Ordered Sn distribution adjacent to the precipitate-matrix interface in a Mg-9.8wt.%Sn alloy

The major interface between β-Mg3Sn precipitate plate and the α-Mg matrix in a Mg-9.8wt.% alloy has been investigated using aberrationcorrected scanning transmission electron microscopy and first-principles calculations. It is found that Sn atoms orderly distribute in the single layer of the α-Mg matrix immediately adjacent to the broad surface of β at the early stage of ageing. These Sn atoms substitute Mg atoms located at the centers of equilateral triangles constituted by three Mg columns in the outmost layer of β. First-principles calculations suggest that the ordered Sn distribution is energetically favored and it not only decreases the interfacial energy of the β-matrix interface but also hinders the occurrence of 1/3<01■0>αshear that thickens the β plate.