Abstract:A modified cellular automaton method based on the lowest energy principle has been applied to simulate the microstructure evolution and dynamic recrystallization (DRX) behavior during the hot deformation.The simulated results show that the impediment of the grain boundaries and second phase particles to the dislocation movement contributes to the nucleation of dynamic recrystallization.For the DRX microstructure,the distribution of grain size follows Weibull function and the average number of grain sides increases gradually to an ideal value of 6 with the increasing strain.The coupled cellular automaton -finite element model can be successfully used to investigate the complicated multi - pass deformation process.The morphology and topology including the distributions of grain size and the number of grain side were investigated and their dependency on the deformation conditions was also discussed in the present paper. The comparisons between the simulated and experimental results show that the present CA -FEM model can be used as another effective method to simulate and predict the plastic deformation of large - scale metallic workpiece.

The kinetics of dynamic recrystallization(DRX) during the hot compression process of AZ91 magnesium alloy was investigated based on the cellular automata simulation.The simulation results indicate that the fraction of DRX increases with strain increase and the velocity of DRX increases with process temperature increase.The relationship between the average grain size in the final microstructure and Zener-Hollomom parameter follows an inverse power law with the exponent of -0.05.During a compression process,the average size of total grains decreases rapidly in an initial stage,and then slowly to a steady value;the average size of initial grains decreases linearly to zero;the average size of recrystallized grains increases to a peak value and then decreases slowly to a steady value.Multi-cycle recrystallizaiton occurs concurrently in the matrix,resulting in a single peak on each flow curve.

The deformation behavior and microstructure evolution characteristics of the AZ91 magnesium alloy during hot compression process is studied by the electron back-scattered diffraction pattern (EBSP) approach. The results suggest that dynamic recrystalliztion (DRX) occurs during the compression process. The DRX in turn refines the grains. When the strain rate is decreased, the average grain size, the fractions of large-size grains and the fraction of large-side grains in the final microstructures are increased. The peak stress of the flow stress curve increases along with the increase of the Zener-Hollomon parameter.