The Development of Grain Structure During Axisymmetric Extrusion of AA3003 Aluminum Alloys

A mathematical model using the commercial finite element method software package DEFORM 2D was developed and validated to model extrusion of AA3xxx aluminum alloys rods. Using a simple approach based on the initial grain size and material flow during extrusion, the deformed grain thickness during and after extrusion could be predicted with good accuracy. The model predicted deformed grain thickness, which, in conjunction with knowledge of the subgrain size during deformation, was used to predict the occurrence of the creation of a different microstructure near the surface of the extrudate as compared to the centre. The model predicts with good accuracy the deformed grain thickness and how it varies spatially both through the diameter of the extruded rod and along its length. The model predicts that the deformed grain thickness decreases dramatically from the center to the surface of the extrudate and how this is impacted by the extrusion ratio. Applying a cutoff value of the subgrain size, allows the prediction of the critical radius beyond which a more granular microstructure occurs at the surface. Optical microscopy and orientation imaging microscopy of the extruded AA3xxx rods were used to validate the model predictions of the deformed grain structure, both in terms of the grain thickness and the critical radius, beyond which the microstructure becomes more granular close to the rod surface.