Macrosegregation of ternary Al–4·5wt-%Cu–1·0wt-%Mg alloy in horizontal direct chill casting: implementation of non-equilibrium microsegregation model

Abstract

An extended and modified continuum mixture model for macrosegregation in solidifying alloys is applied to the case of horizontal direct chill casting (HDC) of a ternary Al–4·5Cu–1·0Mg (wt-%) alloy. A thermodynamic closure model for a Al–Cu–Mg alloy is coupled with an extended mixture continuum model to obtain steady state macrosegregation fields for the different casting parameters (e.g. casting speed, inlet superheat and inlet plenum position) in this study. Macrosegregation calculations were performed assuming that the solid forms a rigid and stationary network in all parts of the mushy zone. A microsegregation non-equilibrium model is used to calculate phase fraction compositions and phase distributions. The Cu exhibits more segregation compared to the previous study of a binary Al–Cu alloy, while Mg has a similar segregation profile in all cases but less pronounced. The phase compositions show that Cu is mostly distributed in secondary and ternary phases, while Mg is uniformly configured in the primary (Al) and ternary phase (Al2CuMg). The primary Al phase is dominant (over 90%) in all cases, with highest peaks in depleted regions below the centreline of slab, except in the case where the inlet plenum is positioned on the bottom of the refractory plate due to a different flow pattern.