JP2009000700A - Joining method and structure of dissimilar metals - Google Patents

Abstract

[PROBLEMS] To prevent corrosion caused by contact between dissimilar metals and ensure excellent corrosion resistance without increasing the weight of joints or increasing costs due to new capital investment, and at the joint interface of dissimilar metal joints. Dissimilar metal joining method capable of preventing strength reduction due to remaining material and joining structure by such method are provided.
When performing resistance spot welding of materials to be joined 1 and 2 made of dissimilar metals stacked via a seal material S, for example, an electrode E1 whose tip is divided into a plurality of movable pieces 13 is used. By moving the movable piece 13 that is in contact with the material to be bonded 1 during pressure in the outer peripheral direction of the bonded portion, the fluidity of the material to be bonded 1 in the softened solid state is promoted, and the adhesion at the bonding interface is improved. Then, the sealing material S is discharged from the joint portion to enhance the adhesion at the joint interface.
[Selection] Figure 3

Description

  The present invention relates to a joining technique by resistance welding of dissimilar metals, and in particular, in order to prevent galvanic corrosion caused by a difference in ionization tendency of joined materials, a sealing material made of an insulating material is interposed between the joined materials. The present invention relates to a joining method of dissimilar metals joined by resistance spot welding in a state, a joining structure by the joining method, and a resistance spot welding apparatus used for such joining.

  In recent years, in addition to steel, which has been widely used in the past, automobile body members made of light metal such as aluminum alloy (for example, aluminum alloy roof panels) have been applied to automobile bodies. Has been done.

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 welding an aluminum alloy and a steel material as described above, intermetallic compounds such as Fe ₂ Al ₅ and FeAl _{3 that} are brittle and high in hardness are generated. Control of the compound is required.

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

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

In addition, friction welding can be applied to such dissimilar metal joining, but such a friction welding method has limited objects such as joining of rotating bodies having good symmetry.
Furthermore, explosive deposition and hot rolling are also known, but there are many problems in equipment and efficiency, and there is a problem that it is difficult to apply widely to general dissimilar metal joining.

  As an example that has been improved to solve such a problem, a clad material composed of two kinds of materials having the same combination as the kind of dissimilar metal is interposed between different kinds of metal materials so that the same kind of materials are in contact with each other. In this state, 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 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 to a thickness of 2 μm or more, and this plated surface is superimposed on the aluminum material to energize it. However, a method of joining these materials in such a manner that the plating layer is preferentially melted and the steel material side is hardly melted is disclosed (see Patent Document 2).

On the other hand, it is known that when dissimilar metals are used in combination at the bonding sites of various members, the dissimilar metals come into contact with each other and are electrically connected, thereby promoting corrosion.
Corrosion due to the contact of different metals is considered to occur due to potential difference between the metals due to the difference in the ionization tendency of the metal, and the corrosion current flows. As a measure to prevent corrosion due to the contact of different metals, For example, a first member made of steel and a second member made of, for example, aluminum or an alloy thereof are joined by a joining means such as a rivet or a reinforcing member with a sealing material interposed between the two members. A joint structure for vehicle body members has been proposed (see Patent Document 3).

In addition, a member in which an iron-based material and aluminum or an aluminum alloy material are joined is immersed in a solution containing a fluoro complex ion and zinc ion, so that a dense, strong and high adhesiveness is formed in the vicinity of the joint, and aluminum and iron It is known that metallic zinc having an intermediate ionization tendency is deposited to improve the corrosion resistance against dissimilar metal contact at the joint (see Patent Document 4).
JP-A-4-127773 JP-A-6-39558 JP 2000-272541 A JP 2005-154844 A

  However, in the method described in Patent Document 1, since a clad material is used, two plates should be joined originally, which means that three pieces are joined. Along with the insertion of the clad material, a fixing process is required, and it is necessary to incorporate new equipment into the current welding line, which increases the cost. In addition, for example, when aluminum and steel are joined, aluminum clad steel itself is produced by joining dissimilar materials to each other, and therefore, an inexpensive clad material with strict production conditions and stable performance is obtained. There is a problem that itself is difficult.

  Moreover, in the method of patent document 2 which resistance-welds in the state which gave the aluminum plating to the steel surface, in order to destroy the strong oxide film which exists in the aluminum surface, when joining an aluminum plating surface and aluminum material It is necessary to input a large amount of heat, and a brittle intermetallic compound is generated at the interface between the aluminum plating and the steel, which may cause destruction.

