Materials Science and Engineering A 413–414 (2005) 98–104 Effect of melt flow on macro- and microstructure evolution during solidification of an Al–4.5% Cu alloy A.N. Turchin a,∗ , D.G. Eskin a , L. Katgerman b a Netherlands Institute for Metals Research, Rotterdamseweg 137, 2628AL Delft, The Netherlands b Delft University of Technology, Department of Material Science and Engineering, Rotterdamseweg 137, 2628AL Delft, The Netherlands Received in revised form 14 July 2005 Abstract Melt flow plays a significant role in structure formation and redistribution of solid phase in liquid during solidification processes. The effect of melt flow along the solidification front on macro- and microstructure of an aluminium alloy is investigated. An electromagnetic pump is used as a tool to create the controlled forced flow of liquid metal. The experiments are performed on an Al–4.5% Cu alloy in a wide range of melt flow velocities and temperatures. Simulations of melt flow and solidification using “computational fluid dynamics” software are applied to clarify the structure formation and to obtain the temperature gradient along the solidification front. It is observed that the constant melt flow influences the structure formation, growth direction and grain size during solidification, i.e. the grain morphology changes from equiaxed under no-flow conditions to columnar under constant flow. The effect of melt flow on dendrite arm spacing is more complex. © 2005 Elsevier B.V. All rights reserved. Keywords: Aluminium alloy; Columnar structure; Equiaxed structure; Melt flow; Solidification 1. Introduction Melt flow plays a very important role in all casting processes. The main aim in the research of melt flow in metallurgy is to understand the behaviour and to find the means to control the fluid flow. During the last 40 years, major advances have been made towards an increased understanding of the effects of melt flow on the structure evolution. The areas of interest are focused on the understanding and predicting the following aspects: how melt flow affects grain structure and columnar to equiaxed tran- sition; thermal gradients (particularly along the solidification front) and solidification rate; segregation patterns. To verify and understand experimental results, the simulations of melt flow and the modelling of structure have been developed during the last two decades. The columnar to equiaxed transition (CET), which is the most important effect of melt flow, is a complex phe- nomenon in which columnar growth is interrupted by equiaxed growth. Several theories were developed to explain the CET, including heterogeneous nucleation in the undercooled liquid ∗ Corresponding author. Tel.: +31 152785351; fax: +31 152786730. E-mail address: a.turchin@nimr.nl (A.N. Turchin). in the central region of a casting [1,2]; floating grains from the upper surface of the casting [3]; “big-bang” nucleation at the mould wall [4]; crystal multiplication due to thermo-mechanical fragmentation promoted by forced convection [5–8]. Melt flows occurring during casting change the grain mor- phology, affecting the size and distribution of grains. In addition to promoting the CET, melt flow is found to influence the growth behaviour of the columnar grains [4–6,8–11]. Firstly, flow reduces the width of the columnar zone and, secondly, the columnar grains are observed to orient themselves in the upstream direction, i.e. into the direction of flow, which is attributed to flow-induced asymmetric thermal or concentra- tion fields around the growing crystal [1]. Feathery grains are a specific growth morphology that is found in aluminium alloys developed under conditions of strong convection and high ther- mal gradients [9]. Microstructure is also strongly affected by melt flow. For instance, the dendritic shape obtained under conditions of natural convection changes to a discernibly globular form when electro- magnetic stirring was applied [5,12], which is also demonstrated by Monte-Carlo simulations [13]. Induced fluid flow strongly influences the segregation pat- tern in solidified alloys by affecting shrinkage flow [14] and 0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2005.09.020