Abstract
The effect of sample preparation on a pre-aged Al–Mg–Si–Cu alloy has been evaluated using atom probe tomography. Three methods of preparation were investigated: electropolishing (control), Ga+ focused ion beam (FIB) milling, and Xe+ plasma FIB (PFIB) milling. Ga+-based FIB preparation was shown to introduce significant amount of Ga contamination throughout the reconstructed sample (≈1.3 at%), while no Xe contamination was detected in the PFIB-prepared sample. Nevertheless, a significantly higher cluster density was observed in the Xe+ PFIB-prepared sample (≈25.0 × 1023 m−3) as compared to the traditionally produced electropolished sample (≈3.2 × 1023 m−3) and the Ga+ FIB sample (≈5.6 × 1023 m−3). Hence, the absence of the ion milling species does not necessarily mean an absence of specimen preparation defects. Specifically, the FIB and PFIB-prepared samples had more Si-rich clusters as compared to electropolished samples, which is indicative of vacancy stabilization via solute clustering.
Highlights
Heat-treatable Al alloys, and other light metals such as Mg, are susceptible to room-temperature aging
Unlike Ga+, could provide indications that this method of ion milling does not result in significant artifacts introduced into the nanostructure
This work reveals, quantitively, the substantial impact that ion milling can have on the solute clustering quantification in aluminum alloys using APT
Summary
Heat-treatable Al alloys, and other light metals such as Mg, are susceptible to room-temperature aging. The clustering of solute atoms, which control these performance criteria, is strongly dependent on the vacancy super-saturation (Aruga et al, 2015; Poznak et al, 2018) These solute clusters, in the early stages of aging, are often difficult, if not impossible, to be resolved using transmission electron microscopy (TEM) because of their size and coherent structure within the matrix. APT has equal sensitivity for all elements with an analytical sensitivity of approximately 5 atomic ppm and can reconstruct the spatial location of each atom with near-perfect lattice rectification (Marquis & Hyde, 2010; Larson et al, 2013; Stephenson et al, 2013) These attributes make this technique well suited to reveal the early stages of clustering in light metal alloys during aging at room and elevated temperatures
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