JP2006224148A - Resistance spot welding method for different materials - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the resistance spot welding method for different materials with which resistance spot welding can be carried out with a low electric current, a power source for steel materials can be used, and different materials can be joined at low cost, even in the case of joining different materials, such as an aluminum material and a steel material. <P>SOLUTION: Disclosed is the method for joining different materials, the method for carrying out resistance spot welding of a steel material (material 4 to be welded) and an aluminum or an aluminum alloy material (material 3 to be welded). At least one electrode 1 has an electrode diameter of D, wherein the diameter d (d<D) of the part in contact with the material to be welded at the tip end of the electrode is 3.6 to 7.5 mm. In the resistance spot welding method of different materials, the electric current to be applied to the electrodes 1, 2 is as low as 15 kA or below. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for resistance spot welding of dissimilar materials to obtain a composite structure of a steel material and an aluminum-based (aluminum or aluminum alloy) material used as various structural materials for automobiles and vehicles.

  Aluminum or aluminum alloy (hereinafter collectively referred to as aluminum-based) materials are used in automobiles and vehicles as lightweight structural materials. In this case, the aluminum-based material is often used as a composite material combined with a steel material due to various factors such as cost, strength, and vehicle body rigidity. For this purpose, it is necessary to join an aluminum-based material and a steel material.

  In the case of steel materials, a resistance spot welding method is widely used as a simple joining method. Therefore, application of resistance spot welding is also demanded for joining aluminum-based materials and steel materials. As a resistance spot welding method for dissimilar materials (hereinafter referred to as different materials), Patent Document 1 discloses a technique for resistance spot welding of an aluminum-plated steel material and an aluminum alloy material.

JP2003-145278

  However, the resistance spot welding method for aluminum-based materials has a drawback that a large current is required because the thermal conductivity of the aluminum-based materials is good. The same applies to the case where one of the materials to be welded is a steel material, not aluminum-based materials. Therefore, in the resistance spot welding method between an aluminum-based material and a steel material, a large-current welding power source is required, and a welding power source for steel materials cannot be used. For this reason, it is necessary to use a welding power source dedicated to the aluminum-based material for resistance spot welding between the aluminum-based material and the steel material, and there is a problem that the cost increases.

  The present invention has been made in view of such problems, and even in the heterogeneous joining of aluminum-based materials and steel materials, resistance spot welding can be performed at a low current, and a power source for steel materials can be used. It is an object of the present invention to provide a resistance spot welding method for different materials that can be joined at different costs.

  The dissimilar material resistance spot welding method according to the present invention is a dissimilar material resistance spot welding method in which a steel material and aluminum or an aluminum alloy material are resistance spot welded. At least one of the electrodes has an electrode diameter D and the tip of the electrode An electrode having a convex curved surface with a radius of curvature and a tip diameter d of the electrode tip of 3.6 to 7.5 mm is used.

  In this dissimilar material resistance spot welding method, the current applied to the electrode is, for example, a low current of 15 kA or less.

  According to the present invention, since the diameter of the portion of the electrode tip that comes into contact with the workpiece is set small and the electrode tip is rounded, the current density is sufficiently high even at a low current of 15 kA or less. , Can be resistance spot welding stably.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a longitudinal sectional view showing a resistance spot welding method for dissimilar materials according to an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of the electrode. A material to be welded 3 made of an aluminum-based material and a material to be welded 4 made of a steel material are stacked, and the materials to be welded 3 and 4 are sandwiched by a pair of electrodes 1 and 2. As the material of the electrode, a copper alloy such as chrome copper or zircon copper can be used. When the thickness of the material 3 to be welded is t1 and the thickness of the material 4 to be welded is t2, the example shown in the figure is t2> t1, but the thicknesses of the materials 3 and 4 to be welded are the same (t1 = t2). It may be t1> t2. In the illustrated example, the electrode 1 has a smaller diameter than the electrode 2 and the small-diameter electrode 1 is in contact with the material to be welded having a thickness t1, but the combination of the electrodes 1 and 2 and the materials 3 and 4 to be welded is Not only the illustrated example but all modes are possible, and the diameters of the electrode 1 and the electrode 2 may be the same. At least one of the electrodes 1 uses a curved surface portion having a radius of curvature (tip diameter) d satisfying 3.6 to 7.5 mm, and pressurizing the materials 3 and 4 to be welded. And the combination of the electrode 1 and the to-be-welded material 3 or 4 is set. The applied pressure is usually 1.0 kN to 10.0 kN.

