Comparative Research on Nanometer and Micrometer Grain Growth of Polycrystalline AZ31 Magnesium by Phase Field Models

¹ School of Mechanical Engineering, Wuhan Polytechnic University, P. R. China
² Special Vehicle Techology Center, The fourth Academy of China Aerospace Science & Inoustry Corp, P. R. China

^a wuy611@163.com
^b xiasi_85@163.com
^* Corresponding author: wuy611@163.com

Abstract

Nanometer scale and micron scale grain growth of polycrystalline AZ31 Magnesium alloy have been comparatively studied by phase field simulation, and the models are established under realistic spatial-temporal scales. The expression of local free energy density function is modified due to the different initial state of grain growth process at nano scale. The term of grain boundary range is to explain the physical backgrounds of the order parameter gradients at grain boundary and the diffusion grain boundary, and it is related to the correct gradient and coupling parameters. The simulated results are compared in nano scale and micron scale, they are also compared with experimental results in the literature, in order to find out the mechanisms for nano-structural evolution. It is shown that the grain boundary range will cover two adjacent grains in nano scale polycrystalline while the range should be a constant big value of about 1.2μm for grains in micron scale. It is found that the grain growth rate at nano scale is slower than that at the micron scale, and these simulated results can be proved by the experimental results in the literature. It is found that the grain size fluctuation is more intensely in nano-sized grains than that in micron-sized grains by the quantitative analysis of the mixed degree of grains size in nano-structure and micron-structure in the models.