The structure of a long-period stacking phase in an Mg-Al-Y alloy studied by electron microscopy

A new phase with a 10H-type long-period stacking (LPS) structure was found in an Mg75Al10Y15 alloy annealed at 823K. The LPS structure in the Mg75Al10Y15 alloy annealed at 823K for 2h has an ordered arrangement of L1(2)-type structural Al6Y8 clusters on the two-dimensional plane parallel to the c-plane of hexagonal Mg lattice and a disordered arrangement along the c-axis, whereas a perfectly ordered structure along the c-axis, which has a period with two times of that of the 10H-type LPS structure, was established by annealing at 823K for 24h. The structural model of the ordered LPS phase is proposed by high-resolution images taken with a Cs-corrected scanning transmission electron microscope and also electron diffraction patterns.