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

Abstract

The application discloses a diffusion connection method for improving high-temperature strength of steel / copper dissimilar alloy joints, and aims at solving the problem of low high-temperature strength of the existing steel / copper dissimilar alloy diffusion connection joints.The diffusion connection method comprises the following steps: firstly, a plurality of grooves are formed on the welding surface of at least one of a steel alloy workpiece and a copper alloy workpiece, and titanium carbide particles are filled in the grooves; secondly, a friction stir head is used to perform friction stir surface treatment on the workpiece with the grooves filled with the titanium carbide particles; and thirdly, the welding surfaces of the two workpieces are abutted, a connection pressure is applied, and diffusion connection is carried out at a temperature of 500-950 DEG C in a vacuum diffusion furnace.The workpiece surface is subjected to the friction stir surface treatment, the fine-grained structure of the workpiece surface has more diffusion channels and lower atomic diffusion activation energy, and reliable joints can be obtained at a lower temperature; meanwhile, the distribution of the fine micron or nanometer titanium carbide particles in the structure has a thermal stability enhancement effect on the fine-grained structure, and the fine-grained structure has excellent high-temperature resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to a diffusion bonding method for improving the high-temperature strength of high-steel / copper dissimilar alloy joints. BACKGROUND

[0002] In the industrial manufacturing industry, low-cost widely used high-strength steel alloy materials and copper alloy materials with the advantages of electrical conductivity and thermal conductivity have wide application, and in some specific scenarios such as heat exchanger and radiator equipment structures, there is a reliable connection requirement for the parts of the two. As a method for connecting steel / copper dissimilar alloy materials, diffusion bonding has unique advantages, such as being able to achieve large-area connection, small connection thermal shadow area, and high connection precision, etc.

[0003] However, due to the large difference in physical and chemical properties such as melting point and thermal expansion coefficient between steel alloy and copper alloy materials, and the easy formation of hard and brittle intermetallic compounds at high temperatures at the steel / copper alloy diffusion bonding interface, it is difficult to obtain high mechanical properties for steel / copper dissimilar alloy direct diffusion bonding. In addition, in addition to the requirement for the room temperature performance of the steel / copper joint, the high-temperature strength of the joint is more worthy of attention in the service scenarios of steel / copper joints that bear heat transfer functions such as industrial steel-copper composite flat plate heat exchangers.

[0004] In the current steel / copper dissimilar alloy direct diffusion bonding method, in order to achieve sufficient diffusion and metallurgical bonding of interface atoms, the bonding temperature is generally 800-950℃, which has little effect on the steel alloy structure, but easily causes grain growth and material softening on the copper side of the joint, and the joint has low high-temperature strength. Therefore, the mechanical properties of steel / copper dissimilar alloy joints at high temperatures are difficult to improve, which seriously restricts the application range of dissimilar material joints. Therefore, it is of great significance to develop a bonding method that can effectively improve the high-temperature strength of steel / copper dissimilar alloy joints. SUMMARY

[0005] The purpose of the present application 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 according to the present application is implemented according to the following steps:

[0007] Step 1, pre-prepared groove filled with titanium carbide powder:

[0008] A plurality of grooves are machined on the welding surface of at least one of the steel alloy workpiece and the copper alloy workpiece, and after cleaning, micron or nanometer titanium carbide particles are filled in the grooves to obtain a steel alloy and / or copper alloy workpiece with titanium carbide particles filled in the grooves;

[0009] Step two, friction stir surface complex treatment:

[0010] The steel alloy and / or copper alloy workpiece filled with titanium carbide particles in the groove is subjected to friction stir surface treatment along the groove path using a friction stir head, to obtain a surface-treated steel alloy and / or copper alloy workpiece;

[0011] Step three, diffusion bonding:

[0012] The surface-treated steel alloy and / or copper alloy workpiece is polished and polished, and then the welding surface of the steel alloy workpiece and the welding surface of the copper alloy workpiece are connected, and the connection pressure is applied, to obtain a welding piece, and the welding piece is placed in a vacuum diffusion furnace for diffusion bonding at a temperature of 500-950 DEG C, thereby completing the diffusion bonding of the steel / copper dissimilar alloy.

