Electrochemical behavior of Al3Fe intermetallic compound.

Abstract

The cathodic processes localized to iron rich intermetallic phases on commercial aluminum alloys during corrosion in neutral chloride environments are controlled by the structural and compositional changes occurring on these phases in a locally stable alkaline environment. These phenomena are investigated by conventional electrochemical techniques on synthetically grown Al3Fe crystals. The surface of the crystals is enriched by metallic iron at E<-1.175 VscE as a result of selective aluminum dissolution. In the potential range -1.175<E<-0.72 VSCE, the surface is essentially passive to oxidation resulting from the successive formation of an adsorbed FeOH and the bulk oxides Fe(OH)2 and Fe3O4 with increasing potential. In the range -0.72<E<-0.66 VSCE, a transpassive behavior is observed, characterized by the selective dissolution of aluminum and oxidation of enriched iron into an unprotective oxide, possibly FeOOH. At higher potentials, the surface passivates again by Fe2O3 formation. The significance of these results on aluminum alloy corrosion is discussed. In addition to their role as cathodes, it is argued that these compounds may be contributing directly to pit initiation and the determination of the pitting potential on aluminum alloys.

Real-Time Corrosion Monitoring of Aluminum Alloy Using Scanning Kelvin Probe Force Microscopy

“…The corrosion of aluminum alloys is always localized due to extensive existing micro-galvanic activities between microstructural constituents in the microstructure when exposed to a corrosive electrolyte. [1][2][3][4][5][6][7][8][9][10][11][12] The microstructure of aluminum alloys is by far more complicated than that of stainless steels as various kinds of IMPs with varying sizes, composition, structure, and population density can co-exist, usually being less than 5% in volumetric fraction, but being sufficient to provoke extensive galvanic activities that can lead to rapid corrosion. [1][2][3][4][5][6][7][8][9][10] IMPs are primarily responsible for triggering localized corrosion as they form local galvanic couples with the aluminum matrix.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] The microstructure of aluminum alloys is by far more complicated than that of stainless steels as various kinds of IMPs with varying sizes, composition, structure, and population density can co-exist, usually being less than 5% in volumetric fraction, but being sufficient to provoke extensive galvanic activities that can lead to rapid corrosion. [1][2][3][4][5][6][7][8][9][10] IMPs are primarily responsible for triggering localized corrosion as they form local galvanic couples with the aluminum matrix. IMPs are usually categorized into anodic and cathodic type of compounds.…”