The texture of Mg alloy dendrites is quite different from that of fcc or bcc metals because of the influence of hcp crystal lattice on the dendrite morphology evolutions during solidification. Although the simulations of dendrite morphologies for fcc or bcc metals by cellular automaton (CA) methods have been widely reported, CA simulations of magnesium alloys with hcp crystal lattice have just appeared in recent years. When performing the simulation of Mg alloy dendrites with a CA method on a square mesh, the artificial anisotropy of growth kinetics introduced by the square mesh makes it hard to reflect the texture of Mg alloy dendrites, which shows the six–fold symmetry instead of four–fold symmetry of bcc or fcc metal dendrites.

In the present paper, a two dimensional CA model has been developed for simulating the dendrite morphology evolution of castMg alloys. The model employs two sets of meshes to perform the numerical simulation, where a hexagonal mesh is used to perform CA calculation to reflect the texture of Mg alloy dendrites, and an orthogonal mesh is used to solve the mass transportation equation. The two sets of meshes are coupled by an interpolation method. By employing the two–set mesh method, the texture of Mg alloy dendrites is well reflected and the undesired artificial growth kinetics introduced by square mesh is avoided. In the model, the growth kinetics of dendrite tips was determined by the difference between local equilibrium and local actual compositions obtained by solving the solute transport equation. With this calculation method for growth kinetics, the solid fraction of interface CA cell can be obtained directly from the solute field, which decreases the computational cost greatly. The model was applied to simulate the single dendrite evolution and columnar dendrite growth of AZ91D Mg alloy, as well as multi–dendrite growth and grain size of Mg–10Gd–2Y–0.5Zr (mass fraction, %) alloy step–shaped castings. To validate the current model, permanent mold sample castings of AZ91D Mg alloy and step–shaped castings of Mg–10Gd–2Y–0.5Zr alloy were produced. Optical metallographic examinations were performed on specimens of these two Mg alloys, and grain sizes were measured on solution treated specimens of Mg–10Gd–2Y–0.5Zr alloy. The simulated and experimental results were compared.