Electrochemically Active Sensing Materials and Multi-Material Joints in Aerospace Corrosion Health Monitoring: Transduction, Representativeness and Validation Requirements.

Corrosion of airframe alloys is managed by scheduled inspections rather than measurement. Continuous monitoring could change this. Progress in electrochemically active sensing materials has increased laboratory detectability, yet little has reached operational aircraft. We argue that the limiting factor is not sensitivity but representativeness: whether a sensor's response reflects the true condition of the structure it monitors. We treat aerospace corrosion as a six-stage cascade and map each material and transduction principle onto the stage it observes. We review the electrochemical processing routes that set electrodes' morphology and stability and show that the processing parameters strongly affect reported reproducibility when the process's control is left unstated. We propose an engineering-relevant framework spanning material, environmental, and electrochemical representativeness, plus decision relevance. Across the reviewed corpus, the highest analytical sensitivity tends to coincide with the lowest material representativeness, an apparent qualitative trade-off rather than a demonstrated statistical relationship. No identified system closes the chain from the signal to a damage-based maintenance decision without independent nondestructive verification. Of the performance figures that could be traced to primary studies, none was obtained on an aerospace alloy under airframe-representative exposure, the field's principal gap. At multi-material joints, the problem inverts: carbon-fibre composites drive alloy's dissolution while its own matrix degrades, so surface-treatment processing, rather than sensor choice, sets the outcome. We conclude with a staged evidence architecture that couples continuous sensing to eddy current, ultrasonic, and thermographic inspection.