JP6153744B2 - Manufacturing method of welded joint - Google Patents

Description

  The present invention relates to a method for manufacturing a welded joint, and is particularly suitable for use in joining a steel plate and an aluminum alloy plate by resistance spot welding.

In recent years, in the automotive field, aluminum alloy plates have been partially used for the body and parts to reduce vehicle weight and improve collision safety for the purpose of reducing fuel consumption and reducing carbon dioxide (CO ₂ ) emissions. There is a growing need, especially in the field of hybrid vehicles. On the other hand, spot welding is mainly used in processes such as vehicle body assembly and component mounting. However, when an aluminum alloy plate is partially used, it is necessary to spot weld the aluminum alloy plate and the steel plate. Sex occurs.
Resistance spot welding is performed by Joule heat generated in a plurality of metal plates by energizing each electrode from the front side and the back side of the overlapping portion of the plurality of metal plates with the plate surfaces superimposed on each other. , A method of joining the plurality of metal plates.

Conventionally, when trying to join a steel plate and an aluminum alloy plate by such resistance spot welding, when both the steel plate and aluminum are melted, a brittle intermetallic compound at the joint between the steel plate and the aluminum alloy plate Since (Fe ₂ Al ₅ , FeAl _3, etc.) is generated, it is known that joint strength is reduced (see Patent Documents 1 to 3).
Many methods have been proposed so far in order to suppress the formation of intermetallic compounds when welding an aluminum alloy plate and a steel plate and increase the joint strength.

  In Patent Documents 1 and 2, when resistance spot welding of a steel plate and an aluminum alloy plate is performed, a zinc which causes a eutectic reaction with the steel plate and the aluminum alloy plate is interposed, thereby melting by a eutectic reaction. A technique for discharging the eutectic metal and oxide film formed is disclosed. In Patent Documents 1 and 2, since the eutectic metal of zinc and aluminum melts at a temperature lower than the melting point of aluminum, the oxide film can be removed at a low temperature, and the metal generated at the bonding interface during the bonding process. It is said that the formation of intermetallic compounds can be suppressed. In the technique described in Patent Document 1, in order to discharge the metal or oxide film melted by the eutectic reaction, at least one of the steel plate and the aluminum alloy plate can be easily discharged from the joint portion. The processing to do is done. In the technique described in Patent Document 2, at least one tip portion of the electrode has a curved shape.

  In Patent Document 3, the tip curvature radius R1 of the steel plate side electrode is set to 30 [mm] to 90 [mm], and the tip curvature radius R2 of the aluminum alloy plate side electrode is set to 2.0 <R2 / R1 <6.0. The technology is disclosed. In Patent Document 3, an aluminum melt nugget can be smoothly formed on the joint surface between the steel plate and the aluminum alloy plate without a shortage of the amount of aluminum melted on the joint surface. As a result, the intermetallic compound is joined. It is said that it can be suppressed from being formed on the surface.

Patent Document 4 proposes a method for ensuring the joint strength by defining the thickness of the intermetallic compound produced in the welded portion between the aluminum alloy plate and the steel plate and the area ratio (relative to the joint area). Yes.
Patent Document 5 proposes a method of improving joint strength and corrosion resistance by providing an adhesive layer or the like between joint surfaces in advance when welding an aluminum alloy plate and a steel plate, and using adhesion and welding together. ing.
In addition, for example, there is a method of increasing the joint strength after welding by inserting an aluminum clad steel plate between an aluminum alloy plate and a steel plate, and a method of using mechanical joining with self-piercing rivets together with welding. is there. Welding of light metals such as aluminum that presses against the material to be welded with pressure while rotating the pin to generate frictional heat and welds with this frictional heat and plastic flow generated in the axial direction due to rotation of the pin There is also a method using a friction stir welding method suitable for the above. Further, instead of a general welding method, a method of using friction stir welding in which a welding tool is joined with its frictional heat and stirring force by pressing a rotary tool against the welding material with a strong pressure is also conceivable. In addition, for example, a method for joining a steel plate and an aluminum alloy plate by allowing an aluminum alloy plate to penetrate through a steel pin to contact the steel plate and resistance-welding the contact portion by energizing between the steel pin and the steel plate. Etc. are also conceivable.

