TWO- AND THREE-DIMENSIONAL CELLULAR AUTOMATON MODELS FOR SIMULATING DENDRITE MORPHOLOGY EVOLUTION OF CAST MAGNESIUM ALLOYS

摘要

Two- and three-dimensional cellular automaton (CA) models have been developed for simulating the dendrite morphology evolution of cast magnesium alloys. In the two-dimensional (2-D) model a hexagonal mesh is used to perform CA calculations to reflect the texture of Mg alloy dendrites, and other calculations are carried out by employing an orthogonal mesh. In the three-dimensional (3-D) model, the CA calculation is performed using a mesh that is defined by the hexagonal close-packed (HCP) crystal lattice and other calculations is carried out by using a cubic mesh. The two sets of mesh are coupled by interpolation method. The growth kinetics of dendrite tips is determined by the difference between local equilibrium composition and local actual composition obtained by solving the solute transport equation. To test the capabilities of the model, simulations of 2-D and 3-D columnar dendrite growth as well as 3-D equiaxed growth of single dendrite were carried out. Samples were obtained from AZ91D Mg alloy and Mg-10Gd-2Y-0.5Zr (wt%) Mg alloy castings and optical metallographic examinations were performed for validating the present model. The simulated and experimental results were compared.