Unravelling the characteristics of Al-alloy corrosion at the atomic to nanometre scale by transmission electron microscopy

¹ Department of Materials Science and Engineering, Monash University, Clayton, Victoria, 3800, Australia.
² College of Engineering and Computer Science, The Australian National University, Acton, ACT, 2601, Australia.

^* Corresponding author: shravan.kairy@monash.edu

Abstract

The localised corrosion associated with Mg₂Si in the Al-matrix of an Al-Mg-Si alloy was studied in 0.1 M NaCl at pH 6 by quasi in-situ transmission electron microscopy. Herein, physical imaging of corrosion at the atomic to nanometre scale was performed. Phase transformation and subsequent chemical composition variations associated with the localised corrosion of Mg₂Si were studied. It was observed that corrosion initiated upon Mg₂Si, often preferentially at the interface with the Al-matrix, and propagated until Mg₂Si was completely dealloyed by Mg-dissolution, resulting in an amorphous SiO-rich phase remnant. The SiO-rich remnant became electrochemically inert and did not initiate corrosion in the Al-matrix. This study provides a clear understanding on the localised corrosion of Al-alloys associated with Mg₂Si. In addition, the methodology followed in this study can also be applied to understand the role of precipitates and second phase particles in the localised corrosion of Al-alloy systems.