Method for reducing residual stress of heterogeneous brazed joint
Technical Field
The invention belongs to the technical field of welding, and relates to a method for reducing residual stress of a heterogeneous brazed joint.
Background
After the brazing of the heterogeneous material brazing joint is completed, the heterogeneous material with small shrinkage can prevent the heterogeneous material with large shrinkage from continuously shrinking, the heterogeneous material with large shrinkage can receive tensile stress along the direction of a brazing interface at the moment, and the heterogeneous material with small shrinkage can receive compressive stress along the direction of the brazing interface, so that large residual stress is easily generated on the interface after the brazing joint is welded, cracks or other types of defects occur in the joint, and the bonding strength and the service life are reduced.
Moreover, in the process of cooling the joint, because the residual stress is generated due to the uneven deformation and the phase change deformation caused by the uneven cooling and the different linear expansion coefficients, the strength and the stress fracture resistance of the joint are greatly reduced, and a novel cooling treatment method capable of reducing the residual stress of the joint and improving the comprehensive performance of the joint is urgently needed.
Disclosure of Invention
The invention aims to provide a method for greatly reducing the residual stress of a heterogeneous brazed joint aiming at the problems in the prior art.
The purpose of the invention can be realized by the following technical scheme: a method of reducing residual stress of a heterogeneous brazed joint, the method comprising brazing, the brazing comprising a temperature-raising, holding, and cooling cycle process, the cooling cycle process comprising: and (3) performing at least 2 cycles of cooling, heat preservation, heating and heat preservation, wherein the temperature after cooling is not higher than the temperature after cooling in the previous cooling cycle, and the temperature after heating is not higher than the temperature after heating in the previous cooling cycle.
In the method for reducing the residual stress of the heterogeneous soldered joint, in the cooling cycle treatment process, the temperature after cooling in the first cooling cycle is (0.5 to 0.7) Ts, the temperature after heating is (0.7 to 0.9) Ts, the temperature after cooling in the last cooling cycle is (0.1 to 0.2) Ts, the temperature after heating is (0.15 to 0.3) Ts, and Ts is the solidus temperature of the solder.
Compared with the traditional cooling treatment mode, in the cooling process of the joint, the structural distortion of the joint is caused by uneven cooling, phase change and the like, so that a large amount of residual stress is generated on the joint.
Preferably, in the cooling cycle treatment, the temperature after cooling in the first cooling cycle is (0.6 to 0.7) Ts, and the temperature after reheating is (0.8 to 0.9) Ts: the temperature after cooling in the last cooling cycle is (0.1 to 0.2) Ts, and the temperature after heating is (0.2 to 0.3) Ts.
In the method for reducing the residual stress of the heterogeneous brazed joint, the method further comprises cryogenic circulation treatment after cooling circulation treatment, wherein the cryogenic circulation treatment comprises at least 2 cycles of cooling, heat preservation, heating and heat preservation, and the temperature after cooling in the cryogenic circulation treatment is T 1 The temperature after temperature rise is T 2 ,T 1 The range is (75 to 150) DEG C, T 2 The range is (0.2 to 0.3) Ts, and the temperature is reduced to T in the last cycle 1 And then preserving heat, heating to room temperature or cooling to room temperature after the last circulation is finished, wherein Ts is the solidus temperature of the brazing filler metal.
Preferably, the cooling rate in the cooling cycle treatment and the cooling rate in the deep cooling cycle treatment are both 5 to 20 ℃/min.
Preferably, the holding time in the cooling cycle treatment and the deep cooling cycle treatment is 1 to 5 hours. The two heat preservation times of a single circulation in the cooling circulation treatment or the deep cooling circulation treatment can be the same or different.
Preferably, the temperature rise rate in the cooling cycle treatment and the deep cooling cycle treatment is 5 to 20 ℃/min.
The cryogenic cycle treatment of the invention eliminates movable dislocation in the tissue by the uneven deformation caused by the expansion and contraction effect of heat through the temperature rise and fall cycle treatment between (0.1 to 0.4) Ts and (75 to 150) DEG C, fixes dislocation entanglement and increment, and reduces the residual stress in the tissue.
The invention can greatly reduce the residual stress of the soldered joint through two-stage cooling treatment, and improve the strength and the stress fracture resistance of the joint.