[0013] The present application fills micron or nanometer titanium carbide particles on the surface of steel and copper alloy by pre-grooving, and obtains a complex treatment layer on the surface of the plate by mixing titanium carbide particles through the process of friction stir surface treatment. The surface complex treatment layer undergoes a dynamic recrystallization process due to the severe plastic deformation driving effect caused by friction stir. In this process, the dispersed fine titanium carbide particles are beneficial to multi-point nucleation, and the grain structure is fully refined. The surface structure provides more diffusion channels and lower atomic diffusion activation energy in the steel / copper diffusion bonding, so that reliable connection of the steel / copper interface can be realized at a lower diffusion bonding temperature, and the organization coarsening and material softening of the copper side base material during the connection heat process are relieved. In addition, the titanium carbide particles distributed in the grain boundary and the grain improve the thermal stability of the grain size of the structure, and the pinning strengthening mechanism of the titanium carbide particles in the metal matrix improves the high temperature carrying capacity of the diffusion joint. The present application can realize the improvement of the high temperature strength of the steel / copper dissimilar alloy diffusion joint at a lower connection temperature (650 DEG C-700 DEG C), and has good technical application effect and wide application prospect.

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

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

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

[0017] 3. The present application utilizes the dispersion strengthening of the interface structure distribution and the pinning strengthening effect of the intracrystalline distribution of the nanoparticles, and improves the high temperature strength of the steel / copper diffusion joint;

[0018] 4. The present invention does not require the introduction of a diffusion bonding 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 Schematic diagram of the process of filling titanium carbide particles in a prefabricated groove according to the present invention;

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

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

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

[0023] Figure 5 Comparison diagram of the microstructures of the copper-side base material (a) and the copper material after the composite 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 the high-temperature shear strength of Example 1 and a conventional steel / copper diffusion bonded joint;

[0025] Figure 7 This is a schematic diagram of the principle 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 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:

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

[0028] machining a plurality of grooves on a surface to be welded of at least one of a steel alloy workpiece and a 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 phase treatment:

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

[0031] Step 3: Diffusion connection:

[0032] The surface of the steel alloy and / or copper alloy workpiece to be welded is polished, and then the surfaces to be welded of the steel alloy workpiece and the copper alloy workpiece are butted, a connecting pressure is applied, and a to-be-welded workpiece is obtained. The to-be-welded workpiece is placed in a vacuum diffusion furnace, and diffusion welding is performed at a temperature of 500-950°C, so that the diffusion welding of the steel / copper dissimilar alloy is completed.

[0033] In the process of severe plastic deformation of the friction stir processing, the coarse grains of the base material on the surface of the metal plate are broken and dynamic recrystallization occurs, and the fine micron or nanometer titanium carbide particles introduced through the pre-set groove provide nucleation sites for the recrystallization of the base metal in this process, which is beneficial to obtain an ultra-fine grain structure. After this treatment, the fine-grained structure on the surface of the steel alloy and the copper alloy has more diffusion channels and lower atomic diffusion activation energy, and the diffusion bonding is more sufficient, which is beneficial to obtain a reliable joint at a lower temperature and alleviate the softening of the copper side base material during the connection heat process; at the same time, the distribution of the fine titanium carbide particles in the structure enhances the thermal stability of the fine-grained structure, which can effectively prevent the grain growth and softening of the base material, and the continuous dislocation pinning strengthening effect of the titanium carbide particles near the interface, the steel / copper joint has better high temperature strength. The embodiment can obtain a diffusion welded joint with better high temperature strength, which has excellent technical effect and application prospect.

[0034] The embodiment is suitable for surface complex phase processing of the copper alloy and the steel alloy before diffusion welding, and the copper alloy or the steel alloy can also be subjected to surface complex phase processing.

[0035] Specific embodiment two: The difference between this embodiment and specific embodiment one is that the particle size of the micron or nanometer titanium carbide particles in step one is 0.01-5 μm.

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

[0037] Specific embodiment four: The difference between this embodiment and any one of specific embodiments one to three is that the width of the groove in step one is 0.6-1.4 mm, and the depth of the groove is 0.1-0.3 mm.

[0038] Specific embodiment five: The difference between this embodiment and any one of specific embodiments one to four is that the steel alloy workpiece and the copper alloy workpiece in step one are both plates.

[0039] Sixth embodiment: the difference between this embodiment and one of the first to fifth embodiments is that the rotational speed of the friction stir head is controlled to be 200-1000 rpm, the travel speed is 10-200 mm / min, and the tilt angle is 0-3.5° during the friction stir surface treatment in step two.

[0040] The friction stir head in this embodiment is in the form of a flat shoulder without a pin, a shoulder with an inner concave angle without a pin, or a stirring head with a stirring pin.

[0041] Seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is that the penetration depth of the friction stir head is controlled to be 0.1-0.8 mm during the friction stir surface treatment in step two.

[0042] Eighth embodiment: the difference between this embodiment and one of the first to seventh embodiments is that the connecting pressure is controlled to be 1-30 MPa in step three.

[0043] Ninth embodiment: the difference between this embodiment and one of the first to eighth embodiments is that the diffusion connection is performed at a temperature of 500-850 °C for 10-60 min in step three.

[0044] Tenth embodiment: the difference between this embodiment and the ninth embodiment is that the diffusion connection is performed at a temperature of 650-700 °C for 25-45 min in step three.

