Modelling Grain Deformation during Extrusion of AA3003 using the Finite Element Method

A combination of numerical simulation using the finite element method (FEM), extrusion plant trials and experimental characterization was used to study microstructure changes, specifically geometric dynamic recrystallization, during the hot extrusion process for an AA3003 aluminum alloy. Extrusion plant trials were conducted at the Rio Tinto Alcan Research and Development facility in Jonquiere, Quebec in order to measure load and temperature and obtain samples for microstructure analysis. A 2D FEM based on the commercial code DEFORM was developed for the thermo-mechanical simulation of the extrusion. Load and temperature predictions resulting from this model agree well with the measured values during the pilot plat trials. Using the FEM model, it was estimated that near the surface of the extrudate the thickness of the deformed grains drops below the subgrain size which may cause the deformed grains to pinch-off and geometric dynamic recrystallization. Optical microscopy observations show that in all unrecrystallized extradates there is a transition from a fibrous to a granular structure near the surface that suggests the occurrence of Geometric Dynamic Recrystallization. The effect of extrusion conditions on grain thickness distribution was investigated using the FEM model.