JP 2007-130686 A JP 2007-326146 A JP 2008-200747 A JP 2009-61500 A JP 2008-80394 A

Sumitomo Metal Technology Co., Ltd. Homepage, Thermal conductivity measurement-Temperature gradient method-Internet <URL: http://www.smt-inc.co.jp/research_support/bussei_Thermal_keisha.html> Agne Technology Center website, thermal conductivity, Internet <URL: http://homepage3.nifty.com/agnesokutei/pag21000.htm>

  However, when the present inventors formed welded joints by the techniques described in Patent Documents 1 to 3 and conducted a cross tensile test based on JIS Z 3137, the welded joints by any technique were welded joints. As a result, it was found that the cross tensile strength (CTS) was increased or decreased, and the cross tensile strength of the welded joint was not stable. Moreover, it turned out that a fracture | rupture form may become a favorable fracture | rupture form (plug fracture | rupture) or an unsatisfactory fracture | rupture form (interface fracture | rupture) by a welded joint.

In the techniques described in Patent Documents 1 and 2, eutectic metals and oxide films that melt at a temperature lower than the melting point of aluminum are discharged, and joining using melting of aluminum is not performed. Further, in the techniques described in Patent Documents 3 and 4, since a molten nugget of aluminum is formed on the joint surface between the steel plate and the aluminum alloy plate, a thick aluminum melt-solidified portion is formed on the joint surface between the steel plate and the aluminum alloy plate. The
In addition, the technique described in Patent Document 5 has a problem in that a large amount of brittle intermetallic compound is generated in the welded portion between the steel plate and the aluminum alloy plate, and the bonding strength and corrosion resistance are reduced.
Therefore, as described above, the joint strength (for example, cross tensile strength) of the welded joint produced by the techniques described in Patent Documents 1 to 5 may vary greatly depending on the welded joint, and the fracture form of the welded joint However, it is considered that there is a case where a good fracture form (plug fracture) is not obtained.

  The present invention has been made in view of the above problems, and it is possible to stably obtain a high joint strength as a joint strength of a welded joint formed by resistance spot welding of a steel plate and an aluminum alloy plate. It aims at making it a good fracture form being obtained.

The method for manufacturing a welded joint according to the present invention is such that the aluminum alloy plate and the steel plate are directly overlapped, the aluminum alloy plate side electrode is brought into contact with the aluminum alloy plate and the steel plate side electrode is brought into contact with the steel plate, A spot welded joint manufacturing method for manufacturing a spot welded joint by performing resistance spot welding by applying a welding current while applying a pressure between an aluminum alloy plate side electrode and the steel plate side electrode, the aluminum alloy The thermal conductivity of the plate side electrode is 130 [W / (m · K)] or more and 240 [W / (m · K)] or less, and the thermal conductivity of the steel plate side electrode is 300 [W / (m -K)] or more.

  According to the present invention, the thermal conductivity of the aluminum alloy plate side electrode is 130 [W / (m · K)] or more and 240 [W / (m · K)] or less, and the thermal conductivity of the steel plate side electrode is 300 [W / (m · K)]. W / (m · K)] or more. Accordingly, it is possible to stably obtain a high joint strength as a joint strength of a welded joint formed by resistance spot welding of a steel plate and an aluminum alloy plate and obtain a good fracture form.

It is a figure which shows an example of schematic structure of a resistance spot welding apparatus. It is a figure which shows an example of the shape of an electrode.

  Next, an embodiment of the present invention will be described with reference to the drawings. In addition, since this embodiment demonstrates in detail in order to make an example of the manufacturing method of the spot-welded joint in this invention better understood, unless otherwise specified, this invention is not limited.

