Numerical modeling of subgrain growth of hot extruded Al–4.5Zn–1Mg alloy in the presence of nanosized dispersoids

A numerical framework has been developed for predicting the sizes of subgrains in hot-extruded Al–4.5Zn–1Mg alloy. A combined numerical and analytical approach was taken to correlate subgrain growth rate with the deformation history of the extrudate and with the conditions of cooling after extrusion. Subgrain sizes in the as-deformed condition were calculated from strain, strain rate and temperature values determined from finite-element simulations. Subgrain growth during subsequent cooling was calculated from the mobility of low angle grain boundaries and the net driving force for growth by means of a physical model. The driving force was treated as the difference between stored energy, being inversely proportional to the average subgrain size, and the Zener drag pressure. With this combined approach, the correlations of the average subgrain size at the end of hot extrusion with strain, strain rate and temperature and its further evolution with time were established. Subgrain sizes after hot extrusion at different ram speeds and at different depths from the surface of the extrudate were measured by means of EBSD mapping and the results were compared with model predictions. Good agreement between the experimentally measured average subgrain sizes at the periphery of the extrudates and those predicted from the model was obtained.