EFFECT OF SURFACE DEPLETION OF LITHIUM ON CORROSION BEHAVIOR OF ALUMINUM-ALLOY-8090 IN A MARINE ATMOSPHERE

Aluminium-lithium al toy 8090 is of great interest due to its low dens ity and good mechanical properties. The high reactivity of lithium, ho wever, makes it more prone to corrosion than other alu minium alloys, limiting its use in certain fields. In general, there is an intergranu lar attack with exfoliation in the most severely attacked sections of this alloy in marine and industrial environments. This attack also dep ends on the metallurgical history of the material, i.e. the part of th e ingot from which the specimens are extracted. After one and two year s' exposure to a moderately aggressive marine atmosphere, it was found that the materials taken from the centre of the ingot have a more wid espread attack than specimens taken from the edges. Th is might be exp lained by the differing composition of the specimens according to thei r origin; more precisely, by the uneven distribution of the lithium, w hich tends to spread though the matrix of the ingot and form a lithium -impoverished layer several microns deep as a consequence of the serie s of thermal treatments applied.