A method for eliminating residual stress in a heterogeneous weld joint

Abstract

This invention discloses a method for eliminating residual stress in dissimilar welded joints, comprising: compressing the dissimilar welded joint; heating the compressed welded joint to T℃, and then annealing it in a magnetic field pulse environment; the heating temperature T is 20-40% of the weld melting point. This invention combines compression treatment with low-to-medium temperature magnetic field pulse annealing, which can improve the joint strength while eliminating residual stress in dissimilar welded joints.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and in particular relates to a method for eliminating residual stress in heterogeneous welded joints. Background Technology

[0002] Welding technology has wide applications, including in petrochemicals, aerospace, and marine industries. Its development has significantly contributed to the advancement of manufacturing. With the increasing demands for high-performance, complex composite joints in various applications, dissimilar material joining technologies have emerged. Brazing technology is the most widely used method for welding materials with significant differences in physical properties, particularly in applications requiring precision welding. However, in some ceramic-metal brazed joints with large differences in thermophysical properties (coefficient of thermal expansion and modulus of elasticity), the high residual stress generated within the structure ultimately leads to poor ceramic-metal reliability.

[0003] In brazing, conventional annealing is often used for work hardened materials to eliminate residual stress. However, this method generally faces the problem of the contradiction between the residual stress controlled by the annealing temperature and the efficiency of eliminating residual stress. While prolonged holding at temperature to achieve near-steady-state cooling can effectively reduce final residual stress, its efficiency is extremely low, and the amount of residual stress eliminated depends on the recovery temperature. Summary of the Invention

[0004] Based on the above-mentioned technical problems, the present invention provides a method for eliminating residual stress in heterogeneous welded joints, which combines compression treatment with low-to-medium temperature magnetic field pulse annealing treatment, thereby improving the joint strength while eliminating residual stress in heterogeneous welded joints.

[0005] The specific solution of this invention is as follows:

[0006] This invention provides a method for eliminating residual stress in dissimilar welded joints, comprising: compressing the dissimilar welded joint; heating the compressed welded joint to T℃, and then annealing it in a magnetic field pulse environment; the heating temperature T is 20-40% of the weld melting point.

[0007] Preferably, the plastic deformation of the dissimilar welded joint is increased to 25-40% by compression treatment; more preferably, the plastic deformation of the dissimilar welded joint is increased to 30% by compression treatment.

[0008] Preferably, the compression processing parameters are: compression depth of 0.05-0.5 mm and compression rate of 0.05-0.5 mm / min.

[0009] The heterogeneous welded joints obtained by this invention exhibit 10% ± 5% plastic deformation, which is insufficient to drive microstructure evolution and cannot provide the driving force for subsequent microstructure regulation under magnetic field pulses. Therefore, this invention first employs a compression treatment. On one hand, it introduces appropriate dislocation driving forces into the brazed joint, disrupting the original stress accumulation. The deformation in the low-stress-hardening region is greater than that in the high-stress-hardening region, making the weld more uniform in both stress and microstructure hardening levels—that is, homogenizing the joint stress. On the other hand, the compression treatment introduces additional plastic strain energy into the welded joint, increasing the plastic deformation of the heterogeneous welded joint to 25-40%, thereby providing the driving force for microstructure evolution under subsequent magnetic field pulse regulation.

[0010] Preferably, the heating temperature T is 200-400℃.

[0011] Preferably, the welded joint after compression treatment is rapidly heated to T℃ at a heating rate of 100-120℃ / min; more preferably, the heating rate is 100℃ / min.

[0012] This invention rapidly heats the compressed welded joint to the target temperature without heat preservation, aiming to minimize the loss of strain energy during the heating process in a non-magnetic field environment.

[0013] Preferably, the applied magnetic field strength is >0.1T, and the welded joint is subjected to pulse impact during the cooling process to 80-100℃; the magnetic field strength amplitude is 0.3T; more preferably, the pulse application frequency is 10-15 times / min.

[0014] This invention involves air-cooling annealing of rapidly heated welded joints under a magnetic field pulse environment. This process leverages the dynamic strengthening mechanisms of dislocations, providing a non-thermally controlled method for microstructure regulation. The hardened material under pulse conditions exhibits enhanced dislocation dynamics and a reduced thermodynamic barrier hindering dislocations. The annealing process is accompanied by the dual influence of thermal and magnetic fields. The dynamic effects of the alternating magnetic field environment on metal defects, and the cooling process of electromagnetic pulse-assisted annealing, can alleviate material hardening and enhance stress relief. The microscopic evolution dynamics of electromagnetic pulse-assisted annealing and its interaction with the accumulation of residual stress ultimately address the need for low-temperature annealing, while also revealing the necessity of low-temperature conditions and an applied magnetic field for optimizing stress accumulation throughout the process.

[0015] Preferably, the first base material and the second base material are brazed together using brazing filler metal to obtain a heterogeneous welded joint.

