CN114833410B - Method for reducing residual stress of heterogeneous brazed joint - Google Patents

Abstract

The invention belongs to the technical field of welding, and relates to a method for reducing residual stress of dissimilar brazing joints. When the brazing joint is lowered to a certain temperature, microplastic deformation and micro-precipitation are generated by heating first, reducing residual stress, cooling again to generate residual stress, and then reducing the stress by heating up, reducing the temperature of the joint during the cycle , while reducing the residual stress of the joint. The cryogenic cycle treatment of the present invention eliminates movable dislocations in the tissue and fixes the position of Mis-entanglement, adding value, reducing residual stress inside the brazed joint structure.

Description

A method for reducing residual stress of dissimilar brazed joints

technical field

The invention belongs to the technical field of welding, and relates to a method for reducing residual stress of a heterogeneous brazing joint.

Background technique

After brazing of the dissimilar material brazing joint, the dissimilar material with a small shrinkage will prevent the dissimilar material with a large shrinkage from continuing to shrink. At this time, the dissimilar material with a large shrinkage will be subjected to tensile stress along the brazing interface direction. The dissimilar materials with small shrinkage will be subjected to compressive stress along the direction of the brazing interface, so the brazed joint is prone to generate large residual stress on the interface after welding, resulting in cracks or other types of defects in the joint, thereby reducing the bonding strength and service life.

Furthermore, during the cooling process of the joint, the uneven deformation and phase transformation deformation caused by uneven cooling and different coefficients of linear expansion will generate residual stress, which greatly reduces the strength and stress fracture resistance of the joint. A new cooling treatment method to reduce residual stress of joints and improve the comprehensive performance of joints.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for greatly reducing the residual stress of dissimilar brazing joints in view of the above problems existing in the prior art.

The object of the present invention can be achieved by the following technical solutions: a method for reducing residual stress of a heterogeneous brazing joint, the method includes brazing, and the brazing includes heating, heat preservation, and cooling cycle treatment, and the cooling cycle treatment includes: cooling, At least 2 cycles of heat preservation, heating and heat preservation, and 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 above-mentioned method for reducing residual stress of dissimilar brazing joints, during the cooling cycle treatment, the temperature after cooling in the first cooling cycle is (0.5~0.7) Ts, and the temperature after heating is (0.7~0.9 ) Ts, the temperature after cooling in the last cooling cycle is (0.1~0.2) Ts, the temperature after heating is (0.15~0.3) Ts, and Ts is the solidus temperature of the solder.

Compared with the traditional cooling treatment method, during the cooling process of the joint, a large amount of residual stress is generated in the joint due to the distortion of the tissue structure due to uneven cooling and phase transformation. The heating treatment increases the diffusion driving force of the solid solution elements in the structure, promotes the occurrence of microplastic deformation and micro precipitation in the structure, and can release the residual stress caused by the structural distortion caused by cooling and element solid solution inside the structure, and increase the structural stability. After cooling down again, the residual stress generated is reduced by heating up again, and the temperature of the joint is gradually reduced during the cycle to achieve the purpose of reducing the residual stress of the joint.

Preferably, during the cooling cycle treatment, the temperature after cooling in the first cooling cycle is (0.6~0.7) Ts, and the temperature after heating again is (0.8~0.9) Ts: the temperature after cooling in the last cooling cycle is (0.1~0.2) Ts, the temperature after heating is (0.2~0.3) Ts.

In the above-mentioned method for reducing residual stress of dissimilar brazed joints, the cooling cycle treatment further includes a cryogenic cycle treatment, and the cryogenic cycle treatment includes at least two cycles of cooling, heat preservation, temperature increase, and heat preservation, and cryogenic The temperature after cooling in the cycle treatment is T ₁ , the temperature after heating is T ₂ , the range of T ₁ is -(75~150) ℃, the range of T ₂ is (0.2~0.3) Ts, and the temperature is lowered to T ₁ in the last cycle After heat preservation, heating to room temperature or cooling to room temperature after the last cycle, Ts is the solidus temperature of the solder.

Preferably, the temperature drop rates in the cooling cycle treatment and the cryogenic cycle treatment are both 5 to 20° C./min.

