JP2012152789A - Method for joining dissimilar metal plates by overlapping and electric resistance brazing, and brazing joint formed by the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overlapping and electric resistance brazing method of dissimilar metal plates, especially of a steel plate with an aluminium alloy plate, the method providing a connection having high joint strength without impairing reliability of joining by production of a brittle intermetallic compound layer.SOLUTION: In the method for joining the dissimilar metal plates by overlapping and electric resistance brazing, a foil-like flux-cored brazing filler metal formed by dispersively mixing a fluoride-based flux into an aluminum alloy brazing filler metal containing Si is arranged between the steel plate 1 and the aluminium alloy plate 2, and current conduction is performed by an electrode for spot welding in order to weld the flux-cored brazing filler metal. Thereby, joining is performed.

Description

  The present invention relates to a method for joining dissimilar metal plates by overlapping electric resistance brazing and a brazed joint thereby.

In recent years, there has been a demand for weight reduction of the body of a transport aircraft such as an automobile for the purpose of reducing fuel consumption and reducing CO ₂ emissions. For this reason, the application of aluminum alloy plates that are lighter in weight and superior in energy absorption is increasing in place of steel plates that have been used in the past, particularly for automobile bodies. The aluminum alloy plate referred to here is a generic term for plate-shaped aluminum alloy materials such as aluminum alloy rolled plate materials, extruded materials, and forged materials.

  For example, panels such as outer panels (outer plates) and inner panels (inner plates) of panel structures such as automobile hoods, fenders, doors, roofs, trunk lids, etc., are made of Al-Mg-Si AA (American Aluminum Association). Standard) to JIS6000 series (hereinafter simply referred to as 6000 series) and Al-Mg based AA to JIS5000 series (hereinafter simply referred to as 5000 series) are being used.

  Unless these aluminum alloy plates are all-aluminum automobile bodies, they are inevitably used in a normal automobile body by being joined to a steel plate that has been generally used. Therefore, inevitably, joining of dissimilar metal plates of a steel plate and an aluminum alloy plate (Fe—Al dissimilar material joining) is required.

  However, as a problem when joining this Fe—Al dissimilar material joint by welding, it is due to the formation of an intermetallic compound layer (hereinafter also referred to as a reaction layer) of Fe and Al having high hardness and very brittle at the joint interface. A decrease in bonding strength can be mentioned. In the welding of Fe-Al dissimilar materials by welding, even if the steel plate and the aluminum alloy plate are apparently joined to each other, sufficient bond strength may not be obtained due to the formation of this intermetallic compound layer. Many.

Conventionally, as a method for joining different kinds of metals, mechanical joining methods such as screws, bolts and fitting, solid phase joining methods such as explosive bonding, hot rolling and friction rolling, and further by bonding A method is being considered.
However, mechanical bonding or bonding by bonding has problems in reliability, airtightness, bonding workability, and the like.
In addition, the solid-phase bonding method has a problem in that the shape of the bonding material is largely restricted and the bonding workability is low.

  For this reason, development of a simpler and more workable joining method for dissimilar metals is expected. In particular, the joining of an aluminum alloy plate and a steel plate is an indispensable technique for reducing the weight of automobiles, and therefore, establishment of a joining method using simple and efficient resistance welding is awaited.

  Hereinafter, the current state and problems of electric resistance welding of dissimilar metals will be described by taking up spot welding of an aluminum alloy plate and a steel plate, which are attracting attention from the viewpoint of reducing the weight of the vehicle body.

  In spot welding of an aluminum alloy plate and a steel plate, there is a problem that physical property values such as melting point, electrical resistance, and thermal conductivity are greatly different. For example, when an aluminum alloy plate and a thin steel plate are overlapped and simply subjected to electric resistance welding, the melting point of the aluminum alloy is ½ or less of the melting point of the steel, and the aluminum alloy has a higher thermal conductivity. Since it is large, heat generated by resistance welding is conducted from the steel plate side to the aluminum alloy plate side, and unilateral melting of the aluminum alloy plate occurs. Therefore, damage due to welding of the plate surface on the aluminum alloy plate side becomes large. Further, in such a process, an intermetallic compound is formed at the bonding interface, and nuggets are also formed unevenly. Therefore, good joint strength cannot be obtained.

  In recent years, various bonding methods have been disclosed for such problems.

  In Patent Document 1, a two-layer clad material made of steel and an aluminum alloy is inserted as an insert material between a steel plate and an aluminum alloy plate, and the steel and the steel plate in the two-layer clad material are aluminum in the two-layer clad material. A method is disclosed in which an alloy and an aluminum alloy plate are arranged facing each other and overlapped to perform electrical resistance welding (spot welding).

