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Local mechanical properties in aluminum cast components are inhomogeneous as a consequence of spatial distribution of microstructure, e.g., porosity, inclusions, grain size and arm spacing of secondary dendrites. In this work, the effect of porosity is investigated. Cast components contain voids with different sizes, forms, orientations and distributions. This is approximated by a porosity distribution in the following. The aim of this paper is to investigate the influence of initial porosity, stress triaxiality and Lode parameter on plastic deformation and ductile fracture. A micromechanical model with a spherical void located at the center of the matrix material, called the representative volume element (RVE), is developed. Fully periodic boundary conditions are applied to the RVE and the values of stress triaxiality and Lode parameter are kept constant during the entire course of loading. For this purpose, a multi-point constraint (MPC) user subroutine is developed to prescribe the loading. The results of the RVE model are used to establish the constitutive equations and to further investigate the influences of initial porosity, stress triaxiality and Lode parameter on elastic constant, plastic deformation and ductile fracture of an aluminum die casting alloy. [ABSTRACT FROM AUTHOR]