Studies on filiform corrosion generated on Al and Al-alloy coated sheets

Abstract

The effects of several conditions such as alloying elements, chemical conversion treatment, primary and finish coatings on the filiform corrosion generated on aluminum and its alloy coated sheets were studied by salt spray test, salt water immersion test, and humidity cabinet test.The results obtained were as follows:1. Aluminum of lower purity was more corrosive than that of higher purity. Alloys of 3003 and 5052 were more corrosion resistant than 1100 alloy.2. The effect of chemical conversion was most remarkably observed. The resistance of the sheet treated by chemical conversion was extremely high.3. Since the finish coated film was thicker than the primary coated one, the former was supposed to be more corrosion resistant. However, the finish coated one was not very resistant to the filiform corrosion.4. The filiform corrosion was not so much generated by salt spray test alone. However, after the panel was successively treated by humidity cabinet test, the blister produced by salt spray test induced the filiform corrosion.