The role of grain boundary plane in slip transfer during deformation of magnesium alloys

Slip transfer across grain boundaries (GBs) is an important mechanism for HCP metals to accommodate intergranular deformation incompatibility. In this work, an in-situ SEM/EBSD study was conducted to study basal-slip-induced non-basal slip behavior in a Mg–Y alloy. The indices of dislocation slip systems of slip traces at sample surface were determined by a lattice rotation analysis method based on EBSD images. It was shown that the disorientation angles of GBs have a strong influence on the slip transfer behavior. The experimentally determined preferential disorientation angle ranges for basal-slip-induced pyramidal I slip and prismatic slip events have been correlated to the geometrical compatibility between the source and triggered slip systems, in terms of m' criterion. However, a statistic showed that some slip transfer events do not obey the m' criterion. Instead, they are rather sensitive to the GB plane orientations. To reveal the roles played by the GB plane, sectional polishing and EBSD characterization to determine the orientation of GB plane have been conducted. It is revealed that, in addition to the GB disorientation angle, the activation of slip transfer in Mg is essentially dependent on the plane orientation of local GBs. It also demonstrated that the M criterion, based on the match of intersection lines between dislocation slip planes to GB planes and slip directions, was more rational to predict the activated slip systems by the m' criterion. This work emphasizes the importance of GB plane orientation when attempting to understand the slip transfer mechanism in deformed magnesium alloys.