When the present inventors perform resistance spot welding of a steel plate and an aluminum alloy plate, the (total) thermal conductivity of the aluminum alloy plate-side electrode is smaller than the (total) thermal conductivity of the steel plate-side electrode. By doing so, the cross joint tensile strength (CTS) of the welded joint is stabilized at a large value even when using the same resistance spot welding equipment or electrode forming machine as before (the value does not vary greatly depending on the welded joint). In addition, the inventors have obtained the knowledge that plug fracture can be stably obtained as a fracture form of a welded joint (plug fracture with an appropriate plug diameter).
By making the thermal conductivity of the aluminum alloy plate-side electrode smaller than the thermal conductivity of the steel plate-side electrode, it is possible to accelerate the heat generated in the steel plate through the steel plate-side electrode, It is possible to suppress the generated heat from being removed through the aluminum alloy plate side electrode. Thereby, the molten metal which is wide in the surface direction and thin in the thickness direction can be formed (solidified) between the steel plate and the aluminum alloy plate.
Based on the above new findings, the present inventors have conceived the present embodiment described below.

<Resistance spot welding>
FIG. 1 is a diagram illustrating an example of a schematic configuration of a resistance spot welding apparatus. An outline of an example of a method of resistance spot welding the aluminum alloy plate 110 and the steel plate 120 will be described with reference to FIG.
When performing resistance spot welding, first, the aluminum alloy plate 110 and the steel plate 120, which are materials to be welded, are overlapped. In the example illustrated in FIG. 1, the aluminum alloy plate 110 and the steel plate 120 are overlapped one by one. Note that a plurality of at least one of the aluminum alloy plate 110 and the steel plate 120 may be provided.
And by energizing while pressing the aluminum side electrode 210 and the steel plate side electrode 220 so as to be sandwiched from both sides with respect to the overlapping portion of the aluminum alloy plate 110 and the steel plate 120, that is, from the vertical direction in FIG. A molten metal is formed between the aluminum alloy plate 110 and the steel plate 120. After the welding energization is completed, the molten metal is solidified by heat removal by the water-cooled aluminum side electrode 210 and the steel plate side electrode 220 and heat conduction to the steel plate 110 and the aluminum alloy plate 120, and the aluminum alloy plate 110 and the steel plate 120. Formed between.

<Aluminum alloy plate>
Below, an example of the characteristic of the aluminum alloy plate 110 which is one to-be-welded material in this embodiment is explained in full detail.
(Alloy type)
The type of alloy of the aluminum alloy plate 110 is not particularly limited. For example, any type of aluminum alloy such as 5000 (Al—Mg) or 6000 (Al—Mg—Si) that is generally used in automobile bodies can be used without any limitation. .
(Tensile strength)
The tensile strength of the alloy of the aluminum alloy plate 110 is not particularly limited. For example, a thing of about 100-400 MPa class generally used in a car body etc. can be adopted without any limitation.
(Thickness)
The thickness t ₁ (before welding) of the aluminum alloy plate 110 is not particularly limited, and is, for example, about 0.55 [mm] to 2.0 [mm] generally used in an automobile body or the like. An aluminum alloy plate having a thickness of can be used without any limitation.

<Steel plate>
Below, an example of the characteristic of the steel plate 120 which is the other to-be-welded material of this embodiment is explained in full detail.
(Steel grade)
The steel type of the steel plate 120 is not particularly limited. For example, extremely low C type (ferrite main structure), Al-k type (structure containing pearlite in ferrite), two-phase structure type (for example, structure containing martensite in ferrite, structure containing bainite in ferrite) Any type of steel sheet may be used, such as a processing-induced transformation type (structure containing retained austenite in ferrite), a fine crystal type (ferrite main structure), or the like. Regardless of the type of steel plate, by applying the spot welded joint manufacturing method of this embodiment, the aluminum alloy plate and the steel plate can be produced while suppressing the formation of intermetallic compounds without impairing the properties of the steel plate. Can be welded, and a highly reliable spot joint (welded part) can be obtained.

