In the present work the fluxing technique was applied to the Sn-51 wt.% Se hypoeutectic alloy. The aim was to study the influence of the undercooling on the microstructure of this alloy, particularly concerning the formation of oriented microstructure and even some metastability occurrence. High undercooling (63 degreesC) was achieved for the primary SnSe phase leading to an oriented microstructure in the firstly solidified region. Although the undercooling for the eutectic was not so high (19 degreesC) morphological changes were observed. The rapid movement of the interface interfered with cooperative eutectic growth producing an irregular eutectic in the first region to solidify followed by a fine lamellar and directional eutectic. In order to detect some supersaturated solid solution in the SnSe phase a precise lattice parameter measurement was done from the accurate performed X-ray diffraction (XRD) on the firstly solidified region of the sample. (C) 2003 Elsevier B.V. All rights reserved.37541671142146