Bimetallic corrosion evaluation of the π-Al8Mg3FeSi6 phase/Al couple in acidic, neutral and alkaline aqueous solutions using the scanning vibrating electrode technique

Abstract

The influence of variations in pH and time on the bimetallic corrosion of π-Al8Mg3FeSi6 phase and pure aluminum in acidic, neutral and basic solutions has been evaluated by potentiodynamic polarization and scanning vibrating electrode technique (SVET) in combination with Energy dispersive X-ray spectroscopy (EDX). The bimetallic corrosion of π-Al8Mg3FeSi6/Al couple was found to depend on time and pH. Polarization tests show that at pH 2 (acidic) and pH 6 (near-neutral), the π- phase functions as the anode while Al functioned as the cathode, whereas the opposite was observed at pH 13 (basic). SVET scans show that in pH 2 and 13 solutions, cathodic fluxes emerge from π- phase, and the anodic fluxes develop from Al. Whereas in pH 6 solution, self-dissolution of π- phase occurs and both cathodic anodic processes develop on the π- phase with no conspicuous electrochemical activity on Al. The rigor of the bimetallic coupling of π- phase and Al was more pronounced at pH 2 and 13 and the order of the intensity of the galvanic effect is pH 13 > pH 2 > pH 6. EDX surface analysis indicates preferential discharge of more electropositive elements in π-Al8Mg3FeSi6 phase in solution. In acidic and neutral environments selective dissolution of Mg/Al in π- phase the occurs, in near neutral solutions selective dissolution of Mg occurs, in alkaline environments selective dissolution of Al occurs; these lead to the enrichment of more noble elements which have a direct impact on the galvanic polarity of the π-Al8Mg3FeSi6 in the long term.