On the other hand, in the technique described in Patent Document 3, since the melting point and the linear expansion coefficient of both materials are different, welding is avoided and mechanical fastening such as rivets and bolts is adopted. There exists a problem that the weight and cost of a joining member increase.
Furthermore, in the technique described in Patent Document 4, the joined member is immersed in a solution containing a fluoro complex ion and zinc ion. However, only zinc deposited on the surface of the joining material is used for an automobile part. In addition to not being able to satisfactorily satisfy the required corrosion resistance performance, incorporating a process of immersing car body parts in such a solution in the production process of automobiles is a new facility such as an immersion tank. The problem is that it requires investment and increases costs.

  The present invention has been made in view of the above-described problems in the conventional dissimilar metal joining method, and the purpose thereof is to increase the weight of the joint and to increase the cost due to new equipment investment, A dissimilar metal joining method capable of preventing corrosion due to contact with dissimilar metals to ensure excellent corrosion resistance and preventing strength reduction due to residual seal material at the joint interface of dissimilar metal joints, and joining by such a method To provide a structure.

  As a result of intensive studies aimed at achieving the above object, the present inventors have conducted, for example, resistance spot welding in a state where a sealing material is interposed between materials to be joined made of different kinds of metals to be joined. By moving the tip of the welding electrode, vibrating or rotating the electrode, the flow of at least one of the materials to be joined in the softened solid state is promoted, and the adhesion between the materials to be joined By taking measures to improve the above, it has been found that the discharge performance of the sealing material is improved and the above problems can be solved, and the present invention has been completed.

  The present invention is based on such knowledge, and in the dissimilar metal joining method of the present invention, for example, when the resistance spot welding is performed between the joined materials made of dissimilar metals overlapped with each other through the sealing material, By using an electrode divided into a plurality of movable pieces or applying vibration to the electrode, the flow of the material to be joined in the softened solid state is promoted and the adhesion at the joining interface is improved. It is characterized by doing.

Further, the dissimilar metal joining structure of the present invention is resistance spot welded by the joining method described above, and the materials to be joined are directly joined together, and the periphery of the joined portion is surrounded by a sealing material. It is characterized by being.
And the resistance spot welding apparatus of this invention is used suitably for the said joining method of this invention, Comprising: The flow of the to-be-joined material of the softened solid-phase state is accelerated | stimulated, and the adhesiveness of a joining interface is improved. Means, for example, is characterized in that the tip portion includes an electrode divided into a plurality of movable pieces, an electrode that can vibrate or rotate, and the like.

  According to the present invention, when resistance materials are welded to each other, which are made of dissimilar metals superposed via a sealing material, the flow of the materials to be joined in the softened solid state is promoted, and the adhesion at the joining interface is improved. Therefore, the sealing material is smoothly discharged from the joint part to the surroundings, and the sealing material is effectively lost from the joint interface without remaining in the joint part. A strong joint structure can be obtained.

  Below, the joining method of the dissimilar metals of this invention is demonstrated in detail and concretely based on drawing.

In the dissimilar metal joining method of the present invention, as described above, at the time of resistance spot welding of both materials in a state where the sealing material is interposed between the materials to be joined made of different metals, at least one of the two materials is used. Although measures are taken to improve the fluidity in the softened solid phase state and improve the adhesion between the materials to be joined, such means include, for example, a plurality of tip portions in contact with the materials to be joined. By using the welding electrode divided into the movable pieces, the movable piece can be moved outward from the center of the joint at the time of joining, that is, during energization / pressurization.
In addition, a welding electrode having a shape in which the tip surface in contact with the material to be joined is inclined with respect to the axial load direction, or vibration in a direction substantially parallel to the joining surface is applied to the welding electrode during energization and pressurization. It is also possible to give a rotational motion to the welding electrode.

  The dissimilar metal joining method of the present invention, as described above, for preventing corrosion due to contact between dissimilar metals, enhances the discharge performance from the joint portion of the sealing material interposed between both dissimilar materials, thereby having corrosion resistance, Since it is intended to achieve both prevention of reduction in bonding strength due to the remaining seal material, as a combination of materials to be bonded, as long as the combination of seal materials is necessary to prevent electrolytic corrosion, There is no particular limitation.

