JP2674383B2 - Aluminum resistance welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding method for aluminum.

[0002]

2. Description of the Related Art In recent years, the introduction of aluminum has been promoted in order to reduce the weight of automobile bodies. In order to use aluminum for the body of an automobile, spot welding of an aluminum plate is indispensable. However, aluminum is
High thermal and electrical conductivity compared to steel materials. Therefore, in resistance welding of aluminum, even if the same current is applied, less heat is generated as compared with steel, and the generated heat is more likely to escape. Therefore, it is necessary to perform concentrated heating by applying a large current for a short time. For example, when spot-welding steel plates having the same plate thickness or aluminum plates to each other, welding of aluminum plates requires a welding current three times as large as welding of steel plates, and the energization time is 1/7 to 1/1 /. Must be shortened to 8.

From the above, the current spot welding conditions for aluminum are as follows: welding current 20 to 50 k
A, the value of the energization time is about 5 to 10 cycles is used, and as the characteristic of the welding machine, it is required to supply a large current accurately in a short time. In response to such a demand, the most common single-phase AC welding machine has a low power factor, and thus it is difficult to supply a large current for a short time to obtain a sound joint. Therefore, in order to perform spot welding of aluminum, it is necessary to introduce new equipment such as an inverter control rectification type welding machine and a three-phase rectification type welding machine in place of the conventional welding machine.

By the way, even in resistance welding of aluminum,
It is considered possible to obtain a sound joint with existing steel welding equipment if heat generation can be concentrated on the joint surface and power source power can be used effectively. As such a method for intensively heating the bonding interface, a method of interposing an insert material between the materials to be bonded is disclosed in Welding Society Papers, Vol. 3, (1985) No. 4, P683-690. . And here, in resistance welding of stainless steels, BNi
By using the material of the series as the insert material, the resistance between the joint surfaces becomes five times or more, the joint surfaces are intensively heated by the electric current heating, and the joint interface is uniformly heated. It has been reported that a strong joint is obtained.

[0005]

However, the centralized heating method using this insert material can be applied to stainless steel but is difficult to apply to aluminum. This is because there is a possibility that the constituent elements of the insert material may react with aluminum, which is the material to be welded, to generate a brittle intermetallic compound at the joint interface, and reduce the joint strength. Therefore, at present, it is inevitable to introduce new equipment to replace the welding equipment for steel.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a resistance welding method for aluminum which can obtain an excellent welded joint with a small current.

[0007]

[Means for Solving the Problems] Even in resistance welding of aluminum, in order to secure sufficient joint strength with a small current,
Centralized heating of the joint surface is considered essential. However, in the concentrated heating method using a known insert material, as described above, a brittle metal compound is generated at the joint interface, and the joint strength is reduced. Therefore, the present inventors conducted various investigations and studies on measures for preventing embrittlement of the bonding interface. As a result, they have found that it is effective to use a clad material in which a resistor is sandwiched by aluminum as an insert material. In addition, it was also found that in the clad material, the thickness ratio between the resistor and aluminum is important.

The present invention has been made on the basis of the above findings, and a resistor having a specific resistance not less than twice that of aluminum is sandwiched between aluminum, and the thickness of the aluminum is not less than ¼ and not more than 6 times the thickness of the resistor. The gist of a resistance welding method for aluminum is characterized in that the following clad material is interposed between aluminum materials to be welded and the aluminum material is resistance-welded.

[0009]

The principle of concentrated heating in the resistance welding method for aluminum according to the present invention will be described with reference to FIG. For comparison, a concentrated heating method using a conventional insert material is shown in FIG. 1
Is an aluminum material to be welded, 2 is a clad material, 2a and 2b are resistors and aluminum constituting the clad material 2, and 3 is an insert material used for conventional concentrated heating.

In the aluminum resistance welding method of the present invention, when a current is passed between the aluminum materials 1 and 1,
The resistor 2a of the clad material 2 sandwiched between them is concentratedly heated to a high temperature, and the heat is applied to the aluminum 2 on both sides.
It is transmitted to the aluminum materials 1 and 1 via b and 2b. As a result, even with a small current, aluminum 2b and aluminum material 1
The joint surface with and is heated to a temperature necessary for forming a nugget, and both are welded.

At this time, the resistor 2 in the clad material 2
Since the so-called clad interface between a and aluminum 2b is metallurgically bonded, the resistance is small and heat generation is suppressed. Therefore, a problematic intermetallic compound does not occur. Further, since the joint surface between the aluminum 2b and the aluminum material 1 is the same material joint surface, there is no possibility of producing an intermetallic compound.

