JP5051608B2 - Method of joining dissimilar metals by resistance spot welding - Google Patents

Description

The present invention relates to a joining technique by resistance spot welding of dissimilar metals such as a steel material and an aluminum alloy material, and more particularly, a third metal material interposed as an insert material between the two metal materials as the material to be joined and the material to be covered. The present invention relates to a method for joining dissimilar metals using a eutectic reaction generated between the joining materials.

Generally, when dissimilar metals are joined, if both of the materials to be joined are melted like welding of the same kind of materials, a fragile intermetallic compound may be generated, and sufficient joint strength may not be obtained.
For example, when different types of aluminum alloy and steel are welded, intermetallic compounds such as Fe ₂ Al ₅ and FeAl _{3 that} are brittle and hard are generated. Therefore, in order to ensure joint strength, control of these intermetallic compounds is required. Is required.

  However, a dense and strong oxide film is formed on the aluminum alloy surface, and in order to remove it, it is necessary to administer a large amount of heat at the time of bonding. As a result, there is a problem that a thick intermetallic compound layer grows and the strength of the joint portion is lowered.

  Therefore, when such dissimilar metal materials are used in combination, conventionally, these materials have been joined by mechanical fastening with bolts or rivets, but in this case the weight and cost increase. There is a problem.

In addition, friction welding is put into practical use for joining different kinds of metals. However, such a friction welding method has a limited object such as joining of rotating bodies having good symmetry.
Furthermore, explosion deposition and hot rolling are also known, but there are many problems in terms of equipment and efficiency, and there is a problem that they cannot be widely applied to general dissimilar metal joining.

  As an improvement example of such a problem of dissimilar metal bonding, a clad material composed of the same two kinds of materials as the dissimilar metal is interposed between the dissimilar metal materials so that the same kind of materials are in contact with each other. A method of performing resistance welding with an energization time of 10 ms or less has been proposed (see Patent Document 1).

In resistance welding of aluminum and steel, the surface of the steel in contact with the aluminum material is plated with an aluminum alloy or pure aluminum having an Al content of 20 wt% or more so as to have a thickness of 2 μm or more. A method of joining these materials by energizing them, preferentially melting the plating layer and hardly melting the steel material side is disclosed (see Patent Document 2).
JP-A-4-127773 JP-A-6-39558

  However, in the case of the method described in Patent Document 1 using a clad material, the two plates should be joined together, which means that the three pieces are joined. At the same time, a fixing process is required, and it is necessary to incorporate new equipment into the current welding line, which causes a cost increase. In addition, for example, when aluminum and steel are joined, aluminum clad steel itself is also produced by joining dissimilar materials to each other, so that it is difficult to obtain an inexpensive clad material with strict production conditions and stable performance. There is a problem.

  On the other hand, in the method described in Patent Document 2 in which resistance welding is performed in a state where aluminum plating is performed on the steel surface, when the aluminum plating surface and the aluminum material are joined, the strong oxide film existing on the aluminum surface is destroyed. It was necessary to input a large amount of heat, and a brittle intermetallic compound was generated at the interface between the aluminum plating and the steel, which could cause destruction.

The present invention has been made in view of the above-described problems in conventional methods for joining dissimilar metals, and the object of the present invention is to generate intermetallic compounds in the joining process when joining dissimilar metals by resistance spot welding. It is an object of the present invention to provide a dissimilar metal joining method capable of removing an oxide film at a joining interface while suppressing the above-described problem and capable of firmly joining new surfaces.

  As a result of intensive investigations to achieve the above object, the inventors of the present invention have developed a third metal that causes a eutectic reaction between at least one metal of these materials between different metal materials to be joined. By interposing the material and causing eutectic melting at the time of joining, the oxide film can be removed at a temperature lower than the melting point of the base metal dissimilar metal, and it is not necessary to input large heat input. It has been found that the above object can be achieved by making the tip of the electrode used for resistance spot welding a curved surface, and the present invention has been completed.