However, a dense and strong oxide film is formed on the surface of the material to be joined, such as the joining of steel and aluminum alloy materials as described in the background art section, and the brittle intermetallic compound has high hardness. In the case of a combination of materials that are likely to generate, a material made of a third metal that causes eutectic melting between at least one of the materials to be joined and at least one of the materials to be joined is interposed. It is desirable to join by causing eutectic melting.
In this case, an oxide film, a eutectic melt, and other various reaction products are generated in the bonding process, and it is necessary to discharge these impurities from the bonding interface. Therefore, the application of the present invention is more effective. It will be something.

As the eutectic reaction, for example, in an Al—Zn alloy, it is known that the eutectic reaction occurs at 655 K which is much lower than the melting point of Al of 933 K and the melting point of Zn of 692.5 K.
Therefore, by using this to create eutectic melting of Al and Zn and using it for bonding actions such as oxide film removal and interdiffusion during bonding of aluminum materials, low-temperature bonding can be performed, so Fe ₂ Al ₅ And the growth at the joint interface of intermetallic compounds such as FeAl ₃ can be extremely effectively suppressed.

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 described above, 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, it is not necessary to control the composition. An 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 a Zn-Al alloy instead of zinc, The composition must be at least 95% zinc.

  In the case of a combination of a steel material and an aluminum alloy material as described above, the third metal material interposed between the two materials is 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), 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, the metal The oxide film can be removed at a low temperature at which no intermetallic compound is formed, and the formation of intermetallic compounds at the joining interface during the joining process can be suppressed, thus enabling strong joining.
In the joining method of the present invention, a welding electrode in which a tip portion that comes into contact with a material to be joined is divided into a plurality of movable pieces, an electrode whose tip surface is inclined, or vibration or rotation is applied to the electrode. Since the fluidity in the softened solid state of the material to be joined is enhanced, the discharge of contaminants such as oxide films, eutectic melts, and reaction products in the joining process together with the sealing material is prevented. Since it is performed more effectively, the adhesion between the materials to be joined is increased, and the joining strength of the dissimilar material joint can be improved.

  In the present invention, the third metal material interposed between the two materials and the sealing material is not limited to the pure metal as described above, and eutectic metals include binary alloys and ternary alloys. An alloy containing at least one of these metals may be used.

  In the present invention, as a specific means for interposing the third metal material between the materials to be joined, an insert material made of the third metal material is inserted between the dissimilar metal materials that are the materials to be joined. However, it is desirable that at least one of the materials to be bonded be coated with a third material in advance by plating or the like, and thereby the step of sandwiching the third material as an insert material between the materials to be bonded. It can be omitted, the work efficiency is improved, and after the plating layer melted by the eutectic reaction is discharged around the joint together with impurities on the surface, a very clean new surface appears from the bottom of the plating layer. Strong joining is possible.

  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.

  Next, the embodiment of the present invention will be described by taking the joining of an aluminum alloy sheet and a galvanized steel sheet as an example.

FIG. 1 is an overall view of an AC type spot welding apparatus used in the dissimilar metal joining method of the present invention, in which an aluminum alloy plate 1 and a galvanized steel plate 2 are used as a rust-proof seal material S therebetween. Overlaid with a thermosetting structural adhesive applied.
In addition, as the sealing material S, in addition to applying such an insulating adhesive, a thin sheet-like material made of an insulating resin can be sandwiched.

FIG. 2 shows a specific structure of the welding electrode E1 shown in FIG. 1. In this example, the upper electrode E1 in contact with the aluminum alloy plate 1 is the outer periphery of the electrode. It is mainly composed of a hollow cylindrical holder 11 to be configured, a drive core 12 instructed to be movable up and down at the center thereof, and four movable pieces 13 arranged on the lower end side of the drive core 12 in the figure. The movable piece 13 is supported between the drive core 12 and a stopper 11a formed at the lower end of the holder 11 so as to be movable in the horizontal direction.
The movable piece 13 is urged toward the center by the coil spring 14, and the upper end surface of each movable piece 13 and the lower end surface of the drive core 12 are in contact with each other through a tapered surface. When the drive core 12 is pushed downward in the figure, the four movable pieces 13 move from the center side to the outer peripheral direction against the elastic force of the coil spring 14.

  Using the resistance spot welding apparatus equipped with the electrode E1 having the structure shown in FIG. 2, the joining of the aluminum alloy plate 1 and the galvanized steel plate 2 is started, and energization and pressurization by the electrodes E1 and E2 are performed. Then, the drive core 12 is pushed down and the movable pieces 13 expand in the outer circumferential direction, so that the fluidity of the heated and softened material to be joined, particularly the aluminum alloy plate 1, is increased, and the sealing material S, followed by eutectic melting Contaminants including substances, oxide films, and other reaction products become discharged D, which is efficiently extruded from the bonding interface, and due to the remaining strength of the sealing material S and discharged D, due to contact with dissimilar metals Corrosion resistance deterioration can be prevented.

