Melting and resolidification processes during the initial transients in the mushy zone of a metal alloy in a steep temperature gradient have been studied. Changes of microstructure, temperature distribution and solute concentration in the mushy zone are characterised, and microstructural changes in grain size and morphology are quantified. All phenomena occur before stationary gradients are reached in an early initial transient period which is studied in detail for the first time. A stationary gradient is attained in an unexpectedly short time. The mechanisms leading to the observed changes of the microstructure and to the acceleration of mass transport out of the mushy zone are discussed. (C) 2007 Elsevier B.V. All rights reserved.