Modelling of semi-solid processing using a modified temperature-dependent power-law model

Abstract

A fairly simple one-phase rheological model has been implemented into a commercial fluid flow finite element software to simulate mould filling during the semi-solid processing (thixoforming) of aluminium alloys. This model is of purely viscous nature. Its temperature-dependent viscosity is a power-law function of the shear rate with a shear rate cut-off. The constitutive parameters of this model were determined for a rheocast A356 alloy. For that purpose, simulation results were compared with instrumented thixoforming experiments performed on a production-scale injection machine. The selected configuration was that of a transient flow near a bifurcation, i.e. obstruction of an established Poiseuille-type flow by a shaft placed at the centre of a tube. Using these parameters, the model was then further validated by comparing the simulation of an axisymmetric reservoir mould filling with the shape of solidified shells obtained after interrupted injection experiments.