Micromechanical modelling of the elastic–viscoplastic response of metallic alloys under rapid compression in the semi-solid state

Semi-solid processing is used commercially to produce a variety of components and it is therefore important to be able to model the die fill. Micromechanical modelling is one approach to this. Here we compare the micromechanical predictions for the load vs. displacement, in tests where a cylindrical billet is rapidly compressed, with previous experimental findings for an A356 aluminium alloy. Purely viscoplastic modelling is shown to be inadequate. We propose a new model that clearly associates the elastic-type response with the saturated solid skeleton. This gives much more accurate prediction of the initial peak and of the form of the curve as the skeleton breaks down under load. In agreement with experiment, the model predicts the time for the solid skeleton breakdown and that the peak load increases with increasing ram speed and with decreasing fraction liquid.