In this research an aluminum alloy Al-7Si-0.3Mg (A356.1) was cast by a semi-solid casting technique. The parameters like stirring time, temperature and heat treatment conditions on mechanical properties were investigated and obtained optimum conditions. The cylindrical specimens with a height of 40 mm and a diameter of 160 mm were cast in a permanent mould. Mechanical properties plus fracture surfaces of specimens were identified as brittle or ductile fracture. Results showed that the optimum temperature and time for semi-solid cast A356.1 aluminum alloy, with 700-rpm shear rate were 590 degrees C and 20 min, respectively. The most appropriate heat treatment cycle, to achieve the best tensile properties was annealing at 520 degrees C for 6 h, followed by quenching in 40 degrees C water and then aging at 160 degrees C for 6 h. The most important feature of this study was the conversion of fracture mechanism mode from brittle to ductile in result of changing the morphology of globules and the matrix. (c) 2005 Elsevier B.V. All rights reserved.1693382387