Electrodeposition of organofunctional silanes and its influence on structural adhesive bonding

Four different organofunctional silanes were selected and deposited on chemically pretreated aluminum surfaces by immersion and electrodeposition techniques. The surface morphology, comparison of elemental constituents, and surface free energies of silane-coated aluminum were investigated by low voltage scanning electron microscopy (LVSEM), low voltage X-ray analysis (LVXA), and contact angle measurement, respectively. The initial bond strength and long-term durability were evaluated with epoxy adhesive by lap shear tests. The deposition of silane coupling agents enhanced the bond durability of aluminum/epoxy joints under heat and humidity conditions. Also the performance of silane coupling agents depended on the application method. The electrodeposition technique produced a more uniform coverage of silane on the aluminum surface and, thus, was generally more effective than the immersion technique in improving bond performance.