In situ monitoring of the microstructural corrosion mechanisms of zinc–magnesium–aluminium alloys using time lapse microscopy

A novel technique has been developed that enables in situ monitoring of the microstructural wet corrosion mechanisms of zinc–(1–2 wt.% magnesium)–(1–2 wt.% aluminium) galvanising alloys using time lapse optical microscopy. The technique enabled the imaging of the progression of anodic attack, the development of corrosion product rings radially to the anode and pH gradients between anodes and cathodes using an indicator. It was found that corrosion initiated in the binary and ternary eutectic regions within the microstructure of the alloy with preferential de-alloying of MgZn2 lamellae. After eutectic dissolution, anodic attack proceeded on the primary zinc rich dendrites.

► Wet corrosion of a Zn–Al–Mg alloy at a microstructural level was observed.
► Time lapse showed developing anodes and cathodes, pH gradient within microstructure.
► Novel cell showed preferential anodic attack of Mg rich eutectic phase in the alloy.
► SEM images before and after corrosion showed de-alloying of Mg rich eutectic phases.
► After de-alloying primary Zn rich phase was then attacked.