Bonding process and interfacial reaction in horizontal twin-roll casting of steel/aluminum clad sheet

Asymmetrical and lower heat transport caused by the cladding strip during twin-roll casting (TRC) of clad sheet makes the process window narrow compared with traditional TRC. The effect of pouring temperature on process stability is more remarkable when it is relatively high under high casting speed and casting speed becomes a leading factor when its value is low. The inter-diffusion zone width at the Al/Fe interface depends on the solid/semi-solid contacting time. The longer the time is, the wider the inter diffusion zone. A widest zone of 3.8 mu m is attained under condition of casting speed of 1.25 m/min and pouring temperature of 720 degrees C. Bonding strength of clad sheet by TRC depends on inter-diffusion zone width and rolling reduction. Proper combinations of inter-diffusion zone width and rolling reduction can result in same high bonding strength. The highest bonding strength of 16 N/mm is attained under a combination of rolling reduction of 29% and inter-diffusion zone of 3.7 mu m. The wetting of aluminum melt on steel surface is uneven and insufficient as a result of short contacting time in TRC. As a result, same rolling reduction in TRC induces lower bonding strength than in roll bonding process. Bonding strength of clad sheet by TRC decreases when the surface of the steel strip is brushed, as a result of decrement of actual contacting area. (C) 2017 Elsevier B.V. All rights reserved.