The heat affected zone (HAZ) of friction stir welded Al 7075 T7 shows diminished corrosion resistance properties when compared with the parent material. Corrosion attack in this region of the weld is primarily intergranular and is associated with the presence of precipitate free zones. Current TEM research conducted at Brigham Young University by Dr. Bin Cai finds a correlation between precipitate free zone (PFZ) width and grain boundary geometry. As both grain boundary geometry and the PFZ are associated with modes of failure in 7XXX aluminum, this paper makes a comparison of grain boundary character distributions (GBCD) in the HAZ and the parent metal via multi-section plane five-parameter stereology. The stereology is conducted in a convenient macroscopic coordinate frame, associated with the HAZ. This is the first investigation to determine the GBCD in the HAZ of friction-stirred weld material and requires multiple section plane sampling. It is discovered that aluminum here exhibits the property of non-sidedness, a long assumed but unproven characteristic. Further comparisons between the two microstructures are conducted relative to (2-dimensional) grain boundary network connectivity, recovered from EBSD data in each section plane. It is shown that the relative fraction of grain boundaries of misorientation character associated with smaller PFZ size is larger in the HAZ as compared to the parent material. A commensurate decrease in the connectivity (radius of gyration) of grain boundaries of character conducive to larger PFZ size is also found in the HAZ, relative to the parent material. Distribution of inclinations changes as a function of grain boundary geometry. Surface area per unit volume of CSL and low angle random (LAR) misorientations increases in the HAZ, while high angle random (HAR) boundaries decrease. In the case of LAR and some CSL boundaries, a reorientation occurs in which macroscopic normals of these interfaces rotate. It is anticipated that these significant changes in the GBCD within the HAZ could be important in terms of understanding the post-weld mechanical and physical properties in friction-stirred materials.

The grain boundary network (GBN) of polycrystalline materials changes during grain growth, affecting the material's properties. This research presents the results of fully anisotropic grain growth simulations. We perform simulations using three GB energy functions: an energy function that considers a GB's 5 degrees of freedom, the Read-Shockley model, and isotropic. We analyze the impact of these energy functions on the morphological evolution and various microstructural statistics, such as crystallographic texture and triple junction distribution. The results demonstrate that while individual grain evolution varies with GB energy function, certain microstructural statistics reach similar steady states across different models. In addition, we perform simulations using a diverse set of initial microstructures sampled from the texture hull to investigate their influence on the evolutionary trajectory during grain growth. We find a universal increase in the sharpness of orientation distribution functions (ODFs) and a positive correlation between texture strength and its sharpening rate. Additionally, the evolution of the GBN exhibits an increase in low-angle grain boundaries. Finally, we develop a method for predicting microstructural evolution as an alternative to expensive traditional grain growth simulations. Using the dataset from the previous simulations, we train a diffusion model to reconstruct the morphology of the evolved microstructure and a GBN spectrum predictive model to reconstruct the texture. The alternative method is almost ten times faster at producing an evolved microstructure than a traditional grain growth level set method. Overall, this work enhances our understanding of grain growth and the impact of the GB energy and initial texture on the evolution of the microstructure.