Papers by Author: Zhi Qiang Han

Abstract: A three-dimensional (3-D) cellular automaton (CA) model for simulating the dendrite morphology of cast Mg alloys has been developed. In the model a technique based on two sets of mesh is utilized to perform the simulation to reproduce the texture of Mg dendrites. The CA calculation is performed using a set of mesh that is defined by the hexagonal close-packed (HCP) crystal lattice, and other computations are carried out by using a cubic mesh. The two sets of mesh are coupled by using interpolation method. The kinetics of the solid-liquid interface is obtained directly by the difference between local equilibrium composition and local actual composition given by the solute transport equation. The model was used to simulate 3-D columnar growth of sixteen grains and 3-D equiaxed growth of a single dendrite of AZ91D alloy. Permanent mold castings of AZ91D alloy were produced and sampled for optical metallographic examinations, and the simulated results were compared with the metallographic results.

Abstract: A cellular automaton (CA) model has been developed for simulating the microstructure evolution and dendrite morphology of cast magnesium alloys. 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. Two sets of meshes, a hexagonal mesh and an orthogonal mesh, are used in the model to perform the simulation. The hexagonal mesh is used to perform CA calculation to reflect the texture of Mg alloy dendrites, and the orthogonal mesh is used to solve the solute transport equations. The model was applied to simulate single dendrite evolution and columnar dendrites growth of AZ91D Mg alloy, as well as multi-grain growth of Mg-10Gd-2Y-0.5Zr (wt%) Mg alloy. Permanent mold step-shaped castings of the two Mg alloys were poured and metallographic examinations were carried out for validating the present model. The simulation results agree well with metallographic results. The model can be applied to simulate the microstructure evolution and dendrite morphology of magnesium alloys.

Abstract: In this paper, a simplified cellular automaton (CA) model was proposed for modeling the evolution of microstructure in solidification process of AZ91D magnesium alloy. Since the calculation time was significantly reduced, it might be used to predict the microstructure field of a real Mg component after solidification. The stochastic nucleation, competitive growth processes of many grains with various crystallographic orientations and the formation of eutectic structure were also taken into account. Furthermore, step castings were poured with sand and permanent molds and metallographic experiments were carried out for validating the developed models. It was shown that the simulation results are in good agreement with those obtained in the experiments.