An Environmentally-Friendly Process for Bonding Aluminum Using Aqueous Metasilicate Sol-Gel and Silane Adhesion Promoters

Abstract

Abstract Bonding aluminum metal and its alloys with epoxy adhesives is sensitive to process variables, particularly surface contamination and moisture exposure. In the past, several surface modification schemes have been developed to improve the epoxy-bonding of aluminum. The present work describes a simple process that produces significant improvement in strength and durability of epoxy-bonded aluminum. In this process, aluminum surfaces are first rinsed with dilute sodium metasilicate solution followed by a dilute aqueous epoxysilane solution. The combination of the two materials exhibits a bond strength synergism as measured by bondline fracture toughness. The treated aluminum surface also exhibits a significant increase in bond strength tolerance to contamination and moisture exposure. The effect of epoxysilane chemical structure on bond durability was examined, as was the role of the silicate surface treatment.