Numerical modelling of the aluminium extrusion process and comparison with results obtained from industrially extruded complex sections.

Abstract

This thesis reports the analysis of extruded products by Forge2009® and EBSD produced by the investigator in the BOAL plant. The 3D FEM module was used to study the required load, the temperature evolution, surface formation of the extrudate and material flow during the process. The effect of varying process conditions on the selected geometries were investigated and verified by means of experiment. Considering the difficulty in performing the experiments (high temperature and high strain rates) the simulation results can be considered to be acceptable. The simulations were performed with the implicit finite element code Forge2009® with user input written in Visual Fortran®. Alloy EN AW-6082 was selected on the basis that is a commonly used extrusion material in industry. A range of simulations were designed which would produce differing structures to those experienced within the industry. The effect of variation of the bridge design for hollow dies and the effect of variation of the sink in for solid dies was investigated. 3D simulations were performed to investigate the effect of these variations in the design features on extrusion process parameters. The process parameters which are likely to be affected are load, deflection, velocity and temperature. The results indicated that the design of the die affected the process parameters. The microstructure evolution during the extrusion process was investigated for the selected complex geometries. The following microstructure features were included in the investigations: Recrystallised grain size, subgrain size, misorientation, dislocation density and volume fraction recrystallised. Simulations were performed using physically-based mathematical microstructure models integrated into FEM through its Fortran® subroutine interface. Experiments were performed to investigate the effects of varying process conditions on the microstructure. For hollow section, the emphasis was placed on the study of the complicated metal flow and the seam welding quality. EBSD analyses were performed to investigate the substructure. Surface cracking was modelled and compared with experiments. The agreement between the predicted microstructures using associated models and experimental measurements were acceptable. Predicted cracking show good correlation with experimental results