Metastable precipitate phases in Mg–9.8 wt%Sn alloy. (1st February 2018)

• Record Type: Journal Article
• Authors: Liu, C.Q.; Chen, H.W.; Liu, H.; Zhao, X.J.; Nie, J.F.
• Is Part Of: Acta materialia. Volume 144(2018)
• Page Start: 590
• Page End: 600
• Publication Date: 2018-02-01
• Subjects: Magnesium alloys -- Precipitation -- HAADF-STEM -- Ageing -- Shockley partial dislocations; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2017.10.023
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Aberration-corrected scanning transmission electron microscopy has been used to characterize precipitates in a binary Mg–9.8 wt%Sn alloy aged in the temperature range 100–250 °C. In contrast to the traditional view that precipitation in Mg–Sn based alloys involves exclusive formation of the equilibrium phase β (Mg2 Sn, face-centered cubic), we found the formation of a GP zone and a metastable phase, designated β′, prior to the equilibrium β phase. The GP zone has a plate morphology with its habit plane parallel to the basal plane of the matrix phase. The β′ phase also has a plate morphology with its habit plane parallel to the magnesium basal plane. It has a L12 structure (space group P m 3 ¯ m, lattice parameter a = 0.453 nm) and a Mg3 Sn composition. The orientation relationship between the β′ precipitate and the magnesium matrix is such that (11 1 ¯ )β′ // (0001)α and [011]β′ // [2 1 ¯ 1 ¯ 0]α . The β′ phase forms from GP zones and the magnesium matrix. Its formation is similar to the classical hcp → fcc transformation that involves generation and motion of Shockley partial dislocations on (0002)α . With prolonged ageing, some β′ precipitates transform in situ to the β phase. Graphical abstract: Image