Effect of low-angle grain boundary and twin on precipitation mechanism in pre-rolled AZ91 magnesium alloy

Low-angle grain boundary and twin significantly affect precipitation behavior. Twins were introduced into AZ91 magnesium alloys by pre-rolling. And then, aging treatment was carried out in pre-rolled AZ91 magnesium alloys to investigate the precipitation behavior. The results show that the low-angle grain boundary and the extension twin provide the nucleation position for second phase, while double twin with low-elastic strain energy is not favored for the segregation of Al atom, causing that the precipitate hardly nucleates. Second phase firstly precipitates in the low-angle grain boundary and the twin boundary, followed by precipitating inside the twin. The low-angle grain boundary-induced lath-shaped second phase is attributed to dislocation, while the twin-induced precipitate is mainly affected by dislocation and stacking fault. From thermodynamic perspective, the morphology of twin-induced precipitate firstly displays spherical shape and then grows into lath-like shape.