In the method for reducing the residual stress of the heterogeneous soldered joint, the soldering specifically includes soldering and connecting the first base material and the second base material by using a solder, and the soldering and connecting satisfy the following calculation formula:
wherein alpha is 1 Is a first base material expansion coefficient, T is a solder joint welding temperature, sigma 1 To apply stresses parallel to the brazing interface of the first base material, E 1 Is the first parent material elastic modulus, alpha 2 Is the second parent material expansion coefficient, sigma 2 To apply stress parallel to the brazing interface of the second base material, E 2 The second base material elastic modulus, t is room temperature.
As a matter of preference,
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it is further preferable that the concentration of the organic compound,
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it is still further preferred that,
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under the condition of room temperature of 20 ℃, a first parent metal and a second parent metal of the heterogeneous material have the same length L and have different linear expansion coefficients, and the linear expansion coefficient of the first parent metal is alpha 1 The linear expansion coefficient of the second base material is alpha 2 ,α 1 Greater than alpha 2 At the time of brazing, the first base material and the second base material are addedHeating to brazing temperature T, wherein the linear expansion amounts of the two are respectively Delta L 1 /L=α 1 ×(T-20),ΔL 2 /L =α 2 ×(T-20),ΔL 1 /L is greater than Δ L 2 and/L, after brazing with the brazing filler metal, forming an integral joint by the first base material and the second base material, and theoretically, respectively generating linear shrinkage delta L when the first base material and the second base material are cooled to room temperature 1 /L =α 1 ×(T-20),ΔL 2 /L =α 2 X (T-20), but the first base material and the second base material form an integral body after welding, the second base material with a small shrinkage prevents the first base material from continuing to shrink, and at this time, the first base material receives tensile stress in the direction of the brazing interface, and the second base material receives compressive stress in the direction of the brazing interface, so that residual stress occurs after the brazed joint is welded. The elastic modulus of the invention is E when heating 1 First base material and elastic modulus of E 2 Second base material applying prestress sigma 1 And prestress σ 2 . The wire deformation amount of the first base material is DeltaL 1 /L =α 1 ×(T-20)+σ 1 /E 1 Prestressed σ 1 For compressive stress, the line is deformed by an amount Δ L 1 the/L is reduced. The linear deformation amount of the second base material is DeltaL 2 /L =α 2 ×(T-20)+σ 2 /E 2 Prestressing σ 1 The wire is deformed by an amount DeltaL for tensile stress 2 increasing/L, and finally controlling to enable the linear deformation of the two to be close to each other, thereby achieving the purpose of reducing the residual stress after the joint is welded.
Preferably, when σ is 1 In case of =0, the brazed joint satisfies the following calculation formula:
preferably, when σ is 2 In case of =0, the brazed joint satisfies the following calculation formula:
due to the elastic modulus when heatedIs E 1 First base material and elastic modulus of E 2 Second base material applying prestress sigma 1 And prestress σ 2 The invention can also apply stress to one of the base metals during heating to enable the linear deformation of the base metals to be close to each other, thereby achieving the purpose of reducing the residual stress after the joint is welded.
In the above method for reducing the residual stress of the heterogeneous soldered joint, the solder comprises at least one of nickel-based, copper-based, silver-based, aluminum-based, zinc-based and tin-based solders.
In the above method of reducing residual stress of the dissimilar brazed joint, the first base material includes at least one of carbon steel, alloy steel, aluminum alloy, and copper alloy.
In the above method of reducing the residual stress of the dissimilar brazed joint, the second base material includes at least one of cemented carbide, ceramic, carbon steel, alloy steel, and copper alloy.
Preferably, when the first base material is carbon steel, the second base material is one of cemented carbide, ceramics, alloy steel, and copper alloy.
Preferably, when the first base material is alloy steel, the second base material is one of cemented carbide, ceramics, carbon steel, and copper alloy.
Preferably, when the first base material is an aluminum alloy, the second base material is one of a cemented carbide, a ceramic, a carbon steel, an alloy steel, and a copper alloy.
Preferably, when the first base material is a copper alloy, the second base material is one of cemented carbide, ceramics, carbon steel, and alloy steel.
In the method for reducing the residual stress of the heterogeneous brazed joint, the welding surface of the first base material or the second base material comprises at least one of a groove and a hole.
In one of the above-described methods of reducing residual stress of a heterogeneous brazed joint, the groove or hole cross-section includes at least one of an arc and a square.
According to the invention, the grooves or the holes are processed on the brazing surface of the first base material or the second base material, the cross sections of the grooves or the holes can be arc or square, and the grooves or the holes can cut off the stress integrity generated in the cooling shrinkage deformation process, so that the residual stress is reduced.
