•New potentiometric Al3+ion-selective microelectrode for corrosion monitoring on aluminum-based materials.•SECM imaging of local ion concentration distributions over 2098-T351 al-cu-li alloy welded by FSW.•Spatial resolution of Al3+ local concentrations arising from the base material and from distinct weld zones.•High active domains for Al3+ associated to microgalvanic coupling were resolved and characterized.•Electrochemical data correlate well with high-resolution XPS spectra of the tested surfaces. A novel potentiometric Al3+−ion selective microelectrode (ISME), with internal solid contact, based on the use of a neutral carrier morin as ionophore is reported. The ability of the ISME to image local ion concentration distributions was tested on aluminum alloy surfaces freely corroding in an aqueous solution containing chloride ions. The microelectrode was then used as the sensing tip for scanning electrochemical microscopy (SECM) in potentiometric operation to monitor the reactive sites associated with the dissolution of aluminum that developed in the 2098−T351 Al−Cu−Li alloy as a result of welding by the Friction Stir Welding (FSW) process. The ISME detected differences in the local concentrations of Al3+ species arising from the 2098−T351 Al−Cu−Li alloy (base material) and from the coupled weld joint/heat affected zones (WJ/HAZ) of the alloy produced by the FSW process. More active domains for Al3+ dissolution were found in the HAZ regions coupled to WJ, more specially in the HAZ of the advancing side (AS). These results demonstrate that the Al3+−ISME presented in this work can be used to monitor corrosion sites on aluminum alloys surfaces with combined chemical and spatial resolution. Display omitted