre-processing of the transition metal ring column, the upper metal column, and the lower metal column is 1.6 to 3.2.

[0018] Preferably, the excess portions of the inner and outer layers are removed by machining, and the projected area of ​​the conical segment accounts for 50% to 60% of the total cross-sectional area.

[0019] The present invention also provides a dissimilar metal transition connection structure, which is welded by the dissimilar metal transition connection structure welding method described in any one of the above.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] Compared to traditional long-term heat-preservation diffusion (which utilizes interfacial micro-region plastic deformation to break the oxide film) processes, this invention significantly reduces the amount of brittle interfacial compounds, solving the problem of difficulty in improving the strength of diffusion welds made from dissimilar materials. Once the pressure head reaches its limit, the workpiece will no longer deform, ensuring that the final part dimensions meet requirements. This method does not require additional internal or external support molds, nor does it require the addition or plating of an intermediate layer, significantly reducing costs and improving process efficiency.

[0022] It solves the problems of difficult removal of dissimilar metal oxide films and low weld strength caused by the generation of a large number of brittle intermetallic compounds during long-term diffusion process. Compared with traditional long-term high-temperature and high-pressure diffusion welding, the weld strength and welding efficiency of the products are significantly improved. It is especially suitable for core components of power pipelines, transfer valves and thermal control systems with high requirements for product performance and reliability. Attached Figure Description

[0023] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0024] Figure 1 A welding flowchart for dissimilar metal transition joint structures;

[0025] Figure 2 This is a schematic diagram of the pre-welding assembly of a dissimilar metal transition connection structure.

[0026] Figure 3 A schematic diagram showing the post-weld processing effect of a dissimilar metal transition connection structure;

[0027] Figure 4 This is a post-weld microstructure diagram of the dissimilar metal transition connection structure in Example 1.

[0028] The diagram shows: transition metal ring column 1, lower metal tube column 2, upper metal tube column 3, and guide column 4. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0030] like Figures 1-3 As shown, this embodiment provides a welding method for a dissimilar metal transition connection structure, including:

[0031] S1, the transition metal ring column 1 is processed into a conical ring with a certain angle, the upper metal tube column 3 is processed with a corresponding conical surface, and the lower metal tube column 2 is processed with a corresponding conical surface and guide column 4;

[0032] S2, the transition metal ring column 1 is assembled with the upper metal tube column 3 and the lower metal tube column 2. The assembled whole is placed in the middle of the upper and lower cover plates, and the limiting pads are placed at equal distances around it.

[0033] S3. The entire assembly is placed in a vacuum diffusion welding equipment, vacuumed, heated and pressurized, and oxides on the metal surface are removed by using inclined plane friction and extrusion deformation. The pressure is increased step by step. After the pressure head displacement reaches the limit and no longer changes, it is kept at the temperature for a period of time. After cooling to room temperature in the furnace, the product is taken out.

[0034] S4, by machining to remove the excess parts of the inner and outer layers, a dissimilar metal transition connection structure is obtained.

[0035] In one embodiment, the transition metal ring 1 is made of copper or aluminum alloy.

[0036] In one embodiment, the upper metal column 3 and the lower metal column 2 are made of stainless steel or high-temperature alloy.

[0037] In one embodiment, the angle between the inclined surface of the transition metal ring 1, which is machined into a conical ring, and the vertical direction is 35° to 50°.

[0038] In one embodiment, the limiting pad is made of graphite and is lower than the height of the workpiece.

[0039] In one embodiment, after placing the limiting pads at equal intervals around the perimeter, it is ensured that the deformation of the softer metal reaches 2.5% to 10%.

[0040] In one embodiment, the specific process of diffusion welding includes: evacuating the furnace to a vacuum level of 1×10⁻⁶. -2 After Pa, heating begins. Once the temperature reaches 100℃~200℃ below the melting temperature of the lower-melting-point metal, pressure is applied at 1~5MPa. The pressure is gradually increased in 3~5 stages until the pressure head reaches its limit and no longer deforms. The product is then kept at this temperature for 10~20 minutes and then removed after cooling to room temperature in the furnace.

[0041] In one embodiment, the surface roughness of the surfaces to be welded after pre-processing of the transition metal ring column 1, the upper metal tube column 3, and the lower metal tube column 2 is 1.6 to 3.2.

[0042] In one embodiment, machining is used to remove excess portions of the inner and outer layers, and the projected area of ​​the conical segment accounts for 50% to 60% of the total cross-sectional area.

