A 3-D coupled hydromechanical granular model for simulating the constitutive behavior of metallic alloys during solidification

Abstract

A three-dimensional (3-D) coupled hydromechanical granular model has been developed and validated to directly predict, for the first time, hot tear formation and stress-strain behavior in metallic alloys during solidification. This granular model consists of four separate 3-D modules: (i) the solidification module is used to generate the solid-liquid geometry at a given solid fraction; (ii) the fluid flow module (FFM) is used to calculate the solidification shrinkage and deformation-induced pressure drop within the intergranular liquid; (iii) the semi-solid deformation module (SDM) simulates the rheological behavior of the granular structure; and (iv) the failure module (FM) simulates crack initiation and propagation. Since solid deformation, intergranular flow and crack initiation are deeply linked together, the FFM, SDM and FM are coupled processes. This has been achieved through the development of a new three-phase interactive technique that couples the interaction between intergranular liquid, solid grains and growing voids. The results show that the pressure drop, and consequently hot tear formation, depends also on the compressibility of the mushy zone skeleton, in addition to the well-known contributors (lack of liquid feeding and semi-solid deformation).

Prediction of Hot Tear Formation in Vertical DC Casting of Aluminum Billets Using a Granular Approach

“…5. Figure 3 shows a qualitative comparison of the evolution in the semisolid microstructure during the tensile deformation between (I) predictions of the granular model and (II) observations via x-ray tomography 12 at three different times of deformation.…”

“…where v 1 is the microscopic liquid velocity, f 1 is the feeding coefficient, 5 and p m the metallostatic pressure at g s = 0. Using Darcy's law to approximate fluid flow in the mushy zone exterior to the representative volume, f 1 at the surface z = L z is calculated to be 2 9 10 À2 lm/Pa/s.…”

“…During semisolid deformation tests, cracks form on the cast surface because ambient air can fill the growing cavity of the crack. In this situation, the criterion for crack formation is based on the overpressure required to overcome the capillary forces at the liquid-gas interface, 5,6 and thus, a hot tear will form once the liquid pressure in a channel is such that…”

“…The deformation predictions obtained from this model were validated against experimental tensile test data acquired from semisolid aluminum alloys. 5 In the current work, the hydromechanical coupled granular model is used to predict the formation of hot tearing in an industrial aluminum alloy, AA5182, during semicontinuous DC casting of round billets.…”

“…The hydromechanical coupled model for solidification and semisolid deformation, [3][4][5] which was recently developed by Sistaninia et al uses a granular approach to fulfill the above requirements and simulate hot tearing. The use of a granular approach enables each grain to exist as a discrete element while allowing for efficient simulation of an ensemble of grains making up the microstructure.…”