Prediction of Static Recrystallisation after Extrusion of Shaped Aluminium Sections

Abstract

Extrusions experience large deformations at discontinuities when they traverse the die land, leading to considerable modifications to the average deformation parameters when compared to the remainder of the extrusion. The distribution of structure is therefore greatly inhomogeneous. Reference to both empirical and physical models of the recrystallisation process indicate that nucleation and growth will differ at these locations in those alloys that are usually solution treated and aged subsequent to the deformation process. Since static recrystallisation has a significant influence on many of the properties of the extrudate, it is therefore essential to provide the methodology to predict these variations. In the work presented, a physical model based on dislocation density, subgrain size and misorientation is integrated into the commercial FEM codes, FORGE2® and FORGE3® to study the microstructure changes. Axi-symmetrical and shape extrusion are presented as examples. The evolution of the substructure influencing static recrystallisation is studied. The metallurgical behaviour of axi-symmetric extrusion and that of shape extrusion are compared. The predicted results show good agreement with experimental measurement. The distribution of equivalent strain, temperature compensated strain rate and temperatures are also presented to aid in interpretation.