Environmentally Benign Sol-Gel Surface Treatment for Aluminum Bonding Applications

摘要

A surface treatment process for aluminum using sol-gel chemistry has been developed that produces strong adhesive bonds without the rinse water requirements of traditional anodizing or etching processes. In this process, an acid catalyzed sol composed of zirconium alkoxide and a silane coupling agent in water was applied to etched or grit blasted aluminum substrates by immersion or spraying. After drying at 212 deg F for 1 hour, panels were primed with Cytec BR127 or XBR6757 (nonchromated, waterborne) primer and bonded in an autoclave using Hysol 9628 adhesive. The ASTM D 3762 Wedge Test was used to screen performance. The waterbased sol-gel formulation has superior performance to more traditional alcohol-based formulations used early in this program. The best formulation, using glycidoxytrimethoxysilane as the coupling agent, showed less than 0.25 inch crack extension after exposure to 140 deg F and 100% relative humidity for 336 hours. Failure in the crack growth region appears to be cohesive. In general, the waterborne XBR6757 showed better performance than the solvent based BR127. Further characterization of the coating is needed to understand interaction effects between adherend alloy, surface preparation, sol preparation, and application technique.