Corrosion of an Al–Mg–Si alloy under MgCl2 solution droplets

The corrosion behavior of an Al–0.63Mg–0.28Si alloy under droplets of MgCl2 solution in environments of 75% and 33% RH was studied using a Kelvin Probe. The equilibrium chloride concentrations in these two environments are 5.8 and 9.8 M chloride, respectively. In the 33% RH environment, metastable pitting was the main form of corrosion. In some cases at 75% RH, the potential baseline decreased slowly by hundreds of millivolts and remained at the lower value. These samples exhibited filiform-like corrosion inside micro-droplets that formed outside of the main MgCl2 drop. A model for the filiform-like attack in a micro-droplet is presented.

► Studied corrosion behavior of Al–Mg–Si alloy under MgCl2 solution droplets using Kelvin Probe.
► In most cases, only metastable pitting observed associated with OCP transients.
► In particular combinations of droplet size and RH, stable filiform-like attack seen outside drop.
► Stable filiform-like corrosion observed to occur inside micro-droplet outside of main drop.
► A model for the micro-droplet formation and filiform growth was presented.