Static recovery in hot rolling.

The final properties of hot rolled products depend on the microstructure developed during the hot rolling process. The kinetics of thermomechanical events which determine the microstructure depend very much on the strain accumulated at each deformation. Aluminium and its alloys exhibit a high static recovery which reduces the strain in the interpass times, although this strain may be retrieved when applying a second deformation. This thesis is about determining the extent of static recovery in hot rolling in terms of a magnitude called 'Retained Strain', to be used in a computer model for hot rolling. A methodology to measure the extent of static recovery and retrieval of strain is proposed. This methodology is based on the development of empirical equations which were obtained after analysing experimental data from plane strain compression tests from two different sources. In the analysed data the extent of static recovery is related to the deformation conditions so that a relationship between static recovery and the Zener-Hollomon parameter is established. The retrieval of strain depends on the time interval between deformations, so that after very short intervals the strain retrieves immediately, even at very small second strains, but after very long intervals strain may not retrieve at all. The Sheffield Model for hot Rolling is modified to include simulation of static recovery and retrieval of strain. Industrial schedules for Al-l%Mg and c.p. A1 are studied. With the 'Recovery model' recrystallization is inhibited. With the 'Retrieved model' the effects of recovery are almost eliminated. Modelling recovery and retrieval of strain has little effect on industrial hot rolling schedules designed to produce a full recrystallized final microstructure, but it is expected to have a major influence on other hot rolling schedules where a final fine subgrain microstructure, characteristic of recovery, is required.