  In the present invention, the diameter d of the curved surface portion having the radius of curvature at the tip of at least one electrode 1 of the pair of electrodes is set to satisfy the range of 3.6 to 7.5 mm. As a result, the area where the electrode 1 and the workpiece 3 are in contact with each other is smaller than in the case of the conventional electrode. For this reason, even if the current is as low as 15 kA or less, the current density is sufficiently large. Accordingly, since resistance can be energized at a high current density during resistance spot welding, stable resistance spot welding can be performed stably. When the electrode tip diameter d is smaller than 3.6 mm, the nugget produced by resistance spot welding becomes too small, and the strength of the joint is not sufficiently high. On the other hand, when the electrode tip diameter d is larger than 7.5 mm, as described in Table 1 described later, the fracture strength of the weld joint is equal to or greater than the joint strength of resistance spot welding between aluminum-based materials, The minimum current value required to obtain a sufficiently high joint strength exceeds 15 kA, and it becomes impossible to use a welding power source for steel as a welding power source. For this reason, at least one of the electrodes 1 is set so that the electrode tip diameter d at the tip thereof satisfies the range of 3.6 to 7.5 mm. Of course, the electrodes 1 and 2 are not limited to having different diameters as shown in FIG.

  In the present invention, the electrode tip diameter d of the electrode tip portion needs to satisfy 3.6 to 7.5 mm, and the electrode tip portion needs to have a convex curved surface having a radius of curvature. Due to the roundness of the electrode tip, the following effects are obtained. As shown in FIG. 3A, when spot welding is performed, the center between the electrodes is often shifted. In that case, the material to be welded sandwiched between the displaced electrodes comes into contact with the electrodes in a slightly inclined state. Even in such a case, since the tip of the electrode has a convex curved surface, the area of the contact portion is maintained at an appropriate area without largely changing, and an appropriate welding current density can be obtained. On the other hand, in the case of an electrode with a flat tip, as shown in FIG. 3 (b), the center shifts between the electrodes, and when the cost material and the electrode are inclined, the area of the contact portion is greatly reduced. Therefore, the current density is excessively increased and the generation of dust causes poor welding. Therefore, the tip of the electrode needs to be a convex curved surface having a radius of curvature.

  The shape of the resistance welding electrode is defined in Table 1 of JIS C9304. The electrode shape prescribed | regulated to Table 1 of JISC9304 is shown in FIG. In this regulation, DR (dome radius) type, CR (conical radius) type and ER (eccentric radius) type have a contact portion in contact with the material to be welded on the electrode tip, and the electrode tip portion. Can be used in the resistance spot welding method of the present invention since it has a convex curved surface with a radius of curvature and is rounded. However, for example, in the case of an electrode that has a hemispherical shape like the R (radius) type and makes point contact with the material to be welded, there is no contact portion having a finite diameter, and the electrode life is surely inferior. Not practical. Further, even when the tip portion has a finite diameter contact portion with the material to be welded, such as a CF (conical frustum) type, when the tip portion of the electrode is flat, the electrodes do not fit as described above. In the case of such an electrode, the electrode tip is not perpendicular to the material to be joined, but it is locally contacted to increase the current density, resulting in extremely high dust generation frequency. Is not appropriate in maintaining. The same applies to the eccentric type and the point type.

  Next, the operation of the resistance spot welding method for dissimilar materials constructed as described above will be described. In the present invention, since the electrode tip diameter d at the tip of at least one of the electrodes 1 satisfies 3.6 to 7.5 mm, even if the current flowing through the contact portion of this electrode 1 is 15 kA or less, the current density Is sufficiently high, a current having a high current density can be supplied to the aluminum-based material, and a resistance spot weld having a high joint strength can be obtained stably. As a result, the current density should be large enough to obtain high joint strength by resistance spot welding of aluminum-based materials, and the current itself should be 15 kA or less, as low as resistance spot welding of steel materials. It is possible to use a power source for steel.

  In addition, this invention is not restricted to the said embodiment, A various deformation | transformation is possible. For example, the electrodes 1 and 2 may have the same shape, and the electrode 1 whose tip end has an electrode tip diameter d is not in contact with an aluminum-based material as in the above embodiment, but is in contact with a steel material. You may do it.

