SVET and SIET Study of Galvanic Corrosion of Al/MgZn₂in Aqueous Solutions at Different pH

The galvanic corrosion behavior of synthesized MgZn 2 intermetallic particle coupled with Al in 0.1 M NaCl solutions across pH 2 to12 has been studied using the scanning vibrating electrode technique (SVET), the scanning ion-selective electrode technique (SIET) and X-ray photoelectron spectroscopy (XPS). Results indicate the galvanic dissolution of MgZn 2 depends on pH as well as exposure time. SVET current density maps reveal that MgZn 2 is anodic relative to Al at pH 2 but cathodic at pH 12, while self-dissolution of MgZn 2 prevails at pH 4 and 6. However, the galvanic coupling effect is more pronounced at pH 2 and 12. SIET maps of H + and Cl − ion distribution reveal evidence of local alkalization on MgZn 2 and migration of Cl − ions away from MgZn 2 surface at pH 4 and 6 due to significant accumulation of OH − ions. Preferential dissolution of Mg occurs leading to segregation of Mg compounds in the outer layers of the film and Zn enrichment on the matrix/solution interface. In slightly acidic and near neutral solutions MgO/Mg(OH) 2 dominates the outer layers and MgO/Mg(OH) 2 /ZnO dominates the inner layers, however, at pH 12 a stable MgO/Mg(OH) 2 passive film is formed.