Mechanism of Al Alloy Corrosion and the Role of Chromate Inhibitors

This report summarizes a 5-year MURI program focused on the mechanism of corrosion inhibition of Al alloys by chromates. This involves understanding how chromate acts in organic primer coatings, in conversion coatings on Al alloys, and in solution as a dissolved species. Other work was concerned with the mechanisms of Al alloy corrosion even in the absence of chromate. The findings have addressed the formation mechanism of Cr-containing surface layers, the structure and composition of those layers, the release of chromate from those layers, the migration of chromate to active corrosion sites, and the mechanism by which chromate inhibits the corrosion. Cr-containing films were found to be an effective cathodic inhibitor, even at monolayer amounts. Such films also inhibited breakdown, and are therefore also anodic inhibitors.