ANODIC-DISSOLUTION AND PROTECTION OF ALUMINUM-ALLOY-7075 IN HYDROXIDESOLUTIONS

Dissolution of Al 7075 (UNS A97075) in sodium hydroxide (NaOH) solutio ns results information of a black, loosely adherent film of corrosion products that provides partial protection in the aqueous environment. Optical and scanning microscopy showed the reaction product film is a bilayer, with a thin, adherent inner layer and a thicker, more fragile outer layer. The reaction mechanism involves the dissolution of alumi num followed by formation of a precipitated film. Corrosion protection at moderate hydroxide concentrations is provided by the use of a part ially fluorinated amino-surfactant or a silicon nitride (Si3N4) coatin g prepared by ion beam-assisted deposition.