The present invention is based on the above knowledge, and in the dissimilar metal bonding method of the present invention, a third metal made of a metal different from these metal materials is interposed between the metal materials different from each other. The material is interposed, and a part of the oxide film of one of the materials to be bonded is destroyed by local contact with the third material by pressurization and energization with an electrode, When expanding the eutectic melting that occurs between the third material, destroying the oxide film at the bonding interface, and excluding the oxide film together with the eutectic molten metal from the bonding interface to perform resistance spot welding of the materials to be bonded An electrode having a curved surface at the tip is used as at least one of the electrodes.

  According to the present invention, when different metal materials different from each other are joined by resistance spot welding, a third metal material that causes a eutectic reaction with at least one of these metal materials is interposed between both metal materials, Since current is applied and pressed using an electrode having a curved surface at least at one of the ends, eutectic melting is caused between the third metal material and the one metal material by resistance heating, thereby joining. The oxide film can be removed at a low temperature lower than the melting point of the base metal material, and the control of the bonding interface temperature is possible, so that the formation of intermetallic compounds is suppressed and at the same time the eutectic formed in the bonding process. Smooth discharge of metal, oxide film on the surface of the material to be bonded, reaction products, etc. from the bonded part can be realized, and a structure in which the new surfaces of the material to be bonded are firmly bonded together can be obtained. These can be prevented strength reduction caused by the remaining, so that strong bonding state can be obtained.

  Below, the joining method of the dissimilar metals of this invention by resistance welding is demonstrated further in detail and concretely.

FIG. 1 shows an Al—Zn based binary phase diagram. As shown in the figure, the eutectic point (T _E ) in the Al—Zn system is 655 K, which is much higher than the melting point 933 K of Al. Eutectic reactions occur at low temperatures.
Therefore, by using the eutectic points shown in the figure to create eutectic melting of Al and Zn, and using them for bonding actions such as oxide film removal and interdiffusion during bonding of aluminum materials, low temperature bonding can be performed. Therefore, it is possible to extremely effectively suppress the growth at the joint interface of intermetallic compounds such as Fe ₂ Al ₅ and FeAl ₃ .

Here, eutectic melting is melting using a eutectic reaction, and when the composition of an interdiffusion region formed by mutual diffusion of two metals (or alloys) becomes a eutectic composition, the holding temperature If is equal to or higher than the eutectic temperature, a liquid phase is formed by the eutectic reaction. For example, in the case of aluminum and zinc, the melting point of aluminum is 933 K, the melting point of zinc is 692.5 K, and this eutectic metal melts at 655 K which is lower than the respective melting points.
Therefore, a reaction occurs when the clean surfaces of both metals are brought into contact and heated to 655K or higher. This is called eutectic melting, and Al-95% Zn has a eutectic composition, but the eutectic reaction itself is a constant change unrelated to the alloy components, and the alloy composition only increases or decreases the amount of eutectic reaction. Absent.

On the other hand, a strong oxide film is present on the surface of the aluminum material, which is physically destroyed by plastic deformation of the aluminum material caused by energization and pressurization during resistance welding.
That is, microscopic projections on the surface of the material rub against each other by pressurization, so eutectic melting occurs from the part where aluminum and zinc contact due to local destruction of some oxide films, and this liquid phase is generated. By accelerating the reaction in which the nearby oxide film is crushed and decomposed and further eutectic melting spreads over the entire surface, the destruction of the oxide film and the joining via the liquid phase are achieved.

  Since the eutectic composition is spontaneously achieved by interdiffusion, composition control is not necessary. The essential condition is that a low melting eutectic reaction exists between the two metals or alloys. In the case of eutectic melting of aluminum and zinc, when using Zn-Al alloy instead of zinc, The composition must be at least 95% zinc.

2A to 2E are schematic views showing a dissimilar metal joining process according to the present invention.
First, as shown in FIG. 2 (a), a galvanized steel sheet 1 provided with a galvanized layer 1p functioning as a third metal material that forms a eutectic with Al on the surface, and an aluminum alloy material 2 are provided. As shown in FIG. 2B, the galvanized steel sheet 1 and the aluminum alloy material 2 are stacked so that the galvanized layer 1p is on the inside. An oxide film 2 c is generated on the surface of the aluminum alloy material 2.

