On the coprecipitation crystallography in a Mg-7Sn-1Mn-2Ag-1Zn alloy

Abstract

In multicomponent alloys, different precipitates always form in association with one other. Compared with the precipitates that form individually, little attention has been given to the crystallography of coprecipitates. In this study, we reported and interpreted the novel crystallography of the ε'-Mg54Ag17 coprecipitates observed in a Mg-7Sn-1Mn-2Ag-1Zn alloy. Two types of coprecipitates, i.e.,ε'-Mg54Ag17/β-Mg2Sn and ε'-Mg54Ag17/ε'-Mg54Ag17 were both observed. The ε'-Mg54Ag17 phase with the orientation relationship of (0 0 2)ε'//(0 0 0 2)α, [2 0 0]ε'//[1 1 −2 0]α is present in both coprecipitates. It exhibits the same orientation relationship and interfacial orientations as those phases that formed individually, but is characterized by an opposite facet size order and a new interface between the coprecipitates, resulting in a distinctly different morphology. For both ε'/β and ε'/ε' coprecipitates, the interface between the two precipitates exhibits a much better lattice match than the initial ε'/α interface, indicating preferred heterogeneous nucleation sites for the later-formed precipitates in the alloy.