Direct visualization of β phase causing intergranular forms of corrosion in Al–Mg alloys

•Nanometer sized β phase in Al-10% Mg is first clearly visualized with SEM.•Nanometer sized β phase in wrought alloy 5083 is first clearly visualized with SEM.•Grain boundary decorating β phase and isolated sponge-like β phase are shown.•This phase is confirmed to be β phase using composition analysis.

For a more effective examination of microstructure in Al–Mg alloys, a new etching solution has been developed; dissolved ammonium persulfate in water. It is demonstrated how β phase (Al3Mg2) in Al–Mg alloys respond to this solution using samples of a binary Al–Mg alloy and a commercial 5083 aluminum alloy. Nanometer sized β phase is clearly visualized for the first time using scanning electron microscopy (SEM) instead of transmission electron microscopy (TEM). It is anticipated that direct and unambiguous visualization of β phase will greatly augment intergranular corrosion research in 5xxx series aluminum alloys.