[0043] The transition metal ring 1 is machined into a conical ring with a certain angle and assembled with the upper metal tube 3 and the lower metal tube 2. During the process of gradually increasing the pressure to the maximum pressure, the softer metal continuously deforms. Under the constraint of the metal tube guide post 4, the harder metal continuously embeds itself into the softer metal. At the same time, due to the intense friction between the two materials, fresh interfaces are constantly exposed at the contact surface, which helps to break the oxide layer of the original interface, promotes tight bonding at the interface, and improves the closure efficiency of interface pores. Meanwhile, the contact surfaces move slowly relative to each other during this process, avoiding the generation and growth of brittle compounds at the interface. Finally, a high-strength bond at the interface can be achieved through only a short period of atomic diffusion.

[0044] Example 1

[0045] The transition metal ring 1 is machined into a conical ring with a certain angle, the angle between the inclined surface and the vertical direction is 35°, and the roughness of the surface to be welded after pre-machining is 1.6. The upper metal column is machined with a corresponding conical surface, and the lower metal column is machined with a corresponding conical surface and guide post 4. The transition metal is a copper alloy, and the upper and lower metal columns are stainless steel. The transition metal ring 1 is assembled with the upper and lower metal columns, and the whole assembly is placed in the middle of the upper and lower cover plates. Limiting pads made of graphite are placed at equal intervals around it, and the limiting pads are lower than the height of the workpiece to ensure that the deformation of the softer metal reaches 2.5%. Then it is placed in a vacuum diffusion welding equipment. The diffusion welding process includes: evacuating the furnace to 1×10 -2 Heating begins after Pa, and once the temperature reaches 100°C below the melting temperature of the lower-melting-point metal, pressure is applied at 1 MPa, gradually increasing to the maximum pressure in three stages until the pressure head reaches its limit and no further deformation occurs. The temperature is then maintained for 10 minutes, and the product is removed after cooling to room temperature in the furnace. Excess portions of the inner and outer layers are removed by machining, ensuring the projected area of ​​the conical section accounts for 50% of the total cross-sectional area, thus obtaining the dissimilar metal transition connection structure, as shown below. Figure 4 As shown.

[0046] Example 2

[0047] The transition metal ring 1 is machined into a conical ring with a certain angle, the angle between the inclined surface and the vertical direction is 40°, and the roughness of the surface to be welded after pre-machining is 1.6. The upper metal column is machined with a corresponding conical surface, and the lower metal column is machined with a corresponding conical surface and guide post 4. The transition metal is a copper alloy, and the upper and lower metal columns are high-temperature alloys. The transition metal ring 1 is assembled with the upper and lower metal columns, and the whole assembly is placed in the middle of the upper and lower cover plates. Limiting pads made of graphite are placed at equal intervals around it, and the limiting pads are lower than the height of the workpiece to ensure that the deformation of the softer metal reaches 5%. Then it is placed in a vacuum diffusion welding equipment. The diffusion welding process includes: evacuating the furnace to 1×10 -2Heating begins after Pa, and once the temperature reaches 150°C below the melting temperature of the lower-melting-point metal, pressure is applied at 2 MPa. This pressure is increased in four stages until the pressure head reaches its limit and no further deformation occurs. The product is then held at this temperature for 15 minutes and allowed to cool to room temperature in the furnace before being removed. Excess portions of the inner and outer layers are removed by machining, ensuring the projected area of ​​the conical section accounts for 55% of the total cross-sectional area, thus obtaining the dissimilar metal transition connection structure.

[0048] Example 3

[0049] The transition metal ring 1 is machined into a conical ring with a certain angle, the angle between the inclined surface and the vertical direction is 45°, and the roughness of the surface to be welded after pre-machining is 3.2. The upper metal column is machined with a corresponding conical surface, and the lower metal column is machined with a corresponding conical surface and guide post 4. The transition metal is aluminum alloy, and the upper and lower metal columns are stainless steel. The transition metal ring 1 is assembled with the upper and lower metal columns, and the whole assembly is placed in the middle of the upper and lower cover plates. Limiting pads made of graphite are placed at equal intervals around it, and the limiting pads are lower than the height of the workpiece to ensure that the deformation of the softer metal reaches 7.5%. Then it is placed in a vacuum diffusion welding equipment. The diffusion welding process includes: evacuating the furnace to 1×10 -2 Heating begins after Pa, and once the temperature reaches 200°C below the melting temperature of the lower-melting-point metal, pressure is applied at 4 MPa, gradually increasing to the maximum pressure in four stages until the pressure head reaches its limit and no further deformation occurs. The pressure is then maintained for 15 minutes, and the product is removed after cooling to room temperature in the furnace. Excess portions of the inner and outer layers are removed by machining, ensuring the projected area of ​​the conical section accounts for 55% of the total cross-sectional area, thus obtaining the dissimilar metal transition connection structure.