[0016] Preferably, the first base material is selected from at least one of ceramics, carbon steel, alloy steel, aluminum alloy, and copper alloy; the second base material is selected from at least one of cemented carbide, ceramics, carbon steel, alloy steel, copper alloy, and aluminum alloy; the first base material and the second base material are different.

[0017] Preferably, the solder is selected from at least one of nickel-based, copper-based, silver-based, aluminum-based, zinc-based, and tin-based solders.

[0018] The beneficial effects of this invention are:

[0019] This invention introduces micro-defects and residual stress into the brazed joint structure through compression, providing a driving force for the evolution of the structure while driving the uniform distribution of structural stress. Subsequently, a low-to-medium temperature magnetic field pulse annealing treatment is applied, thereby providing a strain-induced pulse-assisted joint residual stress elimination method.

[0020] The method described in this invention can simultaneously reduce residual stress and restore the plasticity of the brazing filler metal. This dual optimization greatly improves the upper limit of the optimization of the joint's residual strength. Attached Figure Description

[0021] Figure 1 This is a diagram of the brazed joints of AlN-Cu.

[0022] Figure 2 Elemental distribution diagram of AlN-Cu brazed joint;

[0023] Figure 3 The stress distribution cloud diagram of the brazed structure during the compression process in Example 1 is shown, where 3a is before compression, 3b is after compression, and 3c is after unloading.

[0024] Figure 4 The image shows the strain energy distribution cloud diagram of the AlN-Cu brazed joint in Example 1, where 4a represents the area before compression and 4b represents the area after compression unloading.

[0025] Figure 5 The diagram shows the annealing temperature conditions, pulse environment, and measurement method for AlN-Cu brazed joints, where 5a represents the annealing temperature conditions and pulse environment; and 5b represents the measurement method.

[0026] Figure 6 The diagram shows the shear performance of the brazed AlN-Cu joint after treatment. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0028] The following examples and comparative examples all pertain to the processing of AlN-Cu brazing joints. These AlN-Cu brazing joints use aluminum nitride ceramic and TP2 copper as base materials. The intermediate layer of the brazing filler metal consists of 99.9% pure silver-copper foil (Ag28Cu72) and 99.9% pure titanium foil. Appropriate basis weights are selected to maintain the Ag28Cu72-Ti2 composition ratio of the brazing filler metal. The foil sheets are cut to 4.5mm × 4.5mm with equal area, and the thickness is ground to ensure the silver-copper foil weighs 2 × 10⁻⁶. -2 g.

[0029] The specific method for preparing AlN-Cu brazed joints is as follows:

[0030] (1) Stack the foils from bottom to top in the following order: copper-silver copper foil-titanium foil-silver copper foil-aluminum nitride. Figure 1 As shown, after stacking, the parts are fixed with glue to obtain the workpiece to be brazed;

[0031] (2) The brazing process is as follows: The workpiece to be brazed is placed in a vacuum brazing furnace, and the temperature is increased from room temperature to 300℃ at a heating rate of 10℃ / min, and held for 30 min; then the temperature is increased to 850℃ at a heating rate of 10℃ / min, and held for 10 min; then the temperature is decreased to 300℃ at a cooling rate of 10℃ / min, and cooled to room temperature in the furnace. The elemental distribution of the brazed joint prepared in this way is as follows: Figure 2 As shown.

[0032] The weld melting point of the AlN-Cu brazed joint is 780℃.

[0033] Example 1

[0034] A method for eliminating residual stress in dissimilar welded joints includes:

[0035] S1, Compression Processing

[0036] The AlN-Cu brazed joint was compressed at a rate of 0.1 mm / min at room temperature, thereby increasing the plastic deformation of the AlN-Cu brazed joint by 30%.

[0037] This step introduces a suitable dislocation driving force into the AlN-Cu brazed joint, disrupting the original stress accumulation while avoiding destructive effects on the base material. During the cooling stage of AlN-Cu brazed joint formation, because the coefficient of thermal expansion of Cu is greater than that of AlN ceramic, the resulting joint is warped, bulging towards the AlN ceramic side. Through compression treatment, during the compression stage, because the lateral deformation of Cu is greater than that of AlN ceramic, the final AlN-Cu brazed joint is warped, bulging towards the Cu side.

[0038] Stress distribution cloud diagram of brazed structure during compression process as shown in the figure. Figure 3 As shown, 3a represents before compression, 3b represents after compression, and 3c represents after unloading. It can be seen that with increasing pressure, the multiple different plastic deformation zones within the brazing seam, initially caused by uneven residual thermal stress, will undergo further hardening. This hardening is influenced by differences in local stress levels and hardening levels. The original stress level within the brazing seam, gradually increasing from the inside out, will cause the deformation during compression to decrease from the inside out. Therefore, the superposition of stresses caused by compression will further homogenize the stress and hardening levels of the brazing seam.

[0039] The strain energy distribution cloud map of the AlN-Cu brazed joint is shown below. Figure 4 As shown, 4a is before compression, and 4b is after compression and unloading. It can be seen that through compression treatment, the reshaping of joint deformation directly reduces the peak stress of the joint, and the strain energy density tends to be uniform.

