Preparation of Steel/Aluminum Laminated Composites by Differential Temperature Rolling with Induction Heating

Both cold-rolled and hot-rolled steel/aluminum laminated composites exhibited obvious strain-hardening of steel layer because the rolling temperature, limited by the melting point of aluminum (about 660 degrees C), was lower than dynamic recrystallization temperature of steel (about 710 degrees C). This led to poor deformation ability of composite plates and subsequent processing cracks. And the initial bonding of cold-rolled steel/aluminum composite plates usually required more than 50% highly first pass reduction, which resulted in high requirement for rolling mill capacity, especially for medium or thick size composite plates. To solve above two problems simultaneously, in this study, the steel/aluminum composite plates were prepared by differential temperature rolling (DTR) with induction heating in an argon atmosphere. The bonding properties and microstructure of the steel/aluminum laminated composites were studied, and the effect of DTR process on the bonding properties was analyzed compared with the cold rolling process. The results show that dynamic recovery and recrystallization occurred with equiaxed grains appearing in the structure of the rolled carbon steel due to the higher heating temperature of the steel layer, and an equiaxed fine grain zone with an average grain size of approximately 5 pm was formed near the interface of the steel side, which greatly reduced the hardening phenomenon of the laminated composites compared with the cold rolled clad plate. The micro-interface of DTR steel/aluminum clad plate was tightly bonded without holes and gaps. The diffusion width of Al and Fe elements across the interface reached 2.4 pm, indicating the clad plate achieved a good metallurgical bonding state, and the fine grained zone near the interface improved the properties of the sheet. The combined effect made the shear strength of the DTR clad plates much higher than that of the cold-rolled plate. At 45% reduction, the shear strength of DTR composite plate reached 85 MPa, which was 7 times of cold-rolled composite plate with the same reduction (12 MPa). The fracture of cold-rolled composite plate occurred at the steel/aluminum interface, showing brittle fracture, while the fracture of DTR clad plates occurred in the aluminum alloy matrix with a large number of dimples in the shear section, showing the characteristics of plastic fracture.