[0045] Example one: the diffusion connection method for improving the high-temperature strength of a steel / copper dissimilar alloy joint is implemented according to the following steps:

[0046] Step one, pre-groove filled with titanium carbide powder:

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

[0048] Step two, friction stir surface treatment:

[0049] A friction stir head is used to perform friction stir surface treatment on the copper alloy workpiece with titanium carbide particles filled in the grooves along the groove path, the rotational speed of the friction stir head is controlled to be 400 rpm, the travel speed is 120 mm / min, the tilt angle is 0.5°, and the penetration depth is 0.2 mm, to obtain a surface-treated copper alloy workpiece, and the schematic diagram of the friction stir surface treatment in this example is shown in Figure 2 ;

[0050] Step three, diffusion connection:

[0051] The surface treated copper alloy workpiece and the steel alloy workpiece are polished respectively, the material of the steel alloy workpiece is 1Cr18Ni9 steel alloy, then the steel alloy workpiece and the copper alloy workpiece are butted, a connecting pressure of 5 MPa is applied, a diffusion joint is obtained, the diffusion joint is placed in a vacuum diffusion furnace, diffusion connection is carried out at a temperature of 650℃ for 30 min, so that the diffusion connection of the steel / copper dissimilar alloy is completed, and a schematic diagram of the vacuum diffusion connection in the embodiment is shown in Figure 3

[0052] The friction stir head in the embodiment adopts a pinless stir head form with an inner concave angle on the shoulder end face.

[0053] After the process in the embodiment, the diffusion joint of the C11000 copper alloy and the 1Cr18Ni9 steel alloy in the first embodiment is compared with the direct diffusion joint of the C11000 copper alloy and the 1Cr18Ni9 steel alloy, Figure 4 As shown in the figure, the titanium carbide particles are dispersed in the copper side structure near the joint interface. Figure 5 The microstructure comparison diagram of the copper base material (a) after the friction stir complex phase treatment (b) and the untreated copper base material (a) after the thermal cycle at room temperature and 700℃ for 30 min is shown in the figure, it can be seen from the figure that the friction stir surface complex phase treatment has a significant size refinement effect on the copper base material grains, and the grains grow slightly after the thermal cycle, but the growth rate is much lower than that of the untreated base material under the same thermal cycle condition. The comparison test shows that the titanium carbide particles have obvious effects on promoting multi-point nucleation, refining grains and improving the thermal stability of fine grains.

[0054] In the process of severe plastic deformation of the friction stir treatment in the embodiment, the coarse grains of the base material in the structure on the surface of the metal plate are broken and dynamic recrystallization occurs, and the nano titanium carbide particles introduced through the pre-set groove provide crystal nucleation sites in this process, which is beneficial to obtain a ultra-fine grain structure. After the treatment, the fine grain structure on the surface of the steel alloy and the copper alloy has more diffusion channels and lower atomic diffusion activation energy, and the diffusion combination is more sufficient, which is beneficial to obtain a reliable joint at a lower temperature and relieve the softening of the copper side base material during the connection heat process; at the same time, the distribution of the micron or nano titanium carbide particles in the structure enhances the thermal stability of the fine grain structure, which can effectively avoid the grain growth and material softening of the base material, and the continuous pinning reinforcement of the titanium carbide particles near the interface in the metal matrix, the steel / copper joint has excellent high temperature resistance.

[0055] The steel / copper diffusion connection joint in the first embodiment is subjected to high temperature shear test, and the test results are compared with those of the steel / copper direct diffusion joint, as shown in Figure 6 ​The test found that the average shear strength of the joint obtained in Example One at room temperature, 400°C and 700°C test temperature was 84 MPa, 71 MPa and 49 MPa respectively, and the shear strength of the steel / copper direct diffusion joint (the diffusion connection parameters remained the same as those in Example One) without surface treatment in the control group at room temperature, 400°C and 700°C test temperature was 68 MPa, 36 MPa and 13 MPa respectively, and the corresponding improvement rate was 23.5%, 97.2% and 276.9% respectively. It can be seen that the present embodiment can significantly improve the strength of the steel / copper diffusion joint, especially the high temperature strength of the joint.

[0056] For the process implementation effect of the present application, it can effectively improve the high temperature strength of the steel / copper diffusion joint, and the effect is mainly realized through the technical principle as Figure 7 shown: the fine-grained structure with organizational thermal stability characteristics is obtained by friction stir surface complex phase treatment, so as to improve the interdiffusion 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 dispersedly distributed in the copper alloy grains and grain boundaries near the interface have pinning strengthening effect on the matrix structure, thereby comprehensively improving the plasticity and strength of the joint.