  Next, the oxide film 2c is locally broken at the microscopic contact portion of the material surface as shown in FIG. 2 (c) by pressurization by the electrode of the resistance spot welding apparatus and heating by energization.

  As a result, local contact between zinc and aluminum occurs, and as shown in FIG. 2 (d), eutectic melting of zinc and aluminum occurs and oxidizes together with the eutectic molten metal 3 according to the temperature state at that time. The film 2c and impurities at the bonding interface are discharged to the outside of the bonded portion, and a predetermined bonding area is secured. As a result, as shown in FIG. 2 (e), the new surfaces of aluminum and steel are directly bonded to each other. A strong metal bond between 1 and the aluminum alloy material 2 is obtained.

As a specific combination of the materials to be bonded in the dissimilar metal bonding method of the present invention, for example, a combination of a steel material and an aluminum alloy material can be mentioned, and as a third metal material interposed between both materials at this time, The material is not particularly limited as long as it is a material that forms a low melting point eutectic with an aluminum alloy. For example, besides zinc (Zn) described above, copper (Cu), tin (Sn), silver (Ag) ), Nickel (Ni), or the like can be used.
In other words, the eutectic metal of these metals and Al melts at a temperature lower than the melting point of the aluminum alloy material, which is the base material. Therefore, even in the joining of steel materials and aluminum alloy materials where fragile intermetallic compounds are easily formed, Thus, the oxide film can be removed, the formation of intermetallic compounds at the bonding interface during the bonding process can be suppressed, and strong bonding becomes possible.

Further, when considering that the joining method of the present invention is applied to the assembly of an automobile body, the material to be joined is mostly a combination of steel and aluminum, but in the future, steel and magnesium, or aluminum and magnesium. Combinations of these are also possible.
When joining the steel material and magnesium, it is possible to produce a eutectic reaction between zinc and magnesium plated on the steel material side in the same manner as in the examples described later. Furthermore, even when aluminum and magnesium are joined, zinc or silver can be used as the third metal material.

  In the present invention, the third metal material need not be limited to the pure metal as described above, and eutectic metals include both binary alloys and ternary alloys. Therefore, at least one of these eutectic metals exists. An alloy containing a metal may be used.

  In the dissimilar metal joining method of the present invention, a third metal material that causes a eutectic reaction with these materials is interposed between the dissimilar metal materials to be joined as described above, and at least one of the dissimilar metal materials When the resistance spot welding is performed by causing eutectic melting between the first metal and the third material, an electrode having a curved surface at the tip is used as at least one of the electrodes. As a specific means for interposing the material between the materials to be joined, for example, an insert material made of a third metal material can be inserted between the dissimilar metal materials that are the materials to be joined. .

  In addition, it is desirable that at least one of the materials to be bonded be pre-plated with the third material, so that the step of sandwiching the third material as an insert material between the materials to be bonded can be omitted, and work efficiency is improved. At the same time, after the plating layer melted by the eutectic reaction is discharged around the joint together with the impurities on the surface, a very clean new surface appears from the bottom of the plating layer, which enables stronger bonding. .

  For example, when dissimilar joining of the above-mentioned aluminum alloy material or magnesium alloy material and steel material is performed, the surface is pre-plated with zinc, which is a third metal material that forms a low melting point eutectic with aluminum or magnesium. So-called galvanized steel sheets can be used, and in this case, no special preparation is required, and ordinary commercial steel materials plated with zinc for rust prevention purposes can be used as they are. It is possible to simply and inexpensively join different metals firmly and easily.

  In the dissimilar metal joining method of the present invention, at the time of resistance spot welding, at least one tip portion of an electrode used for pressurization / energization of a material to be joined is used in a curved shape. Thus, various impurities such as eutectic metal, oxide film, and reaction product generated in the joining process are smoothly discharged from the joined portion, and the new surfaces of the materials to be joined are firmly joined together.

At this time, as the curved surface shape of the electrode tip, the increase in the radius of curvature R of the tip is uniform so as to qualitatively show the relationship between the radius of curvature R of the electrode tip for spot welding and the strength factor in FIG. Contributes to the increase of current density distribution region and pressure distribution region and contributes to strength improvement, while lowering discharge properties from the joint of third material, eutectic molten metal, removed oxide film, etc. Therefore, these contaminants remain at the bonding interface, resulting in a decrease in strength.
Therefore, as shown in the drawing, the strength of the dissimilar material joint can be increased by using an electrode having a radius of curvature R in a region where both of these can be achieved.

