Metal casting is a process known to mankind for millennia. The first copper castings
date back to about 3000 B.C. in Mesopotamia (modern day Iraq). Throughout history,
the applications of casting (tools, weapons, etc.) have practically dictated the
course of civilization. After 5000 years of technological advances, metal casting is
as relevant as ever.

At Los Alamos National Laboratory, metal casting is undertaken in several
facilities. Computer simulations of casting operations provide a predictive
capability that minimizes the need for costly and accident-prone experiments and
trial-and-error.

Several phase changes typically occur in casting operations. First, a solid material
is melted via Joule heating and then poured into a mold. Afterwards, the
high-temperature liquid solidifies adopting the desired shape of the mold. Finally,
the casting undergoes a series of solid-solid phase changes as it reaches room
temperature. Therefore, the modeling of phase-change is crucial in any simulation of
casting processes. The temperature range at which the phase change occurs depends on the composition of the alloy (a relationship described in the equilibrium phase diagram of the alloy). The composition, however, changes with space and time throughout the casting as the alloying elements are transported throughout the
liquid and diffused through the solid.

Heat transfer in the system and phase-change are closely related, therefore TRUCHAS solves the equations for enthalpy and phase change in a coupled fashion. Enthalpy rather than temperature is employed as the independent variable, a technique favored when modeling phase-change problems. The coupled system of equations includes enthalpy transport by conduction,radiation,convection, and Joule heating as well as equilibrium relations stemming from the phase diagram representation.