Crystallography of the precipitates formed on {10-11} twin boundary in Mg Al alloys

Abstract {10 1 ¯ 1} contraction twinning is an important deformation mode in Mg alloy, which can be easily activated during sheet rolling process. The introduction of twin boundaries in Mg alloys can promote the nucleation of fine precipitates, leading to better mechanical properties. However, the crystallographic characteristic of the precipitates formed on {10 1 ¯ 1} twin boundaries has rarely been reported before. In this work, the crystallography of the Mg17Al12 precipitates formed on {10 1 ¯ 1} twin boundary (TB) in a Mg Al alloy was systematically studied by transmission electron microscopy. It was for the first time revealed that the precipitates formed at either broad TB or twin tip hold an identical orientation relationship, i.e., [2 1 ¯ 1 ¯ 0]α//[11 1 ¯ ]β and (01 1 ¯ 1)α//(011)β with both the matrix and the twin. Such preferred crystallographic orientation should be driven by the minimization of the total energy between the matrix-precipitate interface and the twin-precipitate interface.