Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The effects of electromagnetic stirring, ultrasonic treatment (UT), and their combination on the Si particles refinement in a hypereutectic Al-Si alloy (A390) were examined. All three physical methods yielded a considerable change in the shape and size of the particles, with UT producing the finest size. The creation of holes inside the Si particles via the explosion of cavitation bubbles was determined to occur before fragmentation of primary Si. In addition, transmission electron microscopy analysis revealed twin formation on primary Si particles by application of an external field in the liquid. UT of the melt was sufficient to produce fine primary Si particles with average size of similar to 12 A mu m. The primary Si particles refinement and eutectic Si modification improved the mechanical properties.26419001907Conselho Nacional de Desenvolvimento Cientifico e Tecnologico CNPq [190088/2014-1]Fundacao de Amparo a Pesquisa do Estado de Silo Paulo (FAPESP) [2013-09961-3, 2015-22143-3]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)