Insitu SVET studies on the current density distribution on dissolving of Mg, MgZn2, Mg2Si and Al4Cu2Mg8Si7 surfaces in NaCl solutions

Abstract

Purpose This paper aims to acquire the current density distribution on dissolving of Mg, MgZn2 (η -phase), Mg2Si (ß-phase) and Al4Cu2Mg8Si7 (Q-phase) surface in NaCl solutions. Design/methodology/approach MgZn2 (η -phase), Mg2Si (ß-phase) and Al4Cu2Mg8Si7 (Q-phase) are important intermetallic compounds found in aluminum alloys. Insitu scanning vibrating electrode technique (SVET) was used to acquire the current density distribution on dissolving of Mg, MgZn2 (η -phase), Mg2Si (ß-phase) and Al4Cu2Mg8Si7 (Q-phase) surface in NaCl solutions scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) was used to characterize the corroded surface. Findings SVET maps reveal that these compounds display characteristic dissolution features. Mg and MgZn2 displayed localized anodic and cathodic sites while that of Al4Cu2Mg8Si7 > Mg2Si displayed a diffused distribution of anodic and cathodic sites. The magnitude of the integrated anodic current densities on the compounds was noted to decrease with the progress of time, and the order of the magnitude of the current density with respect to the compounds is Mg > Mg2Si > Al4Cu2Mg8Si7 > MgZn2. SEM/EDX reveal that the highest mass loss recorded after the SVET test was manifested by Mg2Si followed by MgZn2 then Al4Cu2Mg8Si7. Originality/value Auxiliary information on the current density distribution on the corroding sample surface at the microscopic scale has been provided by SVET thereby taking care of certain limitations of traditional corrosion monitoring techniques such as gravimetric, hydrogen evolution and electrochemical measurements.