  Further, Patent Document 2 discloses that an oxide film on the surface of an aluminum alloy plate is obtained by interposing a fluoride-based flux in a bonded portion between a steel plate and an aluminum alloy plate, and heating and pressing the bonded portion by spot welding or the like. A method of welding while dissolving and removing is disclosed.

Further, in Patent Document 3, in a method of joining a steel plate and an aluminum alloy plate by spot welding, a Cu alloy layer is disposed on the surface to be joined on the steel plate side, and a fluoride system is provided on the surface to be joined on the aluminum alloy plate side. A spot welding joining method between a steel plate and an aluminum alloy plate characterized by applying a flux and joining is disclosed.
In this joining method, the oxide film on the surface of the aluminum alloy plate is melted by the melted fluoride-based flux, and the melt is pushed out to the edge of the joined portion, thereby causing an oxidation that causes electric current variation during welding. The coating is removed from the surface of the aluminum alloy plate, and the steel plate and the aluminum alloy plate are joined using a molten Cu alloy as a brazing material.

  In recent years, a non-corrosive flux method (see Non-Patent Documents 1 to 3) in which the flux residue after brazing does not exhibit corrosiveness is also attracting attention as a brazing method for aluminum alloys.

Japanese Patent Laid-Open No. 4-55066 JP 2003-48077 A JP 2004-351507 A

W.E.Cooke, T.E.Wright and I.A.Hirshfield: Furnace Brazing of Aluminum with a Non-Corrosive Flux, Weld.J., 57 (1978), No. 12, 23. D.G.W.Claydon and A. Sugihara: Brazing Aluminum Automotive Heat Exchanger Assemblies Using a Non-Corrosive Flux Process.SAE International Congress Technical Paper Series, 831121. (1983). N.I.Stward: Mechanistic Aspects of the NOCOLOCK Flux Brazing Process Furnace Brazing Aluminum with a Non-Corrosive Flux.SAE International Congress Technical Paper Series, 870186 (1987).

  However, in the method of spot welding using the two-layer clad material as in Patent Document 1, it is necessary to insert the clad material between the iron-based material and the aluminum-based material and temporarily fix it, so that the joining work is complicated. At the same time, the reliability of the jointed joint is lowered due to misalignment of the two-layer clad material. In addition, the two-layer clad material used for joining is manufactured by joining an iron-based material and an aluminum-based material, but the two-layer clad material is not easy to manufacture, and an inexpensive and stable performance two-layer clad material is used. It was difficult to obtain.

Moreover, since patent document 2 uses only a fluoride type flux without using a clad material or a brazing material as an insert material, almost no molten metal is generated on the joint surface during welding. Therefore, there is a problem that sufficient bonding strength cannot be obtained.
Further, when flux is coated (applied) on the bonding interface, the electric resistance becomes too high, the current heating becomes unstable, and the reliability of the welded portion is lowered.

  Further, since Patent Document 3 is energized through a fluoride flux layer having a high electrical resistance, scattering tends to occur at the initial stage of welding and welding becomes unstable. In addition, since the melting point of a copper alloy is higher than the melting point of an aluminum-based material, a complex of aluminum and copper or copper and iron is present at the interface between the aluminum alloy plate and the steel plate when the copper alloy is melted. An intermetallic compound is formed. As a result, there was a problem that the joint strength was not stable.

  Therefore, the present invention has been made in view of the above circumstances, has few restrictions such as brazing application conditions, is excellent in versatility, and has a reaction layer (between metals) that is fragile to the joint (brazing portion). And a method of superimposing electrical resistance brazing of dissimilar metal plates, particularly a steel plate and an aluminum alloy plate, which can obtain a joint having high joint strength without generating a compound layer) It aims at providing the brazing joint by it.

  The gist of the present invention aimed at solving the above problems is as follows.

