3D connectivity of eutectic Si as a key property defining strength of Al-Si alloys

The relationship between microstructure and mechanical behavior of the eutectic phase in hypoeutectic Al-Si alloys is analyzed empirically using two experimental and thirteen synthetic microstructures. For all microstructures, a morphological analysis is combined with mechanical stress-strain simulations performed via finite element method (FEM). The synthetic microstructures are generated by a stochastic microstructure model that gives a realistic description of the eutectic Si in Al-Si alloys. The stochastic model was developed on the basis of a 3D image of a real Sr-modified Al-Si alloy and is used to generate a large variety of virtual 3D structures of eutectic Si that differ from each other by the number of Si particles, their degree of branching, and connectivity. In the simulation study, it is shown that highly connected and branched morphologies of Si are beneficial to the strength of the material. Besides, when the connectivity of Si is low, i.e. when an Al matrix is reinforced by discrete (disconnected) particles of Si, the strength of the material increases with the number of those particles. The Euler number is shown to be highly effective in characterizing the connectivity and is closely related to the strength of the material. (C) 2016 Elsevier B.V. All rights reserved.