Effect of bulk structure of amino silane primer on the strength and durability of aluminum/epoxy joints

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Abstract
The strength and durability in wet environment of aluminum/epoxy/aluminum joints are investigated as a function of structural changes of γ aminopropyltriethoxy silane (γ‐APS) primer at the interface. Both dry and wet strengths exhibit strong dependencies on both the thickness and the extent of drying of γ‐APS prior to joint formation. Generally, dry strength decreases with increasing thickness of γ‐APS primer, and increases with dehydration of γ‐APS at any given thickness. Strength retention of the joints after exposure to water at 55°C also improves dramatically when the adsorbed γ‐APS is extensively dried. These results are analogous to earlier observations with α‐Al2O3/polyethylene joint system. In aluminum joints, porous oxide substrate facilitates the mechanical interlocking mechanism, and its interplay with both the thickness and the extent of cure of γ‐APS is analyzed by characterizing the fractured surfaces using scanning electron microscopy (SEM) electron spectroscopy for chemical analysis (ESCA).