[0057] Example Two: The difference between the present embodiment and Example One is that a plurality of grooves are machined on the surface of the C11000 copper alloy plate and the 1Cr18Ni9 steel alloy plate respectively in Step One, the groove depth is 0.2 mm, the groove width is 1 mm, and the average particle size of the titanium carbide particles filled in the grooves is 5 μm after cleaning and drying, thereby obtaining the copper alloy workpiece with titanium carbide particles filled in the grooves.

[0058] Example Three: The diffusion connection method for improving the high temperature strength of the steel / copper dissimilar alloy joint in the present embodiment is implemented according to the following steps:

[0059] Step One, pre-groove filling titanium carbide powder:

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

[0061] Step Two, friction stir surface complex phase treatment:

[0062] The copper alloy workpiece and the steel alloy workpiece filled with titanium carbide particles in the groove are respectively subjected to friction stir surface treatment along the groove path using a friction stir head, 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 penetration depth is 0.15 mm, so as to obtain the surface-treated copper alloy workpiece and the surface-treated steel alloy workpiece;

[0063] Step three, diffusion bonding:

[0064] The surfaces to be welded of the surface-treated copper alloy workpiece and the surface-treated steel alloy workpiece are respectively polished, then the surfaces to be welded of the steel alloy workpiece and the copper alloy workpiece are abutted, a bonding pressure of 5 MPa is applied, so as to obtain a workpiece to be welded, the workpiece to be welded is placed in a vacuum diffusion furnace, and diffusion bonding is performed at a temperature of 700 ℃ for 60 min, so as to complete the diffusion bonding of the steel / copper dissimilar alloy.

[0065] The joint obtained in Example Three is subjected to room temperature and high temperature shear tests at 25 ℃ and 700 ℃, and the shear strengths at room temperature and 700 ℃ are 95 MPa and 61 MPa respectively. The shear strengths of the steel / copper direct diffusion bonding joint (the diffusion bonding parameters are consistent with those of Example Three) in the control group without surface treatment at room temperature and 700 ℃ are 83 MPa and 35 MPa respectively.

Claims

1. A diffusion bonding method for improving high temperature strength of a steel / copper dissimilar alloy joint, characterized by The diffusion bonding method for improving the high-temperature strength of steel / copper dissimilar alloy joints is realized according to the following steps: Step one, pre-preparing grooves filled with titanium carbide powder: A plurality of grooves are processed on the welding surface of at least one of the steel alloy workpiece and the copper alloy workpiece, and after cleaning, micron or nanometer titanium carbide particles are filled in the grooves to obtain a steel alloy and / or copper alloy workpiece with titanium carbide particles filled in the grooves; Step two, friction stir surface complex treatment: A friction stir head is used to perform friction stir surface treatment on the steel alloy and / or copper alloy workpiece with titanium carbide particles filled in the grooves along the groove path to obtain a surface-treated steel alloy and / or copper alloy workpiece; Step three, diffusion bonding: The welding surface of the surface-treated steel alloy and / or copper alloy workpiece is polished, then the welding surfaces of the steel alloy workpiece and the copper alloy workpiece are butted, a bonding pressure is applied, a welding piece is obtained, and the welding piece is placed in a vacuum diffusion furnace for diffusion bonding at a temperature of 650-700℃ for 25-45min, thereby completing the diffusion bonding of the steel / copper dissimilar alloy.

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

3. The diffusion bonding method for improving high temperature strength of steel / copper dissimilar alloy joint according to claim 1, characterized by The copper alloy in step one is pure copper, brass, bronze or white copper; the steel alloy is low alloy steel, high speed steel, die steel or stainless steel.

4. The diffusion bonding method of enhancing high temperature strength of a steel / copper dissimilar alloy joint according to claim 1, characterized by The width of the groove in step one is 0.6-1.4mm, and the depth of the groove is 0.1-0.3mm.

5. The diffusion bonding method for improving high temperature strength of steel / copper dissimilar alloy joint according to claim 1, characterized by The steel alloy workpiece and the copper alloy workpiece in step one are both plate materials.

6. The diffusion bonding method of enhancing high temperature strength of a steel / copper dissimilar alloy joint according to claim 1, characterized by In step two, the rotation speed of the friction stir head during the friction stir surface treatment process is controlled to be 200-1000rpm, the travel speed is controlled to be 10-200mm / min, and the inclination angle is controlled to be 0-3.5°.

7. The diffusion bonding method of enhancing high temperature strength of a steel / copper dissimilar alloy joint according to claim 1, characterized by In step two, the penetration depth of the friction stir head during the friction stir surface treatment process is controlled to be 0.1-0.8mm.

8. The diffusion bonding method of enhancing high temperature strength of a steel / copper dissimilar alloy joint according to claim 1, characterized by In step three, the bonding pressure is controlled to be 1-30MPa.

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