Compared with the prior art, the invention has the following beneficial effects:
1. when the temperature of the joint is reduced to a certain temperature, the joint is subjected to temperature rise treatment firstly to generate micro plastic deformation and micro precipitation, the residual stress is reduced, the residual stress is generated after the temperature is reduced again, the stress is reduced by temperature rise again, the temperature of the joint is reduced gradually in the circulating process, and compared with the traditional temperature reduction treatment mode, the joint temperature reduction device can greatly reduce the residual stress of the joint;
2. the cryogenic circulation treatment of the invention utilizes the temperature rise and drop circulation between (0.1 to 0.4) T and (75 to 150) DEG C to eliminate the movable dislocation in the tissue due to the uneven deformation generated by the effect of expansion caused by heat and contraction caused by cold, fix the dislocation entanglement and increment, and reduce the residual stress in the tissue of the soldered joint;
3. the invention has the elasticity modulus E when being heated 1 First base material and elastic modulus of E 2 Second base material applying prestress sigma 1 And prestress σ 2 Finally, the linear deformation of the two components is close to each other during brazing, so that the purpose of reducing the residual stress of the welded joint is achieved;
4. according to the invention, the integrity of the stress generated in the process of cutting, cooling and shrinking deformation is reduced by arranging the grooves or holes on the brazing surfaces of the first base metal and the second base metal, so that the residual stress is reduced.
Drawings
FIG. 1 is an electron microscope image of the brazing interface of a 316L stainless steel and alumina ceramic brazing sample of example 5; in the figure, 100, alumina ceramics, 200, 316L stainless steel, 300, ag71Cu26Ti3 brazing filler metal.
FIG. 2 is a macroscopic picture and an electron microscope picture of the surface of the alumina ceramic of the 316L stainless steel and alumina ceramic brazing sample in the comparative example 2.
FIG. 3 is an electron microscope image of the brazing interface of 316L stainless steel and alumina ceramic brazing sample in comparative example 2 at different magnifications; in the figure, 100, alumina ceramics, 200, 316L stainless steel, 300, ag71Cu26Ti3 brazing filler metal.
FIG. 4 is a schematic view of a cooling cycle process in brazing according to example 1.
FIG. 5 is a schematic view of a cryogenic cycle treatment in brazing according to example 1.
FIG. 6 is a schematic view of a trench according to example 7; 1. YG20 cemented carbide, 200, 316L stainless steel, 3, groove.
Detailed Description
The following are specific examples of the present invention and further describe the technical solutions of the present invention, but the present invention is not limited to these examples.
Example 1:
s1, setting the expansion coefficient as alpha 1 =18×10 -6 /. Degree.C.and elastic modulus E 1 316L stainless steel of =206GPa, the expansion coefficient is alpha 2 =6×10 -6 /. Degree.C.and elastic modulus E 2 And (3) grinding and ultrasonically cleaning the YG20 hard alloy with the hardness of =14.5GPa to remove surface scale and impurities.
S2, respectively coating silver brazing agents on brazing surfaces of 316L stainless steel and YG20 hard alloy, then adding BAg65CuZn brazing filler metal on a brazing interface at 750 ℃, preserving heat for 5min after the brazing filler metal is molten, cooling and reducing stress of a brazed joint, and checking the national standard GB/T10046-2018 silver brazing filler metal, wherein the solidus line temperature of the brazing filler metal BAg65CuZn used in the embodiment is = Ts 670 ℃;
the brazed joint after the brazing connection is subjected to cooling circulation treatment as shown in fig. 4, and the cooling circulation treatment specifically comprises the following steps:
(1) Cooling to 0.6Ts =402 ℃ at a cooling rate of 10 ℃/min for 2h, and then heating to 0.8Ts =536 ℃ at a heating rate of 10 ℃/min for 2h.
(2) The soldered joint is cooled to 0.5Ts =335 ℃ at the cooling rate of 10 ℃/min and is kept for 2h, and then the soldered joint is heated to 0.7Ts =469 ℃ at the heating rate of 10 ℃/min and is kept for 2h.
(3) The joint is cooled to 0.4Ts =268 ℃ at a cooling rate of 10 ℃/min and is kept for 2h, and then is heated to 0.6Ts =401 ℃ at a heating rate of 10 ℃/min and is kept for 2h.
(4) Cooling the joint to 0.4Ts =268 ℃ at a cooling rate of 10 ℃/min, and keeping the temperature for 2h, and then heating to 0.5Ts =335 ℃ at a heating rate of 10 ℃/min, and keeping the temperature for 2h.