[1] An electrode for spot welding is disposed between a steel plate and an aluminum alloy plate by placing a foil-like flux-filled brazing material in which a fluoride-based flux is dispersed and mixed in an aluminum alloy brazing material containing Si. A joining method by overlapping electric resistance brazing of dissimilar metal plates, characterized in that the flux-containing brazing material is melted and joined by energization by means of electrical welding.
[2] The joining method by overlapping electric resistance brazing of dissimilar metal plates according to [1], wherein a thickness of the flux-cored brazing material is 10 to 700 μm.
[3] The content of the fluoride-based flux in the flux-containing brazing material is 5 to 20% with respect to the mass of the flux-containing brazing material, according to [1] or [2] Joining method by overlapping electric resistance brazing of different metal plates.
[4] Any one of [1] to [3], wherein the fluoride flux is a mixed flux of KAlF ₄ , K ₂ AlF ₅ .H ₂ O, K ₃ AlF _6, and AlF _3. The joining method by overlapping electric resistance brazing of the dissimilar metal plates described in the item.
[5] The overlapping electric resistance brazing of dissimilar metal plates according to any one of [1] to [4], wherein the aluminum alloy brazing material has a Si content of 7 to 12% by mass. Joining method.
[6] The adhesive according to any one of [1] to [5], wherein an adhesive is interposed between the steel plate and the aluminum alloy plate so as to surround an outer periphery of the flux-cored brazing material. The joining method by overlapping electric resistance brazing of the dissimilar metal plates described.
[7] The joining method by overlapping electric resistance brazing of dissimilar metal plates according to [6], wherein the thickness of the aluminum alloy brazing material is 50 to 500 μm.
[8] A molten brazing material having a steel plate, an aluminum alloy plate, and a brazing portion formed between the steel plate and the aluminum alloy plate, and the brazing portion joins the steel plate and the aluminum alloy plate. A brazed joint comprising: a portion and an unmelted brazing material portion formed in at least a part of the periphery of the molten brazing material portion and containing a residual flux dispersed therein.
[9] The brazed joint according to [8], wherein an adhesive layer made of an adhesive is formed around the brazed portion.

  According to the present invention, an aluminum alloy brazing material containing Si is used as a brazing material, and the aluminum alloy brazing material is filled with a fluoride-based flux to form a flux-filled brazing material. The steel plate and the aluminum alloy plate are brazed with the molten flux-containing brazing material while the oxide film on the surface of the aluminum alloy plate is removed by the fluoride-based flux in the flux-containing brazing material. It is possible to prevent the formation of a brittle intermetallic compound layer at the joint (brazing portion). As a result, it is possible to prevent a decrease in bonding reliability. That is, it is possible to provide a joining method by overlapping electric resistance brazing of dissimilar metal plates capable of forming a joint having high joint strength.

It is a general | schematic process figure explaining the joining method by the overlap electrical resistance brazing of the dissimilar metal plate which is embodiment of this invention. It is a cross-sectional schematic diagram of the brazed joint which is embodiment of this invention.

  A joining method by overlapping electric resistance brazing of dissimilar metal plates according to an embodiment to which the present invention is applied and a brazed joint by the same will be described, but the present invention is not limited to the following embodiment.

  As shown in FIG. 1, the joining method by overlapping electric resistance brazing of dissimilar metal plates in this embodiment is performed by adding fluoride flux to an aluminum alloy brazing material containing Si between a steel plate 1 and an aluminum alloy plate 2. A foil-like flux-filled brazing material 3 is dispersed and mixed, and the flux-filled brazing material 3 is melted by energizing the electrodes 4a and 4b for spot welding, so that the steel plate 1 and the aluminum alloy plate 2 are melted. And join.

  Hereinafter, each requirement and the reason for each condition of the overlapping electric resistance brazing method for dissimilar metal plates in this embodiment will be described in detail.

  First, the type of the steel sheet 1 used in the joining method in the present embodiment is not particularly limited, and is 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), work-induced transformation type (structure containing residual austenite in ferrite), fine crystal type (ferrite main structure), etc. It may be a steel plate of a mold. Moreover, the plate | board thickness of such a steel plate 1 is not specifically limited, either, The thickness of about 0.50-2.3 mm employ | adopted with a motor vehicle body may be sufficient. Further, the tensile strength is not particularly limited, and may be about 270 to 1470 MPa used in an automobile body.

Moreover, the surface layer of such a steel plate 1 may be plated, and the type of the plating layer is also Zn-based (Zn, Zn—Fe, Zn—Ni, Zn—Al, Zn—Al—Mg, etc.), Al Any system (such as Al—Si) may be used. Further, when plating is performed, the basis weight of the plating layer is not particularly limited, but is preferably 100/100 (g / m ² ) or less on both surfaces of the steel plate.
The types of plating include alloyed hot dip galvanizing (Zn-Fe), hot dip galvanizing (Zn), hot dip zinc alloy plating (Zn-Al-Mg-Si and Zn-Al-Si), and electrogalvanized. Examples thereof include plating (Zn), electrolytic zinc alloy plating (Zn—Ni), and molten aluminum plating (Al—Si).

  The type of the aluminum alloy plate 2 used in the bonding method in the present embodiment is not particularly limited, as in the case of the steel plate 1, and is 5000 (Al-Mg) -based and 6000 (Al-Mg-Si) used in an automobile body. Any standard aluminum alloy plate may be used. Moreover, the plate | board thickness of such an aluminum alloy plate 2 is not specifically limited, either, The thickness of about 0.55-2.0 mm employ | adopted with a motor vehicle body etc. may be sufficient. Further, the tensile strength is not particularly limited, and may be 100 to 400 MPa class used in an automobile body.