  Specifically, if one of the materials to be joined is an aluminum alloy material, the plate thickness is t, and the curvature radius of the electrode tip surface is R, the curvature radius R is 50 mm when the plate thickness t is less than 0.8 mm. When the plate thickness t is 0.8 mm or more and less than 1.6 mm, the curvature radius R is less than 75 mm, and when the plate thickness t is 1.6 mm or more and less than 2.3 mm, the curvature radius R is in the range of 10 mm or more and less than 75 mm. Further, when the plate thickness t is 2.3 mm or more and 3.2 mm or less, it is desirable that the radius of curvature R is in the range of 10 mm or more and less than 150 mm, thereby making the temperature uniform in the nugget formation region in the joint surface, The eutectic melting that occurs in the bonding process at the bonding interface and the discharge properties of the oxide film on the surface of the material to be bonded can be achieved at the same time, and a firm bonding structure between the new surfaces of the bonding material can be obtained more reliably. It becomes possible.

  In addition, when the inside of the circular area of the diameter d at the center of the electrode tip surface is a curved surface, when the curvature radius of the curved surface is r, and the center curved surface diameter d is 6.4 mm or less, the curvature is When the radius r is less than 50 mm and the curved surface diameter d is more than 6.4 mm and less than 9.4 mm, the curvature radius r is less than 75 mm and when the curved surface diameter d is 9.4 mm or more and 11.5 mm or less, the curvature radius. It is desirable that r be 10 mm or more and less than 150 mm, and by doing so, the same effect as described above can be obtained.

Further, with respect to the electrode shape described above, the tip portion is curved, and as shown in FIGS. 4A to 4C, the cross-sectional shape (cross-section parallel to the bonding surface) is not circular or square, but is horizontally long. It is also desirable to have a simple shape.
By using the electrode E1 having such a cross-sectional shape, the distance from the center of the electrode to the periphery of the joint is shortened. Therefore, eutectic melting that occurs in the joining process at the joining interface, long sides such as an oxide film on the surface of the material to be joined The discharge from the side is promoted, and a high-strength joint joint can be obtained. Furthermore, by shortening the distance from the center of the electrode to the periphery of the joint, the temperature distribution in the joint surface is also made uniform, and a good and uniform joint interface is obtained. As a result, a high-strength joint joint can be obtained.

  Moreover, in such an electrode having a cross-sectional shape, when the cross-sectional area is constant (current density is constant), the width dimension of the electrode can be reduced. Therefore, by applying such an electrode to spot welding, The width of the joint can be reduced, and the material cost and weight can be reduced.

In the examples described later, as shown in FIG. 4C, the aspect ratio (b / a) of the electrode cross section is 3.0, but in the present invention, the aspect ratio a of the electrode cross section is used. If there is a difference between the lengths of b and b, it will be discharged from the long side selectively from the relationship of the discharge distance, and the discharge will be promoted more effectively than the combination of equal sides having the same length. . Therefore, it is preferable to use the electrode having a shape in the range of 1.1 <b / a <5.0.
The electrode cross-sectional shape is not only a rectangular cross-section as shown in FIG. 4C, but also a pseudo-ellipse (oval type) with a rectangular corner dropped, a polygon such as an ellipse, a rhombus, etc. Those with different dimensions can be applied.

At this time, as the electrode arrangement direction, it is desirable to match the longitudinal direction of the electrode cross section with the longitudinal direction of the joining flange portion, so that the joining flange width can be reduced as described above, and the design and design can be reduced. It is possible to improve the material cost and weight.
In addition, eutectic melting that occurs during the joining process, oxide film on the surface of the material to be joined, and discharge from the joining interface of the sealing material described later are mainly performed from the long side of the electrode in the flange width direction. It becomes possible to discharge smoothly.

