Diffusion bonding method for improving high-temperature strength of steel / copper dissimilar alloy joint

Abstract

The invention discloses a diffusion bonding method for improving the high-temperature strength of a steel / copper dissimilar alloy joint. The problem that an existing steel / copper dissimilar alloy diffusion bonding joint is low in high-temperature strength is solved. The diffusion bonding method comprises the following steps: 1, processing a plurality of grooves in a to-be-welded surface of at least one of a steel alloy workpiece and a copper alloy workpiece, and filling titanium carbide particles in the grooves; secondly, a stirring friction head is used for conducting stirring friction surface treatment on the workpiece with the grooves filled with the titanium carbide particles; and thirdly, the to-be-welded faces of the two workpieces are in butt joint, connection pressure is applied, and diffusion connection is conducted in a vacuum diffusion furnace at the temperature ranging from 500 DEG C to 950 DEG C. According to the method, through stirring friction surface treatment, a fine grain structure on the surface of a workpiece has more diffusion channels and lower atom diffusion activation energy, a reliable joint can be obtained at a low temperature, and meanwhile, distribution of fine micron or nano titanium carbide particles in the structure plays a role in enhancing the thermal stability of the fine grain structure; the excellent high-temperature resistance is realized.

Description

Technical Field

[0001] The invention relates to a diffusion connection method for improving the high temperature strength of a high-steel / copper dissimilar alloy joint. Background Art

[0002] In the industrial manufacturing industry, low-cost and widely used high-strength steel alloy materials and copper alloy materials with advantages in electrical and thermal conductivity are widely used. In certain specific scenarios, such as heat exchangers and radiators, there is a need for reliable connection of the two components. As a method for connecting steel / copper dissimilar alloy materials, diffusion bonding has unique advantages, such as large-area connection, small connection heat shadow area, and high connection accuracy.

[0003] However, due to the large differences in the melting point, thermal expansion coefficient and other physical and chemical properties of steel alloys and copper alloys, and the fact that hard and brittle intermetallic compounds are easily generated at the diffusion bonding interface of steel and copper alloys at high temperatures, it is difficult to obtain high mechanical properties by direct diffusion bonding of steel / copper dissimilar alloys. In addition, in addition to the requirements for room temperature performance of steel / copper joints, in service scenarios where steel / copper joints are used for heat transfer functions, such as industrial steel-copper composite flat plate heat exchangers, the high-temperature strength of the joints is more worthy of attention.

[0004] In the current direct diffusion connection method of steel / copper dissimilar alloys, in order to achieve sufficient diffusion and metallurgical bonding of interface atoms, the connection temperature is generally between 800 and 950°C. This temperature range has little effect on the structure of the steel alloy, but it is easy to cause grain growth and softening of the parent material on the copper side of the joint, and the joint has low high-temperature strength. As a result, it is difficult to improve the mechanical properties of steel / copper dissimilar alloy joints at high temperatures, which seriously restricts the application scope of dissimilar material joints. Therefore, it is of great significance to develop a connection method that can effectively improve the high-temperature strength of steel / copper dissimilar alloy joints. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of low high temperature strength of existing steel / copper dissimilar alloy diffusion bonding joints and to provide a diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints.

[0006] The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints of the present invention is implemented according to the following steps:

[0007] Step 1: Prefabricate the groove and fill it with titanium carbide powder:

[0008] Processing a plurality of grooves on the surface to be welded of at least one of the steel alloy workpiece and the copper alloy workpiece, and filling the grooves with micrometer or nanometer titanium carbide particles after cleaning to obtain a steel alloy and / or copper alloy workpiece with the grooves filled with titanium carbide particles;

[0009] Step 2: Friction stir surface complex treatment:

[0010] Using a friction stir head to perform friction stir surface treatment on a steel alloy and / or copper alloy workpiece filled with titanium carbide particles in the groove along a groove path to obtain a surface treated steel alloy and / or copper alloy workpiece;

[0011] Step 3: Diffusion connection:

[0012] The surface to be welded of the surface treated steel alloy and / or copper alloy workpiece is ground and polished, and then the surfaces to be welded of the steel alloy workpiece and the copper alloy workpiece are butted against each other, and connection pressure is applied to obtain the welded parts, which are then placed in a vacuum diffusion furnace and diffusion-bonded at a temperature of 500 to 950° C., thereby completing the diffusion bonding of the steel / copper dissimilar alloys.