Further, the surface layer of the aluminum alloy plate 2 may be plated, and the type of the plating layer may be any of Zn, Zn—Fe, Zn—Ni, Zn—Al, Zn—Al—Mg, etc. Good. Further, when plating is performed, the basis weight of the plating layer is not particularly limited, but is preferably 100/100 (g / m ² ) or less on both surfaces of the aluminum alloy plate.
Further, as the type of plating, like the steel plate 1, electrogalvanizing (Zn) and electrozinc alloy plating (Zn—Ni, Zn—Fe, Zn—Ni, Zn—Al, Zn—Al—Mg, etc.) are mentioned. It is done.

Next, the flux-cored brazing material 3 in this embodiment will be described.
The shape of the flux-cored brazing material 3 used in the present embodiment is a foil, and the thickness d of the flux-cored brazing material 3 is preferably in the range of 10 to 700 μm. Thus, by controlling the thickness d of the flux-cored brazing material 3, a suitable resistance heating value is obtained when the steel sheet 1 and the aluminum alloy plate 2 are joined by energizing and melting the flux-cored brazing material 3. And the amount (melt) of the molten flux-containing brazing filler metal 3 can be stably secured.
If the thickness d is less than 10 μm, the amount of melt generated at the time of brazing is small, so that an unjoined portion is likely to occur between the aluminum alloy plate 2 and the steel plate 1, which is not preferable. Furthermore, the wettability may be reduced. On the other hand, if the thickness d exceeds 700 μm, the amount of resistance heat generated by energization increases, and the heat escape (heat conduction loss) of the resistance heat generation to the electrode decreases, resulting in a large amount of melting on the surface of the steel sheet 1. This is not preferable because the growth of an intermetallic compound of Fe and Al may be promoted.
Moreover, in this embodiment, the magnitude | size of the flux-cored brazing material 3 should just be more than the diameter of the melting part (molten brazing filler metal part 4a: refer FIG. 2) of the flux-cored brazing material 3 formed by electricity supply.

In the present embodiment, when the steel plate 1 and the aluminum alloy plate 2 are joined, when the adhesive is used together with the flux-cored brazing material 3 as described above, the thickness d ′ of the flux-cored brazing material 3 is It is preferable to be in the range of 50 to 500 μm. By controlling the thickness d ′ within such a range, the flux-containing brazing material 3 (unmelted brazing material portion 4b: see FIG. 2) that remains without being melted immediately below the electrode after energization is applied to the adhesive. It can be made to function as an appropriate spacer of the adhesive layer made of, and the adhesive strength can be secured stably. In order to secure the adhesive strength more stably, the thickness d ′ is more preferably in the range of 100 to 300 μm.
If the thickness d ′ is less than 50 μm, the adhesive is pushed out from between the aluminum alloy plate 2 and the steel plate 1 when joining, which is not preferable. On the other hand, if the thickness d ′ is too thick, exceeding 500 μm, the adhesive strength is lowered, which is not preferable.
Detailed description of the adhesive will be described later.

Next, the fluoride flux will be described.
The fluoride flux in this embodiment is dispersed and mixed in an aluminum alloy brazing material containing Si. Further, since this fluoride-based flux is granular and dispersed so as to be distributed substantially uniformly in the aluminum alloy brazing material, the heat generation becomes uniform when the flux-containing brazing material 3 is heated during energization. Moreover, variation in electrical resistance in the flux-filled brazing material 3 can be suppressed, and as a result, excessive Joule heat generation can be suppressed.

In this embodiment, the fluoride flux is preferably a mixed flux of KAlF ₄ , K ₂ AlF ₅ .H ₂ O, K ₃ AlF ₆ , and AlF ₃ . When such a mixed flux is dispersed in the aluminum alloy brazing material, the electric resistance of the flux-filled brazing material 3 during energization can be made suitable, and a Joule heat generation amount can be ensured.
In general, the flux used for removing the oxide film on the surface of the aluminum alloy plate 2 includes chloride + fluoride flux. However, since such a flux is highly corrosive, it is washed and removed after bonding. There is a need. On the other hand, in the fluoride-based flux in the present embodiment, the flux residue after bonding is insoluble in water, so that it is not necessary to remove it by washing.

Moreover, as a mixed flux of this embodiment, the nocolok flux (brand name) by ALCAN can be mentioned, for example. The Nocolok flux has a chemical composition of Al: 16.0 to 19.5%, F: 48 to 54.5%, K: 26.5 to 32.5%, KAlF ₄ , K ₂ AlF ₅ · H ₂ O, K ₃ AlF ₆ , AlF ₃ mixed flux.

