Solid-liquid phase change process widely exists in many applications and acts important roles. Facing the deficiency of existing research, an apparatus was designed to measure the motion of mushy zone inside alloys. In this study, the temperature distribution inside the alloy bar, the heat flux at the cooling interface, average interface heat transfer coefficient, evolutions of phase boundaries and mushy zone in the solidification process were obtained. The effects of cooling condition and physical properties of alloy on the motion of the mushy zone were discussed. The results suggest that the evolution of liquidus boundary is controlled by sensible heat in liquid zone and interface heat flux at the cooling interface. By contrast, the evolution of solidus boundary is governed by sensible and latent heat released by mushy zone as well as heat flux at the cooling interface. Moreover, the increase of thermal diffusion inside the alloy, Biot number and Stefan number lower the max-length of the mushy zone and shorten the solidification time. Finally, dimensionless correlations were developed to predict the motion of mushy zone in the solidification process. (C) 2016 Elsevier Ltd. All rights reserved.