On the cathodic dissolution of Al and Al alloys

•The cathodic dissolution of pure Al and AA6061 aluminum alloy is measured.•Cathodic dissolution of Al occurs with a stoichiometry of 4.62 ± 0.22 OH−/Al3+ over several orders of magnitude of cathodic current.•Cathodic dissolution of SiO2 observed at high cathodic current.•Mg2+ species precipitated on the surface perhaps in the form of MgSiO3.•Aln[Fem,Mn1−m]Si phases serve as local cathodes forming “trenches” around the intermetallic particles.

The cathodic dissolution of aluminum and aluminum alloys is a potentially important but poorly understood phenomenon. In this work, the dissolution of pure Al and AA6061 aluminum alloy under cathodic polarizations was investigated. The dissolution rates of the base metal and minor alloying elements were measured in real time using atomic emission spectroelectrochemistry. These data were used to verify the stoichiometry of 4.62 ± 0.22 hydroxides per dissolved Al ion for pure Al. It was found that at high cathodic currents, the cathodic dissolution of SiO2 was observed while Mg2+ species precipitated on the surface perhaps in the form of MgSiO3. These precipitated solid phases did not alter the OH/Al stoichiometry. The Aln[Fem,Mn1−m]Si phases appear to serve as local cathodes accelerating Al dissolution leading to the formation of “trenches” around the intermetallic particles.