Moreover, in this embodiment, it is preferable that content of fluoride type flux shall be 5 to 20% with respect to the total weight of the flux-containing brazing material 3. The ability to remove the oxide on the surface of the aluminum alloy plate 2 can be exhibited by dispersing the fluoride-based flux in such a content range.
More specifically, the fluoride-based flux in the flux-containing brazing material 3 melted during energization removes the oxide formed on the surface of the aluminum alloy plate 2. However, if the content of the fluoride-based flux is too small, the ability of eliminating the oxide on the surface of the aluminum alloy plate 2 is lowered, and the electric resistance of the flux-filled brazing material 3 is lowered, thereby obtaining sufficient Joule heat generation. It is not preferable because it cannot be done. On the other hand, when the content of the fluoride-based flux is too large, a part of the fluoride-based flux remains in the flux-containing brazing material 3 after brazing, which may reduce the joint strength. For this reason, it is preferable to make content of a fluoride type flux into 5 to 20% with respect to the total weight of the brazing filler metal 3 with a flux.

  In the present embodiment, the particle size of the granular fluoride-based flux dispersed in the aluminum alloy brazing material may be smaller than the plate thickness of the flux-containing brazing material 3, but may be 10 to 30 μm in diameter. preferable. By making the particle diameter within such a range, the amount of Joule heat generated during energization can be made suitable.

Next, the aluminum alloy brazing material will be described.
In the present embodiment, the Si content in the aluminum alloy brazing material is preferably 7 to 12% by mass. Thus, the melting point (liquidus temperature) of the aluminum alloy brazing material can be lowered by adding an appropriate amount of Si. That is, since the aluminum alloy brazing material can be melted at a temperature lower than the melting point of the steel plate 1 and the aluminum alloy plate 2, brazing can be performed at a lower temperature. As a result, the diffusion rate of aluminum (Al) into the steel plate 1 or iron (Fe) into the aluminum alloy plate 2 can be reduced.
If the content of Si in the aluminum alloy brazing material is too small, the effect of lowering the melting point of the aluminum alloy brazing material is not sufficiently exhibited, so that the steel plate 1 and the aluminum alloy plate as the materials to be joined are excessively melted. This is not preferable because of fear. On the other hand, if the Si content is too large, the composition of the aluminum alloy brazing material becomes an Ai-Si hypereutectoid composition, which is not preferable because it cannot be applied as a brazing material.
In the present embodiment, the melting point of the aluminum alloy brazing material is preferably 580 to 620 ° C.

Here, it is a manufacturing method of the flux-cored brazing material 3 in the present embodiment. For example, the fluoride-based flux according to the present embodiment is substantially uniform in an aluminum alloy having the alloy composition of the aluminum alloy brazing material as described above. The aluminum alloy lump kneaded so as to be distributed in the above can be produced by warm rolling so as to have the thickness of the flux-containing brazing material 3 as described above.
In addition, the manufacturing method of the flux-filled brazing material 3 in this embodiment is not limited to this.

Moreover, in this embodiment, when joining the steel plate 1 and the aluminum alloy plate 2, an adhesive agent surrounds the outer periphery of the flux-cored brazing material 3 as described above between the steel plate 1 and the aluminum alloy plate 2. It is preferable to sandwich and join.
In the present embodiment, the flux-cored brazing material 3 other than the flux-cored brazing material 3 corresponding to directly under the electrode remains without melting. For this reason, the remaining unmelted flux-cored brazing material 3 (see FIG. 2) serves as an appropriate spacer for the adhesive layer formed by the adhesive. Therefore, in this embodiment, the adhesive is used in combination with the steel plate 1 and aluminum. When joining with the alloy plate 2, adhesive strength can be ensured and joining strength can be raised more.
Note that, as described above, if the flux-filled brazing material 3 is too thin, the unmelted flux-filled brazing material that functions as a spacer also becomes thin. Therefore, when performing joint using an adhesive, the adhesive is aluminum. It will be extruded from between the alloy plate 2 and the steel plate 1. On the other hand, if the flux-filled brazing material 3 is too thick, the unmelted flux-filled brazing material that functions as a spacer also becomes thick, so that the adhesive strength by the adhesive decreases. For this reason, in order to ensure adhesive strength stably, it is more preferable that the thickness d ′ of the flux-cored brazing material 3 is 100 to 300 μm.
In addition, although it does not specifically limit as an adhesive agent, For example, an epoxy-type 1 liquid heat-curing adhesive and a 2 liquid room temperature effect type adhesive can be used.

