Direct Observation of PFIB-Induced Clustering in Precipitation-Strengthened Al Alloys by Atom Probe Tomography

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.