The crystallography of lath-shaped Mg2Sn precipitates in a Mg–Sn–Zn–Mn alloy

Lath-shaped β-Mg2Sn precipitates with (near) Burgers OR in α-Mg matrix are found to be enclosed by three to four pairs of facets. The habit plane (HP) is (1 1 0)β//(0 0 0 1)α, while the major side facet (MSF) is (−1 1 1)β or 0.36° from (1 2 −3 0)α, the trace of which is about 10° from [1 −1 0 0]α. The minor side facet with a higher frequency of appearance is (1 −1 1)β//(−2 1 1 0)α, while that with a lower frequency of appearance is (1 −1 0 0)α or 0.50° from (−1 1 −3)β. Based on geometrical models, the MSF is proposed to obey a Δg parallelism rule, which requires a rotation of −0.15° from the exact Burgers OR. The calculated OR and morphology agree well with the observed ones.

► The crystallographic morphology of lath-shaped Mg2Sn precipitates is measured quantitatively in a Mg–Sn–Zn–Mn alloy. ► The measured morphology is interpreted by geometrical models. ► The Mg2Sn precipitates form quite different morphologies under the same OR measured.