[0013] The present invention adopts the method of pre-grooving to fill micron or nano titanium carbide particles on the surface of steel and copper alloy, and obtains a multi-phase treatment layer of titanium carbide particle phase mixed on the surface of the plate by the process of stir friction surface treatment. The surface multi-phase treatment layer undergoes a dynamic recrystallization process due to the violent plastic deformation driving effect brought by stir friction. In this process, the dispersed fine titanium carbide particles are conducive to multi-point nucleation, and the organization structure with fully refined grains is obtained. The surface organization provides more diffusion channels and lower atomic diffusion activation energy in steel / copper diffusion connection, thereby realizing reliable connection of steel / copper interface at a lower diffusion connection temperature, alleviating the organization coarsening and material softening problems of copper side parent material during the connection heat process. In addition, the titanium carbide particles distributed at the grain boundary and in the crystal improve the thermal stability of the organization grain size, and the pinning strengthening mechanism of titanium carbide particles in the metal matrix improves the high temperature bearing capacity of the diffusion joint. The present invention can realize the high temperature strength improvement of steel / copper dissimilar alloy diffusion joint at a lower connection temperature (650℃~700℃), and has good technical application effect and broad application prospects.

[0014] The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints of the present invention includes the following beneficial effects:

[0015] 1. The present invention improves the atomic mutual diffusion coefficient on the surface of steel and copper alloy, reduces the diffusion connection temperature, and avoids the softening of the copper side base material during the connection heat process;

[0016] 2. The present invention improves the thermal stability of the fine grain size of the organization near the bonding interface through complex phase treatment, and the fine grain structure improves the plasticity and strength of the joint;

[0017] 3. The present invention utilizes the diffusion strengthening of nanoparticles on the interface structure distribution and the pinning strengthening effect of the intracrystalline distribution to improve the high temperature strength of the steel / copper diffusion joint;

[0018] 4. The present invention does not need to introduce a diffusion connection intermediate layer, thus avoiding the damage of the intermediate layer material to the heat transfer and electrical conductivity of the steel / copper joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The schematic diagram of the process of filling titanium carbide particles in a prefabricated groove of the present invention;

[0020] Figure 2 Schematic diagram of the friction stir surface multiphase treatment process in the present invention;

[0021] Figure 3 Schematic diagram of the diffusion bonding process in the present invention;

[0022] Figure 4 A comparison diagram of the interface microstructures of the diffusion bonding method in Example 1 and the conventional diffusion bonding of steel / copper;

[0023] Figure 5 The microstructure comparison diagrams of the copper side base material (a) and the copper material after the complex phase treatment (b) in Example 1 after thermal cycling at room temperature and 700°C respectively;

[0024] Figure 6 This is a comparison chart of high temperature shear strength between Example 1 and conventional steel / copper diffusion bonded joints;

[0025] Figure 7 The schematic diagram of the diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints according to the present invention. DETAILED DESCRIPTION

[0026] Specific implementation method 1: The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints in this implementation method is implemented according to the following steps:

[0027] Step 1: Prefabricate the groove and fill it with titanium carbide powder:

[0028] Processing a plurality of grooves on the surface to be welded of at least one of the steel alloy workpiece and the copper alloy workpiece, and filling the grooves with micrometer or nanometer titanium carbide particles after cleaning to obtain a steel alloy and / or copper alloy workpiece with the grooves filled with titanium carbide particles;

[0029] Step 2: Friction stir surface complex treatment:

[0030] Using a friction stir head to perform friction stir surface treatment on a steel alloy and / or copper alloy workpiece filled with titanium carbide particles in the groove along a groove path to obtain a surface treated steel alloy and / or copper alloy workpiece;

[0031] Step 3: Diffusion connection:

[0032] The surface to be welded of the surface treated steel alloy and / or copper alloy workpiece is ground and polished, and then the surfaces to be welded of the steel alloy workpiece and the copper alloy workpiece are butted against each other, and connection pressure is applied to obtain the welded parts, which are then placed in a vacuum diffusion furnace and diffusion-bonded at a temperature of 500 to 950° C., thereby completing the diffusion bonding of the steel / copper dissimilar alloys.

