Constitutive and stochastic models to predict the effect of casting defect on the mechanical properties of high pressure die cast AlSi9Cu3(Fe) alloys

The effect of casting defects on mechanical properties of a high-pressure die-cast AlSi9Cu3(Fe) alloy is reported. A series of U-shaped structural components are cast using a combination of injection parameters and pouring temperatures in order to generate different types and amount of casting defects throughout the casting. It has been found that castings contain defects, primarily pores and oxides, and that the presence and distribution of these defects are highly sensitive to the process conditions. Moreover, significant variations of the defect distribution have, however, been found in castings produced under the same conditions, indicating the stochastic nature of defects in die castings. The tensile properties are affected by the amount and distribution of defects and are determined by the defect area fraction. The influence of casting defects on mechanical properties are investigated through a theoretical verification based on constitutive and stochastic models. The analytical approach, based on the Ghosh constitutive model of tension instability, correctly indicates the trends of the experimental results, while the Weibull statistics evidences how the scale parameter and the Weibull modulus are strongly affected by the casting conditions. An integrated stochastic-analytical approach is then proposed and it appears to be applicable to describe the tensile properties in terms of fractographic defects and cumulative failure probability Pi.