Effect of grain boundary misorientation on discontinuous precipitation in an AZ91 alloy

摘要

A scanning electron microscopy (SEM)-based electron backscatter diffraction (EBSD) analysis showed that the discontinuous precipitation (DP) reaction rate was dependent on the geometry of the grain boundary in Mg-9Al-1Zn (wt.%) alloys. DP converted a supersaturated solid solution,δ ₀ (magnesium (Mg)-rich solid solution), into a two-phaseδ + γ aggregate, withδ being a precipitated Mg₁₇Al₁₂ (intermetallic phase) behind a migrating reaction front. The near-special grain boundary was rather inactive, whereas most of the random high-angle boundaries promoted the reaction. Prior deformation (hot rolling to achieve up to 80% thickness reduction) had no effect on the frequency of special-grain boundaries.