Characterization of dislocation structures and their influence on processing of aluminum alloys

A proper understanding of the relationships that connect processing conditions, microstructural evolution and mechanical properties is required to optimize the processing parameters, reduce alloy content and improve product quality. This requires significant effort in performing accurate analysis of deformed microstructure, identifying important microstructural parameters influencing stress response and developing a physically based model that incorporates these microstructural parameters. Most models are based on observed phenomenology of the process and therefore fail to predict stress-strain behavior beyond a given set of observations. Current research is aimed towards making contribution in the areas of (i) microstructural characterization, (ii) understanding the influence of various microstructural parameters on the evolution of dislocation structures and (iii) on relating the physically measurable microstructural parameters to stress response.; New strategies to analyze the local orientation gradient in deformed single crystals are introduced. Interrogation of the dislocation substructure is accomplished by extracting information gleaned from small point to point misorientations as measured by electron back-scatter diffraction (EBSD). Microstructural evolution during small strain deformation of 3003, 5005, and 6022 Al alloys was investigated using EBSD and transmission electron microscopy (TEM) techniques. The variables observed to influence the deformation behavior include alloy chemistry, crystallite lattice orientation, character and morphology of neighboring grains and precipitate morphologies. The difference in the evolution of dislocation structures of the 3 alloys is attributed to their alloy content. Quantitative parameters obtained from microstructural characterization of 5005 and 6022 Al alloys were analyzed by a multiple regression analysis technique to determine the relative influence of various microstructural parameters on the observed stress response. The GND density was determined to be the most important measured parameter affecting the yield stress. Experimental and statistical analysis showed a linear relationship between yield stress and average GND density. The yield strength model was developed for 6022 alloy connecting the observed stress response with experimentally determined microstructural parameters.