(Tensile strength)
The tensile strength of the steel plate 120 is not particularly limited, and any tensile strength steel plate can be used without any limitation. For example, a steel plate having a tensile strength of about 270 to 1470 MPa, which is generally used in an automobile body or the like, can be used without any limitation.
(Plating)
Although the steel plate 120 in which a plating layer is further provided on the surface layer can be employed, the type of the plating layer applied at this time is not limited at all. For example, as a kind of plating layer, Zn type (Zn, Zn-Fe, Zn-Ni, Zn-Al, Zn-Al-Mg, Zn-Al-Mg-Si, etc.), Al type (Al-Si, etc.) Any plating layer such as Sn-based (Sn—Zn or the like) may be used. Also, the basis weight of these plating layers is not particularly limited, but the basis weight on both sides is preferably 100 [g / m ² ] or less. If the amount of plating exceeds 100 [g / m ² ] per side, the plating layer may become an obstacle during welding. In addition, you may employ | adopt the steel plate 120 in which the plating layer is not provided in the surface layer.
(Thickness)
The thickness t ₂ (before welding) of the steel plate is not particularly limited, and for example, a thickness of about 0.50 [mm] to 2.3 [mm] generally used in an automobile body or the like. The used steel plate can be employed without any limitation. If the thickness t _{2 of the} steel sheet is less than 0.5 [mm], the strength and rigidity necessary for the structural member and the structural material cannot be ensured. On the other hand, since other joining processes can be applied to the steel sheet having a thickness t ₂ exceeding 2.3 [mm], the necessity of using resistance spot welding is low.

<Electrode>
(Thermal conductivity of the aluminum alloy plate side electrode)
The thermal conductivity λ ₁ of the aluminum alloy plate side electrode 210 is set to 130 [W / (m · K)] or more and 240 [W / (m · K)] or less.
When the thermal conductivity λ ₁ of the aluminum alloy plate-side electrode 210 is less than 130 [W / (m · K)], welding is significantly generated between the aluminum alloy plate-side electrode 210 and the aluminum alloy plate 110, and welding is performed. May become unstable. On the other hand, when the thermal conductivity λ ₁ of the aluminum alloy plate-side electrode 210 exceeds 240 [W / (m · K)], the cooling effect of the aluminum alloy plate 110 by the aluminum alloy plate-side electrode 210 increases, so that a desired value is obtained. It is difficult to secure the plug diameter, and the shape of the welded joint may not be stable. As a result, the form of plug rupture becomes unstable.

In order to obtain the aluminum alloy plate side electrode 210 having the thermal conductivity λ ₁ in such a range, the aluminum alloy plate side electrode 210 is made of, for example, Cu-70W (Cu: 30 [mass] as a material for electrical contacts. %], W: 70 [mass%]). However, the material of the aluminum alloy plate side electrode 210 is not limited to Cu-70W as long as the thermal conductivity λ ₁ is in the above-described range.
Here, the measurement of the thermal conductivity λ ₁ of the aluminum alloy plate-side electrode 210 is performed, for example, by the temperature gradient method described in Non-Patent Documents 1 and 2 or the laser flash method described in Non-Patent Document 2. It can be carried out by a known method such as a hot wire method. Therefore, detailed description thereof is omitted here.