Preferably, the holding time in the cooling cycle treatment and the cryogenic cycle treatment is both 1-5h. The two holding times of a single cycle in the cooling cycle treatment or the cryogenic cycle treatment may be the same or different.

Preferably, the temperature increase rates in the cooling cycle treatment and the cryogenic cycle treatment are both 5 to 20° C./min.

The cryogenic cycle treatment of the present invention eliminates movable dislocations in the tissue through the heating and cooling cycle treatment between (0.1~0.4) Ts and -(75~150) ℃, and the uneven deformation caused by the effect of thermal expansion and cold contraction eliminates and fixes Dislocations are entangled and added value, reducing residual stress inside the tissue.

The invention can greatly reduce the residual stress of the brazed joint through two-stage cooling treatment, and improve the strength and stress fracture resistance of the joint.

In the above-mentioned method for reducing residual stress of dissimilar brazed joints, brazing specifically includes using brazing material to connect the first base metal and the second base metal by brazing, and the brazing connection satisfies the following calculation formula:

where α ₁ is the expansion coefficient of the first base metal, T is the welding temperature of the brazed joint, σ ₁ is the stress applied parallel to the brazing interface of the first base metal, E ₁ is the elastic modulus of the first base metal, and α ₂ is the first Two base metal expansion coefficients, σ ₂ is the stress applied parallel to the brazing interface of the second base metal, E ₂ is the elastic modulus of the second base metal, and t is the room temperature.

。As a preference,

.

。Further preferably,

.

。More preferably,

.

At room temperature of 20°C, the first base metal and the second base metal of the dissimilar material have the same length L, and the two have different linear expansion coefficients. The linear expansion coefficient of the first base metal is α ₁ , and the second base metal The coefficient of linear expansion is α ₂ , and α ₁ is greater than α ₂ . During brazing, the first base metal and the second base metal are heated to the brazing temperature T, and the linear expansions of the two are ΔL ₁ /L= α ₁ ×(T-20), ΔL ₂ /L =α ₂ ×(T-20), ΔL ₁ /L is greater than ΔL ₂ /L, after brazing is completed, the first base metal and the second base metal are To form an integral joint, when cooled to room temperature, the two theoretically need to produce line shrinkage ΔL ₁ /L =α ₁ × (T-20), ΔL ₂ /L =α ₂ × (T-20), but welding After the first base metal and the second base metal form a whole, the second base metal with a small shrinkage will prevent the first base metal from continuing to shrink. The base metal is subjected to compressive stress in the direction of the brazed interface, so the brazed joint will generate residual stress after welding. The present invention applies prestress σ ₁ and prestress σ ₂ to the first base material with elastic modulus E ₁ and the second base material with elastic modulus E ₂ during heating. The linear deformation amount of the first base material is ΔL ₁ /L =α ₁ ×(T-20)+σ ₁ /E ₁ , and the prestress σ ₁ is a compressive stress, which reduces the linear deformation amount ΔL ₁ /L. The linear deformation of the second base metal is ΔL ₂ /L =α ₂ ×(T-20)+σ ₂ /E ₂ , the prestress σ ₁ is the tensile stress, and the linear deformation ΔL ₂ /L is increased. Finally, by controlling , so that the linear deformation of the two is close, so as to achieve the purpose of reducing the residual stress of the joint after welding.

Preferably, when σ ₁ =0, the soldered connection satisfies the following calculation formula:

。

.

Preferably, when σ ₂ =0, the soldered connection satisfies the following calculation formula:

。

.

Since it is difficult to apply the prestress σ ₁ and the prestress σ ₂ to the first base material with the elastic modulus E ₁ and the second base material with the elastic modulus E ₂ during heating, the present invention can also be achieved by heating At the same time, stress is applied to one of the base metals, so that the linear deformation of the two is close, and the purpose of reducing the residual stress after welding of the joint is realized.

In the above-mentioned method for reducing residual stress of a heterogeneous brazing joint, the brazing filler metal includes at least one of nickel-based, copper-based, silver-based, aluminum-based, zinc-based and tin-based brazing filler metals.

