Prediction of structure during shaped extrusion and subsequent static recrystallisation during the solution soaking operation

Abstract

Material which forms the surface and subcutaneous layers of an extrudate experience large deformations when they traverse the die land, which, added to the inhomogeneity caused by the dead metal zone leads to considerable modifications to the 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 indicates 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 modified and 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 an agreement with the experimental measurement. Importantly the properties of hard alloys improve as the temperature of the extrusion is raised. This phenomenon is discussed and theoretically justified.