Role of microstructure in relation to the toughness of hypoeutectic Al-Si casting alloy

In the present investigation, the toughness of A1-8Si casting alloy has been evaluated by an instrumented Charpy impact test machine, using U-notched specimens. In attempting to identify the role of the microstructure in relation to toughness, a number of microstructural parameters, including dendrite spacing (λd), mean free path (MFP) across the dendrites (i.e., edge-to-edge dendrites spacing), in addition to Si particle size, morphology and spacing, are considered. It has been found that the microstructural change has affected the toughness of the alloy under investigation in two ways, namely an increase in the initiation energy required for fracture, and an increase in the propagation energy of fracture. The presence of fine Si particles of low aspect ratio and with a beneficial degree of sphericity has affected the initiation energy as a result of an improvement in the resistance to void initiation. In the case of propagation energy of fracture, the void size and its effect of local strain concentrati...