JPH0724581A - Resistance welding method for aluminum and steel - Google Patents

Abstract

(57) [Summary] [Purpose] Performs sound resistance welding of aluminum and steel without using insert materials. [Structure] A plating layer 2 made of a metal having a melting point lower than that of the steel 1 is formed on the surface of the steel 1. The resistor 4 is inserted between the plated layer 2 and the aluminum 3. Plating layer 2 and resistor 4
It is prevented that heat is concentrated on the joint interface of 1 and the joint interface of the resistor 4 and the aluminum 3 and the nugget is formed deviated to the aluminum 3 side. Due to the heat generation, the plated layer 2 is preferentially melted, and the melting of the steel 1 is suppressed to suppress the formation of intermetallic compounds.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a resistance welding method for aluminum and steel.

[0002]

2. Description of the Related Art It is known that in welding aluminum and steel, a sufficient brittle strength cannot be obtained because an extremely brittle intermetallic compound is formed at the joint interface. Until now, mechanical joining methods such as bolts, screws, and fitting have been used for joining such dissimilar metals, but there are problems in reliability and airtightness of the joined joint.

In order to solve this problem, various solid phase bonding methods have been tried, but there are limits to their application. For example, friction welding is limited to the joining of rotating bodies with good symmetry, and there are defects in equipment and efficiency in the explosive welding method and hot rolling method.

Therefore, a relatively simple and reliable welding method for dissimilar metals using a clad material has recently been proposed. This method is a method in which welding is performed through a clad material having two kinds of metal materials that are the same as the respective different kinds of metals to be joined on both sides, and the feature is that the use of the clad material enables the joining of dissimilar metals. It is in the point of replacing with the joining of.

Regarding resistance welding of aluminum and steel, a method of performing spot welding by inserting a clad plate of aluminum and steel between respective thin plates is disclosed in, for example, Japanese Patent Laid-Open No. 4-55066. Further, from the viewpoint that it is possible to suppress the formation of an intermetallic compound at the joint interface by preventing direct contact between aluminum and steel at the initial stage of energization, the spot welding method of inserting Mg between aluminum and steel ( JP-A-4-1438
3) or a method of forming a plating layer having a melting point equal to or lower than the melting point of aluminum on the surface of steel in contact with aluminum (JP-A-4-251676).

[0006]

However, in spot welding of aluminum and steel using a clad insert material, the clad material is inserted between the aluminum plate and the steel plate, so that two plates are joined together with three plates. It becomes the joining of plates. Therefore, when considering the actual construction, there is a problem that an inserting process and a fixing process of the insert material are required, and new equipment must be incorporated into the current welding line.

Further, since the clad material itself is manufactured by joining aluminum and steel, the manufacturing conditions are strict, and it is difficult to obtain a cheap and stable product.

On the other hand, in spot welding of aluminum and steel using an Mg insert material, Mg at the joint interface is exothermicly melted at the initial stage of energization, and due to the heat and the heat of the steel itself, a part of the steel is melted and joined. Since there is a concern that a brittle intermetallic compound may be formed at the interface, it is difficult to obtain a sound welded portion like when a clad insert material is used.

Further, in the method of forming a plating layer having a melting point of aluminum or less on the steel sheet side, heat is generated mainly in the steel base material, so that the steel base material is significantly melted and there is a great concern that an intermetallic compound is formed. Welding conditions are significantly limited.

It is an object of the present invention to provide a resistance welding method for aluminum and steel which can perform sound welding without using a clad material.

[0011]

A method for resistance welding aluminum and steel according to the present invention is a resistance welding method in which a metal having a melting point lower than that of steel is plated on a joint surface on the steel side, and heat is generated by energizing between the plating layer and aluminum. The feature is that welding is performed with the body interposed.

[0012]

FIG. 1 is a schematic diagram showing spot welding as a welding mode in the resistance welding method of the present invention. 1 is thin plate steel, 2 is a plating layer formed on the joining surface of steel 1, 3 is thin plate aluminum to be joined to steel 1, 4 is a plating layer 2
Resistor inserted between the aluminum and aluminum 3,
Reference numerals 5 and 5 are electrodes for spot welding.

