New insights into corrosion initiation and propagation in a hot-dip Al-Zn-Mg-Si alloy coating via multiscale analytical microscopy
Majid Laleh, Thomas Jurak, Kateryna Gusieva, Joe Williams, Wayne Renshaw, Simon Correnti, Jason Hodges, Azdiar A. Gazder
Abstract
Multiscale analytical microscopy provides new mechanistic insights into the corrosion processes within a pre-painted hot-dip Zn-55Al-2Mg-1.5Si coated steel exposed to a coastal environment. This study is the first to conclusively show that corrosion initiation is not only affected by the electrochemical activities of constituent phases but also by their morphology. Corrosion initiates when sub-micron Zn particles within the Zn-Al binary eutectic dissolve. Thereafter, corrosion propagates by the dissolution of large Zn particles and by Mg dealloying from MgZn 2 and Mg 2 Si intermetallic phases. The late stages record the corrosion of primary Al-rich dendrites, leading to a volumetric expansion in corrosion product. • Multiscale microscopy was used to provide new insights into corrosion processes within a hot dip coating. • Corrosion initiation was found to not only affected by electrochemical activities of constituent phases but also by their morphology. • Sub-micron Zn particles in the Zn-Al binary eutectic were the first phase to preferentially dissolve during the initiation of corrosion.