(Thermal conductivity of steel plate side electrode)
The thermal conductivity λ ₂ of the steel plate side electrode 220 is set to 300 [W / (m · K)] or more.
When the thermal conductivity λ ₂ of the steel plate side electrode 220 is less than 300 [W / (m · K)], the temperature rise on the steel plate 120 side becomes significant in the welded joint 100, and thereby the aluminum alloy pressed by the electrode The shape of the welded joint becomes unstable, for example, the reduction in the plate thickness of the plate 110 increases. As a result, the joint strength decreases.
In order to obtain the steel plate side electrode 220 having the thermal conductivity λ ₂ in such a range, the steel plate side electrode 220 may be a copper alloy (for example, Cr alloy described in JIS Z 3234 (copper alloy electrode material for resistance welding)). -Cu (chromium copper) or alumina-dispersed copper) can be employed. However, the material of the steel plate side electrode 220 is not limited to Cr—Cu or alumina-dispersed copper as long as the thermal conductivity λ ₂ is in the above-described range.

(Shape of electrode tip)
FIG. 2 is a diagram illustrating an example of the shape of an electrode. Specifically, FIG. 2 (a) is a diagram showing a DR electrode defined in JIS C 9304 (1999), and FIG. 2 (b) is an R defined in JIS C 9304 (1999). It is a figure which shows a shape electrode.
R-shaped electrode shown in FIG. 2 (b), becomes constant without radius of curvature changes in the tip (see the radius of curvature R ₂ of FIG. 2 (b)), and the electrode outer diameter D and the tip diameter W same It becomes. On the other hand, in the DR-type electrode shown in FIG. 2A, the radius of curvature at the tip changes in two stages (see the curvature radii R ₁ and R ₃ in FIG. 2A), and the electrode outer diameter D and tip diameter. W is different. The radius of curvature R ₁ at the tip of the DR electrode refers to the radius of curvature closer to the tip of these two stages of radii of curvature. As shown in FIG. 2A, the curvature radius R ₁ on the distal end side is larger than the curvature radius R ₃ on the proximal end side.

As the aluminum alloy plate side electrode 210 and the steel plate side electrode 220, either a DR-type electrode or an R-type electrode may be adopted. Moreover, you may employ | adopt the electrode of the other shape employ | adopted by resistance spot welding as the aluminum alloy plate side electrode 210 and the steel plate side electrode 220. FIG.
Moreover, the curvature radius of the tip of the aluminum alloy plate side electrode 210 and the steel plate side electrode 220 is not particularly limited, but the curvature radius of the tip of the steel plate side electrode 220 should be 40 [mm] or more and 150 [mm] or less. Is preferred. When the curvature radius of the tip of the steel plate side electrode 220 is less than 40 [mm], the contact range of the steel plate side electrode 220 in the steel plate 120 becomes narrow and local heat generation is likely to occur. If it does so, the welding between the steel plate side electrode 220 and the steel plate 120 will become remarkable. On the other hand, when the radius of curvature of the tip of the steel plate side electrode 220 exceeds 150 [mm], the contact range of the steel plate side electrode 220 with the steel plate 120 becomes wide, so that the welding current necessary for resistance heating becomes excessive. If so, scattering occurs frequently.

  The radius of curvature of the tip of the aluminum alloy plate side electrode 210 is the same as the radius of curvature of the tip of the steel plate side electrode 220 (the radius of curvature of the tip of the aluminum alloy plate side electrode 210: the radius of curvature of the tip of the steel plate side electrode 220 = 1). : 1). In this way, the tool tip shape of the electrode tip dresser for the aluminum alloy plate side electrode 210 and the tool tip shape of the electrode tip dresser for the steel plate side electrode 220 can be made the same.

<Welding power source 230>
The welding power source 230 that supplies current to the aluminum alloy plate side electrode 210 and the steel plate side electrode 220 may be either an AC power source or a DC power source. For example, as the welding power source 230, an inverter type DC power source, an inverter type AC power source, a single phase AC power source, or the like can be employed.
<Pressure force>
As for the pressing force, an appropriate condition setting can be selected depending on the plate thickness of the aluminum alloy plate 110 and the steel plate 120 and the shape of the aluminum alloy plate side electrode 210 and the steel plate side electrode 220, but 1.98 [kN] or more. 0 [kN] or less is preferable.
When the applied pressure is less than 1.98 [kN], the contact range of the electrode in the material to be welded becomes small and local heat generation is likely to occur, so that the welding between the electrode and the material to be welded becomes remarkable. On the other hand, if the applied pressure exceeds 5.0 [kN], the amount of pressing of the electrode in the contact range with the material to be welded increases, and the remaining thickness of the welded portion decreases, so the aluminum alloy in the welded portion of the welded joint The thickness of the plate becomes too thin and the joint strength decreases. The applied pressure is a force applied between a pair of the aluminum plate side electrode 210 and the steel plate side electrode 220 facing each other when the welding current described later is passed. (Refer to the arrow line shown in FIG. 1).