The spot welding method for aluminum and steel using the present invention has the following advantages over the general spot welding in which the nugget shown in FIG. 2 is formed.

Steel has a higher melting point, higher electric resistance, and lower thermal conductivity than aluminum. Due to the difference in these physical property values, when aluminum and steel are directly spot-welded, heat generation on the steel side becomes large, and this heat is conducted to the aluminum side having a low melting point. A nugget 6 that is biased to the side of is formed, and a weak intermetallic compound layer 7 of Al-Fe system is formed at the joining interface as the steel 1 melts. As a result, high joint strength cannot be obtained. In other words, this means that even if the steel 1 and the aluminum 3 are spot-welded, if the uneven formation of the nugget 6 is suppressed and the melting of the steel 1 is suppressed to the minimum at the joint interface, high joint strength is obtained. Means to be secured.

In the spot welding method of aluminum and steel using the present invention, the plating layer 2 having a melting point lower than that of steel is formed on the joint surface of the steel 1, and the resistor 4 is provided between the plating layer 2 and the aluminum 3. By being inserted, new bonding interfaces of the plated layer-resistor and resistor-aluminum are formed. As a result, heat is generated preferentially at these joint interfaces at the initial stage of energization, and the inserted resistor 4
As a result of the concentrated heat generation, the formation of a nugget biased toward the aluminum 3 side is suppressed. Further, by this initial heat generation, the plating layer 2 having a lower melting point than the steel is preferentially melted, and by suppressing the melting of the steel 1, the formation of an Al-Fe-based intermetallic compound is suppressed and the soundness is sound. An excellent bonding interface can be obtained. Therefore, high joint strength is secured without using a clad insert material.

That is, in the resistance welding method of the present invention, the resistor forms a new joint interface, and the resistor itself becomes a heat source in the initial stage of energization. While suppressing the melting of the material, promotes preferential melting of the plating layer. When there is no resistor, that is, when only the plating layer exists between the steel and aluminum, not only the plating layer but also the steel base material melts to form an intermetallic compound, so that high joint strength cannot be obtained.

The resistor does not mean a high resistor in terms of its function, but may be an electric conductor, and a metal (including an alloy), an oxide, a nitride or the like can be appropriately used.

In the case of metal, the form of the resistor is generally a foil, but it may be a film formed by plating, vapor deposition, thermal spraying or the like, and may be a coating of the resistor. The application of the resistor specifically means that the conductive powder is applied to the surface of the material by application, and the particle size and density of the powder need not be specified because they can be resistors. Absent.

The thickness of the resistor is not particularly limited, but it is preferably 200 μm or less from the viewpoint of resistance welding of thin plates.

The plating layer preferentially melts at the initial stage of energization to suppress the melting of steel and prevents the formation of intermetallic compounds which causes a significant decrease in joint strength. If there is no plating layer and only the resistor is interposed between steel and aluminum, the steel base material will melt,
Since an intermetallic compound is produced, high strength cannot be obtained.

The composition of the plating layer may be one having a melting point lower than that of steel because of the ease of melting, not to mention pure metal.
Alloys such as elemental and ternary alloys may be used.

The thickness of the plating layer is preferably 2 μm or more in order to obtain the effect of suppressing the intermetallic compound. As for the upper limit of the thickness, an extremely thick plating layer causes deterioration of the plating characteristics and deterioration of stability with the steel base material.
The following is desirable.

The plating is essential on the steel surface on the side to be joined with aluminum, but the steel surface and aluminum surface on the opposite side are not particularly limited. Also, multi-layer plating such as two-layer plating may be used.

The plating method need not be specified in particular, such as hot dipping and electroplating.

Regarding the formation of the intermetallic compound at the bonding interface, which is of concern, even if the resistor or the plating layer used as the insert material contains as a main component a metal that easily forms a brittle intermetallic compound, it is difficult to perform the welding. It melts and is extruded from between the materials to be joined by the pressing force and disappears, so that it does not cause formation of an intermetallic compound.

The aluminum to be joined is not limited to pure aluminum, and various aluminum alloys such as Al-Mg type and Al-Cu type can be used.

