Modeling of microstructural evolution with tracking of equiaxed grain movement for multicomponent Al-Si alloy
- PDF / 1,191,999 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 82 Downloads / 175 Views
I. INTRODUCTION
SOLIDIFICATION of castings is driven by several physical phenomena including nucleation and growth of grains due to melt undercooling, natural convection caused by thermosolutal buoyancy, solidification shrinkage, and grain movement induced by melt convection and shrinkage. They affect the solidification behavior of casting and the final microstructure. Since the microscopic scale of dendritic or eutectic evolution and the macroscopic scale of global heat and fluid flow are different by several orders of magnitude, solving the solidification process as a microscopic problem is not trivial. It requires grid resolutions of at least the dendritic or eutectic arm spacing for numerical modeling so that the detailed morphologies can be captured. Such direct numerical modeling is impractical even with the computational power available today. To make the computational task tractable, micro/macro models have been developed. In the early work on modeling of microstructural evolution, it was assumed that solidification kinetics (SK) does not influence macro/transport (MT), and the two computations were performed uncoupled. Typically, temperature or cooling rate was evaluated with macromodeling, and the microstructure length scale that includes dendrite arm spacing and volumetric grain density was calculated based upon empirical equations correlating it to the local solidification BING JIAN YANG, formerly Postdoctoral Research Scholar, Solidification Laboratory, The University of Alabama, is Research Associate, Department of Materials and Metallurgical Engineering, Queen’s University, Kingston, ON, Canada. DORU M. STEFANESCU, University Research Professor and Director, Solidification Laboratory, and JOSE LEON-TORRES, Graduate Research Assistant, Department of Metallurgical and Materials Engineering, are with The University of Alabama, Tuscaloosa, AL 35487. Manuscript submitted September 26, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS A
time and/or cooling rate. Later, models that solved coupled MT and SK were proposed. The basic assumptions of some relevant models will be summarized in the following paragraphs. A first group of models solve heat conduction combined with SK while neglecting melt convection and solid transport in the calculation domain.[1,2] They are energy-open but mass-closed. The governing equation does not include the convection term. To predict macrosegregation, models that concomitantly solve the mass, energy, momentum, and species macroscopic conservation equations have been proposed.[3,4,5] However, these models do not couple the SK. The solid fraction is determined with the Scheil model or from the lever rule. Convective terms are used in the governing equations, but they ignore the advection of latent heat and solid movement during solidification. Only the heat flux transported by fluid flow is described. Some models ignore shrinkage flow. It is well established that grain movement occurs during equiaxed grain solidification because of natural convection and solidification shrinkag
Data Loading...