<Energization time>
About energization time, although an appropriate condition setting can be selected by the plate | board thickness of the aluminum alloy plate 110 and the steel plate 120, 100 [ms] or more and 300 [ms] or less are preferable.
When the energization time is less than 100 [ms], the pressed aluminum region cannot be heated at the interface between the aluminum alloy plate 110 and the steel plate 120. On the other hand, when the energization time exceeds 300 [ms], the thickness of the aluminum alloy plate at the welded portion of the welded joint becomes too thin, and the joint surface between the steel plate and the aluminum alloy plate cannot be formed sufficiently. The energization time refers to energization between the aluminum plate side electrode 210 and the steel plate side electrode 220 in a state where the aluminum plate side electrode 210 is in contact with the aluminum plate 110 and the steel plate side electrode 220 is in contact with the steel plate 120. It is time to do.

<Welding current>
About welding current, appropriate condition setting can be selected with the plate | board thickness of the aluminum alloy plate 110 and the steel plate 120, energization time, and applied pressure. The welding current is a current that flows in a closed circuit including the welding power source 230, the aluminum plate side electrode 210, the aluminum plate 110, the steel plate 120, and the steel plate side electrode 220. That is, the welding current is a current that flows between the aluminum plate side electrode 210 and the steel plate side electrode 220 in a state where the aluminum plate side electrode 210 is in contact with the aluminum plate 110 and the steel plate side electrode 220 is in contact with the steel plate 120. It is.

<Summary>
As described above, in the present embodiment, the thermal conductivity λ ₁ of the aluminum alloy plate-side electrode 210 is 130 [W / (m · K)] or more and 240 [W / (m · K)] or less, and the steel plate side The thermal conductivity λ ₂ of the electrode 220 was set to 300 [W / (m · K)] or more. Therefore, by adopting an electrode with such a thermal conductivity, the cross tensile strength (CTS) of the welded joint is stabilized at a large value without introducing a special device or the like (the value varies greatly depending on the welded joint). In addition, a plug fracture can be stably obtained as a fracture form of the weld joint. Therefore, it is possible to form a highly reliable welded joint excellent in joint strength of the welded portion while ensuring good workability when joining the steel plate and the aluminum alloy plate by resistance spot welding. Thereby, for example, in the automotive field, the entire vehicle body can be obtained by applying the method described in the present embodiment to processes such as manufacturing of automobile parts reduced in weight by application of a partial aluminum alloy plate and assembly of the vehicle body. Benefits such as lower fuel consumption and reduced carbon dioxide (CO ₂ ) emissions can be fully enjoyed, and its social contribution is immeasurable.

  It should be noted that the embodiments of the present invention described above are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. Is. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

  Next, examples (invention examples and comparative examples) are shown. In addition, this invention is not limited to the Example shown below.

