Wild avalanches and mild fluctuations during filiform corrosion of Mg in NaCl solution

The filiform corrosion of Mg in NaCl solution was characterized by acoustic emission spectroscopy, measurements of the free-corrosion potential, and optical observations under in situ conditions. Three stages of corrosion were identified: an incubation period, localized attack, and filament propagation. The corrosion mechanisms include the Mg dissolution, the breakdown of hydroxide/oxide surface films, and the burst of gas bubbles. Localized attack and filament propagation are distinguished by a gradual transition from correlated avalanches (wild events) to predominantly stochastic processes (mild events), which still contain some weak avalanche signals. Our approach provides a way to monitor corrosion under in situ conditions.