According to the dissimilar metal bonding method described above, the new surfaces of the materials to be bonded made of different metals are directly bonded to each other, and eutectic melting is performed between at least one of the materials to be bonded around the bonded portion. At least one of the generated third material, the material to be joined, the reaction product of the third material and the material to be joined, the reaction product produced in the joining process, etc. is discharged to obtain a convenient structure, and the melting point of the base material The oxide film on the surface of the material to be bonded can be removed at a lower temperature, and the bonding interface temperature is controlled above the eutectic temperature and below the melting point of the material with the lower melting point of both materials to be bonded. The formation of the intermetallic compound can be suppressed, and it is possible to obtain a strong bond by mutual diffusion. At this time, the remaining at the bonding interface such as the third material, eutectic melt, and removed oxide film causes a decrease in strength. Indentation corresponding to the shape of the electrode tip is formed.
When a sealing material described later is sandwiched, the new surfaces of the materials to be bonded are directly bonded to each other, and eutectic melting occurs between at least one material of the materials to be bonded around the bonded portion. 3 material, the material to be bonded, the reaction product of the third material and the material to be bonded, and at least one selected from the group consisting of the reaction material generated in the bonding process, and the sealing material are discharged, The portion is shielded (sealed) from the external atmosphere by the discharged sealing material, and an indentation corresponding to the tip shape of the electrode is formed on the surface of the material to be joined.

  When the dissimilar metal joining method described above is applied to the joining of automobile parts, for example, by applying a light alloy such as an aluminum alloy to the roof panel and a galvanized steel sheet to the vehicle body skeleton member, a lightweight, high rigidity and low center of gravity motion A high-performance vehicle can be easily manufactured at low cost, and these components can be provided at low cost.

Furthermore, in the dissimilar metal joining method of the present invention, if necessary, it is possible to join in a state where a sealing material is interposed between at least one of the materials to be joined and the third material, The sealing material prevents water from entering the joint and can simultaneously achieve strength and rust prevention (electrolytic corrosion due to contact with different metals). Furthermore, in the case of resistance welding as in the present invention, the current value can be suppressed by the electrical resistance of the sealing material, and the energy efficiency can be improved.
At this time, by using not only an electrode having a curvature at the tip but a circular cross section but also an electrode having a horizontally long cross section as shown in FIG. Can be discharged.

  In the present invention, as the sealing material, for example, an epoxy resin-based material, a synthetic rubber-based material, a synthetic rubber / PVC-based material, or the like can be used. It can be applied to a sheet, or a sheet can be sandwiched between both materials.

FIG. 5A shows a resistance of a material to be bonded in a state in which the seal material 5 is sandwiched between the galvanized steel plate 1 and the aluminum alloy material 2 by using the electrode E1 having a rectangular cross section as shown in FIG. The procedure for spot welding will be described. The electrodes E1 and E1 are arranged so that the longitudinal direction of the electrode cross section coincides with the longitudinal direction of the joining flange portion of the joined material.
By arranging the electrodes in this way, the flange width can be shortened and the weight can be reduced. Further, as shown in FIG. 12 (b) with respect to FIG. 12 (a), when this joining is used for the aluminum roof and the side member, the joining width (e) can be shortened and the design is improved.
And while the pressing load by these electrodes E1 and E1 increases, the sealing material 5 is discharged | emitted from a joining interface, and when the galvanized steel plate 1 and the aluminum alloy material 2 contact, between both materials via electrodes E1 and E1 Electric current flows, and eutectic melting occurs by the process as shown in FIG. 2, and both materials are joined.

  At this time, since the electrodes E1 and E1 have a rectangular cross section as described above, and the tip portion is a curved surface, the sealing material 5 has a width of the joining flange portion as indicated by an arrow in the figure. The discharged sealing material 5 is smoothly discharged in the direction, and the joint end portion is made watertight, so that different metal contact corrosion due to contact between steel and aluminum can be prevented.

At this time, as shown in FIG. 5 (a), by performing a hat-like process on the side of the galvanized steel sheet 1, the sealing material 5 is easily discharged from the bonding interface. Emission efficiency can be increased.
The hat shape is not only on the galvanized steel sheet 1 side, but also on the aluminum alloy material 2 side as shown in FIG. 5 (b), and on the galvanized steel sheet 1 and aluminum alloy as shown in FIG. 5 (c). You may make it form in both of the material 2. FIG.

