Three-Dimensional Micromechanical Modelling of Deformation Behaviour of Rheocast A356 Alloy

Abstract

In this study, a micromechanical approach is used to investigate the deformation behaviour of rheocast Al–7Si–0.3Mg alloy. The alloy is rheocast using a cooling slope (at 45° and 60° angles) after melt treatment with a grain refiner addition (0.15% by weight Al–5Ti–1B master alloy). The comparison is made with the conventionally cast sample of the same alloy. Microscale instability of the rheocast alloy occurring at the onset of deformation, due to the strain incompatibility between the primary and eutectic phases, causes stress and strain localization as well as a triaxial state of stress, which subsequently governs void initiation and growth in the said alloy. A commercial finite element (FE) code ABAQUS is used to simulate microscale deformation behaviour of the three-dimensional representative volume elements (RVE) of approximated and as well as actual microstructure of the said alloy under uniaxial tensile loading. Although, globally uniaxial tensile loading is applied over the RVEs, however, stress triaxiality causes local variation of stress state, as evident from biaxial tensile stress state observed at grain boundaries of the above-mentioned RVEs, whereas uniaxial tensile stress is observed at the central location of these RVEs. Simulation results reveal that the macroscale deformation behaviour of the said alloy is determined by its microscopic features such as shape, size, distribution (spread of primary Al grains within the volume element) and volume fraction of primary Al grains. Moreover, distribution as well as volume fraction of eutectic Si also plays deciding role in deformation behaviour of the alloy. The FE model predictions of improved deformation behaviour/stress distribution evidenced in the rheocast + grain refined alloy is validated via phase level mechanical properties of the alloy, estimated from nanoindentation.