Abstract

Abstract A new chemical treatment for aluminum alloys with a dilute solution of sodium oxalate was found to improve the corrosion resistance when compared with the conventional boehmite treatment with water and/or triethanolamine solution. When a specimen is treated with the sodium oxalate solution, porous film about 1 µm thick deposits on the alloy surface. The film consists of pseudo-boehmite with a high water content and a small amount of oxalate. The corrosion potential of the treated alloy moves in the negative direction compared with the untreated alloy while the pitting potential moves in the positive, and hence the specimen exhibits higher resistance to pitting corrosion in sodium chloride solution containing cupric ion. The high corrosion resistance is attributed to the diminution of oxygen permeation through the oxide film.

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