Display omitted •pH-dependent electrochemical behaviour of Al3Mg2 has been confirmed.•Galvanic corrosion currents versus pH of coupled Al3Mg2/Al were studied by SVET.•Dealloying element changes from Al to Mg as pH deviates from strong alkaline.•Three models were proposed to depict the corrosion process of Al3Mg2 at pH 2–12. The effects of pH on the electrochemical behaviour of β-phase (Al3Mg2) and its role in corrosion of AA5000 series alloys in NaCl solution were investigated. The galvanic corrosion behaviour of synthesized Al3Mg2 intermetallic particle coupled with Al in 0.01 M NaCl solution over a wide pH window of 2–12 was studied using the scanning vibrating electrode technique (SVET). The results show that bulk Al3Mg2 acts as anode at pH 2–10.5, while cathode at pH 12. The corrosion resistance properties of bulk Al3Mg2 were then evaluated via potentiodynamic polarization and electrochemical impedance spectroscopy tests. Surface characterization were carried out by confocal laser scanning microscope (CLSM), scanning electron microscope (SEM) and X-ray photoelectron spectrometry (XPS). These results indicate that Al3Mg2 exhibits active dissolution of both Al and Mg elements at pH 2, while selective dissolution occurs at pH 3.5–12. At pH 3.5–10.5, any deviation from neutral pH causes a significant increase in the selective dissolution rate of Mg element, which results in a rough outer layer and a relatively compact inner layer of corrosive surface. At pH 12, the selective dissolution of Al element becomes dominant and the formation of compact Mg(OH)2 achieves complete passivity on the surface of Al3Mg2. This work contributes to further understanding of the electrochemical behaviour of β-phase in AA5000 series alloys.