A l u m i n u m-b a s e d a l l o y s a r e t h e m o s t w i d e l y used engineering materials in the automotive and aeronautical industries due to their high strength-toweight ratio and high wear resistance [1-5]. Hypereutectic Al-Si alloys are particularly preferred as they exhibit a low coefficient of thermal expansion and a hightemperature strength [2-11]. These properties are attributed to the presence of the primary silicon phase in the aluminum matrix [7]. The castability of the alloy is also enhanced by the addition of silicon in the alloying process, by improving the melt flow [12]. However, the conventional casting procedures produce coarse grains of the primary silicon. These coarse grains are prone to premature crack initiation and fracture when subjected to tension loading [3,5,6,9] , which decrease the mechanical properties of the alloy [1]. Many methods are used in the refinement and modification of the primary silicon phase to achieve optimum morphology for improving the mechanical