Hydrothermal Stability of Aluminum/Epoxy Adhesive Bonds

Abstract

The effect of silane primers on the failure properties of aluminum/epoxy tapered double cantilever beam (TDCB) specimens was determined. TDCB specimens that were tested in air using increasing loads always failed by propagation of cracks along the center of the bondline at G_lc values between 1.58 and 1.80 × 10⁵ mJ/m² whether primers were used or not. However, γ-aminopropyltriethoxysilane (γ-APS) primers had a significant effect on the time to failure of TDCB specimens subjected to static loads in water at 60°C. The time to failure was always increased when the beams were pretreated with dilute aqueous solutions of γ-APS. The pH at which the primers were applied did not affect the failure charactersitics of the beams but heat treating the primer films before bonding did. The longest times to failure were always obtained when the primer films were dried in air at 100°C for about ten minutes. Shorter or longer drying times always resulted in lower times to failure. Increases in time to failure obtained using primed adherends were related to the ability of the primer films to inhibit hydration of the oxide.