[0033] In the process of severe plastic deformation of the stir friction treatment, the coarse grains of the parent material in the organization of the metal sheet surface are broken and dynamically recrystallized, and the fine micron or nano titanium carbide particles introduced through the preset grooves provide nucleation sites for the recrystallization of the base metal in this process, which is conducive to obtaining an ultrafine grain structure. After this treatment, the fine grain organization on the surface of the steel alloy and the copper alloy has more diffusion channels and lower atomic diffusion activation energy, and its diffusion bonding is more complete, which is conducive to obtaining a reliable joint at a lower temperature and alleviates the softening of the copper side parent material during the connection heat process; at the same time, the distribution of fine titanium carbide particles in the organization has an effect of enhancing the thermal stability of the fine grain structure, which can effectively avoid the growth of the parent material grains and the softening of the material, and the continuous dislocation pinning strengthening effect of the titanium carbide particles near the interface is superimposed, and the steel / copper joint has better high temperature strength. This embodiment can obtain a diffusion connection joint with better high temperature strength, and has excellent technical effects and application prospects.

[0034] This embodiment is suitable for performing a friction stir surface complex phase treatment on the copper alloy and the steel alloy before diffusion bonding, and can also be used to perform a surface complex phase treatment on only the copper alloy or only the steel alloy.

[0035] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that the particle size of the micron or nano titanium carbide particles in step 1 is 0.01 to 5 μm.

[0036] Specific implementation method three: The difference between this implementation method and specific implementation method one or two is that the material of the copper alloy described in step one is pure copper, brass, bronze or white copper; the steel alloy is low alloy steel (Q345B, 14CrMnMoVB), high speed steel (W18Cr4V), mold steel (Cr12, 4Cr5MoSiV) or stainless steel (1Cr17Ti, Cr18Ni9).

[0037] Specific implementation method 4: This implementation method is different from specific implementation methods 1 to 3 in that the width of the groove in step 1 is 0.6-1.4 mm, and the depth of the groove is 0.1-0.3 mm.

[0038] Specific implementation mode 5: The difference between this implementation mode and specific implementation modes 1 to 4 is that in step 1, both the steel alloy workpiece and the copper alloy workpiece are plates.

[0039] Specific implementation method 6: This implementation method is different from specific implementation methods 1 to 5 in that during the friction stir surface treatment in step 2, the rotation speed of the friction stir head is controlled to be 200-1000 rpm, the travel speed is 10-200 mm / min, and the inclination angle is 0-3.5°.

[0040] The friction stirring head described in this embodiment is in the form of a needle-free flat shoulder, a needle-free shoulder with an inner concave angle, or a stirring head with a stirring needle.

[0041] Specific implementation method seven: The difference between this implementation method and any one of specific implementation methods one to six is ​​that in the process of the friction stir surface treatment in step two, the depth of the friction stir head is controlled to be 0.1 to 0.8 mm.

[0042] Specific implementation eight: This implementation differs from any one of specific implementations one to seven in that the connection pressure in step three is controlled to be 1-30 MPa.

[0043] Specific embodiment 9: This embodiment is different from specific embodiments 1 to 8 in that in step 3, the diffusion bonding is performed at a temperature of 500 to 850° C. for 10 to 60 minutes.

[0044] Specific embodiment ten: This embodiment is different from specific embodiment nine in that in step three, the diffusion bonding is performed at a temperature of 650 to 700° C. for 25 to 45 minutes.

[0045] Embodiment 1: The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints in this embodiment is implemented according to the following steps:

[0046] Step 1: Prefabricate the groove and fill it with titanium carbide powder:

[0047] A plurality of grooves are machined on the surface of a C11000 copper alloy plate, the groove depth is 0.2 mm, the groove width is 1 mm, and titanium carbide particles with an average particle size of 5 μm are filled in the grooves after cleaning and drying, thereby obtaining a copper alloy workpiece with titanium carbide particles filled in the grooves;

[0048] Step 2: Friction stir surface complex treatment:

[0049] A friction stir head is used to perform friction stir surface treatment on a copper alloy workpiece filled with titanium carbide particles in the groove along the groove path. The rotation speed of the friction stir head is controlled to be 400 rpm, the travel speed is 120 mm / min, the inclination angle is 0.5°, and the plunge treatment depth is 0.2 mm to obtain a copper alloy workpiece after surface treatment. The schematic diagram of the friction stir surface treatment in this embodiment is shown in FIG. Figure 2 As shown;

[0050] Step 3: Diffusion connection:

[0051] The surfaces to be welded of the copper alloy workpiece and the steel alloy workpiece after surface treatment are respectively ground and polished. The material of the steel alloy workpiece is 1Cr18Ni9 steel alloy. Then, the surfaces to be welded of the steel alloy workpiece and the copper alloy workpiece are connected to each other, and a connection pressure of 5 MPa is applied to obtain the welded parts. The welded parts are placed in a vacuum diffusion furnace and diffusion-bonded at a temperature of 650° C. for 30 minutes, thereby completing the diffusion bonding of the steel / copper dissimilar alloys. The schematic diagram of the vacuum diffusion bonding of this embodiment is shown in FIG. Figure 3 shown.

