Atomic-resolution chemical mapping of ordered precipitates in Al alloys using energy-dispersive X-ray spectroscopy

Abstract

Scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDS) is a common technique for chemical mapping in thin samples. Obtaining high-resolution elemental maps in the STEM is jointly dependent on stepping the sharply focused electron probe in a precise raster, on collecting a significant number of characteristic X-rays over time, and on avoiding damage to the sample. In this work, 80 kV aberration-corrected STEM-EDS mapping was performed on ordered precipitates in aluminium alloys. Probe and sample instability problems are handled by acquiring series of annular dark-field (ADF) images and simultaneous EDS volumes, which are aligned and non-rigidly registered after acquisition. The summed EDS volumes yield elemental maps of Al, Mg, Si, and Cu, with sufficient resolution and signal-to-noise ratio to determine the elemental species of each atomic column in a periodic structure, and in some cases the species of single atomic columns. Within the uncertainty of the technique, S and β'' phases were found to have pure elemental atomic columns with compositions Al 2 CuMg and Al 2 Mg 5 Si 4 , respectively. The Q' phase showed some variation in chemistry across a single precipitate, although the majority of unit cells had a composition Al 6 Mg 6 Si 7.2 Cu 2 .

Atomic Structures of Precipitates in Al–Mg–Si Alloys with Small Additions of Other Elements

“…There 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 are also several reports showing slightly different Q compositions, Al4Cu2Mg8Si7 [94], Al5Cu2Mg8Si6 [102], within AlxCu2Mg12-xSi7 [94]. It has been suggested possible Cu-Mg compositional fluctuations in the Q phase by DFT and APT studies [103,104] and also recently by energy dispersive X-ray spectroscopy (EDS) imaging with atomic resolution [78].…”

“…Some density functional theory (DFT) studies show possible Mg-Al compositional fluctuations, Mg(6-x)Al(1+x)Si4 (0 ≤ x ≤ 2) [77]. Furthermore, by atomic resolution energy dispersive X-ray spectroscopy (EDS), it has recently been demonstrated [78] that Al is incorporated in β". Such observations of Al incorporation and calculated compositional fluctuations cannot explain the stability of Si-Si bonds proposed as the "Si nanopillars" based on Mg5Si6 in ref.…”

Structural and compositional study of precipitates in under-aged Cu-added Al-Mg-Si alloy

“…The structures and the compositions of β” and Q’ precipitates have been studied intensively in past, and those of β” precipitates have been suggested as monoclinic with Mg 5 Si 6 21 , 36 , Mg 5 Al 2 Si 4 37 , or Al 3 Mg 4 Si 4 20 stoichiometry, and those of Q’ as hexagonal with Al 3 Mg 9 Si 7 Cu 2 31 , 38 , 39 or Al 6 Mg 6 Si 7 Cu 2 40 stoichiometry. Wenner et al .…”

Membrane Processes during the Regeneration of Galvanic Solution

“…X-ray microanalysis conducted using the scanning electron microscope REM-106-i (manufactured by "SELMI", Ukraine) allowed determination of chemical elements in the samples of the studied cathodic deposits on the basis of energy values of the characteristic X-ray peaks of each chemical element [15,16]. To determine the elementary composition the samples were placed on a double-sided carbon adhesive tape.…”