Direct evidence of hydrogen bubble evolution as an acoustic emission source in metal corrosion

Hydrogen (H 2 )-bubble evolution has been proposed as an important source of acoustic emission (AE) during metal corrosion since 1976. However, direct evidence is still lacking. Here, we report a simple yet effective strategy to spatiotemporally isolate single H 2 -bubble events in sodium sulfate droplet corrosion of AZ31 alloy, which are synchronously captured by AE-driven high-speed observations. The individual AE waveform is directly related to the two-stage evolution of a single bubble, including detachment and bursting. Furthermore, by linking H 2 evolution to the corrosion process, H 2 -bubble evolution-AE signals may provide a unique approach to evaluate the microstructure-dependent corrosion rate of Mg alloys. ● Droplet corrosion in AZ31 can spatiotemporally isolate single H 2 -bubble events. ● AE signal drives high-speed observations of the evolution of a single H 2 bubble. ● Specific two-part AE waveform is related to bubble detachment and bubble bursting. ● AE amplitude and rise time seem to largely depend on the bubble radius. ● The AE signals of H 2 bubble evolution is related to the localized corrosion rate.