Effect of microstructure on the corrosion behaviour of extruded heat exchanger aluminium alloys

Aluminium extrusions used for heat transfer applications are exposed to corrosive environments, which can eventually lead to perforation of the tube by pitting. In this study, the effect of microstructure on the corrosion behaviour of extruded AA3XXX series alloys has been investigated. It was revealed that pits developed were purely crystallographic and a drop testing procedure was developed to simulate the seawater acetic acid test in a laboratory environment. The drop testing experiment has been successfully employed to study the early stages of pitting for different surface finishes. Selected pits were studied with in-SEM nanotomography. Stable pits initiated on areas free of second-phase particles, in the vicinity of grain boundaries. When the corrosion front reached a grain boundary plane, pit propagation was interrupted in the direction perpendicular to the plane and the corrosion front followed grain boundaries, corroding one grain body more than its neighbour. A mechanistic understanding of crystallographic pitting corrosion has been developed. Copyright © 2013 John Wiley & Sons, Ltd. Copyright © 2013 John Wiley & Sons, Ltd.