Journal of Alloys and Compounds 470 (2009) 589–599 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Cellular growth during transient directional solidification of hypoeutectic Al–Fe alloys Pedro R. Goulart, Kleber S. Cruz, Jos ´ e E. Spinelli, Ivaldo L. Ferreira, No ´ e Cheung, Amauri Garcia ∗ Department of Materials Engineering, State University of Campinas, UNICAMP, PO Box 6122, 13083-970 Campinas, SP, Brazil article info Article history: Received 15 January 2008 Received in revised form 3 March 2008 Accepted 6 March 2008 Available online 14 April 2008 Keywords: Metals and alloys Microstructure Thermal analysis abstract Investigations have been made of the solidification structure of three hypoeutectic Al–Fe alloys, which were directionally solidified under unsteady-state heat flow conditions. The experiments have been car- ried out by using a casting assembly, which was designed in such way that the heat was extracted only through the water-cooled system at the casting bottom, promoting vertical upward directional solidifi- cation. A combined theoretical/experimental approach was used in order to quantitatively determine the solidification parameters: tip growth rate and cooling rate of Al–0.5 wt%Fe, Al–1.0 wt%Fe and Al–1.5 wt%Fe alloys castings. The experimental results include transient metal/mold heat transfer coefficients, h g , deter- mined from comparisons between the experimental thermal profiles in castings and the simulations provided by a finite difference heat flow program. Cellular microstructures prevailed along the entire cast- ings for any alloy experimentally examined. The cell spacing variation with cooling rate and tip growth rate has been characterized by -0.55 and -1.1 experimental power laws, respectively. The experimental cell spacings were compared with the theoretical predictions furnished by cellular growth models. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Aluminum–iron alloys are of considerable commercial interest, partly because iron is almost invariably present at significant lev- els (0.2–1.0wt%). Iron is added intentionally in some alloys, e.g.: Al–Cu–Ni alloys to increase the high-temperature strength; Al–Ni alloys to increase the corrosion resistance in presence of steam at elevated temperatures and in conductor materials in order to increase the mechanical strength without substantial conductivity loss [1,2]. Under equilibrium solidification conditions, any iron in excess of its solid solubility limit (0.04 wt%Fe) forms a eutectic consti- tuted by an Al-rich primary phase and intermetallic Al 3 Fe particles. However, during non-equilibrium solidification typical of DC cast- ings considerably different cooling rate exists at the ingot surface and at the center, causing the formation of metastable Al m Fe and Al 6 Fe intermetallic phases in addition to the stable Al 3 Fe phase [3]. According to Allen et al. [4], the as-cast structures obtained from DC casting operations are also characterized by high levels of macrosegregation, which is a consequence of an enrichment of iron content near the surface of the Al–Fe castings caused by solution rejection during solidification. It is well known that ∗ Corresponding author. E-mail address: amaurig@fem.unicamp.br (A. Garcia). changes in the alloy composition and cooling rate during solidifi- cation can affect not only the cellular/dendritic growth but also the distribution of eutectic mixture and intermetallic particles. Such modifications may strongly influence mechanical strength and cor- rosion resistance. Some recent studies have pointed out the effect of microstructure, and particularly of the scale of the dendritic array on the resulting mechanical properties [5–9]. If the dendrite arm spacing is reduced, then the mechanical properties of the cast alloy are invariably improved. Further, it has also been recently reported in the literature that the macrostructural and the microstructural morphologies have a strong influence on the corrosion resistance [9–14]. Many studies have been made of the “as-solidified” microstruc- tures of binary alloys in order to determine the interdependence of cellular and dendrite arm spacings and solidification parame- ters, both theoretically and experimentally [15–34]. Data on arm spacings have been derived from alloys which have been melted in situ and then unidirectionally solidified under steady-state or transient conditions. Recently, G ¨ und ¨ uz et al. [34] have investigated the relationship between the processing parameters and cellular spacing during steady-state solidification of Al–Ti dilute alloys at high growth rates. However, studies focusing on experimental cel- lular spacings for transient solidification conditions remain scarce in the literature. Rocha et al. [26] and Rosa et al. [33] have car- ried out solidification experiments with hypoeutectic Sn–Pb and Pb–Sb alloys, respectively. They essentially observed that, under 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.03.026