TearSim: A two-phase model addressing hot tearing formation during aluminum direct chill casting

Abstract

A two-phase mathematical model for the study of hot tearing formation is presented. The model accounts for the main phenomena associated with the formation of hot tears, i.e., the lack of feeding at the late stages of solidification and the localization of viscoplastic deformation. The model incorporates an advanced viscoplastic constitutive model for the coherent part of the mushy zone, allowing for the possibility of dilatation/densification of the semisolid skeleton under applied deformation. Based on quantities computed by the model, a hot tearing criterion is proposed where liquid feeding difficulties and viscoplastic deformation at the late stages of solidification are taken into account. The model is applied to study hot tearing formation during the start-up phase for direct-chill (DC) casting of extrusion ingots, and to discuss the effect of different phenomena and process parameters. The modeling results are also compared to experimentally measured hot tearing susceptibilities, and the model is able to reproduce known experimental trends such as the effect of the casting speed and the importance of the design of the starting block.

Cold Cracking Development in AA7050 Direct Chill–Cast Billets under Various Casting Conditions

“…[18] Between this temperature and the so-called merge-properties temperature, low-temperature strain hardening equations (Ludwik and ALSPEN) are merged with the mushy zone equations (cohesion model), [30] and details on the models may be found elsewhere. [31] The merge-properties temperature is defined to be a few degrees below the solidus 728 K (455°C). Between the merge-properties temperature and rigidity temperature (onset of thermal contraction in the mushy zone, 832 K (559°C), which was measured experimentally by authors using the solidification contraction setup [32] ), the cohesion model [30] was used to simulate the thermomechanical behavior of the material in the mushy zone.…”

Cold cracking in DC-cast high strength aluminum alloy ingots: An intrinsic problem intensified by casting process parameters

“…The extended Ludwik's equation [30] and ALSPEN equations [27] were used to simulate the viscoplastic behavior of the material below the onset temperature of strain hardening (390 • C) [27]. Between this temperature and the so-called merge-properties-temperature, low temperature strain hardening equations (Ludwik and ALSPEN) are merged with the mushy zone equations (a cohesion model) [31] and details on the models may be found elsewhere [32]. The merge-propertiestemperature is defined to be a few degrees below the solidus (455 • C).…”

Two-Phase Modeling of Hot Tearing in Aluminum Alloys: Applications of a Semicoupled Method

“…This term becomes a source term in the mass conservation equation. The latter is combined with Darcy's law for the calculation of the pressure p l in the liquid, to give [8] …”

“…From the modeling point of view, continuum-scale approaches have been developed, in order to predict the occurrence of hot tears at least semiquantitatively. [7,8] In order to obtain a quantitative numerical tool for the prediction of hot tearing, several important contributions have been reported. First, a description of the mechanical behavior of mushy alloys is necessary.…”

“…Moreover, they must be addressed at the scale of the entire process. A method for doing this was proposed recently by M'Hamdi et al; [8] the resulting software is known as TearSim (SINTEF Materials Technology, Oslo, Norway). These authors proposed a fully coupled resolution scheme in which both the interdendritic feeding and the deformation of the casting are calculated simultaneously.…”