Nonchemical Surface Treatment for Aluminum Alloys

The state-of-the-art chemical surface treatments for adhesive bonding of aluminum alloys, such as phosphoric acid anodizing PAA are the basis of the present high-strength and durable adhesive bonds. Because of increasingly strict regulations on the use of wet chemicals, the Materials Directorate at Wright Laboratories initiated a research program to develop alternative nonchemical techniques that do not produce waste and are not detrimental to health and environment. This report describes the development of a nonchemical process, based on ion beam enhanced deposition IBED. The process consists of various steps, the major ones being grit blasting with 50 micrometers Al2O3 grit and deposition of proportional to - Al2O3 with IBED. The resulting surface is dense and corrosion resistant, and provides an excellent basis for adhesive bonding. Strength and durability studies on peel and wedge type specimens is equivalent to that of anodized specimens. Surface analytical studies, Scanning Electron Microscopy SEM, Transmission Electron Microscopy TEM, X-ray Photoelectron Spectroscopy XPS, Fourier Transform Infrared Spectroscopy FTIR, and Atomic Force Microscopy AFM, as well as electrochemical studies were used to characterize the surface and determine the mechanism of adhesion.