Hot deformation and processing maps of multiphase metals

The thermo-mechanical shaping processes, such as rolling, forging and extrusion as well as the heat treatment, determine the properties of a material. The developed microstructure during hot deformation is the result of deformation mechanisms such as dynamic recovery and dynamic recrystallisation. The hot deformation can also result in damage and flow localisation, especially in multiphase metal based materials. Several models have been proposed to correlate the parameters of the deformation process (temperature, strain and strain rate) and of the pre- and post- heat treatments (temperature-time history) with the flow behaviour and the microstructure. Following this objective, the processing maps concepts were developed based on the dynamic materials model (DMM) and later, the modified DMM introduced some modifications at the calculations of the processing maps. The processing maps are extensively used with good results not only for one-phase materials but also for multiphase ones. Even so, the phenomena predicted by the models are not based on microstructural features of the deforming material as the maps are based on general thermodynamics this leads still some questionable points related to the materials microstructure interpretation. The aim of this project is to find the correlation of the relevant microstructural changes with thermodynamic parameters. New characterization techniques such as EBSD and synchrotron, combined with traditional characterisation methods are proposed to reveal the microstructural features developed after/during hot deformation. The quality of the obtained data and of the experimental tests will be improved by the combination of finite element models to locate the precise deformation parameters in the sample, and the Gleeble simulation machine. This work will concentrate on microstructural studies related to the hot deformation of metals with different compositions, stacking fault energies, diffusion parameters and phase combinations: age hardenable aluminium alloys, alpha-beta and near beta titanium alloys, low carbon steels and magnesium alloys. The results will be correlated to the processing maps, and finally, a knowledge based relationship will be established to interpret the J co-content defined in the basics of the dynamic materials model by microstructural properties.

The project dealt with the use, application and discussion of processing maps in the hot forming of metallic materials. During forming processes of metals, microstructural changes and sometimes damage take place. These characteristics determine later the mechanical properties of the product. The idea behind the processing maps is to determine the processing parameters, namely the temperature and deformation velocity, at which the metal has a good formability and damage, does not occur. Within this project the hot formability of four different materials were tested: 3 light alloys (titanium, magnesium and aluminium alloys) and two plain steels. Different types of processing maps were tested and compared. We found that the widely used processing maps developed in the past can be replaced by simpler and physically based deformation maps. This strong statement will have direct impact in the scientific community as well as in the industry of manufacturing of metals.