[0050] Example 4

[0051] The transition metal ring 1 is machined into a conical ring with a certain angle, the angle between the inclined surface and the vertical direction is 50°, and the roughness of the surface to be welded after pre-machining is 3.2. The upper metal column is machined with a corresponding conical surface, and the lower metal column is machined with a corresponding conical surface and guide post 4. The transition metal is aluminum alloy, and the upper and lower metal columns are high-temperature alloys. The transition metal ring 1 is assembled with the upper and lower metal columns, and the whole assembly is placed in the middle of the upper and lower cover plates. Limiting pads made of graphite are placed at equal intervals around it, and the limiting pads are lower than the height of the workpiece to ensure that the deformation of the softer metal reaches 10%. Then it is placed in a vacuum diffusion welding equipment. The diffusion welding process includes: evacuating the furnace to 1×10 -2 Heating begins after Pa, and once the temperature reaches 200°C below the melting temperature of the lower-melting-point metal, pressure is applied at 5 MPa, gradually increasing to the maximum pressure in five stages until the pressure head reaches its limit and no further deformation occurs. The pressure is then maintained for 20 minutes, and the product is removed after cooling to room temperature in the furnace. Excess portions of the inner and outer layers are removed by machining, ensuring the projected area of ​​the conical section accounts for 60% of the total cross-sectional area, thus obtaining the dissimilar metal transition connection structure.

[0052] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", 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 application 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 limitations on this application.

[0053] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A welding method for a dissimilar metal transition connection structure, characterized in that, include: S1, the transition metal ring column (1) is processed into a conical ring with a certain angle, the upper metal column (3) is processed with a corresponding conical surface, and the lower metal column (2) is processed with a corresponding conical surface and guide column (4). S2, the transition metal ring column (1) is assembled with the upper metal tube column (3) and the lower metal tube column (2), and the assembled whole is placed in the middle of the upper and lower cover plates, with limiting pads placed at equal distances around it; S3. Place the whole unit in a vacuum diffusion welding equipment, evacuate, heat and pressurize, and remove the oxides on the metal surface by using inclined plane friction and extrusion deformation. Increase the pressure step by step. After the pressure head displacement reaches the limit and no longer changes, keep it at the temperature for a period of time, and then take out the product after cooling to room temperature in the furnace. S4. The excess portions of the inner and outer layers of the product are removed by machining to obtain a dissimilar metal transition connection structure.

2. The welding method for dissimilar metal transition connection structures according to claim 1, characterized in that, The transition metal ring (1) is made of copper or aluminum alloy.

3. The welding method for dissimilar metal transition connection structures according to claim 1, characterized in that, The upper metal column (3) and the lower metal column (2) are made of stainless steel or high-temperature alloy.

4. The welding method for dissimilar metal transition connection structures according to claim 1, characterized in that, The angle between the inclined surface of the transition metal ring column (1) processed into a conical ring and the vertical direction is 35° to 50°.

5. The welding method for dissimilar metal transition connection structures according to claim 1, characterized in that, The limiting pad is made of graphite and is lower than the height of the workpiece.

6. The welding method for dissimilar metal transition connection structures according to claim 1, characterized in that, After placing the limiting pads at equal intervals around the perimeter, ensure that the deformation of the softer metal reaches 2.5% to 10%.

7. The welding method for dissimilar metal transition connection structures according to claim 1, characterized in that, The specific process of diffusion welding includes: evacuating the furnace to a vacuum level of 1×10⁻⁶. -2 After Pa, heating begins. Once the temperature reaches 100℃~200℃ below the melting temperature of the lower-melting-point metal, pressure is applied at 1~5MPa. The pressure is gradually increased in 3~5 stages until the pressure head reaches its limit and no longer deforms. The product is then kept at this temperature for 10~20 minutes and then removed after cooling to room temperature in the furnace.

8. The welding method for dissimilar metal transition connection structures according to claim 1, characterized in that, The surface roughness of the transition metal ring column (1), the upper metal tube column (3) and the lower metal tube column (2) after pre-processing is 1.6 to 3.

2.

9. The welding method for dissimilar metal transition connection structures according to claim 1, characterized in that, Excess portions of the inner and outer layers are removed by machining, and the projected area of ​​the conical section accounts for 50% to 60% of the total cross-sectional area.

10. A dissimilar metal transition connection structure, characterized in that, It is welded by the dissimilar metal transition connection structure welding method described in any one of claims 1 to 9.

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