  3 (a) to 3 (f) are schematic views of the joining process involving eutectic melting, and FIG. 3 (a) shows the state of the material to be joined before joining is started. The galvanized steel sheet 2 having a surface coated with a galvanized layer 2p functioning as a third metal material that forms a eutectic with Al is overlapped so that the galvanized layer 2p is on the inside, As described above, the sealing material S is applied, and the oxide film 1 c is formed on the surface of the aluminum alloy plate 1.

Next, when these welded materials are relatively pressed by the welding electrodes E1 and E2, as shown in FIG. 3B, the sealing material S is discharged from the central portion of the joint portion to the outer peripheral portion, and the central portion is zinc. The plating layer 2p and the oxide film 1c on the surface of the aluminum alloy plate 1 are in direct contact with each other.
Here, when a mechanical or thermal impact is applied by pressurization and energization, the oxide film is locally broken as shown in FIG.

As a result, local contact between zinc and aluminum occurs, and eutectic melting of zinc and aluminum occurs as shown in FIG. 3 (d) when the temperature is maintained above the eutectic point temperature of zinc and aluminum.
And as shown in FIG.3 (e), the oxide film 1c and the impurity (not shown) of a joining interface with the eutectic molten metal become the discharge | emission matter D by the further press of an electrode, and are discharged | emitted around a junction part. However, the sealing material is also discharged, and a predetermined joining area is secured.

At this time, as the electrode of the aluminum alloy plate 1, the electrode E1 provided with the movable piece 13 at the tip is used to promote plastic flow in the softened solid state of the aluminum alloy. This improves the adhesion of the sealing material S and the discharge D from the joined portion.
Thereafter, the new surfaces of aluminum and steel are directly joined to each other, and a diffusion reaction layer Ld is formed between the galvanized steel plate 2 and the aluminum alloy plate 1 as shown in FIG. Can do.

  FIG. 4 is an enlarged view showing the central portion of the joint structure obtained in this way, and the contaminants such as the sealing material S, oxide film, and eutectic reactant are removed from the joint interface, and the diffusion reaction layer The joint where Ld is formed has a structure surrounded by the discharge D and further the sealing material S, so that it is completely shielded from the corrosive environment and has excellent corrosion resistance against contact corrosion of dissimilar metals. It is possible to achieve both strength and corrosion resistance.

  At this time, as shown in FIG. 5, by opening a space in the center of the four movable pieces 13, it becomes possible to flow current in a ring shape, and even when the current value is the same, The outer peripheral diameter can be increased, and the bonding strength can be improved efficiently.

  In addition, as a standard of joining conditions at the time of using the above-mentioned electrode E1, when the aluminum alloy plate 1 is a 6000 series alloy having a plate thickness of 1 mm and the galvanized steel plate 2 is a plate thickness of 0.55 mm having a plating thickness of 20 μm The conditions of a welding current of 24000 A, energization time of 0.2 seconds, and a pressing force of about 300 kgf can be employed.

  FIG. 6 shows another example of means for promoting plastic flow in the softened solid phase state of the materials to be joined and improving the adhesion between the materials to be joined. As shown in FIG. By using an electrode in which the tip surface of E2, that is, the contact surface with the materials to be bonded 1 and 2 is inclined with respect to the axial load direction, the force in the in-plane pruning direction at the bonding interface is effective with a simple structure. Can be generated.

  That is, when a load is applied in the axial direction of the upper and lower electrodes E1, E2 provided with such an inclined surface 15, a force in the in-plane shear direction which is a component force is applied, In particular, the plastic flow of the aluminum alloy plate 1 having the lower melting point is promoted, the adhesion at the bonding interface is improved, and contaminants such as the sealing material S, oxide film, and eutectic reaction product remain at the bonding interface. Therefore, both the joint strength and the corrosion resistance can be ensured as in the case of using the electrodes shown in FIGS. 2 and 5.

  FIG. 7 shows still another example of means for improving fluidity in a softened solid phase state of a material to be joined and improving adhesion at the joining interface. Here, as shown in FIG. A vibrator 20 for applying horizontal vibration is attached to the electrode E1 on the side in contact with the plate 1, and the vibration can be applied to the electrode E1 in a direction substantially parallel to the joint surface during joining. By vibrating the electrode E1 by the element 20, the plastic flow of the material to be joined, particularly the aluminum alloy plate 1, can be promoted, and the adhesion at the joining interface can be improved.