Further, the joining method by brazing according to the present embodiment is not limited to the two-layer stack of the steel plate 1 and the aluminum alloy plate 2, and may be three or more stacks. In addition, each steel plate and aluminum alloy plate in that case may be different thickness and different materials.
For example, as a combination of plates in the case of three-layer joining, there is a combination in which another steel plate (intermediate steel plate) is inserted between a steel plate (outermost steel plate) and an aluminum alloy plate (outermost aluminum alloy plate). Can be mentioned. In this case, the bonding interface is formed between the outermost steel plate and the intermediate steel plate and between the intermediate steel plate and the outermost aluminum alloy plate.
In the case of such three-layer joining, the flux-cored brazing material 3 according to the present embodiment is sandwiched only between the outermost aluminum alloy plate and the intermediate steel plate, and the intermediate steel plate and the outermost steel plate are directly stacked. . In this state, the intermediate steel plate and the outermost layer aluminum alloy plate are brazed when sandwiched between the electrodes, applied with pressure, and energized and heated, but the intermediate steel plate and the outermost layer steel plate are subjected to normal resistance spot welding. It will be. However, even in such a case, the effects of the present embodiment can be sufficiently exhibited, and sufficient joint strength between the steel plate and the aluminum alloy plate can be obtained.

A steel plate 1, an aluminum alloy plate 2 and a flux-cored brazing material 3 as described above are prepared, energized with an electrode for spot welding, and joined by performing electrical resistance brazing. The joining conditions at this time are not particularly limited. For example, the welding current may be 5 to 20 kA, the applied pressure may be 1 to 5 kN, and the joining time may be in the range of 0.1 to 1 s.
In the present embodiment, as the spot welder, for example, a single-phase AC spot welder, an inverter AC spot welder, an inverter DC spot welder, or the like can be used.
Further, as in the present embodiment, by using the above-described materials and performing electric resistance brazing, it is not necessary to strictly control the melting temperature of the brazing material, and the soldering will be more easily and stably performed. Only the material can be melted, and the steel plate 1 and the aluminum alloy plate 2 can be brazed. That is, since excessive melting of the steel plate 1 and the aluminum alloy plate 2 can be prevented, generation of intermetallic compounds can be suppressed, and as a result, joint strength can be improved.

  Next, the brazed joint 10 according to this embodiment formed by the joining method by brazing as described above will be described with reference to FIG.

  As shown in FIG. 2, the brazed joint 10 in the present embodiment includes a steel plate 1, an aluminum alloy plate 2, and a brazed portion 4 formed between the steel plate 1 and the aluminum alloy plate 2. The non-molten brazing material is formed by attaching the brazing portion 4a to the molten brazing material portion 4a for joining the steel plate 1 and the aluminum alloy plate 2 and at least part of the periphery of the molten brazing material portion 4a and containing the residual flux. Part 4b.

In the brazed joint 10 of the present embodiment, the flux-filled brazing material other than the molten brazing material portion 4a directly under the electrode remains without melting. That is, the unmelted brazing filler metal portion 4b remains at least at a part around the molten brazing filler metal portion 4a.
The unmelted brazing filler metal portion 4b contains a residual flux in a dispersed manner. Residual flux is affected by the energization of the brazing filler metal used as the brazing material, which is not affected by energization. However, it is a general term for those that have been modified without melting.

In the present embodiment, an adhesive layer made of an adhesive may be formed around the brazing part 4. In this case, the unmelted brazing filler metal part 4b functions as an appropriate spacer of the adhesive layer, and can secure adhesive strength.
Moreover, it is preferable that the thickness of the unmelted brazing filler metal part 4b at this time is 50 to 500 μm. By setting the unmelted brazing filler metal portion 4b within such a thickness range, the adhesive strength can be stably secured.

  According to the joining method by overlapping electric resistance brazing of dissimilar metal plates according to the present invention as described above, an aluminum alloy brazing material is used as the brazing material, and a granular fluoride system is used in the aluminum alloy brazing material. Since the flux is filled, an excessive increase in the electrical resistance of the aluminum alloy brazing material can be suppressed as compared with the case where an aluminum alloy brazing material coated with the flux is used as the brazing material. Thereby, it can prevent that a weak reaction layer (intermetallic compound layer) produces | generates in the brazing part between dissimilar metal plates. As a result, it is possible to prevent a decrease in bonding reliability. That is, the joining method which can form the junction part which has high joint strength can be provided.

  Further, as the brazing filler metal according to the present invention, by using a flux-cored brazing material in which a granular fluoride flux is filled so as to be distributed almost uniformly in the aluminum alloy brazing filler metal, the electric power in the flux-cored brazing material is used. The variation in resistance can be controlled, and as a result, the amount of Joule heat generated by the flux-containing brazing material can be suitably set. Thereby, a good joint strength can be secured.

  Moreover, since what contains Si is used as the aluminum alloy brazing material according to the present invention, the melting point of the aluminum alloy brazing material can be lowered. That is, since the aluminum alloy brazing material can be melted at a temperature lower than the melting point of the steel plate and the aluminum alloy plate, brazing can be performed at a lower temperature. As a result, the diffusion rate of Fe into the steel sheet or the aluminum alloy sheet can be reduced. Thereby, it is possible to suppress the production | generation and growth of an intermetallic compound.

