Crystallographic characterization of Al18Mg3Ti2 intermetallic phase in Al-Zn-Mg-Cu-Zr-Ti alloy

We studied the crystallographic characteristics of the Al18Mg3Ti2 intermetallic phase in a solutiontreated Al-7.6Zn-2.6Mg-2.0Cu-0.1Zr-0.07Ti (wt.%) alloy utilizing transmission electron microscopy (TEM). Cubic spinel Al18Mg3Ti2 intermetallic phase features {111) faceted interfaces with the Al matrix. Selected-area electron diffraction pattern, stereographic projection, and atomic projection studies indicated four possible orientation relationships between the Al18Mg3Ti2 phase and the Al matrix, which are categorized by a misorientation angle (theta) at {111) planes of each phase (i.e., theta = +/- m, 70.5 degrees +/- m, where m = 12-14 degrees). High resolution TEM analyses confirmed that the growth of the Al18Mg3Ti2 intermetallic phase is based on the ledge mechanism on the {111) interfaces along with multiple {111) twinning. This growth mechanism of the Al18Mg3Ti2 phase contributes to the formation of faceted morphologies with {111) interfaces. The interface between the Al18Mg3Ti2 phase and Al matrix provides a heterogeneous nucleation site for the L1(2)-precipitate and a Zn-rich phase. (c) 2020 Elsevier B.V. All rights reserved.