Precipitation of the β-phase and Corrosion Behavior of an Al-6.8 wt.% Mg Alloy

Abstract

This study was performed on the Al-Mg alloy with the chemical composition: Al-Mg6.8-Mn0.51-Fe0.2-Si0.1. As-received cold rolled material (O-temper) was subjected to (i) cold rolling and annealing at 265°C and 320°C, followed by (ii) sensitization treatment at 100°C. Microstructure characterization showed that the preferential sites for β-phase precipitation were grain boundaries and preexisting Mn-rich particles. The annealing temperature had significant effect on the β-phase morphology: microstructure of sensitized specimens annealed at 265°C was characterized by formation of discontinuous particles, while annealing at 320°C resulted in the formation of the thin film at grain boundaries. Presence of the thin film induced corrosion resistance degradation and also affected grain boundary morphology: initially smooth, curved grain boundaries became strongly faceted.