PITTING CORROSION OF ELECTRODEPOSITED ALUMINUM-MANAGANESE ALLOYS

The corrosion behavior of a series of electrodeposited Al-Mn alloys ha s been investigated. Three different microstructures were examined. A supersaturated face-centered cubic (fcc) structure was produced with u p to 5 atomic percent (a/o) Mn. Deposits containing 5-22 a/o Mn were c omposed of a glassy phase in combination with a supersaturated (1 a/o Mn) fcc phase, while alloys with 22-26 a/o Mn were single-phase metall ic glasses. The pitting characteristics of these materials, in aqueous chloride solutions, were controlled by the alloy microstructure. Rela tive to aluminum, a 250 to 400 mV increase in the pitting potential wa s observed for the single-phase Al-Mn alloys. In contrast, the dual-ph ase material exhibited pitting potentials closer to that of aluminum d ue to selective pitting of the (1 a/o Mn) fcc phase. The enhanced pitt ing resistance of single-phase Al-Mn alloys is remarkable in view of t he reactive nature of elemental manganese.