Pitting Corrosion of Electrodeposited Aluminum‐Manganese Alloys

The corrosion behavior of a series of electrodeposited Al‐Mn alloys has been investigated. Three different microstructures were examined. A supersaturated face‐centered cubic (fcc) structure was produced with up to 5 atomic percent (a/o) Mn. Deposits containing 5–22 a/o Mn were composed 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 metallic glasses. The pitting characteristics of these materials, in aqueous chloride solutions, were controlled by the alloy microstructure. Relative to aluminum, a 250 to 400 mV increase in the pitting potential was observed for the single‐phase Al‐Mn alloys. In contrast, the dual‐phase material exhibited pitting potentials closer to that of aluminum due to selective pitting of the (1 a/o Mn) fcc phase. The enhanced pitting resistance of single‐phase Al‐Mn alloys is remarkable in view of the reactive nature of elemental manganese.