Weldment of different materials and resistance spot welding method

摘要

A joined part of an aluminum-coated steel sheet and an aluminum sheet is composed of an intermetallic compound layer which exists in a region in which a part of a coated layer exists before the joining and an aluminum melted and solidified part which also exists on the side of the aluminum sheet to enclose the intermetallic compound layer. The atoms existing on the surface of the aluminum melted and solidified part are intermetallic-bonded with atoms which exist on the surface of the steel sheet except in the region in which the intermetallic compound layer exists seen in the plan view. Further, the area of the intermetallic compound layer is limited to 60% or less of the total area of the joined part at the interface between the aluminum-coated steel sheet and the aluminum sheet. Thus, the area of the aluminum melted and solidified part exceeds 40% of the total area of the joined part. The strong joining having a high fracture energy can be provided at a high efficiency.