Prediction of grain structure and texture evolution after high temperature extrusion of aluminum alloys

To engineer the mechanical response of the material, it is crucial to predict the microstructure after thermomechanical processing and relate properties to the microstructure. In this study, the relationship between the features of the deformed state after axisymmetric extrusion of aluminum at high temperatures (e.g., the subgrain size distribution and the disorientation distribution) and the final recrystallized texture was investigated. It aims to systematically change the features of the deformed state by generating different initial synthetic microstructures and using them as inputs for a phase field model to predict the recrystallized texture. The characteristics of the deformed state and the recrystallized state were analyzed for extruded 3XXX aluminum samples with two different homogenization heat treatments. The subgrain size distribution and disorientation distribution in different texture fibres of the deformed state, i.e., ||ED and ||ED, were extracted to construct a baseline condition. After verifying that 2D simulations could be used to capture the essential phenomena in 3D, the role of the microstructural features was investigated using 2D simulations. First, the subgrain size distribution and disorientation distribution were changed from baseline condition by ±50% for individual grains with ||ED or ||ED. Second, for a mixture of grains with ||ED and ||ED orientations, ||ED baseline condition was used, then subgrain size distribution and disorientation distribution were changed by ±50% for ||ED grains. Third, an input microstructure from experimental EBSD measurements was simulated. For the first scenario, a narrower distribution and a wider disorientation distribution resulted in a larger final average subgrain size which was rationalized based on the evolution of these microstructural features. For the second scenario, the tail of the subgrain size distribution and the width of disorientation distribution within ||ED was found to have a large impact on the final texture. This was explained by the probability of large grains with high angle disorientation in ||ED fibres growing preferentially to pinch-off grains with ||ED orientations. For the third scenario, only ||ED volume fraction could be predicted accurately compared to the experiment. Possible sources of error were identified and discussed.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat

Synergistic inhibition effect of thionine and zinc ions on carbon steel corrosion in acidic media

In this research, the inhibition effect of thionine (Thn) and its synergistic effect with Zn2+ on the corrosion of a carbon steel A106 sample in 0.5 M sulfuric acid has been investigated using electrochemical potentiodynamic polarization technique and weight loss tests. Using Tafel polarization plots and corrosion rate calculations, it was revealed that Thn act as an effective inhibitor. It was found that the results of weight loss test and polarization method are in good agreement. The synergistic effect of zinc ions on the corrosion inhibition of steel in the presence of various concentrations of Thn was investigated, too. The addition of zinc ions enhances the inhibition efficiency considerably. Maximum inhibition efficiency was achieved about 97% for a system containing 20 ppm Thn and 16.7 mM Zn2+. The presence of zinc ions increases the degree of surface coverage. The synergism parameters "S", calculated from surface coverage, are found to be larger than unity for some of Thn concentrations. Thn behaved as a mixed type inhibitor in H2SO4 solution. It was investigated too, that the adsorption of Thn on the metal surface was obeyed Langmuir adsorption isotherm and adsorption was performed spontaneously. Investigating the adsorption mechanism proved that it is possible to form a complex between the initial Zn2+ layer on the steel surface with the protonated form of thionine

Large-Scale Multi-Phase-Field Simulation of 2D Subgrain Growth

The characteristics of subgrains in a deformed state after the high-temperature deformation of aluminum alloys control the subsequent recrystallization process and corresponding mechanical properties. In this study, systematic 2D phase-field simulations have been conducted to determine the role of deformed state parameters such as subgrain size and disorientation distributions on subgrain growth in an individual grain representing a single crystallographic orientation. The initial subgrain size and disorientation distributions have been varied by ±50%. To have a statistically relevant number of subgrains, large-scale simulations have been conducted using an in-house-developed phase-field code that takes advantage of distributed computing. The results of these simulations indicate that the growth of subgrains reaches a self-similar regime regardless of the initial subgrain structure. A narrower initial subgrain size distribution leads to faster growth rates, but it is the initial disorientation distribution that has a larger impact on the growth of subgrains. The results are discussed in terms of the evolution of the average diameter of subgrains and the average disorientation in the microstructure.Applied Science, Faculty ofNon UBCMaterials Engineering, Department ofReviewedFacultyResearche