UBC Theses and Dissertations
Mathematical modelling of the microstructure and texture changes during hot tandem rolling of AA5182 and AA5052 aluminum alloys Wells, Mary A.
A mathematical model to predict the through-thickness microstructure and texture changes during hot tandem rolling has been developed for two commercially significant aluminum alloys - AA5182 and AA5052. The model includes a plasticity component to model the temperature and deformation during rolling as well as an interpass component to model the microstructure, texture and temperature changes which occur in the strip between the rolling passes. The plasticity model was developed using a commercial finite element package DEFORM - a 2-D transient Lagrangian model which couples the thermal and deformation phenomena which occur during strip rolling and is able to predict the temperature, strain rate and strain distribution in the strip at any position in the roll bite. The interstand model includes semi-empirical equations describing the microstructure (percent recrystallization and recrystallized grain size) and texture changes occurring in the strip between the rolling passes. The interstand model also includes a temperature module to predict the through-thickness temperature distribution in the strip based on the one-dimensional heat conduction equation which is solved by a finite difference method. The semi-empirical equations used in the interstand model were developed using experimental data for the two alloys. The experimental programme was carried out at Alcan International's Banbury and Kingston Laboratories, as well as at the Atomic Energy of Canada Limited Chalk River Laboratories. The experimental programme involved plane strain compression testing industrial rolled samples of AA5182 and AA5052 aluminum alloys based on a test matrix which covered similar temperature, strain and strain rate conditions as those seen in industrial hot tandem rolling. The samples were given a single deformation and then quenched immediately to preserve the as-deformed structure. The samples were then heat-treated in a salt bath for various lengths of time and the percent recrystallization, recrystallized grain size and texture changes during recrystallization were measured. A temperature compensated time parameter was used to convert the isothermal recrystallization and texture kinetics to non-isothermal applications. Validation of the model using industrial data and samples indicated that it gave reasonable predictions for the temperature, grain size and volume fraction of some of the deformation texture components after recrystallization was completed. However, the model tended to over-estimate the mill loads in the last stands for both the AA5182 and AA5052 alloys and tended to underestimate the amount of cube and S texture in the recrystallized strip. A sensitivity analysis of the process parameters indicated that both the microstructure and texture were most sensitive to the rolling temperature. Indicating the need for good control of temperature during rolling operations as well as accurate temperature predictions for process modelling activities.
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