In the above-mentioned method for reducing residual stress of a dissimilar brazed joint, the first base material includes at least one of carbon steel, alloy steel, aluminum alloy, and copper alloy.

In the above-mentioned method for reducing residual stress of a heterogeneous brazing joint, the second base material includes at least one of cemented carbide, ceramics, 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, ceramic, alloy steel, and copper alloy.

Preferably, when the first base material is alloy steel, the second base material is one of cemented carbide, ceramic, carbon steel, and copper alloy.

Preferably, when the first base material is an aluminum alloy, the second base material is one of cemented carbide, ceramic, carbon steel, alloy steel, and 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 above-mentioned method for reducing residual stress of a dissimilar brazed joint, the welding surface of the first base metal or the second base metal includes at least one of grooves and holes.

In the above-mentioned method for reducing residual stress of a heterogeneous brazed joint, the cross section of the groove or the hole includes at least one of an arc shape and a square shape.

In the present invention, grooves or holes are processed on the brazing surface of the first base metal or the second base metal, and the cross-sections of the grooves and holes can be arc or square, and the grooves or holes of the present invention can be cut off during cooling shrinkage deformation. stress integrity, thereby reducing residual stress.

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

1. In the present invention, when the joint is lowered to a certain temperature, microplastic deformation and micro precipitation are generated by first heating treatment, reducing residual stress, and after cooling down again, residual stress is generated, and the stress is reduced by heating again, and gradually reduces in the cycle process. The joint temperature, compared with the traditional cooling treatment method, the present invention can greatly reduce the residual stress of the joint;

2. The cryogenic cycle treatment of the present invention eliminates movable dislocations in the tissue due to the uneven deformation caused by the thermal expansion and cold contraction effect through the heating and cooling cycle between (0.1~0.4) T and -(75~150) °C. Fix dislocation entanglement, increase value, reduce the residual stress inside the brazed joint structure;

3. The present invention applies prestress σ ₁ and prestress σ ₂ to the first base material with elastic modulus E ₁ and the second base material with elastic modulus E ₂ during heating, and finally makes both of them during brazing. The amount of line deformation is close to that, so as to achieve the purpose of reducing the residual stress of the joint after welding;

4. The present invention reduces residual stress by arranging grooves or holes on the brazing surfaces of the first base metal and the second base metal to cut off the stress integrity generated during the cooling shrinkage deformation process.

Description of drawings

Figure 1 is the electron microscope picture of the brazing interface of the brazing sample of 316L stainless steel and alumina ceramic in Example 5; in the figure, 100, alumina ceramic, 200, 316L stainless steel, 300, Ag71Cu26Ti3 solder.

Figure 2 is the macroscopic picture of the brazed sample of 316L stainless steel and alumina ceramic and the surface electron microscope picture of alumina ceramic in Comparative Example 2.

Figure 3 is the electron microscope pictures of the brazing interface of the 316L stainless steel and alumina ceramic brazing samples in Comparative Example 2 under different magnifications; in the figure, 100, alumina ceramics, 200, 316L stainless steel, 300, Ag71Cu26Ti3 solder.

FIG. 4 is a schematic diagram of cooling cycle treatment in brazing in Example 1. FIG.

FIG. 5 is a schematic diagram of cryogenic cycle treatment in brazing in Example 1. FIG.

Fig. 6 is a schematic diagram of grooves in Example 7; 1. YG20 cemented carbide, 200, 316L stainless steel, 3. grooves.

Detailed ways

The following are specific embodiments of the present invention to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

Example 1:

S1. Set the expansion coefficient as α ₁ =18×10 ^-6 /°C and the elastic modulus as E ₁ =206GPa 316L stainless steel, set the expansion coefficient as α ₂ =6×10 ^-6 /°C and the elastic modulus as E ₂ =14.5GPa YG20 cemented carbide is ground and ultrasonically cleaned to remove surface oxide scale and impurities.

