Effect of the steel sheet surface hardening state on interfacial bonding strength of embedded aluminum–steel composite sheet produced by cold roll bonding process

Three kinds of surface hardening states of the steel sheet were obtained by different mechanical surface preparation methods with flap disc and steel circumferential brushes before cold roll bonding of embedded 1060 aluminum-08Al steel composite sheets, and the influence of steel sheet surface hardening state on the interfacial bonding strength of the composite sheet and the related mechanism were studied. The results showed that numerous cracks formed between the broken work-hardened surface layer and its steel matrix during cold roll bonding, resulting in a large number of fragments at the interface, which was the main reason for the reduction of the bonding strength. It is an effective method for reducing the work-hardened surface layer hardness to improve the bonding strength of the composite sheet. The nano-hardness of the steel surface treated by flap disc was 4.5 GPa which was close to that (4.4 GPa) of the steel matrix, while the nano-hardnesses of the steel surfaces treated by the steel brushes made of Ф 0.3 mm wires and Ф 0.1 mm wires were 8.6 GPa and 5.7 GPa, respectively. For the thickness reduction of 25%, the peel strengths of the composite sheets whose original steel sheet surface were treated by the steel brush made of Ф 0.3 mm wires and Ф 0.1 mm wires were 0.9 N/mm and 2.9 N/mm, respectively, while the peel strength of the composite sheet whose steel sheet surface was treated by flap disc significantly rose to 14.9 N/mm.