In Situ Microtomographically Monitored and Electrochemically Controlled Corrosion Initiation and Propagation in AlMgSi Alloy AA6016

Corrosion susceptibility and the type of corrosion in AlMgSi alloys depend strongly on microstructure. However, it is still unclear what microstructural features trigger corrosion initiation. The direct correlation of second-phase particles with the corrosion propagation path has also never been thoroughly explored. In this work, the role of second-phase particles in corrosion initiation and propagation were studied in alloy AA6016 by using a microelectrochemically controlled microtomography technique. Three topics are discussed in detail, the role of Fe-containing intermetallics, the effect of MgSi particles, and an evidenced type of directed corrosion (exfoliation-like attack): ( i ) Intergranular corrosion initiates preferentially in Fe-containing intermetallics located at grain boundaries. However, its propagation path is not promoted by these intermetallics. ( ii ) MgSi particles do not act as transition sites to in-depth corrosion propagation, even if they dissolve. ( iii ) A type of corrosion called exfoliation-like attack is observed. It is characterized by straight attack into the bulk material. The propagation is found to be independent of grain boundaries and second-phase particles.