The microstructure of the melt-spun Al-23 wt% Sr alloy has been investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The phases present in the melt-spun Al-23 Sr alloy are identified to be alpha-Al and Al4Sr, identical to those in the ingot-cast alloy. Rapid solidification has a marked effect on the morphology of the primary Al4Sr phase and the preferred orientations of its dendrites in the Al-23 Sr alloy. The primary Al4Sr phase in the melt-spun Al-23 Sr alloy is dendritic, quite different from the coarse slab-like Al4Sr in the ingot-cast alloy. Some primary Al4Sr dendrites develop into secondary branches in directions 45degrees to the dendrite trunks but others continue to branch in the directions perpendicular to the trunks. Moreover, tertiary and higher-order branches are also observed in the melt-spun Al-23 Sr alloy. The preferred crystallographic orientations of the Al4Sr dendrites with 45degrees and 90degrees branches are determined to be the <1 0 0> and <1 1 0> directions, respectively. Rapid solidification enhances the formation of the Al4Sr dendrites with 45degrees branches in the <1 0 0> direction. (C) 2002 Elsevier Science B.V. All rights reserved.