In this paper, the basic bonding mechanism between two materials of practical importance is identified. One of the materials is carbon steel, which has been aluminized on its surface by immersion in molten aluminum. This step produced a Fe-Al intermetallic compound layer. The other material is an AI-Pb alloy (a bearing material). The two materials were hot roll bonded together. It was found that the Fe-Al intermetallic compound broke into discontinuous blocks during the hot rolling operation. The block of intermetallic compound remained bonded to the steel, The overall bond between the AI-Pb strip and the steel strip resulted from two different bonds. The AI-Pb strip and the Fe-Al intermetallic compound (this is called the "block bond" in this paper) and the AI-Pb strip and the bart steel surface in the area where the block separated from the steel substrate (this is called the "blank bond" in this paper), The effects of dipping time and thickness of the intermetallic layer as well as the fractional amount of blank interfaces on the interfacial bonding strength were investigated. The total bonding strength mainly depended on that of blank interfaces and the area fraction of blank interfaces. There was a linear relationship between total bonding strength and fraction of blank interfaces, The bonding strength of blank interfaces was four times as high as that of the block interfaces. The fraction of blank interfaces increased with increasing intermetallic thickness values below 73 mum and decreased beyond 73 mum.
