An integrated numerical model was applied to simulate the mold filling and solidification process as well as predict the occurrence of relative casting defects for a rotor hub casting. The goal was to conduct a numerical experimentation to obtain an optimal alloy design of ductile cast iron for the rotor hub casting. A computer-aided engineering software based on the finite element method was employed in this study. Numerical simulations were conducted for the rotor hub casting with two different types of alloy composition for ductile cast iron. The mold filling and solidification process were examined to predict the occurrence and extent of casting defects and a better alloy design was then proposed based on the simulated results to alleviate casting defects of the rotor hub casting. Copyright © 2010 John Wiley & Sons, Ltd.