[0052] The friction stirring head of this embodiment adopts the form of a needle-free stirring head with a concave angle on the end face of the shaft shoulder.

[0053] After the process of this embodiment, the diffusion joint of C11000 copper alloy and 1Cr18Ni9 steel alloy obtained in the first embodiment is compared with the direct diffusion joint of C11000 copper alloy and 1Cr18Ni9 steel alloy. Figure 4 The microstructure of the joint interface is shown. From the figure, it can be observed that titanium carbide particles are dispersed in the copper side structure near the joint interface. Figure 5 The following are the microstructure comparison diagrams of the copper base material (a) treated with friction stir multiphase treatment (b) and untreated at room temperature and 700℃ thermal cycle for 30 minutes. It can be seen from the figure that the friction stir surface multiphase treatment has a significant size refinement effect on the copper base material grains. At the same time, the microstructure grains grow slightly after thermal cycle, but the growth rate is much lower than that of the base material without treatment under the same thermal cycle conditions. This comparative test shows that titanium carbide particles have a significant effect on promoting multi-point nucleation, refining grains and improving the thermal stability of fine grain size.

[0054] In the process of severe plastic deformation of the stir friction treatment in this embodiment, the coarse grains of the parent material in the organization of the metal plate surface are broken and dynamically recrystallized, and the nano-titanium carbide particles introduced through the preset grooves provide crystal nucleation sites in this process, which is conducive to obtaining an ultrafine grain structure. After this treatment, the fine grain organization on the surface of the steel alloy and the copper alloy has more diffusion channels and lower atomic diffusion activation energy, and its diffusion bonding is more complete, which is conducive to obtaining a reliable joint at a lower temperature and alleviates the softening of the copper side parent material during the connection heat process; at the same time, the distribution of fine micron or nano titanium carbide particles in the organization has an effect of enhancing the thermal stability of the fine grain structure, which can effectively avoid the growth of the parent material grains and the softening of the material, and the continuous pinning strengthening effect of the titanium carbide particles in the metal matrix near the superposition interface, the steel / copper joint has excellent high temperature resistance.

[0055] A high temperature shear test was performed on the steel / copper diffusion bonded joint in Example 1, and the test results were compared with those of the steel / copper direct diffusion joint. Figure 6As shown. The test found that the average shear strength of the joint obtained in Example 1 at room temperature, 400°C and 700°C test temperatures were 84MPa, 71MPa and 49MPa respectively, and the shear strength of the steel / copper direct diffusion bonding joint without surface treatment in the control group (the diffusion bonding parameters were consistent with Example 1) at room temperature, 400°C and 700°C test temperatures were 68MPa, 36MPa and 13MPa respectively, and the corresponding improvement rates were 23.5%, 97.2% and 276.9% respectively. It can be seen that this embodiment can significantly improve the strength of the steel / copper dissimilar alloy diffusion bonding joint, especially the high temperature strength of the joint.

[0056] As for the process effect of the present invention, it can effectively improve the high temperature strength of the steel / copper diffusion bonded joint, and its effect is mainly achieved by Figure 7 The technical principle shown is achieved by: the friction stir surface complex phase treatment obtains a fine-grained structure with thermal stability characteristics, thereby improving the mutual diffusion coefficient of the steel / copper interface and the metallurgical bonding strength of the diffusion joint. Under high-temperature load conditions, the fine titanium carbide particles dispersed in the copper alloy crystals and grain boundaries near the interface have a pinning and strengthening effect on the matrix structure, thereby comprehensively improving the plasticity and strength of the joint.

[0057] Embodiment 2: This embodiment differs from Embodiment 1 in that in step 1, a plurality of grooves are processed on the surfaces of the C11000 copper alloy plate and the 1Cr18Ni9 steel alloy plate respectively, the groove depth being 0.2 mm and the groove width being 1 mm, and titanium carbide particles with an average particle size of 5 μm are filled in the grooves after cleaning and drying to obtain a copper alloy workpiece with titanium carbide particles filled in the grooves.