(5) Cooling the joint to 0.3Ts =201 ℃ at a cooling rate of 10 ℃/min, and keeping the temperature for 2h, and then heating to 0.4Ts =268 ℃ at a heating rate of 10 ℃/min, and keeping the temperature for 2h.
(6) Cooling the joint to 0.1Ts =67 ℃ at a cooling rate of 10 ℃/min, and keeping the temperature for 2h, and then heating to 0.3Ts =201 ℃ at a heating rate of 10 ℃/min, and keeping the temperature for 2h.
Then, as shown in fig. 5, the cryogenic cycle treatment is performed, the cycle number is 2, and the cryogenic cycle treatment specifically includes the following steps: the temperature of the soldered joint is reduced to-75 ℃ at the cooling rate of 10 ℃/min and is preserved for 2h, and then the temperature is increased to 0.3Ts =201 ℃ at the heating rate of 10 ℃/min and is preserved for 2h.
And finally, cooling the soldered joint to-75 ℃ at a cooling rate of 10 ℃/min, preserving the temperature for 2h, and then heating the soldered joint to room temperature at a heating rate of 10 ℃/min.
Example 2:
the only difference from example 1 is that the number of cycles of the treatment of the cryogenic cycle was 4.
Example 3:
the only difference from example 1 is that the cryogenic cycle treatment was not performed.
Example 4:
the only difference from example 1 is that the 316L stainless steel is loaded with a compressive stress parallel to the braze interface of 50MPa when brazed at 750 ℃.
Example 5:
s1, setting the expansion coefficient as alpha 1 =18×10 -6 /. Degree.C.and elastic modulus E 1 316L stainless steel of =206GPa, the expansion coefficient is alpha 2 =8×10 -6 /. Degree.C.and elastic modulus E 2 And (4) grinding and ultrasonically cleaning the alumina ceramic of which the density is 380GPa to remove surface oxide scales and impurities.
S2, adding an Ag71Cu26Ti3 brazing filler metal on a 316L stainless steel and alumina ceramic brazing interface at 860 ℃, preserving heat for 5min after the brazing filler metal is molten, and carrying out cooling and stress relief treatment on a brazed joint, wherein the solidus temperature of the Ag71Cu26Ti3 brazing filler metal used in the embodiment is Ts =773 ℃;
and carrying out cooling circulation treatment on the brazed joint after brazing connection, wherein the cooling circulation treatment specifically comprises the following steps:
(1) Cooling to 0.6Ts =464 ℃ at a cooling rate of 10 ℃/min, and keeping the temperature for 2h, and then heating to 0.8Ts =618 ℃ at a heating rate of 10 ℃/min, and keeping the temperature for 2h.
(2) And cooling the soldered joint to 0.5Ts =387 ℃ at a cooling rate of 10 ℃/min, and keeping the temperature for 2h, and then heating to 0.7Ts =541 ℃ at a heating rate of 10 ℃/min, and keeping the temperature for 2h.
(3) Cooling the joint to 0.4Ts =309 ℃ at a cooling rate of 10 ℃/min, and keeping the temperature for 2h, and then heating to 0.6Ts =464 ℃ at a heating rate of 10 ℃/min, and keeping the temperature for 2h.
(4) Cooling the joint to 0.4Ts =309 ℃ at a cooling rate of 10 ℃/min, and keeping the temperature for 2h, and then heating to 0.5Ts =387 ℃ at a heating rate of 10 ℃/min, and keeping the temperature for 2h.
(5) The joint is cooled to 0.3Ts =232 ℃ at a cooling rate of 10 ℃/min and is kept for 2h, and then is heated to 0.4Ts =309 ℃ at a heating rate of 10 ℃/min and is kept for 2h.
(6) The joint is cooled to 0.1Ts =77 ℃ at a cooling rate of 10 ℃/min and is kept for 2h, and then is heated to 0.3Ts =232 ℃ at a heating rate of 10 ℃/min and is kept for 2h.
Then, carrying out cryogenic circulating treatment, wherein the circulating frequency is 2, and the cryogenic circulating treatment specifically comprises the following steps: the temperature of the soldered joint is reduced to-75 ℃ at the cooling rate of 10 ℃/min and is kept for 2h, and then the temperature is increased to 0.3Ts =232 ℃ at the heating rate of 10 ℃/min and is kept for 2h.
And finally, cooling the brazing joint to-75 ℃ at a cooling rate of 10 ℃/min, preserving the temperature for 2h, and then heating the brazing joint to room temperature at a heating rate of 10 ℃/min.