  Further, at this time, as shown in FIGS. 6A to 6C, the recess 2 g is provided in advance in the joint flange portion of the aluminum alloy material 2, or the recess 1 g is provided in the flange portion of the galvanized steel sheet 1. When the sealing material 5 discharged from the joint portion enters the recesses 2g and 1g, the sealing material 5 is smoothly discharged from the joint portion, and the width of the flange portion is wide. However, the discharge of the sealing material 5 can be performed efficiently.

  FIG. 7 shows a situation in which the long side of the electrode E1 is arranged in parallel to the flange edge as described above. By adopting such an electrode arrangement, the sealing material 5 from the long side of the electrode E1 is shown. As a result of promoting the discharge in the flange width direction (arrow direction), the mutual interference of the sealing material 5 in the longitudinal direction of the joining flange is reduced, the flow of the sealing material 5 is not delayed, and the sealing material 5 is efficiently discharged from the joining interface. can do. In addition, the design and design can be improved by shortening the joint flange width, and the weight of the member can be reduced.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited at all by these Examples.

Example 1
6000 series aluminum alloy material 2 having a thickness of 0.6 mm to 3.2 mm and zinc having a thickness of 0.55 mm to 2.8 mm using an AC power source type resistance spot welding apparatus as shown in FIG. Bonding with the plated steel sheet 1 was performed.
In addition, about the galvanization thickness of the galvanized steel plate 1, the thing of the plating thickness of about 20 micrometers was used.

At this time, joining was performed using electrodes E2 and E2 having a tip shape as shown in FIG. 9 and having an electrode diameter of 16 mm and a radius of curvature R of the tip surface of 5 mm to 200 mm. The curvature radius R of the front end surface is determined according to the thickness of the material to be joined. As an example, welding conditions in a combination of a galvanized steel sheet having a thickness of 0.55 mm and a 6000 series aluminum alloy material having a thickness of 1.0 mm are shown. The curvature radius R of the electrode tip is 40 mm, the welding current is 30000 A, and the energization time is 0. Bonding was performed for 24 seconds at a pressure of 300 kgf. When the sealing material is added, the welding current can be suppressed as described above as compared with the case where there is no sealing material. Further, since the remaining seal material leads to a decrease in strength, it is desired that the seal material be discharged well in order to secure the joint strength. Therefore, compared to the case where there is no seal material, the optimum region of the electrode tip shape when there is a seal material is the degree that does not impair the uniformity of the uniform current density distribution and pressure distribution when the plate thickness of the material to be joined is the same. Slightly shifts to a region where the curvature is small.
The strength of each spot welded joint is investigated, and the results without seal material are shown in Table 1. Note that the joint strength is extremely good when it greatly exceeds the JIS standard (JIS Z 3140) between aluminum materials. “◎”, those that pass the above JIS standards are evaluated as “good”, those that are slightly below the above JIS standards are evaluated as “bad”, those that are below the above JIS standards are evaluated as “poor”, and these symbols Is described in the table.

  As a result, for example, in the case of an aluminum alloy material having a plate thickness t of 1.0 mm, when the curvature radius R is 5 mm or 10 mm, it is better than the JIS standard, and when the curvature radius R is 20 mm, 40 mm or 50 mm, Good, slightly poor when the radius of curvature R was 75 mm, and poor when the radius of curvature R exceeded 100 mm. Moreover, when the plate | board thickness of aluminum alloy material became large, the tendency for the suitable range of the curvature radius R of an electrode front end surface to transfer to the large-diameter side was confirmed in connection with it.

