JPH05228643A - Resistance welding method for different metals - Google Patents

Abstract

PURPOSE:To reduce the size and weight of a joint part by interposing specific insulating terminals between the joint surfaces of materials to be joined and executing resistance welding by energization for an extremely short period of time. CONSTITUTION:The insulating particles 3 having <=70mum grain size are interposed at 1 to 20 pieces per 1mm<2> between the joint surfaces of the materials 1, 2 which are to be joined and consist of different materials. The resistance welding is executed by the energization for the extremely short period of time by using electrodes 4, 5. Any insulating particles are usable, insofar as these [articles having >=10<8>OMEGA.mm electric resistance; for example, ceramics, such as Al2O3 and SiO2, and oxides, etc., are exemplified. Plastics are equally usable. The different metals include, for example, steel, aluminum, titanium, nickel or the combinations of the alloys thereof. As a result, the material cost is reduced.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a resistance welding method for dissimilar metals such as aluminum and steel, and steel and titanium.

[0002]

2. Description of the Related Art In welding of dissimilar metals such as aluminum and steel, and steel and titanium, it is known that a sufficient joint strength cannot be obtained because an intermetallic compound is formed at the joint interface to cause embrittlement. ing. Further, in resistance welding, the electric resistances of the materials to be joined are different. For example, in the case of spot welding of an aluminum alloy and steel, as shown in FIG. 3, the nugget 9 is biased toward the steel plate 8 having a large electric resistance. There is also a problem that the nugget 9 is hardly formed on the side of the formed aluminum alloy plate 7 having a low electric resistance.

In order to solve such a problem, by using a clad material having two kinds of metal materials, which are the same as the respective dissimilar metals to be joined, on both sides, the dissimilar metal joining is replaced by welding of the same kind of metal. A method of joining dissimilar metals is, for example, “light metal” (vol. 27 (1989) V
o. 10). According to this, in the case of spot welding of aluminum alloy and steel, as shown in FIG.
The aluminum alloy and steel clad plate 6 is used, the aluminum alloy plate 7 is spot-welded on the aluminum alloy side, and the steel plate 8 is formed on the steel side.
Are spot welded.

[0004]

In resistance welding using a clad material, since welding is of the same kind of metal, the joining strength is sufficient. However, due to the use of clad material,
It goes without saying that the joint portion becomes large and the weight increases, and various restrictions are imposed as compared with the case of directly welding dissimilar metals. In addition, cost increase cannot be avoided.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a resistance welding method for dissimilar metals capable of economically joining dissimilar metals with sufficient strength.

[0006]

[Means for Solving the Problems] By the way, even in resistance welding of similar metals, in welding aluminum to aluminum or aluminum alloy to each other, the electric conductivity and thermal conductivity of the materials are relatively high, and the generated heat is small and the generated heat escapes. Since it is easy, heat is concentrated by a large current for a short time (usually about 120 ms). When this heat concentration is used for resistance welding of dissimilar metals, a molten layer is momentarily thinned at the joint interface, so even if the electrical resistance and thermal conductivity of the materials are different, only one material is thick nugget. It is considered that the

On the basis of this idea, the present inventor planned direct resistance welding of dissimilar metals by energizing for a short time and conducted various experiments. As a result, for example, in the case of spot welding of aluminum alloy and steel, 50 μm is required to form the nugget uniformly.
It was found that energization for an extremely short time of about m or less is required. However, at the same time, it has been clarified that such an extremely short time energization may cause insufficient heat quantity, and that the energization path becomes unstable, and the joining strength is not stable. Therefore, as a result of further research, if fine insulating particles are dispersed between the surfaces to be joined, even if electricity is applied for an extremely short time, a sufficient and stable joining strength can be obtained by positive heat application to the joining interface. It was discovered that

The present invention has been made on the basis of such knowledge, and the grain size between the joining surfaces of the joined materials made of different metals is 70
A gist of a resistance welding method for dissimilar metals is characterized by performing resistance welding by energizing for an extremely short time in a state where 1 to 20 insulating particles having a size of μm or less are present per 1 mm ² .

[0009]

FIG. 1 shows an embodiment of the present invention and shows the case of spot welding. At the time of welding, first, the fine insulating particles 3 are formed on at least the welded portion between the materials to be joined 1 and 2.
Sandwich. Next, the materials to be welded 1 and 2 are sandwiched between the electrodes 4 and 5, a load is applied to the welded portion, and in this state, the welded portion is energized for an extremely short time.

FIG. 2 shows a state change due to energization of a welded portion. Due to the presence of the insulator 3, the materials to be joined 1 and 2 can locally flow a current through the electrical contact portion when the electrodes are pressed. Then, the portions where the insulator 3 does not exist are joined to obtain sufficient strength. In addition, since the current can be locally applied, it is possible to join at a lower current than in the past.