S2. Apply the silver flux to the brazing surfaces of 316L stainless steel and YG20 cemented carbide respectively, then add BAg65CuZn brazing filler metal at the brazing interface at 750°C, keep the brazing filler metal for 5 minutes after melting, and perform the brazing process on the brazed joints. Cooling stress relief treatment, check the national standard GB/T 10046-2018 silver solder, the solidus temperature of the solder BAg65CuZn used in this example is Ts=670℃;

The brazed joint after brazing connection is subjected to cooling cycle treatment as shown in Figure 4. The cooling cycle treatment specifically includes the following steps:

(1) Cool to 0.6Ts=402°C at a cooling rate of 10°C/min for 2 hours, and then heat up to 0.8Ts=536°C at a heating rate of 10°C/min for 2 hours.

(2) The brazed joint was cooled to 0.5Ts=335°C for 2 hours at a cooling rate of 10°C/min, and then heated to 0.7Ts=469°C for 2 hours at a heating rate of 10°C/min.

(3) The joint was cooled to 0.4Ts=268°C at a cooling rate of 10°C/min for 2 hours, and then heated to 0.6Ts=401°C at a heating rate of 10°C/min for 2 hours.

(4) The joint was cooled to 0.4Ts=268°C at a cooling rate of 10°C/min for 2 hours, and then heated to 0.5Ts=335°C at a heating rate of 10°C/min for 2 hours.

(5) The joint was cooled to 0.3Ts=201°C at a cooling rate of 10°C/min for 2 hours, and then heated to 0.4Ts=268°C at a heating rate of 10°C/min for 2 hours.

(6) The joint was cooled to 0.1Ts=67°C at a cooling rate of 10°C/min for 2 hours, and then heated to 0.3Ts=201°C at a heating rate of 10°C/min for 2 hours.

Then, the cryogenic cycle treatment as shown in Figure 5 is carried out, and the number of cycles is 2. The cryogenic cycle treatment specifically includes the following steps: the brazing joint is cooled to -75 °C for 2 hours at a cooling rate of 10 °C/min, and then maintained at a temperature of 10 °C for 2 hours. /min heating rate to 0.3Ts = 201 ℃ for 2h.

Finally, the brazed joint was cooled to -75°C at a cooling rate of 10°C/min for 2 hours, and then heated to room temperature at a heating rate of 10°C/min.

Example 2:

The only difference from Example 1 is that the number of cycles of cryogenic cycle treatment is 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 a compressive stress of 50 MPa parallel to the brazing interface is applied to the 316L stainless steel during brazing at 750°C.

Example 5:

S1. Set the expansion coefficient as α ₁ =18×10 ^-6 /°C and the elastic modulus as E ₁ =206GPa 316L stainless steel, set the expansion coefficient as α ₂ =8×10 ^-6 /°C and the elastic modulus as E ₂ =380GPa alumina ceramics are ground and ultrasonically cleaned to remove surface oxide scale and impurities.

S2. Add Ag71Cu26Ti3 brazing filler metal on the brazing interface of 316L stainless steel and alumina ceramic at 860°C. After the brazing filler metal is melted, keep the temperature for 5 minutes, and then cool the brazed joint to reduce stress. The Ag71Cu26Ti3 brazing filler metal used in this example has The solidus temperature is Ts=773℃;

The brazed joint after brazing connection is subjected to cooling cycle treatment, and the cooling cycle treatment specifically includes the following steps:

(1) Cool to 0.6Ts=464°C at a cooling rate of 10°C/min for 2 hours, and then heat up to 0.8Ts=618°C at a heating rate of 10°C/min for 2 hours.

(2) The brazed joint was cooled to 0.5Ts=387°C at a cooling rate of 10°C/min for 2 hours, and then heated to 0.7Ts=541°C at a heating rate of 10°C/min for 2 hours.

(3) The joint was cooled to 0.4Ts=309°C at a cooling rate of 10°C/min for 2 hours, and then heated to 0.6Ts=464°C at a heating rate of 10°C/min for 2 hours.

(4) The joint was cooled to 0.4Ts=309°C at a cooling rate of 10°C/min for 2 hours, and then heated to 0.5Ts=387°C at a heating rate of 10°C/min for 2 hours.

(5) The joint was cooled to 0.3Ts=232°C at a cooling rate of 10°C/min for 2 hours, and then heated to 0.4Ts=309°C at a heating rate of 10°C/min for 2 hours.

