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] [2] [3] [4] [5] . Hypereutectic Al-Si alloys are particularly preferred as they exhibit a low coefficient of thermal expansion and a hightemperature strength [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] . These properties are attributed to the presence of the primary silicon phase in

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... 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