[0058] Embodiment 3: The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints in this embodiment is implemented according to the following steps:

[0059] Step 1: Prefabricate the groove and fill it with titanium carbide powder:

[0060] A plurality of grooves were processed on the surface of the chromium-zirconium copper plate, with a groove depth of 0.15 mm and a groove width of 1 mm; a plurality of grooves were processed on the surface of the SUS441 stainless steel alloy plate, with a groove depth of 0.2 mm and a groove width of 1 mm, and the grooves were filled with titanium carbide particles with an average particle size of 20 nm after cleaning and drying, thereby obtaining a copper alloy workpiece and a steel alloy workpiece with titanium carbide particles filled in the grooves;

[0061] Step 2: Friction stir surface complex treatment:

[0062] A friction stir head is used to perform friction stir surface treatment on a copper alloy workpiece and a steel alloy workpiece respectively along a groove path with titanium carbide particles in the groove, wherein the rotation speed of the friction stir head is controlled to be 400 rpm, the travel speed is 80 mm / min, the inclination angle is 0.5°, and the plunge treatment depth is 0.15 mm, to obtain a copper alloy workpiece and a steel alloy workpiece after the surface treatment;

[0063] Step 3: Diffusion connection:

[0064] The surfaces to be welded of the copper alloy workpiece and the steel alloy workpiece after surface treatment were ground and polished respectively, and then the surfaces to be welded of the steel alloy workpiece and the copper alloy workpiece were butted against each other, and a connection pressure of 5 MPa was applied to obtain the welded parts, which were then placed in a vacuum diffusion furnace and diffusion-bonded at a temperature of 700°C for 60 minutes, thereby completing the diffusion bonding of the steel / copper dissimilar alloys.

[0065] In this example, room temperature and high temperature shear tests of the joint were carried out at 25°C and 700°C. The shear strengths of the joint obtained in Example 3 were 95MPa and 61MPa at room temperature and 700°C, respectively. The shear strengths of the steel / copper direct diffusion bonded joint without surface treatment in the control group (the diffusion bonding parameters were consistent with those in Example 3) were 83MPa and 35MPa at room temperature and 700°C test temperatures, respectively.

Claims

1. A diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints, characterized in that The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints is implemented according to the following steps: Step 1: Prefabricate the groove and fill it with titanium carbide powder: Processing a plurality of grooves on the surface to be welded of at least one of the steel alloy workpiece and the copper alloy workpiece, and filling the grooves with micrometer or nanometer titanium carbide particles after cleaning to obtain a steel alloy and / or copper alloy workpiece with the grooves filled with titanium carbide particles; Step 2: Friction stir surface complex treatment: Using a friction stir head to perform friction stir surface treatment on a steel alloy and / or copper alloy workpiece filled with titanium carbide particles in the groove along a groove path to obtain a surface treated steel alloy and / or copper alloy workpiece; Step 3: Diffusion connection: The surface to be welded of the surface treated steel alloy and / or copper alloy workpiece is ground and polished, and then the surfaces to be welded of the steel alloy workpiece and the copper alloy workpiece are butted against each other, and connection pressure is applied to obtain the welded parts, which are then placed in a vacuum diffusion furnace and diffusion-bonded at a temperature of 500 to 950° C., thereby completing the diffusion bonding of the steel / copper dissimilar alloys.

2. The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints according to claim 1 is characterized in that In step 1, the particle size of the micron or nano titanium carbide particles is 0.01 to 5 μm.

3. The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints according to claim 1, characterized in that The copper alloy described in step 1 is made of pure copper, brass, bronze or nickel silver; the steel alloy is low alloy steel, high speed steel, die steel or stainless steel.

4. The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints according to claim 1, characterized in that In step 1, the width of the groove is 0.6-1.4 mm, and the depth of the groove is 0.1-0.3 mm.

5. The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints according to claim 1, characterized in that In step 1, the steel alloy workpiece and the copper alloy workpiece are both plates.

6. The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints according to claim 1, characterized in that During the friction stir surface treatment in step 2, the rotation speed of the friction stir head is controlled to be 200-1000 rpm, the travel speed is 10-200 mm / min, and the inclination angle is 0-3.5°.

7. The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints according to claim 1, characterized in that During the friction stir surface treatment process in step 2, the depth of the friction stir head is controlled to be 0.1 to 0.8 mm.

8. The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints according to claim 1, characterized in that In step 3, the connection pressure is controlled to be 1-30 MPa.

9. The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints according to claim 1, characterized in that In step 3, diffusion bonding is performed at a temperature of 500 to 850° C. for 10 to 60 minutes.

10. The diffusion bonding method for improving the high temperature strength of steel / copper dissimilar alloy joints according to claim 9, characterized in that In step 3, diffusion bonding is performed at a temperature of 650 to 700° C. for 25 to 45 minutes.

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