Papers by Author: Asbjørn Mo

Abstract: A constitutive equation for thermal strain in the mushy zone has recently been established [1]. The parameters in this constitutive relation are in the present study determined for the commercial alloys A356, AA2024, AA6061 and AA7075 in addition to an Al-4 wt% Cu alloy by combining experimentally measured contraction of a cast sample with thermomechanical simulations. The constitutive equation for thermal strain in the mushy zone reflects that there is no thermal strain in the solid part of the mushy zone at low solid fractions and that the thermal strain in the mushy zone approaches thermal contraction in fully solid as the solid fraction increases towards one. Experiments were performed at cooling rates in the range from 2 to 5.5 °C/s. The solid fractions when the tested alloys start to contract, gs^th , are in the range from 0.63 to 0.94. Grain refinement increases gs^th for all the tested alloys.

Abstract: An experimental set-up for investigating macrosegregation formation due to deformation of an isotropic metallic mushy zone is presented. In the experiment, a semisolid Al-5.9wt%Cu sample is isothermally and non-uniformly compressed. Concentration and eutectic fraction are measured along selected lines, after quenching the sample. Results show that interdendritic liquid is pressed out of the central part of the sample to its outer part, increasing the concentration in this region. The experimental test is then addressed by a two-phase continuum model recently presented elsewhere. The modelling results show the same tendencies observed experimentally, although local variations in composition are not well correlated. Suggestions for future work are made.