  While joining is performed by energizing and pressurizing under the same conditions while vibrating the electrode E1 by the vibrator 20, a region in which fluidity is improved and adhesion is improved by changing the amplitude of horizontal vibration at this time. , The bonding in a desired region can be realized, and contaminants such as the sealing material S, oxide film, and eutectic reaction product can be smoothly removed from the bonding interface, and the sealing material A high-strength joint structure can be obtained without leaving S or discharge D at the joint interface, and both joint strength and corrosion resistance can be achieved.

As a means for promoting the plastic flow of the materials to be joined and improving the adhesion at the joining interface, it is possible to impart rotational motion to the electrode E1, as shown in FIG.
At this time, as a rotation mechanism that applies a rotational force to the electrode E1, for example, as shown in FIG. 9A, a motor rotation mechanism that transmits the rotation of the electric motor 30 provided outside by a spur gear 31 and 32 at a reduced speed. Alternatively, a rotating mechanism using an air turbine 35 as shown in FIG. 9B can be employed.

By such a mechanism, by energizing and pressing under the same conditions while rotating the electrode E1, the plastic flow of the aluminum alloy plate 1 is promoted, the adhesion at the joining interface is improved, and the sealing material S and the interface are improved. Various contaminants intervening in the joint can be smoothly removed from the joint interface, and the joint strength and corrosion resistance can be achieved at the same time without leaving the sealant S and the discharge D at the joint interface.
By using such a rotation mechanism, the force in the in-plane pruning direction at the bonding interface can be generated relatively uniformly over the entire surface, and a more uniform and stable bonding state can be obtained. .

It is the schematic which shows the whole structure of the resistance spot welding apparatus used for this invention. It is the schematic which shows the joining procedure by the electrode structure provided with the movable piece, and the said electrode as one Embodiment of this invention. (A)-(f) is process drawing which shows the joining process of the aluminum alloy and galvanized steel plate with eutectic melting. It is an expanded sectional view which shows the joining structure of the aluminum alloy and galvanized steel plate by the process shown in FIG. It is the schematic which shows the modification of the electrode shown in FIG. 2 as other embodiment of this invention. It is the schematic which shows the joining point by the electrode provided with the inclined surface as other embodiment of this invention. It is the schematic which shows the joining procedure of the dissimilar metal performed while giving a vibration to an electrode with a vibrator | oscillator as other embodiment of this invention. It is the schematic which shows the joining point of the dissimilar metal performed while giving rotational motion to an electrode as further another embodiment of this invention. (A) And (b) is the schematic which shows the structural example of the rotation mechanism of the electrode shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum alloy plate galvanized steel plate 2 Galvanized steel plate 13 Movable piece 15 Inclined surface 20 Vibrator 30 Electric motor 35 Air turbine S Seal material E1 Welding electrode E2 Welding electrode

Claims (9)

  It is characterized by promoting the flow of softened solid-state materials to be joined and improving the adhesion at the joint interface when resistance materials are welded to each other. Dissimilar metal joining method.   The dissimilar metal joining method according to claim 1, wherein a welding electrode in which a tip portion in contact with a material to be joined is divided into a plurality of movable pieces is used.   2. The dissimilar metal joining method according to claim 1, wherein a welding electrode whose contact surface with the material to be joined is inclined with respect to the axial load direction is used.   The dissimilar metal joining method according to claim 1, wherein the welding electrode is joined while applying vibration in a direction substantially parallel to the joining surface.   The dissimilar metal joining method according to claim 1, wherein joining is performed while applying a rotational motion to the welding electrode.   6. A material comprising a third metal that causes eutectic melting between at least one of the materials to be bonded and the sealing material is interposed between at least one of the materials to be bonded. The dissimilar metal joining method according to any one of the items.   7. The dissimilar metal joint according to claim 6, wherein the materials to be joined are a galvanized steel plate and an aluminum alloy plate, respectively, and zinc plated on the galvanized steel plate is used as a third metal material. Method.   A joining structure of dissimilar metals characterized in that the periphery of a joint portion joined by the method according to any one of claims 1 to 7 and directly joined to each other is surrounded by a sealing material. .   A resistance spot welding apparatus comprising means for promoting fluidity of a softened solid-state joined material and improving adhesion at a joining interface.

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