An environmentally-friendly process for bonding aluminum using aqueous metasilicate sol-gel and silane adhesion promoters

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 epox ysilane solution. The combination of the tare materials exhibits a bond str ength synergism as measured by bondline fracture toughness. The treated alu minum surface also exhibits a significant increase in bond strength toleran ce to contamination and moisture exposure. The effect of epoxysilane chemic al structure on bond durability was examined, as was the role of the silica te surface treatment.