Effects of eutectic silicon particles on tensile properties and fracture toughness of A356 aluminum alloys fabricated by low-pressure-casting, casting-forging, and squeeze-casting processes

Effects of eutectic silicon particles on tensile properties and fracture toughness of three A356 aluminum alloys were investigated in this study. These A356 alloys were fabricated by casting processes such as low-pressure-casting, casting-forging, and squeeze-casting, and their tensile properties and fracture toughness were analyzed in relation with microfracture mechanism study. All the cast A356 alloys contained eutectic Si particles segregated along solidification cells, and the distribution of Si particles was modified by squeeze-casting and casting-forging processes. Microfracture observation results showed that eutectic Si particles segregated along solidification cells were cracked first, but that aluminum matrix played a role in blocking crack propagation. The cast-forged alloy had the best hardness, strength, ductility, and fracture toughness because of the matrix strengthening and homogeneous distribution of eutectic Si particles due to forging process. The squeeze-cast alloy was considerably refined and densified, but this refined microstructure resulted in the reduced spacing between eutectic Si particles which worked as fracture initiation sites, thereby leading to the lower fracture toughness than the PC alloy. (c) 2007 Elsevier B.V. All rights reserved.