[0040] S2, Magnetic field pulse assisted annealing

[0041] The AlN-Cu brazed joint after compression treatment was rapidly heated to 200℃ at 100℃ / min. Then, the AlN-Cu brazed joint was air-cooled and annealed in a magnetic field pulse environment with an applied magnetic field strength of 0.3T. During the cooling process to 80-100℃, the brazed joint was subjected to pulse impact, with a pulse application frequency of 10 times / min.

[0042] Example 2

[0043] A method for eliminating residual stress in dissimilar welded joints includes:

[0044] S1. Compression process: Same as in Example 1;

[0045] S2, Magnetic field pulse assisted annealing

[0046] The AlN-Cu brazed joint after compression treatment was rapidly heated to 400℃ at 100℃ / min. Then, the AlN-Cu brazed joint was air-cooled and annealed in a magnetic field pulse environment with an applied magnetic field strength of 0.3T. During the cooling process to 80-100℃, the brazed joint was subjected to pulse impact, with a pulse application frequency of 10 times / min.

[0047] The annealing temperature conditions and pulse environment used in the above embodiments are as follows: Figure 5 As shown in (a), it can be seen that the pulse frequency used in the above embodiment is 10 times / min. The magnetic pulse signal is obtained by measuring the induced voltage of the magnetic induction coil. The measurement method is as follows: Figure 5 (b)

[0048] Comparative Example 1

[0049] A method for eliminating residual stress in dissimilar welded joints includes:

[0050] S1. Compression process: Same as in Example 1;

[0051] S2. Annealing: The AlN-Cu brazed joint after compression treatment is rapidly heated to 200℃ at 100℃ / min, and then air-cooled for annealing.

[0052] Comparative Example 2

[0053] A method for eliminating residual stress in dissimilar welded joints includes:

[0054] S1. Compression process: Same as in Example 1;

[0055] S2. Annealing: The AlN-Cu brazed joint after compression treatment is rapidly heated to 400℃ at 100℃ / min, and then air-cooled for annealing.

[0056] The shear properties of the AlN-Cu brazed joints after the above examples and comparative examples were tested using an MTS CMT4204 universal testing machine. The specific test methods and results are as follows:

[0057] The AlN-Cu brazed joints prepared in the above embodiments and comparative examples were placed in a shearing fixture, and the shearing force was applied at a rate of 0.5 mm·min. -1 The loading rate is applied to ensure that the shear force acts at the joint, and the force and displacement curves during this process are recorded. The loading is stopped when the loading force drops sharply, and the maximum load is recorded.

[0058] Shear strength is calculated using the following formula:

[0059]

[0060] In the formula, τ is the shear strength, in MPa.

[0061] —Maximum shear force, kN;

[0062] Scs — The cross-sectional area of ​​the specimen parallel to the shear force, in mm² 2 .

[0063] Shear performance test results are as follows Figure 6 As shown.

[0064] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method of relieving residual stresses in a dissimilar weld joint, characterized by, include: The dissimilar welded joints are subjected to compression treatment; the compressed welded joints are heated to T℃ and then annealed in a magnetic field pulse environment; the heating temperature T is 20-40% of the weld melting point.

2. The method for eliminating residual stress in dissimilar welded joints according to claim 1, characterized in that, Compression treatment increases the plastic deformation of dissimilar welded joints by 25-40%.

3. The method for eliminating residual stress in heterogeneous welded joints according to claim 1 or 2, characterized in that, The compression parameters are: compression depth of 0.05-0.5mm and compression rate of 0.05-0.5mm / min.

4. The method for eliminating residual stress in heterogeneous welded joints according to claim 1 or 2, characterized in that, The heating temperature T is 200-400℃.

5. The method for eliminating residual stress in dissimilar welded joints according to claim 1 or 2, characterized in that, The compressed welded joint is rapidly heated to T℃ at a rate of 100-120℃ / min.

6. The method for eliminating residual stress in dissimilar welded joints according to claim 1 or 2, characterized in that, The applied magnetic field strength is >0.1T, and the welded joint is subjected to pulse impact during the cooling process to 80-100℃.

7. The method for eliminating residual stress in heterogeneous welded joints according to claim 1 or 2, characterized in that, The first base material and the second base material are brazed together using brazing filler metal to obtain a heterogeneous welded joint.

8. The method for eliminating residual stress in dissimilar welded joints according to claim 7, characterized in that, The first base material is selected from at least one of ceramics, carbon steel, alloy steel, aluminum alloy, and copper alloy; the second base material is selected from at least one of cemented carbide, ceramics, carbon steel, alloy steel, copper alloy, and aluminum alloy; the first base material and the second base material are different.

9. The method for eliminating residual stress in dissimilar welded joints according to claim 7, characterized in that, The solder is selected from at least one of nickel-based, copper-based, silver-based, aluminum-based, zinc-based, and tin-based solders.

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