Combined high resolution Scanning Kelvin probe-Scanning electrochemical microscopy investigations for the visualization of local corrosion processes

An integrated SKP-SECM system was successfully optimised with respect to improved lateral resolution. An aluminum alloy was synthesised by solidification of a liquid melt of pure Al, Cu and Mg metal powders in order to visualize single S-phase intermetallic particles (IMPs) using a newly proposed “glass free” SKP-SECM tip. The obtained IMPs were randomly distributed in the solid solution matrix of the alloy and their average chemical composition was in agreement with that of S-phase IMPs in commercially available AA2024-T351 alloys. The S-phase IMPs were localized in the SKP mode of the SKP-SECM system. The increased electrochemical activity of the S-phase IMPs was visualized using the feedback mode of SECM and the in situ consumption of O2 on the surface of a single S-phase IMP was visualized in the redox-competition mode of the SECM using the same tip. Thus, the local Volta potential difference obtained in the SKP mode could be overlaid with the local electrochemical activity for O2 reduction.