Microstructures are the strategic link between materials processing and materials behavior. The microstructural scales of dendrites, such as primary and secondary arm spacings, control the segregation profiles and the formation of secondary phases within interdendritic regions, which determine the properties of cast structures. A small number of studies have been conducted in order to analyze the effects of melt convection within the interdendritic region. In this article, the influence of thermosolutal convection on dendrite arm spacings is experimentally examined in the downward vertical unsteady-state directional solidification of Sn-Pb hypoeutectic alloys. The main predictive theoretical models for dendritic spacings are compared with the experimental observations. (c) 2005 Elsevier B.V All rights reserved.591316911695