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

The present invention provides 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 t 1 of 0.3 to 3.0 mm and an aluminum material 2 having a sheet thickness t 2 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 t 2 0.5 to 100 t 2 0.5 mm 2 , the area of a portion where the thickness of the interface reaction layer is from 0.5 to 3 [mu]m is 10 t 2 0.5 mm 2 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 [mu]m 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 technology for joining steel materials and aluminum materials required in the assembly process of transportation vehicles such as automobiles and railway vehicles, machine parts, building structures, etc., by spot welding. Background technique [0002] Spot welding is usually used to join metal members of the same type. However, if it can be applied to the joining of dissimilar metal members such as iron-based materials (hereinafter referred to as steel materials) and aluminum-based materials (collectively referred to as pure aluminum and aluminum alloys, hereinafter referred to as aluminum materials) (dissimilar joints) , it can greatly contribute to weight reduction and the like. [0003] However, in the case of joining steel and aluminum materials, brittle intermetallic compounds are easily formed at the joint, so it is difficult to obtain a high-strength joint (joint strength) with certain reliability. Therefore...

AI Technical Summary

Problems solved by technology

However, when the steel material and the aluminum material are insulated with an organic resin film or the like, contact corrosion can be suppressed, but spot welding itself becomes difficult by conducting electricity between the two.

Therefore, there is a problem that the joint strength of the dissimilar material joint body at the time of spot welding is lowered instead.

[0030] Therefore, the actual situation is that an effective method for improving the joint strength of a joint of dissimilar materials formed by joining steel and aluminum materials by spot welding and at the same time suppressing contact corrosion has not been proposed so far.

[0031] In addition, there is also a problem that the spot weldability of galvanized steel sheets, which are widely used in steel materials such as automobile body panels, is inferior to bare steel sheets in the case of dissimilar joints of steel and aluminum.

Since this Zn-Fe compound is brittle, the joint strength which is the starting point of fracture is significantly reduced

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