Acta Materialia 50 (2002) 2199–2207 www.actamat-journals.com Computational and experimental investigation of microsegregation in an Al-rich Al–Cu–Mg–Si quaternary alloy X. Yan a , S. Chen b , F. Xie a , Y.A. Chang a,* a Department of Materials Science and Engineering, University of Wisconsin-Madison, 1509 University Avenue, Madison, WI 53706-1595, USA b CompuTherm, LLC, 437 S. Yellowstone Dr., Suite 217, Madison, WI 53719, USA Received 23 March 2001; received in revised form 4 July 2001; accepted 4 July 2001 Abstract A new micromodel was developed to predict the microstructure and microsegregation in multicomponent alloys during dendritic solidification. The micromodel was directly coupled with multicomponent phase diagram calculations using a user friendly and robust phase diagram calculation engine—PanEngine. Solid back diffusion, undercooling and coarsening effects were included in this model, and the experimentally measured cooling curves were used as the inputs to carry out the microsegregation calculations. Microsegregation in Al–4.5 wt%Cu–1 wt%Si–0.5 wt%Mg alloy was experimentally investigated from directional solidification and electron probe microanalysis. Calculated results using this model are in accord with the experimental data, while results from the Scheil model deviate significantly from the experimental data.  2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved. Keywords: Al–Cu–Mg–Si quaternary alloy; Microsegregation; Solidification; Modeling 1. Introduction The Al–Cu–Mg–Si system is the basis of a large group of cast and wrought aluminum alloys. A basic understanding of the thermodynamics, phase relations, and the solidification behavior of the sys- tem is essential in developing new materials, as well as for improving the performance of existing commercial alloys. Meanwhile, microsegregation * Corresponding author. Tel.: +1-608-262-3732; fax: +1- 608-262-0389. E-mail address: chang@engr.wisc.edu (Y.A. Chang). 1359-6454/02/$22.00  2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved. PII:S1359-6454(01)00431-1 phenomena are of technical importance since they have implications on the properties of the alloys. For example, the formation of brittle non-equilib- rium phases can cause a deterioration in the mech- anical properties. Variations of concentration can lead to an inhomogeneous precipitation distri- bution after a heat treatment and therefore poor fatigue behavior. Segregation can also decrease other physical properties such as corrosion resist- ance. So, accurate predictions of microsegregation and microstructure in metallic alloys are highly important. One of the key parameters needed in the micromodeling of solidification of an alloy is the