Regarding steel, for example, carbon steel having a C content of 0.5 mass% or less, alloy steel, and stainless steel (SPCC, SPCD,
SPCE, SUS304, etc.) can be used.

As the welding machine, a single-phase AC welding machine, a condenser welding machine, or an inverter welding machine can be used.

As the welding conditions, it is desirable to use short-time welding in which the initial heat generation at the joint interface can be fully utilized. When the welding time is long, for example, when it is 200 ms or more, heat generation of the steel progresses and the heat is conducted to aluminum, so that there is a concern that a nugget biased to the aluminum side is formed.

[0030]

EXAMPLES Examples and comparative examples of the present invention will be described below.

Example 1 A cold rolled steel sheet having a thickness of 1.0 mm has an Al content of 10 to 90 on one side.
A mass% Al-Mn alloy, pure Al, was electroplated to a thickness of about 8 μm. Further, Al-30 mass% Mn was plated to a thickness of 1 to 400 μm by a hot dipping method or an electroplating method. Further, Al-Si, Al-Ni, and Al-Zn alloys and Ni, Cu, and Zn pure metals were electroplated to a thickness of 8 μm. For comparison, Nb, Ta, and Mo, which are typical refractory metals, were coated to a thickness of about 8 μm by a vapor deposition method.

Then, a resistor was inserted between the plated layer of each plated steel plate and the aluminum plate to perform spot welding.

The resistors are Ni, Cu, Al--Si,
Al-Mn, Ag, Ti, Ta, Zr foils (thickness of 0.
1 mm), an oxide film (Al ₂ O ₃ , Si) having a thickness of 0.003 to 0.1 μm formed by oxidation on the surface of the plating layer.
O ₂ ), Cu, Ni, A with a particle size of 30 μm on the surface of the plating layer
l ₂ O _3, the powders of SiO ₂ 1 m ² per 1-100
The coating film formed by individual coating was used. The aluminum plate was an Al-Mg alloy (A5052) with a thickness of 1.0 mm.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

[Table 5]

After welding, the joint obtained was subjected to the cross tension test shown in FIG. 3 to investigate the fracture form. The results are shown in Table 1
It shows in Table 5. Evaluation ◯ indicates fracture of the base material, and x indicates fracture of materials other than the base material.

The examples of the present invention showed high joint strength except when the plating layer was extremely thin and the welding time was too long.

Example 2 SPCC, SPCD, SPC having a plate thickness of 1.0 mm as steel
E, SAPH310, SUS304, A1050, A2217, A with a plate thickness of 1.0 mm as aluminum
Similar tests were carried out using 3003, A5083, A6061 and A7075.

The plating layer is an electroplating layer made of Al-30 mass% Mn and having a thickness of 8 μm (unit weight: 20 g / m ² ).
The resistor was an Al-Si foil with a thickness of 100 μm. Also,
All welding conditions are welding time 1ms, welding current 60k
A, the pressing force was 1960 N.

The results are shown in Tables 6 and 7. INDUSTRIAL APPLICABILITY The present invention can be applied to various kinds of materials to be bonded and exerts excellent bonding strength improvement results.

[0044]

[Table 6]

[0045]

[Table 7]

[0046]

As is apparent from the above description, the resistance welding method for aluminum and steel according to the present invention does not use a clad insert material but uses a plating layer and a resistor directly coated on the steel surface as an insert material. Sound welding. Therefore, in the actual construction, the step of inserting the insert material and the step of fixing the insert material are unnecessary, and the number of steps can be significantly reduced. Further, compared with the clad insert material, the cost of the plating layer and the resistor is low, and the quality is stable, so that the economical efficiency and the stability of the joint strength are high.

[Brief description of drawings]

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

FIG. 2 is a schematic view showing a formation state of a nugget by a conventional method.

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

[Explanation of symbols]

 1 Steel 2 Plating Layer 3 Aluminum 4 Resistor 5 Electrode

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Claims (1)

[Claims] 1. In resistance welding of aluminum and steel,
A resistance welding method for aluminum and steel, characterized in that a metal having a melting point lower than that of steel is plated on the steel-side joint surface, and a resistor that generates heat when energized is interposed between the plated layer and aluminum to perform welding. .