Correlation between grain boundary misorientation and the discontinuous precipitation reaction in Mg-10 wt.% Al alloy

The correlation between the geometry of the grain boundaries (GBs) and the kinetics of the discontinuous precipitation (DP) reaction in a Mg-10 wt. % Al alloy has been studied. The GBs were categorized as special or random by using the electron back-scattered diffraction (EBSD) technique and theoretical tables of the coincidence site lattice. The analysis showed convincingly the absence of low-angle GBs and no distinguished maximum on the GB misorientation angle distribution in this hexagonal system. The DP cells appeared predominantly at nonspecial (random) orientations, confirming that the initiation and growth of the reaction products occur at high-angle GBs. Generally, some orientations which are inactive after 20 min became active after 40 min of ageing at 500 K. For each rotation axis, there were several misorientation angles (no special ones) for which a maximum growth distance of DP reaction was observed. (C) 2002 Elsevier Science B.V. All rights reserved.