Abstract

Materials which form the surface and subcutaneous layers of an extrudate experience large deformations when they traverse the die land, which, added to the inhomogeneous caused by the dead metal zone, leads to considerable modifications to the deformation parameters when compared with 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 (SRX) 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 present work, 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 changes of the microstructure. Axisymmetrical and shape extrusion are presented as examples. The evolution of the substructure influencing SRX is studied. The metallurgical behaviours of axisymmetric extrusion and that of shape extrusion are compared. The predicted results show an agreement with the experimental measurement. The distribution of equivalent strain, temperature compensated strain rate and temperatures is also presented to aid in interpretation. Importantly the properties of hard alloys improve with the increase in the temperature of the extrusion. This phenomenon is discussed and theoretically justified.