(Example 2)
In the same manner as in Example 1, the AC power source type resistance spot welding apparatus shown in FIG. 8 was used, and a 6000 series aluminum alloy material 2 having a thickness of 1.0 mm and a galvanized steel sheet 1 having a thickness of 0.55 mm (plating) And a thickness of about 5 μm).
At this time, it has a tip shape as shown in FIG. 10, the electrode diameter D is 16 mm, the curved surface processing range diameter d of the tip center portion is 6.4 mm to 11.5 mm, and the curvature radius r of the curved surface is 5 mm. Bonding was performed using the electrodes E2 and E2 in the range of ˜200 mm. The curvature radius r of the curved surface at the tip is determined according to the curved surface processing range diameter d. As an example, the welding conditions in the combination of a galvanized steel sheet having a thickness of 0.55 mm and a 6000 series aluminum alloy material having a thickness of 1.0 mm are shown. The curvature radius r of the electrode is 75 mm, the curved surface processing range diameter d is 8 mm, welding Joining was performed at an electric current of 24000 A, an energization time of 0.24 seconds, and a pressure of 200 kgf. Similarly, when the sealing material is inserted, the welding current can be suppressed as described above as compared with the case where there is no sealing material. As described above, since the remaining seal material leads to a decrease in strength, good discharge of the seal material is desired for securing the joint strength. Therefore, compared to the case where there is no seal material, the optimum region of the electrode tip shape when there is a seal material is the degree that does not impair the uniformity of the uniform current density distribution and pressure distribution when the plate thickness of the material to be joined is the same. Slightly shifts to a region where the curvature is small.
The strength of each spot welded joint was investigated, and the results in the case of no sealant are shown in Table 2.
In addition, the evaluation criteria of joint strength are the same as the said Example 1.

  As a result, for example, when the curved surface processing range diameter d at the center of the electrode tip is 8.0 mm, when the radius of curvature r of the tip is 5 mm or 10 mm, it is better than the JIS standard, and the radius of curvature r is 20 mm or 40 mm. It was found that the film was extremely good when the radius of curvature was 50 mm, slightly poor when the radius of curvature r was 75 mm, and poor when the radius of curvature r exceeded 100 mm. Further, when the machining range diameter d of the electrode tip portion was increased, the tendency that the preferred range of the curvature radius r of the tip surface also slightly shifted to the larger diameter side was recognized.

(Example 3)
Using an AC power source type resistance spot welding apparatus as shown in FIG. 8, as shown in FIGS. 11 (a) and 11 (b), a galvanized steel sheet 1 having a thickness of 0.55 mm and a thickness of 1.0 mm When the pillar or sill comprising the 6000 series aluminum alloy material 2 and having the joining flange portion is assembled, the electrode E2 having a cylindrical shape with a diameter of 15 mm, the tip portion having a curved shape as shown in FIG. 9, and FIG. As shown, the flange portions were each resistance spot welded using an electrode E1 having a rectangular cross section of 12 mm × 4 mm.
As welding conditions, a welding current of 30000 A, energization time of 12 cycles, and a pressure of 120 kgf were employed.

  As a result, since the electrode tip has a curved surface in any case, reaction products such as zinc, molten eutectic metal, and oxide film are smoothly discharged from the bonding interface, and the new surfaces of the materials to be bonded are As shown in FIG. 11 (b), it was confirmed that the material was directly and firmly joined, but compared to the flange width b when using a cylindrical electrode as shown in FIG. 11 (a). When the electrodes are used, if the cross-sectional areas are the same, the electrode width can be reduced. Therefore, the joint flange width c can be reduced, and the weight of the component and the material cost can be reduced. did it.

Example 4
Using an AC power source type resistance spot welding apparatus as shown in FIG. 8, as shown in FIG. 12, a vehicle body skeleton member composed of a rail outer 11 a and a rail inner 11 b made of a galvanized steel plate having a thickness of 0.55 mm is used. When joining the roof panel 12 made of a 6000 series aluminum alloy material having a plate thickness of 1.0 mm, spot welding is performed using the electrode E1 having a rectangular cross section as shown in FIG. As shown in FIG. 12B, the joint width e between the roof panel 12 and the vehicle body frame member can be made smaller than the joint width d in the conventional method of joining using rivets. As the degree of freedom of shape increases, design and design are improved.
Furthermore, since the roof panel 12 is a light alloy and the vehicle body skeleton member is a galvanized steel sheet, a vehicle with high movement performance that is lightweight, highly rigid and has a low center of gravity can be manufactured at low cost.

