Grain Boundary Character Distribution in the Heat-Affected Zone of Friction Stir-Processed AL 7075 T7

摘要

Current transmission electron microscopy (TEM) research (Cai et al., 2006) in the heat-affected zone (HAZ) of friction stir-welded Al 7075 T7 finds a correlation between precipitate-free zone (PFZ) width and grain boundary (GB) geometry. Based on these correlations, this article makes a comparison of grain boundary character distributions (GBCD_s) in the HAZ and the parent metal via multisection plane five-parameter stereology. The stereology is conducted in a convenient macroscopic coordinate frame, associated with the HAZ. Further comparisons between the two microstructures are conducted relative to two-dimensional (2-D) GB network connectivity, recovered from electron backscatter diffraction (EBSD) data in each section plane. It is shown that the relative fraction of GB_s 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 GB_s 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 GB geometry. Surface area per unit volume of low-angle random (LAR) misori-entations increases in the HAZ, while high-angle random (HAR) and coincident site lattice (CSL) boundaries decrease. In the case of LAR and some CSL boundaries, a reorientation occurs in which macroscopic normals of these interfaces rotate.