Effects of annealing and cold roll-bonded interface on the microstructure and mechanical properties of the embedded aluminum-steel composite sheet.

Embedded aluminum-steel composite sheets used in heat exchanger were produced by cold roll bonding (CRB). The influences of annealing temperature and annealing time on the microstructure and the bonding strength of the composite sheet were investigated. The recrystallization of the steel layer began at 525 °C and finished at 600 °C. With the increase of the annealing temperature, the peel strength of the composite sheet whose original steel sheet surface was treated by scratch brush initially increased and then decreased, which was resulted from the competition of the mechanical locking and metallurgical bonding. After annealing, the cracks which formed between the broken work-hardened steel surface layer and its matrix during cold roll bonding remained. The composite sheet produced by CRB with the steel surface treatment of flap disc had less interfacial defects, higher bonding quality, higher diffusion rate of Al and Fe atoms at the interface and larger metallurgical bonding extent than the composite sheet produced by CRB with the steel surface treatment of scratch brush under the same conditions of annealing, which was helpful to shorten annealing time, reduce energy consumption and improve production efficiency.