Microstructure and fracture of SiC-particulate-reinforced cast A356 aluminum alloy composites

Abstract

A microstructural analysis of local microfracture of cast A356 Al-SiCp composites fabricated by permanent mold re-casting and squeeze-casting methods was made. Notch fracture toughness tests were conducted on these composites to identify critical fracture parameters using a stress-modified critical-strain criterion. The composite microstructure shows continuous networks of densely populated SiC and eutectic Si particles along the intercellular regions. Squeeze casting produces a more homogeneous structure and larger spacing of brittle particles and increases the tensile ductility and fracture toughness, while strength levels are almost identical to the re-casting case. The calculated values of the microstructurally characteristic distance l* for the re-cast and squeeze-cast composites are about 40 mu m, which is comparable to the average sizes of the intercellular network. However, the reference critical strain <(epsilon)over bar>(0)* for squeeze casting is larger than that for re-casting, showing a trend to higher ductility and fracture toughness.