Misorientation angle analysis near the growth front of abnormally growing grains in 5052 aluminum alloy

Misorientation measurements at the growth front of abnormally growing grains in 5052 aluminum alloy were made using electron back-scattered diffraction (EBSD). When a three-dimensional morphology of solid-state wetting along a triple junction line is observed on a two-dimensional section, two kinds of morphologies could be observed. One is a morphology of penetrating the grain boundary when the section is parallel to the triple junction line. The other is morphology of a three or four-sided grain with a negative grain boundary curvature when the section is vertical to the triple junction line. Many morphologies of penetrating the grain boundary were observed at the growth front of abnormally growing grains. Grain boundary energies, which were estimated from misorientation measurements of the three grains in the penetrating morphology, satisfied the energetic condition for wetting along the triple junction line. Misorientation measurements showed that some matrix grains away from the growth front of abnormally growing grains had the same crystallographic orientation as that of the abnormally growing grain. Repeated EBSD measurements on each serial section show that these grains were actually identical to the abnormally growing grain, being connected three dimensionally. These results imply that the abnormal grain growth in 5052 aluminum alloy occurs by the mechanism of sub-boundary enhanced solid-state wetting.