Further, according to the joining method of the different metal plates according to the present invention by the overlapping electric resistance brazing, the fluoride flux melted at the time of brazing dissolves the oxide film formed on the surface of the aluminum alloy plate, and generates Joule heat. As a result, the aluminum alloy in the brazing filler metal melted on the surface of the aluminum alloy plate can realize a strong fusion welding state.
In addition, the fluoride-based flux melted at the time of brazing simultaneously activates the oxide film on the surface of the steel sheet or the galvanized layer when galvanized, and the aluminum alloy in the brazing material melted by Joule heat generation. Can be wetted on the surface of the steel plate, and can achieve the joining by brazing the steel plate and the aluminum alloy plate.

Moreover, in the joining method by overlapping electric resistance brazing of dissimilar metal plates according to the present invention, it is possible to further increase the joining strength and the joining rigidity between the aluminum alloy plate and the steel plate by using the adhesive bonding together. .
Also, in dissimilar metal joining such as aluminum alloy plate and steel plate, electrolytic corrosion and crevice corrosion occur at the place where contact between dissimilar metals occurs, and the corrosion resistance is inferior than when joining the same metal. Have the problem of end. However, dissimilar metals can be electrically insulated by applying and bonding an adhesive so as to surround the outer periphery of the brazing material as in the present invention. As a result, the occurrence of electrolytic corrosion and crevice corrosion can be prevented, and deterioration of the bonding strength can be suppressed.

In the brazed joint according to the present invention, when an adhesive layer made of an adhesive is formed around the brazed portion, the unmelted brazing filler metal portion functions as an appropriate spacer for the adhesive layer. The adhesive strength of the attached joint can be secured.
Further, by setting the unmelted brazing filler metal portion at this time to a suitable thickness, the adhesive strength can be secured stably. As a result, the joint strength and joint rigidity of the joint can be further increased.

  Examples The effects of the present invention will be described below with reference to examples, but the present invention is not limited to the conditions used in the following examples.

First, various steel plates and aluminum alloy plates conforming to the standards as shown in Table 1 were prepared, some of the steel plates were plated, and the basis weight per side was the amount shown in Table 1. Moreover, the plate | board thickness of a steel plate and an aluminum alloy plate is as showing in Table 1.
In addition, the steel plate of Table 1 is described based on Japan Iron and Steel Federation standard JFSA2001 (cold rolled steel plate) and JFSA3011 (plated steel plate).

Next, 30 mm × 50 mm plate pieces were cut out from the steel plates and aluminum alloy plates shown in Table 1 to prepare test pieces.
Next, the test pieces were overlapped with a combination of test pieces (plate assembly) as shown in Table 2, and at this time, a flux-containing brazing material was inserted between the test pieces. For test number 22, a flux-containing brazing material was inserted between the plate type A1 and the plate type S6.
The flux-containing brazing material used in this example will be described. First, an aluminum alloy lump flux-filled brazing material is prepared in which a nocollock flux (manufactured by ALCAN) is distributed almost uniformly in an aluminum alloy brazing material, which is a chemical component defined in JIS Z 3263. did. Table 2 shows the type of aluminum alloy brazing material and the content (wt%) of the nocolok flux.
Next, the brazing material of such an aluminum alloy lump was warm-rolled so as to have a foil thickness as shown in Table 2 to obtain a foil-like brazing material. In the present example, the size of the flux-cored brazing material was 20 mm in diameter.

Next, the flux-cored brazing material was inserted between the test pieces and the test pieces were overlapped, and the test piece was joined at the center. The joining conditions at this time are as shown in Table 2.
In the present embodiment, a single-phase AC spot welder is used for energization heating, and the electrode is a DR type having a diameter of 16 mm, a tip diameter of 6 mm, and a tip R of 40 mm (JIS C 9304) chromium copper (JIS Z 3234). The thing of was used.

In addition, about the test numbers 5-7, the adhesive agent was apply | coated between the test pieces previously, and the brazing material containing a flux was inserted after that, and it joined. As the adhesive, a one-component heat curing type EW2020 (manufactured by Sumitomo 3M Co., Ltd.) mainly composed of an epoxy resin was used, and the coating amounts were 100, 300, and 500 μm in terms of coating thicknesses in test numbers 5 to 7, respectively. did.
The brazed joint was created as described above.
Hereinafter, a method for evaluating the bonding strength (peeling strength) of the brazed joint will be described.

  As a method for evaluating the peel strength of the brazed joint, ten peel test specimens were prepared for each brazed joint of each test number based on JIS Z 3144, and a peel test was performed. In addition, about the test numbers 5-7, the influence on the peeling strength of an adhesive agent was considered and the peel test was done before the adhesive agent hardened | cured. Table 2 shows the evaluation results of peel strength obtained by the peel test.

