Coupled CA-FE simulation for dynamic recrystallization of magnesium alloy during hot extrusion

Abstract

In the present research, the dynamic recrystallization (DRX) behavior of a newly-developed Mg–Al–Zn–RE alloy with abundant second-phase particles during hot extrusion is investigated by coupling finite element (FE) and cellular automaton (CA) models. A two-dimensional CA model is developed to quantitatively and topologically evaluate the DRX process during deformation with constant forming conditions. Considering the fact that second-phase particles with various sizes extensively exist in the studied Mg–Al–Zn–RE magnesium alloy, models of DRX nucleation and grain growth velocity are modified. The coefficients of the modified CA model are calibrated by isothermal compression experiments of the magnesium alloy. Subsequently, the CA model is coupled with FE analysis to investigate the DRX behavior during the hot extrusions of the Mg–Al–Zn–RE alloy. The DRX behavior of the magnesium alloy at different stages and positions of extruded plates is simulated by the established model. Finer grains near the edge than in the inner of the plates result from higher strain and strain rate. The influence of extrusion conditions on microstructural evolution is explored. Under the employed forming conditions, average grain size decreases 28–62 times from as-cast and solution-treated to as-extruded state due to grain refinement by DRX. With increasing initial billet temperature or extrusion speed, average grain size increases. The finest grains are obtained at the initial billet temperature of 623 K and the extrusion speed of 7.83 mm/s. Low initial billet temperature or high extrusion speed benefits homogeneous grain distribution. The simulated results are in good agreement with experimental ones.