2019 Volume 105 Issue 1 Pages 38-47
The microstructure of the bonding interface was investigated for a roll bonded 2-ply clad sheet of 16Cr-stainless steel and aluminum. Structural changes with heat treatment performed after roll-bonding were also investigated. At the bonding interface of as-rolled specimen, intermediate layer with a thickness of about 20 nm is formed. This intermediate layer is uniform without breakage, but has an uneven interfacial surface, consisting of a mixture of various oxides. Since there is no direct contact between the base metal at this bonding interface and atomic diffusion beyond the intermediate layer is not observed, it is considered that the clad sheet is bonded via this intermediate layer. When the heat treatment is performed at a temperature of 300 to 500 degree of centigrade after rolling, the bonding strength increased because the internal structure of the intermediate layer is reconstituted into a uniform layer with the same thickness of about 20 nm consisting of mainly Al amorphous oxides and α-Fe separated into islands inside the intermediate layer. At this time, atomic diffusion beyond the intermediate layer does not occur, presumably owing to the role of the intermediate layer as a diffusion barrier. Furthermore, when the heat treatment temperature rises to 550 degree of centigrade or higher, intermetallic compounds of θ-FeAl3 and η-Fe2Al5 are formed at a thickness of around 10 μm at the joining interface resulting in the interfacial fracture between these intermetallic compounds and the aluminum base metal.