It is a graph which shows the eutectic point in an Al-Zn type binary phase diagram. (A)-(e) is process drawing which shows roughly the joining process of the dissimilar metal by this invention. It is a graph which illustrates qualitatively the relationship between the radius of curvature R of the spot welding electrode tip and the strength factor. It is the longitudinal cross-sectional view (a), perspective view (b), and cross-sectional view (c) which show an example of embodiment of the electrode used for this invention. It is a perspective view which shows the example which carries out resistance spot welding of the to-be-joined material which clamped the sealing material between the galvanized steel plate and the aluminum alloy material using the electrode E which has a rectangular cross section. It is a perspective view which shows the example which formed the recessed part into which a sealing material flows in into a to-be-joined material at the time of resistance spot welding of the to-be-joined material shown in FIG. It is a perspective view which shows notionally the discharge condition of the sealing material at the time of arrange | positioning the long side of an electrode in parallel with a flange edge. It is the schematic which shows the resistance spot welding apparatus used for the Example of this invention. It is explanatory drawing which shows the electrode shape and the resistance spot welding procedure used for Example 1 of this invention. It is explanatory drawing which shows the electrode shape and the resistance spot welding procedure used for Example 2 of this invention. It is a perspective view explaining the resistance spot welding point of a motor vehicle member as Example 3 of the present invention. It is sectional drawing explaining the resistance spot welding procedure of a motor vehicle member as Example 3 of this invention.

Explanation of symbols

1 Galvanized steel sheet (material to be joined)
1p Zinc plating layer (third material)
1g Concavity 2 Aluminum alloy material (material to be joined)
2g Concave part 5 Sealing material E1, E2 Electrode

Claims (9)

A third material made of a metal different from the above metal material is interposed between the materials to be joined which are made by stacking different metal materials, and an oxide film of one material of the material to be joined by pressurization and energization by an electrode A portion of the material is destroyed and brought into local contact with the third material, and the eutectic melting generated between the one material and the third material is expanded from the contact portion as a starting point, thereby forming an oxide film at the bonding interface. Dissimilar metal bonding characterized in that an electrode having a curved surface at the tip is used as at least one of the electrodes when breaking and removing the oxide film together with the eutectic molten metal from the bonding interface to perform resistance spot welding. Method.   2. The dissimilar metal joining method according to claim 1, wherein a third material is inserted into at least one of the materials to be joined and is covered or covered between the materials to be joined.   3. The dissimilar metal joining method according to claim 2, wherein one of the materials to be joined is a galvanized steel sheet, and the zinc plated on the galvanized steel sheet is used as the third material.   The dissimilar metal joining method according to any one of claims 1 to 3, wherein dimensions in a longitudinal and transverse direction in a cross-sectional shape substantially parallel to the joining surface of the electrode are different.   The dissimilar metal according to claim 4, wherein a joining flange portion is provided in the material to be joined, and the longitudinal direction of the electrode coincides with the longitudinal direction of the joining flange portion when joining the material to be joined at the flange portion. Joining method.   When the other material to be joined is an aluminum alloy material, the radius of curvature of the tip surface of the electrode is R, and the plate thickness of the aluminum alloy material is t, when t <0.8 mm, R <50 mm, 0 0.8 mm ≦ t <1.6 mm, R <75 mm, 1.6 mm ≦ t <2.3 mm, 10 mm ≦ R <75 mm, 2.3 mm ≦ t ≦ 3.2 mm, 10 mm ≦ R <150 mm The dissimilar metal joining method according to claim 1, wherein the dissimilar metal joining method is provided.   The central portion of the tip surface of the electrode has a curved surface with a radius of curvature r over a circular region having a diameter d. When d ≦ 6.4 mm, r <50 mm and 6.4 mm <d <9.4 mm. 4. The dissimilar metal bonding method according to claim 1, wherein r <75 mm, and 9.4 mm ≦ d ≦ 11.5 mm, 10 mm ≦ r <150 mm. .   6. The dissimilar metal joining method according to claim 4, wherein a sealing material is interposed between at least one of the materials to be joined and the third material.   9. The dissimilar metal joining method according to claim 8, wherein a recess into which the sealing material discharged from the joining portion flows is formed in at least one of the materials to be joined.

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