Effect of surface nitridingtreatment in a steel plate on the interfacial bonding strength of the aluminum/steel clad sheets by the cold roll bonding process

Steel sheets (08Al) with nitriding treatment and with normal wire brushing surface preparation were bonded with aluminum alloy (4A60), respectively, by cold roll bonding (CRB) process. The interface of clad sheets and the surface of the component metals after peeling off were investigated by optical microscopy (OM) and scanning electron microscopy (SEM). The peel strength of the two types Al/steel clad sheets was evaluated by peeling test. The experimental results indicated that a homogeneous Fe3N hardened and brittle layer with an average thickness of 10 µm formed on the surface of steel layer subject to salt bath nitriding treatment. More cracks and gapes formed at the interface of the Al/nitrided St clad sheets than those at the Al/brushed St clad sheets during the CRB process. The degree of contact and the bonded surface area in the Al/nitrided St sheets is higher than those in the Al/brushed St sheets at a given reduction, contributing to the enhancement of bonding strength in the former case. Meanwhile, the peel strength of the Al/nitrided St clad sheets is higher than that of the Al/brushed St clad sheets, reaching 15.9 N/mm and 10.9 N/mm, respectively, at the same reduction of 60%. In addition, the bonding mechanism of the Al/nitrided St clad sheets is discussed and it is consistent with the film theory.