Two-phase modeling of mushy zone parameters associated with hot tearing

Abstract

A two-phase continuum model for an isotropic mushy zone is presented. The model is based upon the general volume-averaged conservation equations, and quantities associated with hot tearing are included, i.e., after-feeding of the liquid melt due to solidification shrinkage is taken into account as well as thermally induced deformation of the solid phase. The model is implemented numerically for a one-dimensional model problem with some similarities to the aluminium direct chill (DC) casting process. The variation of some key parameters that are known to influence the hot-tearing tendency is then studied. The results indicate that both liquid pressure drop due to feeding difficulties and tensile stress caused by thermal contraction of the solid phase are necessary for the formation of hot tears. Based upon results from the one-dimensional model, it is furthermore concluded that none of the hot-tearing criteria suggested in the literature are able to predict the variation in hot-tearing susceptibility resulting from a variation in all of the following parameters: solidification interval, cooling contraction of the solid phase, casting speed, and liquid fraction at coherency.

A coupled thermomechanical, thermal transport and segregation analysis of the solidification of aluminum alloys on molds of uneven topographies

“…Clearly, the peak value is observed for a 566 Cu concentration of 1.8%, which makes this particular alloy 567 most susceptible to hot-tearing. This observation was previously 568 made in [17,18] and verified in the numerical studies of Tan and 569 Zabaras in [25], where inverse segregation and solute transport 570 were neglected. Non-uniform heat extraction at the metal-mold 571 to that observed in [25].…”

The importance of viscoplastic strain rate in the formation of center cracks during the start-up phase of direct-chill cast aluminum extrusion ingots

“…As suggested elsewhere, [1,6,10,23] these quantities are studied at a position for which the solid fraction has a given critical value here taken to be 0.95, [23] which corresponds to a temperature of 600°C. Note that this critical position does not correspond to a material point.…”

“…In addition to the casting speed, [7] parameters such as grain refinement, starting block material and shape, and water cooling are also known to have an effect on the hot tearing tendency. [8,9] Recent two-phase models [10,11] attempt to quantify the interactions between liquid feeding and thermally-induced deformation in the mushy zone. The purpose of the present work is to identify, by comparison between experimental observations and computer simulation, a physical quantity whose variation could best explain the observed trends in center cracks during the start-up phase of DC cast round extrusion ingots.…”

Rheological behavior of Al-Cu alloys during solidification constitutive modeling, experimental identification, and numerical study

“…These thermal strains can lead to the formation of casting defects such as macrosegregations (if liquid feeding is able to accommodate tensile strains) or porosity that may degenerate into hot tears. In order to understand the formation of these defects, important modeling efforts have been carried out recently toward the development of thermomechanical models for the solidification of alloys [4,5,6] and of hot tearing criteria. [7] At some point, these models require constitutive equations addressing the rheological behavior of the mushy zone.…”