Abstract
Fracture toughness of unidirectionally solidified Al-7%Si and Al-7%Si-0.3Mg alloys was evaluated. Size, shape and distribution of silicon particles were varied by controlling freezing rate and subsequent solution heat treatment time at 530°C. Refining and morphological change of the silicon particles from acicular to granular by prolonged solution heat treatment cause considerable increase in the absorbed energy. Increase in the absorbed energy of the alloys solution treated for a short time up to 5hrs was resulted from increases both in initiation (Ei) and propagation energies (Ep), and that for a prolonged time was resulted only from increase in Ep. Proper solution heat treatment of the alloys having smaller arm spacing leaded to higher impact strength because of the difficulty of crack propagation. The fracture toughness was increased with reducing the radius of curvature at the tip of silicon particles. The alloys solution heat treated for 5hrs contained finest silicon particles and had the maximum fracture toughness.
