Joint product between steel product and aluminum material, spot welding method for the joint product, and electrode chip for use in the joint product

Abstract

To provide a joint product of a steel product and an aluminum material, and a spot welding method for the joint product, ensuring that spot welding with high bonding strength can be performed. In one embodiment, a steel product 1 having a sheet thickness t₁ of 0.3 to 3.0 mm and an aluminum material 2 having a sheet thickness t₂ of 0.5 to 4.0 mm are joined together by spot welding to form a joint product of a steel product and an aluminum produce. In this joint product, the nugget area in the joint part is from 20×t₂^0.5 to 100×t₂^0.5 mm², the area of a portion where the thickness of the interface reaction layer is from 0.5 to 3 μm is 10×t₂^0.5 mm² or more, and the difference between the interface reaction layer thickness at the joint part center and the interface reaction layer thickness at a point distant from the joint part center by a distance of one-fourth of the joint diameter D_c is 5 μm or less. According to this construction, there can be provided a dissimilar material joint product with excellent bonding strength, which can be formed by an existing spot welding apparatus at a low cost without newly using other materials such as clad material or without newly adding a separate step, and a spot welding method for the dissimilar material joint product.

Description

TECHNICAL FIELD[0001]The present invention relates to a technique of joining a steel product with an aluminum material by spot welding, which is required in the assembling process of a transit vehicle such as automobile and railway vehicle, a mechanical part, a building structure or the like.BACKGROUND ART[0002]Spot welding generally joins together similar metal members with each other. However, if it is applicable to joining of dissimilar metal members (dissimilar material joint product), for example, joining of an iron-based material (hereinafter simply referred to as a “steel product”) and an aluminum-based material (a generic term for pure aluminum and aluminum alloys; hereinafter simply referred to as an “aluminum material”), this can greatly contribute to weight saving and the like.[0003]However, in joining together a steel product and an aluminum material, a brittle intermetallic compound is readily produced at the joint part and it is very difficult to obtain a joint part ha...

AI Technical Summary

Benefits of technology

[0067]According to the present invention constructed as above, at the dissimilar material joining of a steel product with an aluminum material by spot welding, an interface reaction layer having an optimal thickness range in a large area can be formed while obtaining a relatively large nugget area and the bonding strength of the dissimilar material joint product can be enhanced. Accordingly, when forming a dissimilar material joint product of a steel product and an aluminum material by spot welding, an existing spot welding apparatus can be used, unlike conventional techniques, without newly using other materials or newly adding a separate step and in turn, a great cost reduction can be realized.

[0068]Consequently, the joint product of the present invention can be very usefully applied as various structural members in a transit vehicle such as automobile and railway vehicle, a mechanical part, a building structure and the like. Therefore, the usage of a dissimilar material joint product of a steel product and an aluminum material can be greatly expanded by the present invention.

[0069]Also, the present inventors have found that in joining together dissimilar materials, that is, a steel product and an aluminum material, by spot welding, it is important to control the area or thickness distribution of the interface reaction layer formed and for obtaining high bonding strength, to effect suppression control of the time spent to form an interface reaction layer between the steel and the aluminum material. For the suppression control of the interface reaction layer-forming time, previous formation of a suppression layer on the material is found to be important.

[0070]In the present invention, a suppression layer not only effecting suppression control of the interface reaction layer-forming time but als

Problems solved by technology

However, in joining together a steel product and an aluminum material, a brittle intermetallic compound is readily produced at the joint part and it is very difficult to obtain a joint part having reliably high strength (bonding strength).

Accordingly, joining for such a dissimilar material joint product (joint product of dissimilar metal members) has been conventionally performed using a bolt, a rivet or the like, but this has a problem in the coupling joint reliability, airtightness, cost and the like.

However, all of these methods involve not a simple spot welding but a spot welding in multiple layers, require a separate step such as plating or working, raise an issue that new equipment must be incorporated into the existing welding line, or incur a rise of the welding cost.

Furthermore, these methods all have many problems in view of operation, such as severe limitations on the welding conditions.

However, in Patent Document 8, the strength is 80 kgf and is insufficient, though the breaking is a base material rup

Images