Oscar Mauricio Prada Ramirez

Differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM) maps projected electric/magnetic fields through the phase sensitivity of segmented low‐angle detectors. Although typically applied to atomic‐resolution imaging at low beam currents, STEM‐DPC is here demonstrated as a rapid micro and nanoscale image‐segmentation tool for materials characterization with particular focus on advanced aluminum alloys. Decomposition of false‐color DPC micrographs in hue–saturation–value space enables simultaneous identification and quantification of nanoclusters, GP zones, intermediate precipitate phases, dislocation cores, and associated strain fields within a single field of view. The method is demonstrated across multiple alloy systems, including clustering and strain‐field mapping in a deformed AlMgZn(Cu) crossover alloy, precipitate identification in a paint‐baked automotive sheet alloy, phase‐variant segmentation in overaged AA7075‐T7, and nanopore and nanoparticle detection in an anodic coating on AA2024‐T3. Coupling DPC with neural‐network segmentation further enables automated grain‐boundary delineation and quantification in nanocrystalline aluminum thin films. Combined with STEM‐EDX, DPC‐based segmentation enables correlative microstructural analysis, establishing DPC as a rapid complement to techniques such as SPED and 4D‐STEM.

In this work, the localised corrosion behaviour of friction stir welded (FSW) AA7050-T76511 alloy was studied using micro-electrochemical scanning methods combined with surface characterisation. The study focused on macro galvanic interactions between the stir zone (SZ) and thermo-mechanically/heat-affected zones (TMAZ/HAZ), considering distinct initial micro-structures created by an L-bent pre-welding configuration at advancing and retreating sides. Agar-visualisation, local electrochemical impedance spectroscopy and scanning vibrating electrode technique revealed significant galvanic coupling. The TMAZ/HAZ regions behaved anodically relative to the SZ, with notably higher electrochemical activity observed at the AS. These findings demonstrate the critical influence of initial microstructural differences on corrosion susceptibility in FSW AA7050 alloys.

In this study, we explore the corrosion resistance of AA2198‐T8 alloy in friction stir‐welded zones, focusing on microstructure changes and resulting corrosion susceptibility. Macrogalvanic coupling effects are observed in weldment under corrosive conditions, particularly in the welding joint (WJ), heat‐affected zones, and base metal (BM). Severe localized corrosion is prevalent in anodic zones, revealing intricate trenching patterns around micrometric particles in cathodic domains. Investigating isolated zones exposes SLC across all welding‐affected regions and BM, underscoring the involvement of microgalvanic cells in corrosion. The novel utilization of a syringe cell as an electrochemical tool proves to be instrumental in delineating the electrochemical characteristics of welding testing zones. Notably, stir zone within WJ emerges as the region depicting the lowest corrosion resistance, a critical finding substantiated by localized electrochemical impedance spectroscopy. These insights into the interplay of electrochemical phenomena and microstructural attributes have implications for advancing corrosion mitigation strategies and alloy engineering in materials science.

The effect of different surface treatments on the corrosion resistance of the AA2098 Al–Cu–Li alloy has been investigated. Surface characterization was performed using 3D optical profilometry, energy dispersive X-ray spectroscopy and scanning electron microscopy. The corrosion resistance of the 2098 alloy after the surface treatments was investigated in 0.1 mol L ⁻¹ NaCl solution by electrochemical techniques and microscopy. Corrosion results showed that the untreated and the chemically etched surfaces were more active than the mechanically abraded and mechanically polished surfaces owing to differences in the nature of the native oxides formed after the surface treatments. Corrosion rate and mode were also affected by how close the exposed surface was to the mid-thickness region of the AA2098-T351 plate relative to the actual top surface (before polishing). This is associated with the variation in the volume fraction and distribution of the T1 phase as the mid-thickness region of the AA2098-T351 plate is approached.