Casting defects and the tensile properties of an Al-Si-Mg alloy

Samples containing either entrapped dress and oxide films, gas porosity or small drilled holes have been used to study the effect of different types of defects on the tensile behaviour of an Al-7Si-0.4Mg casting alloy. The tensile properties show little or no correlation with the bulk porosity content, especially in the case of samples containing dress and oxide films. In contrast, the decrease in tensile ductility and strength correlates with the area fraction of defects in the fracture surface of the samples. The experimental results are in agreement with the predictions of a simple analysis based on models for the growth of a plastic instability in a tensile sample.