  The steel plate of the material to be welded 4 is preferably coated with an aluminum-based coating layer on the surface thereof. This coating layer can be formed by means such as hot dipping or thermal spraying. This coating layer is pure aluminum or an aluminum alloy containing, for example, 15% or less of Si and 5% or less of Fe. Various steel materials such as mild steel, high-tensile steel, and stainless steel can be applied as the steel plate, and the shape of the iron-based welded material is not limited to a plate material, and can be applied to a shaped steel or the like. It should be noted that an N enriched layer of N: 3.0 atomic% or more is formed at the interface between the base steel containing 0.002 to 0.020 mass% of N in the steel and the molten aluminum plating layer. preferable.

  Pure aluminum and various aluminum alloys can be applied as the aluminum-based material of the material 3 to be welded. Further, the shape of the aluminum-based material is not limited to the case where the whole is a plate material, and can be applied to various shapes of extruded shapes or cast materials.

  Examples of the present invention will be described below to explain the effects of the present invention. As shown in FIG. 1, the materials to be welded 3 and 4 were resistance spot welded by a pair of electrodes 1 and 2. The electrode had a diameter D of 16 mm. An aluminum-plated steel plate having a thickness of 1.0 mm was used as the workpiece 4 and a JIS A6061 aluminum alloy plate having a thickness of 1.0 mm was used as the workpiece 3. Table 1 below shows the tip diameter of the electrode used and the minimum current value Imin (kA) energized by resistance spot welding. The DR type and R type indicating the electrode shape are electrode shapes defined in JISC9304. The energization time was adjusted in the range of 80 msec to 800 msec so that a good joint was obtained.

  This minimum current value Imin is obtained by performing a cross tensile test on a test piece cut out from a resistance spot welded material and having a breaking strength of 1.5 kN or more, where the breaking portion is an aluminum base material. Is the minimum current value when. In the table, “-” indicates that a joint having a breaking strength of 1.5 kN was not obtained.

  As can be seen from Table 1, when the electrode tip diameter d of the tip portion of at least one of the steel material side electrode and the aluminum-based material side electrode satisfies the range of 3.6 to 7.5 mm, the minimum current value Imin is 11.5 to 15.0 kA, and even at such a low current, the breaking strength in the cross tension test is 1.5 kN or more, and excellent strength characteristics such that the breaking position is on the aluminum base material side. I was able to get it.

  On the other hand, when the electrode tip diameter d at the tip of both electrodes was 3.3 mm, even if the current density was increased by reducing the diameter, the current itself was too small to obtain a good joint. . In addition, in the case of the electrode tip diameter d of the tip portion of both electrodes of 8.0 mm and the R-type electrode, a relatively high current of 16.0 kA or more was required in order to obtain a desired bonding strength. In addition, in the case of the electrode tip diameter d of the tip portion of one electrode being 3.3 mm, the electrode tip diameter d of the tip portion of the other electrode being 8.0 mm and the R type electrode, and vice versa, Even when trying to increase the current density, the current itself was too small to obtain a good joint.

  According to the present invention, since spot welding between an aluminum material and a steel material can be performed by a conventionally used low current welding power source for steel materials, the advantages of both aluminum-based materials and steel materials are utilized. A joined structure can be easily obtained, which is useful for the production of various structural members for vehicle structures and heat exchangers.

It is longitudinal direction sectional drawing which shows the resistance spot welding method of the dissimilar material which concerns on embodiment of this invention. Similarly, it is a longitudinal cross-sectional view of the electrode contact portion. It is a figure which shows how to hit when the center of an electrode shift | deviates. It is a figure which shows the electrode shape prescribed | regulated to Table 1 of JISC9304.

Explanation of symbols

1, 2: Electrodes 3, 4: Materials to be welded

Claims (2)

In a resistance spot welding method for different materials in which a steel material and aluminum or an aluminum alloy material are resistance spot welded, at least one of the electrodes has a convex curved surface with an electrode diameter of D and an electrode tip having a radius of curvature. Further, a resistance spot welding method for different materials, wherein an electrode having a tip diameter d of 3.6 to 7.5 mm is used. 2. The method of spot spot welding for dissimilar materials according to claim 1, wherein the current applied to the electrode is 15 kA or less.

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