  As for the inventive examples to which the present invention was applied, the peel strength was good in any brazed joint. Moreover, also in the test number 22 which is a three-layer brazed joint, the peel strength did not decrease and good strength could be obtained.

  For test number 1, the peel strength deteriorated because the steel plate and the aluminum alloy plate were joined with each other without inserting a brazing filler metal between the plates. This is probably because a brittle intermetallic compound layer was formed at the joint.

  For test No. 3, the flux-cored brazing material was inserted and joined, but the flux-filled brazing material was too thin, so that it was not possible to secure a sufficient amount of flux-filled brazing material, and the joint interface was wet. It is considered that the peel strength was lowered as a result.

  On the other hand, for test number 8, since the flux-filled brazing material was too thick, the resistance heating value increased, the amount of melting on the steel sheet surface increased, and the growth of the intermetallic compound of Fe and Al was promoted. As a result, it is considered that the peel strength has decreased.

  For Test No. 9, pure aluminum of Alloy No. 1050 was used as the main component of the flux-cored brazing material, so that an intermetallic compound of Fe and Al was produced excessively, resulting in a decrease in peel strength. It is thought.

  For test No. 12, the content of Nocolok flux in the flux-cored brazing material was too small, so that the ability to eliminate oxides on the aluminum alloy sheet surface was lost, and the electric resistance of the flux-cored brazing material was reduced sufficiently. It was considered that since the Joule heat generation could not be obtained, the wettability of the bonding interface was lowered, and as a result, the peel strength was lowered.

  On the other hand, for test number 15, since the content of the nocollock flux in the flux-filled brazing material was too much, the nocolok flux remained in the brazing material after joining, resulting in a decrease in peel strength. It is thought.

  For test number 23, only the aluminum alloy brazing material containing no nocollock flux was inserted and joined between the plates as the brazing material, so that the ability to eliminate oxides on the surface of the aluminum alloy plate by the nocolok flux was not exhibited. In addition, the electrical resistance was lowered and sufficient Joule heat generation could not be obtained. For this reason, it is considered that the wettability of the bonding interface is greatly lowered, and as a result, the peel strength is lowered.

  Note that almost the same results were obtained in tests of various steel types and different plate thicknesses, and the effects of the present invention were the same in experiments in which the plating type, basis weight, etc. were changed. It was.

DESCRIPTION OF SYMBOLS 1 ... Steel plate 2 ... Aluminum alloy plate 3 ... Brazing filler metal 4 ... Brazing part 4a ... Melt brazing part 4b ... Unmelted brazing part 5a, 5b ... Electrode 10 ... Brazed joint

Claims (9)

  Between the steel plate and the aluminum alloy plate, a foil-type flux-filled brazing material in which a fluoride-based flux is dispersed and mixed in an aluminum alloy brazing material containing Si is arranged and energized by an electrode for spot welding. And joining the different brazing metal plates by electrical resistance brazing.   The method for joining by dissimilar metal plate overlapping electric resistance brazing according to claim 1, wherein a thickness of the flux-cored brazing material is 10 to 700 μm.   The dissimilar metal according to claim 1 or 2, wherein a content of the fluoride-based flux in the flux-cored brazing material is 5 to 20% with respect to a weight of the flux-cored brazing material. Bonding method by overlapping electric resistance brazing of plates. The fluoride-based _{flux, KAlF 4, K 2 AlF 5} · H 2 O, according to any one of claims 1 to 3, characterized in that a flux mixture of K 3 AlF ₆ and AlF ₃ Joining method by overlapping electric resistance brazing of different metal plates.   The Si content of the aluminum alloy brazing material is 7 to 12 mass%, and the joining method by overlapping electric resistance brazing of dissimilar metal plates according to any one of claims 1 to 4 .   The heterogeneous material according to any one of claims 1 to 5, wherein an adhesive is sandwiched and joined between the steel plate and the aluminum alloy plate so as to surround an outer periphery of the brazing filler metal. Joining method by overlapping electric resistance brazing of metal plates.   The thickness of the said flux-filled brazing material shall be 50-500 micrometers, The joining method by the overlapping electrical resistance brazing of the dissimilar metal plate of Claim 6 characterized by the above-mentioned. Steel sheet,
An aluminum alloy plate,
A brazed portion formed between the steel plate and the aluminum alloy plate,
The brazing part is formed in at least a part of the periphery of the molten brazing material part for joining the steel plate and the aluminum alloy plate, and an unmelted brazing material containing residual flux dispersed therein A brazed joint characterized by comprising a part.   The brazed joint according to claim 8, wherein an adhesive layer made of an adhesive is formed around the brazed portion.

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