In each of Examples 1 to 12, resistance spot welding was performed under the following conditions to produce a welded joint (cross tensile test piece), and the cross tensile strength (CTS) of each welded joint was measured. The cross tension test piece is a test piece specified in JIS Z 3137 (1999), and the cross tension test was performed in accordance with JIS Z 3137 (1999).
Aluminum alloy plate-side electrode: R-shaped electrode as defined in JIS C 9304 (1999) (curvature radius of tip = 80 [mm])
Steel plate side electrode: R-shaped electrode specified in JIS C 9304 (1999) (curvature radius of tip = 80 [mm])
Aluminum alloy plate: A6022 (6000 series aluminum alloy) (plate thickness = 1.2 [mm])
Steel plate: Hot dip galvannealed (GA) steel plate (270 MPa class) (plate thickness = 1.4 [mm])
Energizing time: 200 [ms]
Welding power source: Inverter type DC power source For the welding current, a welding current having a pitch of 0.3 [kA] was increased, and a cross tension test piece was produced at each welding current. In Table 2, the minimum value among the welding currents that flowed when producing the cross tensile test piece in which the plug was formed in the cross tensile test is shown as the minimum value of the welding current. On the other hand, in Table 2, the welding current flowed when a cross tensile test piece having a plug formed in the cross tensile test was produced, and the smallest among the welding currents in which scattering was observed during resistance spot welding. Is shown as the maximum value of the welding current.

In Examples ₁ and 4 to 9, resistance spot welding was performed by changing the material (thermal conductivity λ ₁ ) of the aluminum alloy side electrode.
In Examples 1 to 3, resistance spot welding was performed with different applied pressures.
In Examples 10, 11, and 12, resistance spot welding was performed by changing the material (thermal conductivity) λ ₁ ) of the steel plate side electrode from that in Examples 1, 2, and 3, respectively.

Examples 1 to 7 are examples of the present invention, and the form of fracture after the cross tension test is a stable plug fracture in all ranges from the minimum value to the maximum value of the welding current, and the cross tensile strength (CTS) is It was 0.8 [kN] or more that can be regarded as a practically sufficient strength.
On the other hand, in Example 8, the thermal conductivity λ ₁ of the aluminum alloy side electrode is lower than 130 [W / (m · K)]. For this reason, when the welding current was the maximum value, the aluminum alloy side electrode was welded to the aluminum alloy plate, and a welded joint could not be produced ("electrode welding" in the column of the minimum value of the plug diameter number 8). , See “-” in the CTS minimum value column). Moreover, the maximum value of the cross tensile strength (CTS) was less than 0.8 [kN].

In Example 9, the thermal conductivity λ ₁ of the aluminum alloy side electrode exceeds 240 [W / (m · K)]. For this reason, the minimum value of the cross tensile strength (CTS) was less than 0.8 [kN] (see the column of the minimum value of CTS number 9). Further, when the welding current was increased, unstable plug fracture occurred (the plug was not obtained), and the plug diameter could not be measured ("-" in the column of maximum plug diameter No. 9). (See the “Unstable plug rupture” column in the Maximum column). For this reason, the maximum value of the welding current could not be specified (see “−” in the column of the maximum value of the welding current No. 9).

Moreover, in Examples 10-12, the heat conductivity (lambda) ₂ of a steel plate side electrode is less than 300 [W / (m * K)]. For this reason, the minimum value of the cross tensile strength (CTS) was less than 0.8 [kN] (see the column of the maximum value of CTS Nos. 10 to 12).

  110: Aluminum alloy, 120: Steel plate, 210: Aluminum alloy plate side electrode, 220: Steel plate side electrode, 230: Welding power source

Claims (1)

With the aluminum alloy plate and the steel plate directly superimposed, the aluminum alloy plate side electrode is brought into contact with the aluminum alloy plate and the steel plate side electrode is brought into contact with the steel plate, and the aluminum alloy plate side electrode and the steel plate side electrode are brought into contact with each other. A spot welded joint manufacturing method for manufacturing a spot welded joint by performing a resistance spot welding by applying a welding current while applying a pressure between
The aluminum alloy plate side electrode has a thermal conductivity of 130 [W / (m · K)] or more and 240 [W / (m · K)] or less,
The method of manufacturing a spot-welded joint, wherein the steel plate-side electrode has a thermal conductivity of 300 [W / (m · K)] or more.

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