When the conventional concentrated heating method using the insert material is applied to aluminum, the brittle intermetallic compound is generated on the joint surface because of the aluminum material 1 and the insert material 3.
This is because a nugget is formed on the dissimilar material joint surface with and the constituent elements of the insert material 3 are melted, mixed, or diffused therein.

Of the findings that form the basis of the present invention, the most important thing is to control the plate thickness of aluminum and the resistor.
By controlling the heat generation at the joint surface,
That is to obtain altitude .

The clad material used in the resistance welding of aluminum of the present invention is manufactured by a known method such as rolling, explosion deposition, diffusion, etc., and the manufacturing method is not particularly limited.

Since the resistor constituting the clad material is heated to a high temperature with a small current, it has a specific resistance of aluminum (2.6 μm).
6μΩ ・ c
m ² or more is desirable. Examples of such materials include stainless steel (70 μΩ · cm), Fe (9.71 μΩ · cm)
cm), Ti (42 μΩ · cm), Ta (12.45 μΩ)
・ Cm), Ni (6.84μΩ ・ cm), Zr (40μΩ
・ Cm) can be given.

The thickness of aluminum constituting the clad material is expressed as a ratio with respect to the thickness of the resistor and is not less than ¼ and not more than 6 times, preferably about 1 to 3 times. Because, if the aluminum is too thick, the heat generated by the resistor is absorbed by the aluminum, the nugget does not grow sufficiently at the joining surface between the aluminum, and the joining strength is insufficient, and conversely,
If the aluminum is too thin as compared with the resistor, the molten metal generated at the joining surface between the aluminum reacts with the resistor to form a brittle intermetallic compound therebetween. The pair of aluminum plates in the clad material need not have the same plate thickness.

The total thickness of the clad material is related to the capacity of the welder, etc., and is preferably 2 mm or less for a maximum of about 20 kA.

[0018]

Embodiments of the present invention will be described below.

An aluminum plate having a plate thickness of 0.8 mm was spot-welded under various conditions using various clad materials in which resistors made of Fe, SUS, Ti, Ta, Zr, and Ni were sandwiched by aluminum as insert materials. The clad material is manufactured by the hot rolling method, and the total thickness is constant (2.0 mm).
The ratio of the thickness of the resistor to the thickness of aluminum was changed variously.
For comparison, a single layer insert made of Ni was also used. After welding, a cross tension test shown in FIG. 3 was performed to evaluate the strength of each welded joint in a fracture mode. Table 1 shows the results.

The button shown in the table is a rupture mode seen in the cross tension test of the spot welded part, and a rupture occurs from the periphery of the nugget to the base metal to form a buttonhole-like shape, which is sufficient. It occurs when welding is achieved.
On the other hand, flat means a flat fracture surface with small plastic deformation, and indicates that sufficient welding was not performed.

If no insert material was used, a welding current of 30 kA was required to obtain sufficient joint strength. Further, even if the insert material is used, if this is a Ni single layer, a brittle layer is formed at the joint interface at a welding current of 30 kA and sufficient strength cannot be obtained. Also, 1
At about 2 kA, sufficient heat cannot be generated at the bonding interface, and similarly sufficient strength cannot be obtained. On the other hand, when the three-layer clad material having the resistance sandwiched by aluminum was used, sufficient joint strength could be obtained even when the welding current was 12 kA. However, when the thickness of aluminum in the clad material was too large or too small with respect to the thickness of the resistor, sufficient joint strength could not be obtained with a welding current of 12 kA.

[0022]

[Table 1]

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

[0024]

As is apparent from the above description, the resistance welding method for aluminum according to the present invention can obtain a sound welded joint with much less electric current than directly welding aluminum. Therefore, welding with a general-purpose welding machine for steel or the like becomes possible, and it is not necessary to introduce new equipment.
Further, even if new equipment is introduced, a small capacity can be used, and the effect of reducing the cost required for the equipment is great.

[Brief description of the drawings]

FIG. 1 is an explanatory view of concentrated heating in an aluminum resistance welding method of the present invention.

FIG. 2 is an explanatory diagram of conventional concentrated heating.

FIG. 3 is an explanatory diagram of a cross tension test.

[Explanation of symbols]

 1 Aluminum material to be welded 2 Clad material 2a Resistor constituting clad material 2b Aluminum constituting clad material 2

Claims (1)

(57) [Claims] 1. A clad material in which a resistor having a specific resistance not less than twice that of aluminum is sandwiched between aluminum and the thickness of the aluminum is not less than ¼ and not more than 6 times the thickness of the resistor should be welded. A resistance welding method for aluminum, characterized by interposing between the aluminum materials and resistance welding the aluminum materials.