Step S2, the brazing process is carried out under the condition that the vacuum degree is 10 -3 In a vacuum furnace under MPa.
Example 6:
the only difference from example 5 is that the 316L stainless steel is loaded with a compressive stress of 50MPa parallel to the brazing interface when brazed at 860 c.
Example 7:
the only difference from example 1 is that the brazing interface is provided with grooves as shown in fig. 6, wherein 1, YG20 cemented carbide, 200, 316L stainless steel, 3, grooves.
The groove is generally arranged on the base metal with larger volume, is suitable for being used in the preparation of large-scale soldered joints, can fully release stress, improves the performance of the soldered joints and prolongs the service life.
Comparative example 1:
the difference from the example 1 is only that the soldered joint after soldering connection is directly cooled to 0.3Ts =201 ℃ at a cooling rate of 10 ℃/min and is kept at the temperature for 2h without performing the circulating cooling treatment and the cryogenic circulating treatment.
Comparative example 2:
the only difference from example 5 is that, without performing the circulation cooling treatment and the cryogenic circulation treatment, the soldered joint after the soldering connection was directly cooled to room temperature at a cooling rate of 10 ℃/min.
Table 1: residual stress results of brazed joints prepared in examples 1 to 6 and comparative examples 1 to 2
Examples
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First base material
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Second base material
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Residual stress/MPa
|
Example 1
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316L stainless steel
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YG20 hard alloy
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35
|
Example 2
|
316L stainless steel
|
YG20 hard alloy
|
33
|
Example 3
|
316L stainless steel
|
YG20 hard alloy
|
46
|
Example 4
|
316L stainless steel
|
YG20 hard alloy
|
32
|
Example 5
|
316L stainless steel
|
Alumina ceramics
|
46
|
Example 6
|
316L stainless steel
|
Alumina ceramics
|
42
|
Comparative example 1
|
316L stainless steel
|
YG20 hard alloy
|
134
|
Comparative example 2
|
316L stainless steel
|
Alumina ceramics
|
Cracking of ceramics |
FIG. 1 is an electron microscope image of the brazing interface of a 316L stainless steel and alumina ceramic brazing sample of example 5; in the figure, 100, alumina ceramics, 200, 316L stainless steel, 300, ag71Cu26Ti3 brazing filler metal. As can be seen from the figure, the brazed joint subjected to the cooling cycle treatment and the cryogenic cycle treatment has a complete interface and no cracks, which shows that the residual stress is extremely small, and almost has no obvious influence on the strength and the stress fracture resistance of the joint.
FIG. 2 is a macroscopic picture and an electron microscope picture of the surface of the alumina ceramic of the 316L stainless steel and alumina ceramic brazing sample in comparative example 2; FIG. 3 is an electron microscope image of the brazing interface of 316L stainless steel and alumina ceramic brazing sample in comparative example 2 under different magnifications; in the figure, 100, alumina ceramics, 200, 316L stainless steel, 300, ag71Cu26Ti3 brazing filler metal. As is clear from the figure, cracks were generated in the brazed joint not subjected to the circulation cooling treatment and the deep cooling circulation treatment, both in the surface and in the interior of the ceramic, indicating that the residual stress exceeded the fracture strength of the alumina ceramic base material.
As described above, the present invention eliminates the movable dislocations in the structure by the uneven deformation caused by the expansion/contraction effect of heat by the cooling cycle treatment and the deep cooling cycle treatment, entangles and increases the fixed dislocations, and reduces the residual stress in the structure of the soldered joint.
The technical scope of the invention claimed by the embodiments of the present application is not exhaustive, and new technical solutions formed by equivalent replacement of single or multiple technical features in the technical solutions of the embodiments are also within the scope of the invention claimed by the present application; in all the embodiments of the present invention, which are listed or not listed, each parameter in the same embodiment only represents an example (i.e., a feasible embodiment) of the technical solution, and there is no strict matching and limiting relationship between the parameters, wherein the parameters may be replaced with each other without departing from the axiom and the requirements of the present invention, unless otherwise specified.
The technical means disclosed by the scheme of the invention are not limited to the technical means disclosed by the technical means, and the technical scheme also comprises the technical scheme formed by any combination of the technical characteristics. While the foregoing is directed to embodiments of the present invention, it will be appreciated by those skilled in the art that various changes may be made in the embodiments without departing from the principles of the invention, and that such changes and modifications are intended to be included within the scope of the invention.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.