LAUSR

Abstract Mg2Sn precipitates growing along ⟨1 1 2 ¯ 0⟩Mg are the dominant strengthening phase in aged Mg-Sn-based alloys. They were reported to exhibit an ‘lath’ morphology with an rational orientation relationship (OR) of (1 1 0)β//(0 0 0 1)α, [0 0 1]β//[1 1 2 ¯ 0]α in previous studies. In this work, the ⟨1 1 2 ¯ 0⟩Mg Mg2Sn in an aged Mg-Sn-Mn alloy was found to actually have a long-lenticular-like morphology. The lenticular Mg2Sn contains a midrib separating two pairs of broad interfaces and one pair of side interfaces. Both of the broad interfaces deviate from the (0 0 0 2)Mg plane by about 8°. The distinct morphology is associated with an near-rational OR of (1 1 0)β//(0 0 0 1)α, and [0 0 1]β 0.6° from [1 1 2 ¯ 0]α. Using the secondary constrained coincidence lattice model, the OR was revealed to make good lattice matching realized across two pairs the interfaces. The detailed interfacial structure of the two interfaces were both predicted to contain an arrays of periodically distributed structural ledges, and each ledge is associated with a misfit-compensating dislocation. These defects configurations show reasonable well agreement with HRTEM results.