Environmentally Benign Conversion Coatings for Aircraft Alloys

Over the past two decades, environmental concerns have arisen regarding almost every aspect of treating metals to prevent corrosion. Commercially available conversion coatings for aluminum and magnesium alloys often require the use of toxic, corrosive chemicals, and in some cases, sophisticated electrical equipment. The most effective ingredients in these anticorrosive products have traditionally been based on chromium compounds. In order to achieve the same type of surface morphology and chemistry necessary for effective corrosion inhibition with chromium compounds, a novel pretreatment method is proposed. This involves using peroxide precursors in combination with chromium-free co-oxidants to form stable mixed oxide layers over metal surfaces. The novel combinations of metal surface active compounds will be incorporated into new types of sol-gel-derived chemical conversion coatings to suppression. These properties will be tested on common nonferrous aircraft alloys by salt fog resistance and electrochemical impedance analysis. The pretreatment systems are designed to be easily applied, to use no chromium compounds, and to form strong inter-layer bonds for durable coating adhesion.