A rationale for the quality index of Al-Si-Mg casting alloys

The quality index introduced on empirical grounds by Drouzy, Jacob and Rich ard(1) is widely used by the casting industry as a tool for predicting the effect of solidification rate, chemical additions and heat treatment on the ductility and tensile strength of Al-7Si-Mg casting alloys. A drawback of the approach is its lack of physical justification. A simple analytical mod el is used to derive the quality index charts for Al-7Si-0.4 Mg alloys and to provide a physical meaning to the parameters involved. It is shown that the quality index relates to the fraction of uniform deformation available to the material. The application of the concept to Cu-containing alloys is also discussed.