The HT250/ZL101A bimetal composite cylinders were manufactured by the combination of hot-dipping and casting technology. The diffusion interfaces in different conditions were investigated by means of field emission scanning electron microscope（FESEM）. The results indicate that the Al melt conditions play a decisive role in the formation and growth of diffusion layer. It is concluded that cast iron dip in ZL101A melt at 700 ℃ for 10 min. In addition

with increasing in dipping time

distinct changes of the thickness and morphology of diffusion layers can be ignored and diffusion layer thickness keeps approximately 30 μm

which may be related to the formation of τ5-Al8Fe2Si phase at the interface acted as a barrier to further diffusion of Al atoms.