Interface formation and bonding mechanism of embedded aluminum-steel composite sheet during cold roll bonding

Embedded aluminum-steel composite sheet was produced by cold roll bonding (CRB), and the interface formation process and the bonding mechanism in the CRBed deformation zone of the composite sheet were studied. The interface microstructure evolution in the deformation zone of the composite sheet produced under a typical experiment condition (0.5 mm thick aluminum sheet, 3.75 mm thick steel sheet and a rolling reduction of 65%) was analyzed. When the deformation amount in the deformation zone was less than 35%, the aluminum layer and the steel layer were combined mainly by mechanical bonding and a wavy interface formed. When the deformation amount increased to 50%, a dozen nanometers thick diffusion layer of Al and Fe atoms which contained ~ 2 nm thick amorphous layer formed at the interface, indicating that a certain extent of metallurgical bonding at the interface was achieved. Instead of deformation-induced heat, severe shear deformation at the interface generated during CRB was mainly responsible for forming amorphous layer and achieving metallurgical bonding at the aluminum/steel interface. When the thickness of the aluminum sheet reduced from 1.0 to 0.10 mm, the reduction required for achieving preliminary metallurgical bonding decreased from 60% to 40%. Decreasing the thickness of aluminum sheet can induce the increase of interfacial shear deformation, which was favorable for improving the metallurgical bonding of the composite sheet.