(6) The joint was cooled to 0.1Ts=77°C at a cooling rate of 10°C/min for 2 hours, and then heated to 0.3Ts=232°C at a heating rate of 10°C/min for 2 hours.

Then, cryogenic cycle treatment is performed, and the number of cycles is 2. The cryogenic cycle treatment specifically includes the following steps: the brazing joint is cooled down to -75 °C for 2 hours at a cooling rate of 10 °C/min, and then heated at a heating rate of 10 °C/min. Incubate at 0.3Ts=232°C for 2h.

Finally, the brazed joint was cooled to -75°C at a cooling rate of 10°C/min for 2 hours, and then heated to room temperature at a heating rate of 10°C/min.

The brazing process in step S2 is all performed in a vacuum furnace with a vacuum degree of 10 ^-3 MPa.

Example 6:

The only difference from Example 5 is that a compressive stress of 50 MPa parallel to the brazing interface is applied to the 316L stainless steel during brazing at 860°C.

Example 7:

The only difference from Example 1 is that the brazing interface is provided with grooves as shown in Figure 6, wherein 1. YG20 cemented carbide, 200, 316L stainless steel, 3. grooves.

Grooves are generally set on larger base metals and are suitable for the preparation of large brazed joints, which can fully relieve stress, improve the performance of brazed joints, and increase service life.

Comparative Example 1:

The only difference from Example 1 is that the circulatory cooling treatment and cryogenic circulation treatment are not performed, and the brazed joint after brazing connection is directly cooled to 0.3Ts=201 ℃ at a cooling rate of 10 ℃/min and kept for 2 hours.

Comparative Example 2:

The only difference from Example 5 is that the circulatory cooling treatment and cryogenic circulation treatment are not performed, and the brazed joint after brazing connection is directly cooled to room temperature at a cooling rate of 10° C./min.

Table 1: Residual stress results of brazed joints prepared in Examples 1-6 and Comparative Examples 1-2

Example first base metal second base metal Residual stress/MPa Example 1 316L stainless steel YG20 cemented carbide 35 Example 2 316L stainless steel YG20 cemented carbide 33 Example 3 316L stainless steel YG20 cemented carbide 46 Example 4 316L stainless steel YG20 cemented carbide 32 Example 5 316L stainless steel Alumina ceramics 46 Example 6 316L stainless steel Alumina ceramics 42 Comparative Example 1 316L stainless steel YG20 carbide 134 Comparative Example 2 316L stainless steel Alumina ceramics Ceramic cracking

Figure 1 is the electron microscope picture of the brazing interface of the brazing sample of 316L stainless steel and alumina ceramic in Example 5; in the figure, 100, alumina ceramic, 200, 316L stainless steel, 300, Ag71Cu26Ti3 solder. It can be seen from the figure that the interface of the brazed joint after cooling cycle treatment and cryogenic cycle treatment is complete and no cracks are generated, indicating that the residual stress is extremely small and has almost no significant effect on the strength and stress fracture resistance of the joint.

Figure 2 is the macroscopic picture of the brazing sample of 316L stainless steel and alumina ceramic in Comparative Example 2 and the surface electron microscope picture of the alumina ceramic; Figure 3 is the brazing interface of the 316L stainless steel and alumina ceramic brazing sample in Comparative Example 2 under different magnifications The electron microscope picture; in the picture, 100, alumina ceramics, 200, 316L stainless steel, 300, Ag71Cu26Ti3 solder. It can be seen from the figure that the brazed joints without cyclic cooling treatment and cryogenic circulation treatment have cracks on the surface and inside of the ceramic, indicating that the residual stress exceeds the fracture strength of the alumina ceramic base metal.

To sum up, the present invention eliminates movable dislocations in the tissue through cooling cycle treatment and cryogenic cycle treatment of uneven deformation caused by thermal expansion and contraction effects, fixed dislocations are entangled and added value, and reduce internal brazing joint tissue. Residual Stress.

