Rapid Evaluation of Conversion Coating Degradation Using Automated Scanning Electrochemical Microscopy Approach Curves

This work aims to quantify electron transfer kinetics from intermediate feedback in automated scanning electrochemical microscopy (SECM) approach curves. Automated tip approach curves are proposed as a high-throughput method to characterize and detect active corrosion sites in conversion coated aluminum alloys. This represents a fast and quantitative SECM methodology for evaluating local conversion coating degradation by combining information provided by multiple feedback curves of the ultramicroelectrode (UME) tip. As proof of concept, a series of automated SECM approach curves is presented for AA2024-T3 samples coated with a Zr-based conversion coating. An accelerated activation treatment applied to the conversion coating prior to SECM analysis is proposed to achieve a detectable feedback contrast at early stages of degradation. Heterogeneous degradation of the conversion coating is quantified by variations in electron transfer kinetics as a function of the UME tip location. The use of automated tip approach curves demonstrates greater potential for rapid and remote detection of active coating degradation sites in the vicinity of the tip, overcoming the limitations of conventional SECM mapping by the feedback mode. Characterizing a large surface area through the automated acquisition of a strategically spaced set of tip approach curves provides spatial resolution comparable to that of SECM imaging for the detection of active coating degradation sites.