The insulating particles have an electric resistance (internal resistance) of 1
As long as at least 0 ⁸ Ω · mm, for example, Al ₂ O
Ceramics such as ₃ and SiO ₂ , oxides, etc. may be mentioned, and plastics may be used. If the grain size becomes too large, there will be no contact points on the surfaces to be joined.
It is set to 0 μm or less. However, if it becomes extremely small, it becomes smaller than the surface roughness of the surfaces to be joined, and the effect of the concentrated resistance disappears. The amount of the insulating particles becomes difficult energized with too much, if too small to reverse the effect of the constriction resistance is reduced, and 20 per 1 mm ^2. In order to interpose the insulating particles between the surfaces to be joined, for example, the insulating particles are scattered on the surface of one of the joined materials, and the other joined material is superposed. Industrially, it is preferable to mix insulating particles with an adhesive and apply it to the surfaces to be joined.

The load applied between the surfaces to be welded during welding depends on the combination of the thicknesses of the materials to be welded. For example, a thin steel sheet having a thickness of 0.6 to 1.0 mm, a thickness of 0.6 to 1 .2mm Al
The alloy plate is preferably 200 to 450 kgf. The energization time must be shortened in order to form the nugget evenly on both surfaces to be joined. However, since the time depends on the plate thickness of the materials to be joined and the like, it is difficult to specify it specifically, but in general spot welding with a plate thickness of 0.6 to 1.2 mm, 50 mS or less is desirable. The welding current needs to be increased if the applied pressure is increased even if the plate thickness is the same. Generally speaking, the welding current is 12000 to 25000 A when the plate thickness is 0.6 to 1.2 mm.

The welding machine to be used may be a general-purpose machine such as a single-phase alternating current welding machine, a condenser type welding machine, an inverter type direct current welding machine or the like, regardless of its type. However, it must be able to supply the necessary current within a predetermined time.

Examples of the dissimilar metals include steel, aluminum, titanium, nickel, and combinations of these alloys.

[0015]

EXAMPLES Examples of the present invention will be described below.

A steel plate having a thickness of 0.8 mm (JIS SPCD
Aluminum alloy plate (JIS 505) with the same thickness as S10C)
In the spot welding of 2), insulating particles made of Al ₂ O ₃ having a adjusted grain size were interposed between the joint surfaces. The electrode is made of chrome copper, and the tip shape is CF type (tip diameter 5.0 m
m) was used. The material to be welded was a tensile test piece having a width of 30 mm and a length of 100 mm, and after welding at an overlap margin of 30 mm, the material was subjected to a shear tensile test to examine the strength and fracture position. The number of samples was 5 under the same conditions. S
When the insulating particles made of io ₂ were used, the same investigation was conducted for the combination of steel and titanium, and nickel and aluminum alloy. The survey results are shown in Table 1. Breakage status A
Indicates no interface, B indicates interface fracture (fracture inside nugget), and C indicates fracture of the base metal.

[0017]

[Table 1]

The aluminum alloys can be satisfactorily joined by energizing for a short time of 100 mS (No. 1). However, steel and aluminum alloy cannot be satisfactorily joined by short-time energization of about 100 mS (No. 2). When the energization time is set to an extremely short time of 50 mS or less, the bonding strength is considerably improved depending on the test piece, but the stability of the bonding strength is extremely low (No.
3, 4).

In contrast to these comparative examples, in the examples of the present invention in which Al ₂ O ₃ particles and current for a very short time are combined, a sufficient bonding strength is obtained and the variation thereof is small (N
o. 5-7). Even when the insulating particles are SiO ₂ and the dissimilar metals are steel and titanium and nickel and aluminum alloys, sufficient and stable joint strength can be similarly obtained (No. 12 to 1).
4). However, if the particle size of the Al ₂ O ₃ particles is too large or if the amount thereof is unsuitable, defective bonding occurs in some or all of the test pieces, and defective bonding occurs even when the energization time is too long (No. .8-11).

Although the above embodiment is a spot welding method, the present invention is not limited to this, and projection welding,
It can be applied to various resistance welding such as seam welding.

[0020]

As is apparent from the above description, the resistance welding method for dissimilar metals of the present invention directly and stably dissimilarly dissimilar metals, which have been impossible to directly weld until now. Therefore, the joint portion is smaller and lighter than the welding method using the insert material. Also, the material cost is reduced. Therefore, a great effect can be obtained in promoting the introduction of the composite material structure in the fields of automobiles, railway vehicles, shipbuilding, building materials, etc., which require a large amount of welded parts.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a bonding state in the present invention.

FIG. 3 is a schematic diagram showing a welded portion when different kinds of metals are directly welded by spot welding.

FIG. 4 is a schematic diagram showing a conventional method for welding dissimilar metals.

[Explanation of symbols]

 1, 2 Materials to be bonded 3 Insulating particles 4,5 Electrodes

Claims (1)

[Claims] 1. Insulating particles having a particle size of 70 μm or less between 1 and ² per 1 mm ² are between the joining surfaces of joining materials made of dissimilar metals.
A resistance welding method for dissimilar metals, characterized by performing resistance welding by energizing for an extremely short time in a state where 0 pieces are interposed.