The non-exhaustive points in the technical scope of the present invention and the new technical solutions formed by the equivalent replacement of single or multiple technical features in the technical solutions of the embodiments are also claimed in the present invention. At the same time, in all the enumerated or unenumerated embodiments of the solution of the present invention, each parameter in the same embodiment only represents an example of its technical solution (that is, a feasible solution), and there is no difference between the various parameters. There is a strict relationship of cooperation and limitation, wherein each parameter can be replaced with each other unless it is specifically stated unless it violates the axioms and the requirements of the present invention.

The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed by the above-mentioned technical means, but also include technical solutions composed of any combination of the above-mentioned technical features. The above is the specific embodiment of the present invention, it should be pointed out that for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can also be made, and these improvements and modifications are also regarded as It is the protection scope of the present invention.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention pertains can make various modifications or additions to the described specific embodiments or substitute in similar manners, but will not deviate from the spirit of the present invention or go beyond the definitions of the appended claims range.

Claims (9)

1. a method for reducing residual stress of dissimilar brazing joints, the method comprises brazing, and the brazing comprises heating, thermal insulation, cooling cycle processing, it is characterized in that, cooling cycle processing comprises: cooling, thermal insulation, heating, thermal insulation At least 2 cycles, and 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; The brazing specifically includes brazing the first base metal and the second base metal with brazing filler metal, and the brazing connection satisfies the following calculation formula:

, where α ₁ is the expansion coefficient of the first base metal, T is the welding temperature of the brazed joint, σ ₁ is the stress applied parallel to the brazing interface of the first base metal, E ₁ is the elastic modulus of the first base metal, and α ₂ is The expansion coefficient of the second base metal, σ ₂ is the stress applied parallel to the brazing interface of the second base metal, E ₂ is the elastic modulus of the second base metal, and t is the room temperature. 2. The method for reducing residual stress of dissimilar brazing joints according to claim 1, characterized in that, during the cooling cycle treatment, the temperature after cooling in the first cooling cycle is (0.5~0.7) Ts, and after heating The temperature of the solder is (0.7~0.9) Ts, the temperature after cooling in the last cooling cycle is (0.1~0.2) Ts, the temperature after heating is (0.15~0.3) Ts, and Ts is the solidus temperature of the solder. 3. The method for reducing residual stress of dissimilar brazing joints according to claim 2, characterized in that, during the cooling cycle treatment, the temperature after cooling in the first cooling cycle is (0.6~0.7) Ts, and after heating The temperature is (0.8~0.9)Ts, the temperature after cooling in the last cooling cycle is (0.1~0.2)Ts, and the temperature after heating is (0.2~0.3)Ts. 4. The method for reducing residual stress of dissimilar brazed joints according to claim 1, characterized in that, after the cooling cycle treatment, it also includes a cryogenic cycle treatment, and the cryogenic cycle treatment includes cooling, heat preservation, temperature increase, and heat preservation. At least 2 cycles, the temperature after cooling in the cryogenic cycle treatment is T ₁ , the temperature after heating is T ₂ , the range of T ₁ is -(75~150) ℃, the range of T ₂ is (0.2~0.3) Ts, and finally In _one cycle, the temperature is lowered to T1, then kept warm, heated to room temperature, or cooled to room temperature after the last cycle, Ts is the solidus temperature of the solder. 5. The method for reducing residual stress of a heterogeneous brazed joint according to claim 1, wherein the brazed connection satisfies the following calculation formula:

. 6. The method for reducing residual stress of a heterogeneous brazing joint according to claim 1, wherein the solder comprises at least one of nickel-based, copper-based, silver-based, aluminum-based, zinc-based and tin-based solders kind. 7 . The method for reducing residual stress of a heterogeneous brazing joint according to claim 1 , wherein the first base material comprises at least one of carbon steel, alloy steel, aluminum alloy, and copper alloy. 8 . 8. The method for reducing residual stress of a heterogeneous brazed joint according to claim 1, wherein the second base material comprises at least one of cemented carbide, ceramic, carbon steel, alloy steel, and copper alloy. 9 . The method for reducing residual stress of a dissimilar brazed joint according to claim 1 , wherein the welding surface of the first base metal or the second base metal comprises at least one of grooves and holes. 10 .

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